@article{AlrefaiMondalWrucketal.2019,
  author    = {Alrefai, Anas and Mondal, Suvendu Sekhar and Wruck, Alexander and Kelling, Alexandra and Schilde, Uwe and Brandt, Philipp and Janiak, Christoph and Schoenfeld, Sophie and Weber, Birgit and Rybakowski, Lawrence and Herrman, Carmen and Brennenstuhl, Katlen and Eidner, Sascha and Kumke, Michael Uwe and Behrens, Karsten and G{\"u}nter, Christina and M{\"u}ller, Holger and Holdt, Hans-J{\"u}rgen},
  title     = {Hydrogen-bonded supramolecular metal-imidazolate frameworks: gas sorption, magnetic and UV/Vis spectroscopic properties},
  series = {Journal of Inclusion Phenomena and Macrocyclic Chemistry},
  volume    = {94},
  journal   = {Journal of Inclusion Phenomena and Macrocyclic Chemistry},
  number    = {3-4},
  publisher = {Springer},
  address   = {Dordrecht},
  issn      = {1388-3127},
  doi       = {10.1007/s10847-019-00926-6},
  pages     = {155 -- 165},
  year      = {2019},
  abstract  = {By varying reaction parameters for the syntheses of the hydrogen-bonded metal-imidazolate frameworks (HIF) HIF-1 and HIF-2 (featuring 14 Zn and 14 Co atoms, respectively) to increase their yields and crystallinity, we found that HIF-1 is generated in two different frameworks, named as HIF-1a and HIF-1b. HIF-1b is isostructural to HIF-2. We determined the gas sorption and magnetic properties of HIF-2. In comparison to HIF-1a (Brunauer-Emmett-Teller (BET) surface area of 471m(2) g(-1)), HIF-2 possesses overall very low gas sorption uptake capacities [BET(CO2) surface area=85m(2) g(-1)]. Variable temperature magnetic susceptibility measurement of HIF-2 showed antiferromagnetic exchange interactions between the cobalt(II) high-spin centres at lower temperature. Theoretical analysis by density functional theory confirmed this finding. The UV/Vis-reflection spectra of HIF-1 (mixture of HIF-1a and b), HIF-2 and HIF-3 (with 14 Cd atoms) were measured and showed a characteristic absorption band centered at 340nm, which was indicative for differences in the imidazolate framework.},
  language  = {en}
}
@article{AntoniouPashalidisGessneretal.2011,
  author    = {Antoniou, Stella and Pashalidis, I. and Gessner, Andre and Kumke, Michael Uwe},
  title     = {The effect of humic acid on the formation and solubility of secondary solid phases (Nd(OH)CO3 and Sm(OH)CO3)},
  series = {Radiochimica acta : international journal for chemical aspects of nuclear science and technology},
  volume    = {99},
  journal   = {Radiochimica acta : international journal for chemical aspects of nuclear science and technology},
  number    = {4},
  publisher = {De Gruyter},
  address   = {Berlin},
  issn      = {0033-8230},
  doi       = {10.1524/ract.2011.1812},
  pages     = {217 -- 223},
  year      = {2011},
  abstract  = {The formation of secondary Ln(III) solid phases (e.g. Nd(OH)CO3 and Sm(OH)CO3) has been studied as a function of the humic acid (HA) concentration in 0.1 M NaClO4 aqueous solution and their solubility has been investigated in the neutral pH range (6.5-8) under normal atmospheric conditions. Nd(III) and Sm(III) were selected as analogues for trivalent lanthanide and actinide ions. The solid phases under investigation have been prepared by alkaline precipitation and characterized by TGA, ATR-FTIR, XRD, TRLFS, DR-UV-Vis and Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicate that Nd(OH)CO3 and Sm(OH)CO3 are stable and remain the solubility limiting solid phases even in the presence of increased HA concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurs, the inorganic (Ln(OH)CO3) and the organic phase (HA), which is adsorbed on the particle surface of the former. Nevertheless, HA affects the particle size of the solid phases. Increasing HA concentration results in decreasing crystallite size of the Nd(OH)CO3 and increasing crystallite size of the Sm(OH)CO3 solid phase, and affects inversely the solubility of the solid phases. However, this impact on the solid phase properties is expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere.},
  language  = {en}
}
@article{AntoniouPashalidisGessneretal.2011,
  author    = {Antoniou, Stella and Pashalidis, Ioannis and Gessner, Andre and Kumke, Michael Uwe},
  title     = {Spectroscopic investigations on the effect of humic acid on the formation and solubility of secondary solid phases of Ln(2)(CO3)(3)},
  series = {Journal of rare earths},
  volume    = {29},
  journal   = {Journal of rare earths},
  number    = {6},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1002-0721},
  doi       = {10.1016/S1002-0721(10)60490-5},
  pages     = {516 -- 521},
  year      = {2011},
  abstract  = {The formation of secondary Ln(III) solid phases (e.g., Nd-2(CO3)(3) and Sm-2(CO3)(3)) was studied as a function of the humic acid concentration in 0.1 mol/L NaClO4 aqueous solution in the neutral pH range (5-6.5). The solid phases under investigation were prepared by alkaline precipitation under 100\% CO2 atmosphere and characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), time-resolved laser fluorescence spectroscopy (TRLFS), diffuse reflectance ultraviolet-visible (DR-UV-Vis), Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicated that Nd-2(CO3)(3) and Sm-2(CO3)(3) were stable and remained the solubility limiting solid phases even in the presence of increased humic acid concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system, decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurred, the inorganic (Ln(2)(CO3)(3)) and the organic phase (HA), which was adsorbed on the particle surface of the former. Nevertheless, humic acid affected the particle size of the solid phases. Increasing humic acid concentration resulted in decreasing crystallite size of the Nd-2(CO3)(3) and increasing crystallite size of the Sm-2(CO3)(3) solid phase, and affected inversely the solubility of the solid phases. However, this impact on the solid phase properties was expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere.},
  language  = {en}
}
@article{BastianNacakRoddatisetal.2020,
  author    = {Bastian, Philipp U. and Nacak, Selma and Roddatis, Vladimir and Kumke, Michael Uwe},
  title     = {Tracking the motion of lanthanide ions within core-shell-shell NaYF4 nanocrystals via resonance energy transfer},
  series = {The journal of physical chemistry : C},
  volume    = {124},
  journal   = {The journal of physical chemistry : C},
  number    = {20},
  publisher = {American Chemical Society},
  address   = {Washington, DC},
  issn      = {1932-7447},
  doi       = {10.1021/acs.jpcc.0c02588},
  pages     = {11229 -- 11238},
  year      = {2020},
  abstract  = {Lanthanide resonance energy transfer (LRET) was used to investigate the motion of dopant ions during the synthesis of core-shell-shell-nanocrystals (NCs) that are frequently used as frequency upconversion materials. Reaction conditions (temperature, solvent) as well as lattice composition and precursors were adapted from a typical hydrothermal synthesis approach used to obtain upconversion nanoparticles (UCNPs). Instead of adding the lanthanide ions Yb3+/Er3+ as the sensitizer/activator couple, Eu3+/Nd3+ as the donor/acceptor were added as the LRET pair to the outer shell (Eu-3) and the core (Nd-3). By tailoring the thickness of the insulation shell ("middle shell"), the expected distance between the donor and the acceptor was increased beyond 2 R-0, a distance for which no LRET is expected. The successful synthesis of core- shell-shell NCs with different thicknesses of the insulation layer was demonstrated by high-resolution transmission electron microscopy measurement. The incorporation of the Eu3+ ions into the NaYF4 lattice was investigated by high-resolution time-resolved luminescence measurements. Two major Eu3+ species (bulk and surface) were found. This was supported by steady-state as well as time-resolved luminescence data. Based on the luminescence decay kinetics, the intermixing of lanthanides during synthesis of core- shell UCNPs was evaluated. The energy transfer between Eu3+ (donor) and Nd3+ (acceptor) ions was exploited to quantify the motion of the dopant ions. This investigation reveals the migration of Ln(3+) ions between different compatiments in core-shell NCs and affects the concept of using core-shell architectures to increase the efficiency of UCNPs. In order to obtain well-separated core and shell structures with different dopants, alternative concepts are needed.},
  language  = {en}
}
@article{BastianYudeGuerenuKurganovaetal.2020,
  author    = {Bastian, Philipp U. and Yu, Leixiao and de Guere{\~n}u Kurganova, Anna Lopez and Haag, Rainer and Kumke, Michael Uwe},
  title     = {Bioinspired confinement of upconversion nanoparticles for improved performance in aqueous solution},
  series = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  volume    = {124},
  journal   = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  number    = {52},
  publisher = {American Chemical Society},
  address   = {Washington, DC},
  issn      = {1932-7447},
  doi       = {10.1021/acs.jpcc.0c09798},
  pages     = {28623 -- 28635},
  year      = {2020},
  abstract  = {The resonance energy transfer (RET) from NaYF4:Yb,Er upconverting nanoparticles (UNCPs) to a dye (5-carboxytetramethylrhodamine (TAMRA)) was investigated by photoluminescence experiments and microscale thermophoresis (MST). The dye was excited via RET from the UCNPs which was excited in the near-infrared (NIR). The change of the dye diffusion speed (free vs coupled) was investigated by MST. RET shows significant changes in the decay times of the dye as well as of the UCNPs. MST reveals significant changes in the diffusion speed. A unique amphiphilic coating polymer (customized mussel protein (CMP) polymer) for UCNP surface coating was used, which mimics blood protein adsorption and mussel food protein adhesion to transfer the UCNP into the aqueous phase and to allow surface functionalization. The CMP provides very good water dispersibility to the UCNPs and minimizes ligand exchange and subsequent UCNP aging reactions because of the interlinkage of the CMP on the UCNP surface. Moreover, CMP provides N-3-functional groups for dick chemistry-based functionalization demonstrated with the dye 5-carboxytetramethylrhodamine (TAMRA). This establishes the principle coupling scheme for suitable biomarkers such as antibodies. The CMP provides very stable aqueous UCNP dispersions that are storable up to 3 years in a fridge at 5 degrees C without dissolution or coagulation. The outstanding properties of CMP in shielding the UCNP from unwanted solvent effects is reflected in the distinct increase of the photoluminescence decay times after UCNP functionalization. The UCNP-to-TAMRA energy transfer is also spectroscopically investigated at low temperatures (4-200 K), revealing that one of the two green Er(III) emission bands contributes the major part to the energy transfer. The TAMRA fluorescence decay time increases by a factor of 9500 from 2.28 ns up to 22 mu s due to radiationless energy transfer from the UCNP after NIR excitation of the latter. This underlines the unique properties of CMP as a versatile capping ligand for distinctly improving the UCNPs' performance in aqueous solutions, for coupling of biomolecules, and for applications for in vitro and in vivo experiments using UCNPs as optical probes in life science applications.},
  language  = {en}
}
@misc{BurekDenglerEmmerlingetal.2019,
  author    = {Burek, Katja and Dengler, Joachim and Emmerling, Franziska and Feldmann, Ines and Kumke, Michael Uwe and Stroh, Julia},
  title     = {Lanthanide Luminescence Revealing the Phase Composition in Hydrating Cementitious Systems},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {808},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-44243},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-442433},
  pages     = {14},
  year      = {2019},
  abstract  = {The hydration process of Portland cement in a cementitious system is crucial for development of the high-quality cement-based construction material. Complementary experiments of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time-resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time-dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium-silicate-hydrates (C-S-H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C-S-H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.},
  language  = {en}
}
@article{BurekDenglerEmmerlingetal.2019,
  author    = {Burek, Katja and Dengler, Joachim and Emmerling, Franziska and Feldmann, Ines and Kumke, Michael Uwe and Stroh, Julia},
  title     = {Lanthanide Luminescence Revealing the Phase Composition in Hydrating Cementitious Systems},
  series = {ChemistryOpen},
  volume    = {8},
  journal   = {ChemistryOpen},
  number    = {12},
  publisher = {Wiley-VCH-Verl.},
  address   = {Weinheim},
  issn      = {2191-1363},
  doi       = {10.1002/open.201900249},
  pages     = {1441 -- 1452},
  year      = {2019},
  abstract  = {The hydration process of Portland cement in a cementitious system is crucial for development of the high-quality cement-based construction material. Complementary experiments of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time-resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time-dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium-silicate-hydrates (C-S-H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C-S-H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.},
  language  = {en}
}
@article{BurekEidnerKukeetal.2018,
  author    = {Burek, Katja and Eidner, Sascha and Kuke, Stefanie and Kumke, Michael Uwe},
  title     = {Intramolecular deactivation processes of electronically excited Lanthanide(III) complexes with organic acids of low molecular weight},
  series = {Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy},
  volume    = {191},
  journal   = {Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {1386-1425},
  doi       = {10.1016/j.saa.2017.09.012},
  pages     = {36 -- 49},
  year      = {2018},
  abstract  = {The luminescence of Lanthanide(Ill) complexes with different model ligands was studied under direct as well as sensitized excitation conditions. The research was performed in the context of studies dealing with deep-underground storages for high-level nuclear waste. Here, Lanthanide(III) ions served as natural analogues for Actinide(III) ions and the low-molecular weight organic ligands are present in clay minerals and furthermore, they were employed as proxies for building blocks of humic substances, which are important complexing molecules in the natural environment, e.g., in the far field of a repository site. Time-resolved luminescence spectroscopy was applied for a detailed characterization of Eu(III), Tb(III), Sm(III) and.Dy(III) complexes in aqueous solutions. Based on the observed luminescence the ligands were tentatively divided into two groups (A, B). The luminescence of Lanthanide(III) complexes of group A was mainly influenced by an energy transfer to OH-vibrations. Lanthanide(Ill) complexes of group B showed ligand-related luminescence quenching, which was further investigated. To gain more information on the underlying quenching processes of group A and B ligands, measurements at different temperatures (77 K <= T <= 353 K) were performed and activation energies were determined based on an Arrhenius analysis. Moreover, the influence of the ionic strength between 0 M <= 1 <= 4 M on the Lanthanide(III) luminescence was monitored for different complexes, in order to evaluate the influence of specific conditions encountered in host rocks foreseen as potential repository sites.},
  language  = {en}
}
@article{BurekKrauseSchwotzeretal.2018,
  author    = {Burek, Katja and Krause, Felix and Schwotzer, Matthias and Nefedov, Alexei and S{\"u}ssmuth, Julia and Haubitz, Toni and Kumke, Michael Uwe and Thissen, Peter},
  title     = {Hydrophobic Properties of Calcium-Silicate Hydrates Doped with Rare-Earth Elements},
  series = {ACS sustainable chemistry \& engineering},
  volume    = {6},
  journal   = {ACS sustainable chemistry \& engineering},
  number    = {11},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {2168-0485},
  doi       = {10.1021/acssuschemeng.8b03244},
  pages     = {14669 -- 14678},
  year      = {2018},
  abstract  = {In this study, the apparent relationship between the transport process and the surface chemistry of the Calcium-Silicate Hydrate (CSH) phases was investigated. For this purpose, a method was developed to synthesize ultrathin CSH phases to be used as a model substrate with the specific modification of their structure by introducing europium (Eu(III)). The structural and chemical changes during this Eu(III)-doping were observed by means of infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and time-resolved laser fluorescence spectroscopy (TRLFS). These alterations of the CSH phases led to significant changes in the surface chemistry and consequently to considerable variations in the interaction with water, as evidenced by measurements of the contact angles on the modified model substrates. Our results provide the basis for a more profound molecular understanding of reactive transport processes in cement-based systems. Furthermore, these results broaden the perspective of improving the stability of cement-based materials, which are subjected to the impact of aggressive aqueous environments through targeted modifications of the CSH phases.},
  language  = {en}
}
@article{ChemuraHaubitzPrimusetal.2020,
  author    = {Chemura, Sitshengisiwe and Haubitz, Toni and Primus, Philipp A. and Underberg, Martin and H{\"u}lser, Tim and Kumke, Michael Uwe},
  title     = {Europium-doped Ceria-Gadolinium mixed oxides},
  series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  volume    = {124},
  journal   = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  number    = {24},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1089-5639},
  doi       = {10.1021/acs.jpca.0c03188},
  pages     = {4972 -- 4983},
  year      = {2020},
  abstract  = {Gadolinium-doped ceria or gadolinium-stabilized ceria (GDC) is an important technical material due to its ability to conduct O2- ions, e.g., used in solid oxide fuel cells operated at intermediate temperature as an electrolyte, diffusion barrier, and electrode component. We have synthesized Ce1-xGdxO2-y:Eu3+ (0 <= x <= 0.4) nanoparticles (11-15 nm) using a scalable spray pyrolysis method, which allows the continuous large-scale technical production of such materials. Introducing Eu3+ ions in small amounts into ceria and GDC as spectroscopic probes can provide detailed information about the atomic structure and local environments and allows us to monitor small structural changes. This study presents a novel approach to structurally elucidate europium-doped Ce1-xGdxO2-y:Eu3+ nanoparticles by way of Eu3+ spectroscopy, processing the spectroscopic data with the multiway decomposition method parallel factor (PARAFAC) analysis. In order to perform the deconvolution of spectra, data sets of excitation wavelength, emission wavelength, and time are required. Room temperature, time-resolved emission spectra recorded at lambda(ex) = 464 nm show that Gd3+ doping results in significantly altered emission spectra compared to pure ceria. The PARAFAC analysis for the pure ceria samples reveals a high-symmetry species (which can also be probed directly via the CeO2 charge transfer band) and a low-symmetry species. The GDC samples yield two low-symmetry spectra in the same experiment. High-resolution emission spectra recorded under cryogenic conditions after probing the D-5(0)-F-7(0) transition at lambda(ex) = 575-583 nm revealed additional variation in the low-symmetry Eu3+ sites in pure ceria and GDC. The total luminescence spectra of CeO2-y:Eu3+ showed Eu3+ ions located in at least three slightly different coordination environments with the same fundamental symmetry, whereas the overall hypsochromic shift and increased broadening of the D-5(0)-F-7(0) excitation in the GDC samples, as well as the broadened spectra after deconvolution point to less homogeneous environments. The data of the Gd3+-containing samples indicates that the average charge density around the Eu3+ ions in the lattice is decreased with increasing Gd3+ and oxygen vacancy concentration. For reference, the Judd-Ofelt parameters of all spectra were calculated. PARAFAC proves to be a powerful tool to analyze lanthanide spectra in crystalline solid materials, which are characterized by numerous Stark transitions and where measurements usually yield a superposition of different contributions to any given spectrum.},
  language  = {en}
}
@article{DeMicheleAstLoqueetal.2013,
  author    = {De Michele, Roberto and Ast, Cindy and Loque, Dominique and Ho, Cheng-Hsun and Andrade, Susana L. A. and Lanquar, Viviane and Grossmann, Guido and Gehne, Soeren and Kumke, Michael Uwe and Frommer, Wolf B.},
  title     = {Fluorescent sensors reporting the activity of ammonium transceptors in live cells},
  series = {ELIFE},
  volume    = {2},
  journal   = {ELIFE},
  number    = {3},
  publisher = {ELIFE SCIENCES PUBLICATIONS LTD},
  address   = {CAMBRIDGE},
  issn      = {2050-084X},
  doi       = {10.7554/eLife.00800},
  pages     = {22},
  year      = {2013},
  abstract  = {Ammonium serves as key nitrogen source and metabolic intermediate, yet excess causes toxicity. Ammonium uptake is mediated by ammonium transporters, whose regulation is poorly understood. While transport can easily be characterized in heterologous systems, measuring transporter activity in vivo remains challenging. Here we developed a simple assay for monitoring activity in vivo by inserting circularly-permutated GFP into conformation-sensitive positions of two plant and one yeast ammonium transceptors (\&rsquo;AmTrac and \&rsquo;MepTrac\&rsquo;). Addition of ammonium to yeast cells expressing the sensors triggered concentration dependent fluorescence intensity (FI) changes that strictly correlated with the activity of the transporter. Fluorescence-based activity sensors present a novel technology for monitoring the interaction of the transporters with their substrates, the activity of transporters and their regulation in vivo, which is particularly valuable in the context of analytes for which no radiotracers exist, as well as for cell-specific and subcellular transport processes that are otherwise difficult to track.},
  language  = {en}
}
@article{DemetriouPashalidisNicolaidesetal.2013,
  author    = {Demetriou, Antri and Pashalidis, Ioannis and Nicolaides, Athanassios V. and Kumke, Michael Uwe},
  title     = {Surface mechanism of the boron adsorption on alumina in aqueous solutions},
  series = {Desalination and water treatment : science and engineering},
  volume    = {51},
  journal   = {Desalination and water treatment : science and engineering},
  number    = {31-33},
  publisher = {Taylor \& Francis Group},
  address   = {Philadelphia},
  issn      = {1944-3994},
  doi       = {10.1080/19443994.2013.764354},
  pages     = {6130 -- 6136},
  year      = {2013},
  abstract  = {The adsorption of boron (boric acid) from aqueous solutions on alumina has been investigated at pH 8.0, I=0.1M NaClO4, T=22 +/- 3 degrees C, and under normal atmospheric conditions. The characterization of the adsorbed species was performed by Raman spectroscopy and the spectroscopic speciation was assisted by theoretical DFT calculations. Evaluation of the spectroscopic data points to the formation of inner-sphere surface complexes and indicates the formation of two different types of adsorbed boron species. The theoretical calculations corroborate the spectroscopic data and indicate that at low boron concentration the monodentate surface species dominates, whereas increased boron concentration favors the formation of a bidentate surface species. Assuming low coverage, the conditional formation constant for the monodentate surface species has been evaluated to be log=4.1 +/- 0.1.},
  language  = {en}
}
@article{DoscheKumkeArieseetal.2003,
  author    = {Dosche, Carsten and Kumke, Michael Uwe and Ariese, Freek and Bader, Arjen N. and Gooijer, Cees and Dosa, P. I. and Han, S. and Miljanic, Ognjen S. and Vollhardt, K. Peter C. and Puchta, Ralph and Hommes, N. J. R. V.},
  title     = {Shpol'skii spectroscopy and vibrational analysis of [N]phenylenes},
  year      = {2003},
  language  = {en}
}
@article{DoscheKumkeLoehmannsroebenetal.2004,
  author    = {Dosche, Carsten and Kumke, Michael Uwe and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Ariese, Freek and Bader, Arjen N. and Gooijer, Cees and Miljanic, Ognjen S. and Iwamoto, M. and Vollhardt, K. Peter C. and Puchta, Ralph and Hommes, N. J. R. V.},
  title     = {Deuteration effects on the vibronic structure of the fluorescence spectra and the internal conversion rates of triangular [4]phenylene},
  issn      = {1463-9076},
  year      = {2004},
  abstract  = {Deuteration effects on the vibronic structure of the emission and excitation spectra of triangular [ 4] phenylene (D-3h [4]phenylene) were studied using laser-excited Shpol'skii spectroscopy (LESS) in an octane matrix at 4.2 K. For correct assignment of the vibrational modes, the experimental results were compared with calculated frequencies (B3LYP/6-31G*). CH vibrations were identified by their characteristic isotopic shifts in the spectra of deuterated triangular [4]phenylenes. Two CC stretching modes, at 100 cm(-1) and 1176 cm(-1), suitable as probes for bond strength changes in the excited state, were identified. The isotope effect on the internal conversion rates of triangular [4] phenylene was evaluated from measurements of temperature dependent lifetime. Isotope dependency and the magnitude of the internal conversion rates indicate that internal conversion in triangular [4] phenylene is most likely induced by CH vibrations. The results obtained by LESS and lifetime measurements were compared with PM3 PECI calculations of the excited state structure. The theoretical results and the relation between ground and excited state vibration energies of the 1176 cm(-1) probe vibration indicate a reduction of bond alternation of the central cyclohexatriene ring in the excited state},
  language  = {en}
}
@article{DraffehnEichhorstWiesneretal.2016,
  author    = {Draffehn, Soeren and Eichhorst, Jenny and Wiesner, Burkhard and Kumke, Michael Uwe},
  title     = {Insight into the Modification of Polymeric Micellar and Liposomal Nanocarriers by Fluorescein-Labeled Lipids and Uptake-Mediating Lipopeptides},
  series = {Langmuir},
  volume    = {32},
  journal   = {Langmuir},
  publisher = {American Chemical Society},
  address   = {Heidelberg},
  issn      = {0743-7463},
  doi       = {10.1021/acs.langmuir.6b01487},
  pages     = {6928 -- 6939},
  year      = {2016},
  abstract  = {Encapsulation of diagnostic and therapeutic compounds in transporters improves their delivery to the point of need. An even more efficient treatment of diseases can be achieved using carriers with targeting or protecting moieties. In the present work, we investigated micellar and liposomal nanocarriers modified with fluorescein, peptides, and polymers that are covalently bound to fatty acids or phospholipids to ensure a self-driven incorporation into the micelles or liposomes. First, we characterized the photophysics of the fluorescent probes in the absence and in the presence of nanocarriers. Changes in the fluorescence decay time, quantum yield, and intensity of a fluorescein-labeled fatty acid (fluorescein-labeled palmitic acid [fPA]) and a fluorescein-labeled lipopeptide (P2fA2) were found. By exploiting these changes, we investigated a lipopeptide (P2A2 as an uptake-mediating unit) in combination with different nanocarriers (micelles and liposomes) and determined the corresponding association constant K-ass values, which were found to be very high. In addition, the mobility of fPA was exploited using fluorescence correlation spectroscopy (FCS) and fluorescence depolarization (FD) experiments to characterize the nanocarriers. Cellular uptake experiments with mouse brain endothelial cells provided information on the uptake behavior of liposomes modified by uptake-mediating P2A2 and revealed differences in the uptake behavior between pH-sensitive and pH-insensitive liposomes.},
  language  = {en}
}
@article{DraffehnKumke2016,
  author    = {Draffehn, Soeren and Kumke, Michael Uwe},
  title     = {Monitoring the Collapse of pH-Sensitive Liposomal Nanocarriers and Environmental pH Simultaneously: A Fluorescence-Based Approach},
  series = {Molecular pharmaceutics},
  volume    = {13},
  journal   = {Molecular pharmaceutics},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1543-8384},
  doi       = {10.1021/acs.molpharmaceut.5b00064},
  pages     = {1608 -- 1617},
  year      = {2016},
  abstract  = {Nowadays, the encapsulation of therapeutic compounds in so-called carrier systems is a very smart method to achieve protection as well as an improvement of their temporal and spatial distribution. After the successful transport to the point of care, the delivery has to be released under controlled conditions. To monitor the triggered release from the carrier, we investigated different fluorescent probes regarding their response to the pH-induced collapse of pH-sensitive liposomes (pHSLip), which occurs when the environmental pH falls below a critical value. Depending on the probe, the fluorescence decay time as well as fluorescence anisotropy can be used equally as key parameters for monitoring the collapse. Especially the application of a fluorescein labeled fatty acid (fPA) enabled the monitoring of the pHSLips collapse and the pH of its microenvironment simultaneously without interference. Varying the pH in the range of 3 < pH < 9, anisotropy data revealed the critical pH value at which the collapse of the pHSLips occurs. Complementary methods, e.g., fluorescence correlation spectroscopy and dynamic light scattering, supported the analysis based on the decay time and anisotropy. Additional experiments with varying incubation times yielded information on the kinetics of the liposomal collapse.},
  language  = {en}
}
@article{EisoldBehrendsWessigetal.2016,
  author    = {Eisold, Ursula and Behrends, Nicole and Wessig, Pablo and Kumke, Michael Uwe},
  title     = {Rigid Rod-Based FRET Probes for Membrane Sensing Applications},
  series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry},
  volume    = {120},
  journal   = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1520-6106},
  doi       = {10.1021/acs.jpcb.6b07285},
  pages     = {9935 -- 9943},
  year      = {2016},
  abstract  = {Oligospirothioketal (OSTK) rods are presented as an adjustable scaffold for optical membrane probes. The OSTK rods are readily incorporated into lipid bilayers due to their hydrophobic backbones. Because of their high length-over-diameter aspect ratio, only a minimal disturbance of the lipid bilayer is caused. OSTK rods show outstanding rigidity and allow defined labeling with fluorescent dyes, yielding full control of the orientation between the dye and OSTK skeleton. This. allows the construction of novel Forster resonance energy transfer probes with highly defined relative orientations of the transition dipole moments of the donor and acceptor dyes and makes the class of OSTK probes a power-fill, flexible toolbox for optical biosensing applications. Data on steady-state and time-resolved fluorescence experiments investigating the incorporation of coumarin- and [1,3]-dioxolo[4,5-f][1,3]benzo-dioxole-labeled OSTKs in large unilamellar vesicles are presented as a show case.},
  language  = {en}
}
@article{EisoldKupstatKlieretal.2014,
  author    = {Eisold, Ursula and Kupstat, Annette and Klier, Dennis Tobias and Primus, Philipp-A. and Pschenitza, Michael and Niessner, Reinhard and Knopp, Dietmar and Kumke, Michael Uwe},
  title     = {Probing the physicochemical interactions of 3-hydroxy-benzo[a]pyrene with different monoclonal and recombinant antibodies by use of fluorescence line-narrowing spectroscopy},
  series = {Analytical \& bioanalytical chemistry},
  volume    = {406},
  journal   = {Analytical \& bioanalytical chemistry},
  number    = {14},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1618-2642},
  doi       = {10.1007/s00216-013-7584-8},
  pages     = {3387 -- 3394},
  year      = {2014},
  abstract  = {Characterization of interactions between antigens and antibodies is of utmost importance both for fundamental understanding of the binding and for development of advanced clinical diagnostics. Here, fluorescence line-narrowing (FLN) spectroscopy was used to study physicochemical interactions between 3-hydroxybenzo[a]pyrene (3OH-BaP, as antigen) and a variety of solvent matrices (as model systems) or anti-polycyclic aromatic hydrocarbon antibodies (anti-PAH). We focused the studies on the specific physicochemical interactions between 3OH-BaP and different, previously obtained, monoclonal and recombinant anti-PAH antibodies. Control experiments performed with non-binding monoclonal antibodies and bovine serum albumin (BSA) indicated that nonspecific interactions did not affect the FLN spectrum of 3OH-BaP. The spectral positions and relative intensities of the bands in the FLN spectra are highly dependent on the molecular environment of the 3OH-BaP. The FLN bands correlate with different vibrational modes of 3OH-BaP which are affected by interactions with the molecular environment (pi-pi interactions, H-bonding, or van-der-Waals forces). Although the analyte (3OH-BaP) was the same for all the antibodies investigated, different binding interactions could be identified from the FLN spectra on the basis of structural flexibility and conformational multiplicity of the antibodies' paratopes.},
  language  = {en}
}
@article{EisoldSellrieMemczaketal.2018,
  author    = {Eisold, Ursula and Sellrie, Frank and Memczak, Henry and Andersson, Anika and Schenk, J{\"o}rg A. and Kumke, Michael Uwe},
  title     = {Dye tool box for a fluorescence enhancement immunoassay},
  series = {Bioconjugate chemistry},
  volume    = {29},
  journal   = {Bioconjugate chemistry},
  number    = {1},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1043-1802},
  doi       = {10.1021/acs.bioconjchem.7b00731},
  pages     = {203 -- 214},
  year      = {2018},
  abstract  = {Immunochemical analytical methods are very successful in clinical diagnostics and are nowadays also emerging in the control of food as well as monitoring of environmental issues. Among the different immunoassays, luminescence based formats are characterized by their outstanding sensitivity making this format especially attractive for future applications. The need for multiparameter detection capabilities calls for a tool box of dye labels in order to transduce the biochemical reaction into an optically detectable signal. Here, in a multiparameter approach each analyte may be detected by a different dye with a unique emission color (covering the blue to red spectral range) or a unique luminescence decay kinetics. In the case of a competitive immunoassay format for each of the different dye labels an individual antibody would be needed. In the present paper a slightly modified approach is presented using a 7-aminocoumarin unit as the basic antigen against which highly specific antibodies were generated. Leaving the epitope region in the dyes unchanged but introducing a side group in positon 3 of the coumarin system allowed us to tune the optical properties of the coumarin dyes without the necessity of new antibody generation. Upon modification of the parent coumarin unit the full spectral range from blue to deep red was accessed. In the manuscript the photophysical characterization of the coumarin derivatives and their corresponding immunocomplexes with two highly specific antibodies is presented. The coumarin dyes and their immunocomplexes were characterized by steady-state and time-resolved absorption as well as emission spectroscopy. Moreover, fluorescence depolarization measurements were carried out to complement the data stressing the different binding modes of the two antibodies. The binding modes were evaluated using the photophysics of 7-aminocoumarins and how it was affected in the respective immunocomplexes, namely, the formation of the intramolecular charge transfer (ICT) as well as the twisted intramolecular charge transfer (TICT). In contrast to other antibody-dye pairs reported a distinct fluorescence enhancement upon formation of the antibody-dye complex up to a factor of SO was found. Because of the easy emission color tuning by tailoring the coumarin substitution for the antigen binding in nonrelevant position 3 of the parent molecule, a dye tool box is on hand which can be used in the construction of competitive multiparameter fluorescence enhancement immunoassays (FenIA).},
  language  = {en}
}
@article{EisoldSellrieSchenketal.2015,
  author    = {Eisold, Ursula and Sellrie, Frank and Schenk, J{\"o}rg A. and Lenz, Christine and St{\"o}cklein, Walter F. M. and Kumke, Michael Uwe},
  title     = {Bright or dark immune complexes of anti-TAMRA antibodies for adapted fluorescence-based bioanalysis},
  series = {Analytical \& bioanalytical chemistry},
  volume    = {407},
  journal   = {Analytical \& bioanalytical chemistry},
  number    = {12},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1618-2642},
  doi       = {10.1007/s00216-015-8538-0},
  pages     = {3313 -- 3323},
  year      = {2015},
  abstract  = {Fluorescence labels, for example fluorescein or rhodamin derivatives, are widely used in bioanalysis applications including lateral-flow assays, PCR, and fluorescence microscopy. Depending on the layout of the particular application, fluorescence quenching or enhancement may be desired as the detection principle. Especially for multiplexed applications or high-brightness requirements, a tunable fluorescence probe can be beneficial. The alterations in the photophysics of rhodamine derivatives upon binding to two different anti-TAMRA antibodies were investigated by absorption and fluorescence-spectroscopy techniques, especially determining the fluorescence decay time and steady-state and time-resolved fluorescence anisotropy. Two monoclonal anti-TAMRA antibodies were generated by the hybridoma technique. Although surface-plasmon-resonance measurements clearly proved the high affinity of both antibodies towards 5-TAMRA, the observed effects on the fluorescence of rhodamine derivatives were very different. Depending on the anti-TAMRA antibody either a strong fluorescence quenching (G71-DC7) or a distinct fluorescence enhancement (G71-BE11) upon formation of the immune complex was observed. Additional rhodamine derivatives were used to gain further information on the binding interaction. The data reveal that such haptens as 5-TAMRA could generate different paratopes with equal binding affinities but different binding interactions, which provide the opportunity to adapt bioanalysis methods including immunoassays for optimized detection principles for the same hapten depending on the specific requirements.},
  language  = {en}
}
@article{EngelhardKumkeLoehmannsroeben2006,
  author    = {Engelhard, Sonja and Kumke, Michael Uwe and L{\"o}hmannsr{\"o}ben, Hans-Gerd},
  title     = {Examples of the application of optical process and quality sensing (OPQS) to beer brewing and polyurethane foaming processes},
  issn      = {1618-2642},
  doi       = {10.1007/s00216-005-3364-4},
  year      = {2006},
  abstract  = {Optical methods play an important role in process analytical technologies (PAT). Four examples of optical process and quality sensing (OPQS) are presented, which are based on three important experimental techniques: near- infrared absorption, luminescence quenching, and a novel method, photon density wave (PDW) spectroscopy. These are used to evaluate four process and quality parameters related to beer brewing and polyurethane (PU) foaming processes: the ethanol content and the oxygen (O-2) content in beer, the biomass in a bioreactor, and the cellular structures of PU foam produced in a pilot production plant},
  language  = {en}
}
@article{GehneFlehrKienzleretal.2012,
  author    = {Gehne, S{\"o}ren and Flehr, Roman and Kienzler, Andrea Altevogt Nee and Berg, Maik and Bannwarth, Willi and Kumke, Michael Uwe},
  title     = {Dye dynamics in three-color FRET samples},
  series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry},
  volume    = {116},
  journal   = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry},
  number    = {35},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1520-6106},
  doi       = {10.1021/jp3064273},
  pages     = {10798 -- 10806},
  year      = {2012},
  abstract  = {Time-resolved emission data (fluorescence decay and fluorescence depolarization) of two three-color Forster resonance energy transfer (tc-FRET) systems consisting of a carbostyril donor (D), a ruthenium complex (Ru) as relay dye, and a Cy5 derivative (Cy) or, optionally, an anthraquinone quencher (Q) were carefully analyzed using advanced distribution analysis models. Thereby, it is possible to get information on the flexibility and mobility of the chromophores which are bound to double stranded (ds) DNA. Especially the distance distribution based on the analysis of the fluorescence depolarization is an attractive approach to complement data of fluorescence decay time analysis. The distance distributions extracted from the experimental data were in excellent agreement with those determined from accessible volume (AV) simulations. Moreover, the study showed that for tc-FRET systems the combination of dyes emitting on different time scales (e.g., nanoseconds vs microseconds) is highly beneficial in the distribution analysis of time-resolved luminescence data in cases where macromolecules such as DNA are involved. Here, the short lifetimes can yield information on the rotation of the dye molecule itself and the long lifetime can give insight in the overall dynamics of the macromolecule.},
  language  = {en}
}
@article{GehneSydowDatheetal.2013,
  author    = {Gehne, S{\"o}ren and Sydow, Karl and Dathe, Margitta and Kumke, Michael Uwe},
  title     = {Characterization of cell-penetrating lipopeptide micelles by spectroscopic methods},
  series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry},
  volume    = {117},
  journal   = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry},
  number    = {46},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1520-6106},
  doi       = {10.1021/jp406053g},
  pages     = {14215 -- 14225},
  year      = {2013},
  abstract  = {The transport of bioactive compounds to the site of action is a great challenge. A promising approach to overcome application-related problems is the development of targeting colloidal transport systems, such as micelles which are equipped with uptake mediating moieties. Here, we investigated a set of novel lipopeptides which exhibit a surfactant-like structure due to attachment of two palmitoyl chains to the Nterminus of cationic or anionic amino acid sequences. We analyzed the association behavior of these lipopeptides by using 5(6)-carboxyfluorescein (CF)-labeled derivatives as a fluorescent probe and different spectroscopic methods such as fluorescence anisotropy and fluorescence correlation spectroscopy (FCS). The photophysical properties as well as the diffusion and rotational movements of the CF-labeled lipopeptides were exploited to determine the cmc and the size of the micelles consisting of lipopeptides. We could distinguish cationic and anionic lipopeptides by their association behavior and by studying the interactions with mouse brain capillary endothelial cells (b.end3). The cationic derivatives turned out to be very strong surfactants with a very low cmc in the micromolar range (0.5-14 mu M). The unique combination of micelle-forming property and cell-penetrating ability can pave the road for the development of a novel class of efficient drug carrier systems.},
  language  = {en}
}
@article{GrunzelPilarekSteinbruecketal.2014,
  author    = {Grunzel, Petra and Pilarek, Maciej and Steinbrueck, Doerte and Neubauer, Antje and Brand, Eva and Kumke, Michael Uwe and Neubauer, Peter and Krause, Mirja},
  title     = {Mini-scale cultivation method enables expeditious plasmid production in Escherichia coli},
  series = {Biotechnology journal : systems \& synthetic biology, nanobiotech, medicine},
  volume    = {9},
  journal   = {Biotechnology journal : systems \& synthetic biology, nanobiotech, medicine},
  number    = {1},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1860-6768},
  doi       = {10.1002/biot.201300177},
  pages     = {128 -- 136},
  year      = {2014},
  abstract  = {The standard procedure in the lab for plasmid isolation usually involves a 2-mL, 16 h over-night cultivation in 15-mL bioreaction tubes in LB medium. This is time consuming, and not suitable for high-throughput applications. This study shows that it is possible to produce plasmid DNA (pDNA) in a 1.5-mL microcentrifuge tube with only 100 L cultivation volume in less than 7 h with a simple protocol. Compared with the standard LB cultivation for pDNA production reaching a final pDNA concentration range of 1.5-4 mu g mL(-1), a 6- to 10-fold increase in plasmid concentration (from 10 up to 25 mu g mL(-1) cultivation volume) is achieved using an optimized medium with an internal substrate delivery system (EnBase (R)). Different strains, plasmids, and the applicability of different inoculation tools (i.e. different starting ODs) were compared, demonstrating the robustness of the system. Additionally, dissolved oxygen was monitored in real time online, indicating that under optimized conditions oxygen limitation can be avoided. We developed a simple protocol with a significantly decreased procedure time, enabling simultaneous handling of more samples, while a consistent quality and a higher final pDNA concentration are ensured.},
  language  = {en}
}
@article{HaubitzDrobotTsushimaetal.2021,
  author    = {Haubitz, Toni and Drobot, Bj{\"o}rn and Tsushima, Satoru and Steudtner, Robin and Stumpf, Thorsten and Kumke, Michael Uwe},
  title     = {Quenching mechanism of uranyl(VI) by chloride and bromide in aqueous and non-aqueous solutions},
  series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  volume    = {125},
  journal   = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  number    = {20},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1089-5639},
  doi       = {10.1021/acs.jpca.1c02487},
  pages     = {4380 -- 4389},
  year      = {2021},
  abstract  = {A major hindrance in utilizing uranyl(VI) luminescence as a standard analytical tool, for example, in environmental monitoring or nuclear industries, is quenching by other ions such as halide ions, which are present in many relevant matrices of uranyl(VI) speciation. Here, we demonstrate through a combination of time-resolved laser-induced fluorescence spectroscopy, transient absorption spectroscopy, and quantum chemistry that coordinating solvent molecules play a crucial role in U(VI) halide luminescence quenching. We show that our previously suggested quenching mechanism based on an internal redox reaction of the 1:2-uranyl-halide-complex holds also true for bromide-induced quenching of uranyl(VI). By adopting specific organic solvents, we were able to suppress the separation of the oxidized halide ligand X-2(center dot-) and the formed uranyl(V) into fully solvated ions, thereby "reigniting" U(VI) luminescence. Time-dependent density functional theory calculations show that quenching occurs through the outer-sphere complex of U(VI) and halide in water, while the ligand-to-metal charge transfer is strongly reduced in acetonitrile.},
  language  = {en}
}
@article{HaubitzFudickarLinkeretal.2020,
  author    = {Haubitz, Toni and Fudickar, Werner and Linker, Torsten and Kumke, Michael Uwe},
  title     = {pH-sensitive fluorescence switching of pyridylanthracenes},
  series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  volume    = {124},
  journal   = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  number    = {52},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1089-5639},
  doi       = {10.1021/acs.jpca.0c09911},
  pages     = {11017 -- 11024},
  year      = {2020},
  abstract  = {9,10-substituted anthracenes are known for their useful optical properties like fluorescence, which makes them frequently used probes in sensing applications. In this article, we investigate the fundamental photophysical properties of three pyridyl-substituted variants. The nitrogen atoms in the pyridinium six-membered rings are located in the ortho-, meta-, and para-positions in relation to the anthracene core. Absorption, fluorescence, and transient absorption measurements were carried out and were complemented by theoretical calculations. We monitored the photophysics of the anthracene derivatives in chloroform and water investigating the protonated as well as their nonprotonated forms. We found that the optical properties of the nonprotonated forms are strongly determined by the anthracene chromophore, with only small differences to other 9,10-substituted anthracenes, for example diphenyl anthracene. In contrast, protonation leads to a strong decrease in fluorescence intensity and lifetime. Transient absorption measurements and theoretical calculations revealed the formation of a charge-transfer state in the protonated chromophores, where electron density is shifted from the anthracene moiety toward the protonated pyridyl substituents. While the para- and ortho-derivatives' charge transfer is still moderately fluorescent, the meta-derivative is affected much stronger and shows nearly no fluorescence. This nitrogen-atom-position-dependent sensitivity to hydronium activity makes a combination of these fluorophores very attractive for pH-sensing applications covering a broadened pH range.},
  language  = {en}
}
@article{HaubitzJohnFreyseetal.2020,
  author    = {Haubitz, Toni and John, Leonard and Freyse, Daniel and Wessig, Pablo and Kumke, Michael Uwe},
  title     = {Investigating the Sulfur "Twist" on the Photophysics of DBD Dyes},
  series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  volume    = {124},
  journal   = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  number    = {22},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1089-5639},
  doi       = {10.1021/acs.jpca.0c01880},
  pages     = {4345 -- 4353},
  year      = {2020},
  abstract  = {The so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes are a new class of fluorescent dyes, with tunable photophysical properties like absorption, fluorescence lifetime, and Stokes shift. With the development of sulfur based DBDs, this dye class is extended even further for possible applications in spectroscopy and microscopy. In this paper we are investigating the basic photophysical properties and their implications for future applications for S-4-DBD as well as O-4-DBD. On the basis of time-resolved laser fluorescence spectroscopy, transient absorption spectroscopy, and UV/vis-spectroscopy, we determined the rate constants of the radiative and nonradiative deactivation processes as well as the energy of respective electronic states involved in the electronic deactivation of S-4-DBD and of O-4-DBD. For S-4-DBD we unraveled the triplet formation with intersystem crossing quantum yields of up to 80\%. By TD-DFT calculations we estimated a triplet energy of around 13500-14700 cm(-1) depending on the DBD dye and solvent. Through solvent dependent measurements, we found quadrupole moments in the range of 2 B.},
  language  = {en}
}
@article{HaubitzJohnWessigetal.2019,
  author    = {Haubitz, Toni and John, Leonard and Wessig, Pablo and Kumke, Michael Uwe},
  title     = {Photophysics of Acyl- and Ester-DBD Dyes},
  series = {the journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  volume    = {123},
  journal   = {the journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  number    = {22},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1089-5639},
  doi       = {10.1021/acs.jpca.9b02973},
  pages     = {4717 -- 4726},
  year      = {2019},
  abstract  = {A new generation of wavelength-tunable, fluorescent dyes, so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes, were developed a few years ago, and they showed great potential as probes, for example, for fluorescence microscopy. However, their photophysics is not fully explored and leaves open questions regarding their large fluorescence Stokes shifts and sensitivity to solvent conditions of differently substituted DBD dyes. To improve the understanding of the influence of the substitution pattern of the DBD dyes on their respective photophysics, transient absorption spectroscopy (TAS) was used, that is, a pump-probe experiment on the femtosecond timescale. TAS allows measurements of excited states, ground state recovery, solvent relaxation, and fluorescence properties on time scales of up to several nanoseconds. Two different DBD dye samples were investigated: aryl- and ester-substituted DBD dyes. Experiments were carried out in solvents with different polarities using different excitation energies and at different viscosities. Based on the experimental data and theoretical calculations, we were able to determine the conformational changes of the molecule due to electronic excitation and were able to investigate solvent relaxation processes for both types of DBD dyes. By generalizing the theory for quadrupole-induced solvent relaxation developed by Togashi et al., we derived quadrupole moments of both molecules in the ground and excited state. Our data showed differences in the binding of polar solvent molecules to the dyes depending on the substituent on the DBD dye. In the case of water as the solvent, an additional efficient quenching process in the electronically excited state was revealed, which was indicated by the observation of solvated electrons in the TAS signals.},
  language  = {en}
}
@article{HaubitzTsushimaSteudtneretal.2018,
  author    = {Haubitz, Toni and Tsushima, Satoru and Steudtner, Robin and Drobot, Bj{\"o}rn and Geipel, Gerhard and Stumpf, Thorsten and Kumke, Michael Uwe},
  title     = {Ultrafast Transient Absorption Spectroscopy of UO(2)(2+)and [UO2Cl](+)},
  series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  volume    = {122},
  journal   = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  number    = {35},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1089-5639},
  doi       = {10.1021/acs.jpca.8b05567},
  pages     = {6970 -- 6977},
  year      = {2018},
  abstract  = {For the only water coordinated "free" uranyl (VI) aquo ion in perchlorate solution we identified and assigned several different excited states and showed that the (3)Delta state is the luminescent triplet state from transient absorption spectroscopy. With additional data from other spectroscopic methods (TRLFS, UV/vis) we generated a detailed Jablonski diagram and determined rate constants for several state transitions, like the inner conversion rate constant from the (3)Phi state to the (3)Delta state transition to be 0.35 ps(-1). In contrast to luminescence measurements, it was possible to observe the highly quenched uranyl(VI) ion in highly concentrated chloride solution by TAS and we were able to propose a dynamic quenching mechanism, where chloride complexation is followed by the charge transfer from the excited state uranyl(VI) to chloride. This proposed quenching route is supported by TD-DFT calculations.},
  language  = {en}
}
@article{HesseKlierSgarzietal.2018,
  author    = {Hesse, Julia and Klier, Dennis Tobias and Sgarzi, Massimo and Nsubuga, Anne and Bauer, Christoph and Grenzer, Joerg and H{\"u}bner, Rene and Wislicenus, Marcus and Joshi, Tanmaya and Kumke, Michael Uwe and Stephan, Holger},
  title     = {Rapid Synthesis of Sub-10nm Hexagonal NaYF4-Based Upconverting Nanoparticles using Therminol((R))66},
  series = {ChemistryOpen : including thesis treasury},
  volume    = {7},
  journal   = {ChemistryOpen : including thesis treasury},
  number    = {2},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {2191-1363},
  doi       = {10.1002/open.201700186},
  pages     = {159 -- 168},
  year      = {2018},
  abstract  = {We report a simple one-pot method for the rapid preparation of sub-10nm pure hexagonal (-phase) NaYF4-based upconverting nanoparticles (UCNPs). Using Therminol((R))66 as a co-solvent, monodisperse UCNPs could be obtained in unusually short reaction times. By varying the reaction time and reaction temperature, it was possible to control precisely the particle size and crystalline phase of the UCNPs. The upconversion (UC) luminescence properties of the nanocrystals were tuned by varying the concentrations of the dopants (Nd3+ and Yb3+ sensitizer ions and Er3+ activator ions). The size and phase-purity of the as-synthesized core and core-shell nanocrystals were assessed by using complementary transmission electron microscopy, dynamic light scattering, X-ray diffraction, and small-angle X-ray scattering studies. In-depth photophysical evaluation of the UCNPs was pursued by using steady-state and time-resolved luminescence spectroscopy. An enhancement in the UC intensity was observed if the nanocrystals, doped with optimized concentrations of lanthanide sensitizer/activator ions, were further coated with an inert/active shell. This was attributed to the suppression of surface-related luminescence quenching effects.},
  language  = {en}
}
@misc{HesseKlierSgarzietal.2018,
  author    = {Hesse, Julia and Klier, Dennis Tobias and Sgarzi, Massimo and Nsubuga, Anne and Bauer, Christoph and Grenzer, J{\"o}rg and H{\"u}bner, Ren{\´e} and Wislicenus, Marcus and Joshi, Tanmaya and Kumke, Michael Uwe and Stephan, Holger},
  title     = {Rapid synthesis of sub-10 nm hexagonal NaYF4-based upconverting nanoparticles using Therminol® 66},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {613},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-42351},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423515},
  pages     = {10},
  year      = {2018},
  abstract  = {We report a simple one-pot method for the rapid preparation of sub-10nm pure hexagonal (-phase) NaYF4-based upconverting nanoparticles (UCNPs). Using Therminol((R))66 as a co-solvent, monodisperse UCNPs could be obtained in unusually short reaction times. By varying the reaction time and reaction temperature, it was possible to control precisely the particle size and crystalline phase of the UCNPs. The upconversion (UC) luminescence properties of the nanocrystals were tuned by varying the concentrations of the dopants (Nd3+ and Yb3+ sensitizer ions and Er3+ activator ions). The size and phase-purity of the as-synthesized core and core-shell nanocrystals were assessed by using complementary transmission electron microscopy, dynamic light scattering, X-ray diffraction, and small-angle X-ray scattering studies. In-depth photophysical evaluation of the UCNPs was pursued by using steady-state and time-resolved luminescence spectroscopy. An enhancement in the UC intensity was observed if the nanocrystals, doped with optimized concentrations of lanthanide sensitizer/activator ions, were further coated with an inert/active shell. This was attributed to the suppression of surface-related luminescence quenching effects.},
  language  = {en}
}
@article{HoangHaubitzKumke2018,
  author    = {Hoang, Hoa T. and Haubitz, Toni and Kumke, Michael Uwe},
  title     = {Photophysics of "Floppy" Dyadsas Potential Biomembrane Probes},
  series = {Journal of fluorescence},
  volume    = {28},
  journal   = {Journal of fluorescence},
  number    = {5},
  publisher = {Springer},
  address   = {New York},
  issn      = {1053-0509},
  doi       = {10.1007/s10895-018-2286-4},
  pages     = {1225 -- 1237},
  year      = {2018},
  abstract  = {In the study a dyad (C6 probe), constructed of two dyes with highly different hydrophobicities, was investigated by steady-state and time-resolved spectroscopic techniques in chloroform, methanol, and in phospholipid vesicles, respectively. The dyad was built on two dyes: the lipophilic benzo[a]pyrene (BaP) and the hydrophilic sulforhodamine B (SRB). The dyes were linked via a short, but flexible alkyl chain (six C-atoms). Based on their spectroscopic properties, BaP and SRB showed a very efficient non-radiative resonance energy transfer in solution. Incorporation into a lipid bilayer limited the relative flexibility (degree of freedom) between donor and acceptor and was used for the investigation of fundamental photophysical aspects (especially of FRET) as well as to elucidate the potential of the dyad to probe the interface of vesicles (or cells). The location of the two dyes in vesicles and their respective accessibility for interactions with dye-specific antibodies was investigated. Based on the alteration of the anisotropy, on the rotational correlation time as well as on the diffusion coefficient the incorporation of the C6 probe into the vesicles was evaluated. Especially the limitation in the relative movements of the two dyes was considered and used to differentiate between potential parameters, that influence the energy transfer in the dyad. Transient absorption spectroscopy (TAS) and pulsed-interleave single molecule fluorescence experiments were performed to better understand the intramolecular interactions in the dyad. Finally, in a showcase for a biosensing application of the dyads, the binding of an SRB-specific antibody was investigated when the dyad was incorporated in vesicles.},
  language  = {en}
}
@article{HoangMertensWessigetal.2018,
  author    = {Hoang, Hoa T. and Mertens, Monique and Wessig, Pablo and Sellrie, Frank and Schenk, J{\"o}rg A. and Kumke, Michael Uwe},
  title     = {Antibody Binding at the Liposome-Water Interface},
  series = {ACS Omega},
  volume    = {3},
  journal   = {ACS Omega},
  number    = {12},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {2470-1343},
  doi       = {10.1021/acsomega.8b03016},
  pages     = {18109 -- 18116},
  year      = {2018},
  abstract  = {Different signal amplification strategies to improve the detection sensitivity of immunoassays have been applied which utilize enzymatic reactions, nanomaterials, or liposomes. The latter are very attractive materials for signal amplification because liposomes can be loaded with a large amount of signaling molecules, leading to a high sensitivity. In addition, liposomes can be used as a cell-like "bioscaffold" to directly test recognition schemes aiming at cell-related processes. This study demonstrates an easy and fast approach to link the novel hydrophobic optical probe based on [1,3]dioxolo[4,5-f]-[1,3]benzodioxole (DBD dye mm239) with tunable optical properties to hydrophilic recognition elements (e.g., antibodies) using liposomes for signal amplification and as carrier of the hydrophobic dye. The fluorescence properties of mm239 (e.g., long fluorescence lifetime, large Stokes shift, high photostability, and high quantum yield), its high hydrophobicity for efficient anchoring in liposomes, and a maleimide bioreactive group were applied in a unique combination to build a concept for the coupling of antibodies or other protein markers to liposomes (coupling to membranes can be envisaged). The concept further allowed us to avoid multiple dye labeling of the antibody. Here, anti-TAMRA-antibody (DC7-Ab) was attached to the liposomes. In proof-of-concept, steady-state as well as time-resolved fluorescence measurements (e.g., fluorescence depolarization) in combination with single molecule detection (fluorescence correlation spectroscopy, FCS) were used to analyze the binding interaction between DC7-Ab and liposomes as well as the binding of the antigen rhodamine 6G (R6G) to the antibody. Here, the Forster resonance energy transfer (FRET) between mm239 and R6G was monitored. In addition to ensemble FRET data, single-molecule FRET (PIE-FRET) experiments using pulsed interleaved excitation were used to characterize in detail the binding on a single-molecule level to avoid averaging out effects.},
  language  = {en}
}
@article{KienzlerFlehrGehneetal.2012,
  author    = {Kienzler, Andrea Altevogt Nee and Flehr, Roman and Gehne, S{\"o}ren and Kumke, Michael Uwe and Bannwarth, Willi},
  title     = {Verification and biophysical characterization of a New Three-Color Forster Resonance-Energy-Transfer (FRET) System in DNA},
  series = {Helvetica chimica acta},
  volume    = {95},
  journal   = {Helvetica chimica acta},
  number    = {4},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {0018-019X},
  doi       = {10.1002/hlca.201100460},
  pages     = {543 -- 555},
  year      = {2012},
  abstract  = {We report on a new three-color FRET system consisting of three fluorescent dyes, i.e., of a carbostyril (=quinolin-2(1H)-one)-derived donor D, a (bathophenanthroline)ruthenium complex as a relay chromophore A1, and a Cy dye as A2 (FRET=Forster resonance-energy-transfer) (cf. Fig. 1). With their widely matching spectroscopic properties (cf. Fig. 2), the combination of these dyes yielded excellent FRET efficiencies. Furthermore, fluorescence lifetime measurements revealed that the long fluorescence lifetime of the Ru complex was transferred to the Cy dye offering the possibility to measure the whole system in a time-resolved mode. The FRET system was established on double-stranded DNA (cf. Fig. 3) but it should also be generally applicable to other biomolecules.},
  language  = {en}
}
@article{KienzlerFlehrKrameretal.2011,
  author    = {Kienzler, Andrea and Flehr, Roman and Kramer, Rolf A. and Gehne, Soeren and Kumke, Michael Uwe and Bannwarth, Willi},
  title     = {Novel Three-Color FRET Tool Box for Advanced Protein and DNA Analysis},
  series = {Bioconjugate chemistry},
  volume    = {22},
  journal   = {Bioconjugate chemistry},
  number    = {9},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1043-1802},
  doi       = {10.1021/bc2002659},
  pages     = {1852 -- 1863},
  year      = {2011},
  abstract  = {We report on a new three-color FRET system which we were able to verify in peptides as well as in synthetic DNA. All three chromophores could be introduced by a building block approach avoiding postsynthetic labeling. Additional features are robustness, matching spectroscopic properties, high-energy transfer, and sensitivity. The system was investigated in detail on a set of peptides as well as an array of tailored oligonucleotides. The detailed analysis of the experimental data and comparison with theoretical considerations were in excellent agreement. It is shown that in the case of polypeptides specific interaction with the fluorescence probes has to be considered. In contrast with DNA, the fluorescence probes did not show any indications of such interactions. The novel three-color FRET toolbox revealed the potential for applications studying fundamental processes of three interacting molecules in life science applications.},
  language  = {en}
}
@article{KietzkeNeherKumkeetal.2004,
  author    = {Kietzke, Thomas and Neher, Dieter and Kumke, Michael Uwe and Montenegro, Rivelino V. D. and Landfester, Katharina and Scherf, Ullrich},
  title     = {A nanoparticle approach to control the phase separation in polyfluorene photovoltaic devices},
  year      = {2004},
  abstract  = {Polymer solar cell devices with nanostructured blend layers have been fabricated using single- and dual- component polymer nanospheres. Starting from an electron-donating and an electron-accepting polyfluorene derivative, PFB and F8BT, dissolved in suitable organic solvents, dispersions of solid particles with mean diameters of ca. 50 nm, containing either the pure polymer components or a mixture of PFB and F8BT in each particle, were prepared with the miniemulsion process. Photovoltaic devices based on these particles have been studied with respect to the correlation between external quantum efficiency and layer composition. It is shown that the properties of devices containing a blend of single-component PFB and F8BT particles differ significantly from those of solar cells based on blend particles, even for the same layer composition. Various factors determining the quantum efficiency in both kinds of devices are identified and discussed, taking into account the spectroscopic properties of the particles. An external quantum efficiency of ca. 4\% is measured for a device made from polymer blend nanoparticles containing PFB:F8BT at a weight ratio of 1:2 in each individual nanosphere. This is among the highest values reported so far for photovoltaic cells using this material combination},
  language  = {en}
}
@article{KlierKumke2015,
  author    = {Klier, Dennis Tobias and Kumke, Michael Uwe},
  title     = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale},
  series = {RSC Advances : an international journal to further the chemical sciences},
  journal   = {RSC Advances : an international journal to further the chemical sciences},
  number    = {5},
  publisher = {RSC Publishing},
  address   = {London},
  issn      = {2046-2069},
  doi       = {10.1039/C5RA11502G},
  pages     = {67149 -- 67156},
  year      = {2015},
  abstract  = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.},
  language  = {en}
}
@misc{KlierKumke2015,
  author    = {Klier, Dennis Tobias and Kumke, Michael Uwe},
  title     = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-89618},
  pages     = {67149 -- 67156},
  year      = {2015},
  abstract  = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.},
  language  = {en}
}
@article{KlierKumke2015,
  author    = {Klier, Dennis Tobias and Kumke, Michael Uwe},
  title     = {Analysing the effect of the crystal structure on upconversion luminescence in Yb3+,Er3+-co-doped NaYF4 nanomaterials},
  series = {Journal of materials chemistry C ; Materials for optical and electronic devices},
  journal   = {Journal of materials chemistry C ; Materials for optical and electronic devices},
  number    = {3},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2050-7526},
  doi       = {10.1039/C5TC02218E},
  pages     = {11228 -- 11238},
  year      = {2015},
  abstract  = {NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to Tan = 700 °C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different Tan were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 °C < Tan < 600 °C the hexagonal lattice phase was dominant. For Tan < 300 °C hardly any change in the lattice phase could be deduced, whereas for Tan > 600 °C a back transfer to the α-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of Tan on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of Gfull/R is highly effected by the laser power only when the β-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 °C < Tan < 300 °C, which was not possible with the standard techniques.},
  language  = {en}
}
@misc{KlierKumke2015,
  author    = {Klier, Dennis Tobias and Kumke, Michael Uwe},
  title     = {Analysing the effect of the crystal structure on upconversion luminescence in Yb3+,Er3+-co-doped NaYF4 nanomaterials},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-89630},
  pages     = {11228 -- 11238},
  year      = {2015},
  abstract  = {NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to Tan = 700 °C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different Tan were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 °C < Tan < 600 °C the hexagonal lattice phase was dominant. For Tan < 300 °C hardly any change in the lattice phase could be deduced, whereas for Tan > 600 °C a back transfer to the α-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of Tan on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of Gfull/R is highly effected by the laser power only when the β-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 °C < Tan < 300 °C, which was not possible with the standard techniques.},
  language  = {en}
}
@article{KlierKumke2015,
  author    = {Klier, Dennis Tobias and Kumke, Michael Uwe},
  title     = {Analysing the effect of the crystal structure on upconversion luminescence in Yb3+, Er3+-co-doped NaYF4 nanomaterials},
  series = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  volume    = {3},
  journal   = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  number    = {42},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2050-7526},
  doi       = {10.1039/c5tc02218e},
  pages     = {11228 -- 11238},
  year      = {2015},
  abstract  = {NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to T-an = 700 degrees C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different T-an were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 degrees C < T-an < 600 degrees C the hexagonal lattice phase was dominant. For T-an < 300 degrees C hardly any change in the lattice phase could be deduced, whereas for T-an > 600 degrees C a back transfer to the alpha-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of T-an on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of G(full)/R is highly effected by the laser power only when the beta-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 degrees C < T-an < 300 degrees C, which was not possible with the standard techniques.},
  language  = {en}
}
@article{KlierKumke2015,
  author    = {Klier, Dennis Tobias and Kumke, Michael Uwe},
  title     = {Upconversion Luminescence Properties of NaYF4:Yb:Er Nanoparticles Codoped with Gd3+},
  series = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  volume    = {119},
  journal   = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  number    = {6},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1932-7447},
  doi       = {10.1021/jp5103548},
  pages     = {3363 -- 3373},
  year      = {2015},
  abstract  = {The temperature-dependent upconversion luminescence of NaYF4:Yb:Er nanoparticles (UCNP) containing different contents of Gd3+ as additional dopant was characterized. The UCNP were synthesized in a hydrothermal synthesis and stabilized with citrate in order to transfer them to the water phase. Basic characterization was carried out using TEM and DLS to determine the average size of the UCNP. The XRD technique was used to investigate the crystal lattice of the UCNP. It was found that due to the presence of Gd3+, an alteration of the lattice phase from a to beta was induced which was also reflected in the observed upconversion luminescence properties of the UCNP. A detailed analysis of the upconversion luminescence spectraespecially at ultralow temperaturesrevealed the different effects of phonon coupling between the host lattice and the sensitizer (Yb3+) as well as the activator (Er3+). Furthermore, the upconversion luminescence intensity reached a maximum between 15 and 250 K depending on Gd3+ content. In comparison to the very complex temperature behavior of the upconversion luminescence in the temperature range <273 K, the luminescence intensity ratio of H-2(11/2)-> I-4(15/2) to S-4(3/2)-> I-4(15/2) (R = G1/G2) in a higher temperature range can be described by an Arrhenius-type equation.},
  language  = {en}
}
@article{KlierKumke2015,
  author    = {Klier, Dennis Tobias and Kumke, Michael Uwe},
  title     = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale},
  series = {RSC Advances},
  volume    = {5},
  journal   = {RSC Advances},
  number    = {82},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2046-2069},
  doi       = {10.1039/c5ra11502g},
  pages     = {67149 -- 67156},
  year      = {2015},
  abstract  = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure beta crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.},
  language  = {en}
}
@article{KramerFlehrLayetal.2009,
  author    = {Kramer, Rolf A. and Flehr, Roman and Lay, Myriam and Kumke, Michael Uwe and Bannwarth, Willi},
  title     = {Comparative studies of different quinoline derivatives as donors in fluorescence-resonance-energy-transfer (FRET) : systems in combination with a (Bathophenanthroline)ruthenium(II) complex as acceptor},
  issn      = {0018-019X},
  doi       = {10.1002/hlca.200900235},
  year      = {2009},
  language  = {en}
}
@article{KramerKainmuellerFlehretal.2008,
  author    = {Kramer, Rolf A. and Kainm{\"u}ller, Eva K. and Flehr, Roman and Kumke, Michael Uwe and Bannwarth, Willi},
  title     = {Quenching of the long-lived Ru(II)bathophenanthroline luminescence for the detection of supramolecular interactions},
  year      = {2008},
  language  = {en}
}
@article{KukeMarmodeeEidneretal.2010,
  author    = {Kuke, S. and Marmodee, Bettina and Eidner, Sascha and Schilde, Uwe and Kumke, Michael Uwe},
  title     = {Intramolecular deactivation processes in complexes of salicylic acid or glycolic acid with Eu(III)},
  issn      = {0584-8539},
  year      = {2010},
  abstract  = {The complexation of Eu(III) by 2-hydroxy benzoic acid (2HB) or glycolic acid (GL) was investigated using steady- state and time-resolved laser spectroscopy. Experiments were carried out in H2O as well as in D2O in the temperature range of View the MathML source. The Eu(III) luminescence spectra and luminescence decay times were evaluated with respect to the temperature dependence of (i) the luminescence decay time ;, (ii) the energy of the View the MathML source transition, (iii) the width of the View the MathML source transition, and (iv) the asymmetry ratio calculated from the luminescence intensities of the View the MathML source and View the MathML source transition, respectively. The differences in ligand-related luminescence quenching are discussed. Based on the temperature dependence of the luminescence decay times an activation energy for the ligand-specific non-radiative deactivation in Eu(III)-2HB or Eu(III)-GL complexes was determined. It is stressed that ligand-specific quenching processes (other than OH quenching induced by water molecules) need to be determined and considered in detail, in order to extract speciation- relevant information from luminescence data (e.g., estimation of the number of water molecules nH2O in the first coordination sphere of Eu(III)). In case of 2HB, conclusions drawn from the evaluation of the Eu(III) luminescence are compared with results of a X-ray structure analysis.},
  language  = {en}
}
@phdthesis{Kumke2005,
  author    = {Kumke, Michael Uwe},
  title     = {Huminstoffe und organische Modellliganden und ihre Wechselwirkung mit Metallionen und polyzyklischen aromatischen Kohlenwasserstoffen},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6066},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {Immobilisierung bzw. Mobilisierung und Transport von Schadstoffen in der Umwelt, besonders in den Kompartimenten Boden und Wasser, sind von fundamentaler Bedeutung f{\"u}r unser ({\"U}ber)Leben auf der Erde. Einer der Hauptreaktionspartner f{\"u}r organische und anorganische Schadstoffe (Xenobiotika) in der Umwelt sind Huminstoffe (HS). HS sind Abbauprodukte pflanzlichen und tierischen Gewebes, die durch eine Kombination von chemischen und biologischen Ab- und Umbauprozessen entstehen. Bedingt durch ihre Genese stellen HS außerordentlich heterogene Stoffsysteme dar, die eine Palette von verschiedenartigen Wechselwirkungen mit Schadstoffen zeigen. Die Untersuchung der fundamentalen Wechselwirkungsmechanismen stellt ebenso wie deren quantitative Beschreibung h{\"o}chste Anforderungen an die Untersuchungsmethoden. Zur qualitativen und quantitativen Charakterisierung der Wechselwirkungen zwischen HS und Xenobiotika werden demnach analytische Methoden ben{\"o}tigt, die bei der Untersuchung von extrem heterogenen Systemen aussagekr{\"a}ftige Daten zu liefern verm{\"o}gen. Besonders spektroskopische Verfahren, wie z.B. lumineszenz-basierte Verfahren, besitzen neben der hervorragenden Selektivit{\"a}t und Sensitivit{\"a}t, auch eine Multidimensionalit{\"a}t (bei der Lumineszenz sind es die Beobachtungsgr{\"o}ßen Intensit{\"a}t IF, Anregungswellenl{\"a}nge lex, Emissionswellenl{\"a}nge lem und Fluoreszenzabklingzeit tF), die es gestattet, auch heterogene Systeme wie HS direkt zu untersuchen. Zur Charakterisierung k{\"o}nnen sowohl die intrinsischen Fluoreszenzeigenschaften der HS als auch die von speziell eingef{\"u}hrten Lumineszenzsonden verwendet werden. In beiden F{\"a}llen werden die zu Grunde liegenden fundamentalen Konzepte der Wechselwirkungen von HS mit Xenobiotika untersucht und charakterisiert. F{\"u}r die intrinsische Fluoreszenz der HS konnte gezeigt werden, dass neben molekularen Strukturen besonders die Verkn{\"u}pfung der Fluorophore im Gesamt-HS-Molek{\"u}l von Bedeutung ist. Konformative Freiheit und die Nachbarschaft zu als Energieakzeptor fungierenden HS-eigenen Gruppen sind wichtige Komponenten f{\"u}r die Charakteristik der HS-Fluoreszenz. Die L{\"o}schung der intrinsischen Fluoreszenz durch Metallkomplexierung ist demnach auch das Resultat der ver{\"a}nderten konformativen Freiheit der HS durch die gebundenen Metallionen. Es zeigte sich, dass abh{\"a}ngig vom Metallion sowohl L{\"o}schung als auch Verst{\"a}rkung der intrinsischen HS-Fluoreszenz beobachtet werden kann. Als extrinsische Lumineszenzsonden mit wohl-charakterisierten photophysikalischen Eigenschaften wurden polyzyklische aromatische Kohlenwasserstoffe und Lanthanoid-Ionen eingesetzt. Durch Untersuchungen bei sehr niedrigen Temperaturen (10 K) konnte erstmals die Mikroumgebung von an HS gebundenen hydrophoben Xenobiotika untersucht werden. Im Vergleich mit Raumtemperaturexperimenten konnte gezeigt werden, dass hydrophobe Xenobiotika an HS-gebunden in einer Mikroumgebung, die in ihrer Polarit{\"a}t analog zu kurzkettigen Alkoholen ist, vorliegen. F{\"u}r den Fall der Metallkomplexierung wurden Energietransferprozesse zwischen HS und Lanthanoidionen bzw. zwischen verschiedenen, gebundenen Lanthanoidionen untersucht. Basierend auf diesen Messungen k{\"o}nnen Aussagen {\"u}ber die beteiligten elektronischen Zust{\"a}nde der HS einerseits und Entfernungen von Metallbindungsstellen in HS selbst angeben werden. Es ist dabei zu beachten, dass die Experimente in L{\"o}sung bei realen Konzentrationen durchgef{\"u}hrt wurden. Aus Messung der Energietransferraten k{\"o}nnen direkte Aussagen {\"u}ber Konformations{\"a}nderungen bzw. Aggregationsprozesse von HS abgeleitet werden.},
  subject      = {Fluoreszenz},
  language  = {de}
}
@article{KumkeDoscheFlehretal.2006,
  author    = {Kumke, Michael Uwe and Dosche, Carsten and Flehr, Roman and Trowitzsch-Kienast, Wolfram and L{\"o}hmannsr{\"o}ben, Hans-Gerd},
  title     = {Spectroscopic characterization of the artificial siderophore pyridinochelin},
  issn      = {0939-5075},
  year      = {2006},
  language  = {en}
}
@misc{KumkeEidner2005,
  author    = {Kumke, Michael Uwe and Eidner, Sascha},
  title     = {Fluorescence and energy transfer processes of humic substances and related model compounds in terbium complexes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12255},
  year      = {2005},
  abstract  = {The fluorescence properties and the fluorescence quenching by Tb3+ of substituted benzoic acid were investigated in solution at different pH. The substituted benzoic acids were used as simple model compounds for chromophores present in humic substances (HS). It is shown that the fluorescence properties of the model compounds resemble fluorescence of HS quite well. A major factor determining the fluorescence of model compounds are proton transfer reactions in the electronically excited state. It is intriguing that the fluorescence of the model compounds was almost not quenched by Tb3+ while the HS fluorescence was decreased very effectively. From our results we concluded that proton transfer reactions as well as conformational reorientation processes play an important role in the fluorescence of HS. The luminescence of bound Tb3+ was sensitized by an energy transfer step upon excitation of the model compounds and of HS, respectively. For HS the observed sensitization was dependent on its origin indicating differences 1) in the connection between chromophores and binding sites and 2) in the energy levels of the chromophore triplet states. Hence, the observed sensitization of the Tb3+ luminescence could be useful to characterize structural differences of HS in solution. Interlanthanide energy transfer between Tb3+ and Nd3+ was used to determine the average distance R between both ions using the well-known formalism of luminescence resonance energy transfer. R was dependent on the origin of the HS reflecting the difference in structure. The value of Rmin seemed to be a unique feature of the HS. It was further found that upon variation of the pH R also changed. This demonstrates that the measurement of interlanthanide energy transfer can be used as a direct method to monitor conformational changes in HS.},
  language  = {en}
}
@article{KumkeEidnerKrueger2005,
  author    = {Kumke, Michael Uwe and Eidner, Sascha and Kr{\"u}ger, Tobias},
  title     = {Fluorescence quenching and luminescence sensitization in complexes of Tb3+ and Eu3+ with humic substances},
  year      = {2005},
  abstract  = {Intrinsic fluorescence quenching of humic substances (HS) and the sensitization of Ln(3+) luminescence (Ln3+ Tb3+, Eu3+) in HS complexes were investigated. Both measurements yielded complementary information on the complexation of metals by HS. Large differences between fulvic acids(FA)and humic acids (HA) were found. From time-resolved luminescence measurements it is concluded that a combination of energy transfer and energy back transfer between HS and Ln(3+) is responsible for the observed luminescence decay characteristics. In the case of Eu3+, an additional participation of charge-transfer states is suggested. A new concept for the evaluation of the sensitized luminescence decays of Ln(3+) was adapted},
  language  = {en}
}
@misc{KumkeKlier2015,
  author    = {Kumke, Michael Uwe and Klier, Dennis Tobias},
  title     = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-102677},
  pages     = {67149 -- 67156},
  year      = {2015},
  abstract  = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.},
  language  = {en}
}
@article{KumkeLoehmannsroeben2009,
  author    = {Kumke, Michael Uwe and L{\"o}hmannsr{\"o}ben, Hans-Gerd},
  title     = {Introduction to fluorescence spectroscopy},
  year      = {2009},
  language  = {en}
}
@article{KumkeOhlenbuschFrimmel2000,
  author    = {Kumke, Michael Uwe and Ohlenbusch, G. and Frimmel, Fritz Hartmann},
  title     = {Sorption of phenols to dissolved organic matter investigaded by solid phase micriextrakrion},
  year      = {2000},
  language  = {en}
}
@article{KumkeSpechtFrimmel2000,
  author    = {Kumke, Michael Uwe and Specht, C. H. and Frimmel, Fritz Hartmann},
  title     = {Characterization of NOM adsorption to clay minerals by sizs exclusion chromatography},
  year      = {2000},
  language  = {en}
}
@article{KumkeZwienerAbbtBraunetal.2000,
  author    = {Kumke, Michael Uwe and Zwiener, Christian and Abbt-Braun, Gudrun and Frimmel, Fritz Hartmann},
  title     = {Spectroscopic characterization of fulvic acid fractions of a contaminated groundwater},
  year      = {2000},
  language  = {en}
}
@article{KupstatKumkeHildebrandt2011,
  author    = {Kupstat, Annette and Kumke, Michael Uwe and Hildebrandt, Niko},
  title     = {Toward sensitive, quantitative point-of-care testing (POCT) of protein markers miniaturization of a homogeneous time-resolved fluoroimmunoassay for prostate-specific antigen detection},
  series = {The analyst : the analytical journal of the Royal Society of Chemistry},
  volume    = {136},
  journal   = {The analyst : the analytical journal of the Royal Society of Chemistry},
  number    = {5},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {0003-2654},
  doi       = {10.1039/c0an00684j},
  pages     = {1029 -- 1035},
  year      = {2011},
  abstract  = {Point-of-care testing (POCT) systems which allow for a sensitive, quantitative detection of protein markers are extremely useful for the early detection and therapy progress monitoring of cancer. However, currently commercially available POCT devices are mainly limited to the qualitative detection of protein markers. In this study we demonstrate the successive miniaturization of a sensitive and fast assay for the quantitative detection of prostate-specific antigen (PSA) using a well established and clinically approved homogeneous time-resolved fluoroimmunoassay technology (TRACE (R)) on a commercial plate-reader system (KRYPTOR (R)). Regarding the initial requirements for the development of POCT devices we applied a 30-fold assay volume reduction (150 mu L to 5 mu L) to achieve a reasonable lab-on-a-chip volume and a 24-fold and 120-fold excitation pulse energy reduction to achieve reasonable pulse energies for low-cost miniature excitation sources. Due to highly efficient optimization of key POCT parameters our miniaturized PSA assay achieved a 30\% increased sensitivity and a 2-fold improved limit of detection compared to the standard plate-reader method. Our results demonstrate the successful implementation of key parameters for a significant miniaturization and for cost reduction in the clinically approved KRYPTOR (R) platform for protein detection. The technological alterations required are easy-to-implement and can be immediately adapted for more than 30 diagnostic protein markers already available for the KRYPTOR (R) platform. These features strongly recommend our assay format to be utilized in innovative, sensitive, quantitative POCT of protein markers.},
  language  = {en}
}
@article{KupstatRitschelKumke2011,
  author    = {Kupstat, Annette and Ritschel, Thomas and Kumke, Michael Uwe},
  title     = {Oxazine Dye-Conjugated DNA Oligonucleotides Forster Resonance Energy Transfer in View of Molecular Dye-DNA Interactions},
  series = {Bioconjugate chemistry},
  volume    = {22},
  journal   = {Bioconjugate chemistry},
  number    = {12},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1043-1802},
  doi       = {10.1021/bc200379y},
  pages     = {2546 -- 2557},
  year      = {2011},
  abstract  = {In this work, the photophysical properties of two oxazine dyes (ATTO 610 and ATTO 680) covalently attached via a C6-amino linker to the 5'-end of short single-stranded as well as double-stranded DNA (ssDNA and dsDNA, respectively) of different lengths were investigated. The two oxazine dyes were chosen because of the excellent spectral overlap, the high extinction coefficients, and the high fluorescence quantum yield of ATTO 610, making them an attractive Forster resonance energy transfer (FRET) pair for bioanalytical applications in the far-red spectral range. To identify possible molecular dye-DNA interactions that cause photophysical alterations, we performed a detailed spectroscopic study, including time-resolved fluorescence anisotropy and fluorescence correlation spectroscopy measurements. As an effect of the DNA conjugation, the absorption and fluorescence maxima of both dyes were bathochromically shifted and the fluorescence decay times were increased. Moreover, the absorption of conjugated ATTO 610 was spectrally broadened, and a dual fluorescence emission was observed. Steric interactions with ssDNA as well as dsDNA were found for both dyes. The dye-DNA interactions were strengthened from ssDNA to dsDNA conjugates, pointing toward interactions with specific dsDNA domains (such as the top of the double helix). Although these interactions partially blocked the dye-linker rotation, a free (unhindered) rotational mobility of at least one dye facilitated the appropriate alignment of the transition dipole moments in doubly labeled ATTO 610/ATTO 680-dsDNA conjugates for the performance of successful FRET. Considering the high linker flexibility for the determination of the donor-acceptor distances, good accordance between theoretical and experimental FRET parameters was obtained. The considerably large Forster distance of similar to 7 nm recommends the application of this FRET pair not only for the detection of binding reactions between nucleic acids in living cells but also for monitoring interactions of larger biomolecules such as proteins.},
  language  = {en}
}
@article{LippoldEidnerKumkeetal.2017,
  author    = {Lippold, Holger and Eidner, Sascha and Kumke, Michael Uwe and Lippmann-Pipke, Johanna},
  title     = {Dynamics of metal-humate complexation equilibria as revealed by isotope exchange studies - a matter of concentration and time},
  series = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society},
  volume    = {197},
  journal   = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0016-7037},
  doi       = {10.1016/j.gca.2016.10.019},
  pages     = {62 -- 70},
  year      = {2017},
  abstract  = {Complexation with dissolved humic matter can be crucial in controlling the mobility of toxic or radioactive contaminant metals. For speciation and transport modelling, a dynamic equilibrium process is commonly assumed, where association and dissociation run permanently. This is, however, questionable in view of reported observations of a growing resistance to dissociation over time. In this study, the isotope exchange principle was employed to gain direct insight into the dynamics of the complexation equilibrium, including kinetic inertisation phenomena. Terbium(III), an analogue of trivalent actinides, was used as a representative of higher-valent metals. Isotherms of binding to (flocculated) humic acid, determined by means of Tb-160 as a radiotracer, were found to be identical regardless of whether the radioisotope was introduced together with the bulk of stable Tb-159 or subsequently after pre-equilibration for up to 3 months. Consequently, there is a permanent exchange of free and humic-bound Tb since all available binding sites are occupied in the plateau region of the isotherm. The existence of a dynamic equilibrium was thus evidenced. There was no indication of an inertisation under these experimental conditions. If the small amount of Tb-160 was introduced prior to saturation with Tb-159, the expected partial desorption of Tb-160 occurred at much lower rates than observed for the equilibration process in the reverse procedure. In addition, the rates decreased with time of pre-equilibration. Inertisation phenomena are thus confined to the stronger sites of humic molecules (occupied at low metal concentrations). Analysing the time-dependent course of isotope exchange according to first-order kinetics indicated that up to 3 years are needed to attain equilibrium. Since, however, metal-humic interaction remains reversible, exchange of metals between humic carriers and mineral surfaces cannot be neglected on the long time scale to be considered in predictive transport models.},
  language  = {en}
}
@article{LippoldEidnerKumkeetal.2012,
  author    = {Lippold, Holger and Eidner, Sascha and Kumke, Michael Uwe and Lippmann-Pipke, Johanna},
  title     = {Diffusion, degradation or on-site stabilisation - identifying causes of kinetic processes involved in metal-humate complexation},
  series = {Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry},
  volume    = {27},
  journal   = {Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry},
  number    = {1},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0883-2927},
  doi       = {10.1016/j.apgeochem.2011.11.001},
  pages     = {250 -- 256},
  year      = {2012},
  abstract  = {The applicability of equilibrium models for humic-bound transport of toxic or radioactive metals is affected by kinetic processes leading to an increasing inertness of metal-humic complexes. The chemical background is not yet understood. It is widely believed that bound metals undergo an in-diffusion process within the humic colloids, changing from weaker to stronger binding sites. This work is focussed on the competition effect of Al(III) on complexation of Tb(III) or Eu(III) as analogues of trivalent actinides. By using ion exchange and spectroscopic methods, their bound fractions were determined for solutions of Al and humic acid that had been pre-equilibrated for different periods of time. Whilst the amount of bound Al remained unchanged, its blocking effect was found to increase over a time frame of 2 days, which corresponds to the kinetics of the increase in complex inertness reported in most pertinent studies. Thus, the derived "diffusion theory'' turned out to be inapplicable, since it cannot explain an increase in competition for the "initial'' sites. A delayed degradation of polynuclear species (as found for Fe) does not occur. Consequently, the temporal changes must be based on structural rearrangements in the vicinity of bound Al, complicating the exchange or access. Time-dependent studies by laser fluorescence spectroscopy (steady-state and time-resolved) yielded evidence of substantial alterations, which were, however, immediately induced and did not show any significant trend on the time scale of interest, suggesting that the stabilisation process is based on comparatively moderate changes.},
  language  = {en}
}
@article{LuschtinetzDoscheKumke2009,
  author    = {Luschtinetz, Franziska and Dosche, Carsten and Kumke, Michael Uwe},
  title     = {Influence of streptavidin on the absorption and fluorescence properties of cyanine dyes},
  issn      = {1043-1802},
  doi       = {10.1021/Bc800497v},
  year      = {2009},
  abstract  = {Cyanine dyes have become widely used fluorescence labels in clinical and biological chemistry. In particular, cyanine dyes with excitation wavelengths lambda(ex) > 600 nm are often used in biological applications. However, aggregation behavior and matrix effects on cyanine fluorescence are not fully understood yet and interfere with the data interpretation. In this study, we analyzed the spectroscopic characteristics of a model system consisting of the biotinylated cyanine dyes DY-635 and DY-647 and their streptavidin conjugates. On the basis of the spectroscopic data, the interaction processes between cyanine dye molecules and proteins are discussed. Binding to streptavidin had a significant influence on both fluorescence and anisotropy decays of the cyanine dyes investigated. In particular, the fluorescence anisotropy was significantly altered, making it a promising detection parameter for bioanalytical applications in connection with the cyanine dyes used in the present study. In order to evaluate the time-resolved anisotropy, the introduction of a sophisticated kinetic model was required to describe the contributions from different fluorescing species properly. The rotational motion of streptavidin-bound dyes was analyzed using the associated anisotropy model, which allowed discrimination between contributions from different microenvironments. The anisotropy decay times increased by a factor of up to 20 due to protein binding.},
  language  = {en}
}
@misc{LopezdeGuerenuBastianWessigetal.2019,
  author    = {L{\´o}pez de Guere{\~n}u, Anna and Bastian, Philipp and Wessig, Pablo and John, Leonard and Kumke, Michael Uwe},
  title     = {Energy transfer between tm-doped upconverting nanoparticles and a small organic dye with large stokes shift},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe},
  number    = {961},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-47224},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-472240},
  pages     = {19},
  year      = {2019},
  abstract  = {Lanthanide-doped upconverting nanoparticles (UCNP) are being extensively studied for bioapplications due to their unique photoluminescence properties and low toxicity. Interest in RET applications involving UCNP is also increasing, but due to factors such as large sizes, ion emission distributions within the particles, and complicated energy transfer processes within the UCNP, there are still many questions to be answered. In this study, four types of core and core-shell NaYF4-based UCNP co-doped with Yb3+ and Tm3+ as sensitizer and activator, respectively, were investigated as donors for the Methyl 5-(8-decanoylbenzo[1,2-d:4,5-d ']bis([1,3]dioxole)-4-yl)-5-oxopentanoate (DBD-6) dye. The possibility of resonance energy transfer (RET) between UCNP and the DBD-6 attached to their surface was demonstrated based on the comparison of luminescence intensities, band ratios, and decay kinetics. The architecture of UCNP influenced both the luminescence properties and the energy transfer to the dye: UCNP with an inert shell were the brightest, but their RET efficiency was the lowest (17\%). Nanoparticles with Tm3+ only in the shell have revealed the highest RET efficiencies (up to 51\%) despite the compromised luminescence due to surface quenching.},
  language  = {en}
}
@article{LopezdeGuerenuBastianWessigetal.2019,
  author    = {L{\´o}pez de Guere{\~n}u, Anna and Bastian, Philipp and Wessig, Pablo and John, Leonard and Kumke, Michael Uwe},
  title     = {Energy Transfer between Tm-Doped Upconverting Nanoparticles and a Small Organic Dye with Large Stokes Shift},
  series = {Biosensors : open access journal},
  volume    = {9},
  journal   = {Biosensors : open access journal},
  number    = {1},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2079-6374},
  doi       = {10.3390/bios9010009},
  pages     = {17},
  year      = {2019},
  abstract  = {Lanthanide-doped upconverting nanoparticles (UCNP) are being extensively studied for bioapplications due to their unique photoluminescence properties and low toxicity. Interest in RET applications involving UCNP is also increasing, but due to factors such as large sizes, ion emission distributions within the particles, and complicated energy transfer processes within the UCNP, there are still many questions to be answered. In this study, four types of core and core-shell NaYF4-based UCNP co-doped with Yb3+ and Tm3+ as sensitizer and activator, respectively, were investigated as donors for the Methyl 5-(8-decanoylbenzo[1,2-d:4,5-d ']bis([1,3]dioxole)-4-yl)-5-oxopentanoate (DBD-6) dye. The possibility of resonance energy transfer (RET) between UCNP and the DBD-6 attached to their surface was demonstrated based on the comparison of luminescence intensities, band ratios, and decay kinetics. The architecture of UCNP influenced both the luminescence properties and the energy transfer to the dye: UCNP with an inert shell were the brightest, but their RET efficiency was the lowest (17\%). Nanoparticles with Tm3+ only in the shell have revealed the highest RET efficiencies (up to 51\%) despite the compromised luminescence due to surface quenching.},
  language  = {en}
}
@article{LopezdeGuerenuKurganovaKlierHaubitzetal.2022,
  author    = {L{\´o}pez de Guere{\~n}u Kurganova, Anna and Klier, Dennis Tobias and Haubitz, Toni and Kumke, Michael Uwe},
  title     = {Influence of Gd3+ doping concentration on the properties of Na(Y,Gd)F-4},
  series = {Photochemical \& photobiological sciences / European Society for Photobiology},
  volume    = {21},
  journal   = {Photochemical \& photobiological sciences / European Society for Photobiology},
  number    = {2},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1474-905X},
  doi       = {10.1007/s43630-021-00161-4},
  pages     = {235 -- 245},
  year      = {2022},
  abstract  = {We present a systematic study on the properties of Na(Y,Gd)F-4-based upconverting nanoparticles (UCNP) doped with 18\% Yb3+, 2\% Tm3+, and the influence of Gd3+ (10-50 mol\% Gd3+). UCNP were synthesized via the solvothermal method and had a range of diameters within 13 and 50 nm. Structural and photophysical changes were monitored for the UCNP samples after a 24-month incubation period in dry phase and further redispersion. Structural characterization was performed by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) as well as dynamic light scattering (DLS), and the upconversion luminescence (UCL) studies were executed at various temperatures (from 4 to 295 K) using time-resolved and steady-state spectroscopy. An increase in the hexagonal lattice phase with the increase of Gd3+ content was found, although the cubic phase was prevalent in most samples. The Tm3+-luminescence intensity as well as the Tm3+-luminescence decay times peaked at the Gd3+ concentration of 30 mol\%. Although the general upconverting luminescence properties of the nanoparticles were preserved, the 24-month incubation period lead to irreversible agglomeration of the UCNP and changes in luminescence band ratios and lifetimes.},
  language  = {en}
}
@article{MarangEidnerKumkeetal.2009,
  author    = {Marang, Laura and Eidner, Sascha and Kumke, Michael Uwe and Benedetti, Marc F. and Reiller, Pascal E.},
  title     = {Characterization of competitive binding of Eu(III)/Cu(II) and Eu(III)/Ca(II) to Gorleben humic acid},
  issn      = {0016-7037},
  doi       = {10.1016/j.gca.2009.05.011},
  year      = {2009},
  language  = {en}
}
@article{MarangEidnerKumkeetal.2009,
  author    = {Marang, Laura and Eidner, Sascha and Kumke, Michael Uwe and Benedetti, Marc F. and Reiller, Pascal E.},
  title     = {Spectroscopic characterization of the competitive binding of Eu(III), Ca(II) and Cu(II) to a sedimentary originated humic acid},
  issn      = {0009-2541},
  doi       = {10.1016/j.chemgeo.2009.03.003},
  year      = {2009},
  abstract  = {The competition between REE, alkaline earth and d-transition metals for organic matter binding sites is still an open field of research; particularly, the mechanisms governing these phenomena need to be characterized in more detail. In this study, we examine spectroscopically the mechanisms of competitive binding of Eu(III)/Cu(II) and Eu(III)/ Ca(II) pair to Gorleben humic acid (HA), as previously proposed in the framework of the NICA-Donnan model. The evolution of time-resolved laser induced luminescence spectra of humic-complexed Eu(Ill) showed two strikingly different environments for a comparable bound proportion for Cu(II) and Ca(II). Cu(II) seems to compete more effectively with Eu(III) inducing its release into the Donnan phase, and into the bulk solution as free Eu3+. This is evidenced both by the shapes of the spectra and by the decrease in the luminescence decay times. In contrast with that, Ca(II) induces a modification of the HA structure, which enhances the luminescence of humic-bound Eu(III), and causes a minor modification of the chemical environment of the complexed rare earth ion.},
  language  = {en}
}
@article{MarangReillerEidneretal.2008,
  author    = {Marang, Laura and Reiller, Pascal E. and Eidner, Sascha and Kumke, Michael Uwe and Benedetti, Marc F.},
  title     = {Combining spectroscopic and potentiometric approaches to characterize competitive binding to humic substances},
  doi       = {10.1021/Es702858p},
  year      = {2008},
  abstract  = {In an area that contains high concentrations of natural organic matter, it is expected that it plays an important role on the behavior of rare earth elements (REE), like europium, and of trivalent actinides. Competitive interactions with H+, inorganic species, major cations, e.g. Ca(II) or Mg(II), could influence these metals transport and bioavailability. Competitive experiments between cations, which can bind differently to humic substances and Eu3+,will bring an improved understanding of the competitive mechanisms. The aim of this study is to acquire data for Eu(III)/Cu(II) and Eu(III)/Ca(II) competitive binding to a sedimentary originated humic acid (Gorleben, Germany). The NICA-Donnan parameters for Ca2+, Cu2+, and Eu3+ obtained from competitive binding experiments using Ca2+ or Cu2+ ion selective electrodes were used to model time-resolved laser fluorescence spectroscopy (TRLFS) measurements. Eu3+ and Cu2+ are in direct competition for the same type of sites,whereas Ca2+ has an indirect influence through electrostatic binding.},
  language  = {en}
}
@article{MarmodeedeKlerkArieseetal.2009,
  author    = {Marmod{\´e}e, Bettina and de Klerk, Joost and Ariese, Freek and Gooijer, Cees and Kumke, Michael Uwe},
  title     = {Metal binding by humic substances : characterization by high-resolution-lanthanide-ion-probe-spectroscopy (HR- LIPS)},
  issn      = {0932-0784},
  year      = {2009},
  abstract  = {In ultra-low-temperature experiments at 4.7 K the luminescence of Eu(III) bound to different hydroxy- and methoxybenzoic acids and to humic substances (HS) was investigated. The benzoic acid derivatives were used as simple model compounds for common metal-binding structures in HS. The Eu(III) luminescence was directly excited by means of a pulsed dye laser, scanning through the D-5(0) -> F-7(0) transition of Eu(III) and subsequently, high-resolution total luminescence spectra (TLS) were recorded. Based on the thorough analysis of the high-resolution TLS conclusions were drawn with respect to the number of different complexes formed and to the symmetry of the complexes. The crystal-field strength parameter N-nu(B-2q) was dependent on the electrostatic forces induced by the ligands as well as on the symmetry of the complexes. The formation of thermodynamically stable complexes was found to be slow even for small model ligands such its 2-hydroxybenzoic acid. Comparison between the model compounds and HS clearly revealed that the carboxylate group is the dominant binding site in HS. Indices for the formation of chelates, e.g. similar to 2- hydroxybenzoic acid, were not found for HS.},
  language  = {en}
}
@article{MarmodeedeKlerkArieseetal.2009,
  author    = {Marmod{\´e}e, Bettina and de Klerk, Joost S. and Ariese, Freek and Gooijer, Cees and Kumke, Michael Uwe},
  title     = {High-resolution steady-state and time-resolved luminescence studies on the complexes of Eu(III) with aromatic or aliphatic carboxylic acids},
  issn      = {0003-2670},
  doi       = {10.1016/j.aca.2009.06.006},
  year      = {2009},
  abstract  = {Eu(III) luminescence spectroscopy, both in the steady-state and the time-resolved mode, is an appropriate technique to study the properties of complexes between heavy metal ions and humic substances (HS), which play a key role in the distribution of metal species in the environment. Unfortunately, room temperature luminescence spectra of Eu(III) complexes with aromatic and aliphatic carboxylic acids - model compounds of HS binding sites - are too broad to fully exploit their potential analytical information content. It is shown that under cryogenic conditions fluorescence-line- narrowing (FLN) is achieved, and the highly resolved spectra provide detailed information on the complexes. Ten model ligands were investigated. Total luminescence spectra (TLS) were recorded, using the D-5(0) -> F-7(0) transition for excitation and the D-5(0) -> F-7(1) and D-5(0) -> F-7(2) transitions for emission. The energy of the excitation transition depends on the ligand involved and the structure and composition of the complex. For most ligands, discontinuities in the high-resolution TLS indicated that more species, i.e. distinct complex structures, coexisted in the sample. Selective excitation was performed to measure the species-associated luminescence decay times tau. The latter strongly depend on nearby OH oscillators from coordinating water molecules or ligand hydroxyl groups. Furthermore, the asymmetry ratios r, defined as the intensity ratio of the D-5(0) -> F-7(2) and D-5(0) -> F-7(1) transitions, were calculated and the variation of the excitation energy E-exc with the splitting of the F-7(1) triplet (Delta E) was determined. which yielded the crystal field strength parameter N-nu(B-2q), as well as the crystal field parameters B-20 and B-22. An in-depth analysis of the results is presented, providing detailed information on the number of coexisting complexes, their stoichiometry, the number of water molecules in the first coordination sphere and their geometry (symmetry point group).},
  language  = {en}
}
@article{MarmodeeKlerkdeKumkeetal.2008,
  author    = {Marmod{\´e}e, Bettina and Klerk de, Joost and Kumke, Michael Uwe and Ariese, Freek and Gooijer, Cees},
  title     = {Spectroscopic investigations of complexes between Eu(III) and aromatic carboxylic ligands},
  doi       = {10.1016/j.jallcom.2007.04.150},
  year      = {2008},
  abstract  = {In order to obtain information on the number and symmetry of the different Eu3+ complexes formed with several hydroxybenzoic acids, ultra-low temperature luminescence measurements at 4.7 K were carried out. Hydroxybenzoic acids were used as simple model compounds for metal binding structures in humic substances (HS). Information on the complexes was extracted from high-resolution total luminescence spectra (TLS), which were obtained by scanning through the D-5(0) <-- F-7(0) transition of Eu(III) with a pulsed dye laser and measuring the emission in the wavelength range of the D- 5(0) --> F-7(0) and D-5(0) --> F-7(0) transitions simultaneously. By extracting the crystal field strength parameter N- v(B-2q) from the TLS, it was found that N-v(B-2q) was not directly correlated with the excitation energy. Further, the symmetry of the individual complexes formed was extracted from the experimental data. (C) 2007 Elsevier B.V. All rights reserved.},
  language  = {en}
}
@misc{MondalBehrensMatthesetal.2014,
  author    = {Mondal, Suvendu Sekhar and Behrens, Karsten and Matthes, Philipp R. and Sch{\"o}nfeld, Fabian and Nitsch, J{\"o}rn and Steffen, Andreas and Primus, Philipp-Alexander and Kumke, Michael Uwe and M{\"u}ller-Buschbaum, Klaus and Holdt, Hans-J{\"u}rgen},
  title     = {White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-79953},
  pages     = {4623 -- 4631},
  year      = {2014},
  abstract  = {Co-doping of the MOF 3∞[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a-d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+.},
  language  = {en}
}
@article{MondalBehrensMatthesetal.2015,
  author    = {Mondal, Suvendu Sekhar and Behrens, Karsten and Matthes, Philipp R. and Sch{\"o}nfeld, Fabian and Nitsch, J{\"o}rn and Steffen, Andreas and Primus, Philipp-Alexander and Kumke, Michael Uwe and M{\"u}ller-Buschbaum, Klaus and Holdt, Hans-J{\"u}rgen},
  title     = {White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+},
  series = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  volume    = {18},
  journal   = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  number    = {3},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2050-7534},
  doi       = {10.1039/C4TC02919D},
  pages     = {4623 -- 4631},
  year      = {2015},
  abstract  = {Co-doping of the MOF 3∞[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a-d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+.},
  language  = {en}
}
@article{MondalBehrensMatthesetal.2015,
  author    = {Mondal, Suvendu Sekhar and Behrens, Karsten and Matthes, Philipp R. and Sch{\"o}nfeld, Fabian and Nitsch, J{\"o}rn and Steffen, Andreas and Primus, Philipp-Alexander and Kumke, Michael Uwe and M{\"u}ller-Buschbaum, Klaus and Holdt, Hans-J{\"u}rgen},
  title     = {White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+},
  series = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  volume    = {3},
  journal   = {Journal of materials chemistry : C, Materials for optical and electronic devices},
  number    = {18},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {2050-7526},
  doi       = {10.1039/c4tc02919d},
  pages     = {4623 -- 4631},
  year      = {2015},
  language  = {en}
}
@article{MuellerFoerstendorfSteudtneretal.2019,
  author    = {M{\"u}ller, Katharina and Foerstendorf, Harald and Steudtner, Robin and Tsushima, Satoru and Kumke, Michael Uwe and Lef{\`e}vre, Gr{\´e}gory and Rothe, J{\"o}rg and Mason, Harris and Szab{\´o}, Zolt{\´a}n and Yang, Ping and Adam, Christian K. R. and Andr{\´e}, R{\´e}mi and Brennenstuhl, Katlen and Chiorescu, Ion and Cho, Herman M. and Creff, Ga{\"e}lle and Coppin, Fr{\´e}d{\´e}ric and Dardenne, Kathy and Den Auwer, Christophe and Drobot, Bj{\"o}rn and Eidner, Sascha and Hess, Nancy J. and Kaden, Peter and Kremleva, Alena and Kretzschmar, Jerome and Kr{\"u}ger, Sven and Platts, James A. and Panak, Petra and Polly, Robert and Powell, Brian A. and Rabung, Thomas and Redon, Roland and Reiller, Pascal E. and R{\"o}sch, Notker and Rossberg, Andr{\´e} and Scheinost, Andreas C. and Schimmelpfennig, Bernd and Schreckenbach, Georg and Skerencak-Frech, Andrej and Sladkov, Vladimir and Solari, Pier Lorenzo and Wang, Zheming and Washton, Nancy M. and Zhang, Xiaobin},
  title     = {Interdisciplinary Round-Robin Test on molecular spectroscopy of the U(VI) Acetate System},
  series = {ACS omega / American Chemical Society},
  volume    = {4},
  journal   = {ACS omega / American Chemical Society},
  number    = {5},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {2470-1343},
  doi       = {10.1021/acsomega.9b00164},
  pages     = {8167 -- 8177},
  year      = {2019},
  abstract  = {A comprehensive molecular analysis of a simple aqueous complexing system. U(VI) acetate. selected to be independently investigated by various spectroscopic (vibrational, luminescence, X-ray absorption, and nuclear magnetic resonance spectroscopy) and quantum chemical methods was achieved by an international round-robin test (RRT). Twenty laboratories from six different countries with a focus on actinide or geochemical research participated and contributed to this scientific endeavor. The outcomes of this RRT were considered on two levels of complexity: first, within each technical discipline, conformities as well as discrepancies of the results and their sources were evaluated. The raw data from the different experimental approaches were found to be generally consistent. In particular, for complex setups such as accelerator-based X-ray absorption spectroscopy, the agreement between the raw data was high. By contrast, luminescence spectroscopic data turned out to be strongly related to the chosen acquisition parameters. Second, the potentials and limitations of coupling various spectroscopic and theoretical approaches for the comprehensive study of actinide molecular complexes were assessed. Previous spectroscopic data from the literature were revised and the benchmark data on the U(VI) acetate system provided an unambiguous molecular interpretation based on the correlation of spectroscopic and theoretical results. The multimethodologic approach and the conclusions drawn address not only important aspects of actinide spectroscopy but particularly general aspects of modern molecular analytical chemistry.},
  language  = {en}
}
@article{OnalSassHurpinetal.2017,
  author    = {Onal, Emel and Sass, Stephan and Hurpin, Jeanne and Ertekin, Kadriye and Topal, Sevinc Zehra and Kumke, Michael Uwe and Hirel, Catherine},
  title     = {Lifetime-Based Oxygen Sensing Properties of palladium(II) and platinum(II) meso-tetrakis(4-phenylethynyl)phenylporphyrin},
  series = {Journal of fluorescence},
  volume    = {27},
  journal   = {Journal of fluorescence},
  publisher = {Springer},
  address   = {New York},
  issn      = {1053-0509},
  doi       = {10.1007/s10895-016-2022-x},
  pages     = {861 -- 868},
  year      = {2017},
  abstract  = {High oxygen permeable [poly(TMSP)] nanofibers incorporating porphyrin macrocycle as luminescence indicators were prepared by electrospinning technique. The porphyrins involves were modified by i) introducing phenylacetylide substituents on the para position of the phenyl moieties and ii) varying the metal centers [Pt(II) or Pd(II)] of the meso-tetrakisphenylporphyrins. A set of nanofibers; (Pt-TPP)NF, (Pd-TPP)NF, (Pt-TPA)NF and (Pd-TPA)NF were obtained to study their structure-activity relationship toward oxygen. The lifetime-based technique was privileged to take advantage of their long-lived phosphorescent properties. A two-fold enhancement was observed for (Pt-TPA)NF and (Pd-TPA)NF compared to (Pt-TPP)NF and (Pd-TPP)NF demonstrating the positive effect of the phenylacetylide moieties on the lifetime. Also, Silver nanoparticles were included in nanofibers to investigate their influence on lifetime-based oxygen sensitivity, showing that the presence of AgNPs only affects (Pd-TPA)NF.},
  language  = {en}
}
@article{PilarYesteCarlosHernandezGarridoKumkeetal.2022,
  author    = {Pilar Yeste, Maria and Carlos Hernandez-Garrido, Juan and Kumke, Michael Uwe and Alvarado, Sarah and Cauqui, Miguel Angel and Juan Calvino, Jose and Primus, Philipp-Alexander},
  title     = {Low-temperature growth of reactive pyrochlore nanostructures on Zirconia-supported ceria},
  series = {ACS applied nano materials},
  volume    = {5},
  journal   = {ACS applied nano materials},
  number    = {5},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {2574-0970},
  doi       = {10.1021/acsanm.2c00416},
  pages     = {6316 -- 6326},
  year      = {2022},
  abstract  = {The use of a catalyst support for the design of nanoscale heterogeneous catalysts based on cerium oxide offers vast possibilities for future catalyst development, particularly with regard to an increased focus on the use of renewable biogas and an emerging hydrogen economy. In this study, zirconia-supported ceria catalysts were synthesized, activated by using different thermochemical treatments, and characterized by way of temperature-programmed reduction (TPR), oxygen storage capacity, Xray diffraction, electron microscopy, and luminescence spectroscopy using Eu3+ as a spectroscopic probe. Through reduction-oxidation pretreatment routines, reactive pyrochlore structures were created at temperatures as low as 600 degrees C and identified through TPR and electron microscopy experiments. A structural relationship and alignment of the crystal planes is revealed in high-resolution scanning transmission electron microscopy experiments through the digital diffraction patterns. Low-temperature pretreatment induces the formation of reactive pyrochlore domains under retention of the surface area of the catalyst system, and no further morphological changes are detected. Furthermore, the formation of pyrochlore domains achieved through severe reduction and mild reoxidation (SRMO) treatments is reversible. Over multiple alternating SRMO and severe reduction and severe reoxidation (SRSO) treatments, europium spectroscopy and TPR results indicate that pyrochlore structures are recreated over consecutive treatments, whenever the mild oxidation step at 500 degrees C is the last treatment (SRMO, SRMO-SRSO-SRMO, etc.).},
  language  = {en}
}
@article{PrimusKumke2012,
  author    = {Primus, Philipp-A. and Kumke, Michael Uwe},
  title     = {Flash photolysis study of complexes between salicylic acid and lanthanide ions in water},
  series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  volume    = {116},
  journal   = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory},
  number    = {4},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1089-5639},
  doi       = {10.1021/jp2043575},
  pages     = {1176 -- 1182},
  year      = {2012},
  abstract  = {In the natural environment humic substances (HS) represent a major factor determining the speciation of metal ions, e.g., in the context of radionuclide migration. Here, due to their intrinsic sensitivity and selectivity, spectroscopic methods are often applied, requiring a fundamental understanding of the photophysical processes present in such HS-metal complexes. Complexes with different metal ions were studied using 2-hydroxybenzoic acid (2HB) as a model compound representing an important part of the chelating substructures in HS. In flash photolysis experiments under direct excitation of 2HB in the absence and the presence of different lanthanide ions, the generation and the decay of the 2HB triplet state, of the phenoxy radical, and of the solvated electron were monitored. Depending on the lanthanide ion different intracomplex processes were observed for these transient species including energy migration to and photoreduction of the lanthanide ion. The complexity of the intracomplex photophysical processes even for small molecules such as 2HB underlines the necessity to step-by-step approach the photochemical reactivity of HS by using suitable model compounds.},
  language  = {en}
}
@article{PrimusMenskiYesteetal.2015,
  author    = {Primus, Philipp-Alexander and Menski, Antonia and Yeste, Maria Pilar and Cauqui, Miguel Angel and Kumke, Michael Uwe},
  title     = {Fluorescence Line-Narrowing Spectroscopy as a Tool to Monitor Phase Transitions and Phase Separation in Efficient Nanocrystalline CexZr1-xO2:Eu3+ Catalyst Materials},
  series = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  volume    = {119},
  journal   = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  number    = {19},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1932-7447},
  doi       = {10.1021/acs.jpcc.5b01271},
  pages     = {10682 -- 10692},
  year      = {2015},
  abstract  = {Despite the wide range of industrial applications for ceria-zirconia mixed oxides (CexZr1-xO2), the complex correlation between their atomic structure and catalytic performance is still under debate. Catalytically interesting CexZr1-xO2 nanomaterials can form homogeneous solid solutions and, depending on the composition, show phase separation under the formation of small domains. The characterization of homogeneity and atomic structure of these materials remains a major challenge. High-resolution emission spectroscopy recorded under cryogenic conditions using Eu3+ as a structural probe in doped CeZrO2 nanoparticles offers an effective way to identify the different atomic environments of the Eu3+ dopants and, subsequently, to monitor structural parameters of the ceria-zirconia mixed oxides. It is found that, in stoichiometric CeZrO2:Eu3+, phase separation occurs at elevated temperatures beginning with the gradual formation of (pseudo)cubic crystallites in the amorphous materials at 500 degrees C and a sudden phase separation into tetragonal, zirconia-rich and cubic, ceria-rich domains over 900 degrees C. The presented technique allows us to easily monitor subtle changes even in amorphous, high surface area samples, yielding structural information not accessible by conventional techniques such as X-ray diffraction (XRD) and Raman. Moreover, in reference experiments investigating the reducibility of largely unordered Ce0.2Zr0.8O2:Eu3+, the main reduction peak in temperature-programmed reduction measurements appeared at exceptionally low temperatures below 200 degrees C, thus suggesting the outstanding potential of this oxide to activate catalytic oxidation reactions. This effect was found to be dependent on the amount of Eu3+ dopant introduced into the CeZrO2 matrix as well as to be connected to the atomic structure of the catalyst material.},
  language  = {en}
}
@article{PrimusRitschelSigueenzaetal.2014,
  author    = {Primus, Philipp-Alexander and Ritschel, Thomas and Sigueenza, Pilar Y. and Cauqui, Miguel Angel and Hernandez-Garrido, Juan Carlos and Kumke, Michael Uwe},
  title     = {High-resolution spectroscopy of europium-doped ceria as a tool to correlate structure and catalytic activity},
  series = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  volume    = {118},
  journal   = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  number    = {40},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1932-7447},
  doi       = {10.1021/jp505467r},
  pages     = {23349 -- 23360},
  year      = {2014},
  abstract  = {Site-selective emission spectra of Eu3+-doped CeO2 nanoparticles up to the D-5(0) - F-7(5) transition were recorded under cryogenic conditions to identify the local structure around the Eu3+ dopants in ceria. It is found that pretreatment conditions are crucial for the redistribution of dopants from a broad variety of environments to six well-defined lattice sites. The influence of the dopant and the host structure on the catalytic activity was investigated. A relationship between structure and reactivity is discussed. It is shown that oxygen transport is most efficient in particles with a pronounced amorphous character.},
  language  = {en}
}
@article{RadziukSkirtachGessneretal.2011,
  author    = {Radziuk, Darya and Skirtach, Andre and Gessner, Andre and Kumke, Michael Uwe and Zhang, Wei and M{\"o}hwald, Helmuth and Shchukin, Dmitry},
  title     = {Ultrasonic Approach for Formation of Erbium Oxide Nanoparticles with Variable Geometries},
  series = {Langmuir},
  volume    = {27},
  journal   = {Langmuir},
  number    = {23},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0743-7463},
  doi       = {10.1021/la203622u},
  pages     = {14472 -- 14480},
  year      = {2011},
  abstract  = {Ultrasound (20 kHz, 29 W. cm(-2)) is employed to form three types of erbium oxide nanoparticles in the presence of multiwalled carbon nanotubes as a template material in water. The nanoparticles are (i) erbium carboxioxide nanoparticles deposited on the external walls of multiwalled carbon nanotubes and Er(2)O(3) in the bulk with (ii) hexagonal and (iii) spherical geometries. Each type of ultrasonically formed nanoparticle reveals Er(3+) photoluminescence from crystal lattice. The main advantage of the erbium carboxioxide nanoparticles on the carbon nanotubes is the electromagnetic emission in the visible region, which is new and not examined up to the present date. On the other hand, the photoluminescence of hexagonal erbium oxide nanoparticles is long-lived (mu s) and enables the higher energy transition ((4)S(3/2)-(4)I(15/2)), which is not observed for spherical nanoparticles. Our work is unique because it combines for the first time spectroscopy of Er(3+) electronic transitions in the host crystal lattices of nanoparticles with the geometry established by ultrasound in aqueous solution of carbon nanotubes employed as a template material. The work can be of great interest for "green" chemistry synthesis of photoluminescent nanoparticles in water.},
  language  = {en}
}
@article{RaschKumkeLoehmannsroeben2008,
  author    = {Rasch, Claudia and Kumke, Michael Uwe and L{\"o}hmannsr{\"o}ben, Hans-Gerd},
  title     = {Mykotoxine in Getreide spektroskopisch erfassen},
  year      = {2008},
  language  = {de}
}
@article{RoethleinMiettinenBorwankaretal.2014,
  author    = {Roethlein, Christoph and Miettinen, Markus S. and Borwankar, Tejas and Buerger, Joerg and Mielke, Thorsten and Kumke, Michael Uwe and Ignatova, Zoya},
  title     = {Architecture of polyglutamine-containing fibrils from time-resolved fluorescence decay},
  series = {The journal of biological chemistry},
  volume    = {289},
  journal   = {The journal of biological chemistry},
  number    = {39},
  publisher = {American Society for Biochemistry and Molecular Biology},
  address   = {Bethesda},
  issn      = {0021-9258},
  doi       = {10.1074/jbc.M114.581991},
  pages     = {26817 -- 26828},
  year      = {2014},
  abstract  = {The disease risk and age of onset of Huntington disease (HD) and nine other repeat disorders strongly depend on the expansion of CAG repeats encoding consecutive polyglutamines (polyQ) in the corresponding disease protein. PolyQ length-dependent misfolding and aggregation are the hallmarks of CAG pathologies. Despite intense effort, the overall structure of these aggregates remains poorly understood. Here, we used sensitive time-dependent fluorescent decay measurements to assess the architecture of mature fibrils of huntingtin (Htt) exon 1 implicated in HD pathology. Varying the position of the fluorescent labels in the Htt monomer with expanded 51Q (Htt51Q) and using structural models of putative fibril structures, we generated distance distributions between donors and acceptors covering all possible distances between the monomers or monomer dimensions within the polyQ amyloid fibril. Using Monte Carlo simulations, we systematically scanned all possible monomer conformations that fit the experimentally measured decay times. Monomers with four-stranded 51Q stretches organized into five-layered beta-sheets with alternating N termini of the monomers perpendicular to the fibril axis gave the best fit to our data. Alternatively, the core structure of the polyQ fibrils might also be a zipper layer with antiparallel four-stranded stretches as this structure showed the next best fit. All other remaining arrangements are clearly excluded by the data. Furthermore, the assessed dimensions of the polyQ stretch of each monomer provide structural evidence for the observed polyQ length threshold in HD pathology. Our approach can be used to validate the effect of pharmacological substances that inhibit or alter amyloid growth and structure.},
  language  = {en}
}
@article{RothLoehmannsroebenKelzetal.2008,
  author    = {Roth, Martin M. and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Kelz, A. and Kumke, Michael Uwe},
  title     = {innoFSPEC : fiber optical spectroscopy and sensing},
  isbn      = {978-0-819-47228-1},
  year      = {2008},
  language  = {en}
}
@article{SchimkaKlierdeGuerenuetal.2019,
  author    = {Schimka, Selina and Klier, Dennis Tobias and de Guerenu, Anna Lopez and Bastian, Philipp and Lomadze, Nino and Kumke, Michael Uwe and Santer, Svetlana},
  title     = {Photo-isomerization of azobenzene containing surfactants induced by near-infrared light using upconversion nanoparticles as mediator},
  series = {Journal of physics : Condensed matter},
  volume    = {31},
  journal   = {Journal of physics : Condensed matter},
  number    = {12},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {0953-8984},
  doi       = {10.1088/1361-648X/aafcfa},
  pages     = {9},
  year      = {2019},
  abstract  = {Here we report on photo-isomerization of azobenzene containing surfactants induced during irradiation with near-infrared (NIR) light in the presence of upconversion nanoparticles (UCNPs) acting as mediator. The surfactant molecule consists of charged head group and hydrophobic tail with azobenzene group incorporated in alkyl chain. The azobenzene group can be reversible photo-isomerized between two states: trans- and cis- by irradiation with light of an appropriate wavelength. The trans-cis photo-isomerization is induced by UV light, while cis-trans isomerization proceeds either thermally in darkness, or can be accelerated by exposure to illumination with a longer wavelength typically in a blue/green range. We present the application of lanthanide doped UCNPs to successfully switch azobenzene containing surfactants from cis to trans conformation in bulk solution using NIR light. Using Tm-3(+) or Er-3(+) as activator ions, the UCNPs provide emissions in the spectral range of 450 nm < lambda(em) < 480 nm (for Tm-3(+), three and four photon induced emission) or 525 nm < lambda(em) < 545 nm (for Er-3(+), two photon induced emission), respectively. Especially for UCNPs containing Tm-3(+) a good overlap of the emissions with the absorption bands of the azobenzene is present. Under illumination of the surfactant solution with NIR light (lambda(ex) = 976 nm) in the presence of the Tm-3(+)-doped UCNPs, the relaxation time of cis-trans photo-isomerization was increased by almost 13 times compared to thermally induced isomerization. The influence of thermal heating due to the irradiation using NIR light was shown to be minor for solvents not absorbing in NIR spectral range (e.g. CHCl3) in contrast to water, which shows a distinct absorption in the NIR.},
  language  = {en}
}
@article{SchottKretzschmarAckeretal.2014,
  author    = {Schott, Juliane and Kretzschmar, Jerome and Acker, Margret and Eidner, Sascha and Kumke, Michael Uwe and Drobot, Bjoern and Barkleit, Astrid and Taut, Steffen and Brendler, Vinzenz and Stumpf, Thorsten},
  title     = {Formation of a Eu(III) borate solid species from a weak Eu(III) borate complex in aqueous solution},
  series = {Dalton transactions : a journal of inorganic chemistry, including bioinorganic, organometallic, and solid-state chemistry},
  volume    = {43},
  journal   = {Dalton transactions : a journal of inorganic chemistry, including bioinorganic, organometallic, and solid-state chemistry},
  number    = {30},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1477-9226},
  doi       = {10.1039/c4dt00843j},
  pages     = {11516 -- 11528},
  year      = {2014},
  abstract  = {In the presence of polyborates (detected by B-11-NMR) the formation of a weak Eu(III) borate complex (lg beta(11) similar to 2, estimated) was observed by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation of this solid in solution was investigated by TRLFS as a function of the total boron concentration: the lower the total boron concentration, the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD and solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid.},
  language  = {en}
}
@misc{SchottKretzschmarAckeretal.2014,
  author    = {Schott, Juliane and Kretzschmar, Jerome and Acker, Margret and Eidner, Sascha and Kumke, Michael Uwe and Drobot, Bj{\"o}rn and Barkleit, Astrid and Taut, Steffen and Brendler, Vinzenz and Stumpf, Thorsten},
  title     = {Formation of a Eu(III) borate solid species from a weak Eu(III) borate complex in aqueous solution},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98774},
  pages     = {13},
  year      = {2014},
  abstract  = {In the presence of polyborates (detected by 11B-NMR) the formation of a weak Eu(III) borate complex (lg β11 ∼ 2, estimated) was observed by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation of this solid in solution was investigated by TRLFS as a function of the total boron concentration: the lower the total boron concentration, the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD and solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid.},
  language  = {en}
}
@article{SchulerLipmanSteinbachetal.2005,
  author    = {Schuler, Benjamin and Lipman, Everett A. and Steinbach, P. J. and Kumke, Michael Uwe and Eaton, W. A.},
  title     = {Polyproline and the "spectroscopic ruler" revisited with single-molecule fluorescence},
  issn      = {0027-8424},
  year      = {2005},
  abstract  = {To determine whether Forster resonance energy transfer (FRET) measurements can provide quantitative distance information in single-molecule fluorescence experiments on polypeptides, we measured FRET efficiency distributions for donor and acceptor dyes attached to the ends of freely diffusing polyproline molecules of various lengths. The observed mean FRET efficiencies agree with those determined from ensemble lifetime measurements but differ considerably from the values expected from Forster theory, with polyproline treated as a rigid rod. At donor-acceptor distances much less than the Forster radius R-o, the observed efficiencies are lower than predicted, whereas at distances comparable to and greater than R-0, they are much higher. Two possible contributions to the former are incomplete orientational averaging during the donor lifetime and, because of the large size of the dyes, breakdown of the point-dipole approximation assumed in Forster theory. End-to-end distance distributions and correlation times obtained from Langevin molecular dynamics simulations suggest that the differences for the longer polyproline peptides can be explained by chain bending, which considerably shortens the donor-acceptor distances},
  language  = {en}
}
@article{SchwarzeMuellerAstetal.2014,
  author    = {Schwarze, Thomas and Mueller, Holger and Ast, Sandra and Steinbr{\"u}ck, Dorte and Eidner, Sascha and Geißler, Felix and Kumke, Michael Uwe and Holdt, Hans-J{\"u}rgen},
  title     = {Fluorescence lifetime-based sensing of sodium by an optode},
  series = {Chemical communications},
  volume    = {50},
  journal   = {Chemical communications},
  number    = {91},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1359-7345},
  doi       = {10.1039/c4cc06112h},
  pages     = {14167 -- 14170},
  year      = {2014},
  abstract  = {We report a 1,2,3-triazol fluoroionophore for detecting Na+ that shows in vitro enhancement in the Na+-induced fluorescence intensity and decay time. The Na+-selective molecule 1 was incorporated into a hydrogel as a part of a fiber optical sensor. This sensor allows the direct determination of Na+ in the range of 1-10 mM by measuring reversible fluorescence decay time changes.},
  language  = {en}
}
@article{SchwarzeMuellerAstetal.2014,
  author    = {Schwarze, Thomas and M{\"u}ller, Holger and Ast, Sandra and Steinbr{\"u}ck, D{\"o}rte and Eidner, Sascha and Geißler, Felix and Kumke, Michael Uwe and Holdt, Hans-J{\"u}rgen},
  title     = {Fluorescence lifetime-based sensing of sodium by an optode},
  series = {Chemical Communications},
  journal   = {Chemical Communications},
  editor    = {Kumke, Michael Uwe},
  publisher = {The Royal Society Chemistry},
  address   = {Cambridge},
  issn      = {0022-4936},
  pages     = {14167 -- 14170},
  year      = {2014},
  abstract  = {We report a 1,2,3-triazol fluoroionophore for detecting Na+ that shows in vitro enhancement in the Na+-induced fluorescence intensity and decay time. The Na+-selective molecule 1 was incorporated into a hydrogel as a part of a fiber optical sensor. This sensor allows the direct determination of Na+ in the range of 1-10 mM by measuring reversible fluorescence decay time changes.},
  language  = {en}
}
@misc{SchwarzeMuellerAstetal.2014,
  author    = {Schwarze, Thomas and M{\"u}ller, Holger and Ast, Sandra and Steinbr{\"u}ck, D{\"o}rte and Eidner, Sascha and Geißler, Felix and Kumke, Michael Uwe and Holdt, Hans-J{\"u}rgen},
  title     = {Fluorescence lifetime-based sensing of sodium by an optode},
  publisher = {The Royal Society of Chemistry},
  address   = {Cambridge},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-76785},
  pages     = {14167 -- 14170},
  year      = {2014},
  abstract  = {We report a 1,2,3-triazol fluoroionophore for detecting Na+ that shows in vitro enhancement in the Na+-induced fluorescence intensity and decay time. The Na+-selective molecule 1 was incorporated into a hydrogel as a part of a fiber optical sensor. This sensor allows the direct determination of Na+ in the range of 1-10 mM by measuring reversible fluorescence decay time changes.},
  language  = {en}
}
@article{SchaeferHuberSeheretal.2012,
  author    = {Sch{\"a}fer, Thorsten and Huber, Florian and Seher, Holger and Missana, Tiziana and Alonso, Ursula and Kumke, Michael Uwe and Eidner, Sascha and Claret, Francis and Enzmann, Frieder},
  title     = {Nanoparticles and their influence on radionuclide mobility in deep geological formations},
  series = {Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry},
  volume    = {27},
  journal   = {Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry},
  number    = {2},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0883-2927},
  doi       = {10.1016/j.apgeochem.2011.09.009},
  pages     = {390 -- 403},
  year      = {2012},
  abstract  = {This article gives an overview of the current status of knowledge concerning the role of nanoparticles (inorganic and organic) in deep geological host rocks and the potential influence of these nanoparticles on radionuclide migration in far-field systems. The manuscript is not intended to be a full review paper or overview paper concerning nanoparticles, here the intention is to refer to recent publications but to highlight the progress made in the 6th framework project IP FUNMIG (Fundamental processes of radionuclide migration) and the open literature over the past 5 a concerning the process understanding of nanoparticle related issues in the three host rock formations investigated, namely: claystones, crystalline rocks and salt rock overburden. The results show inter alia that the inorganic nanoparticle concentration in deep groundwaters of advection dominated systems rarely exceeds 1 mg L (1) and is expected to be in the ng L (1) range in diffusion controlled systems. For organic nanoparticles DOC concentrations up to tens of milligrams in diffusion-controlled indurated clays with molecular sizes mostly <500 Da have been found. Fulvic acid type organics have been identified in crystalline environments and plastic Clay formations (Boom Clay) with molecular sizes <= 300 kDa. Additional sources of inorganic nanoparticles from the repository near-field (compacted bentonite) were identified and the initial erosion rates were determined. The results indicate under stagnant conditions similar to 38 mg cm (2) a (1) for bi-distilled water, similar to 20 mg cm (2) a (1) for glacial melt water (Grimsel groundwater) and very low rates similar to 0.02 mg cm (2) a (1) for 5 mM CaCl2 contact water. The low critical coagulation concentration (CCC) indicative for purely diffusion controlled coagulation of 1 mM L (1) Ca2+ found in bentonite nanoparticle stability analysis matches the low nanoparticle mobilization from compacted bentonite found in these systems.},
  language  = {en}
}
@article{SteinbrueckRaschKumke2008,
  author    = {Steinbr{\"u}ck, D{\"o}rte and Rasch, Claudia and Kumke, Michael Uwe},
  title     = {Photophysics of Ochratoxin A in aqueous solution},
  year      = {2008},
  language  = {en}
}
@article{TechenCzaplaMoellnitzetal.2013,
  author    = {Techen, Anne and Czapla, Sylvia and M{\"o}llnitz, Kristian and Budach, Dennis B. and Wessig, Pablo and Kumke, Michael Uwe},
  title     = {Synthesis and spectroscopic characterization of fluorophore-labeled oligospiroketal rods},
  series = {Helvetica chimica acta},
  volume    = {96},
  journal   = {Helvetica chimica acta},
  number    = {11},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {0018-019X},
  doi       = {10.1002/hlca.201200616},
  pages     = {2046 -- 2067},
  year      = {2013},
  abstract  = {Fluorescence probes consisting of well-established fluorophores in combination with rigid molecular rods based on spirane-type structures were investigated with respect to their fluorescence properties under different solvent conditions. The attachment of the dyes was accomplished by 1,3-dipolar cycloaddition between alkynes and azides (click' reaction) and is a prime example for a novel class of sensor constructs. Especially, the attachment of two (different) fluorophores on opposite sides of the molecular rods paves the way to new sensor systems with less bulky (compared to the conventional DNA- or protein-based concepts), nevertheless rigid spacer constructs, e.g., for FRET-based sensing applications. A detailed photophysical characterization was performed in MeOH (and in basic H2O/MeOH mixtures) for i) rod constructs containing carboxyfluorescein, ii) rod constructs containing carboxyrhodamine, iii) rod constructs containing both carboxyfluorescein and carboxyrhodamine, and iv) rod constructs containing both pyrene and perylene parts. For each dye (pair), two rod lengths with different numbers of spirane units were synthesized and investigated. The rod constructs were characterized in ensemble as well as single-molecule fluorescence experiments with respect to i) specific roddye and ii) dyedye interactions. In addition to MeOH and MeOH/NaOH, the rod constructs were also investigated in micellar systems, which were chosen as a simplified model for membranes.},
  language  = {en}
}
@article{TechenHilleDoscheetal.2012,
  author    = {Techen, Anne and Hille, Carsten and Dosche, Carsten and Kumke, Michael Uwe},
  title     = {Fluorescence study of drug-carrier interactions in CTAB/PBS buffer model systems},
  series = {Journal of colloid and interface science},
  volume    = {377},
  journal   = {Journal of colloid and interface science},
  publisher = {Elsevier},
  address   = {San Diego},
  issn      = {0021-9797},
  doi       = {10.1016/j.jcis.2012.03.063},
  pages     = {251 -- 261},
  year      = {2012},
  abstract  = {The well-known cationic surfactant hexadecyltrimethylammonium bromide (CTAB) was used as a model carrier to study drug-carrier interactions with fluorescence probes (5-hexadecanoylaminofluorescein (HAF) and 2,10-bis-(3-aminopropyloxy)dibenzo[aj]perylene-8,16-dione (NIR 628) by applying ensemble as well as single molecule fluorescence techniques. The impact of the probes on the micelle parameters (critical micelle concentration, average aggregation number, hydrodynamic radius) was investigated under physiological conditions. In the presence of additional electrolytes, such as buffer, the critical micelle concentration decreased by a factor of about 10. In contrast, no influence of the probes on the critical micelle concentration and on average aggregation number was observed. The results show that HAF does not affect the characteristics of CTAB micelles. Analyzing fluorescence correlation spectroscopy data and time-resolved anisotropy decays in terms of the "two-step" in combination with the "wobbling-in-cone" model, it was proven that HAF and NIR 628 are differently associated with the micelles. Based on ensemble and single molecule fluorescence experiments, intra- and intermicellar energy transfer process between the two dyes were probed and characterized.},
  language  = {en}
}
@article{TiseanuFrunzaKumke2004,
  author    = {Tiseanu, Carmen and Frunza, L. and Kumke, Michael Uwe},
  title     = {Time-resolved photoluminescence analysis of distribution and migration of terbium ions in zeolites X},
  year      = {2004},
  abstract  = {The photoluminescence (PL) dynamics of terbium-exchanged zeolites X was investigated upon laser excitation at 355 nm. The results evidenced the presence of at least two terbium main environments with PL lifetimes varying between 391-411 and 753-770 mus. The two-site nature of terbium distribution in zeolites X permitted a quantitative analysis of the migration process of terbium ions inside the pores and cavities upon dehydration in air at 200 degreesC. Besides the increase of the PL lifetimes with about 30\% and 80\% compared to those of the hydrated zeolite, a fraction of almost 30\% of terbium ions was estimated to migrate from the supercages to the neighboring sodalites or hexagonal prisms. Our results evidenced for the first time the capability of time-resolved luminescence spectroscopy in quantitatively tracking for the intrazeolitic migration of lanthanides. (C) 2004 Elsevier B.V. All rights reserved},
  language  = {en}
}
@article{TiseanuGessnerKumkeetal.2008,
  author    = {Tiseanu, Carmen and Geßner, Andre and Kumke, Michael Uwe and Gagea, Bogdan and Parvulescu, Vasile Ion and Martens, Johan},
  title     = {Photoluminescence spectra and dynamics of lanthanide-doped microporous materials},
  doi       = {10.1016/j.jlumin.2007.10.018},
  year      = {2008},
  abstract  = {A series of terbium- and europium-exchanged microporous-mesoporous zeolite Socony Mobil Five (MFI)-type materials such as Zeotile-1 and Zeogrid with varying Si/Al ratios was investigated using FTIR, PXRD, adsorption- desorption isotherms of N-2 at 77 K and time-resolved luminescence spectroscopy. Silylation of the lanthanides-exchanged Zeotile-1 and Zeogrid with hexadecyl trimethoxysilanes via post-synthesis grafting was also studied. The results showed that the lanthanide's photoluminescence spectra and decays were modified due to silylation. The different silylation effects in Zeotile-1 and Zeogrid were correlated with the textural properties of the investigated materials. (C) 2007 Elsevier B.V. All rights reserved.},
  language  = {en}
}
@article{TiseanuGessnerKumkeetal.2008,
  author    = {Tiseanu, Carmen and Geßner, Andre and Kumke, Michael Uwe and Parvulescu, V.},
  title     = {Dehydration and rehydration effects on the photoluminescence properties of terbium-exchanged MFI type materials},
  doi       = {10.1016/j.jnoncrysol.2007.11.017},
  year      = {2008},
  language  = {en}
}
@article{TiseanuKumkeParvulescuetal.2008,
  author    = {Tiseanu, Carmen and Kumke, Michael Uwe and Parvulescu, Vasile Ion and Geßner, Andre and Gagea, Bogdan and Martens, Johan},
  title     = {Europium(3+) : an efficient luminescence probe for the Si to Al ratio and silylation effect in the microporous- mesoporous Zeogrid materials},
  doi       = {10.1021/Jp711337h},
  year      = {2008},
  language  = {en}
}
@article{TiseanuKumkeParvulescuetal.2009,
  author    = {Tiseanu, Carmen and Kumke, Michael Uwe and P{\^a}rvulescu, Vasile Ion and Martens, Johan},
  title     = {Species-related luminescence-structure relationships in europium-exchanged mesoporous material},
  issn      = {0021-8979},
  doi       = {10.1063/1.3086634},
  year      = {2009},
  abstract  = {Europium exchanged into a mesoporous material (Zeotile-1) was extensively characterized with respect to the Si/ Al ratio and surface silylation by using time-resolved emission spectroscopy. Qualitative as well as quantitative details of the europium species-related luminescence-structure relationships were obtained and discussed such as the decay associated spectra, local distortion and structure of the bonding environment, crystal-field strength, radiative relaxation rates, and the quantum efficiency. Thus, two europium species were found in the parent as well as in the silylated materials: one species located on the internal surface and the second inside the 2-2.5 nm pores. The species located on the internal surface is characterized by photoluminescence decay times of 105 mu s <tau < 125 mu s, an asymmetry value R of 0.6 < R < 0.8, and a quantum efficiency of 2\%-2.5\%. Upon silylation, the photoluminescence decay times, the asymmetry values, and the quantum efficiency were increased to 160 mu s <tau < 180 mu s, 1.7 < R < 2.1, and similar to 4\%, respectively. Following silylation, the number of water molecules is reduced in the first coordination shell of the europium species located on the internal surface from eight to nine to about five. On the other hand, the europium species located inside the pores showed a much longer photoluminescence decay time (460 mu s <tau < 560 mu s) and a much higher asymmetry ratio (5 < R < 6.5). The related photoluminescence efficiency was 26\%-30\%. An average of one up to two water molecules in the first coordination shell of the europium species located inside the pores was estimated for both parent and silylated materials.},
  language  = {en}
}
@article{TiseanuLorenzFonfriaGessneretal.2009,
  author    = {Tiseanu, Carmen and Lorenz-Fonfria, Victor A. and Geßner, Andr{\´e} and Kumke, Michael Uwe and Gagea, Bogdan},
  title     = {Comparative luminescence study of terbium-exchanged zeolites silylated with alkoxysilanes},
  issn      = {0957-4522},
  doi       = {10.1007/s10854-008-9597-1},
  year      = {2009},
  abstract  = {Terbium-exchanged ZSM-5, MOR and (H)BEA zeolites were silylated with phenyl-, vinyl- and hexadecyl trimethoxysilanes via a post-synthesis grafting. All samples were investigated by means of PXRD, FT-IR, TGA, physical adsorption, DR-UV-Vis and time-resolved photoluminescence spectroscopy. From the comparison of the photoluminescence decays of terbium-exchanged in parent (non-silylated) and silylated zeolites, it resulted that the silylation efficiency of the various alkoxysilanes is determined by the type of zeolite and follows the sequences: phenyl > vinyl > hexadecyl > parent for ZSM-5, hexadecyl a parts per thousand phenyl a parts per thousand vinyl > parent for MOR and hexadecyl > phenyl a parts per thousand vinyl > a parts per thousand parent for BEA zeolites, respectively.},
  language  = {en}
}
@article{TiseanuLorenzFonfriaParvulescuetal.2008,
  author    = {Tiseanu, Carmen and Lorenz-Fonfria, Victor A. and Parvulescu, Vasile Ion and Geßner, Andre and Kumke, Michael Uwe},
  title     = {Photoluminescence study of terbium-exchanged ultrastable Y zeolites: Number of species, photoluminescence decays and decay-associated spectra},
  doi       = {10.1063/1.2966304},
  year      = {2008},
  language  = {en}
}