TY - JOUR A1 - Schwarze, Thomas T1 - Determination of Pd2+ by fluorescence enhancement caused by an off-switching of an energy- and an electron transfer JF - ChemistrySelect N2 - In this paper, we introduce a fluorescent dye 1, which is able to detect selectively Pd2+ by a clear fluorescence enhancement (FE) in THF. In the presence of eight Pd2+ equivalents, we observed a fluorescence enhancement factor (FEF) of 28.3. The high Pd2+ induced FEF can be explained by an off switching of multiple quenching processes within 1 by Pd2+. In the free dye 1 a photoinduced electron transfer (PET) and energy transfer (ET) takes place and quenches the anthracenic fluorescence. The coordination of eight Pd2+ units by the alkylthio-substituted porphyrazine receptor suppresses the PET and ET quenching process and the anthracenic fluorescence is switched on. KW - Palladium ion KW - electron transfer KW - energy transfer KW - fluorescence KW - porphyrazine Y1 - 2021 U6 - https://doi.org/10.1002/slct.202003975 SN - 2365-6549 VL - 6 IS - 3 SP - 318 EP - 322 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Schwarze, Thomas A1 - Kelling, Alexandra A1 - Sperlich, Eric A1 - Holdt, Hans-Jürgen T1 - Influence of regioisomerism in 9-anthracenyl-substituted dithiodicyanoethene derivatives on photoinduced electron transfer controlled by intramolecular charge transfer JF - ChemPhotoChem N2 - In this paper, we report on the fluorescence behaviour of three regioisomers which consist of two 9-anthracenyl fluorophores and of differently substituted dithiodicyanoethene moieties. These isomeric fluorescent probes show different quantum yields (phi(f)). In these probes, an oxidative photoinduced electron transfer (PET) from the excited 9-anthracenyl fluorophore to the dithiodicyanoethene unit quenches the fluorescence. This quenching process is accelerated by an intramolecular charge transfer (ICT) of the push-pull pi-electron system of the dithiodicyanoethene group. The acceleration of the PET depends on the strength of the ICT unit. The higher the dipole moment of the ICT unit, the stronger the observed fluorescence quenching. To the best of our knowledge, this is the first report of a regioisomeric influence on an oxidative PET by an ICT. KW - anthracene KW - charge transfer KW - electron transfer KW - fluorescence KW - isomerism Y1 - 2021 U6 - https://doi.org/10.1002/cptc.202100070 SN - 2367-0932 VL - 5 IS - 10 SP - 911 EP - 914 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Schwarze, Thomas A1 - Mertens, Monique A1 - Mueller, Peter A1 - Riemer, Janine A1 - Wessig, Pablo A1 - Holdt, Hans-Jürgen T1 - Highly K+-Selective Fluorescent Probes for Lifetime Sensing of K+ in Living Cells JF - Chemistry - a European journal N2 - The new K+-selective fluorescent probes 1 and 2 were obtained by Cu-I-catalyzed 1,3-dipolar azide alkyne cycloaddition (CuAAC) reactions of an alkyne-substituted [1,3]dioxolo[4,5-f][1,3]benzodioxole (DBD) ester fluorophore with azido-functionalized N-phenylaza-18-crown-6 ether and N-(o-isopropoxy) phenylaza-18-crown-6 ether, respectively. Probes 1 and 2 allow the detection of K+ in the presence of Na+ in water by fluorescence enhancement (2.2 for 1 at 2000mm K+ and 2.5 for 2 at 160mm K+). Fluorescence lifetime measurements in the absence and presence of K+ revealed bi-exponential decay kinetics with similar lifetimes, however with different proportions changing the averaged fluorescence decay times ((f(av))). For 1 a decrease of (f(av)) from 12.4 to 9.3ns and for 2 an increase from 17.8 to 21.8ns was observed. Variation of the substituent in ortho position of the aniline unit of the N-phenylaza-18-crown-6 host permits the modulation of the K-d value for a certain K+ concentration. For example, substitution of H in 1 by the isopropoxy group (2) decreased the K-d value from >300mm to 10mm. 2 was chosen for studying the efflux of K+ from human red blood cells (RBC). Upon addition of the Ca2+ ionophor ionomycin to a RBC suspension in a buffer containing Ca2+, the fluorescence of 2 slightly rose within 10min, however, after 120min a significant increase was observed. KW - electron transfer KW - fluorescence lifetime KW - fluorescent probes KW - living cells KW - potassium Y1 - 2017 U6 - https://doi.org/10.1002/chem.201704368 SN - 0947-6539 SN - 1521-3765 VL - 23 SP - 17186 EP - 17190 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Loew, Noya A1 - Bogdanoff, Peter A1 - Herrmann, Iris A1 - Wollenberger, Ursula A1 - Scheller, Frieder W. A1 - Katterle, Martin T1 - Influence of modifications on the efficiency of pyrolysed CoTMPP as electrode material for horseradish peroxidase and the reduction of hydrogen peroxide JF - Electroanalysis : an international journal devoted to fundamental and practical aspects of electroanalysis N2 - A tailor-made horseradish peroxidase (HRP) bulk composite electrode was developed on the basis of pyrolyzed cobalt tetramethoxyphenylporphyrin (CoTMPP) by modifying pore size and surface area of the porous carbon material through varying amounts of iron oxalate and sulfur prior to pyrolyzation. The materials were used to immobilize horseradish peroxidase (HRP). These electrodes were characterized in terms of their efficiency to reduce hydrogen peroxide. The heterogeneous electron transfer rate constants of different materials were determined with the rotating disk electrode method and a k(S) (401 +/- 61 s(-1)) exceeding previously reported values for native HRP was found. KW - cobalt porphyrin KW - electron transfer KW - horseradish peroxidase KW - hydrogen peroxide KW - immobilization Y1 - 2006 U6 - https://doi.org/10.1002/elan.200603664 SN - 1040-0397 VL - 18 IS - 23 SP - 2324 EP - 2330 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Peng, Lei A1 - Utesch, Tillmann A1 - Yarman, Aysu A1 - Jeoung, Jae-Hun A1 - Steinborn, Silke A1 - Dobbek, Holger A1 - Mroginski, Maria Andrea A1 - Tanne, Johannes A1 - Wollenberger, Ursula A1 - Scheller, Frieder W. T1 - Surface-Tuned Electron Transfer and Electrocatalysis of Hexameric Tyrosine-Coordinated Heme Protein JF - Chemistry - a European journal N2 - Molecular modeling, electrochemical methods, and quartz crystal microbalance were used to characterize immobilized hexameric tyrosine-coordinated heme protein (HTHP) on bare carbon or on gold electrodes modified with positively and negatively charged self-assembled monolayers (SAMs), respectively. HTHP binds to the positively charged surface but no direct electron transfer (DET) is found due to the long distance of the active sites from the electrode surfaces. At carboxyl-terminated surfaces, the neutrally charged bottom of HTHP can bind to the SAM. For this "disc" orientation all six hemes are close to the electrode and their direct electron transfer should be efficient. HTHP on all negatively charged SAMs showed a quasi-reversible redox behavior with rate constant k(s) values between 0.93 and 2.86 s(-1) and apparent formal potentials E-app(0)' between -131.1 and -249.1 mV. On the MUA/MU-modified electrode, the maximum surface concentration corresponds to a complete monolayer of the hexameric HTHP in the disc orientation. HTHP electrostatically immobilized on negatively charged SAMs shows electrocatalysis of peroxide reduction and enzymatic oxidation of NADH. KW - electrochemistry KW - electron transfer KW - heme proteins KW - molecular modeling KW - monolayers Y1 - 2015 U6 - https://doi.org/10.1002/chem.201405932 SN - 0947-6539 SN - 1521-3765 VL - 21 IS - 20 SP - 7596 EP - 7602 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Kielb, Patrycja A1 - Sezer, Murat A1 - Katz, Sagie A1 - Lopez, Francesca A1 - Schulz, Christopher A1 - Gorton, Lo A1 - Ludwig, Roland A1 - Wollenberger, Ursula A1 - Zebger, Ingo A1 - Weidinger, Inez M. T1 - Spectroscopic Observation of Calcium-Induced Reorientation of Cellobiose Dehydrogenase Immobilized on Electrodes and its Effect on Electrocatalytic Activity JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - Cellobiose dehydrogenase catalyzes the oxidation of various carbohydrates and is considered as a possible anode catalyst in biofuel cells. It has been shown that the catalytic performance of this enzyme immobilized on electrodes can be increased by presence of calcium ions. To get insight into the Ca2+-induced changes in the immobilized enzyme we employ surface-enhanced vibrational (SERR and SEIRA) spectroscopy together with electrochemistry. Upon addition of Ca2+ ions electrochemical measurements show a shift of the catalytic turnover signal to more negative potentials while SERR measurements reveal an offset between the potential of heme reduction and catalytic current. Comparing SERR and SEIRA data we propose that binding of Ca2+ to the heme induces protein reorientation in a way that the electron transfer pathway of the catalytic FAD center to the electrode can bypass the heme cofactor, resulting in catalytic activity at more negative potentials. KW - cellobiose dehydrogenase KW - electron transfer KW - enzyme catalysis KW - spectroelectrochemistry KW - surface-enhanced vibrational spectroscopy Y1 - 2015 U6 - https://doi.org/10.1002/cphc.201500112 SN - 1439-4235 SN - 1439-7641 VL - 16 IS - 9 SP - 1960 EP - 1968 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Ast, Sandra A1 - Fischer, Tobias A1 - Müller, Holger A1 - Mickler, Wulfhard A1 - Schwichtenberg, Mathias A1 - Rurack, Knut A1 - Holdt, Hans-Jürgen T1 - Integration of the 1,2,3-Triazole "Click" Motif as a potent signalling element in metal ion responsive fluorescent probes JF - Chemistry - a European journal N2 - In a systematic approach we synthesized a new series of fluorescent probes incorporating donoracceptor (D-A) substituted 1,2,3-triazoles as conjugative -linkers between the alkali metal ion receptor N-phenylaza-[18]crown-6 and different fluorophoric groups with different electron-acceptor properties (4-naphthalimide, meso-phenyl-BODIPY and 9-anthracene) and investigated their performance in organic and aqueous environments (physiological conditions). In the charge-transfer (CT) type probes 1, 2 and 7, the fluorescence is almost completely quenched by intramolecular CT (ICT) processes involving charge-separated states. In the presence of Na+ and K+ ICT is interrupted, which resulted in a lighting-up of the fluorescence in acetonitrile. Among the investigated fluoroionophores, compound 7, which contains a 9-anthracenyl moiety as the electron-accepting fluorophore, is the only probe which retains light-up features in water and works as a highly K+/Na+-selective probe under simulated physiological conditions. Virtually decoupled BODIPY-based 6 and photoinduced electron transfer (PET) type probes 35, where the 10-substituted anthracen-9-yl fluorophores are connected to the 1,2,3-triazole through a methylene spacer, show strong ion-induced fluorescence enhancement in acetonitrile, but not under physiological conditions. Electrochemical studies and theoretical calculations were used to assess and support the underlying mechanisms for the new ICT and PET 1,2,3-triazole fluoroionophores. KW - charge transfer KW - click chemistry KW - electron transfer KW - fluorescent probes KW - metal ions Y1 - 2013 U6 - https://doi.org/10.1002/chem.201201575 SN - 0947-6539 VL - 19 IS - 9 SP - 2990 EP - 3005 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Wawrzinek, Robert A1 - Ziomkowska, Joanna A1 - Heuveling, Johanna A1 - Mertens, Monique A1 - Herrmann, Andreas A1 - Schneider, Erwin A1 - Wessig, Pablo T1 - DBD Dyes as Fluorescence Lifetime Probes to Study Conformational Changes in Proteins JF - CHEMISTRY-A EUROPEAN JOURNAL N2 - Previously, [1,3]dioxolo[4,5-f][1,3]benzodioxole (DBD)-based fluorophores used as highly sensitive fluorescence lifetime probes reporting on their microenvironmental polarity have been described. Now, a new generation of DBD dyes has been developed. Although they are still sensitive to polarity, in contrast to the former DBD dyes, they have extraordinary spectroscopic properties even in aqueous surroundings. They are characterized by long fluorescence lifetimes (10-20ns), large Stokes shifts (approximate to 100nm), high photostabilities, and high quantum yields (>0.56). Here, the spectroscopic properties and synthesis of functionalized derivatives for labeling biological targets are described. Furthermore, thio-reactive maleimido derivatives of both DBD generations show strong intramolecular fluorescence quenching. This mechanism has been investigated and is found to undergo a photoelectron transfer (PET) process. After reaction with a thiol group, this fluorescence quenching is prevented, indicating successful bonding. Being sensitive to their environmental polarity, these compounds have been used as powerful fluorescence lifetime probes for the investigation of conformational changes in the maltose ATP-binding cassette transporter through fluorescence lifetime spectroscopy. The differing tendencies of the fluorescence lifetime change for both DBD dye generations promote their combination as a powerful toolkit for studying microenvironments in proteins. KW - dyes KW - pigments KW - electron transfer KW - fluorescent probes KW - maleimides KW - MalF KW - photoelectron transfer Y1 - 2013 U6 - https://doi.org/10.1002/chem.201302368 SN - 0947-6539 SN - 1521-3765 VL - 19 IS - 51 SP - 17349 EP - 17357 PB - WILEY-V C H VERLAG GMBH CY - WEINHEIM ER -