TY - JOUR A1 - Öner, Ibrahim Halil A1 - Querebillo, Christine Joy A1 - David, Christin A1 - Gernert, Ulrich A1 - Walter, Carsten A1 - Driess, Matthias A1 - Leimkühler, Silke A1 - Ly, Khoa Hoang A1 - Weidinger, Inez M. T1 - High electromagnetic field enhancement of TiO2 nanotube electrodes JF - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition N2 - We present the fabrication of TiO2 nanotube electrodes with high biocompatibility and extraordinary spectroscopic properties. Intense surface-enhanced resonance Raman signals of the heme unit of the redox enzyme Cytochromeb(5) were observed upon covalent immobilization of the protein matrix on the TiO2 surface, revealing overall preserved structural integrity and redox behavior. The enhancement factor could be rationally controlled by varying the electrode annealing temperature, reaching a record maximum value of over 70 at 475 degrees C. For the first time, such high values are reported for non-directly surface-interacting probes, for which the involvement of charge-transfer processes in signal amplification can be excluded. The origin of the surface enhancement is exclusively attributed to enhanced localized electric fields resulting from the specific optical properties of the nanotubular geometry of the electrode. KW - electromagnetic field enhancement KW - photonic crystals KW - spectro-electrochemistry KW - surface-enhanced Raman spectroscopy KW - TiO2 nanotubes Y1 - 2018 U6 - https://doi.org/10.1002/anie.201802597 SN - 1433-7851 SN - 1521-3773 VL - 57 IS - 24 SP - 7225 EP - 7229 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Zülicke, Lutz A1 - Zuhrt, Christian A1 - Chapuisat, Xavier A1 - Saint-Espés, Cécile T1 - Internal dynamics of simple floppy molecules Y1 - 1994 ER - TY - JOUR A1 - Zülicke, Lutz A1 - Ragnetti, Francesca A1 - Neumann, Rainer A1 - Zuhrt, Christian T1 - Ionized Van-der-Waals systems : structure and interactions JF - Technical Report / Institute of Physical and Theoretical Chemistry, Potsdam Y1 - 1996 VL - 1996, 01 PB - Univ. CY - Potsdam ER - TY - JOUR A1 - Zülicke, Lutz A1 - Ragnetti, Francesca A1 - Neumann, Rainer T1 - Ionized Van-der-Waals systems : structure and interactions Y1 - 1997 ER - TY - JOUR A1 - Zühlke, Martin A1 - Zenichowski, Karl A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd T1 - Subambient pressure electrospray ionization ion mobility spectrometry JF - International journal for ion mobility spectrometry : official publication of the International Society for Ion Mobility Spectrometry N2 - The pressure dependence of sheath gas assisted electrospray ionization (ESI) was investigated based on two complementary experimental setups, namely an ESI-ion mobility (IM) spectrometer and an ESI capillary - Faraday plate setup housed in an optically accessible vacuum chamber. The ESI-IM spectrometer is capable of working in the pressure range between 300 and 1000 mbar. Another aim was the assessment of the analytical capabilities of a subambient pressure ESI-IM spectrometer. The pressure dependence of ESI was characterized by imaging the electrospray and recording current-voltage (I-U) curves. Qualitatively different behavior was observed in both setups. While the current rises continuously with the voltage in the capillary-plate setup, a sharp increase of the current was measured in the IM spectrometer above a pressure-dependent threshold voltage. The different character can be attributed to the detection of different species in both experiments. In the capillary-plate experiment, a multitude of charged species are detected while only desolvated ions attribute to the IM spectrometer signal. This finding demonstrates the utility of IM spectrometry for the characterization of ESI, since in contrast to the capillary-plate setup, the release of ions from the electrospray droplets can be observed. The I-U curves change significantly with pressure. An important result is the reduction of the maximum current with decreasing pressure. The connected loss of ionization efficiency can be compensated by a more efficient transfer of ions in the IM spectrometer at increased E/N. Thus, similar limits of detection could be obtained at 500 mbar and 1 bar. KW - Ion mobility spectrometry KW - Electrospray ionization KW - Subambient pressure KW - Imaging Y1 - 2017 U6 - https://doi.org/10.1007/s12127-017-0215-x SN - 1435-6163 SN - 1865-4584 VL - 20 SP - 47 EP - 56 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Zühlke, Martin A1 - Sass, Stephan A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd T1 - Real-Time Reaction Monitoring of an Organic Multistep Reaction by Electrospray Ionization-Ion Mobility Spectrometry JF - ChemPlusChem N2 - The capability of electrospray ionization (ESI)-ion mobility (IM) spectrometry for reaction monitoring is assessed both as a stand-alone real-time technique and in combination with HPLC. A three-step chemical reaction, consisting of a Williamson ether synthesis followed by a hydrogenation and an N-alkylation step, is chosen for demonstration. Intermediates and products are determined with a drift time to mass-per-charge correlation. Addition of an HPLC column to the setup increases the separation power and allows the determination of further species. Monitoring of the intensities of the various species over the reaction time allows the detection of the end of reaction, determination of the rate-limiting step, observation of the system response in discontinuous processes, and optimization of the mass ratios of the starting materials. However, charge competition in ESI influences the quantitative detection of substances in the reaction mixture. Therefore, two different methods are investigated, which allow the quantification and investigation of reaction kinetics. The first method is based on the pre-separation of the compounds on an HPLC column and their subsequent individual detection in the ESI-IM spectrometer. The second method involves an extended calibration procedure, which considers charge competition effects and facilitates nearly real-time quantification. KW - electrospray ionization KW - HPLC KW - ion mobility spectrometry KW - reaction mechanisms KW - reaction monitoring Y1 - 2017 U6 - https://doi.org/10.1002/cplu.201700296 SN - 2192-6506 VL - 82 SP - 1266 EP - 1273 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Zühlke, Martin A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Zenichowski, Karl A1 - Diener, Marc A1 - Linscheid, Michael W. T1 - An electrospray ionization-ion mobility spectrometer as detector for high-performance liquid chromatography JF - European journal of mass spectrometry N2 - The application of electrospray ionization (ESI) ion mobility (IM) spectrometry on the detection end of a high-performance liquid chromatograph has been a subject of study for some time. So far, this method has been limited to low flow rates or has required splitting of the liquid flow. This work presents a novel concept of an ESI source facilitating the stable operation of the spectrometer at flow rates between 10 mu L min(-1) and 1500 mu L min(-1) without flow splitting, advancing the T-cylinder design developed by Kurnin and co-workers. Flow rates eight times faster than previously reported were achieved because of a more efficient dispersion of the liquid at increased electrospray voltages combined with nebulization by a sheath gas. Imaging revealed the spray operation to be in a rotationally symmetric multijet-mode. The novel ESI-IM spectrometer tolerates high water contents (<= 90%) and electrolyte concentrations up to 10 mM, meeting another condition required of high-performance liquid chromatography (HPLC) detectors. Limits of detection of 50 nM for promazine in the positive mode and 1 mu M for 1,3-dinitrobenzene in the negative mode were established. Three mixtures of reduced complexity (five surfactants, four neuroleptics, and two isomers) were separated in the millisecond regime in stand-alone operation of the spectrometer. Separations of two more complex mixtures (five neuroleptics and 13 pesticides) demonstrate the application of the spectrometer as an HPLC detector. The examples illustrate the advantages of the spectrometer over the established diode array detector, in terms of additional IM separation of substances not fully separated in the retention time domain as well as identification of substances based on their characteristic IMs. KW - ESI KW - IMS KW - HPLC KW - spray imaging KW - neuroleptics KW - pesticides KW - surfactants Y1 - 2015 U6 - https://doi.org/10.1255/ejms.1367 SN - 1469-0667 SN - 1751-6838 VL - 21 IS - 3 SP - 391 EP - 402 PB - WeltTrends CY - Sussex ER - TY - JOUR A1 - Zühlke, Martin A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Andreotti, Sandro A1 - Reinert, Knut A1 - Zenichowski, Karl A1 - Diener, Marc T1 - High-performance liquid chromatography with electrospray ionization ion mobility spectrometry: Characterization, data management, and applications JF - Journal of separation science N2 - The combination of high-performance liquid chromatography and electrospray ionization ion mobility spectrometry facilitates the two-dimensional separation of complex mixtures in the retention and drift time plane. The ion mobility spectrometer presented here was optimized for flow rates customarily used in high-performance liquid chromatography between 100 and 1500 mu L/min. The characterization of the system with respect to such parameters as the peak capacity of each time dimension and of the 2D spectrum was carried out based on a separation of a pesticide mixture containing 24 substances. While the total ion current chromatogram is coarsely resolved, exhibiting coelutions for a number of compounds, all substances can be separately detected in the 2D plane due to the orthogonality of the separations in retention and drift dimensions. Another major advantage of the ion mobility detector is the identification of substances based on their characteristic mobilities. Electrospray ionization allows the detection of substances lacking a chromophore. As an example, the separation of a mixture of 18 amino acids is presented. A software built upon the free mass spectrometry package OpenMS was developed for processing the extensive 2D data. The different processing steps are implemented as separate modules which can be arranged in a graphic workflow facilitating automated processing of data. KW - Amino acids KW - Electrospray ionization KW - Ion mobility spectrometry KW - Pesticides KW - Two-dimensional separations Y1 - 2016 U6 - https://doi.org/10.1002/jssc.201600749 SN - 1615-9306 SN - 1615-9314 VL - 39 SP - 4756 EP - 4764 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Zühlke, Martin A1 - Meiling, Till Thomas A1 - Roder, Phillip A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Bald, Ilko A1 - Löhmannsröben, Hans-Gerd A1 - Janßen, Traute A1 - Erhard, Marcel A1 - Repp, Alexander T1 - Photodynamic inactivation of E. coli bacteria via carbon nanodots JF - ACS omega / American Chemical Society N2 - The increasing development of antibiotic resistance in bacteria has been a major problem for years, both in human and veterinary medicine. Prophylactic measures, such as the use of vaccines, are of great importance in reducing the use of antibiotics in livestock. These vaccines are mainly produced based on formaldehyde inactivation. However, the latter damages the recognition elements of the bacterial proteins and thus could reduce the immune response in the animal. An alternative inactivation method developed in this work is based on gentle photodynamic inactivation using carbon nanodots (CNDs) at excitation wavelengths λex > 290 nm. The photodynamic inactivation was characterized on the nonvirulent laboratory strain Escherichia coli K12 using synthesized CNDs. For a gentle inactivation, the CNDs must be absorbed into the cytoplasm of the E. coli cell. Thus, the inactivation through photoinduced formation of reactive oxygen species only takes place inside the bacterium, which means that the outer membrane is neither damaged nor altered. The loading of the CNDs into E. coli was examined using fluorescence microscopy. Complete loading of the bacterial cells could be achieved in less than 10 min. These studies revealed a reversible uptake process allowing the recovery and reuse of the CNDs after irradiation and before the administration of the vaccine. The success of photodynamic inactivation was verified by viability assays on agar. In a homemade flow photoreactor, the fastest successful irradiation of the bacteria could be carried out in 34 s. Therefore, the photodynamic inactivation based on CNDs is very effective. The membrane integrity of the bacteria after irradiation was verified by slide agglutination and atomic force microscopy. The method developed for the laboratory strain E. coli K12 could then be successfully applied to the important avian pathogens Bordetella avium and Ornithobacterium rhinotracheale to aid the development of novel vaccines. KW - Bacteria KW - Genetics KW - Fluorescence KW - Photodynamics KW - Irradiation Y1 - 2021 U6 - https://doi.org/10.1021/acsomega.1c01700 SN - 2470-1343 VL - 6 IS - 37 SP - 23742 EP - 23749 PB - ACS Publications CY - Washington, DC ER - TY - JOUR A1 - Zuhrt, Christian A1 - Neumann, Rainer A1 - Zülicke, Lutz T1 - Investigation of vibrational states of the ArHCl+ cation in the electronic ground state Y1 - 1999 ER -