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Schroder D.,Czech Institute of Organic Chemistry And Biochemistry
Angewandte Chemie - International Edition | Year: 2010

Figure Presented Cold methane coupling: Recent experiments with trapped Au2+ clusters reveal a catalytic cycle for the dehydrogenative CC coupling of methane to give ethene at temperatures between 200 and 300 K (see scheme). The key novelty of the work is the explicit exploration of the multicollisional regime, which represents an important step to bridge the pressure gap between model studies and real catalysis. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA. Source


Schroder D.,Czech Institute of Organic Chemistry And Biochemistry
Accounts of Chemical Research | Year: 2012

Mechanistic studies form the basis for a better understanding of chemical processes, helping researchers develop more sustainable reactions by increasing the yields of the desired products, reducing waste production, and lowering the consumption of resources and energy overall. Conventional methods for the investigation of reaction mechanisms in solution include kinetic studies, isotope labeling, trapping of reactive intermediates, and advanced spectroscopic techniques. Within the past decade, electrospray ionization mass spectrometry (ESI-MS) has provided an additional tool for mechanistic studies because researchers can directly probe liquid samples by mass spectrometry under gentle conditions.Specifically, ESI-MS allows researchers to identify the molecular entities present in solution over the course of a chemical transformation. ESI-MS is particularly useful for investigations of organic reactions or metal catalysis that involve ionic intermediates. Accordingly, researchers are increasingly using ESI-MS in mechanistic studies and catalyst development. However, a further understanding of the ESI process and how it can facilitate mechanistic studies has not accompanied this increased use of the technique. Therefore, at least in part the ESI-MS method not only has offered great promise for the elucidation of reaction mechanisms but also became a black box with the occasional risk of misinterpretation.In this Account, we summarize applications of ESI-MS for synthetic and mechanistic research. Recently researchers have established direct linkages between gas-phase data obtained via ESI-MS and processes occurring in solution, and these results reveal qualitative and quantitative correlations between ESI-MS measurements and solution properties. In this context, time dependences, concentration series, and counterion effects can serve as criteria that allow researchers assess if the gas-phase measurements correlate with the situation in the solution. Furthermore, we report developments that bridge the gap between gas-phase and solution-phase studies. We also describe predictions derived from ESI-MS that have been verified with solution-phase chemistry experiments. © 2012 American Chemical Society. Source


Kasicka V.,Czech Institute of Organic Chemistry And Biochemistry
Electrophoresis | Year: 2010

The review presents a comprehensive survey of recent developments of high-performance capillary electromigration methods, zone electrophoresis, ITP, IEF, affinity electrophoresis, EKC and electrochromatography, and their application to analysis, preparation and physicochemical characterization of peptides. New approaches to the theoretical description and experimental investigation of electromigration properties of peptides, and to methodology of their separations, such as sample preparation, adsorption suppression, EOF control and detection, are described. New developments in particular CE and CEC modes are reported and several types of their applications to peptide analysis are presented: conventional qualitative and quantitative analysis, determination in biomatrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid and sequence analysis, and peptide mapping of proteins. Few examples of micropreparative peptide separations are shown and capabilities of CE and CEC techniques to provide important physicochemical characteristics of peptides are demonstrated. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA. Source


Schroder D.,Czech Institute of Organic Chemistry And Biochemistry
Physical Chemistry Chemical Physics | Year: 2012

Electrospray ionization is suggested as a complementary technique for the investigation of the solution chemistry of metal salts, which allows us to achieve direct insight into the molecular entities present in solution. While the transfer of the metal ions from solution to the gas phase in the course of the electrospray process is associated with significant changes in concentration, pH, and also composition in the case of mixed solvents, systematic studies of concentration series can provide criteria to assess the extent to which the gas-phase data correlate with the situation in solution. While there does not exist a 11 correlation between mass spectrometric measurements and solution properties, very useful qualitative molecular insights can be achieved and quantitative analysis can be made once the specific circumstances of the ionization process are taken into account. © the Owner Societies 2012. Source


Smith M.B.,University of Colorado at Boulder | Michl J.,University of Colorado at Boulder | Michl J.,Czech Institute of Organic Chemistry And Biochemistry
Chemical Reviews | Year: 2010

Singlet fission is a process in which an organic chromophore in an excited singlet state shares its excitation energy with a neighboring ground-state chromophore and both are converted into triplet excited states. Singlet fission is spin-allowed in the sense that the two resulting triplet excitations produced from an excited singlet are born coupled into a pure singlet state. Like many other internal conversion processes, it can be very fast, particularly in molecular crystals. The wave function of the initially formed pure singlet state 1(TT) is a coherent superposition of the wave functions of these nine sublevels, and their ultimate population will reflect the amplitude of the singlet 1(TT) wave function in each one. As long as the states resulting from singlet fission are of mixed multiplicity, the overall process can also be viewed as a special case of intersystem crossing. Singlet fission does not occur in single small-molecule chromophores, at least not at the usual excitation energies, and is constrained to multichromophoric systems. Source

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