<p>Mass spectrometry-based techniques have been widely used in reaction monitoring due to their high sensitivity and ability to offer structure information by tandem mass spectrometry. We applied nanoelectrospray mass spectrometry (nanoESI-MS) to simultaneously monitor pre-catalysts, catalytic intermediates, reagents, and products of palladium catalyzed Suzuki-Miyaura cross-coupling reactions. A set of Pd cluster ions related to the monoligated Pd (0) active catalyst is detected, and its deconvoluted isotopic distribution reveals contributions from two neutral molecules. One is assigned to the generally accepted Pd (0) active catalyst, seen in MS as the protonated molecule, while the other is suggested to correspond to a deactivated form of Pd catalyst. Oxidative stress testing of the synthetic model catalyst XPhos Pd cyclo-octadiene, performed using oxygen and Fe(III), supported this assignment. Thus, the make-up of the monoligated set of Pd (0) ions appears to indicate the oxidation state of the system. The formation and removal of the oxidative addition intermediate during the catalytic cycle was monitored to provide information on the progress of the transmetalation step. </p> <p> </p> <p><a>Recently, microdroplets created by ambient ionization source have been used as reaction vessels to accelerate organic reactions. Field desorption mass spectrometry under ambient conditions is applied to study solution-phase organic reactions in micro-volumes. Compared to nanoelectrospray, it is noteworthy that radical cations and formation of radical cation products are observed. Three reactions, the hydrazone formation by phenyl hydrazine and indoline-2,3-dione, the Katritzky reaction between a pyrylium salt and anisidine, and the Hantzsch synthesis of 1,4-dihydropyridine, were investigated by this system and reaction acceleration was observed to different extents. The increase in rate relative to that for the corresponding bulk reactions is attributed to solvent evaporation which increases concentration, and to the increase of surface-to-volume ratio with enhanced interfacial reaction rate constants. Later work in this thesis describes explicit solvent calculations to study the energies and structures of the hydrazone formation reaction from phenylhydrazine and indoline-2,3-dione in acidic methanol with density functional tight binding (DFTB) methods. Additionally, the thesis covers MS based methods for determination of isoaspartate and aspartate in peptide by gas-phase chemistry and detection of S-nitrosoglutathione in exhaled breath condensate sample.</a></p>

No description available.

No description available.

No description available.

No description available.

The presented master thesis is devoted to the investigation of reaction intermediates in homogeneous gold catalysis. Electrospray ionization mass spectrometry (ESI-MS) was used as the primary research technique in this study. Delayed reactant labeling was used as the main method. I have focused mainly on the hydration of 1-phenyl-1-propyne catalyzed by the gold complex [Au(IPr)(MeCN)]BF4 (IPr = 1,3-bis(2,6-di-iso-propylphenyl)imidazol-2- ylidene). I have detected two main intermediates containing one or two gold atoms, respectively (monoaurated and diaurated intermediate). I have obtained rate constants for the degradation of the reaction intermediates and their half-lives. I have derived kinetic isotope effects for the formation and the decomposition of the detected intermediates. I have shown that the kinetics of the degradation of both intermediates is identical, therefore I conclude that hydration of alkynes catalyzed by gold complex [Au(IPr)(MeCN)]BF4 proceeds most probably via neutral monoaurated intermediates. These neutral intermediates are detected by ESI-MS as protonated (monoaurated intermediate) or tagged by a second gold cation (diaurated intermediate). Key words: gold catalysis, reaction intermediates, electrospray ionization, mass spectrometry.

Scanning electrochemical microscopy (SECM) was used for the study and characterization of catalytic and electrocatalytic processes occurring at electrodes. The Surface Interrogation mode (SI-SECM) was introduced for the detection and quantification of adsorbed intermediates and products of catalyzed chemical and electrochemical reactions at noble metals (Pt, Au). In SI-SECM two micro electrodes (i.e. an SECM tip and a substrate of the desired material) are aligned concentrically at a micrometric distance where SECM feedback effects operate. A contrast mechanism based on feedback effects allows for the detection of reactive adsorbed intermediates at the substrate: the SECM tip generates a reactive homogeneous species that “micro-titrates” the substrate adsorbates to yield an electrochemical signal that contains information about the amount of intermediate and about its kinetics of reaction with the redox mediator. The technique was used for the study of the reactivity of three model small adsorbates: 1) the reactivity of adsorbed oxygen on Au and Pt with a reducing mediator was explored and suggested the detection of “incipient oxides” at these surfaces; kinetic parameters of the reactivity of Pt oxides with mediators were obtained, fit to theory and used to explain observations about the electrocatalytic behavior of Pt under anodizing conditions; 2) the reactivity of oxidizing mediators with adsorbed hydrogen on Pt was studied and showed the cation of N,N,N,N-tetramethyl-p-phenylenediamine (TMPD) to be a successful interrogation agent, the detection of hydrogen generated by the decomposition of formic acid on Pt at open circuit was investigated; 3) electrogenerated bromine was used to catalytically interrogate carbon monoxide at Pt, this reaction was previously unreported. The mentioned applications of SECM were validated through the use of digital simulations of diffusion in the complex SECM geometry through flexible commercial finite element method software. / text

No description available.

No description available.

No description available.