On the description of reactions in solution

A formulation for diffusion-influenced reactions in solution is given in which reactive and translational contributions are separated, steady state rate-limiting step formulations are generalized to the dynamical case and the influence of different experimental initial conditions is isolated.     

On the ultrafast infrared spectroscopy of anion hydration shell hydrogen bond dynamics

Molecular Dynamics simulations are used to examine the title issue for the I-/HOD/D2O solution system in connection with recent ultrafast infrared spectroscopic experiments. It is argued that the long "modulation time" associated with the spectral diffusion of the OH frequency, extracted in these experiments, should be interpreted as reflecting the escape time of an HOD from the first hydration shell of the I- ion, i.e., the residence time of an HOD in this solvation shell. Shorter time features related to the oscillation of the OH ...I- hydrogen bond and the breaking and making of this bond are also discussed.     

Studies on the application of salts of complex cations to the microscopic detection of anions

Summary Roseocobaltic chloride was found to furnish characteristic crystalline reaction products with oxalates, sulfosalicylic acid, dithionates, ferriand ferrocyanides, silicofluorides and phosphomolybdates. Of these, only the first four reaction products are recommended for identification of the corresponding anions.

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Zusammenfassung Aquo-pentammino-cobaltichlorid gibt mit Dithionat, Ferricyanid, Oxalat und Sulfosalicylat kristallisierte Reaktionsprodukte, die für den Nachweis dieser Ionen geeignet sind.

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Résumé (L) L'aquo-pentammino-cobaltichlorure, forme des dithionates, ferri-cyanures, oxalates et sulfosalicylates cristallins qui conviennent pour la recherche de ces ions.

     

Dynamic effects on reaction rates in a Michael addition catalyzed by chalcone isomerase. Beyond the frozen environment approach

We present a detailed microscopic study of the dynamics of the Michael addition reaction leading from 6'-deoxychalcone to the corresponding flavanone. The reaction dynamics are analyzed for both the uncatalyzed reaction in aqueous solution and the reaction catalyzed by Chalcone Isomerase. By means of rare event simulations of trajectories started at the transition state, we have computed the transmission coefficients, obtaining 0.76 +/- 0.04 and 0.87 +/- 0.03, in water and in the enzyme, respectively. According to these simulations, the Michael addition can be seen as a formation of a new intramolecular carbon-oxygen bond accompanied by a charge transfer essentially taking place from the nucleophilic oxygen to the carbon atom adjacent to the carbonyl group (C (alpha)). As for intermolecular interactions, we find a very significant difference in the evolving solvation pattern of the nucleophilic oxygen in water and in the enzyme. While in the former medium this atom suffers an important desolvation, the enzyme provides, through variations in the distances with some residues and water molecules, an essentially constant electric field on this atom along the reaction progress. Grote-Hynes (GH) theory provides a useful framework to systematically analyze all the couplings between the reaction coordinate and the remaining degrees of freedom. This theory provides transmission coefficients in excellent agreement with the Molecular Dynamics estimations. In contrast, neither the frozen environment approach nor Kramers theory gives results of similar quality, especially in the latter case, where the transmission coefficients are severely underestimated. The (unusual) failure of the frozen environment approach signals the importance of some dynamical motions. Within the context of GH theory, analysis of the friction spectrum obtained in the enzymatic environment, together with normal-mode analysis, is used to identify those motions, of both the substrate and the environment, strongly coupled to the reaction coordinate and to classify them as dynamically active or inactive.     

Reagenzien

Ohne Zusammenfassung     

A stochastic theory of chemical reaction rates. I. Formalism

A class of stochastic processes is studied that can be used to model elementary and complex chemical reactions composed of a series of several distinct steps. Formal correlation function expressions are directly computed for the stochastic model to yield the overall rate constant for the reaction. One of the main results is a formula connecting the overall rate constant to the rate constants characterizing the elementary steps of the reaction.