Bimodal proton transfer in acid-base reactions in water

We investigate one of the fundamental reactions in solutions, the neutralization of an acid by a base. We use a photoacid, 8-hydroxy-1,3,6-trisulfonate-pyrene (HPTS; pyranine), which upon photoexcitation reacts with acetate under transfer of a deuteron (solvent: deuterated water). We analyze in detail the resulting bimodal reaction dynamics between the photoacid and the base, the first report on which was recently published. We have ascribed the bimodal proton-transfer dynamics to contributions from preformed hydrogen bonding complexes and from initially uncomplexed acid and base. We report on the observation of an additional (6 ps)(-1) contribution to the reaction rate constant. As before, we analyze the slower part of the reaction within the framework of the diffusion model and the fastest part by a static, sub-150 fs reaction rate. Adding the second static term considerably improves the overall modeling of the experimental results. It also allows to connect experimentally the diffusion controlled bimolecular reaction models as defined by Eigen-Weller and by Collins-Kimball. Our findings are in agreement with a three-stage mechanism for liquid phase intermolecular proton transfer: mutual diffusion of acid and base to form a "loose" encounter complex, followed by reorganization of the solvent shells and by "tightening" of the acid-base encounter complex. These rearrangements last a few picoseconds and enable a prompt proton transfer along the reaction coordinate, which occurs faster than our time resolution of 150 fs. Alternative models for the explanation of the slower "on-contact" reaction time of the loose encounter complex in terms of proton transmission through a von Grotthuss mechanism are also discussed.     

Boundaries and Harmonic Functions for Random Walks with Random Transition Probabilities

The usual random walk on a group (homogeneous both in time and in space) is determined by a probability measure on the group. In a random walk with random transition probabilities this single measure is replaced with a stationary sequence of measures, so that the resulting (random) Markov chains are still space homogeneous, but no longer time homogeneous. We study various notions of measure theoretical boundaries associated with this model and establish an analogue of the Poisson formula for (random) bounded harmonic functions. Under natural conditions on transition probabilities we identify these boundaries for several classes of groups with hyperbolic properties and prove the boundary triviality (i.e., the absence of non-constant random bounded harmonic functions) for groups of subexponential growth, in particular, for nilpotent groups.     

Limit theorems for random walks with dynamical random transitions

Let be an ergodic and conservative non-singular transformation of (, ,m) (thedynamic environment), let _w be a random probability on a locally compact second countable groupG, and define

Structure and classification of factors

This survey gives a representation of the current state of the theory of factors. The emphasis is on the achievements of the last 15 years, in the first place the papers of A. Connes.Translated from Itogi Nauki i Tekhniki, Sovremennye Problemy Matematiki, Noveishie Dostizheniya, Vol. 26, pp. 127–170, 1985.     

Synthesis of Poly-5-vinylindole Derivatives

5-Vinyl-N-benzylindoline and 5-vinyl-N-benzylindole were synthesized starting from the corresponding 5-formyl derivative, by utilizing the Wittig or Wittig-Horner reactions. The monomers were polymerized by free-radical (AIBN) and anionic (BuLi) catalysts. Poly-5-vinyl-N-benzylindole was converted through suitable reactions to the tryptamine and indole acetic acid derivatives. Poly-5-vinyl-N-benzyl-tryptophane was synthesized by malonic ester synthesis by utilizing the condensation of poly-5-vinyl-N-benzylgramine and diethyl formamidomalonate.     

Synthesis of Indole Derivatives Attached to Polyethylene Oxides)

N-Benzyl 5-, 6-, and 7-bromoindolines were converted to the respective organosodium derivatives and used as initiators for the anionic polymerization of ethylene oxide. The resulting indoline derivatives attached to polyethylene oxide were dehydrogenated to the indole derivatives, which in turn were converted through suitable reactions to the tryptamine and indole acetic acid derivatives.