Solvent effect on the initial state and transition state of anation of pentaammine-aquachromium(III) ion by thiocyanate

Summary Solvent effects on rate constants and activation enthalpies and entropies for the anation of [Cr(NH₃)₅H₂O]²⁺ by SCN^- in aqueous mixtures of MeOH, EtOH, i-PrOH and t-BuOH were analysed into initial and transition state contributions. From kinetic measurements, solubilities of the complex salt and enthalpies of solution, the thermodynamic transfer functions G _inft ^supo , H _inft ^supo and S _inft ^supo , corresponding to the transfer of reactants and activated complex from water to aqueous-organic mixtures, were evaluated. The very small difference in solvation of initial and transition states, indicated by the analysis, seemed to be consistent with the proposed interchange mechanism.     

Acid-base equilibria in nonpolar media. 3. Expanding the spectrophotometric acidity scale in heptane

The UV-vis spectrophotometric ion-pair acidity scale in heptane has been significantly expanded: it includes now 21 bulky CH and NH indicator acids and spans for about 10 pKip units. The phosphazene base t-Bu-P4 was used for deprotonating. The correlations between acidities in heptane versus gas-phase acidities or acidities in DMSO or 1,2-dimethoxyethane have been made for some compounds. It was demonstrated that the substituent effects on the acidity of the studied CH acids are attenuated ca. 1.24 times when the gas phase is substituted for the nonpolar solvent, heptane. In its turn, for the series of NH acids, the latter is found to be a somewhat more differentiating solvent than DMSO.     

Hot recombination of photogenerated ion pairs

The recombination dynamics of ion pairs generated upon electron transfer quenching of perylene in the first singlet excited state by tetracyanoethylene in acetonitrile is quantitatively described by the extended unified theory of photoionization/recombination. The extension incorporates the hot recombination of the ion pair passing through the level-crossing point during its diffusive motion along the reaction coordinate down to the equilibrium state. The ultrafast hot recombination vastly reduces the yield of equilibrated ion pairs subjected to subsequent thermal charge recombination and separation into free ions. The relatively successful fit of the theory to the experimentally measured kinetics of ion accumulation/recombination and free ion yield represents a firm justification of hot recombination of about 90% of primary generated ion pairs.     

Copper(I) and silver(I) complexes of 1,5-methylene- and diethylmethylene-bridged bis(oxazoline) ligands. In situ Cu(II)-catalyzed oxidation of methylene bridge

Silver(I) and copper(I) complexes of C₂-symmetric bis(oxazoline) ligands were studied by UV, NMR, IR, EPR and ES-MS spectroscopies. The stability constants of the Ag-1a and Ag-1b complexes with 1:1 and 1:2 stoichiometries in acetonitrile were determined by NMR spectrometric titrations. The evidence of tetrahedral coordination for complex (Ag(1a)₂(⁺ was obtained from the complexation induced shifts (CIS) and NOEs. Mass spectra revealed the Cu(II) mediated oxidation of methylene bridge in copper complexes of 1a and 1b, which was in accordance with the UV, NMR, IR and EPR findings. The efficiency of Cu(I) complexes of methylene-bridged 1,5-bis(oxazoline)s 1 as chiral catalysts in stereoselective cyclopropanation of styrene with ethyl diazoacetate, was compared to that of the dialkylmethylene-bridged 1,5-bis(oxazoline)s 2.     

Biquaternionic Integral Representations for Massive Dirac Spinors in a Magnetic Field and Generalized Biquaternionic Differentiability

The Dirac equation with a vector potential is considered using a biquaternionic formalism and boundary integral representations for its solutions are obtained. In order to characterize these solutions by a property of local approximability by linearization the corresponding notion of biquaternionic differentiability and its generalization in the sense of Bers (adapted to the spatial case) are given.     

Facile methods of the synthesis of S-trialkylstannyl esters of dithio- and tetrathiophosphoric acids

S-Trialkylstannyl dialkyldithiophosphates 3 and tetrathiophosphates 6 were easily obtained in the reaction of tetraphosphorus decasulfide 1 with trialkylalkoxystannanes 2 or alkylthiostannanes 5 under mild conditions. Tetraphosphorus decasulfide 1 and hexaalkyl distannylsulfides 4 produce tris(trialkylstannyl) tetrathiophosphates 9 .     

N-tributyltin mesylimide—a new water-soluble fungicide

In addition to the known water-soluble tributyltin compounds, N-tributyltin mesylimide [Bu₃SnN-(SO₂Me₂)₂] was prepared and proposed as a fungicide for water-based preservative formulations. The aqueous solubility of the new compound is in the range of 11.0–11.4% w/w at 25 °C and its activity towards moulds (Aspergillus niger) is near that for tributyltin oxide. The compound has an average toxicity (LD₅₀=740 mg kg^?1).     

The Geometry of Lightlike Hypersurfaces of the de Sitter Space

It is proved that the geometry of lightlike hypersurfaces of the de Sitter space Sn+11 is directly connected with the geometry of hypersurfaces of the conformal space Cn. This connection is applied for a construction of an invariant normalization and an invariant affine connection of lightlike hypersurfaces as well as for studying singularities of lightlike hypersurfaces.     

A policy gradient method for semi-Markov decision processes with application to call admission control

Solving a semi-Markov decision process (SMDP) using value or policy iteration requires precise knowledge of the probabilistic model and suffers from the curse of dimensionality. To overcome these limitations, we present a reinforcement learning approach where one optimizes the SMDP performance criterion with respect to a family of parameterised policies. We propose an online algorithm that simultaneously estimates the gradient of the performance criterion and optimises it using stochastic approximation. We apply our algorithm to call admission control. Our proposed policy gradient SMDP algorithm and its application to admission control is novel.     

Quantum theory of super-resolution for optical systems with circular apertures

We present the two-dimensional quantum theory of super-resolution, applicable for a large variety of optical systems with circular pupils. Our theory is formulated in terms of circular prolate spheroidal functions which form the eigen basis of two-dimensional imaging system with circular pupils. We provide, in particular, analytical and numerical results for the point-spread function characterizing reconstruction of optical objects with super-resolution from diffraction-limited images. We evaluate the super-resolution factor as a function of the signal-to-noise ratio in the input object for coherent light and multimode squeezed light.