Polychronous kinetics with nonstationary rate constants. Effect of a medium

Characteristic features of the kinetics of solid-state cage reactions with distributed parameters of the relaxing matrix were considered. Depending on the ratio of the constants of the reaction rate and relaxation of environment, the kinetics of chemical conversions can be either exponential or nonexponential. Plausible reasons for the unsteady-state character of the kinetics of the processes of two types,viz., the reactions of alkyl radicals in amorphous alcohol matrices and conversions in biological systems, were discussed. The main reason for the unsteady-state character of the reactions of the first type is a dispersion of the equilibrium distances between the reagents. Kinetics of the reactions of the second type, such as rebinding of the ligands in the heme-containing proteins (e.g., in myoglobin), is determined by the distances in the pairs of reagents and the relaxation transitions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 469–476, March, 1997.     

Asymptotics of many-electron wavefunctions and calculation of tunnel transitions

A new method for defining the wavefunction asymptotics for many-electron systems in the far-subbarrier region is suggested. The method is based on the Lippman-Schwinger formalism and can provide an accuracy in defining the asymptotics similar to that in the main region of the electron localization (MREL). The wavefunctions in MREL are the basis for obtaining the asymptotics. Molecular, cluster and surface systems are considered. A new approach to the calculation of tunneling transitions is formulated. A general expression for the tunneling current in scanning tunneling microscopy (STM) is obtained which strictly takes into account the penetration factor, the correlation between the tunneling current from individual atoms, and the angular dependence of asymptotics of basic atomic functions. This permits us to state and correctly solve the problem of defining the electron wavefunctions of the surface using the data of the tunneling current measurement at various biases and the positions of the tip.     

Mono- and Diamination of 4,6-Dichloropyrimidine, 2,6-Dichloropyrazine and 1,3-Dichloroisoquinoline with Adamantane-Containing Amines

N-heteroaryl substituted adamantane-containing amines are of substantial interest for their perspective antiviral and psychotherapeutic activities. Chlorine atom at alpha-position of N-heterocycles has been substituted by the amino group using convenient nucleophilic substitution reactions with a series of adamantylalkylamines. The prototropic equilibrium in these compounds was studied using NMR spectroscopy. The introduction of the second amino substituent in 4-amino-6-chloropyrimidine, 2-amino-chloropyrazine, and 1-amino-3-chloroisoquinoline was achieved using Pd(0) catalysis.     

Influence of an External Electric Field on the Charge and Field Distributions in a Metal Tip

Journal of Experimental and Theoretical Physics - The electric field and charge distributions in a nanosized truncated metal cone in a strong electric field have been found. The geometry of the...     

Tunneling spectroscopy of single electron spin

The possibility of detection of the electron spin of a single paramagnetic species (an atom, a radical, or an ion) on the surface was discussed. The analysis was based on spin chemistry laws taking into account the statistics of the spin states of both the tunneling electron and paramagnetic center. The equations for the tunneling current as a function of temperature and magnetic field strength were derived. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1732–1734, September, 1998.     

Shape-persistent linear, kinked, and cyclic oligo(phenylene-ethynylene-butadiynylene)s: self-assembled monolayers

Shape-persistent rigid phenylene-ethynylene-butadiynylenes form lamellar self-assembled monolayers (SAMs) at the HOPG/TCB interface, which were studied by scanning tunneling microscopy (STM) with submolecular resolution. Substitution of the terminating acetylene functions with polar cyanopropyldimethylsilyl groups leads to 2D phase separation and defined rod-rod interactions, which determine the packing distances between the rigid rods. The results stimulated the connection of rigid rods via septiarylene clamp units. They covalently link two rigid rod units and define the intramolecular rod-rod distance that matches the alkoxy substituent chain lengths. The systems can be described as half-ring structures of two rigid rods connected via a rotatable joint unit. These acetylene-terminated half-ring structures were also oligomerized under Cu and Pd catalysis to yield defined acyclic and cyclic oligomers. Detailed STM studies decoded the molecular origin of the surface patterning of such systems. The dodecyloxy side chains are adsorbed along the HOPG main axes and, together with the alkoxy backbone angle, determine the adsorption direction of the adlayers.     

Log-gases on quadratic lattices via discrete loop equations and q-boxed plane partitions

We study a general class of log-gas ensembles on (shifted) quadratic lattices. We prove that the corresponding empirical measures satisfy a law of large numbers and that their global fluctuations are Gaussian with a universal covariance. We apply our general results to analyze the asymptotic behavior of a q-boxed plane partition model introduced by Borodin, Gorin and Rains. In particular, we show that the global fluctuations of the height function on a fixed slice are described by a one-dimensional section of a pullback of the two-dimensional Gaussian free field.Our approach is based on a q-analogue of the Schwinger–Dyson (or loop) equations, which originate in the work of Nekrasov and his collaborators, and extends the methods developed by Borodin, Gorin and Guionnet to quadratic lattices.     

Durability of polyurethanes elastomers

The effect of thermal aging on three different elastomeric polyurethane adhesives was studied. Consequently, an attempt was made to predict the polyurethanes' service lifetimes from the changes in tensile properties, hardness of bulk specimens and adhesion strength properties (lap shear and butt joints) of polycarbonate bonded joints. Aging temperatures ranged from ambient to 70 °C (at 50% relative humidity) for durations from 20 days to 18 months. Experimental results were analyzed according to a kinetic rate theory and using limit values for the various properties. Consequently, service lifetimes were determined and compared to results from actual service life. Predictions of long-term performance from accelerated tests proved to be reasonable for the properties and materials studied.     

Photostimulated electron tunnel transfer in solid matrices

Tunnel recombination of photoseparated charges in frozen vitreous alcoholic solutions of zinc porphyrin (ZnP) and CCl₄ has been investigated. Considerable acceleration of the recombination in such systems when exposed to light in the ZnP⁺ or the CCl₄^? absorption band region is observed. Possible mechanisms which increase the charge recombination efficiency are considered in detail. The acceleration of the tunnel recombination of ZnP⁺ and CCl₄^? under irradiation in the porphyrin absorption band is shown to be due to energy transfer from an excited acceptor to a transferred electron. It is shown that data on the kinetics of photostimulated tunnel reactions can be used to determine the binding energy of a tunnelling electron.