Orthogonalization in momentum space

Since the overlap integral between two functions in position space is the same as the overlap integral between their counterparts in momentum space, there is an intimate connection between orthonormalization procedures in the two spaces. It is pointed out that in certain cases this situation can be used to simplify the orthogonalization.     

NQR investigations in crystalline 2,5-dichloroacetanilide

Two close NQR lines were observed in 2,5-dichloroacetanilide at room temperature at 34.606 MHz and 35.212 MHz as well as at liquid nitrogen temperature at 34.832 MHz and 35.791 MHz, using a self-quenched super-regenerative spectrometer. Analysis of the Zeeman effect on the two lines using a cylindrical single crystal reveals that the crystal belongs to either orthorhombic or monoclinic system. There are two crystallographically equivalent but physically non-equivalent directions for the principal field gradientZ axes making an angle of 77° for both resonance lines. The unit cell contains either two or a multiple of two molecules. There is an in-plane bending of the two C-Cl bonds by 1°. The ionic, single bond and double bond characters of C-C1 bonds for both chlorines are almost equal and are in the ratio 25:74:1.     

Switch in Catalyst State: Single Bifunctional Bi-state Catalyst for Two Different Reactions

Disclosed here is a molecular switch which responds to acid-base stimuli and serves as a bi-state catalyst for two different reactions. The two states of the switch serve as a highly active and poorly active catalyst for two catalytic reactions (namely a hydrogenation and a dehydrogenative coupling) but in a complementary manner. The system was used in an assisted tandem catalysis set-up involving dehydrogenative coupling of an amine and then hydrogenation of the resulting imine product by switching between the respective states of the catalyst.     

双杯芳烃研究进展

双杯芳烃是杯芳烃家族中的重要一员。它由两个杯芳烃单元通过化学键联结而形成,一般常有上缘-下缘、下缘-下缘、下缘-上缘3种桥联方式,其结构更复杂,性质也更为丰富多彩。双杯芳烃具有两个相同或不相同的结合部位,可同时络合两个相同或不相同的底物,还可表现出特殊的协同作用、更强的络合能力、变构象以及粒子雾荡等新的性质。本文根据杯芳烃亚单元的种类,综述了双杯芳烃的研究进展,重点描述了不同桥联方式的双杯[4]芳烃的合成方法,而且对一些具有特殊性能的双杯芳烃进行了较为详细的介绍。最后对双杯芳烃的发展前景作了展望。     

Damped motion in a two-dimensional double well I. Proton tunneling in a hydrogen bond

A model is presented to decribe proton transfer between two sites of a hydrogen bond forming part of a larger molecular complex in a thermal environment. The tunneling motion of the proton is assumed to couple strongly to the end atom vibration of the hydrogen bond via an interaction of the small polaron type. The end atom vibration interacts with the remaining vibrations of the molecular complex and the surrounding medium. These degrees of freedom are treated as an ensemble of harmonic oscillators forming a heat bath and therefore giving rise to a random force acting on, and a damping of, the end atom vibration. Via this vibration the tunneling motion of the proton is damped, too, thus describing an effective transfer from one site to another. The rate coefficient for the transfer reaction is calculated according to Kubo's theor, as an integral over the time correlation function of the reactive flux. Both the end atom vibration and the heat both have an influence on the reaction rate, which therefore depends on both types of coupling constants. The rate constant for systems like a hydrogen bond between two oxygen atoms is not directly related to the tunneling frequency, but may show resonance features when the oscillator frequency is comparable to the level splitting of the two lowest lying proton states.     

Diffusion enhancement in core-softened fluid confined in nanotubes

We study the effect of confinement in the dynamical behavior of a core-softened fluid. The fluid is modeled as a two length scales potential. This potential in the bulk reproduces the anomalous behavior observed in the density and in the diffusion of liquid water. A series of NpT molecular dynamics simulations for this two length scales fluid confined in a nanotube were performed. We obtain that the diffusion coefficient increases with the increase of the nanotube radius for wide channels as expected for normal fluids. However, for narrow channels, the confinement shows an enhancement in the diffusion coefficient when the nanotube radius decreases. This behavior, observed for water, is explained in the framework of the two length scales potential.     

Charge separation in ground-state 1,2,4,5-tetra-substituted benzene derivatives

The conditions required for a formal biradical to exist in a zwitterionic form in the ground state are discussed following the recent experimental observation of zwitterionic structure in the ground state of a quinoid molecule (di-tert-butyl derivative of 2,5-diamino-1,4-benzoquinonediimine, I). A unique characteristic of molecules of this class is the fact that they may be considered as being formed by the union of two radicals, each having an odd number of pi electrons. In the case of I, one fragment carries the two amino group having 7 pi electrons; it acts as the electron donor. The other fragment carries the two oxygen atoms (carrying 5 pi electrons) and acts as an electron acceptor. A model that predicts the properties of these systems is presented, based on previous work on non-Kekule hydrocarbons(2,3) and on the electron donating and attracting properties of the donor and acceptor groups, respectively. The zwitterion is formed by an electron transfer leading to two subunits carrying 6 pi electrons each and may become more stable than the triplet biradical even in the gas phase (i.e., in the absence of an external field) if the ionization potential of the donor is small (of the order of 3-4 eV). In some cases solvation in a polar solvent is required to make the zwitterionic form the lowest energy species on the ground-state surface. The 'spacer' between the donor and acceptor groups (which need not be necessarily derived from an aromatic structure) can be varied and influences the overall dipole moment that is calculated in some cases to be quite large (over 20 D in the gas phase).     

Entanglements in glass

Ground state and elementary excitations (tunnelling modes) in glass are obtained from an analysis of its symmetry, a local gauge invariance. The configuration of glass is represented as a discrete fiber bundle. The base space is a continuous random network, standard model of the structure of covalent glasses. The connection is determined naturally by the elasticity of the network. The bundle is non-trivial, the elastic connection is entangled in one of two ways. Sources of non-triviality are closed loops, threading through odd rings in the network. To restore gauge invariance, tunnelling must occur between the two possible configurations about an odd loop. Entanglement and elementary excitations are labelled by permutations of the covalent bonds incident on an atom.Work supported by the Herbette Foundation.     

Controlling the energy transfer in dipole chains

Processing digital signals on the molecular scale is of great interest. In this paper, we discuss the control of pulselike energy propagation through one-dimensional arrays of dipoles. Three systems are explored. In the first system, a chain of coaxial dipoles is gated by two control dipoles. Changing the orientation of these control dipoles lets us control the transfer of energy in the chain. In the other two systems, the chain-branch system and the two-branch system, two chains are used as an input and the propagation of energy is controlled by sending one or two signals toward the junction. Both systems can operate as a logical AND port. Their geometrical configurations are key to a well-defined control and operation of the AND port.     

Lewis acid sites in boralites

This work is aimed at modeling a framework L-site of a boralite using DFT and a cyclic cluster including one B and two Si atoms. A similar cluster was used earlier as a successful model for an L-site of a zeolite, which allows for the direct comparison of the properties of the two L-sites. It is shown that the boralitic L-site is rather weak. Unlike its zeolitic counterpart, it cannot bind a molecule of ethene or carbon monoxide. Only a base as strong as ammonia can form a stable 1:1 complex with the boralitic L-site. Water is found to bind to the boralitic L-site only if not less than two of its molecules are interacting with the model cluster. As water loading increases, the geometry of the BO₃ fragment undergoes gradual changes indicative of facile hydrolysis of the boralite lattice.     

Switch in Catalyst State: Single Bifunctional Bi‐state Catalyst for Two Different Reactions

Disclosed here is a molecular switch which responds to acid‐base stimuli and serves as a bi‐state catalyst for two different reactions. The two states of the switch serve as a highly active and poorly active catalyst for two catalytic reactions (namely a hydrogenation and a dehydrogenative coupling) but in a complementary manner. The system was used in an assisted tandem catalysis set‐up involving dehydrogenative coupling of an amine and then hydrogenation of the resulting imine product by switching between the respective states of the catalyst.     

Colloid-colloid and colloid-wall interactions in driven suspensions

We investigate the nonequilibrium fluid structure mediated forces between two colloids driven through a suspension of mutually noninteracting Brownian particles as well as between a colloid and a wall in stationary situations. We solve the Smoluchowski equation in bispherical coordinates as well as with a method of reflections, both in linear approximation for small velocities and numerically for intermediate velocities, and we compare the results to a superposition approximation considered previously. In particular, we find an enhancement of the friction (compared to the friction on an isolated particle) for two colloids driven side by side as well as for a colloid traveling along a wall. The friction on tailgating colloids is reduced. Colloids traveling side-by-side experience a solute induced repulsion while tailgating colloids are attracted to each other.     

Spectrometric and Voltammetric Characterization of Obidoxime in Aqueous Solutions

Obidoxime is a pharmacologically active compound used as an acetylcholinesterase reactivator. The scope of this study was to establish correlations between its acid–base and redox equilibria and its mechanism as an acetylcholinesterase reactivator. The obidoxime dicationic structure is modified by the pH of the solvating medium due to tautomeric isomerizations. The possibility of stabilizing its structure as a dicationic, monocationic, and a neutral species was studied by ultraviolet–visible spectrometry and cyclic and differential pulse voltammetry. Spectrometric and voltammetric studies were performed across a large pH interval (2.00–9.80) of the solvating medium. Absorption measurements revealed the existence of three species involved in two tautomeric equilibria implying oxime and nitroso groups. The structure bearing nitroso groups, stabilized at higher pH, is more likely to behave as a nucleophilic agent than the structure with oxime groups, explaining thus its acetylcholinesterase reactivation. The obidoxime voltammetric behavior at a glassy carbon electrode is complex. Both its oxidation and reduction are diffusion-controlled processes. Anodic signals were obtained only at pH values above 6.50 and the oxidation occurs at the anion oxime group involving two electrons and one proton. The obidoxime reduction is pH dependent only for neutral or alkaline media, giving rise to two or even four signals (for pH higher than 7.50) depending on pH. The peak at less positive potentials was always well defined.     

Higher-order contributions to the intermolecular energy in the perturbation treatment of long-range forces in the light of spherical tensor theory

A preliminary account of the full spherical tensor theory of long-range interactions between two molecules based on a Rayleigh-Schrödinger perturbation treatment is given. The isotropic third-order interaction energy expression is then derived. Finally, the interaction between two tetrahedral molecules in the third-order of perturbation is studied as an example. It is shown that, in some cases, higher-order contributions should be taken into account.     

Stereochemistry-Activity Relationships in Olfaction. Odorants containing a proton donor/proton acceptor unit

A novel class of odorants is described where the odor is associated with the interaction of two functional groups, one being an H-donor (AH function), and the other an H -acceptor ( B function). Generally, odor occurs only if the distance between the two structural elements (AH/B system) is less than 3 Å. Bifunctional derivatives of the p-menthane and iridane series served as models for deriving this rule. The stereospecificity of odor perception was an important prerequisite for its establishment.     

Electric-field-induced spin accumulation in polymer light-emitting diodes

An electric-field-induced spin accumulation phenomenon is presented for electroluminescent conjugated polymers as light-emitting diodes (LEDs). When an electric field is applied along a polymer chain and exceeds a critical value, it quenches the luminescence and dissociates the singlet exciton into two carriers with opposite spin signs. Simultaneously, the field drives these two opposite spin carriers to move in opposite directions, leading to spin accumulation at the two ends of the organic material LED, which can be detected through Kerr rotation microscopy.     

An efficient similarity search based on indexing in large DNA databases

Index-based search algorithms are an important part of a genomic search, and how to construct indices is the key to an index-based search algorithm to compute similarities between two DNA sequences. In this paper, we propose an efficient query processing method that uses special transformations to construct an index. It uses small storage and it rapidly finds the similarity between two sequences in a DNA sequence database. At first, a sequence is partitioned into equal length windows. We select the likely subsequences by computing Hamming distance to query sequence. The algorithm then transforms the subsequences in each window into a multidimensional vector space by indexing the frequencies of the characters, including the positional information of the characters in the subsequences. The result of our experiments shows that the algorithm has faster run time than other heuristic algorithms based on index structure. Also, the algorithm is as accurate as those heuristic algorithms.     

Synthesis of two types of nanoparticles in polyelectrolyte capsule nanoreactors and their dual functionality

Polyelectrolyte multilayer capsule reactors (PEMCRs) for the synthesis of two types of nanoparticles were prepared. The tunable PEMCRs containing two different functional groups that can be used to synthesize two types of nanoparticles simultaneously and to control the composition of two types of nanoparticles within the shell of PEMCs. These PEMCRs enabled the composition as well as the amount of the loaded two types of nanoparticles within the shell of PEMCs to be controlled by the copolymer ratio and the number of reaction cycles. Another interesting finding is that, as a result of the synthesis of two types of nanoparticles, these specially designed PEMCs containing both silver and goethite nanocrystals can be used as antimicrobial capsules, which can move by an external magnetic field. Such a technology has the potential for use in sterilization at the desirable sites.