QSPR Modeling of the Reactivity Parameters of Monomers in Radical Copolymerizations

For a series of monomers, QSPR test analysis is performed by optimizing the correlation weights of the local invariants of molecular graphs representing monomer structures in order to construct models of the reactivity parameters of monomers Q and e. This approach may be used as a tool in reactivity predictions for monomers for which no experimental data on Q and e are available.Original Russian Text Copyright © 2004 by A. A. Toropov, V. O. Kudyshkin, N. L. Voropaeva, I. N. Ruban, and S. Sh. Rashidova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 994–998, November–December, 2004.     

Extended molecular connectivity: Prediction of boiling points of alkanes

It is shown that extended molecular connectivity may be used for “structure-property” studies. The statistical parameters of the correlation relations of boiling points with extended molecular connectivity indices found for a sample of alkanes (n = 74) are the following: the best two-parameter correlation r = 0.9948, s = 4.7; the best three-parameter correlation r = 0.9971, s = 3.5. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1154–1159, November–December, 1997.     

TEMPERATURE DEPENDENCE OF CHLOROPHYLL FLUORESCENCE FROM THE LIGHT HARVESTING COMPLEX II OF HIGHER PLANTS

Abstract— Chlorophyll fluorescence spectra of LCHII, the light harvesting complex of photosystem II, have been recorded in the aggregated and trimeric forms for a range of temperatures from 293 to 4 K. At least five long-wavelength emitters in the 682–702 nm region with different temperature dependencies were found in the spectra of the aggregates. At 293 K the yield of LCHII trimers was higher than aggregates by a factor of 4, but, upon lowering the temperature, a fluorescence rise was observed which was much stronger for LCHII aggregates than for LCHII trimers, so that at 4 K their yields were comparable. The implications of these data in terms of the function of LCHII are discussed.     

Characteristics of an amperometric detector for capillary HPLC

The main characteristics of a dual-electrode amperometric detector with a cell of the “cylinder-in-flow” type with a working wire electrode have been investigated. The effective cell volume is 10–40 nl in a system with 0.2–0.4 mm i.d. packed fused-silica columns. Extra-column spreading at the optimum elution rate does not exceed 0.005 μl². The linear range is 10³ at a relative standard deviation of 0.009. The low noise level (2–3 pA) facilitates determination of electro-active substances. The detection limit for catecholamines is of the order of tenths of a femtomole.     

Magnetic and dielectric response of M-type barium hexaferrite

Barium hexaferrite (BaFe₁₂O₁₉) is a promising candidate for ceramics, microwave devices and numerous applications. Barium hexaferrite was synthesised via the sol-gel auto-combustion technique using glycine fuel. The X-ray diffraction technique confirmed the hexagonal structure of the particles with space group P63/mmc. The morphological analysis was performed using the field-emission scanning microscope, and the images displayed the plate-like particle formation. Transmission electron microscopy was employed to determine the average particle size of the sample, which was estimated to be 155.93 nm. The magnetic studies were taken through the vibrating sample magnetometer (VSM) at 300 K, with which the saturation magnetization (M_s), coercivity (H_c), squareness ratio (M_r/M_s), and energy product (BH_max) was calculated, and the particles were validated to be in single domain arrangement. The dielectric properties were investigated through the LCR meter. Koop and Maxwell-Wagner's model was used to interpret charge conduction and the occurrence of relaxations in the system.     

Synthesis and structure of [2-oxo(thioxo)tetrahydropyrimidin-4-yl]calix[4]arenes

Cone-shaped di- and tetrapropoxycalix[4]arenes functionalized at the upper rim with one or two 2-oxo(thioxo)tetrahydropyrimidine residues were synthesized by the Biginelli reaction of formylcalixarenes with urea (thiourea) and methyl acetoacetate. The steric structure of the products was studied by NMR and X-ray diffraction. The Biginelli reaction with dipropoxyformylcalixarene was diastereoselective, and it quantitatively produced the corresponding meso form. Tetrapropoxydiformylcalixarenes under analogous conditions gave rise to equimolar mixtures of racemic and meso compounds. The macrocyclic skeleton of the synthesized pyrimidine-containing calixarenes in crystal and in solution has a flattened cone conformation. (5-Methoxycarbonyl-2-oxotetrahydropyrimidin-4-yl)calixarene molecules in crystal undergo self-organization to form infinite chains via repeated inclusion of the methoxy group into the cavity of the neighboring macrocycle. Selforganization of bis(5-methoxycarbonyl-2-oxotetrahydropyrimidin-4-yl)calixarene with formation of analogous chains involves intermolecular hydrogen bonding NH ... O=C.     

A Uniformly Valid Asymptotic Approach to the Inviscid–Viscous Interaction Theory

An issue in the well-known traditional "crisscross" interaction theory frequently used to describe the boundary layer instability development over curved surfaces is that a strong singularity exists, even in the linear regime, which manifests itself in the form of infinite growth of self-excited oscillations for the wave numbers l = O (1) and k →∞. This implies that something essential is missing in the formulation, making the Cauchy problem mathematically ill posed, and this, in turn, casts doubts on the validity of calculations made earlier by several researchers using the crisscross interaction theory for investigating laminar-turbulent transition. The derivation of the theory, therefore, needs re-examining. In this article, a key approach is taken; namely, a uniformly valid composite asymptotic expansion procedure is proposed in an effort to suppress the unrealistic amplification of the disturbances at any time in space. As a matter of fact, the triple-deck structure of the disturbance field remains intact as a whole and serves as a basis for the extended asymptotic theory. The backbone of the process inherently involves restoring the longitudinal pressure gradient term accounting for the second-order approximation in asymptotic expansions for the outermost and innermost sublayers of the conventional crisscross interaction region. The new system as a result has additional terms depending on a small parameter based on the local reference Reynolds number and the curvature of the surface. The new Cauchy model is eventually free from any singularity in the context of the composite approach. The modified linear dispersion relation is obtained and treated both analytically and numerically, and it is verified that the proposed model becomes well posed for a suitably chosen additional parameter.