Interpretation of longitudinal-acoustical-mode spectra of polymers

The influence of temperature, frequency, and straight-chain-length distribution on the low-frequency Raman-active longitudinal-acoustical-mode (LAM) bands of polymers is discussed. Specifically, the effect of these factors on the intensity of LAM-1, on the ratio of intensities of LAM-1 to LAM-k, and on peak position is computed or estimated. Band halfwidth and chain-length-distribution halfwidth are found not to be simply related. It is shown that the integrated intensity of LAM-1 is very nearly proportional to the total length of straight chains.     

Experimental and theoretical studies of asymmetry of transport properties of modified ultrafiltration membranes

Ultrafiltration membranes based on polyamide and polysulfone modified by polyelectrolytes are produced. The effect of the nature of a polymer matrix and modifier on the rejection ability and diffusion permeability of membranes is studied. The effect of the asymmetry of transport properties, which is manifested at different orientations of membrane with respect to the flow of electrolyte, is quantitatively evaluated. It was demonstrated that the asymmetry of substance transport is more pronounced in the ultrafiltration regime than in the diffusion of sodium chloride solutions. A mathematical model that describes the filtration of binary electrolyte solutions on partially charged two-layer membranes is proposed and the corresponding boundary-value problem is solved analytically. The qualitative correspondence between theoretical calculations and experimental data on the asymmetry effect of the rejection ability of two-layer system is revealed.     

Kinetics of loss of platinum group metals in catalytic oxidation of ammonia

Basic characteristics of ammonia oxidation catalysts based on platinum metals, their composition, wire diameter, and specific mass are presented. An irrecoverable loss of the catalyst in manufacture of regular nitric acid is demonstrated. The loss of catalysts based on platinum-group metals and the effect of various factors on this loss are considered. The effect of various parameters on the ammonia oxidation process is analyzed and an equation describing the process in which platinum-group metals are lost is derived.     

Detailed process of adsorption of alkanes and alkenes on zeolites

The adsorption of alkanes and alkenes on zeolites is investigated by comparing the adsorption characteristics for three types of zeolite: ferrierite, ZSM-5, and mordenite. The activation energy for the diffusion of propane and n-butane on ferrierite and the heat of adsorption of C(2)-C(4) alkanes and alkenes on zeolites and silica are estimated based on Fourier transform infrared spectroscopy, and the diffusion processes in the micropores are elucidated by comparing the results with previously reported activation energies for n-butene diffusion. The adsorption of 1-butene on mordenite is also examined. The structure and process of experimentally observable adsorption is found to differ depending on the type of zeolite and adsorbing molecule, reflecting differences in the sizes of molecules and pores. This differing behavior is utilized to interpret the elementary adsorption processes of alkanes and alkenes on zeolites.     

小环化合物中饱和碳质子化学位移的计算

小环化合物由于其张力、构型、构象和各向异性效应等原因,环碳上质子化学位移缺乏规律性,难以预测,对此作者曾提出一种近似算法。本文根据303种小环化合物中饱和碳质子的化学位移实验数据,将适于计算这类质子化学位移的公式表述为:     

Formation of tubes during self-assembly of bacterial surface layers

Based on experimental studies on tube formation during self-assembly of bacterial surface (S)-layers, a mechanistic model for describing the underlying basic mechanisms is proposed and the effect of process parameters on growth velocity and tube radius is investigated. The S-layer is modeled as a curved sheet with discrete binding sites for the association of monomers distributed along the S-layer edges. Reported changes of the tube radius owing to genetic protein modifications are explained within the framework of continuum mechanics. S-layer growth velocity and shape development are analyzed by Monte Carlo simulation in their dependence on the attachment and detachment frequencies of monomers at the S-layer. For curved S-layer patches, a criterion for the formation of S-layer tubes is derived. Accordingly, tubes can form only within a certain range of the initial monomer concentration. Furthermore, the effect of calcium ion concentration on tube formation is discussed, including recent experimental findings on the calcium effect.     

Concepts of photochemical damage of Photosystem II and the role of excessive excitation

Photoinhibition is one of the most controversial topics in photophysiology. Well into the 21 st century, scientists have not agreed on the mechanism of action, primary site, and roles of excess energy absorbed by photosynthetic pigments. It is recognized that Photosystem II is the most fragile component during photoinhibition and that excess excitation absorbed by the photosynthetic pigments has a strong impact on it. Consensus is yet to come on terminology, guidelines to study photoinhibition, or boundaries of what can be considered photodamage. Some of these controversies are the result of how we understand the phenomenon of photoinhibition, as this is what determines a given experimental design. Thus, how we understand photodamage depends on the philosophical approach of each group. While some efforts have been made in the parametrization of Photosystem II photoinhibition, an updated review about the concepts of photoinhibition of Photosystem II and how to study it is still pending. In this work, a review of the concepts used in the field of photoinhibition is presented, accompanied by a synopsis on the history and mechanisms of action.     

On the mechanism of hydrophobic association of nanoscopic solutes

The hydration behavior of two planar nanoscopic hydrophobic solutes in liquid water at normal temperature and pressure is investigated by calculating the potential of mean force between them at constant pressure as a function of the solute-solvent interaction potential. The importance of the effect of weak attractive interactions between the solute atoms and the solvent on the hydration behavior is clearly demonstrated. We focus on the underlying mechanism behind the contrasting results obtained in various recent experimental and computational studies on water near hydrophobic solutes. The length scale where crossover from a solvent separated state to the contact pair state occurs is shown to depend on the solute sizes as well as on details of the solute-solvent interaction. We find the mechanism for attractive mean forces between the plates is very different depending on the nature of the solute-solvent interaction which has implications for the mechanism of the hydrophobic effect for biomolecules.     

Theoretical methods of investigation of excited states of organic molecules

A brief review of quantum-chemical methods applied to describe excited states of organic molecules is presented. The main emphasis is put on advantages and disadvantages of widely used computational techniques. A brief summary of the performance of such methods and practical recommendations on their use is included.     

Fe的分散程度对煤焦催化加氢气化的影响

在加压固定床反应器上研究了Fe催化剂在不同比表面积煤焦中分散性对催化加氢气化性能的影响,利用XRD、BET、H₂-TPR、FT-IR、TEM、拉曼光谱对煤焦及催化剂进行了分析表征。结果表明,煤焦活性位点和石墨化程度并非影响催化气化反应的唯一因素,而催化剂的分散性对反应影响更大。煤焦的比表面积越大,Fe催化剂在煤焦表面的分散更均匀,催化剂活性组分平均晶粒粒径越小,并可以促进煤催化加氢气化中间相产物Fe₃C的生成,甲烷收率越高。对于比表面积较高的900-char,在氢气压力为2 MPa,温度为750 ℃,Fe负载量为5%（质量分数）时,催化加氢气化甲烷收率可达53%。在900-char上考察了Fe催化剂负载量对催化加氢气化的影响,甲烷收率呈先增加后降低的趋势,Fe负载量存在饱和点。     

Calculations of pH-dependent binding of proteins to biological membranes

Binding of proteins to membranes is often accompanied by titration of ionizable residues and is, therefore, dependent on pH. We present a theoretical treatment and computational approach for predicting absolute, pH-dependent membrane binding free energies. The standard free energy of binding, DeltaG, is defined as -RTln(P(b)/P(f)), where P(b) and P(f) are the amounts of bound and free protein. The apparent pK(a) of binding is the pH value at which P(b) and P(f) are equal. Proteins bind to the membrane in the pH range where DeltaG is negative. The components of the binding free energy are (a) the free energy cost of ionization state changes (DeltaG(ion)), (b) the effective energy of transfer from solvent to the membrane surface, (c) the translational/rotational entropy cost of binding, and (d) an ideal entropy term that depends on the relative volume of the bound and free state and therefore depends on lipid concentration. Calculation of the first term requires determination of pK(a) values in solvent and on the membrane surface. All energies required by the method are obtained from molecular dynamics trajectories on an implicit membrane (IMM1-GC). The method is tested on pentalysine and the helical peptide VEEKS, derived from the membrane-binding domain of phosphocholine cytidylyltransferase. The agreement between the measured and the calculated free energies of binding of pentalysine is good. The extent of membrane binding of VEEKS is, however, underestimated compared to experiment. Calculations of the interaction energy between two VEEKS helices on the membrane suggest that the discrepancy is mainly due to the neglect of protein-protein interactions on the membrane surface.     

Sorption specifics of volatile amines on thin films of acid-base indicators

The sorption specifics of various classes of volatile amines on thin films of organic acid-base indicators is studied by piezoelectric quartz micro weighing. The differences in the sorption behavior of amines on indicator films obtained from ethanolic and acetone solutions are revealed. The influence of the indicator acidity on the sorption of amine vapors is studied. An array of piezoelectric sensors based on thin films of acid-base indicators is developed and an algorithm of registering their responds to amines of different structures is proposed for their separate determination in a mixture.     

Activity of an enzyme immobilized on polyelectrolyte multilayers

The immobilization of α-chymotrypsin on the surface of boron silicate glass microspheres is conducted via the technique of multilayer adsorption of polyelectrolytes. It is shown that the enzyme is adsorbed on both positively and negatively charged surfaces and its activity is partially preserved relative to that in solution. The activity of the enzyme depends on the number of polyectrolyte layers preliminarily adsorbed on glass microspheres and on the charge of the surface. The activity of α-chymotrypsin adsorbed on the negatively charged surface is four times higher than the activity of this enzyme adsorbed on a positively charged surface.     

Features of polytherms of the viscosity of Fe–B melts

It is established that the formation of a viscous film on the surface of a melt is possible during the viscosimetry of Fe–B melts under normal conditions. It is noted that the film has a considerable effect on the results from measurements and can lead to the appearance of additional features on polyterms. Thermodynamic analysis of the composition of surface layers shows that a viscous film contains mainly boron oxide B₂O₃. It is concluded that the evaporation of B₂O₃ from the surface of the alloy produces additional anomalies on the polytherm of viscosity.     

Theory of the effect of small ions on the electrical admittance of macroion solutions

A general theory is given on the electrical admittance of a parallel plate capacitor filled with a conductive medium containing charged particles by considering both their electric atmospheres and the electric field due to charges induced on the electrodes. The theory is applied to a dilute macroion solution with added salt and it is found that the low frequency dielectric response of the solution reflects the motions of the macroion and bound small ions and the effect of motion of the ion atmosphere around the macroion is canceled out by the current due to the induced charges on the electrodes.     

Study of the State of Benzene Molecules Adsorbed on the Surfaces of Organic Derivatives of Kaolinite and Silica

Values and heats of benzene adsorption on modified kaolinite and silica samples are measured by adsorption calorimetry. Entropy diagrams are calculated for benzene adsorbed on these samples. Obtained results are compared to entropy losses theoretically calculated for benzene molecules using the models of ideal localized and nonlocalized adsorption. It is demonstrated that, depending on the type of an inorganic matrix, the nature of a modifier, and the degree of modification, the adsorption of benzene molecules on studied sorbents is described by the models of a supermobile nonlocalized adsorption or a nonlocalized adsorption accompanied by the loss of some rotational degrees of freedom. For a rare case of the supermobile adsorption of benzene on the modified silica, the vibration frequency of its molecules with respect to the surface is calculated.     

镀锡板镀层测试

以８０９８单片机作智能部件研制开发的对镀锡板度测试装置，采用ＳＴＤ标准总线结构，汉字菜单提示，人－机对话方式操作，采用电解剥离法检测电位跃变曲线，根据电流和起始时间计算出镀层厚度，可直接显示，打印测试曲线和分析结果。     

Effect of filler on kinetic characteristics of glass transition in polymer composite materials

Dynamic mechanical spectroscopy and differential scanning calorimetry were used to study the effect of various fillers (carbon fiber, glass fiber, and aramid fiber) on the kinetic characteristics of glass transition in polymer composite materials based on epoxy resin. It is shown that the composite based on carbon fiber is the most fragile among the materials studied, whereas the polymer composite material based on aramid fiber exhibits the lowest rate of variation of the relaxation time above the glass-transition temperature. A relationship is determined between the heat conductivity and fragility of polymer composite materials. The effect of various fillers on the curing kinetics of the epoxy matrix upon glass transition is prognosticated, with the difference in the degree of curing reaching a value of 4–5%. The strongest filler effect on the curing kinetics is observed in the chemically controlled region, which may be due to the catalytic effect of functional groups on the fiber surface.     

Physical principles of catalysis of the curing of epoxy polymers in the presence of carbon nanotubes

A structural interpretation of the catalytic action of carbon nanotubes on the curing of epoxy polymers is proposed. It is based on the fractal analysis ideas. It is shown that essentially the only factor determining the kinetics of the curing process is the microgel structure characterized by its fractal dimension. The most important conclusion from the obtained results is the fact that the reaction rate dependences on the structural parameters are described by the same correlation for the epoxy polymer curing reaction both in the presence and absence of carbon nanotubes. This means that the catalytic effect of carbon nanotubes consists in a change in the structure of microgels.     

Reduction of an Ensemble of Platinum(II) Aquachloride Complexes: Dynamic Effect of the Solvent

Dynamic effect of the solvent is studied for the first time ever for the process that occurs in the vicinity of the activationless region, namely, the reaction of electroreduction of an ensemble of platinum(II) aquachloride complexes on a negatively charged mercury electrode. A sequential analysis of the sucrose influence on the interface structure and the equilibrium solvation energy is performed. Estimates of the above effects are given. These are necessary for subtracting the dependence of the electron transfer rate on the solvent relaxation time from the observed overall dependence on the concentration of the viscosity-forming additive. A procedure for estimating the sucrose concentration in the reaction layer is suggested and on this basis the increase in the local viscosity near the interface, which is caused by the presence of a surface excess of sucrose, is approximately taken into account. The potential interval where the reaction under study occurs in an almost adiabatic mode is determined.