Hydrophilic-interaction chromatography of peptides on hydrophilic and strong cation-exchange columns

Hydrophilic-interaction chromatography (HILIC) was recently introduced as a potentially useful separation mode for the purification of peptides and other polar compounds. The elution order of peptides in HILIC, which separates solutes based on hydrophilic interactions, should be opposite to that obtained in reversed-phase chromatography, which separates solutes based on hydrophobic interactions. Three series of peptides, two of which consisted of positively charged peptides (independent of pH at pH less than 7) and one of which consisted of uncharged or negatively charged peptides (dependent on pH), and which varied in overall hydrophilicity/hydrophobicity, were utilized to examine the separation mechanism and efficiency of HILIC on hydrophilic and strong cation-exchange columns.     

Modelling of ionic concentrations and sulfate production in cloud droplets: use of published aerosol data

Summary In this study a cloud model describing an ascending, adiabatically closed parcel was used to show the influence of the quality of data about the chemical composition of aerosol particles on the model results. The input data for the model were based on measured aerosol chemical compositions which were compiled from literature data. Model results influenced by incomplete chemical characterization of the particles are the radii of the large droplets, which depend on the activation parameter, and the pH-values of the droplets, which depend on the ionic balance of the particles.     

Research of properties of polyfunctional polymeric films

At present the problem of creating materials for medical application, which possess surface thromboresistant and antiseptic properties is of the great importance. The method of creating hydrogel films, containing anticoagulants, biologically active and antiseptic substances on the surface of well-known polymers of medical purity allows to give their surface special functions and properties and to retain the good mechanical properties [1,2]. In the majority of cases, the methods which are used for the creation of such films have a limitations which impede their wide application as they do not allow to obtain surface layers, possessing different medico-biological and physic-chemical properties. The aim of our research was the electroformation of biocompatible, polyfunctional poly(vinyl alcohol) (PVA) films with immobilizied anticoagulant, enzyme and antibiotic on the surface of a composite material on the base of polysiloxane of medical purity [3,4].     

Synthesis and solid-state organization of coil-ring-coil block copolymers

Shape-persistent macrocycles based on the phenyl-ethynyl-butadienyl backbone containing two extraannular hydroxyl groups were prepared by the oxidative coupling of the appropriate phenylethynyl oligomers. Carbodiimide-directed coupling with independently synthesized polystyrene carboxylic acid oligomers led to ABA coil-ring-coil block copolymers in which the central macrocycle serves as rigid and the polystyrene oligomers as flexible elements. Depending on the size of the coil blocks, these structures aggregate in cyclohexane into supramolecular hollow cylindrical brushes in which the rigid core is surrounded by the flexible matrix. However, in the solid state it is not possible to identify a morphology in which isolated channels based on aggregated macrocycles are embedded in a matrix of polystyrene. Detailed X-ray and electron diffraction studies on samples prepared from a solution in cyclohexane under equilibrium conditions show that the material adopts a lamellar morphology in the solid state in which columns of macrocycles are aggregated into layers which are separated by polystyrene.     

Contribution of polymeric swelling to the overall response of capacitive gas sensors

A new method for investigation of the swelling of polymers on exposure to gas or vapour has been devised and tested. It uses an optical profilometer (based on the chromatic aberration of a lens system) which is integrated into a computer-controlled gas-dosing and mixing setup. Gas and/or vapour concentration-dependent measurements have been carried out for thick layers of the polymers commonly used in gravimetric and capacitive gas sensors: poly(acrylic acid) (PAA), poly(vinyl pyrrolidone) (PVP), poly(ether urethane) (PEUT), and polydimethylsiloxane (PDMS). The thickness of PAA, PVP, and PEUT films changed significantly on exposure to humidity. These data have been used to derive the sorption isotherms of the respective polymers, which were found to be Henry or Flory–Huggins isotherms. Comparison of the geometrical (swelling) responses with capacitive responses revealed a strong correlation. The correlation, which occurs because both types of response are proportional to the water content of the polymer, is also valid for polymers with nonlinear gas responses. Finally the geometrical and electrical characteristics of the capacitive samples were used to explain the dependence of the capacitive response of different polymers on the concentration of the target gas or vapour. In this way was deduced that PDMS, which does not swell on exposure to humidity, swells in the presence of 2,3-dimethylpentane, for which no profilometer evaluations are yet available.     

Effects of zwitterionic vesicles on the reactivity of benzoyl chlorides

A systematic study on the solvolysis reaction of substituted benzoyl chlorides in the presence of zwitterionic vesicles of dipalmitoyl phosphatidylcholine (DPPC) has been performed. Size, shape, surface charge, and polarity of the interface of the vesicular aggregates were determined using various techniques. The application of the pseudophase formalism allowed us to obtain the thermodynamic and kinetic coefficients characteristic of the reaction. The effects of vesicular aggregates on the solvolysis of benzoyl chlorides, which are known to be sensitive to the physical properties of the medium, depend on the nature of the substrate. For benzoyl chlorides with electron-donating groups, which react predominantly through a dissociative mechanism which is strongly affected by medium properties, the rate constant decreases as the vesicle concentration increases. On the other hand, for benzoyl chlorides with electron-withdrawing groups, which react mainly via an associative pathway, DPPC vesicles catalyze the solvolysis reaction.     

Theoretical aspects of IR-laser induced dissociation and desorption processes

A theoretical approach to IR-laser induced dissociation and desorption is described which is based on the generally recognized fact that vibrational energy is mainly transferred on the short range repulsive core of the interaction potential. Because of the shortness of the range, it may be assumed that the motion relevant for the vibrational energy transfer takes place on an element dS of the potential surface which is of small dimensions as compared to those of molecules. The Hamiltonian can be transformed into the form which enables elimination of coordinates which are nearly cyclic on dS and to derive the equation of motion for the distance perpendicular to dS which may be regarded as the relevant generalized coordinate for the problem. Its motion is quantized, and the quantum mechanical transition probabilities must be averaged over different surface elements dS. The theory readily reproduces the most striking features of the vibrational predissociation of complexes like Ar.HCl and Ar.HD. It allows physical insight and can also be implemented on more complex systems where presently no other theoretical methods are available.     

A Process Theory of Enzyme Catalytic Power – the Interplay of Science and Metaphysics

Enzymes are protein catalysts of extraordinary efficiency, capable of bringing about rate enhancements of their biochemical reactions that can approach factors of 10²⁰. Theories of enzyme catalysis, which seek to explain the means by which enzymes effect catalytic transformation of the substrate molecules on which they work, have evolved over the past century from the “lock-and-key” model proposed by Emil Fischer in 1894 to models that explicitly rely on transition state theory to the most recent theories that strive to provide accounts that stress the essential role of protein dynamics. In this paper, I attempt to construct a metaphysical framework within which these new models of enzyme catalysis can be developed. This framework is constructed from key doctrines of process thought, which gives ontologic priority to becoming over being, as well as tenets of a process philosophy of chemistry, which stresses environmentally responsive molecular transformation. Enzyme catalysis can now be seen not as enzyme acting on its substrate, but rather as enzyme and substrate entering into a relation which allows them to traverse the reaction coordinate as an ontologic unity.     

Effect of ammonium polyphosphate on combustion and thermal degradation of aliphatic polyamides

Chain fragments with amide and imide groups are the most abundant degradation products of aliphatic polyamides (APA) which derive from scission of the N-alkylamide bond (-CH₂-NH-). In the case of polyamide 6.6 (PA-6.6), also carbodiimide structures and methyl chain ends are formed, which derive from scission of -CH₂-C(=O)- bond. Cyclic compounds can be formed besides chain fragments, depending on the type of APA. Ammonium polyphosphate (APP) reacts with APA on heating forming phosphoric esters which decompose giving products similar to those obtained from pure APA. APP increases the yield of carbodiimides from PA-6.6 which trimerise to triazine structures. The fire retardant mechanism of APP is discussed on the basis of the thermal degradation of the mixtures.     

Nonuniqueness of solution of reverse problem of chemical kinetics for first-order reactions

The question of nonuniqueness of the solution of the reverse problem of chemical kinetics has been investigated. The subject of investigation is the situation in which some of the substances participating in the reaction are not accessible for measurement (intermediate substances). The investigation was performed on models of first-order reactions, using Laplace transforms. Direct mathematical formulas have been derived, through which an answer can be obtained to the question of how many independent functional combinations of constants, and which combinations, and will specifically admit an unambiguous evaluation on the basis of kinetic information on the initial reactants and the reaction products. The reaction of ethylene chlorination is examined as an illustrative example.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 6, pp. 701–708, November–December, 1985.     

Improvement of the Composition of Detergent Solutions for the Removal of Deposits on the Axial-Compressor Blades of Gas-Turbine Units

During the operation of gas-turbine units deposits, which have the form of a conglomerate of hydraulic oil and contaminations from atmosphere air, are accumulated on the axial-compressor blades. Deposits are occasionally removed using solid abrasive or detergent solutions. Only detergent solutions are employed on modern units, because abrasive substances damage the protective sputtering of blades. The detergent solutions that are used have a high cost and are unsafe in use. In this work, a high-performance detergent solution is suggested, which is able to dissolve deposits on the axial-compressor blades of gas-turbine units.     

Photo-oxidation of acrylic-urethane thermoset networks. Relating materials properties to changes of chemical structure

Acrylic-urethane thermoset photo-ageing was investigated by various techniques including IR spectroscopy, dynamic-mechanical thermal analysis (DMTA), and micro-hardness testing. These results were used to identify the sites at which the chain oxidation reaction is initiated and the main pathways through which the degradation reaction proceeds. The chemical modifications induced by photo-ageing were qualitatively and quantitatively correlated with the modifications observed in the architecture and mechanical properties of the thermoset network. The results of this work also allow for the development of a quantitative kinetic model based on the identified mechanisms and a multi-scale approach from the molecular to the macroscopic level, which highlights the effect of the changes of the chemical structure on the modification of the macromolecule arrangement and thus on the mechanical properties. Finally, the impact of stabilisers on material ageing was studied.     

Hydrophobicity of talc basal surface

The hydrophobicity of the talc basal surface is considered in the framework of the concept which relates the properties of layered silicates and their dispersions to the differences between the characteristics of the basal and side surfaces of their particles. The ab initio calculations of the energetics and geometry of the microclusters formed by water molecules adsorbed on the active sites (oxygen ions) located at the perfect basal surface of talc are performed. It is shown that the typical property of the hydrophobic surface is the adsorption of single molecules of water on extremely scarce or weak active sites of the surface, which act as secondary adsorption sites, and subsequent adsorption of water molecules on these secondary sites which results in the formation of ring-like structures. The heat of adsorption on this surface is shown to be essentially lower than the water condensation heat, which is also indicative of the hydrophobicity of the basal surface of talc.     

Effects of the Method of Introducing Iron and Iron Concentration on the Acid and Catalytic Properties of Zeolite

The effects of the method of introducing iron and iron concentration on the acid properties, catalytic activity, and stability of a zeolite in methanol conversion to hydrocarbons were studied. The state of active sites in the zeolite depends on the distribution of the metal in its structure, which depends on the method of zeolite modification. The addition of iron to zeolite increased the catalyst run time between regenerations, and the samples in which iron was introduced at the stage of hydrothermal synthesis exhibited the maximum catalytic stability.     

Viscoelastic properties of single polysaccharide molecules determined by analysis of thermally driven oscillations of an atomic force microscope cantilever

We report on single molecule measurements of the viscoelastic properties of the polysaccharide dextran using a new approach which involves acquiring the power spectral density of the thermal noise of an atomic force microscope cantilever while holding the single molecule of interest under force-clamp conditions. The attractiveness of this approach when compared with techniques which use forced oscillations under constant loading rate conditions is that it is a near-equilibrium measure of mechanical response which provides a more relevant probe of thermally driven biomolecular dynamics. Using a simple harmonic oscillator model of the cantilever-molecule system and by subtracting the response of the free cantilever taking into account hydrodynamic effects, the effective damping zetamol and elastic constant kmol of a single molecule are obtained. The molecular elasticity measured by this new technique shows a dependence on applied force that reflects the chair-boat conformational transition of the pyranose rings of the dextran molecule which is in good agreement with values obtained directly from the gradient of a conventional constant loading rate force-extension curve. The molecular damping is also seen to follow a nontrivial dependence on loading which we suggest indicates that it is internal friction and not work done on the solvent that is the dominant dissipative process.     

硫化镉光催化氧化二苯甲醇的反应

半导体粉能对烯烃, 芳烃等的光催化氧化, 但效率低, 揭示其机理, 研究提高催化效率是研究半导体光催化的突出问题. 本文研究了硫化镉粉末光催化氧化二苯甲醇的反应, 发现能从硫化镉导带上捕获电子的物质都能促使电荷分离, 引发或加速反应, 而自由基猝灭剂却能完全猝灭反应. 本文进一步揭示了硫化镉光催化特性并探讨了反应机理.     

Investigation of the possibility of geometrical electrophoresis

We investigate the possibility of geometrical electrophoresis, which is based on nanofabrication techniques. (GEE) utilizes geometrical effects during electrophoresis, which are generated by physical interactions between walls and a macromolecule confined in spaces smaller than the Flory radius. When a polymer is injected into a small space, confinement energy is usually required. However, the confinement energy form depends on the geometry of the space. In the case of electrophoresis, the electric field itself changes depending on the geometry. Using a nanofabricated quartz chip with a curved channel, we investigated electrophoretic behavior of high molecular weight DNA based on the curvature effect.     

Calorimetric determination of vitrification time and heat capacity of a thermosetting polymer

First observations of a decrease in heat capacity on isothermal vitrification of a thermosetting polymer are reported. The method developed for this study allows simultaneous measurements of both the heat capacity of a material and the enthalpy released as chemical reactions occur under virtually isothermal conditions. Control experiments have been done on a nonstoichiometric composition which does not vitrify and for which total enthalpy released can be measured. During isothermal curing, the heat capacity of a thermoset first increases slightly, undergoes an abrupt decrease in a narrow range of time, and thereafter slowly decreases. The abrupt decrease represents the transition of the liquid to a glassy solid, which is irreversible and which shifts to shorter times as the curing temperature is increased. This transition occurs at different extents of cure for different temperatures. The thermodynamic consequence of kinetic slowing on irreversible conversion of a molecular liquid to a macromolecule under isothermal conditions is similar to that observed on reversible clustering, as a result of decrease in the thermal energy on supercooling a molecular liquid. © 1993 John Wiley & Sons, Inc.     

X-Ray Spectroscopic Investigation of Chemical Bonding in Solids

When an atom is incorporated into a molecule or a crystal, its X-ray spectrum undergoes characteristic changes, the study of which leads to important information on the nature of the chemical bonding and on the electronic structure in a substance. A number of examples are given to illustrate the possibilities of the X-ray spectroscopy of bonded atoms. Special attention is given to the displacement of the Kα lines, from which conclusions can be drawn regarding the charge on a bonded atom, as well as to the investigation of the emission bands resulting from valence electron transitions, which yields information on the energy band structure of the solid. X-ray spectroscopic studies on free molecules and theoretical work on the calculation of the molecular orbitals of simple molecules are finally reported.     

Solvation effects in human serum albumin radiolysis in the presence of dimethyl sulfoxide

PMR and electrophoresis have been applied to examine hydration changes in protein molecules due to the presence of the electron donor dimethylsulfoxide DMSO, which influences the radiolysis of human serum albumin HSA. The reactions of aqueous HSA with added DMSO show that the DMSO on the one hand acts as a protector, which prevents the formation of low-molecular protein forms on reaction with hydroxyl radicals, and on the other alters the protein hydration, which facilitates thiol-di-sulfide exchange, which leads to oligomers.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 107–111, January–February, 1990.