Experimental Study of the Liquid Cathode Components Transfer to the DC Discharge Plasma at Atmospheric Pressure

The transfer processes of solvent and dissolved substances in gas phase from aqueous solutions used as cathodes under the action of atmospheric pressure DC discharge were investigated.The electric field strength in plasma (E), cathode voltage drop (Uc) and rates of solution evaporation were measured. The transfer coefficients were calculated. The effect of transfer processes on plasma physical properties was experimentally studied. The threshold characteristics of cations transfer process were determined

Analysis of the organic solvent effect on the structure of dehydrated proteins by isothermal calorimetry, differential scanning calorimetry and FTIR spectroscopy

This review describes the basic principles of a novel method for studying the structure of the dehydrated proteins in the presence of organic solvents. This method, based on combined calorimetric and FTIR spectroscopic measurements, allows the simultaneous monitoring of the thermochemical parameters (interaction enthalpies, DSC thermograms) of the dried proteins and the corresponding changes in the protein structure in anhydrous organic solvents.This review aims to analyse the effect of organic solvents on dehydrated protein systems in order to understand what intra- and intermolecular processes produce the main effect on the structure and functioning of proteins in low water organic media.Two unrelated proteins with a high α-helix content (human serum albumin, HSA) and with a high β-sheet content (bovine pancreatic α-chymotrypsin, CT) were used as models. Two groups of model organic solvents were used. The first group included hydrogen bond accepting solvents. The second group included hydrogen bond donating liquids.The results obtained showed that:5) The enthalpy and integral structural changes accompanying the interaction of dried proteins with anhydrous organic solvents depend cooperatively on the solvent hydrophilicity. The solvent hydrophilicity was characterized by an excess molar Gibbs energy of water in organic solvent at infinite dilution and 25°C. Based on this solvent hydrophilicity parameter, the solvents were divided into two groups. The first group included hydrophilic solvents such as methanol, ethanol, and dimethylsulphoxide (DMSO). Considerable structural rearrangements were observed in this group of solvents. The interaction enthalpies of the dried proteins with hydrophilic liquids were strongly exothermic. The second group included the hydrophobic and medium hydrophilic liquids such as benzene, dioxane, butanol-1, and propanol-1. The enthalpy and structural changes in the second group of solvents were close to zero.6) The FTIR spectroscopic results can be attributed to the formation of different unfolded states of CT and HSA obtained upon dehydration-, alcohol- and DMSO-induced denaturation. The denatured state obtained in DMSO has a maximal degree of unfolding compared with that observed in alcohols or in the presence of dry air.7) The effect of the organic solvent on the protein structure is "protein selective". On the other hand, the organic solvent-induced integral structural changes versus solvent hydrophilicity profiles do not depend on the predominant form of secondary structure in the protein.8) Heat-induced exothermic peaks were observed on the DSC thermograms of the dried proteins in anhydrous organic solvents in the temperature range 60-105 °C. This means that dehydrated proteins in anhydrous solvents is the non-equilibrium state at room temperature. These results give strong support to the idea that the non-equilibrium status of the dehydrated proteins results from the protein-organic solvent interactions being "frozen" at near room temperature.The thermodynamic and structural data were analysed to give a unified picture of the state of the dried proteins in anhydrous organic solvents. According to this model, the dehydration-induced protein-protein contacts and the potential of the organic solvent to form the hydrogen bonds are key factors in determining the structure of the dehydrated proteins in the liquids under study. © 2011 by Nova Science Publishers, Inc. All rights reserved

A Semi-empirical Mass-loss Rate in Short-period Cataclysmic Variables

The mass-loss rate of donor stars in cataclysmic variables (CVs) is of paramount importance in the evolution of short-period CVs. Observed donors are oversized in comparison with those of isolated single stars of the same mass, which is thought to be a consequence of the mass loss. Using the empirical mass-radius relation of CVs and the homologous approximation for changes in effective temperature T_2, orbital period P, and luminosity of the donor with the stellar radius, we find the semi-empirical mass-loss rate M2_dot of CVs as a function of P. The derived M2_dot is at ~10^(-9.5)-10^(-10) Msun/yr and depends weakly on P when P > 90 min, while it declines very rapidly towards the minimum period when P < 90 min, emulating the P-T_2 relation. Due to strong deviation from thermal equilibrium caused by the mass loss, the semi-empirical M2_dot is significantly different from, and has a less-pronounced turnaround behavior with P than suggested by previous numerical models. The semi-empirical P-M2_dot relation is consistent with the angular momentum loss due to gravitational wave emission, and strongly suggests that CV secondaries with 0.075 Msun < M_2 < 0.2 Msun are less than 2 Gyrs old. When applied to selected eclipsing CVs, our semi-empirical mass-loss rates are in good agreement with the accretion rates derived from the effective temperatures T_1 of white dwarfs, suggesting that M2_dot can be used to reliably infer T_2 from T_1. Based on the semi-empirical M2_dot, SDSS 1501 and 1433 systems that were previously identified as post-bounce CVs have yet to reach the minimal period.Comment: 29 pages, 8 figures, 2 tables; accepted for publication in the Ap

Analysis of the organic solvent effect on the hydration and structure of human serum albumin by infrared spectroscopy

© 2015 by Nova Science Publishers, Inc. All rights reserved. The effect of organic solvent on the hydration and structure of human serum albumin was characterized using infrared spectroscopy in the thermodynamic water activity range from 0 to 0.98 at 25oC. Dioxane was used as a model organic solvent. This organic solvent may be considered as an informative molecular probe for analyzing the effect of hydrogen bonding and hydrophobic interactions on the hydration and structure of proteins. The obtained results show that the hydration and structure of human serum albumin depend markedly on how the protein has been hydrated - whether in the presence or in the absence of organic solvent. Two organic solvent effects on water sorption by human serum albumin were observed: 1. At low water activity (aw0.5), the water sorption isotherm in the presence of dioxane lies above the corresponding isotherm for pure water. This result corresponds to the organic solvent - assisted effect on water binding by human serum albumin. Changes in the structure of human serum albumin were determined from infrared spectra by analyzing the structure of amide I band. It was found that, at low water activity, the protein-protein contacts in the dried protein largely govern its thermodynamic and structural properties. At high water activity, the protein state is determined by the protein-organic solvent and protein-water interactions. The results from the thermodynamic and structural measurements were analysed to give a unified picture of the hydration process in the absence and presence of organic solvent

Adsorption of vapors of water and dioxane on bovine pancreas α-chymotripsin

The isotherms of sorption-desorption of water and water-dioxane vapors on bovine pancreas α-chymotripsin were-measured by IR spectroscopy at 298 K and values of the water activity within 0-0.98. The ability of the enzyme to bind water was found to be strongly dependent on the type of the sorption curve and on whether dioxane is present. A sorption mechanism capable of explaining how the ability of an enzyme to interact with the vapor of an organic solvent depends on the moisture content in the enzyme and the mode of its wetting was proposed. Copyright © 2005 by Pleiades Publishing. Inc

Effect of dioxane on the structure and hydration-dehydration of α-chymotrypsin as measured by FTIR spectroscopy

A new experimental approach based on FTIR spectroscopic measurements was proposed to study simultaneously the adsorption/desorption of water and organic solvent on solid enzyme and corresponding changes in the enzyme secondary structure in the water activity range from 0 to 1.0 at 25°C. The effect of dioxane on the hydration/dehydration and structure of bovine pancreatic α-chymotrypsin (CT) was characterized by means of this approach. Dioxane sorption exhibits pronounced hysteresis. No sorbed dioxane was observed at low water activities (aw 0.5, dioxane increases the amount of water bound by CT during hydration. This behavior was interpreted as a dioxane-assisted effect on water binding. Upon dehydration at low water activities, dioxane decreases the water content at a given a w. This behavior suggests that the suppression in the uptake of water during dehydration may be due to a competition for water-binding sites on chymotrypsin by dioxane. Changes in the secondary structure of CT were determined from infrared spectra by analyzing the structure of amide I band. Dioxane induced a strong band at 1628 cm-1 that was assigned to the intermolecular β-sheet aggregation. Changes in the intensity of the 1628 cm-1 band agree well with changes in the dioxane sorption by CT. An explanation of the dioxane effect on the CT hydration and structure was provided on the basis of hypothesis on water-assisted disruption of polar contacts in the solid enzyme. The reported results demonstrate that the hydration and structure of α-chymotrypsin depend markedly on how enzyme has been hydrated - whether in the presence or in the absence of organic solvent. A qualitative model was proposed to classify the effect of hydration history on the enzyme activity-aw profiles. © 2005 Elsevier B.V. All rights reserved

Effect of hydrogen bond accepting organic solvents on the binding of competitive inhibitor and storage stability of α-chymotrypsin

This review aims to analyse the studies of the competitive inhibitor binding and the storage stability of bovine pancreatic α-chymotrypsin (CT) in organic solvents in order to elucidate what intermolecular processes produce the main effect on the state and functioning of enzymes at high and low water activities in organic media. The binding of competitive inhibitor proflavin and the storage stability of CT in water-organic mixtures were studied in the entire range of thermodynamic water activities (aw) at 25°C. The moderate-strength hydrogen bond accepting solvents (acetonitrile, dioxane, tetrahydrofuran, and acetone) were used as models due to their ability to vary significantly the size, polarity, denaturation capacity, and hydrophobicity.The state of water hydrogen bond network in organic solvents was characterized by thermodynamic and spectroscopic data. The absorption spectra of water in organic solvents were measured by FTIR spectroscopy. The state of water in organic solvents was defined in terms of variations in the integral intensity of water and the contour shape of the band of OH stretching vibrations. Excess chemical potentials, partial molar enthalpies, and entropies of water and organic solvents were simultaneously evaluated at 25°C.The results obtained showed that:4) The proflavin binding and storage stability curves can be unified in the water activity coordinates. At the highest water activities (aw>0.95), the water hydrogen bond network is bond -percolated. In this composition region, the storage stability values are close to 100%.5) At the lowest water activities, the water molecules exist predominantly as single molecules complexed with organic solvent molecules. No proflavin binding was observed at low water activity values in the studied solvents. At aw>0.3, the proflavin binding is sharply increased reaching a maximal value at aw~0.5-0.6. This sharp increase in the enzyme activity occurs only above the threshold water activity level, when the self-associated (H-bonded) water molecules appear in the studied organic solvents.6) In the intermediate composition region, the solution consists of two kinds of clusters, each rich in each component. There is a sharp transition from the water-rich region to the intermediate one. This transition is associated with an anomaly in the thermodynamic, structural, and enzyme activity properties. This transition may involve loss of the bond percolated nature of the hydrogen bond network of liquid water. The residual catalytic activity of CT changes from 100 to 0% in the transition region. A minimum on the competitive inhibitor binding and storage stability curves was observed at aw of 0.8-0.9.The thermodynamic, structural, and enzyme activity data were analysed to give a unified picture of the state of enzymes in low water organic solvents. According to this model, the dehydration-induced protein-protein contacts and the state of water hydrogen bond network play a key role in determining the enzyme activity - water activity profiles in organic liquids. © 2011 by Nova Science Publishers, Inc. All rights reserved

Protein - water interactions: A differential approach

© 2014 by Nova Science Publishers, Inc. All rights reserved. This book is aimed at understanding which molecular parameters control the thermodynamics, structure, and functions of the protein-water systems. Proteins are one of the most important classes of biological molecules. Water binding (hydration or biological water) plays a crucial role in determining the structure, stability, and functions of proteins. Knowledge of processes occurring upon hydration or dehydration of protein macromolecules is very important in biotechnological and pharmaceutical applications of proteins such as their use as biocatalysts, biosensors, and selective adsorbents. There are essential differences between hydration and bulk water surrounding a protein. This means that a characterization of the hydration of protein macromolecules requires elucidating the effects of both the protein on water and vice versa. Therefore, a quantitative estimation of the protein and water contributions to the thermodynamic functions of binary protein-water systems is of considerable fundamental importance and practical interest. This book describes the basic principles of a novel methodology to investigate the protein-water interactions. This methodology is based on the analysis of the excess thermodynamic functions of mixing. The thermodynamic properties (volume V, enthalpy H, entropy S, heat capacity Cp, and Gibbs free energy G) of a real binary water-protein system can be expressed in terms of the excess functions. They are the difference between the thermodynamic function of mixing in a real system and the value corresponding to an ideal system at the same temperature, pressure and composition. For an ideal system, all excess functions are zero. Deviations of the excess functions from zero indicate the extent to which the studied binary system is non-ideal due to strong specific interactions between components (i.e., hydrogen bonding and charge-charge interactions)

A study of the heat capacity of ribonuclease a - water mixtures

© 2014 by Nova Science Publishers, Inc. All rights reserved. Excess heat capacities of the binary system of bovine pancreatic ribonuclease A (RNase A) with water were obtained as a function of composition at 25°C. Differential scanning calorimetry was applied to study hydration dependencies of the excess thermodynamic functions. A major focus of this study aims to show how these thermodynamic quantities correlate with coverage of the protein by the water molecules. The excess partial quantities are found to be sensitive to changes in the water and protein states. At the lowest water weight fractions (w1), the changes of the excess functions can mainly be attributed to water addition. A transition from the glassy to the flexible state of the protein is accompanied by significant changes in the excess partial quantities of water and lysozyme. This transition appears at w1 > of 0.05 when charged groups of the protein are covered. Excess partial quantities reach their fully hydrated values at w1 > 0.5 when coverage of both polar and weakly interacting surface elements is complete. At the highest water contents, water addition has no significant effect on the excess quantities. At w1 > 0.5, changes in the excess functions can solely be attributed to changes in the state of the protein