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

Hydration of α-chymotrypsin: Excess partial enthalpies of water and enzyme

A novel method has been developed for studying simultaneously the excess partial enthalpies of water and the enzyme in the entire range of water content. Bovine pancreatic α-chymotrypsin was used as a model enzyme. The proposed method includes the measurements of the enthalpies of solution of the dried and hydrated enzyme in water at 25 °C. From these thermochemical data the excess partial enthalpies of water and α-chymotrypsin were calculated. The partial quantities are very sensitive to the changes in the state of water and α-chymotrypsin. A transition from the glassy to the flexible state of α-chymotrypsin is accompanied by significant changes in the excess partial enthalpies of water and α-chymotrypsin. This transition appears at water weight fraction (w1) of 0.06 when charged groups of α-chymotrypsin are covered. Excess partial quantities reach their fully hydrated values at w1 > 0.4 when coverage of both polar and weakly interacting surface elements is complete. © 2011 Elsevier B.V. All rights reserved

Α-Chymotrypsin in water-ethanol mixtures: Effect of preferential interactions

© 2017 Elsevier B.V. We investigated preferential interactions of α-chymotrypsin with water–ethanol mixtures at 25 °C. Our approach is based on the analysis of residual enzyme activity and water/alcohol sorption. There are three concentration regimes. α-Chymotrypsin is preferentially hydrated at high water content. The residual enzyme activity is close to 100%. α-Chymotrypsin has a higher affinity for alcohol than for water at intermediate water content. Residual enzyme activity is close to zero in this concentration range. At low water content, ethanol is preferentially excluded from the protein surface. This results in preferential hydration of α-chymotrypsin and significant residual catalytic activity (∼50%) in water-poor ethanol

Gibbs energies, enthalpies, and entropies of water and lysozyme at the inner edge of excess hydration

The aim of this study is to simultaneously monitor the excess partial Gibbs energies, enthalpies, and entropies of water and white egg lysozyme and demonstrate how these quantities correlate with the coverage of the protein macromolecules by water molecules. Isothermal calorimetry and water sorption measurements were applied to characterize the hydration dependencies of the excess thermodynamic functions. The excess partial quantities are found to be sensitive to changes in the water and protein states. At the lowest water weight fractions (w1), changes in the excess functions are primarily attributable to the addition of water. The transition of lysozyme from a glassy (rigid) to a flexible (elastic) state is accompanied by significant changes in the excess partial quantities. When the charged groups on the protein are covered, this transition occurs at w1 = 0.05; when the coverage of both polar and weakly interacting surface elements is complete, the excess partial quantities become hydrated at w1 > 0.5. At the highest water content, water addition has no significant effect on the excess quantities. At w1 > 0.5, changes in the excess functions solely reflect changes in the state of the protein. © 2013 AIP Publishing LLC

Lysozyme in water-acetonitrile mixtures: Preferential solvation at the inner edge of excess hydration

© 2017 Author(s).Preferential solvation/hydration is an effective way for regulating the mechanism of the protein destabilization/stabilization. Organic solvent/water sorption and residual enzyme activity measurements were performed to monitor the preferential solvation/hydration of hen egg-white lysozyme at high and low water content in acetonitrile at 25 °C. The obtained results show that the protein destabilization/stabilization depends essentially on the initial hydration level of lysozyme and the water content in acetonitrile. There are three composition regimes for the dried lysozyme. At high water content, the lysozyme has a higher affinity for water than for acetonitrile. The residual enzyme activity values are close to 100%. At the intermediate water content, the dehydrated lysozyme has a higher affinity for acetonitrile than for water. A minimum on the residual enzyme activity curve was observed in this concentration range. At the lowest water content, the organic solvent molecules are preferentially excluded from the dried lysozyme, resulting in the preferential hydration. The residual catalytic activity is ∼80%, compared with that observed after incubation in pure water. Two distinct schemes are operative for the hydrated lysozyme. At high and intermediate water content, lysozyme is preferentially hydrated. However, in contrast to the dried protein, at the intermediate water content, the initially hydrated lysozyme has the increased preferential hydration parameters. At low water content, the preferential binding of the acetonitrile molecules to the initially hydrated lysozyme was detected. No residual enzyme activity was observed in the water-poor acetonitrile. Our data clearly show that the initial hydration level of the protein macromolecules is one of the key factors that govern the stability of the protein-water-organic solvent systems

Analysis of hydration of ovalbumin by isothermal calorimetry

© 2014 by Nova Science Publishers, Inc. All rights reserved. Isothermal calorimetry was applied to characterize the hydration dependencies of the excess thermodynamic functions of binary proteinwater systems. Here, in particular, the excess partial enthalpies of water and hen egg-white ovalbumin have been determined. The excess partial enthalpies for ovalbumin are compared with the published data for several unrelated globular proteins (ribonuclease A, lysozyme, chymotrypsinogen A, serum albumin, lactoglobulin). These biomacromolecules represent a series of proteins in which the hydrophobicity of proteins is gradually changed over a wide range. It was found that the excess partial quantities for the studied proteins are determined by the hydration of the hydrophilic and hydrophobic protein groups. The more hydrophilic a protein, the more significant a hydrophilic hydration contribution is and vice versa. Ribonuclease A is the most hydrophilic protein in the present study. This protein has the most significant hydrophilic hydration contribution. Lactoglobulin is the most hydrophobic protein under the study. This protein has the most significant hydrophobic hydration contribution. Ovalbumin shows intermediate properties

A study of the hydration of ribonuclease A using densitometry: Effect of the protein hydrophobicity and polarity

The excess volumes of the binary system of ribonuclease A (RNase A) with water were obtained as a function of composition at 25 °C. The excess quantities for RNase A were compared with the published data for several unrelated proteins (lysozyme, serum albumin, lactoglobulin, and chymotrypsinogen A). The hydrophobicity of these proteins is gradually changed over a wide range. It was found that the more hydrophilic a protein is, the more significant the hydrophilic hydration contribution is. RNase A is the most hydrophilic protein in the present study, and it has the most significant hydrophilic hydration contribution. © 2014 Elsevier B.V. All rights reserved

Interaction enthalpies of α-Chymotrypsin with water-1,2- propanediol mixtures as measured by isothermal calorimetry

© 2017 Nova Science Publishers, Inc. All rights reserved.Understanding the physico-chemical regularities of the enzymes in nonaqueous media (organic solvents, ionic liquids) is a topical problem for nonaqueous enzymology and biothechnology. The use of organic solvents as a reaction medium makes it possible to successfully conduct enzymatic reactions with hydrophobic compounds poorly soluble in water. Nonaqueous media provide the possibility of conducting industrially important synthetic reactions (peptide synthesis and esterification) that do not occur in aqueous media. The aim of this work is to give a thermochemical description of the stabilizing/destabilizing effect of organic solvent molecules on the stability of model enzyme (bovine pancreatic a-chymotrypsin) to elucidate what intermolecular processes produce the main effect on the stability and functioning of the enzymes at high and low water content in organic liquids. Isothermal calorimetry measurements were applied to study the stability of a-chymotrypsin in water-alcohol mixtures. Enthalpy changes on the interaction of a-chymotrypsin with water-organic solvent mixtures have been measured using a Setaram BT-2.15 calorimeter at 25oC. The obtained results show that isothermal calorimetry is an effective experimental tool for studying the simultaneous action of water and organic liquids on the stability of enzyme macromolecules. The degree of enzyme stabilization/destabilization depends strongly on the water content in organic solvent

Preferential Solvation/Hydration of α-Chymotrypsin in Water-Acetonitrile Mixtures

© 2017 American Chemical Society.The aim of our study is to monitor the preferential hydration/solvation of the protein macromolecules at low and high water content in water-organic mixtures. Our approach is based on the analysis of the absolute values of the water/organic solvent sorption. We applied this approach to estimate the protein stabilization/destabilization due to the preferential interactions of α-chymotrypsin with water-acetonitrile mixtures. At high water content, α-chymotrypsin is preferentially hydrated. At the intermediate water content, the preferential interaction changed from preferential hydration to preferential binding of acetonitrile. From infrared spectra, changes in the structure of α-chymotrypsin were determined through an analysis of the structure of the amide I band. Acetonitrile augments the intensity of the 1626 cm-1 band assigned to the intermolecular β-sheet aggregates. At low water content, the protein is in a glassy (rigid) state. The H-bond accepting acetonitrile molecules are not effective in solvating the dehydrated protein molecules alone. Therefore, the acetonitrile molecules are preferentially excluded from the protein surface, resulting in the preferential hydration. Advantages of our approach: (i) The preferential interaction parameters can be determined in the entire range of water content in water-organic mixtures. (ii) Our approach facilitates the individual evaluation of the Gibbs energies of water, protein, and organic solvent