Effect of water on the temperatures of human immunoglobulin conformation transitions

A differential thermal analysis of native and denaturated human immunoglobulin (G isotype) and mixtures of the native protein with water over the temperature range of 80–570 K is conducted. Temperatures of the protein conformational transitions and the effect of water on them are investigated. The limit of water solubility in the native protein is determined calorimetrically from the enthalpy of excess water phase melting. A physical state diagram of the immunoglobulin-water system over a wide range of temperatures and component concentrations is built and analyzed.     

Regimes of water droplet evaporation on copper substrates

Distilled water droplet evaporation has been studied on copper substrate surfaces with different degrees of roughness. Data on variations in the contact diameter have been employed to distinguish between the regimes of distilled water droplet spreading over the copper surfaces that proceed after the viscous regime. For each isolated regime, the duration has been determined as a fraction of the total evaporation time and the main physical processes have been described. Variations in contact angles have been analyzed as depending on copper surface temperature. It has been established that, as the substrate temperature is elevated, wetting becomes better, while the adhesion work remains almost unchanged, thereby indicating the absence of chemical and structural transformations at the liquid–substrate interface.     

Creep study of high-esterified pectin gels

A creep study has been made of 2% pectin gels in the 1∶1 water-glycerol mixture in the temperature interval 284.7 to 321.7 °K, and also of water-glycerol pectin gels concentrated to 2–5% at 290.7 °K. Water-glycerol pectin gels by their thermorheological properties are close to water-sucrose gels studied earlier. It is shown that the rate of the relaxation processes is independent of the concentration. The standard break-down enthalpy of the 2% gel cross-links in the temperature interval where rheological properties are measured, is 17–39 kJ · mole^?1.     

Kinetic study on the homogeneous esterification of acetic acid with isoamyl alcohol

The liquid‐phase esterification of acetic acid and isoamyl alcohol has been studied to develop a kinetic model using a sequential experimental design based on the divergence criterion. Data come from batch reactor experiments, performed in the temperature range of 316–363 K. Discrimination among 36 possible kinetic models, written in terms of activity, mole fractions, and molar densities, is possible through the deviance information criterion, as estimated by a Markov chain Monte Carlo technique. The obtained results indicate a negligible heat of reaction and a clear autocatalytic effect of acetic acid on the esterification rate. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 10–18, 2013     

Ultrasonic study of binary aqueous mixtures of three common eutectic solvents

Ultrasonic velocities have been measured for different binary mixtures of common choline chloride-based deep eutectic solvents (DESs), namely, reline, glyceline and ethaline with water, in the range of temperature: 303.15–353.15 K. The experimental data measurements with different mole fractions of DES–water solutions were utilised in fitting four different models for speed of sound. These models correlate the speed of sound with some physical properties such as molar volumes, molar components sound velocity, densities, molecular weights, collision factors etc. A close match was obtained with these models with an average relative error of less than 4% for all data points used. It was observed that the ultrasonic velocity increases with the concentration of DES solvent and decreases with temperature. Moreover, this study roughly indicated that the intermolecular interactions in reline and ethaline aqueous mixtures exist in the form of disruption of dipole–dipole interactions (that varies considerably as a function of DES mixture composition and solution temperature). On the other hand, the interactions on the molecular level in glyceline aqueous solution are mainly due to dipole–dipole intermolecular forces.     

Solubility and thermodynamics of dissolution of helium in water at gas partial pressures of 0.1–100 MPa within a temperature range of 278–353 K

The tables of recommended numerical values for the water solubility of helium at gas partial pressures of 0.1–100 MPa within a temperature range of 278.15–353.15 K are given. The thermodynamic characteristics of dissolution of helium in water at the mentioned parameters of state have been calculated. The independence of the dissolution enthalpy on the pressure has been recognized and explained.     

Ultrasound velocity and density studies in some refined and unrefined edible oils

Density and ultrasonic velocity at a frequency of 3?MHz and in the temperature range 298–333?K are measured in some of the refined and unrefined edible oils, namely coconut oil, castor oil, sunflower oil, kardi (safflower oil) and groundnut oil, which are predominantly used in south India. Velocity has been observed to be decreasing with temperature nonlinearly in some oils in the temperature range studied. This is in agreement with others' observations made in different oils and fats. Velocity change with temperature is attributed to change in intermolecular distance with temperature and the nature of variation depends on the internal molecular dynamics. Density of all the oils has been found to be decreasing with temperature. Various physical parameters such as specific volume, molar sound velocity, adiabatic compressibility, molar compressibility and intermolecular free length have been estimated using measured data on velocity and density.     

Zinc-binding activity of different pectin compounds in aqueous solutions

The zinc-binding activity of different water-soluble pectin compounds varying according to their degree of esterification and of insoluble calcium pectate beads in aqueous solution was studied in a batch sorption system. The zinc uptake by all pectin compounds was highest within the pH range from 4.0 to 7.0. The binding capacities and rates of zinc ions by pectin compounds were evaluated. The Langmuir, Freundlich, and BET sorption models were applied to describe the isotherms and constants. Sorption isotherm data could be well interpreted by the Langmuir equation. The results obtained through the study suggest that pectin compounds are favorable sorbents. The largest number of zinc ions are bound by pectin with the degree of esterification close to zero. Therefore, it can be concluded that low-esterified pectins are more effective substances for elimination of zinc ions from aqueous disposals.     

The Homogeneity Range of Crystalline Tris(8-hydroxyquinoline)gallium

An experimental procedure has been developed for constructing p _i –T diagrams (partial vapor pressure of the ligand-forming component–temperature) for luminescent metal complexes with symmetric organic ligands. The partial 8-hydroxyquinoline vapor pressure–temperature diagram has been constructed for tris(8-hydroxyquinoline)gallium electrophosphor (Gaq₃) in the temperature range 300–617 K at 8-hydroxyquinoline vapor pressures 10^–3–10⁴ Pa, where the homogeneity ranges of different Gaq₃ polymorphs have been determined. Structure-sensitive properties of crystalline materials can be tailored by changing synthesis conditions within the homogeneity range of a phase.     

Volumetric properties of (piperidine + water) binary system: Measurements and modeling

Densities of pure piperidine (CAS No.: 110-89-4) and of its mixtures with water have been measured over the whole range of compositions at temperatures from 283.15 K to 347.15 K using Anton Paar? digital vibrating tube densimeter. The density of this system has been found increasing with mass fraction of water. Excess molar volumes have been calculated using the measured experimental densities and correlated using the Redlich–Kister equation. Redlich–Kister equation parameters have been adjusted on experimental data. In addition, partial molar volumes and partial excess molar volumes at infinite dilution have been calculated for each component.     

Thermodynamic properties of chitosan-based hydrogels in the range 0–350 K

The heat capacity, the temperature, and the enthalpy of physical transformations of hydrogels based on the copolymer of acrylamide and chitosan with N,N-methylene-bis(acrylamide) as a crosslinking agent, hydrogels based on the mixture of poly(vinylpyrrolidone) and chitosan with glutaric aldehyde as the crosslinking agent, and dehydrated hydrogels has been studied in the range 85–350 K with the use of adiabatic vacuum calorimetry. The temperatures and enthalpies of melting of free water in hydrogels have been determined. From the experimental data obtained, the thermodynamic functions C° _p (T), H° (T) ? H°(0), S° (T) ? S°(0), and G° (T) ? H°(0) have been calculated for the temperature range 0–350 K. The ratio of free and bound water in the hydrogels under study has been determined by calorimetry.     

Conformational contribution to the heat capacity of the starch and water system

The heat capacities of starch and starch—water have been measured with adiabatic calorimetry and standard differential scanning calorimetry and are reported from 8 to 490 K. The amorphous starch containing 11–26 wt % (53–76 mol %) water shows a partial glass transition decreasing from 372 to 270 K, respectively. Even the dry amorphous starch gradually increases in heat capacity above 270 K beyond that set by the vibrational density of states. This gradual increase in the heat capacity is identified as part of the glass transition of dry starch that is, however, not completed at the decomposition temperature. The heat capacities of the glassy, dry starch are linked to an approximate group vibrational spectrum with 44 degrees of freedom. The Tarasov equation is used to estimate the heat capacity contribution due to skeletal vibrations with the parameters Θ₁ = 795.5 K, Θ₂ = 159 K, and Θ₃ = 58 K for 19 degrees of freedom. The calculated and experimental heat capacities agree better than ±3% between 8 and 250 K. Similarly, the vibrational heat capacity has been estimated for glassy water by being linked to an approximate group vibrational spectrum and the Tarasov equation (Θ₁ = 1105.5 K and Θ₃ = 72.4 K, with 6 degrees of freedom). Below the glass transition, the heat capacity of the solid starch—water system has been estimated from the appropriate sum of its components and also from a direct fitting to skeletal vibrations. Above the glass transition, the differences are interpreted as contributions of different conformational heat capacities from chains of the carbohydrates interacting with water. The conformational parts are estimated from the experimental heat capacities of dry starch and starch—water, decreased by the vibrational and external contributions to the heat capacity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3038–3054, 2001     

Synthesis of polyampholyte microgels from colloidal salts of pectinic acid and their application as pH-responsive emulsifiers

A novel method for obtaining cross-linked microgels of apple pectin has been introduced. This method is based on the Ugi four-component condensation in colloidal suspensions of pectinic acid and amines. Using various processing parameters (the polysaccharide concentration, the type and density of crosslink, and the optimal pH range), particles with controlled colloidal properties have been obtained. Lightly cross-linked polysaccharide chains acquire anionic character due to deprotonation of the carboxyl groups at pH?9–10. Increasing the degree of cross-linking leads to a polyampholyte microgel, which can be protonated in acidic medium or deprotonated in basic medium. Polyampholyte microgels derived from apple pectin have proved to be an effective Pickering emulsifier at low concentrations and pH?2–3, forming stable oil-in-water emulsions. These Pickering emulsions exhibited pH-responsive behavior: raising the solution pH to 10 resulted in immediate demulsification due to the destabilization of microgel network at the oil–water interface.     

A sustainable method of mitigating acid corrosion of mild steel using jackfruit pectin (JP) as green inhibitor: Theoretical and electrochemical studies

This study is attempted to develop a green corrosion inhibitor from a waste material of Jack fruit (Artocarpus heterophyllus). This method is therefore quite valuable to health, environment, and economic point of view. Pectin is isolated from the jackfruit peel waste using 0.05 ?N oxalic acid and used as an inhibitor for mild steel corrosion in acidic environment as it is highly water soluble. 250–1000 ?ppm of pectin was used in this study at a temperature range of 303–323 ?K. The protection efficiency of jack fruit pectin (JP) in 0.5 ?M HCl was evaluated by conventional weight loss and electrochemical techniques. The potentiodynamic polarization results revealed that JP could effectively reduce the corrosion of mild steel in acidic medium at 1000 ?ppm concentration with an inhibition efficiency of 89.75% and corrosion rate of 2.392 mpy. The mixed type behavior of the inhibitor is identified from Tafel polarization studies. Electrochemical impedance spectroscopy (EIS) measurements suggest that the corrosion inhibition process is kinetically controlled. adsorption and kinetic behavior of the inhibitor also have been studied. Surface manifestations were followed using FESEM and AFM techniques. DFT calculations and Monte Carlo simulations were also carried out to corroborate the experimental results with theoretical outputs and succeeded to a great extent.     

Temperature effect on peak width and column efficiency in subcritical water chromatography

Subcritical water has been recently employed as the mobile phase to eliminate the use of organic solvents in reversed-phase liquid chromatography. Although the influence of temperature on retention in subcritical water chromatography has been reported, the temperature effect on peak width and column efficiency has not yet been quantitatively studied. In this work, several polar and chlorinated compounds are separated using pure subcritical water on Zorbax RX-C8, PRP-1 (polystyrene-divinylbenzene), Hypersil ODS, and ZirChrom-polybutadiene columns. Isothermal separations are performed at temperatures ranging from 60 degrees C to 160 degrees C. The retention time and peak width of analytes are reduced with increasing temperature. However, the column efficiency is either improved or almost unchanged with the increasing temperature in the low-temperature range (lower than the 100 degrees C to 120 degrees C range), but it is decreased when temperature is further raised in the high-temperature range (higher than the 100 degrees C to 120 degrees C range). Therefore, a maximum in column efficiency is obtained at temperatures within the 100 degrees C to 120 degrees C range in most cases.     

Phase transition sensitive to interlayer defects in layered semiconductor TlGaSe2

The structural and thermal properties of ferroelectric–semiconductor TlGaSe₂ with layered crystalline structure have been investigated in 77–300 K temperature range. It is found that all outlined physical properties of TlGaSe₂ are significantly modified near 180 K due to the phase transition (PT). The nature of this PT has been analyzed and it is established that the main peculiarity of such PT is the extreme sensitivity to interlayer bonding. As a result, any manifestations of this PT depend strongly on defects and impurities located between the layers and can be changed by illumination, temperature annealing and applying electric field.     

Investigation of the role of the interplay between water and temperature on the growth of alkylsiloxane submonolayers on silicon

We have investigated the influence of the interplay of the temperature and the water concentration in the adsorption solution on the growth of self-assembled monolayers on silicon using octadecyltrichlorosilane as the precursor. Toluene has been used as the solvent. The morphology of the submonolayer films has been investigated by atomic force microscopy (AFM). The surface coverages have been determined both with ellipsometry and through quantitative evaluation of AFM images. The size distribution of species in the precursor solution has been studied with dynamic light scattering. The influence of water concentrations between 8 and 18 mmol/L has been investigated in the temperature range from 2 to 35 degrees C. Dynamic light scattering revealed a unimodal size distribution of ordered aggregates in solution with a hydrodynamic radius of 200 nm regardless of the temperature and water concentration. However, formation of these features was faster at higher water contents and lower temperatures. Moreover, a characteristic temperature, which was higher for higher water concentrations, was found, above which such aggregates could not be detected anymore. Below this temperature an increase of the aggregate concentration has been observed until a plateau had been reached within a temperature range of approximately 5 degrees C. AFM measurements and ellipsometry on the corresponding submonolayer films showed that this temperature range is also associated with a transition from fast growth via characteristic fractally shaped islands to comparatively slow homogeneous growth via adsorption of individual molecules. The results are discussed in terms of diffusion and adsorption limitations.     

Kinetics of polyesterification III: Solid-state polymerization of polyethylene terephthalate

Experimental studies on the solid-state polymerization (SSP) of polyethylene terephthalate (PET) for the particle sizes of 14–16 mesh at 170–200°C and for the particle sizes of 14–18 mesh at 210–240°C are carried out under a vacuum of about 60 mtorr. Analysis of the data of the concentrations of hydroxyl and carboxyl groups and the number average molecular weight during the SSP allows determinations of the rates of esterification and ester interchange separately. It is found that at the temperature 170–200°C and the particle size 80–100 mesh the SSP is end-group diffusion limiting, and that at the temperature 210–240°C and the particle size 14–16 mesh the ester interchange is ethylene glycol diffusion limiting and the esterification is predominantely end-group diffusion limiting due to higher diffusion rate of water. These phenomena are explored by an assistance of the proposed rate expressions for the end-group diffusion limited reactions and diffusion models for the by-products, water, and ethylene glycol.     

Heat capacity of gold from 80 to 1000 K

The heat capacity of gold has been measured by laserflash calorimetry in the temperature range 80–1000 K. The results are compared with available low- and high-temperature heat capacities, and revised thermodynamic values of gold are given.