Volumetric, acoustic, viscometric, calorimetric and spectroscopic studies to elucidate the effects of citrate and tartrate based food preservatives on the solvation behaviors of acidic amino acids at different temperatures.

The effects of trisodium citrate (TSC) and disodium tartrate (DST) based food preservatives on the hydration behaviors of the amino acids l-aspartic acid (ASP) and l-glutamic acid (GLU) have been studied using thermodynamic, transport, calorimetric and spectroscopic studies. The volumetric, acoustic and viscosity data suggest that hydrophilic-ionic/hydrophilic interactions are predominant in these systems. The calculated parameters are worthwhile for exploring the solutes as structure-breakers, and the solutes undergo pairwise interactions with the co-solutes. The sweetness of both amino acids decreases in the presence of the preservatives. The hydration number and solvation data suggest that these solutes are more hydrated in water. The dominance of dehydration effects in relation to TSC is observed from the positive enthalpy changes in calorimetry studies and the negative chemical shifts in 1H NMR studies.

Hydration characteristics, structural effects and the taste quality of some polyhydroxy compounds in aqueous solutions of nicotinic acid (vitamin B3) at (288.15-318.15) K.

Physicochemical properties elucidating the hydration characteristics and structural effects of polyhydroxy compounds in mixed aqueous solutions offer significant information for the growth of pharmaceutical and food industries. Consequently, standard partial molar volumes and isentropic compressibilities at infinite dilution of saccharides, their derivatives and sugar alcohols in (0.01, 0.05, 0.09 and 0.13) mol kg-1 nicotinic acid(aq) (vitamin B3) solutions have been investigated by experimental density and ultrasonic velocity with respect to temperature. Their transfer values, compressibility hydration numbers, apparent massic volumes and isentropic compressibilities have also been determined. These parameters are important to study the taste behavior of polyhydroxy compounds and intermolecular interactions occurring in ternary mixtures. UV absorption spectra of the studied polyhydroxy compounds have been recorded in 1 × 10-4 mol kg-1 nicotinic acid(aq) solutions. The comparison of present results has been made with the studies reported earlier in l-ascorbic acid, thiamine HCl and pyridoxine HCl.

Effect of potassium chloride on the solvation behavior of caffeine, theophylline and theobromine: Volumetric, viscometric, calorimetry and spectroscopic approach.

The density (ρ), speed of sound (u), viscosity (η) and enthalpy of dilution (q) measurements for methylxanthines (caffeine, theophylline and theobromine) in aqueous medium and in aqueous solutions of (0.10-1.00) mol·kg-1 KCl covering a temperature range T = (288.15-318.15) K and at p = 101.325 kPa have been accomplished using a density and sound velocity meter, Micro-Ubbelohde type capillary viscometer and Isothermal Titration Calorimetry, respectively. Transfer parameters evaluated from the data suggest that competition among various interactions exists at low and high molalities of KCl(aq.) solutions. The increase in bitterness and decrease in hydration number of methylxanthines with the mB values have been observed. The dehydration effect of KCl(aq.) at low molalities on the methylxanthines has also been established using ITC. Positive change in the chemical shifts (1H NMR) and increase in absorption intensity (UV-vis) of methylxanthines in the presence of KCl(aq.) further support our results.

Solvation behavior and sweetness response of carbohydrates, their derivatives and sugar alcohols in thiamine HCl (vitamin B1) and pyridoxine HCl (vitamin B6) at different temperatures.

Volumetric properties are important tools to study the solvation behavior of solutes and reveal valuable information about solute-solute/cosolute interactions. Therefore, standard partial molar volumes at infinite dilution have been calculated from density measurements for monosaccharides, their methoxy and deoxy derivatives, disaccharides and sugar alcohols in (0.05, 0.15, 0.25 and 0.35)molkg-1 thiamine HCl(aq) and pyridoxine HCl(aq) solutions over temperature range (288.15-318.15)K at pressure, p=0.1MPa. The corresponding transfer volumes, expansibilities and apparent massic volumes have been evaluated to examine the solvation behavior and the basic taste quality of studied solutes. UV-Vis absorption study of these solutes has also been carried out in 1.0×10-4molkg-1 thiamine HCl and pyridoxine HCl solutions. Results have been compared with our previously reported studies carried out in l-ascorbic acid (vitamin C). Stereochemical effects on hydration controlled by dominant conformations of studied solutes have also been discussed.

Study on the interactional behaviour of transition metal ions with myoglobin: A detailed calorimetric, spectroscopic and light scattering analysis.

The energetics and the impact on the conformation of heme containing protein myoglobin (Mb) due to the binding of three transition metal ions (Zn2+, Ni2+, and Mn2+) have been investigated using isothermal titration calorimetry (ITC), dynamic light scattering (DLS), UV-vis, and circular dichroism (CD) spectroscopy under physiological conditions. The binding affinity of the order of 104M-1 has been observed for all metal ions from calorimetry as well as from absorption spectroscopy. The binding of these metal ions with Mb is a spontaneous process that exposes the hydrophobic groups away from the protein core as exhibited by the negative Gibbs free energy change (ΔG) and positive heat capacity change (ΔCp) values. Both light scattering and CD results demonstrates that the binding of Zn2+ and Mn2+ ions with Mb results in the folding whereas Ni2+ ion results in the unfolding of the protein. No direct interactions among the transition metal ions and heme moiety of Mb has been observed from absorption study. The results of these studies reveals that Mn2+ ion influences the biological functions of Mb to a larger extent in spite of its lowest affinity followed by Zn2+ and Ni2+ ions.

Physicochemical aspects of the energetics of binding of sulphanilic acid with bovine serum albumin.

The thermodynamic study of the binding of sulphanilic acid with model transport protein bovine serum albumin is a promising approach in the area of synthesizing new sulfa drugs with improved therapeutic effect. Thus, such binding studies play an important role in the rational drug design process. The binding between sulphanilic acid and bovine serum albumin has been studied using calorimetry, light scattering in combination with spectroscopic and microscopic techniques. The calorimetric data reveals the presence of two sequential nature of binding sites where the first binding site has stronger affinity (~10(4)M(-1)) and second binding site has weaker affinity (~10(3)M(-1)). However, the spectroscopic (absorption and fluorescence) results suggest the presence of single low affinity binding site (~10(3)M(-1)) on protein. The contribution of polar and non-polar interactions to the binding process has been explored in the presence of various additives. It is found that sulphanilic acid binds with high affinity at Sudlow site II and with low affinity at Sudlow site I of protein. Light scattering and circular dichroism measurements have been used to study the effect on the molecular topology and conformation of protein, respectively. Thus these studies provide important insights into the binding of sulphanilic acid with bovine serum albumin both quantitatively and qualitatively.

Modulation of physicochemical and spectroscopic properties of l-serine and l-proline by propionate based food preservatives.

To have an insight into the effect of preservatives on various ingredients of processed items, it is important to study their thermodynamic, transport and spectroscopic properties in aqueous solutions to elucidate various solute-co-solute interactions. The densities, viscosities and enthalpies of dilution of l-serine and l-proline have been determined in water and in aqueous solutions of sodium propionate and calcium propionate at different temperatures. The derived parameters elucidate the changes in taste quality and hydration number of l-serine and l-proline in the presence of the studied preservatives. Predominance of dehydration effect has been observed from calorimetry and changes in chemical shifts from nuclear magnetic resonance spectroscopy also support the above results.

Effect of tartarate and citrate based food additives on the micellar properties of sodium dodecylsulfate for prospective use as food emulsifier.

Citrate and tartarate based food preservatives can be used to enhance the emulsifying properties of sodium dodecylsulfate (SDS) based micellar system and thus making it appropriate for food applications. Exploration of interactions between the two species is the key constraint for execution of such ideas. In this work various micellar and thermodynamic parameters of SDS like critical micellar concentration (CMC), standard Gibbs free energy of micellization (ΔG(0)mic.) etc. have been calculated in different concentrations of disodium tartarate (DST) and trisodium citrate (TSC) in the temperature range (288.15-318.15)K from the conductivity and surface tension measurements. The parameters obtained from these studies reveal the competitive nature of both the additives with SDS for available positions at the air/water interface. TSC is found to be more effective additive in order to make SDS micellar system better for its potential applications as food emulsifier.

Volumetric and UV absorption studies on understanding the solvation behavior of polyhydroxy solutes in l-ascorbic acid(aq) solutions at T=(288.15 to 318.15)K.

Thermodynamic and spectroscopic data characterizing the solvation behavior of polyhydroxy compounds are in demand to get better understanding about the mechanisms of taste chemoreception, protein stabilization, etc. Apparent molar volumes for monosaccharides, disaccharides, derivatives, and polyols in (0.05, 0.15, 0.25 and 0.35) mol kg(-1) aqueous solutions of l-ascorbic acid have been determined from density data measured at (288.15, 298.15, 308.15 and 318.15)K under atmospheric pressure. Standard partial molar volumes at infinite-dilution and corresponding volumes of transfer of solutes from water to L-ascorbic acid(aq) have been calculated. Interaction coefficients and standard partial molar expansibilities have also been evaluated. The basic taste quality of studied solutes has been assessed from apparent massic volumes. UV absorption studies support the interactions between solutes and L-ascorbic acid. Influence of pH variation was taken into consideration while evaluating chemical behavior and stability of L-ascorbic acid in aqueous and buffer solutions.

Effect of food preservatives on the hydration properties and taste behavior of amino acids: a volumetric and viscometric approach.

Thermodynamic and transport properties of aqueous solutions are very useful in the elucidation of solute-solvent and solute-solute interactions, which help to understand the hydration and taste behavior of solutes. The densities and viscosities of L-glycine, ß-alanine and L-leucine have been determined in water and in aqueous solutions of sodium propionate (NaP) and calcium propionate (CaP) at temperatures 298.15 and 308.15K. From these data, apparent molar volumes (V2,ϕ), viscosity B-coefficients and corresponding transfer parameters (ΔtrV2,ϕo and ΔtrB) have been calculated. The dB/dT values suggest that L-glycine and ß-alanine act as structure-breaker, while L-leucine acts as structure-maker both in water and in aqueous solutions of NaP and CaP. The decrease in hydration number and change in taste behavior have also been observed with increasing concentration of the cosolute.

Hydration behaviour of some mono-, di-, and tri-saccharides in aqueous sodium gluconate solutions at (288.15, 298.15, 308.15 and 318.15)K: volumetric and rheological approach.

Thermodynamic and transport properties are very useful in providing valuable information regarding the hydration characteristics of saccharides and play a pivotal role in the study of taste behaviour of saccharides in mixed aqueous solutions. The effects of sodium gluconate and other sodium salts on the hydration behaviour and the basic taste quality of saccharides have been studied from measured apparent molar volumes (V2,ϕ), partial molar volumes (V2(°)) at infinite-dilution, and viscosity B-coefficients, of eight monosaccharides, six disaccharides and two trisaccharides in (0.25, 0.50, 1.00 and 1.50)molkg(-1) aqueous sodium gluconate solutions over a temperature range of (288.15-318.15)K and at atmospheric pressure. Partial molar volumes of transfer (ΔtV2(°)) and viscosity B-coefficients of transfer (ΔtB) of saccharides and other parameters such as isobaric expansion coefficients, interaction coefficients (using McMillan-Mayer theory), and dB/dT parameters have also been determined and discussed in terms of solute (saccharide)-cosolute (sodium gluconate) interactions.

Effect of magnesium chloride (2:1 electrolyte) on the aqueous solution behavior of some saccharides over the temperature range of 288.15-318.15 K: a volumetric approach.

Infinite-dilution standard partial molar volumes, V(2)(0), for various mono-, di-, and trisaccharides, and their derivatives (methyl glycosides) at molalities ranging from 0.04 to 0.12 mol kg(-1) in aqueous solutions of magnesium chloride of 0.5, 1.0, 2.0, and 3.0 mol kg(-1), have been evaluated over a range of temperatures from 288.15 to 318.15 K by density measurements employing a vibrating-tube densimeter. These data have been utilized to determine the corresponding standard partial molar volumes of transfer, Δ(t)V(2)(0), of saccharides and methyl glycosides from water to aqueous magnesium chloride solutions. The Δ(t)V(2)(0) values have been found to be positive, and their magnitudes increase with an increasing concentration of magnesium chloride in all cases. Partial molar expansion coefficients, (∂V(2)(0)/∂T)(P) and second derivatives thereof, (∂(2)V(2)(0)/∂T(2))(P) have been estimated. The magnitude of V(2)(0) values increases with an increase in temperature, indicating that hydration effects in solutions are strongly sensitive to temperature. Pair and higher order volumetric interaction coefficients (V(AB), V(ABB)) have also been obtained from Δ(t)V(2)(0) values by using the McMillan-Mayer theory. The various parameters have been discussed in terms of the solute (saccharide or methyl glycoside)-co-solute (magnesium chloride) interactions and are thus used to understand the mixing effects due to these interactions. These results have been compared with those earlier reported in the presence of electrolytes. An attempt is made to interpret the volumetric properties data in terms of the stereochemistry of the solutes.