Abstract
Apparent molar volumes (phi_{V}) of glycine/l-alanine in water and in aqueous citric acid (CA) solutions of varying concentrations, i.e. (0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) mol·kg−1 were determined from density measurements at temperatures T = (288.15, 298.15, 308.15, 310.15 and 318.15) K and at atmospheric pressure. Limiting partial molar volumes (phi_V^{text{o}}) and their corresponding partial molar volumes of transfer (Delta_{text{tr}} phi_{V} ) have been calculated from the phi_{V} data. The negative Delta_{text{tr}} phi_{V} values obtained for glycine/l-alanine from water to aqueous CA solutions indicate the dominance of hydrophilic–hydrophobic/hydrophobic–hydrophilic and hydrophobic–hydrophobic interactions over ion/hydrophilic–dipolar interactions. Further, pair and triplet interaction coefficients, i.e.(V_{text{AB}} );{text{and}}; (V_{text{ABB}} ) along with hydration number (n_{text{H}} ) have also been calculated. The effect of temperature on the volumetric properties of glycine/l-alanine in water and in aqueous CA solutions has been determined from the limiting partial molar expansibilities (partial phi_{V}^{text{o}} /partial T)_{p} and their second-order derivative (partial^{2} phi_{V}^{text{o}} /partial T^{2} )_{{P}}. The apparent specific volumes (nu_{phi} ) for glycine and l-alanine tend to approach sweet taste behavior both in the presence of water and in aqueous CA solutions. The nu_{phi} values for glycine/l-alanine increase with increase in concentration of CA at all temperatures studied. This reveals that CA helps in enhancing the sweet taste behavior of glycine/l-alanine which also supports the dominance of hydrophobic–hydrophobic interactions.
Highlights
Amino acids are the building blocks of proteins, they are regarded as an ideal model for the study of protein functioning and their complex structure [1, 2]
In light of the above facts, presently we report the apparent molar volumes ( V ) of glycine/lalanine in water and in aqueous Citric acid (CA) solutions, mc ≈ (0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) mol·kg−1 at temperatures, T = (288.15, 298.15, 308.15, 310.15 and 318.15) K and at atmospheric pressure, obtained from experimental densities
The apparent molar volumes ( V) of glycine and l-alanine in water and in varying concentrations of aqueous CA solutions were calculated from experimental solution densities ( ) at temperatures T = (288.15, 298.15, 308.15, 310.15 and 318.15) K and at atmospheric pressure, by employing the following equation: V = M∕ − [1000( − o)]∕mA o ρ/ 10-3, kg ·m-3
Summary
Amino acids are the building blocks of proteins, they are regarded as an ideal model for the study of protein functioning and their complex structure [1, 2]. The presence of one hydroxyl and three carboxyl groups in CA provides effective chemical properties so that it can act as an important metabolite in the citric acid cycle (CAC) of all aerobic organisms [21]. It acts as a precursor for the bio-synthesis of many compounds in CAC including AA [22]. In light of the above facts, presently we report the apparent molar volumes ( V ) of glycine/lalanine (both are non-essential amino acids) in water and in aqueous CA solutions, mc (molality of aqueous CA) ≈ (0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) mol·kg−1 at temperatures, T = (288.15, 298.15, 308.15, 310.15 and 318.15) K and at atmospheric pressure, obtained from experimental densities. The volumetric behavior of glycine in aqueous CA solutions (present work) are compared with glycine in aqueous succinic acid (SA) solutions, reported earlier from our laboratory [23]
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