The acoustical and viscometric properties of L-Alanine (neutral, nonpolar) and L-Arginine (basic, charged) in 10% aqueous glycerol have been investigated over a concentration range of 0.01 to 0.1 mol·kg⁻¹ at temperatures T = 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15 K under atmospheric pressure. Experimental measurements of ultrasonic velocity (µ), density (ρ), and viscosity (η) have been used to derive adiabatic compressibility (), apparent molar volume (Φv), partial molar volume (Φ°v), relative viscosity (η/η₀), and solvation number (n_s), Transfer partial molar volume (ΔΦ°v) and transfer partial molar compressibility (ΔΦ°k) from pure water to 10% aqueous glycerol have also been determined for both amino acids at each temperature. L-Arginine exhibited higher ultrasonic velocity values and greater decrease in adiabatic compressibility compared to L-Alanine, reflecting the stronger molecular interactions arising from its positively charged guanidinium side chain. The relative viscosity (η/η₀) values greater than unity for both amino acids confirm strong solute-solvent interactions in 10% aqueous glycerol, with L-Arginine exhibiting higher relative viscosity values than L-Alanine throughout the investigated concentration and temperature range, attributed to the stronger interactions arising from its positively charged guanidinium side chain. The solvation numbers obtained from adiabatic compressibility data indicate a larger solvation sphere around L-Arginine molecules, reflecting stronger solvophilic hydration due to electrostatic interactions of the guanidinium group with surrounding solvent molecules. The transfer partial molar compressibility () values were found to be negative for L-Arginine and positive for L-Alanine across the entire temperature range investigated. This contrasting behavior clearly demonstrates the differential effect of glycerol on the two amino acids — glycerol strengthens and rigidifies the hydration shell of L-Arginine through strong hydrogen bonding interactions with its charged guanidinium group, while it weakens and disrupts the hydration shell of L-Alanine due to the weaker affinity of glycerol for its nonpolar methyl side chain. The results provide clear evidence for the dominant role of side chain polarity and charge in governing the solvation behavior and molecular interactions of amino acids in aqueous glycerol medium, with implications for understanding protein stabilization mechanisms in polyol-containing biological and pharmaceutical systems.

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1. Millero FJ. Molal volumes of electrolytes. Chem Rev. 1971;71(2):147-176.
2. Friedman HL, Krishnan CV. Studies of hydrophobic bonding in aqueous alcohols: enthalpy measurements and model calculations. J Solution Chem. 1973;2(2):119-140.
3. Ali A, Hyder S, Sabir S, Chand D, Nain AK. Volumetric, viscometric, and refractive index behaviour of α-amino acids and their groups' contribution in aqueous D-glucose solution at different temperatures. 2005.
4. Palani R, Geetha A. Acoustical and excess thermodynamic studies of molecular interaction in aqueous mixed solvent systems at 303, 308 and 313 K. Phys Chem Liq. 2009;47(5):542-552.
5. Millero FJ, Lo Surdo A, Shin C. The apparent molal volumes and adiabatic compressibilities of aqueous amino acids at 25 °C. J Phys Chem. 1978;82(7):784-792.
6. Jacobson B, Halonen E, Faurholt C. Intermolecular free lengths in the liquid state. I. Adiabatic and isothermal compressibilities. Acta Chem Scand. 1952;6:1485-1498.
7. Ali A, Khan S, Nabi F. Volumetric, viscometric and refractive index behavior of amino acids in aqueous glycerol at different temperatures. J Serb Chem Soc. 2007;72(5):495-512.
8. Jones G, Dole M. The viscosity of aqueous solutions of strong electrolytes with special reference to barium chloride. J Am Chem Soc. 1929;51(10):2950-2964.
9. Feakins D, Freemantle DJ, Lawrence KG. Transition state treatment of the relative viscosity of electrolytic solutions. Applications to aqueous, non-aqueous and methanol-water systems. J Chem Soc Faraday Trans 1. 1974;70:795-806.
10. Perron G, Desnoyers JE. Volumes and heat capacities of benzene derivatives in water at 25 °C: group additivity of the standard partial molal quantities. Fluid Phase Equilib. 1979;2(4):239-262.

The acoustical and viscometric properties of L-Alanine (neutral, nonpolar) and L-Arginine (basic, charged) in 10% aqueous glycerol have been investigated over a concentration range of 0.01 to 0.1 mol·kg⁻¹ at temperatures T = 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15 K under atmospheric pressure. Experimental measurements of ultrasonic velocity (µ), density (ρ), and viscosity (η) have been used to derive adiabatic compressibility (), apparent molar volume (Φv), partial molar volume (Φ°v), relative viscosity (η/η₀), and solvation number (n_s), Transfer partial molar volume (ΔΦ°v) and transfer partial molar compressibility (ΔΦ°k) from pure water to 10% aqueous glycerol have also been determined for both amino acids at each temperature. L-Arginine exhibited higher ultrasonic velocity values and greater decrease in adiabatic compressibility compared to L-Alanine, reflecting the stronger molecular interactions arising from its positively charged guanidinium side chain. The relative viscosity (η/η₀) values greater than unity for both amino acids confirm strong solute-solvent interactions in 10% aqueous glycerol, with L-Arginine exhibiting higher relative viscosity values than L-Alanine throughout the investigated concentration and temperature range, attributed to the stronger interactions arising from its positively charged guanidinium side chain. The solvation numbers obtained from adiabatic compressibility data indicate a larger solvation sphere around L-Arginine molecules, reflecting stronger solvophilic hydration due to electrostatic interactions of the guanidinium group with surrounding solvent molecules. The transfer partial molar compressibility () values were found to be negative for L-Arginine and positive for L-Alanine across the entire temperature range investigated. This contrasting behavior clearly demonstrates the differential effect of glycerol on the two amino acids — glycerol strengthens and rigidifies the hydration shell of L-Arginine through strong hydrogen bonding interactions with its charged guanidinium group, while it weakens and disrupts the hydration shell of L-Alanine due to the weaker affinity of glycerol for its nonpolar methyl side chain. The results provide clear evidence for the dominant role of side chain polarity and charge in governing the solvation behavior and molecular interactions of amino acids in aqueous glycerol medium, with implications for understanding protein stabilization mechanisms in polyol-containing biological and pharmaceutical systems.

🔒 This is a subscription article

Full text is available to subscribers and institutional members. Please choose an option below to access it.

1. Millero FJ. Molal volumes of electrolytes. Chem Rev. 1971;71(2):147-176.
2. Friedman HL, Krishnan CV. Studies of hydrophobic bonding in aqueous alcohols: enthalpy measurements and model calculations. J Solution Chem. 1973;2(2):119-140.
3. Ali A, Hyder S, Sabir S, Chand D, Nain AK. Volumetric, viscometric, and refractive index behaviour of α-amino acids and their groups' contribution in aqueous D-glucose solution at different temperatures. 2005.
4. Palani R, Geetha A. Acoustical and excess thermodynamic studies of molecular interaction in aqueous mixed solvent systems at 303, 308 and 313 K. Phys Chem Liq. 2009;47(5):542-552.
5. Millero FJ, Lo Surdo A, Shin C. The apparent molal volumes and adiabatic compressibilities of aqueous amino acids at 25 °C. J Phys Chem. 1978;82(7):784-792.
6. Jacobson B, Halonen E, Faurholt C. Intermolecular free lengths in the liquid state. I. Adiabatic and isothermal compressibilities. Acta Chem Scand. 1952;6:1485-1498.
7. Ali A, Khan S, Nabi F. Volumetric, viscometric and refractive index behavior of amino acids in aqueous glycerol at different temperatures. J Serb Chem Soc. 2007;72(5):495-512.
8. Jones G, Dole M. The viscosity of aqueous solutions of strong electrolytes with special reference to barium chloride. J Am Chem Soc. 1929;51(10):2950-2964.
9. Feakins D, Freemantle DJ, Lawrence KG. Transition state treatment of the relative viscosity of electrolytic solutions. Applications to aqueous, non-aqueous and methanol-water systems. J Chem Soc Faraday Trans 1. 1974;70:795-806.
10. Perron G, Desnoyers JE. Volumes and heat capacities of benzene derivatives in water at 25 °C: group additivity of the standard partial molal quantities. Fluid Phase Equilib. 1979;2(4):239-262.