Biomolecular Interactions of Aromatic Amino Acids in Phosphate Buffer-Urea Systems
A Viscometric Analysis of DL-Phenylalanine, L-Tryptophan, and L-Tyrosine at Physiological Temperatures
Keywords:
viscometry, aromatic amino acids, phosphate buffer, Jones-Dole equation, protein stabilityAbstract
The relative and specific viscosities of three aromatic amino acids—DL-phenylalanine, L-tryptophan, and L-tyrosine—were measured in phosphate buffer solutions (pH 6, 7, and 8) containing 0.1 M aqueous urea at temperatures ranging from 303.15 to 328.15 K. The concentration of amino acids varied from 0.01 to 0.09 mol/kg. Absolute viscosities (η), solvent flow times (t₀), and Jones-Dole B-coefficients were determined to elucidate solute-solvent interactions. The results show that viscosity increases with amino acid concentration and decreases with temperature. L-tryptophan exhibits the highest viscosity values among the three amino acids studied, followed by L-tyrosine and DL-phenylalanine. The pH of the buffer solution significantly affects the viscometric behavior, with pH 8 generally showing higher viscosity values compared to pH 6 and 7. Temperature-dependent activation energies were calculated using Arrhenius analysis, revealing distinct energetic barriers for viscous flow in different amino acid systems. These findings provide valuable insights into biomolecular interactions, protein folding mechanisms, and the solution behavior of aromatic amino acids in biological buffer systems.
Downloads
References
Auton, M., Holthauzen, L. M. F. and Bolen, D. W. (2007). Anatomy of energetic changes accompanying urea-induced protein denaturation. Proceedings of the National Academy of Sciences, 104(39), 15317-15322.
Baldwin, R. L. (1986). Temperature dependence of the hydrophobic interaction in protein folding. Proceedings of the National Academy of Sciences, 83(21), 8069-8072.
Banipal, T. S., Kaur, D. and Banipal, P. K. (2000). Apparent molar volume and viscosity studies of some amino acids in aqueous sodium chloride solutions at 298.15 K. Journal of Chemical & Engineering Data, 45(6), 1058-1061.
Bennion, B. J. and Daggett, V. (2003). The molecular basis for the chemical denaturation of proteins by urea. Proceedings of the National Academy of Sciences, 100(9), 5142-5147.
Burley, S. K. and Petsko, G. A. (1985). Aromatic-aromatic interaction: a mechanism of protein structure stabilization. Science, 229(4708), 23-28.
Chauhan, S., Sharma, P. and Kumar, K. (2015). Conductance and viscosity studies of sodium cholate and sodium deoxycholate in aqueous medium and in the presence of amino acids. Journal of Chemical Thermodynamics, 84, 81-88.
Creighton, T. E. (1993). Proteins: Structures and Molecular Properties (2nd ed.). W. H. Freeman and Company.
Dhondge, S. S., Zodape, S. P. and Parwate, D. V. (2017). Volumetric and viscometric studies of some drugs in aqueous solutions at different temperatures. Journal of Chemical Thermodynamics, 113, 40-52.
Dobson, C. M. (2003). Protein folding and misfolding. Nature, 426(6968), 884-890.
Dougherty, D. A. (2013). The cation-π interaction. Accounts of Chemical Research, 46(4), 885-893.
Einstein, A. (1906). Eine neue Bestimmung der Moleküldimensionen. Annalen der Physik, 19(2), 289-306.
Eyring, H. (1936). Viscosity, plasticity, and diffusion as examples of absolute reaction rates. Journal of Chemical Physics, 4(4), 283-291.
Ferguson, W. J., Braunschweiger, K. I., Braunschweiger, W. R., Smith, J. R., McCormick, J. J., Wasmann, C. C., Jarvis, N. P., Bell, D. H. and Good, N. E. (1980). Hydrogen ion buffers for biological research. Analytical Biochemistry, 104(2), 300-310.
Frank, H. S. and Evans, M. W. (1945). Free volume and entropy in condensed systems III. Entropy in binary liquid mixtures; partial molal entropy in dilute solutions; structure and thermodynamics in aqueous electrolytes. Journal of Chemical Physics, 13(11), 507-532.
Friedman, H. L. and Krishnan, C. V. (1973). Thermodynamics of ion hydration. Water: A Comprehensive Treatise, 3, 1-118.
Gekko, K. and Timasheff, S. N. (1981). Mechanism of protein stabilization by glycerol: preferential hydration in glycerol-water mixtures. Biochemistry, 20(16), 4667-4676.
Good, N. E., Winget, G. D., Winter, W., Connolly, T. N., Izawa, S. and Singh, R. M. M. (1966). Hydrogen ion buffers for biological research. Biochemistry, 5(2), 467-477.
Gurney, R. W. (1953). Ionic Processes in Solution. McGraw-Hill Book Company.
Hakin, A. W., Duke, M. M., Klassen, S. A., McKay, R. M. and Preuss, K. E. (1994). Apparent molar volumes and apparent molar heat capacities of aqueous amino acids at 25°C. Canadian Journal of Chemistry, 72(2), 362-368.
Hua, L., Zhou, R., Thirumalai, D. and Berne, B. J. (2008). Urea denaturation by stronger dispersion interactions with proteins than water implies a 2-stage unfolding. Proceedings of the National Academy of Sciences, 105(44), 16928-16933.
Hunter, C. A. and Sanders, J. K. M. (1990). The nature of π-π interactions. Journal of the American Chemical Society, 112(14), 5525-5534.
Jenkins, H. D. B. and Marcus, Y. (1995). Viscosity B-coefficients of ions in solution. Chemical Reviews, 95(8), 2695-2724.
Jones, G. and Dole, M. (1929). The viscosity of aqueous solutions of strong electrolytes with special reference to barium chloride. Journal of the American Chemical Society, 51(10), 2950-2964.
Kauzmann, W. (1959). Some factors in the interpretation of protein denaturation. Advances in Protein Chemistry, 14, 1-63.
Kumar, A., Patel, R. and Singh, S. K. (2010). Volumetric properties of glycine in aqueous protic ionic liquid solutions at different temperatures. Journal of Solution Chemistry, 39(8), 1636-1652.
Kumar, H. and Kishore, N. (2013). Thermodynamics of amino acid transfer from water to aqueous glycerol solutions. Journal of Solution Chemistry, 42(1), 1-9.
Liu, M. and Guo, Z. (2014). Molecular dynamics simulation of the diffusion of amino acids in aqueous solution. Journal of Physical Chemistry B, 118(5), 1404-1412.
McGaughey, G. B., Gagné, M. and Rappé, A. K. (1998). π-Stacking interactions. Alive and well in proteins. Journal of Biological Chemistry, 273(25), 15458-15463.
Meyer, E. A., Castellano, R. K. and Diederich, F. (2003). Interactions with aromatic rings in chemical and biological recognition. Angewandte Chemie International Edition, 42(11), 1210-1250.
Millero, F. J., Lo Surdo, A. and Shin, C. (1978). The apparent molal volumes and adiabatic compressibilities of aqueous amino acids at 25°C. Journal of Physical Chemistry, 82(7), 784-792.
Mondal, J., Stirnemann, G. and Berne, B. J. (2012). When does trimethylamine N-oxide fold a polymer chain and urea unfold it? Journal of Physical Chemistry B, 117(29), 8723-8732.
Neidigh, J. W., Fesinmeyer, R. M. and Andersen, N. H. (2002). Designing a 20-residue protein. Nature Structural Biology, 9(6), 425-430.
Okur, H. I., Hladílková, J., Rembert, K. B., Cho, Y., Heyda, J., Dzubiella, J., Cremer, P. S. and Jungwirth, P. (2017). Beyond the Hofmeister series: ion-specific effects on proteins and their biological functions. Journal of Physical Chemistry B, 121(9), 1997-2014.
Pace, C. N. (1986). Determination and analysis of urea and guanidine hydrochloride denaturation curves. Methods in Enzymology, 131, 266-280.
Patel, S. and Singh, A. K. (2018). Thermodynamic and spectroscopic investigations of amino acids in aqueous ionic liquid solutions. Journal of Molecular Liquids, 265, 733-741.
Roy, M. N., Ekka, D., Saha, S. and Roy, M. C. (2012). Host-guest inclusion complexes of α and β-cyclodextrins with α-amino acids. RSC Advances, 2(30), 11338-11348.
Schwierz, N., Horinek, D., Liese, S., Pirzer, T., Balzer, B. N., Hugel, T. and Netz, R. R. (2020). On the relationship between peptide adsorption resistance and surface contact angle: a combined experimental and simulation single-molecule study. Journal of the American Chemical Society, 134(48), 19628-19638.
Stumpe, M. C. and Grubmüller, H. (2009). Interaction of urea with amino acids: implications for urea-induced protein denaturation. Journal of the American Chemical Society, 129(51), 16126-16131.
Tanford, C. (1968). Protein denaturation. Advances in Protein Chemistry, 23, 121-282.
Wheeler, S. E. and Houk, K. N. (2009). Through-space effects of substituents dominate molecular electrostatic potentials of substituted arenes. Journal of Chemical Theory and Computation, 5(9), 2301-2312.
Yan, Z., Wang, J., Kong, W. and Lu, J. (2016). Effect of temperature on volumetric and viscosity properties of some α-amino acids in aqueous calcium chloride solutions. Fluid Phase Equilibria, 215(2), 143-150.
Zhang, H., Yin, C., Liu, M. and Guo, Z. (2015). Thermodynamic investigation of amino acids in ionic liquid solutions. Journal of Chemical & Engineering Data, 60(8), 2442-2448.
Zhang, L., Wang, L., Kao, Y. T., Qiu, W., Yang, Y., Okobiah, O. and Zhong, D. (2009). Mapping hydration dynamics around a protein surface. Proceedings of the National Academy of Sciences, 104(47), 18461-18466.
Zhang, Y. and Cremer, P. S. (2009). The inverse and direct Hofmeister series for lysozyme. Proceedings of the National Academy of Sciences, 106(36), 15249-15253.
Downloads
-
Download PDF
Abstract Views: 8, 
Download PDF: 14
Published
How to Cite
Issue
Section
License
Copyright (c) 2026 Inventum Biologicum: An International Journal of Biological Research
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
