Theoretical Thermodynamic Study of Solvent Effects on Serine and Threonine Amino Acids at Different Temperatures

Document Type: Research Paper

Author

Chemistry Department, Faculty of Science, Arak Branch, Islamic Azad University, P.O. Box: 38135-567, Arak, Iran

Abstract

The thermodynamic functions such as enthalpy (H), Gibbs free energy (G) and entropy (S) of Serine
and Threonine amino acids were theoretically studied at different condition (solvents and
temperatures) by using Gussian o3, software. First, the structural optimization of isolated Serine and
Threonine were done in the gas phase by using the Hartree-Fock (HF) level of theory with 3-21G, 6-
31G and 6-311G basis sets. Moreover, vibrational frequencies were calculated in gas phase on the
optimized geometries at the same level of theory to obtain enthalpy (H) Gibbs free energy (G) and
entropy (S) at 7 different temperatures such as (25, 27, 29, 31, 33, 35 and 37°C).Then, the solvent
effects are taken into via the self-consistent reaction field (SCRF=PCM) model. Therefore, all of the
calculations were repeated in various solvents (Water, Methanol and Ethanol) and 7 different
temperatures (25, 27, 29, 31, 33, 35 and 37°C). Thermodynamically analysis shows the relative
enthalpy changes (H) Gibbs free energy changes (G) are negative values but the entropy changes
(S) are positive values for Serine and Threonine molecules. Also, the results shows, with increasing
dielectric constant of solvent and increasing of temperature the stability of considered molecules
increases.

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