theoretical thermodynamic study of solvent effects on serine and threonine amino acids at different temperatures

the thermodynamic functions such as enthalpy (h), gibbs free energy (g) and entropy (s) of serineand threonine amino acids were theoretically studied at different condition (solvents andtemperatures) by using gussian o3, software. first, the structural optimization of isolated serine andthreonine 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 theoptimized geometries at the same level of theory to obtain enthalpy (h) gibbs free energy (g) andentropy (s) at 7 different temperatures such as (25, 27, 29, 31, 33, 35 and 37°c).then, the solventeffects are taken into via the self-consistent reaction field (scrf=pcm) model. therefore, all of thecalculations were repeated in various solvents (water, methanol and ethanol) and 7 differenttemperatures (25, 27, 29, 31, 33, 35 and 37°c). thermodynamically analysis shows the relativeenthalpy 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 increasingdielectric constant of solvent and increasing of temperature the stability of considered moleculesincreases.