Transfer energetics of a series of homologous α-amino acids and hence of CH2 group—a possible probe for the solvent effect on hydrophobic hydration and the three-dimensional-structuredness of aqueous cosolvents

Chemical Transfer Energetics of a Series of Homologous α-Amino Acids in Quasi-Aprotic 2-Methoxyethanol–Water Mixtures

“…Here the standard deviations (s f ) were estimated for all solubility values to characterize the precision and are shown in Table 1. Here it is important to note that the most of the solubility data of the experimental amino acids in pure water corroborate excellently with the literature data that are summarized in Table S1 [12,19,20,[24][25][26][27][28][29][30][31][32].…”

“…There are several methods [38][39][40][41][42][43] for the determination of the activity coefficients that involve various theoretical aspects and assumptions. But for simplicity, in many earlier studies the activity coefficient was assumed to be unity [11,12,15,17,[19][20][21][22][23][24]44] during the determination of the Gibbs energy of several amino acids in solution.…”

“…Moreover, our main concern in the current study is to determine and characterize the total transfer Gibbs energy (DG 0 t ðiÞ) in such binary solvent mixtures; therefore, we also have assumed here that the contribution of activity coefficient is negligible [11,12,15,17,[19][20][21][22][23][24]44]. DG 0 t ðiÞ is also related as DG 0 t ðiÞ ¼ DG 0 s ðiÞ À DG 0 R ðiÞ, where DG 0 t ðiÞ, DG 0 s ðiÞ and DG 0 R ðiÞ are the Gibbs energies of the amino acid solutions in co-solvent (aqueous ME) and reference solvent, water, respectively.…”

“…The required diameters of glycine, alanine, DL-a-amino-butyric acid and DL-nor-valine are 5.64, 6.16, 6.58 and 6.92 Å , respectively, as given in Refs. [17,19]. Dipole moment values of a-amino acids are 15.7 D for glycine, 15.9 D for DL-alanine and 16 D for DL-a-amino-butyric acid and DL-nor-valine [35] used as subscript with different parameters to identify the involvement with co-solvent and reference solvent, respectively).…”

“…A known mass (of about 0.2-0.3 g) of filtered saturated solution was transferred to a dry conical flask from solution thermostated at all experimental temperatures. The saturated solubility analyses of Gly, Ala, Aba and Val were made by the 'formol titrimetric method' [4,11,12,[19][20][21][22][23] using freshly standardized (0.05 molÁL -1 ) NaOH (GR, E Merck; [99.0 %) solution and 1 % alcoholic phenolphthalein solution as indicator. The solubilities were measured at the natural pHs of the solutions.…”