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

Abstract

The zwitterionic solvation behavior of a series of the homologous a-amino acids glycine (Gly), DL-alanine (Ala), DL-a-amino butyric acids (Aba) and DL-nor-valine (Val), in water and in aqueous mixtures of 2-methoxyethanol, have been studied at equidistant temperature intervals in the range of 288.15-308.15 K, using the solubility method. The solubility data were analyzed according to the 'formol titrimetric' process. Standard Gibbs energies DG 0 t ðiÞ and entropies DS 0 t ðiÞ of transfer were calculated and are discussed. The observed DG 0 t ðiÞ and TDS 0 t ðiÞ versus composition profiles are complicated because of the various interaction effects. The chemical effects of the transfer Gibbs energies DG 0 t;ch ðiÞ and entropies of transfer TDS 0 t;ch ðiÞ have been obtained after elimination of the cavity effect, estimated by the scaled particle theory and dipole-dipole interaction effects, calculated by use of the Keesom orientation expression. The chemical contributions to transfer energetics of homologous a-amino acids are guided by the combined effects of increased dispersion interaction, basicity and decreased acidity, hydrogen bonding effects and hydrophilic hydration of aqueous 2-methoxy ethanol as compared to that of reference solvent, water. In this context the solvating characters of protic ethylene glycol are also referred to for comparison.

Solvation Descriptors for Zwitterionic α-Aminoacids; Estimation of Water–Solvent Partition Coefficients, Solubilities, and Hydrogen-Bond Acidity and Hydrogen-Bond Basicity

“…There is less data for α-aminobutanoic acid, but log P values into wet octan-1-ol 2 and wet butan-1-ol are available, 32 and solubilities in water, 45,46,49,50 organic solvents, 41,42,44,45 and water–ethanol 37 mixtures have been determined for dl -α-aminobutanoic acid. Values of log C and derived values of log P are in Table 8, the latter using a value of 0.333 for log C w for water.…”

“…Values of log P from water to wet butan-1-ol and wet octan-1-ol are known for norvaline, 2,32 and solubilities of dl -norvaline are available in water, log C w = −0.168, 44,45 and in a limited number of organic solvents, 41,42,44−46 as shown in Table 9. Wang et al 51 have determined solubilities of l -norvaline in methanol, ethanol, and their aqueous mixture but not in water itself.…”

“…log P values for partition to wet octan-1-ol (−2.26) and to wet butan-1-ol (−1.14) are known, 2,32 and solubilities are available in water, organic solvents, 34,35,37,43 water–methanol, 34,36,45 and water–ethanol mixtures. 37,53 The solubilities of l -valine and dl -valine differ somewhat.…”

Electrolytic Effect on the Solubility and Solvation Thermodynamics of l-Serine and l-Isoleucine in Aqueous Media

“…Amino acids have been important not only in the biological ground but also in various fields of industry like chemical, food, pharmaceutical, foundation, and eco-friendly plastics for a long time. − Information about the solubility of protein building units, that is, amino acids in various cosolvent mixtures in the presence and absence of electrolytes, is noteworthy for researchers in the pharmaceutical field as this is involved in drug purification, preformulation analysis, and design of pharmaceutical dosage. , Different thermodynamic parameters like free energy are related to the solubilities of these molecules. Temperature plays a crucial role in characterizing the interaction between ions and small molecules with biomolecules in the experimental solution. − A lot of studies on amino acids have established that their solubilities and solvation thermodynamics determine their biochemical role in animal metabolism. − In many cases, it has been seen that thermodynamic parameters were very much helpful in characterizing the conformational changes of biomacromolecules such as proteins. , With the addition of electrolytes in the solution of these molecules, the chemical reactivity and zwitterionic characters have been seen to direct other biophysical roles such as protein folding and unfolding. − Otherwise, amino acids are usually used as model compounds for more complex molecules like proteins. However, a more attentive study of the electrolytic effect on amino acid solution is still enviable to expose the molecular type of interaction between electrolyte ions and protein functional groups. , That is why in this study, we started a project regarding the solubility and solvation thermodynamics of some amino acids in aqueous electrolyte solutions.…”