Homotactic enthalpic pairwise interactions of four deoxynucleosides (dU, dC, dG, dT) in dimethylformamide (DMF)+water mixtures at 298.15K

Temperature Dependences and Enthalpic Discrimination of Homochiral Pairwise Interactions of Six α-Amino Acid Enantiomers in Pure Water

“…However, among various possible interaction configurations of two homochiral hydrated α-amino acid molecules, only the one formed between the opposite charges of zwitterions is hypothesized to be favorable and prevailing in aqueous solutions, resulting in the depression of the cooperativity of hydrophobic interaction. The possibility of detecting chiral recognition in solutions of small molecules by microcalorimetry has been our recent ongoing interest. − We have found that, when homochiral pairwise interaction occurs in aqueous solutions containing highly polar aprotic cosolvents like dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), a small but significant energetic difference between S–S and R–R (or L–L and D–D) enantiomeric pairs can be found, i.e., | h SS | > | h RR | or | h LL | > | h DD |. − In the present case, though the largest difference of h xx between L–L and D–D pairs of each α-amino acid is only up to 47 J·kg·mol –2 , and the existence of possible experimental errors cannot be ruled out completely, we still believe that the enthalpic discrimination (i.e., | h LL | > | h DD |) is a real phenomenon for the systems under study. The L–L pair is considered to be the more preferentially selected configuration than the D–D pair because of the best juxtaposition of hydrophobic or hydrophilic side-chains on L-α-carbons, in coordination with electrostatic interaction between the “heads” of α-amino acids.…”

“…As is well-known, the stability of biological macromolecules like proteins is controlled by various weak nonbonding interactions between α-amino acid residues and other biochemical components in aqueous solutions. − Homotactic or heterotactic enthalpic pairwise interaction coefficients ( h xx or h xy ) obtained from the framework of the McMillan–Mayer theory are particularly useful for understanding solute–solute and solute–solvent noncovalent interactions. , Over the past several decades, great efforts have been made by many research groups to gain insight into the thermodynamics of complex nonbonding interactions in biological model solution systems. − However, most of the studies have been carried out only at T = 298.15 K, and therefore the temperature dependences of h xx or h xy coefficients and the relevant mechanisms have remained unknown or not very clear, though some attempts have been made for this problem. − Considering that the first derivative of enthalpic pairwise interaction coefficient ( h 2 ) on temperature T ((∂ h 2 /∂ T ) p ) equals the second virial coefficient of isobaric heat capacity ( c p,2 ), and the latter seems to be more sensitive to the structural change of water in the hydration shell of solutes, it is of greater interest to investigate the temperature dependence of h 2 . Recently, we have paid much attention to the solvent and substituent effects on homotactic enthalpic pairwise interactions of small biochemical compounds in aqueous mixed solvents containing highly polar cosolvents like dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) at 298.15 K, and the phenomena of enthalpic discrimination in these systems has been explored. − In the present work, we have measured the dilution enthalpies of six enantiomers of typical α-amino acids (Scheme ) in pure water at different temperatures by isothermal titration calorimetry (ITC), and the temperature dependences and enthalpic discrimination of homochiral pairwise interactions are discussed mainly. We hope to gain insight into how the studied α-amino acids play key roles on the stability of proteins like collagens …”

Enthalpic pairwise self-interactions of urea and its four derivatives in (dimethylformamide + water) mixtures rich in water at T = 298.15 K

“…As x DMF increases, though the h 2 values of each compound increase monotonously, they exhibit different extents of response to solvent alteration. As is well known, partial dehydration of hydration sheaths makes positive contribution to h 2 [42]. The main factor affecting the trend of h 2 is attributed to structural alteration (reorganization) of (DMF + water) mixture, especially the reconstruction of solvation shells of solutes, which will lead to a considerable energetic effect and make a direct variation of h 2 coefficient [45].…”

“…In our previous works [41][42][43][44][45], dilution enthalpy of many kinds of biological small molecules in the (dimethylformamide (DMF) + water) mixtures have been determined using isothermal titration calorimetry (ITC), and enthalpic discrimination effects of chiral isomers (e.g. D-or L-a-amino acids) and position isomers (e.g.…”

A study on Volumetric and Viscometric Properties for the Mixtures of DMF and Other Alcohols from Temperatures ranges 303.15K to 323.15K

“…A DMF molecule can interact with an alkanol molecule by virtue of better hydrogen bond acceptor ability of its oxygen atom, resulting in structural and packing effects. Volumetric, viscometric and related thermodynamic properties for the mixtures containing DMF were recently reported in the literature [13][14][15][16][17][18][19][20].…”