Peptide-Peptide Interactions in Water and Concentrated Urea Solutions. Review

A review is presented on some recent developments in the thermodynamics of aqueous solutions of organic substances, that can be considered as models of the repeating units of naturally occurring polypeptides and proteins. The attention is firstly focused on the solute-solvent interactions as basis to understand some aspects of the solute-solute interactions. The solvent in fact, especially in dilute solutions, seems to take active part in these interactions. All these poorly specific interactions, as are repeated for each aminoacid residue, must be considered in the conformational treatments of the stability of proteins. Preliminary interesting data are also reported, concerning model peptide-model peptide and other interactions in concentrated aqueous solution of urea, that is a usual denaturing medium for proteins and biopolymers. The unexpected and stimulating results suggest that, in this solvent, the hydrophilic interactions are screened, probably because polar groups are preferentially solvated by urea. Moreover the highly polar urea-water mixtures seem still to exert a kind of "lipophobic" effect against the alkylic chains of the considered solutes.