The Solubility and Conformation of Protected Tri- to Heptapeptides in a Variety of Organic Solvents and the Classification of Organic Solvents Based on Their Solvating Potential for Protected Peptides

Abstract The solubility in a variety of organic solvents was examined for 75 kinds of protected tri- to heptapeptide fragments of E. coli ribosomal protein L7/L12. The organic solvents examined were classified into six groups mainly by considering their solvating potential and supplementarily by using their acceptor number (AN) and donor number (DN). The result of the classification of the organic solvents was practically explained by the DN and AN of the organic solvents, indicating that the electron-donating or -accepting ability of organic solvents is much more important for the solvation of protected peptides than their ability to form van der Waals interactions. Nevertheless, the solvation mechanism of protected peptides in organic solvents could be explained by two types of intermolecular interactions, namely, intermolecular hydrogen bonding and van der Waals interactions. The <SPβ> values of protected peptieds, difined in a previous paper, properly reflected their β-sheet-structure stability in a variety of organic solvents regardless of their amino acid sequence. The solubility of protected peptides in organic solvents was also strongly related to their <SPβ> values. In fact, peptides having a low <SPβ> value were easily soluble in various organic solvents and had an unordered structure in solution.