Lack of water transport by amino acid side chains or peptides entering a nonpolar environment.

Water has been reported to enter cyclohexane in association with 3-methylindole, a model compound representing the side chain of tryptophan. Entrainment of water would cloud the interpretation of measured partition coefficients as a simple index of hydrophobicity. NMR and isotope-exchange experiments indicate that the reported entrainment of water resulted from unrecognized exchange of 3H from water into the -NH- group of the indole ring. A more detailed analysis shows that no significant amounts of excess water (less than 0.1 molecule/molecule of solute) enter cyclohexane with molecules representing the side chains of tryptophan, phenylalanine, threonine, lysine, or the peptide bond itself.