SOLVATION STATE OF THE TYR SIDE-CHAIN IN PEPTIDES - AN FT-IR AND O-17 NMR APPROACH

Detailed studies of the O-17 NMR chemical shifts of the COH group of p-cresol and tyrosine derivatives as a function of pH and in a variety of solvents revealed an unusually large titration shift upon the deprotonation of the phenol group and a very small chemical shift variation as a function of solvent hydrogen-bonding ability. Similarly the nu(CO) stretching frequencies exhibit a very small variation as a function of solvent hydrogen-bonding ability, and discrete hydrogen-bonded species could not be identified. In contrast, the in-plane COH bending frequencies of these compounds have been shown to be very sensitive to hydrogen-bond interactions, and discrete hydrogen-bonded species could be identified. The applicability of this novel methodology to peptide hormones is demonstrated in the case of Leu-enkephalin in aqueous solution.