Studies on kyotorphin and d-kyotorphin in aqueous solution by Raman spectroscopy

Raman spectra of kyotorphin [l-Tyr–l-Arg] and d-Kyotorphin [l-Tyr–d-Arg] dipeptides in water and heavy water solutions are reported for the first time in the 1800–200 cm−1 range. Vibrational assignments have been made for many of the observed frequencies on the basis of group frequency considerations as well as comparison with accepted assignments for certain vibrational modes in the amino acid residues of the dipeptides. Hydrogen bonded state of the tyrosine phenoxyl group was found to change depending on the concentration, and H2O/D2O of the aqueous solutions of kyotorphin analogues. Investigation of the amide I and amide III bands of kyotorphin analogues indicates conformational alteration depending on either phases (solid or aqueous solution; in the case of KTP) or on deuteration of the solution (H2O/D2O; in the case of d-KTP).