Solid-State NMR and X-ray Diffraction Study of Structure and Dynamics of Dihydrate and Anhydrous Form of Tyr-Ala-Phe

Tyr-d-Ala-Phe is a “message sequence” of naturally occurring opioid peptides, deltorphin I (Tyr-d-Ala-Phe-Asp-Val-Val-Gly-NH2), deltorphin II (Tyr-d-Ala-Phe-Glu-Val-Val-Gly-NH2), and dermorphin (Tyr-d-Ala-Phe-Gly-Tyr-Pro-Ser-NH2). Analogous heptapeptides containing l-alanine instead of d-alanine are not biologically active. In a previous paper (J. Phys. Chem. B 2004, 108 (14), 4535−4545), we reported X-ray and NMR data for Tyr-d-Ala-Phe. In the current report, we present structural studies of Tyr-Ala-Phe, a “false message sequence” of opioid peptides. It has been found that Tyr-Ala-Phe crystallizes in two forms, as anhydrate (Form I) and dihydrate (Form II). Crystal and molecular structure of both forms was established by means of low-temperature X-ray measurements. Form I is orthorhombic with space group P212121, while II is hexagonal with space group P65. Solid-state NMR was employed to study the structure and molecular dynamics of I and II. Analysis of cross-polarization buildup curves and 13C chemical...