Cryst. Growth Des., 2009, 9 (9), pp 4051–4059

Solid-State NMR and X-ray Diffraction Study of Structure and Dynamics of Dihydrate and Anhydrous Form of Tyr-Ala-Phe
Katarzyna Trzeciak-Karlikowska, Anna Bujacz, Agata Jeziorna, Włodzimierz Ciesielski†, Grzegorz D. Bujacz, Jarosław Gajda†, Danuta Pentak and Marek J. Potrzebowski*

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 shift tensor (CST) parameters obtained by a two-dimensional PASS experiment have revealed a dramatic difference in the molecular motion of both modifications. 13C T1 relaxation times have provided further evidence confirming distinct molecular dynamics. The attempt to understand the role of the stereochemistry of Ala residue in opioid peptide sequences in relation to intramolecular interactions and preorganization mechanisms is presented.