Crystal structure of L-N-acetylhistidine monohydrate: an open and closed case.

L-N-Acetylhistidine crystallizes from aqueous solution as the monohydrate. The crystals are triclinic, space group P1, with two formula units per cell. The structural solution was accomplished by direct methods. The two independent molecules have very different conformations, one open and one closed. These two conformations are compared with those found in other histidine structures.

Platinum interactions with nucleic acids: insights from model compounds.

A systematic review of the molecular structures of a large number of platinum(II) complexes with purine and pyrimidine bases and their nucleosides and nucleotides is presented. From these studies it is evident that the endocyclic nitrogen donor atoms of the heterocyclic purine and pyrimidine bases are dominant metal binding sites for Pt(II). Secondary interactions involving the exocyclic functional groups of the bases and the phosphate moiety of nucleotides are also noted. For Pt(II) complexes containing two adjacent (cis) bases, it is further indicated that intracomplex and intercomplex base-base interactions are of particular importance, giving rise in some cases to discontinuous helical arrays of Pt(II) complexes. These helical arrays may provide some insights into platinized-DNA polymers. Attention is also given to polynuclear species which are models for the family of mixed-valent platinum-pyrimidine blues. Finally, an attempt is made to extend the results of small molecule studies to give insights into the general area of Pt(II)-DNA chemistry and, in particular, the mode of action of the active anti-neoplastic agent cisPt.

Conformational properties of the osmium tetraoxide bispyridine ester of 1-methylthymine and a comment on the linearity of the trans O=Os=O group.

The preparation and crystal and molecular structure of the osmium tetraoxide bispyridine ester of 1-methylthymine are reported. The complex crystallizes in the triclinic system, space group P1, with a = 11.493(6)A, b = 16.655(7)A, c = 6.082(2)A, alpha = 92.07(3) degrees, beta = 90.58(3) degrees, gamma = 71.36(4) degrees, V = 1102.4 A3, Dm = 1.85(1) g cm-3, DC = 1.84 g cm-3. The unit cell contains 2 osmium tetraoxide bispyridine esters of 1-methylthymine, 2 waters of crystallization and 1 disordered pyridine of solvation. Intensities for 3814 independent reflections were collected by counter methods. The structure was solved by standard heavy-atom techniques and has been refined by full-matrix least squares, based on F, to a final R value of 0.065. The osmium complex binds as a cis osmate ester to the C(5)-C(6) bond of the methylated pyrimidine in a fashion which is expected to be similar to the binding of the complex to thymidine residues in nucleic acids. The conformation of the 1-methylthymine ester is that of a half chair with C(6) showing a substantial deviation, 0.55 A, from the best mean plane of the thymine moiety. The primary coordination sphere about the Os(VI) atom is completed by 2 axial Os=O bonds and the binding of the 2 pyridine ligands in cis positions in the equatorial plane containing the ester linkages. The O=Os=O group is substantially nonlinear, 164.0(5) degrees, and this nonlinearity is attributed to intracomplex electronic effects.