The structure of [D‐Hyi², L‐Hyi⁴]meso‐valinomycin revealed by X‐Ray analysis

Abstract

Direct x-ray analysis has been used to determine the crystal structure of [D-Hyi2, L-Hyi4]meso-valinomycin (cyclo[-D-Val-D-Hyi-L-Val-L-Hyi-(D-Val-L-Hyi-L-Val-D-+ ++Hyi)2-], C60H102N6O18), which crystallized from acetone with two solvent molecules. The crystals are trigonal, space group P32, number of molecules per unit cell Z = 3, cell parameters a = b = 15.2085 (8) A, c = 29.3250 (9) A, gamma = 120 degrees. The standard (R) and weighted (Rw) reliability factors after refinement of the atomic coordinates for C, N, and O atoms in the anisotropic thermal motion approximation, allowing for isotropic H atom contributions, were 0.070 and 0.082, respectively. The molecule adopts a distorted bracelet structure which is stabilized by six N-H ... O = C 4----1 type intramolecular hydrogen bonds. The side chains predominantly occupy external pseudoaxial positions relative to the cylindrical axis of the molecule. In contrast to meso-valinomycin, only four of the six Val carbonyl oxygen atoms are directed inwards to form a coordination centre for the molecule, and the carbonyl oxygen atoms of residues D-Val1 and L-Val3 are twisted outward and point away from the centre of the molecule. Although the analogue has a partially formed ion-binding center, it is inaccessible because the hydrophobic isopropyl groups of the D-Hyi2 and L-Hyi4 residues screen the molecular cavity on both sides.

Leaf Surface Sesquiterpene Alcohols of the Potato (Solanum tuberosum) and Their Influence on Colorado Beetle (Leptinotarsa decemlineata Say) Feeding

“…We therefore decided to separate this compound from L. palustre in order to compare the chromatographic and spectroscopic data with that of potato sesquiterpene alcohol I. The molecular structure of ledol from the essential oil of L. palustre was elucidated by X-ray analysis (10), so its stereochemistry is known.…”

Ab initio direct methods: practical advice for getting beyond the first 300 atoms

“…atoms, Pletnev, Mikhailova, Ivanov, Langs, Grochulski & Duax, 1991) is chosen to clarify further the nature of these special kinds of triples. This structure is quite unusual in that the two strongest triples, those with the largest A values, actually represent an inconsistent pair, as is indicated in Table 5.…”

Frequency statistical method for evaluating cosine invariants of three-phase relationships

“…These structures included ILED, C6oH~o2N60~8, P21212~, N = 84 (Pletnev, Galitskii, Ivanov, Smith, Weeks & Duax, 1980); ACE, C6oHlo2N60~8.2C3H60, P32, N=92 (Pletnev, Mikhailova, Ivanov, Langs, Grochulski & Duax, 1991); ENKA, C72H9oN6018 , P1, N =96 (Smith & Kristenansky, 1991); HEXIL, C8oH136N8024.14H20, P212121, N=126 (Pletnev, Ivanov, Langs, Strong & Duax, 1992) and GRAMA, C198H28oNa0034.15C2HsOH, …”