Structure of Cyanoacetylhydrazones of Aldehydes and Ketones

1D ¹H and ^{1 3}C, and 2D ¹H NOESY NMR were used to establish that cyanoacetylhydrazones of aliphatic and aromatic aldehydes and ketones in CDCl₃ and (CD₃)₂SO solutions have a linear structure, exist as a mixture of geometric isomers by the C = N bond, and exhibit hindered amide rotation.     

De novo design of fibrils made of short alpha-helical coiled coil peptides.

BACKGROUND: The alpha-helical coiled coil structures formed by 25-50 residues long peptides are recognized as one of Nature's favorite ways of creating an oligomerization motif. Known de novo designed and natural coiled coils use the lateral dimension for oligomerization but not the axial one. Previous attempts to design alpha-helical peptides with a potential for axial growth led to fibrous aggregates which have an unexpectedly big and irregular thickness. These facts encouraged us to design a coiled coil peptide which self-assembles into soluble oligomers with a fixed lateral dimension and whose alpha-helices associate in a staggered manner and trigger axial growth of the coiled coil. Designing the coiled coil with a large number of subunits, we also pursue the practical goal of obtaining a valuable scaffold for the construction of multivalent fusion proteins. RESULTS: The designed 34-residue peptide self-assembles into long fibrils at slightly acid pH and into spherical aggregates at neutral pH. The fibrillogenesis is completely reversible upon pH change. The fibrils were characterized using circular dichroism spectroscopy, sedimentation diffusion, electron microscopy, differential scanning calorimetry and X-ray fiber diffraction. The peptide was deliberately engineered to adopt the structure of a five-stranded coiled coil rope with adjacent alpha-helices, staggered along the fibril axis. As shown experimentally, the most likely structure matches the predicted five-stranded arrangement. CONCLUSIONS: The fact that the peptide assembles in an expected fibril arrangement demonstrates the credibility of our conception of design. The discovery of a short peptide with fibril-forming ability and stimulus-sensitive behavior opens new opportunities for a number of applications.     

X-ray diffraction study of phase transitions in iron(II) trisnioximate hexadecylboronate clathrochelate complex

Crystals of the iron(II) nioximate hexadecylboronate clathrochelate complex—FeNx ₃(BHd)₂ [tris(μ-1,2-cyclohexanedionedioximato-O:O′)di-n-hexadecyldiborato(2?)-N,N′, N″,N?, N?,N″?]iron(II)—are investigated by differential scanning calorimetry and X-ray diffraction. Two structural phase transitions are revealed at T _cr1 = 290(3) K and T _cr2 = 190(3) K. The crystal structures of phases I, II, and III are determined by X-ray diffraction analysis at 303, 243, and 153 K, respectively. It is demonstrated that the I ? II phase transition is due to a change in the system of translations, and the II ? III phase transition is accompanied only by a jumpwise change in the unit cell parameters. The possible mechanisms of phase transitions are discussed in terms of geometry and molecular packing of FeNx ₃(BHd)₂ in all three phases.     

Crystal and molecular structure of 2-acetyl-4-phenyl-5-benzyl-piperidino-5H-1,3,4-selenadiazole

Lensovet Leningrad Technological Institute and A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, Moscow. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 2, pp. 180–182, March–April, 1992.