Beta-Turn Conformations In Crystal-Structures Of Model Peptides Containing Alpha,Alpha-Di-N-Propylglycine And Alpha,Alpha-Di-N-Butylglycine

The crystal state conformations of three peptides containing the alpha, alpha-dialkylated residues, alpha,alpha-di-n-propylglycine (Dpg) and alpha,alpha-di-n-butylglycine (Dbg), have been established by x-ray diffraction. Boc-Ala-Dpg-Ala-OMe (I) and Boc-Ala-Dbg-Ala-OMe (III) adopt distorted type II beta-turn conformations with Ala (1) and Dpg/Dbg (2) as the corner residues. In both peptides the conformational angles at the Dxg residue (I: phi = 66.2 degrees, psi = 19.3 degrees; III: phi = 66.5 degrees, psi = 21.1 degrees) deviate appreciably from ideal values for the i + 2 residue in a type II beta-turn. In both peptides the observed (N...O) distances between the Boc CO and Ala(3) NH groups are far too long (I: 3.44 Angstrom; III: 3.63 Angstrom) for an intramolecular 4 --> 1 hydrogen bond. Boc-Ala-Dpg-Ala-NHMe (II) crystallizes with two independent molecules in the asymmetric unit. Both molecules IIA and IIB adopt consecutive beta-turn (type III-III in IIA and type III-I in IIB) or incipient 3(10)-helical structures, stabilized by two intramolecular 4 --> 1 hydrogen bonds. In all four molecules the bond angle N-C-alpha-C' (tau) at the Dxg residues are greater than or equal to 110 degrees. The observation of conformational angles in the helical region of phi,psi space at these residues is consistent with theoretical predictions.

NMR Investigations on Di- and Tri-Azanaphthalenes Oriented in Liquid Crystals

Proton NMR spectra of 1,3-diazanaphthalene and 1,2,4-triazanaphthalene have been investigated in the nematic phase of three liquid crystals. The spectral analysis provided direct dipole-dipole couplings which have been used to derive the molecular structure. Geometry of the phenyl ring in both the molecules deviates from the regular hexagonal structure. Signs of the order parameter of the largest magnitude are opposite in liquid crystals with positive diamagetic anisotropies.

Synthesis and Reactions of Binuclear Diolefin Rhodium(I) Compounds bridged by Nitrogen Heterocycles, Crystal Structure of Dichloro-Di-1,5-Cyclooctadiene(Mu-Pyrazine)-Dirhodium(I) [[Rh(1,5-C8h12)Cl]2(Mu-C4h4n2)]

Binuclear complexes of rhodium(I) of the type [(dien)(X)Rh(μ-N-N)Rh(X)(dien)] (dien = 1,5-cyclooctadiene or norbornadiene; N-N = pyrazine, 4,4′-bipyridine or Phenazine and X = Cl or Br) with bridging heterocycles have been isolated and their reactions with carbon monoxide, 2,2′-bipyridine and 1,10-phenanthroline investigated. The crystal structure of [(COD)(Cl)Rh(μ-pyrazine)Rh(Cl)(COD)] has been determined.

Structure-reactivity correlation in inclusion complexes: deoxycholic acid di-tert-butyl thioketone

Ultraviolet irradiation of crystalline molecular inclusion complexes of deoxycholic acid with di-tert-butyl thioketone results in no reaction. The structure of the above complex has been determined via X-ray diffraction. The absence of expected photoreactions. namely, photoreduction and photooxidation, is rationalized on the basis of the X-ray structure analysis of the complex.

Resonances, scattering theory, and rigged Hilbert spaces

The problem of decaying states and resonances is examined within the framework of scattering theory in a rigged Hilbert space formalism. The stationary free,''in,'' and ''out'' eigenvectors of formal scattering theory, which have a rigorous setting in rigged Hilbert space, are considered to be analytic functions of the energy eigenvalue. The value of these analytic functions at any point of regularity, real or complex, is an eigenvector with eigenvalue equal to the position of the point. The poles of the eigenvector families give origin to other eigenvectors of the Hamiltonian: the singularities of the ''out'' eigenvector family are the same as those of the continued S matrix, so that resonances are seen as eigenvectors of the Hamiltonian with eigenvalue equal to their location in the complex energy plane. Cauchy theorem then provides for expansions in terms of ''complete'' sets of eigenvectors with complex eigenvalues of the Hamiltonian. Applying such expansions to the survival amplitude of a decaying state, one finds that resonances give discrete contributions with purely exponential time behavior; the background is of course present, but explicitly separated. The resolvent of the Hamiltonian, restricted to the nuclear space appearing in the rigged Hilbert space, can be continued across the absolutely continuous spectrum; the singularities of the continuation are the same as those of the ''out'' eigenvectors. The free, ''in'' and ''out'' eigenvectors with complex eigenvalues and those corresponding to resonances can be approximated by physical vectors in the Hilbert space, as plane waves can. The need for having some further physical information in addition to the specification of the total Hamiltonian is apparent in the proposed framework. The formalism is applied to the Lee–Friedrichs model and to the scattering of a spinless particle by a local central potential. Journal of Mathematical Physics is copyrighted by The American Institute of Physics.

Hydrogen bonding with mono- and di-carbonyls

The electronic absorption and i.r. spectroscopic studies are reported for the hydrogen bonding systems involving alcohol and various ketones. It is shown that the hydrogen bonding abilities of ketones are determined by the extent of delocalization of the lone pair electrons in their non-bonding molecular orbitals. Evidence for the formation of very weak intermolecular hydrogen bonds between alcohol and the π-electron part of the dicarbonyls has also been presented from the i.r. studies in the 3400–3700 cm−1 region.

Iron(II, III) complexes with N, N'-DI(2-)Pyridyl Thiourea. Moumlssbauer and other spectroscopic studies

Several iron(II, III) complexes of N, N'-di(2-)pyridyl thiourea have been synthesized. The preparation of the complexes from iron(III) salts proceeds through a reduction of iron(III) to iron(II) followed by a subsequent reoxidation. The Moumlssbauer, electronic and infrared spectra of these complexes have been measured. The results are concordant with the coordination of pyridine nitrogens and thiocarbonyl sulfur yielding polymeric complexes. A variable temperature NMR study of the free ligand shows that two conformation are accessible for it in solution at subambient temperatures.

Complexes of rare earth perchlorates with di-2-pyridyl ketone

Abstract is not availabe.

Complexes of lanthanide perchlorates with N,N,N′,N′-tetramethyl-α-carboxamido-O-anisamide and N,N′-di-t-butyl-α-carboxamido-O-anisamide

A survey of the literature on lanthanide coordination compounds reveals that ligands involving ether oxygens as donor atoms have received very little attention [ 11. Only recently have the complexes of lanthanides with cyclic polyethers been characterized [l-3]. We report in this communication that interaction of rareearth perchlorates with two new ligands namely N,N,N’,N’-tetramethyl-u-carboxamido-Oanisamide (TMCA) and N,N’-di-t-butyl-crcarboxamido- 0-anisamide (DTBCA). The two ligands are potentially tridentate possessing two amide moieties and an ether linkage in between. The isolated complexes have been characterized by analysis, electrolytic conductance, infrared and electronic spectra. The ‘H and “C NMR spectra for the diamagnetic La3+ and Y3+ complexes are also discussed.

Unitary Processes with Independent Increments and Representations of Hilbert Tensor Algebras

The aim of this article is to characterize unitary increment process by a quantum stochastic integral representation on symmetric Fock space. Under certain assumptions we have proved its unitary equivalence to a Hudson-Parthasarathy flow.

An HI study of three long-tailed irregular galaxies in the cluster Abell 1367

We present the results on the distribution and kinematics of HI gas with higher sensitivity and in one case of higher spectral resolution as well than reported earlier, of three irregular galaxies CGCG 097073, 097079 and 097087 (UGC 06697) in the cluster Abell 1367. These galaxies are known to exhibit long (50 - 75 kpc) tails of radio continuum and optical emission lines (H alpha) pointing away from the cluster centre and arcs of starformation on the opposite sides of the tails, These features as well as the HI properties, with two of the galaxies (CGCG 097073 and 097079) exhibiting sharper gradients in HI intensity on the side of the tails, are consistent with the HI gas being affected by the ram pressure of the intracluster medium. However the HI emission in all the three galaxies extends to much smaller distances than the radio-continuum and H alpha tails, and are possibly still bound to the parent galaxies. Approximately 20 - 30 per cent of the HI mass is seen to accumulate on the downstream side due to the effects of ram pressure.

Conformation of di-n-propylglycine residues (Dpg) in peptides: crystal structures of a type I-turn forming tetrapeptide and an -helical tetradecapeptide

The crystal structures of two oligopeptides containing di-n-propylglycine (Dpg) residues, Boc-Gly-Dpg-Gly-Leu-OMe (1) and Boc-Val-Ala-Leu-Dpg-Val-Ala-Leu-Val-Ala-Leu-Dpg-Val-Ala-Leu-OMe (2) are presented. Peptide 1 adopts a type I-turn conformation with Dpg(2)-Gly(3) at the corner positions. The 14-residue peptide 2 crystallizes with two molecules in the asymmetric unit, both of which adopt -helical conformations stabilized by 11 successive 5 1 hydrogen bonds. In addition, a single 4 1 hydrogen bond is also observed at the N-terminus. All five Dpg residues adopt backbone torsion angles (, ) in the helical region of conformational space. Evaluation of the available structural data on Dpg peptides confirm the correlation between backbone bond angle NCC() and the observed backbone , values. For > 106° , helices are observed, while fully extended structures are characterized by < 106° . The mean values for extended and folded conformations for the Dpg residue are 103.6° ± 1.7° and 109.9° ± 2.6° , respectively.

Structural and spectral investigations on some new Ni(II) complexes of di-2-pyridyl ketone N(4)-phenylthiosemicarbazone

Ni(II)complexes(1-5)ofdi2pyridylketoneN(4)-phenylthiosemicarbazone (HL) have been synthesized and spectrochemically characterized. Elemental analyses revealed a NiL2 center dot 2H(2)O stoichiometry for compound 1. However, the single crystals isolated revealed a composition NiL, - 0.5(H,0)0.5(DMF). The compound crystallizes into a monoclinic lattice with the space group P-21/n. Complexes 2. 3 and 4 are observed to show a 1:1:1 ratio of metal: thioseicarbazone:gegenion, with the general formula NiLX center dot yH(2)O [X = NCS. Y = 2 for 2; X = Cl, Y = 3 for 3 and X = N-3, y = 4.5 for 4]. Compound 5 is a dimer with a metal:thiosemicarbazone:gegenion ratio of 2:2: 1. with the formula [Ni,L,(SO4)1 - 4H(2)O (c) 2007 Elsevier Ltd. All rights reserved.

Structural and spectral investigations on some new Ni(II) complexes of di-2-pyridyl ketone N(4)-phenylthiosemicarbazone

Ni(II) complexes (1-5) of di-2-pyridyl ketone N(4)-phenylthiosemicarbazone (HL) have been synthesized and spectrochemically characterized. Elemental analyses revealed a NiL2 center dot 2H(2)O stoichiometry for compound 1. However, the single crystals isolated revealed a composition NiL, - 0.5(H,0)0.5(DMF). The compound crystallizes into a monoclinic lattice with the space group P-21/n. Complexes 2. 3 and 4 are observed to show a 1:1:1 ratio of metal: thioseicarbazone:gegenion, with the general formula NiLX center dot yH(2)O [X = NCS. Y = 2 for 2; X = Cl, Y = 3 for 3 and X = N-3, y = 4.5 for 4]. Compound 5 is a dimer with a metal:thiosemicarbazone:gegenion ratio of 2:2: 1. with the formula [Ni,L,(SO4)1 - 4H(2)O (c) 2007 Elsevier Ltd. All rights reserved.