Search results for "conformation"
showing 10 items of 1414 documents
2019
Molecular complexes between glycolic acid and nitrogen were studied in a low-temperature argon matrix with FTIR spectroscopy, and supported by MP2 and BLYPD3 calculations. The calculations indicate 11 and 10 stable complex structures at the MP2 and BLYPD3 levels of theories, respectively. However, only one hydrogen-bonded complex structure involving the most stable SSC conformer of glycolic acid was found experimentally, where the nitrogen molecule is bound with the carboxylic OH group of the SSC conformer. The complex shows a rich site structure variation upon deposition of the matrix in different temperatures and upon annealing experiments, which provide interesting prospects for site-sel…
Über polystannane
1987
Abstract The three compounds Ph4Sn2(X3CCO2)2 were synthesized from Ph2SnH2 and X3CCOOH (X = H, Cl) or by cleavage of two phenyl groups in Ph6Sn2 with Stoichiometric amounts of X3CCOOH (X = Cl, F). The crystal structures (R = 0.041, 0.030, 0.058) show that the Ph4Sn2 units are bridged by two isobidentate acetates resulting in five-coordinated tin atoms. Five crystallographically independent centrosymmetric molecules form three distinct conformers. Bonding parameters (compared with Ph6Sn2): distances d(SnSn) 269, 271, 272, 277 pm; NMR couplings (CDCl3 solution) 1J(SnSn) 16870, 9443, 12915, 4480 Hz; stretching vibrations ν(SnSn) 152, 155, 157, 159 cm−. The ion pairs [Ph4Sn2]2+ [(X3CCO2)2]2−…
Application of Imprinted Synthetic Polymers in Binding Assay Development
2000
The first part of the review describes a method for the synthesis of molecularly imprinted polymers for use in binding assays. The method considers the many factors involved that affect the recognition properties of the materials and describes an approach to screening and optimization of these factors. The second part describes the development of binding assays using such polymers. This includes the use of different labels, the effect of solvent and buffer, the scale of the assay (amount of solid polymer), and how these influence the quality of the assay in terms of sensitivity, selectivity, and speed of analysis.
Solid-state dinuclear-to-trinuclear conversion in an oxalato-bridged chromium(III)-cobalt(II) complex as a new route toward single-molecule magnets.
2011
A novel bis(oxalato)chromium(III) salt of a ferromagnetically coupled, oxalato-bridged dinuclear chromium(III)-cobalt(II) complex of formula [CrL(ox)(2)CoL'(H(2)O)(2)][CrL(ox)(2)]·4H(2)O (1) has been self-assembled in solution using different aromatic α,α'-diimines as blocking ligands, such as 2,2'-bipyridine (L = bpy) and 2,9-dimethyl-1,10-phenanthroline (L' = Me(2)phen). Thermal dehydration of 1 leads to an intriguing solid-state reaction between the S = 3/2 Cr(III) anions and the S = 3 Cr(III)Co(II) cations to give a ferromagnetically coupled, oxalato-bridged trinuclear chromium(III)-cobalt(II) complex of formula {[CrL(ox)(2)](2)CoL'} (2). Complex 2 possesses a moderately anisotropic S =…
Stabilization of an ?-helical conformation in an isolated hexapeptide inhibitor of calmodulin
2001
The conformational properties of two hexapeptides, Ac-LWRILW-NH(2) and its D-amino acid counterpart Ac-lwrilw-NH(2), identified as calmodulin inhibitors using mixture-based synthetic combinatorial library approaches, have been characterised by NMR and CD spectroscopy. The peptides fold into an alpha-helical conformation in aqueous solution. The observed short- and medium-range nuclear Overhauser effects were consistent with the formation of an alpha-helical structure and a reasonably well-defined set of structures was obtained by using restraints from the NMR data in simulated annealing calculations. Analysis of glycine-substitution analogues demonstrated that all the amino acids that make …
Conformational characteristics of homo-oligopeptides of O-benzyl-L-tyrosine+
1983
Conformational studies of X[-L-Tyr(Bzl)-]n-series bound to polyethyleneglycol (X = H2, Nps; n = 3-8) in the solid state and in solvents of different polarities and capabilities of forming hydrogen bonds are reported. By using i.r. absorption, the occurrence of the beta-structure in the higher oligomers in the solid state was established. By means of i.r. absorption and CD the onset of that ordered conformation in solution was assessed as a function of chain length. The effects induced by the presence of the N-protecting group and added base, and by changing the nature of solvent on the conformational preferences of the [-L-Tyr(Bzl)-]n homo-peptides were also examined. The 2-nitrophenylsulph…
Conformational investigation of α,β-dehydropeptides VII*. Conformation of Ac-Pro-ΔAla-NHCH3 and Ac-Pro-(E)-ΔAbu-NHCH3: comparison with (Z)-substitute…
2009
The crystal structure and solution conformation of Ac-Pro-deltaAla-NHCH3 and the solution conformation of Ac-Pro-(E)-deltaAbu-NHCH3 were investigated by X-ray diffraction method and NMR, FTIR and CD spectroscopies. Ac-Pro-deltaAla-NHCH3 adopts an extended-coil conformation in the crystalline state, with all-trans peptide bonds and the deltaAla residue being in a C5 form, phi(1)=-71.4(4), psi(1)=-16.8(4), phi(2)= -178.4(3) and psi(2)= 172.4(3) degrees. In inert solvents the peptide also assumes the C5 conformation, but a gamma-turn on the Pro residue cannot be ruled out. In these solvents Ac-Pro-(E)-deltaAbu-NHCH3 accommodates a beta(II)-turn, but a minor conformer with a nearly planar dispo…
Structure and function of ferredoxin-NADP+-oxidoreductase
1987
The redox-enzyme ferredoxin-NADP-oxidoreductase has been shown to be activated by light and inactivated in the dark. This review will summarize recent data concerning the biochemical characterization of the enzyme compared to its in-vivo activation. Further-more the mechanism of this activation process is discussed as a conformational change caused by the light-driven proton gradient.
Weak non-covalent interactions control the relative molecular orientation in the crystals of N-pentafluorobenzyl aniline derivatives
2010
The crystal structures of N-pentafluorobenzyl aniline derivatives are controlled by versatile aromatic–aromatic interactions between the electron deficient and electron rich aromatics; the parent compound (1) possesses an L shape while protonation (2–5) induces a conformational change resulting in a planar arrangement of molecules which pack in layer type structures with different molecular orientations.
Twisting of the resorcinarene core due to solvent effects upon crystallization
2009
The effect of the crystallization conditions on the conformation of the tetramethoxy resorcinarene skeleton was investigated in acetone solutions, to which was added a second component (less favorable solvent or salt) to promote crystallization. The resorcinarene core was found to adopt three different conformations: crown (I), a pinched crown (II) and a twisted pinched crown (III). In addition, the flexibility of the resorcinarene core was compared with a tetramethoxy resorcinarene derivative, resorcinarene bis-crown, which is in a fixed boat conformation.