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Various Conformations (various + conformation)

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Chemistry	80%

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Coordination Chemistry of Conformation-Flexible 1,2,3,4,5,6-Cyclohexanehexacarboxylate: Trapping Various Conformations in Metal,Organic Frameworks

CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2008
Jing Wang
Abstract To study the conformations of 1,2,3,4,5,6-cyclohexanehexacarboxylic acid (H6L), eleven new coordination polymers have been isolated from hydrothermal reactions of different metal salts with 1e,2a,3e,4a,5e,6a -cyclohexanehexacarboxylic acid (3e+3a, H6LI) and characterized. They are [Cd12(,6 - LII)(,10 - LII)3(,-H2O)6(H2O)6],16.5,H2O (1), Na12[Cd6(,6 - LII)(,6 - LIII)3],27,H2O (2), [Cd3(,13 - LII)(,-H2O)] (3), [Cd3(,6 - LIII)(2,2,-bpy)3(H2O)3],2,H2O (4), [Cd4(,4 - LVI)2(4,4,-Hbpy)4(4,4,-bpy)2(H2O)4],9.5,H2O (5), [Cd2(,6 - LII)(4,4,-Hbpy)2(H2O)10],5,H2O (6), [Cd3(,11 - LVI)(H2O)3] (7), [M3(,9 - LII)(H2O)6] (M=Mn (8), Fe (9), and Ni (10)), and [Ni4(OH)2(,10 - LII)(4,4,-bpy)(H2O)4],6,H2O (11). Three new conformations of 1,2,3,4,5,6-cyclohexanehexacarboxylate, 6e (LII), 4e+2a (LIII) and 5e+1a (LVI), have been derived from the conformational conversions of LI and trapped in these complexes by controlling the conditions of the hydrothermal systems. Complexes 1 and 2 have three-dimensional (3D) coordination frameworks with nanoscale cages and are obtained at relatively low temperatures. A quarter of the LI ligands undergo a conformational transformation into LII while the others are transformed into LIII in the presence of NaOH in 2, while all of the LI are transformed into LII in the absence of NaOH in 1. Complex 3 has a 3D condensed coordination framework, which was obtained under similar reaction conditions as 1, but at a higher temperature. The addition of 2,2,-bipyridine (2,2,-bpy) or 4,4,-bipyridine (4,4,-bpy) to the hydrothermal system as an auxiliary ligand also induces the conformational transformation of H6LI. A new LVI conformation has been trapped in complexes 4,7 under different conditions. Complex 4 has a 3D microporous supramolecular network constructed from a 2D LIII -bridged coordination layer structure by ,-, interactions between the chelating 2,2,-bpy ligands. Complexes 5,7 have different frameworks with LII/LVI conformations, which were prepared by using different amounts of 4,4,-bpy under similar synthetic conditions. Both 5 and 7 are 3D coordination frameworks involving the LVI ligands, while 6 has a 3D microporous supramolecular network constructed from a 2D LII -bridged coordination layer structure by interlayer N4,4,-HbpyH,,,O(LII) hydrogen bonds. 3D coordination frameworks 8,11 have been obtained from the H6LI ligand and the paramagnetic metal ions MnII, FeII, and NiII, and their magnetic properties have been studied. Of particular interest to us is that two copper coordination polymers of the formulae [{CuII2(,4 - LII)(H2O)4}{CuI2(4,4,-bpy)2}] (12,,) and [CuII(Hbtc)(4,4,-bpy)(H2O)],3,H2O (H3btc=1,3,5-benzenetricarboxylic acid) (12,,) resulted from the same one-pot hydrothermal reaction of Cu(NO3)2, H6LI, 4,4,-bpy, and NaOH. The Hbtc2, ligand in 12,, was formed by the in situ decarboxylation of H6LI. The observed decarboxylation of the H6LI ligand to H3btc may serve as a helpful indicator in studying the conformational transformation mechanism between H6LI and LII,VI. Trapping various conformations in metal-organic structures may be helpful for the stabilization and separation of various conformations of the H6L ligand. [source]

Model peptide-based system used for the investigation of metal ions binding to histidine-containing polypeptides

BIOPOLYMERS, Issue 6 2010
Manuela Murariu
Abstract The reaction of histidine-containing polypeptides with toxic and essential metals and the molecular mechanism of complexation has yet to be determined, particularly with respect to the conformational changes of the interacting macromolecules. Therefore, a system of oligopeptides containing histidine residues in various positions of Ala or Gly sequences has been designed and used in heavy metal comparatively binding experiments. The role of spacing residues (Gly and Ala repeats) in selecting the various conformations was investigated. The newly synthesized peptides and metal ion adducts have been characterized by Fourier transform infrared spectroscopy (FTIR) as well as electrospray ion trap mass spectrometry (ESI,MS) and circular dichroism (CD). The analysis of CD-spectra of the four peptides in water revealed that the secondary structure depends much on the position of each amino acid in the peptide backbone. Our peptides system reveals various binding mechanisms of metal ions to peptides depending on the position of histidine residue and the corresponding conformations of Ala or Gly sequences. Biological and medical consequences of conformational changes of metal-bound peptides are further discussed. Thus, the binding of heavy metals to four peptides may serve as a model system with respect to the conformational consequences of the metal addition on the amino acid repeats situated in prion protein. © 2010 Wiley Periodicals, Inc. Biopolymers 93:497,508, 2010. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]

Coordination Chemistry of Conformation-Flexible 1,2,3,4,5,6-Cyclohexanehexacarboxylate: Trapping Various Conformations in Metal,Organic Frameworks

ILLUMINATING THE STRUCTURE AND FUNCTION OF CYS-LOOP RECEPTORS

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 10 2008
Stephan A Pless
SUMMARY 1Cys-loop receptors are an important class of ligand-gated ion channels. They mediate fast synaptic neurotransmission, are implicated in various ,channelopathies' and are important pharmacological targets. Recent progress in X-ray crystallography and electron microscopy has provided a considerable insight into the structure of Cys-loop receptors. However, data from these experiments only provide ,snapshots' of the proteins under investigation. They cannot provide information about the various conformations the protein adopts during transition from the closed to the open and desensitized states. 2Voltage-clamp fluorometry helps overcome this problem by simultaneously monitoring movements at the channel gate (through changes in current) and conformational rearrangements in a domain of interest (through changes in fluorescence) in real time. Thus, the technique can provide information on both transitional and steady state conformations and serves as a real time correlate of the channel structure and its function. 3Voltage-clamp fluorometry experiments on Cys-loop receptors have yielded a large body of data concerning the mechanisms by which agonists, antagonists and modulators act on these receptors. They have shed new light on the conformational mobility of both the ligand-binding and the transmembrane domain of Cys-loop receptors. [source]