Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A unit cell in which three isomers are in an L configuration and one is in a D configuration is inherently asymmetrical. For LDLL mixtures of amino acids with identical chemical structures (apart from chirality), the inter- and intramolecular interactions observed from the 13C CP/MAS NMR spectra are even larger than those which have been observed with mixtures of diastereoisomers in the solid state. This occurs even though the chemical composition of these molecular clusters consists only of nearest neighbor enantiomers. Because D and L isomers have identical chemical shifts, changes in chemical shift and peak intensities of these asymmetrical solid mixtures cannot be unambiguously assigned to either the D or one of the L isomers. In LLDL mixtures of amino acids in which half is L isomers and the other half is DL isomers, the NMR spectra clearly depend upon which amino acid contains the D isomer. Any further structural interpretation of these molecular clusters is equivocal without assigning chemical shifts to the D isomer (or alternatively designated the R, [-] or [+] isomer). Both more rigorous mathematical analysis and new NMR experiments are required which link interactions at chiral centers with NMR spectra of LLDL mixtures in the solid state.
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PMID:13C CP/MAS of LDLL mixtures of amino acids. 781 39

The reaction of [Sn(NMe(2))(2)](2) (1) with 4 equiv of HOCH(2)CMe(3) (HONep) leads to the isolation of [Sn(ONep)(2)](infinity) (2). Each Sn atom is four coordinated with mu-ONep ligands bridging the metal centers; however, if the free electrons of the Sn(II) metal center are considered, each Sn center adopts a distorted trigonal bipyramidal (TBP) geometry. Through (119)Sn NMR experiments, the polymeric compound 2 was found to be disrupted into smaller oligomers in solution. Titration of 2 with H(2)O led to the identification of two unique hydrolysis products characterized by single-crystal X-ray diffraction as Sn(5)(mu(3)-O)(2)(mu-ONep)(6) (3) and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) (4). Compound 3 consists of an asymmetrical molecule that has five Sn atoms arranged in a square-based pyramidal geometry linked by four basal mu-ONep ligands, two facial mu(3)-O, and two facial mu-ONep ligands. Compound 4 was solved in a novel octahedral arrangement of six Sn cations with an asymmetric arrangement of mu(3)-O and mu-ONep ligands that yields two square base pyramidal and four pyramidal coordinated Sn cations. These compounds were further identified by multinuclear ((1)H, (13)C, (17)O, and (119)Sn) solid-state MAS and high resolution, solution NMR experiments. Because of the complexity of the compounds and the accessibility of the various nuclei, 2D NMR experiments were also undertaken to elucidate the solution behavior of these compounds. On the basis of these studies, it was determined that while the central core of the solid-state structures of 3 and 4 is retained, dynamic ligand exchange leads to more symmetrical molecules in solution. Novel products 3 and 4 lend structural insight into the stepwise hydrolysis of Sn(II) alkoxides.
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PMID:Hydrolysis of tin(II) neo-pentoxide: syntheses, characterization, and X-ray structures of [Sn(ONep)(2)](infinity), Sn(5)(mu(3)-O)(2)(mu-ONep)(6), and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) where ONep = OCH(2)CMe(3). 1197 29