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Geometric Isomers (geometric + isomer)
Selected AbstractsDietary Lycopene: Its Properties and Anticarcinogenic EffectsCOMPREHENSIVE REVIEWS IN FOOD SCIENCE AND FOOD SAFETY, Issue 3 2008Preeti Singh ABSTRACT:, Lycopene is the principal pigment of the carotenoids naturally found in tomatoes and is important not only because of the color it imparts but also because of the recognized health benefits associated with its presence. Red tomatoes typically contain about 95% of their lycopene as the all -trans isomer, the most stable form. In tangerine tomatoes, on the other hand, the lycopene is present as tetra-cis -lycopene, a geometric isomer of all -trans lycopene. Lycopene is a major component found in blood serum. This carotenoid has been extensively studied for its antioxidant and cancer-preventing properties. Prevention of heart disease has been shown to be another antioxidant role played by lycopene because it reduces the accumulation of platelets that eventually lead to blood clots, heart attacks, and strokes. In contrast to many other food phytonutrients whose effects have only been studied in animals, lycopene from tomatoes has been repeatedly studied in humans and found to be protective against several cancers, which now include colorectal, prostate, breast, lung, and pancreatic cancers. This review outlines the background information dealing with lycopene and presents the most comprehensive and current understanding of its potential functional role in human health. [source] New Approaches to 12-Coordination: Structural Consequences of Steric Stress, Lanthanoid Contraction and Hydrogen BondingEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2010Anthony S. R. Chesman Abstract The anionic dinitrile ligand dicyanonitrosomethanide (dcnm), C(CN)2(NO),, and the anion resulting from its addition product with water, carbamoylcyanonitrosomethanide (ccnm), C(CN)(CONH2)(NO),, have been incorporated into lanthanoid complexes and display unusual ,2(N,O) nitroso coordination modes. (Et4N)3[Ln(ccnm)6] (1Ln; 1Ln = 1La, 1Ce, 1Pr, 1Nd, 1Sm) and (Me4N)3[Ln(ccnm)6] (2Ln; 2Ln = 2La, 2Ce, 2Pr, 2Nd) are systems containing 12-coordinate homoleptic trianionic lanthanoidate complexes. The nitroso groups of the ccnm ligands form three-membered ring chelates with the lanthanoid metal centre, with the asymmetry of the nitroso ,2 interactions dependent upon the intramolecular N,H···O=N hydrogen bonding. Additional intermolecular hydrogen bonding interactions exist between adjacent amide and nitrile groups giving rise to 3D ,-Po and 6,8-connected (412.63)(420.68) networks in 1Ln and 2Ln, respectively. The compounds (Me4N)3[Ln(dcnm)6] (3Ln; 3Ln = 3La, 3Ce, 3Nd, 3Sm) also contain a 12-coordinate trianionic lanthanoidate complex with the nitroso group exhibiting a highly symmetrical ,2 interaction. The sterically crowded environments of [Ln(18-crown-6)(dcnm)3] (4Ln; 4Ln = 4La, 4Ce, 4Pr, 4Nd) result in a shift towards a more asymmetric ,2 bonding of the nitroso group with decrease in the Ln3+ radius. There is a corresponding increase of the Ln,O,N angle, and one ligand is ,1(O) binding in 4Nd. The dcnm ligands in the discrete complexes [La(phen)3(dcnm)(3,x)Clx], x , 0.25 (5) (phen = 1,10-phenanthroline), (Et4N)[Ce(phen)2(dcnm)4] (6a/b, 6c) and [Ce(phen)2(dcnm)Cl2H2O] (7) display a variety of coordination modes. Complex 5 has 1D chains formed by ,,, stacking of adjacent phen co-ligands. Complexes 6 contain the monoanionic complex [Ce(phen)2(dcnm)4], with two geometric isomers present in the crystal structure of 6a/b. Complex 7 forms extended 1D chains via hydrogen bonding between coordinated water and chloride atoms and an extensive array of face-to-face , interactions. [source] Benzene-1,2-, 1,3-, and 1,4-di- N -substituted carbamates as conformationally constrained inhibitors of acetylcholinesteraseJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 6 2007Ming-Cheng Lin Abstract Benzene-1,2-, 1,3-, and 1,4-di- N -substituted carbamates (1,15) are synthesized as the conformationally constrained inhibitors of acetylcholinesterase and mimic gauche, eclipsed, and anti -conformations of acetylcholine, respectively. All carbamates 1,15 are characterized as the pseudo substrate inhibitors of acetylcholinesterase. For a series of geometric isomers, the inhibitory potencies are as follows: benzene-1,4-di- N -substituted carbamate (para compound) > benzene-1,3-di- N -substituted carbamate (meta compound) > benzene-1,2-di- N -substituted carbamate (ortho compound). Therefore, benzene-1,4-di- N -substituted carbamates (para compounds), with the angle of 180° between two C(benzene),O bonds, mimic the preferable anti C,O/C,N conformers of acetylcholine for the choline ethylene backbone in the acetylcholinesterase catalysis. © 2007 Wiley Periodicals, Inc. J Biochem Mol Toxicol 21:348,353, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20202 [source] Conjugated linoleic acid isomers: Differences in metabolism and biological effectsBIOFACTORS, Issue 1 2009Itziar Churruca Abstract The term conjugated linoleic acid (CLA) refers to a mixture of linoleic acid positional and geometric isomers, characterized by having conjugated double bonds, not separated by a methylene group as in linoleic acid. CLA isomers appear as a minor component of the lipid fraction, found mainly in meat and dairy products from cows and sheep. The most abundant isomer is cis -9,trans -11, which represents up to 80% of total CLA in food. These isomers are metabolized in the body through different metabolic pathways, but important differences, that can have physiological consequences, are observed between the two main isomers. The trans -10,cis -12 isomer is more efficiently oxidized than the cis -9,trans -11 isomer, due to the position of its double bounds. Interest in CLA arose in its anticarcinogenic action but there is an increasing amount of specific scientific literature concerning the biological effects and properties of CLA. Numerous biological effects of CLA are due to the separate action of the most studied isomers, cis -9,trans -11 and trans -10,cis -12. It is also likely that some effects are induced and/or enhanced by these isomers acting synergistically. Although the cis -9,trans -11 isomer is mainly responsible for the anticarcinogenic effect, the trans -10,cis -12 isomer reduces body fat and it is referred as the most effective isomer affecting blood lipids. As far as insulin function is concerned, both isomers seem to be responsible for insulin resistance in humans. Finally, with regard to the immune system it is not clear whether individual isomers of CLA could act similarly or differently. © 2009 International Union of Biochemistry and Molecular Biology, Inc. [source] | ||||||||||