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Cationic Charge (cationic + charge)
Selected AbstractsAn Atropo-Stereogenic Diphosphane Ligand with a Proximal Cationic Charge: Specific Catalytic Properties of a Palladium Complex ThereofEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2008Nathalie Debono Abstract A class of cationic diphosphane ligands combining phosphane and amidiniophosphane moieties is illustrated on the N -methyl,N -naphthylbenzimidazolium framework. The palladium(II) complex thereof is described and compared to the corresponding complex of the analogous neutral diphosphane. Contrary to first-level expectations, the N2C,P and N2CP,Pd bonds in the cationic diphosphane complex are not longer than those occurring in its neutral counterpart. In the cationic ligand, the proximal positive charge is indeed conjugated to one phosphanyl group, and the coordination scheme is tentatively interpreted by resonance of the phosphane,metal dative bond (+N2C,P:,[Pd]) with a carbene,phosphenium dative bond (N2C:,[+P:,Pd]). Despite this peculiar structural feature, the electronic , donation (vs. , acceptation) towards the palladium centre remains lowered in the cationic ligand. This specific property can be a priori valuable in a catalytic process where oxidative addition is not the limiting step. It is indeed shown that although the neutral complex is more active in Suzuki coupling reactions, the cationic complex is more active in Sonogashira-type coupling reactions involving predissociated halide substrates, namely an acyl chloride. These likely atropo-chiral ligands deserve to be resolved for application in asymmetric catalysis.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Hydrolysis of aliphatic naphthalene diimides: effect of charge placement in the side chainsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2008Michelle B. Kim Abstract Water-soluble naphthalene diimides (NDIs) have found uses in a wide variety of applications including as electron acceptors in electron transfer reactions and as molecules that undergo spontaneous organization in aqueous solution. Many studies have looked at their interaction with nucleic acids including work with DNA duplexes, triplexes, quadruplexes, hairpins, and DNA,RNA heteroduplexes. In many of these interactions the NDIs serve as threading intercalators. Herein we describe the reversible hydroxide-catalyzed hydrolysis of NDIs bearing aliphatic side chains, with ring opening first to the monoimide and then to the diamide. Examples with N -methylpyrrolidinium groups placed two (1) and three (5) atoms from the central core were studied. The Ka values for the first and second hydrolyses for 1 were 2.5,±,0.2,×,105 and 2.0,±,0.1,×,102,M,1, respectively; for 5 they were 1.4,±,0.1,×,105 and 44,±,2,M,1, respectively. NDI 1 hydrolyzed 6.8 times faster than 5. The rates for the first and second ring opening of 1 in 100,mM hydroxide measured by stopped-flow were 17.0,±,0.2 and 0.53,±,0.01,s,1, respectively. Capillary electrophoresis in borate buffer showed separation of the diimide and monoimide with the former eluting first. Nuclear magnetic resonance (NMR) showed both the syn and anti isomers of the diamide species. Overall, the rate of hydrolysis of the NDI is increased when the cationic charge is moved closer to the NDI core. Copyright © 2008 John Wiley & Sons, Ltd. [source] The role of eosinophil major basic protein in angiogenesisALLERGY, Issue 3 2009I. Puxeddu Background:, Eosinophil-derived major basic protein (MBP) plays an active role in allergic inflammation and tissue remodelling. However, its role in angiogenesis has not been established as yet. Therefore our objective was to investigate whether MBP exhibits any direct pro-angiogenic effects. Methods:, Rat aortic endothelial cells and human umbilical vascular endothelial cells were cultured with different concentrations of MBP and their viability (Trypan blue exclusion test), proliferation (thymidine incorporation) and capillary-like structure formation (matrigel assay) were investigated in vitro. The angiogenic activity of MBP was then tested in vivo using the chick chorio allantoic membrane (CAM) assay. Results:, Subcytotoxic concentrations of MBP induce endothelial cell proliferation and enhance the pro-mitogenic effect of vascular endothelial growth factor (VEGF), but do not affect their VEGF release. MBP promotes capillarogenesis by endothelial cells seeded on matrigel and sprouting formation in the CAM assay. Furthermore, we have shown that the pro-angiogenic effect of MBP is not due to its cationic charge since stimulation of the CAMs with the synthetic polycation, poly- l -arginine does not induce any angiogenic effects. Conclusions:, These data demonstrate that MBP has pro-angiogenic effects in vitro and in vivo, providing a novel mechanism whereby MBP can participate in tissue inflammation and remodelling in atopic diseases. [source] Elucidation of the solution structure of cardiotoxin analogue V from the Taiwan cobra (Naja naja atra),Identification of structural features important for the lethal action of snake venom cardiotoxinsPROTEIN SCIENCE, Issue 4 2000Gurunathan Jayaraman Abstract The aim of the present study is to understand the structural features responsible for the lethal activity of snake venom cardiotoxins. Comparison of the lethal potency of the five cardiotoxin isoforms isolated from the venom of Taiwan cobra (Naja naja atra) reveals that the lethal potency of CTX I and CTX V are about twice of that exhibited by CTX II, CTX III, and CTX IV. In the present study, the solution structure of CTX V has been determined at high resolution using multidimensional proton NMR spectroscopy and dynamical simulated annealing techniques. Comparison of the high resolution solution structures of CTX V with that of CTX IV reveals that the secondary structural elements in both the toxin isoforms consist of a triple and double-stranded antiparallel ,-sheet domains. Critical examination of the threedimensional structure of CTX V shows that the residues at the tip of Loop III form a distinct "finger-shaped" projection comprising of nonpolar residues. The occurrence of the nonpolar "finger-shaped" projection leads to the formation of a prominent cleft between the residues located at the tip of Loops II and III. Interestingly, the occurrence of a backbone hydrogen bonding (Val27CO to Leu48NH) in CTX IV is found to distort the "finger-shaped" projection and consequently diminish the cleft formation at the tip of Loops II and III. Comparison of the solution structures and lethal potencies of other cardiotoxin isoforms isolated from the Taiwan cobra (Naja naja atra) venom shows that a strong correlation exists between the lethal potency and occurrence of the nonpolar "finger-shaped" projection at the tip of Loop III. Critical analysis of the structures of the various CTX isoforms from the Taiwan cobra suggest that the degree of exposure of the cationic charge (to the solvent) contributed by the invariant lysine residue at position 44 on the convex side of the CTX molecules could be another crucial factor governing their lethal potency. [source] Collective Optical Behavior of Cationic Water-Soluble Dendrimers,ADVANCED MATERIALS, Issue 23-24 2004S. Wang Water-soluble dendrimers containing cationic charges and optically active units on the periphery of the macromolecular structure have been designed. Collective optical behavior of the chromophores on the surface was demonstrated by fluorescence quenching and energy-transfer experiments. These water-soluble dendrimers can be used for optically amplified DNA detection (see Figure) in homogeneous media. [source] | ||||||||||