Covalent Interactions (covalent + interaction)

Distribution by Scientific Domains

Selected Abstracts

Toward a greater appreciation of noncovalent chemical/DNA interactions: Application of biological and computational approaches,

Ronald D. Snyder
Abstract Noncovalent DNA interactions, e.g., DNA intercalation and DNA groove-binding, have not been well studied relative to covalent interactions largely due to the inability of predicting and detecting such events in intact cells. We have adapted an in vitro bleomycin amplification method for DNA intercalation for use in cultured V79 Chinese hamster cells and have validated this approach through the use of a three-dimensional DNA computational docking model that quantifies potential strength of DNA intercalative binding based on electrostatics and hydrogen bonding. For many structural classes of molecules, DNA intercalation is necessary but not sufficient for genotoxicity. The present article reviews our progress to date in predicting and confirming noncovalent binding of drugs and other chemicals and in understanding the mechanistic relationship between intercalation and genotoxicity. Environ. Mol. Mutagen., 2005. © 2005 Wiley-Liss, Inc. [source]

The Assembling of Semiconductor Nanocrystals

Alexey Shavel
Abstract Recent accomplishments in arranging semiconductor nanoparticles in a desired manner are reviewed. Coupling mechanisms utilized for this purpose include electrostatic and covalent interactions, methods like layer-by-layer assembly, solvent-controlled precipitation and surface amination for covalent attachment of nanoparticles are employed. Dipole,dipole interactions are operative in nanocrystal solids and fast Förster energy transfer is observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

The charge capacitance of the chemical bond: Application to bonds containing metals

Asbjørn Holt
Abstract The charge capacitance of metal containing complexes are studied. For molecules with multiple bonding between the metal atoms it is found that the charge capacitance is correlated to the maximum bond order, natural bond order, and to some extent the effective bond order. Furthermore the charge capacitance of some methylidene metal dihydride complexes are studied. These molecules have agostic interactions of varying strength, and it is concluded that this strength is very well reflected in the charge capacitances of the systems. In accordance with the definition of agostic interactions it is therefor concluded that the charge capacitance holds information about the strength of covalent interactions. The effect therefore on the agostic interactions upon substitution of one of the hydrogen atoms with fluorine in the methylidene metal complexes is studied, and found to reduce the agostic interactions. It is also demonstrated that there is an agostic interaction in an ArCrCrAr complex. The distance dependence of the charge capacitance is also discussed. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]

Engineering hydrogen-bonded duplexes

Bing Gong
Abstract Based on several simple, readily available building blocks, oligoamide strands carrying various arrays of hydrogen-bond donors and acceptors, i.e. hydrogen-bonding sequences, have been designed and synthesized. Detailed characterization indicates that these oligoamide strands associate via their hydrogen-bonding edges into doubled stranded pairs (duplexes), which are characterized by programmable sequence specificity and adjustable stability. Using these hydrogen-bonded duplexes as association units, supramolecular structures, such as ,-sheets and non-covalent block copolymers, are obtained by simply mixing the corresponding components. Recently, by incorporating reversible covalent interactions into these hydrogen-bonded duplexes, sequence-specific formation of covalently linked structures has been realized under thermodynamic conditions, which has opened an entirely new avenue to the development of previously unknown dynamic covalent structures such as various block copolymers. Copyright © 2007 Society of Chemical Industry [source]

Characterization of covalent addition products of chlorogenic acid quinone with amino acid derivatives in model systems and apple juice by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

Susanne Schilling
High-performance liquid chromatography (HPLC) coupled to electrospray ionization tandem mass spectrometry (ESI-MSn) was used to study the covalent interactions between chlorogenic acid (CQA) quinone and two amino acid derivatives, tert -butyloxycarbonyl-L-lysine and N -acetyl-L-cysteine. In a model system at pH 7.0, the formation of covalent addition products was demonstrated for both derivatives. The addition product of CQA dimer and tert -butyloxycarbonyl-L-lysine was characterized by LC/MSn as a benzacridine structure. For N -acetyl-L-cysteine, mono- and diaddition products at the thiol group with CQA quinone were found. In apple juice at pH 3.6, covalent interactions of CQA quinone were observed only with N -acetyl-L-cysteine. Taking together these results and those reported by other groups it can be concluded that covalent interactions of amino side chains with phenolic compounds could contribute to the reduction of the allergenic potential of certain food proteins. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Xenobiotic metabolism, genetic polymorphisms and male infertility

ANDROLOGIA, Issue 4-5 2000
H.-C. Schuppe
Male reproductive function may be impaired by various occupational and environmental chemical agents. The majority of these xenobiotics, however, require metabolic activation in order to exert adverse effects via covalent interactions between intermediate metabolites and cellular macromolecules such as DNA or protein. In addition, metabolization may alter endocrine-disrupting properties of xenobiotics. Thus tissue-specific expression and regulation of multiple xenobiotic-metabolizing enzymes are likely to play an important role in chemically induced disorders of male reproductive organs. Recent studies suggest that genetic polymorphisms underlying inter-individual and inter-ethnic variability of xenobiotic metabolism modulate susceptibility to male reproductive disorders. For cytochrome P450 1A1 (CYP1A1), a key enzyme in extra-hepatic metabolic activation of lipophilic xenobiotics, increased frequencies of two genetically linked polymorphisms have been found among infertile men. [source]

The role of disulfide bonds and N-terminus in the structural properties of hepcidins: Insights from molecular dynamics simulations

BIOPOLYMERS, Issue 10 2010
Massimiliano Aschi
Abstract The main purpose of this work is to analyse, by means of molecular dynamics (MD) simulations both structural and mechanical-dynamical differences between Hepcidin-20 and Hepcidin-25 in both oxidized and reduced states in aqueous solution. Results indicate that the presence of disulfide bonds is essential, in both peptides, for maintaining their ,-hairpin motif. As a matter of fact, the lack of this intra-peptide covalent interactions produces an almost immediate deviation from the oxidized, plausibly active, structure in both the systems. Interestingly, reduced Hepcidin-25 turns out to be characterized by a highly fluctuating structure which is found to rapidly span a large number of configurations at equilibrium. On the other hand, loss of disulfide bonds in the shorter peptide, results in a more compact and relatively rigid double-turn structure. Comparison of mechanical,dynamical properties and sidechains,sidechains interactions in oxidized Hepcidin-20 and Hepcidin-25 strongly suggest also the key role of N-terminus in the aggregation tendency of Hepcidin-25. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 917,926, 2010. [source]