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Hydrogen-bonding Ability (hydrogen-bonding + ability)
Selected AbstractsStructure,activity relationships for gene activation oestrogenicity: Evaluation of a diverse set of aromatic chemicalsENVIRONMENTAL TOXICOLOGY, Issue 1 2002T. Wayne Schultz Abstract Structure,activity relationships for oestrogenicity were developed based on 120 aromatic chemicals evaluated in the Saccharomyces cerevisiae -based Lac -Z reporter assay. Relative gene activation was compared to 17,-estradiol and varied over eight orders of magnitude. Analysis of the data compared to 17,-estradiol identified three structural criteria that were related to xenoestrogen activity and potency: (1) the hydrogen-bonding ability of the phenolic ring mimicking the A-ring, (2) a hydrophobic centre similar in size and shape to the B- and C-rings, and (3) a hydrogen-bond donor mimicking the 17,-hydroxyl moiety of the D-ring, especially with an oxygen-to-oxygen distance similar to that between the 3- and 17,-hydroxyl groups of 17,-estradiol. Binding data were segregated into activity clusters including strong, moderate, weak, and detectable gene expression, and those compounds that were inactive. The hydrogen-bonding ability of hydroxy group in the 3-position on 17,-estradiol was observed to be essential for gene activation. Compounds with a 4-hydroxyl substituted benzene ring and a hydrophobic moiety of size and shape equivalent to the B-ring of 17,-estradiol were generally observed to be weakly active compounds. Moderately active compounds have a 4-hydroxyl substituted benzene ring with a hydrophobic moiety equivalent in size and shape to the B- and C-ring of 17,-estradiol, or have a high hydrogen-bond donor capacity owing to the presence of halogens on a nonphenolic ring. Strongly active compounds, similar to 4,4,-diethylethylene bisphenol (DES), possess the same hydrophobic ring structure as described for moderately active compounds and an additional hydroxyl group with an oxygen-to-oxygen distance close to that exhibited by the 3- and 17-hydroxyl groups of 17,-estradiol. © 2002 by Wiley Periodicals, Inc. Environ Toxicol 17: 14,23, 2002 [source] Chlorophyll a Self-assembly in Polar Solvent,Water Mixtures ,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2000Radka Vladkova ABSTRACT The conversion of chlorophyll a (Chl a) monomers into large aggregates in six polar solvents upon addition of water has been studied by means of absorption, fluorescence spectroscopy and fluorescence lifetime measurements for the purpose of elucidating the various environmental factors promoting Chl a self-assembly and determining the type of its organization. Two empirical solvent parameter scales were used for quantitative characterization of the different solvation properties of the solvents and their mixtures with water. The mole fractions of water f1/2 giving rise to the midpoint values of the relative fluorescence quantum yield were determined for each solvent, and then various solvent,water mixture parameters for the f1/2 values were compared. On the basis of their comparison, it is concluded that the hydrogen-bonding ability and the dipole,dipole interactions (function of the dielectric constant) of the solvent,water mixtures are those that promote Chl a self-assembly. The influence of the different nature of the nonaqueous solvents on the Chl aggregation is manifested by both the different water contents required to induce Chl monomer , aggregate transition and the formation of two types of aggregates at the completion of the transition: species absorbing at 740,760 nm (in methanol, ethanol, acetonitrile, acetone) and at 667,670 nm (in pyridine and tetrahydrofuran). It is concluded that the type of Chl organization depends on the coordination ability and the polarizability (function of the index of refraction) of the organic solvent. The ordering of the solvents with respect to the f1/2 values,methanol < ethanol < acetonitrile < acetone < pyridine < tetrahydrofuran,yielded a typical lyotropic (Hofmeister) series. On the basis of this solvent ordering and the disparate effects of the two groups of solvents on the Chl a aggregate organization, it is pointed out that the mechanism of Chl a self-assembly in aqueous media can be considered a manifestation of the Hofmeister effect, as displayed in the lipid-phase behavior (Koynova et al., Eur. J. Biophys. 25, 261,274, 1997). It relates to the solvent ability to modify the bulk structure and to distribute unevenly between the Chl,water interface and bulk liquid. [source] Amino and cyano N atoms in competitive situations: which is the best hydrogen-bond acceptor?ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2001A crystallographic database investigation The relative hydrogen-bond acceptor abilities of amino and cyano N atoms have been investigated using data retrieved from the Cambridge Structural Database and via ab initio molecular orbital calculations. Surveys of the CSD for hydrogen bonds between HX (X = N, O) donors, N,T,C,N (push,pull nitriles) and N,(Csp3)n,C,N molecular fragments show that the hydrogen bonds are more abundant on the nitrile than on the amino nitrogen. In the push,pull family, in which T is a transmitter of resonance effects, the hydrogen-bonding ability of the cyano nitrogen is increased by conjugative interactions between the lone pair of the amino substituent and the C,N group: a clear example of resonance-assisted hydrogen bonding. The strength of the hydrogen-bonds on the cyano nitrogen in this family follows the experimental order of hydrogen-bond basicity, as observed in solution through the pKHB scale. The number of hydrogen bonds established on the amino nitrogen is greater for aliphatic aminonitriles N,(Csp3)n,C,N, but remains low. This behaviour reflects the greater sensitivity of the amino nitrogen to steric hindrance and the electron-withdrawing inductive effect compared with the cyano nitrogen. Ab initio molecular orbital calculations (B3LYP/6-31+G** level) of electrostatic potentials on the molecular surface around each nitrogen confirm the experimental observations. [source] Interactions of trifluroethanol with the Trp-cage peptideBIOPOLYMERS, Issue 2-3 2007Chiradip Chatterjee Abstract It has been suggested that aggregation of fluorinated alcohols in water solutions is involved with the abilities of these alcohols to provoke conformational changes in peptides and proteins. The extent of fluoroalcohol aggregation depends on the degree of fluorination: hexafluoroisopropanol (HFIP) is more extensively aggregated than is TFE. We previously described a study of the interactions of HFIP with the peptide Trp-cage and provided evidence for the formation of long-lived complexes between this fluoroalcohol and the peptide. In the present work, we have examined the interactions of the less-fluorinated TFE with Trp-cage, in order to probe the role of fluoroalcohol aggregation in the phenomena observed. Intermolecular 1H{19F} nuclear Overhauser effects arising from interactions of TFE with the hydrogens of the peptide in a solution containing 42% TFE were determined at sample temperatures from 5 to 45°C. It is shown that the folded state of the peptide under these conditions is essentially the same as that observed in water and in 30% HFIP-water. The observed peptide,solvent NOEs indicate formation of complexes of Trp-cage with TFE that persist for times of the order of 1 ns. The interactions leading to complexes with TFE are somewhat weaker than those involved in complex formation with HFIP. There are no indications that the aggregation of fluoroalcohol is a necessary concomitant of the interactions of TFE or HFIP with Trp-cage. Rather, the stronger and more long-lived interactions of HFIP with Trp-cage appear to be primarily the result of the greater hydrogen-bonding ability and hydrophobicity of this fluoroalcohol. © 2007 Wiley Periodicals, Inc. Biopolymers 87: 115,123, 2007. 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] Allosteric Tuning of the Intra-Cavity Binding Properties of a Calix[6]arene through External Binding to a ZnII Center Coordinated to Amino Side ChainsCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007Ulrich Darbost Dr. Abstract Molecular recognition by calix[6]arene-based receptors bearing three primary alkylamino side chain arms (1) is described. Complexation of ZnII ion provides the dinuclear ,-hydroxo complex , XRD characterization of which, together with solution studies, provided evidence of its hosting of neutral polar organic guests G. Treatment of this complex with a carboxylic acid or a sulfonamide (XH) results in the formation of mononuclear species , one of which (X = Cl) has been characterized by XRD. A dicationic complex is obtained upon treatment of with a mixture of an alkylamine and a strong acid. Each of these ZnII complexes features a tetrahedral metal ion bound to the three amino arms of ligand 1 and to an exogenous ligand (either HO,, X,, or RNH2) sitting outside of the cavity. As a result, the metal ion structures the calixarene core, constraining it in a cone conformation suitable for guest hosting. The receptor properties of these compounds have been explored in detail and are compared with those of the trisammonium receptor , based on the same calixarene core, as well as those of the trisimidazole-based dicationic Zn funnel complexes. This study reveals very different host properties, in spite of the common hydrophobic, ,-basic, and hydrogen-bonding acceptor properties of the calixarene cores. A harder external ligand produces a less polarized receptor that is consequently particularly sensitive to the hydrogen-bonding ability of its guest. The less electron-rich the apical ligand, and a fortiori the trisammonium host, the more sensitive the receptor to the dipole moment of the guest. All this stands in contrast with the funnel Zn complexes, in which the coordination link plays a dominant role. It is also shown that the asymmetry of an exo -coordinated enantiopure amino ligand is sensed by the guest. This supramolecular system nicely illustrates how the receptor properties of a hydrophobic cavity can be allosterically tuned by the environment. [source] | ||||||||||