The gypsy moth, Lymantria dispar, uses pheromones, such as (+)-disparlure, for communication. These pheromones are detected by the sensitive antennae of the male moth and travel through their aqueous environment to the sensory neuron, possibly with assistance from pheromone binding proteins (PBPs). The hydrophobicity of disparlure, which is of primary importance for its interactions with PBPs, can be measured by its partition coefficients. These coefficients for heptane/water and chloroform/water interfaces were obtained in this work experimentally and using molecular dynamics (MD) simulations. The agreement between the experimental and calculated values validates the choice of the force field parameters, which can thus be used in future MD simulations of the PBP-pheromone interactions.Résumé : La lymantride spongieuse, mite gitane, Lymantria dispar, fait appel à des phéromones, tel le (+)-disparlure, pour ses communications. Ces phéromones sont détectées par des antennes sensibles des lymantrides mâles et elles circulent dans leur environnement aqueux vers le neurone sensoriel, peut-être avec l'aide de protéines fixatrices de phéromones (PFP). Le caractère hydrophobe du disparlure qui est d'importance capitale pour ses interactions avec les PFP peut être mesuré par ses coefficients de partition. Dans ce travail, on a mesuré expérimentalement ces coefficients pour les systèmes heptane/eau et chloroforme/eau et on les a aussi calculés par la méthode de la dynamique moléculaire (DM). L'accord entre les valeurs calculées et celles obtenues expérimentalement valide le choix des paramètres de champ de force qui pourront être utilisés dans des simulations ultérieures de DM des interactions PFP/phéromone.Mots-clés : lymantride spongieuse, disparlure, coefficients de partition, caractère hydrophobe, époxyde, paramètres des potentiels optimisés pour des simulations de liquides, simulations de dynamiques moléculaires.[Traduit par la Rédaction]
Two-dimensional potential energy and free energy surfaces are obtained using quantum mechanical and molecular dynamics calculations for four hydrogen transfer reactions in n-hexane solvent: the methyl–methane, n-propyl–n-propane, n-pentyl–n-pentane, and t-butyl–isobutane systems. The resultant surfaces have similar landscapes despite the fact the equilibrated solvent cavities for these systems are notably different in size and shape. The kinetic implications of these landscapes are discussed. The Arrhenius and tunneling kinetics of hydrogen transfer in nonpolar hydrocarbon solute–solvent systems are not expected to show any significant viscosity dependence.
A model graph approach is proposed to discuss topological trends in representative sets of random isomeric hydrocarbon molecules generated on a two-dimensional hexagonal grid and to study the dependence of the dominant structural motifs on parameters of the model. The results of the study are used to infer a more likely structural organization of asphaltene molecules.
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