Examinando por Autor "Jenkins, Samantha"

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    Hydrophobic meddling in small water clusters
    (SPRINGER, 2013-08-01) Hadad, C. Z.; Restrepo, Albeiro; Jenkins, Samantha; Ramirez, Frank; David, Jorge; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
    What would be the effects on the nature of hydrogen bonds, on the energies, and on the overall structural possibilities of replacing some hydrogen atoms by small hydrophobic groups in small water networks? Aiming at investigating this question, we performed an exhaustive search of the conformational space of the (Methanol)2(Water)3 representative model system, characterized the results, and made key comparative analysis with pentameric pure water clusters. The potential energy surface yielded a global minimum structural motif consisting of several puckered ring-like cyclic isomers very close in energy to each other. They are followed by other structural motifs, which, contrary to conventional belief, would also contribute to the properties of a macroscopic sample of this composition. We found that the C-H O interactions play a subordinate structural role and preferably accommodate to the established O-H O based structures. In comparison with the pure (H2O)5 case, we showed that (1) the same basic structural motifs and in a similar hierarchy energy order are obtained, but with a richer structural isomerism; (2) in general, the bonding is reinforced by the increase in the electrostatic and in the "degree of covalency" of the hydrogen-bonding components. Therefore, at least for this small cluster size, methyl groups slightly affect the structural isomerism and reinforce the hydrogen bonding. Additionally, we identified general factors of instability of the more unstable structures. © Springer-Verlag Berlin Heidelberg 2013.
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    Spanning QTAIM topology phase diagrams of water isomers W4, W5 and W6
    (ROYAL SOC CHEMISTRY, 2011-01-01) Jenkins, Samantha; Restrepo, Albeiro; David, Jorge; Yin, Dulin; Kirk, Steven R.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
    Structural and chemical properties of the small water clusters W 4, W5 and W6 are investigated with the theory of atoms and molecules (QTAIM). For the W4, W5 and W 6 clusters, nine, fourteen and twenty-seven conformers, respectively, have been analyzed. For the W4, W5 and W6 clusters one, two and three of these structures, respectively, have not been reported before. We then proceed to extend the W4, W5 and W6 water cluster topology space using QTAIM; the PoincaréHopf topological sum rules are applied to create rules to identify the spanning set of conformer topologies, this includes finding three, ten and eight new distinct topologies that satisfy the PoincaréHopf relation for W4, W5 and W6 respectively. The topological stability of degenerate solutions to the PoincaréHopf relation is compared by evaluating the proximity to rupturing of critical points of the gradient vector field of the charge density. We introduce a QTAIM topology space to replace the inconsistent use of Euclidean geometry to determine whether a cluster is 1-, 2- or 3-D. We show from the topology of the charge density that the conformers of the W 4, W5 clusters are more energetically stable in less compact, planar forms, conversely the conformers of W6 are more energetically stable with compact 3-D topologies. Quantifying the degree of covalent character in the hydrogen bonding for the W4, W5 and W6 clusters independently verifies this finding. Differences in simple rules for the number of hydrogen bonds obeying the BernalFowler ice rules between W4, W5 and W6 reflect the transition from 2-D to 3-D structures being more energetically stable. In addition, we identify a new class of OO bonding interactions that are up to 48% longer than the inter-nuclear separation and appear to be failed hydrogen bonds. © 2011 the Owner Societies.