Examinando por Materia "methanol"

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    Contributions of intermolecular bonding and lubrication to the mechanical behavior of a natural armor
    (ELSEVIER SCI LTD, 2020-01-01) Jiang, H.; Ghods, S.; Weller, E.; Waddell, S.; Ossa, E.A.; Yang, F.; Arola, D.; Jiang, H.; Ghods, S.; Weller, E.; Waddell, S.; Ossa, E.A.; Yang, F.; Arola, D.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de Ingeniería
    Among many dermal armors, fish scales have become a source of inspiration in the pursuit of “next-generation” structural materials. Although fish scales function in a hydrated environment, the role of water and intermolecular hydrogen bonding to their unique structural behavior has not been elucidated. Water molecules reside within and adjacent to the interpeptide locations of the collagen fibrils of the elasmodine and provide lubrication to the protein molecules during deformation. We evaluated the contributions of this lubrication and the intermolecular bonding to the mechanical behavior of elasmodine scales from the Black Carp (Mylopharyngodon piceus). Scales were exposed to polar solvents, followed by axial loading to failure and the deformation mechanisms were characterized via optical mechanics. Displacement of intermolecular water molecules by liquid polar solvents caused significant (p = 0.05) increases in stiffness, strength and toughness of the scales. Removal of this lubrication decreased the capacity for non-linear deformation and toughness, which results from the increased resistance to fibril rotations and sliding caused by molecular friction. The intermolecular lubrication is a key component of the “protecto-flexibility” of scales and these natural armors as a system; it can serve as an important component of biomimetic-driven designs for flexible armor systems. Statement of Significance: The natural armor of fish has become a topic of substantial scientific interest. Hydration is important to these materials as water molecules reside within the interpeptide locations of the collagen fibrils of the elasmodine and provide lubrication to the protein molecules during deformation. We explored the opportunity for tuning the mechanical behavior of scales as a model for next-generation engineering materials by adjusting the extent of hydrogen bonding with polar solvents and the corresponding interpeptide molecular lubrication. Removal of this lubrication decreased the capacity for non-linear deformation and toughness due to an increase in resistance to fibril rotations and sliding as imparted by molecular friction. We show that intermolecular lubrication is a key component of the “protecto-flexibility” of natural armors and it is an essential element of biomimetic approaches to develop flexible armor systems. © 2020 Acta Materialia Inc.
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    Structural characterization of the (MeSH)4 potential energy surface
    (SPRINGER, 2013-05-01) Gomez, Sara; Guerra, Doris; David, Jorge; Restrepo, Albeiro; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
    A random walk on the PES for (MeSH)4 clusters produced 50 structural isomers held together by hydrogenbonding networks according to calculations performed at the B3LYP/6-311++G* * andMP2/6-311++G* * levels. The geometric motifs observed are somewhat similar to those encountered for the methanol tetramer, but the interactions responsible for cluster stabilization are quite different in origin. Cluster stabilization is not related to the number of hydrogen bonds. Two distinct, well-defined types of hydrogen bonds scattered over a wide range of distances are predicted. © Springer-Verlag Berlin Heidelberg 2012.
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    Structural characterization of the (methanol)4 potential energy surface
    (AMER CHEMICAL SOC, 2009-09-24) David, Jorge; Guerra, Doris; Restrepo, Albeiro; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
    In this paper, we report the geometries and properties of the structural isomers obtained from a random walk of the potential energy surface (PES) of the methanol tetramer. Thirty-three structures were obtained after B3LYP/6-31+g* optimization of 94 candidate structures generated from a stochastic search of the PM3 conformational space. The random search was carried out using a recently proposed modified Metropolis acceptance test in the simulated annealing (SA) procedure. Corrections for the basis set superposition error (BSSE) show improvements on the binding energies of the clusters in an average of approximately 2.0 kcal/mol, while geometries are predicted to be less sensitive to BSSE corrections. MP2/aug-cc-pvdz calculations on representative structures did not change the geometries but predicted better binding energies. Highly correlated CCSD(T) energies were calculated on the B3LYP and MP2 stationary points and used to establish relative stabilities. We report several new conformations and group the structures into six distinct geometrical motifs. Only the cyclic tetramers with four primary hydrogen bonds in the same plane are predicted to have significant populations. Secondary hydrogen bonds, those for which the donated proton comes from an alkyl group, lead to a rich conformational space.