Examinando por Materia "Molecular Structure"

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    Ítem
    Fengycin C produced by Bacillus subtilis EA-CB0015.
    (AMER CHEMICAL SOC, 2013-04-26) Villegas-Escobar, Valeska; Ceballos, Isabel; Mira, John J.; Edith Argel, Luz; Orduz Peralta, Sergio; Romero-Tabarez, Magally; Universidad EAFIT. Departamento de Ciencias; Ciencias Biológicas y Bioprocesos (CIBIOP)
    Bacillus subtilis EA-CB0015 was isolated from the phyllosphere of a banana plant and tested for its potential to produce bioactive compounds against Mycosphaerella fijiensis. Using a dual plate culture technique the cell-free supernatant of B. subtilis EA-CB0015 produced inhibition values of 89 +/- 1%. The active compounds were purified by solid-phase extraction and HPLC, and their primary structures determined using mass spectrometry and amino acid analysis. A new fengycin isoform, fengycin C, with the amino acid sequence Glu-Orn-Tyr-Thr-Glu-Val-Pro-Gln-Thr-Ile was isolated. The peptidic moiety differs from fengycin B at position 9 and from fengycin A at positions 6 and 9. The beta-hydroxy fatty acyl chain is connected to the N-terminal of the decapeptide and can be saturated or unsaturated, ranging from 14 to 18 carbons. The C-terminal residue of the peptidic moiety is linked to the tyrosine residue at position 3, forming the branching point of the acyl peptide and the eight-membered cyclic lactone.
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    Ítem
    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.