0000000000082686
AUTHOR
Mario R. Estrada
showing 10 related works from this author
Thermodynamics of competing oxidation reactions of allyl methyl disulfide by hydrogen peroxide: a first principle molecular computational study on th…
2008
Allyl methyl disulfide, a peroxide scavenger, was studied together with three isomeric (two sulfoxides and one epoxide) forms of its mono-oxidized products. After a full conformational study of the reactant and three isomeric oxidized forms, the geometries were optimized at B3LYP/6-31G (d) level of theory. The epoxide form turned and to be more stable than either one of the two isomeric sulfoxides. Changes for Thermodynamic functions of oxidation reactions were calculated and from the δGreaction values the equilibrium constant for the interconversions of the oxidized products were estimated. Bader-type AIM analyses were performed on the electron density, computed at the B3LYP/6-311++G (d,p)…
A full conformational space analysis of bilirubin
2009
Ab initio methods were utilized in a gas-phase systematic conformational search of bilirubin conformers. The whole molecule was divided into four fragments. Most stable conformers of them were employed to build 196 conformers of the complete bilirubin molecule. Initial geometries were optimized using HF/3-21G level of theory and the minimum energy conformers were then reoptimized at B3LYP/6-31G(d) level. Ridge-tile conformer was the most stable one, in perfect agreement with X-ray data. We found that while tetrapyrrole backbone shows some flexibility, propionic acid side chains have a greater influence in bilirubin conformation because they can interact through different hydrogen bond patte…
ChemInform Abstract: Spectroscopic and Theoretical Studies on the Internal Rotational Barrier of 1-Acetylcyclohexene
1987
Abstract MINDO-3 molecular orbital calculations with full geometry optimization have been carried out on 1-acetylcyclohexene (ACH) in order to estimate the rotational barrier for the acetyl group, and to localize the less energetic conformation. MNDO calculations have also been carried out for comparative purposes. Both methods point to the non-delocalized structure with the two π-clouds perpendicular to the less energetic conformation. A decomposition of the barrier energy by means of Fourier analysis is made in order to characterize the contributions to the barrier. The UV spectrum of ACH has been recorded both in vapor phase and in hexane solution. These spectra are related to the one ca…
Theoretical study on hydration of two particular diazanaphthalenes
2005
Abstract Cinnoline (1) and Phthalazine (2), diazanaphthalenes involved in certain biological reactions, have been studied computational with the purpose of comparing their protonation and covalent hydration mechanisms. Geometry optimizations of neutral, mono- and di-protonated cations and hydrated products were performed at HF, DFT/B3LYP levels of theory using 6-311G* basis set and single points energies were calculated at the MP2 level of theory using the same basis set. In agreement with experimental results, calculations predict a two-step mechanism resulting in a hydrated cation in which the OH of the water is located depending on the position of both nitrogen in the diazanaphthalene mo…
Theoretical study of a hydration mechanism in an enaminone pro-drug prototype
2003
Enaminones may act as pro-drugs releasing via proton-catalyzed hydrolysis a primary amine, which may be an actual drug. A hydration mechanism of prototype enaminone (2-propenal-3-amine) has been subjected to quantum chemical studies. All involved compounds were investigated in a search for the most likely reactive form. Results revealed that the proposed reaction pathway is thermodynamically possible.
An ab initio conformational study on captopril
2003
Abstract Captopril can interact regio- and stereo-specifically with various functional groups present at the active site of angiotensin converting enzyme (ACE). Since no X-ray structure of ACE is available, Captopril, as an ACE inhibitor may be used as a ‘molecular caliper’, to estimate upper and lower bound values for separation d, where the mercaptidic terminal group of the molecule is linked to the enzyme Zn2+ cofactor, while the carboxylate links via an hydrogen bond to the guanidine moiety of an arginine side chain. As the results of this Ab Initio study, the conformations of the dianionic form of the full captopril molecule are reported here.
Theoretical study on hydration of symmetrically different diazanaphthalenes
2005
Abstract Quinazoline (symmetrical) and quinoxaline (unsymmetrical), diazanaphthalenes involved in certain biological reactions, have been studied computational with the purpose of comparing their protonation and covalent hydration mechanisms. Geometry optimizations of neutral, mono and diprotonated cations and hydrated products have been carried out at three levels of theory. Geometry optimizations were performed at HF, DFT/B3LYP levels of theory using 6-311G* basis set and single point energies were calculated at the MP2 level of theory using the same basis set. In agreement with experimental results, calculations predict a two steps mechanism resulting in a hydrated cation in which the OH…
ChemInform Abstract: Experimental and Theoretical Studies on the Electronic Spectra of Indole-3-acetic Acid and Its Anionic and Protonated Species.
2010
Abstract The geometrical and electronic structure of indole-3-acetic acid (IAH) have been investigated using the MINDO/3 molecular orbital method, the geometries being optimized by Rinaldi's method. The UV spectrum of IAH has been recorded in different solvents. The corresponding spectra of IAH + 2 and IA − were also respectively obtained, from IAH in different H 2 SO 4 /water mixtures and NaOH solutions. The agreement of experimental spectra with the ones theoretically calculated by the CNDO/M-Cl method after optimization of the κ parameter, is discussed. The p K a values of IAH have also been determined from the IAH + 2 spectra and are compared with literature data.
Theoretical study of selective H3 receptor antagonists of histamine
1993
Abstract The conformations and charge distributions of three selective H3 receptor antagonists of histamine were determined using the MNDO approach. The results suggest that the conformational flexibilities of betahistine, N α-(2-phenylacetyl)histamine and thioperamide are different; however, the low-energy conformations of these compounds show closely related spatial orderings. The MNDO calculations predict a significant population of the N1H form in the imidazole systems of N α-(2-phenylacetyl)histamine and thioperamide. Our results indicate that the conformational behaviour of H3 antagonists is closely similar to that reported for H2 antagonists of histamine. These results emphasize the …
Experimental and theoretical studies on the electronic spectra of indole-3-acetic acid and its anionic and protonated species
1991
Abstract The geometrical and electronic structure of indole-3-acetic acid (IAH) have been investigated using the MINDO/3 molecular orbital method, the geometries being optimized by Rinaldi's method. The UV spectrum of IAH has been recorded in different solvents. The corresponding spectra of IAH + 2 and IA − were also respectively obtained, from IAH in different H 2 SO 4 /water mixtures and NaOH solutions. The agreement of experimental spectra with the ones theoretically calculated by the CNDO/M-Cl method after optimization of the κ parameter, is discussed. The p K a values of IAH have also been determined from the IAH + 2 spectra and are compared with literature data.