Gabriel Cuevas

Bio: Gabriel Cuevas is an academic researcher from National Autonomous University of Mexico. The author has contributed to research in topics: Anomeric effect & Density functional theory. The author has an hindex of 23, co-authored 84 publications receiving 2401 citations. Previous affiliations of Gabriel Cuevas include Spanish National Research Council & Instituto Politécnico Nacional.

The anomeric effect

Abstract: Historical Aspects and Definitions Origin and Consequences of the Anomeric Effect Theoretical Studies of the Anomeric Effect Stereoelectronic Effects Associated with the Anomeric Effect Endo and Exo Anomeric Interactions The Enthalpic Anomeric Effect Second- and Lower-Row Anomeric Interactions The Reverse Anomeric Effect The Kinetic Anomeric Effect Applications of the Anomeric Effect in Organic Synthesis

Molecular Recognition of Saccharides by Proteins. Insights on the Origin of the Carbohydrate−Aromatic Interactions

Abstract: The existence of stabilizing carbohydrate-aromatic interactions is demonstrated from both the theoretical and experimental viewpoints. The geometry of experimentally based galactose-lectin complexes has been properly accounted for by using a MP2/6-31G(d,p) level of theory and by considering a counterpoise correction during optimization. In this case, the stabilizing interaction energy of the fucose-benzene complex amounts to 3.0 kcal/mol. The theoretical results obtained herein indicate that the carbohydrate-aromatic interactions are stabilizing interactions with an important dispersive component and that electronic density between the sugar hydrogens and the aromatic ring indeed exists, thus giving rise to three so-called nonconventional hydrogen bonds. Experimental evidence of the intrinsic tendency of aromatic moieties to interact with certain sugars has also been shown by simple NMR experiments in water solution. Benzene and phenol specifically interact with the clusters of C-H bonds of the alpha face of methyl beta-galactoside, without requiring the well-defined three-dimensional shape provided by a protein receptor, therefore resembling the molecular recognition features that are frequently observed in many carbohydrate-protein complexes.

An Experimental and Theoretical Study of the Substituent Effects on the Redox Properties of 2-[(R-phenyl)amine]-1,4-naphthalenediones in Acetonitrile.

Abstract: We synthesized and analyzed 19 compounds of 3'- (meta-) and 4'- (para-) substituted 2-[(R-phenyl)amine]-1,4-naphthalenediones (PANs) R = p-MeO, p-Me, p-Bu, p-Hex, p-Et, m-Me, m-Et, H, p-Cl, p-Br, m-F, m-Cl, p-COCH(3), m-CN, m-NO(2), m-COOH, and p-COOH. Despite the fact that the nitrogen atom, which binds the quinone with the meta- and para-substituted ring, interferes with the direct conjugation between both rings, the UV-vis spectra of these compounds show the existence of an intramolecular electronic transfer from the respective aniline to the p-naphthoquinone moiety. In accordance with this donor-acceptor character, the cyclic voltammograms of these compounds exhibit two, one-electron reduction waves corresponding to the formation of radical-anion and dianion, where the half-wave potential values vary linearly with the Hammett constants (sigma(x)). The analysis of the different voltammetric parameters (e.g., voltammetric function, anodic/cathodic peak currents ratio, and the separation between the anodic and cathodic potential peaks) show that with the exception of the carboxylic PAN derivatives, all compounds present the same reduction pathway. We investigated the molecular and electronic structures of these compounds using the semiempirical PM3 method and, within the framework of the Density Functional Theory, using the Becke 3LYP hybrid functional with a double zeta split valence basis set. Our theoretical calculations predict that, with the exception of the p-nitro compound, all the compounds are planar molecules where the conjugation degree of the nitrogen lone pair with the quinone system depends on the position and magnitude of the electronic effect of the substituent in the aniline ring. The Laplacians of the critical points (nabla(2)rho), for the C-O bonds, show that the first reduction wave corresponds to the carbonyl group in alpha-position to the aniline, and that the second one-electron transfer is due to the C(4)-O(2) carbonyl reduction. Thus, the higher reaction constant value (rho) obtained for the second one-electron transfer is due to the fact that the displacement of the nonshared electrons of the amino nitrogen merely modifies the electron density of C(4)-O(2) bond. The positive correlation between the LUMO energy values calculated for these compounds and the E(1/2) potentials corresponding to the C(1)-O(1) carbonyl reduction show that the electron addition takes place at the lowest unoccupied molecular orbital, supporting the fact that this wave is also prone to the substituent effect.

Enthalpic nature of the CH/pi interaction involved in the recognition of carbohydrates by aromatic compounds, confirmed by a novel interplay of NMR, calorimetry, and theoretical calculations.

Abstract: Specific interactions between molecules, including those produced by a given solute, and the surrounding solvent are essential to drive molecular recognition processes. A simple molecule such as benzene is capable of recognizing and differentiating among very similar entities, such as methyl 2,3,4,6-tetra-O-methyl-α-d-galactopyranoside (α-Me5Gal), methyl 2,3,4,6-tetra-O-methyl-β-d-galactopyranoside (β-Me5Gal), 1,2,3,4,6-penta-O-acetyl-β-d-galactopyranose (β-Ac5Gal), and methyl 2,3,4,6-tetra-O-methyl-α-d-mannopyranoside (α-Me5Man). In order to determine if these complexes are formed, the interaction energy between benzene and the different carbohydrates was determined, using Calvet microcalorimetry, as the enthalpy of solvation. These enthalpy values were −89.0 ± 2.0, −88.7 ± 5.5, −132.5 ± 6.2, and −78.8 ± 3.9 kJ mol−1 for the four complexes, respectively. Characterization of the different complexes was completed by establishing the molecular region where the interaction takes place using NMR. It was deter...

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Light-emitting diodes

Abstract: Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

Advanced Organic Chemistry

Abstract: Organic Chemistry By Dr. I. L. Finar. Vol. 2: Stereochemistry and the Chemistry of Natural Products. Pp. xi + 733. (London and New York: Longmans, Green and Co., Ltd., 1956.) 40s. net.

Binding Mechanisms in Supramolecular Complexes

Abstract: Supramolecular chemistry has expanded dramatically in recent years both in terms of potential applications and in its relevance to analogous biological systems. The formation and function of supramolecular complexes occur through a multiplicity of often difficult to differentiate noncovalent forces. The aim of this Review is to describe the crucial interaction mechanisms in context, and thus classify the entire subject. In most cases, organic host-guest complexes have been selected as examples, but biologically relevant problems are also considered. An understanding and quantification of intermolecular interactions is of importance both for the rational planning of new supramolecular systems, including intelligent materials, as well as for developing new biologically active agents.