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Papers by Guadalupe Perez-Caballero
International Journal of Quantum Chemistry, 2012
A novel azocompound with two nonequivalents azo groups, 2‐(4‐phenylazoaniline)‐4‐phenylphenol, wa... more A novel azocompound with two nonequivalents azo groups, 2‐(4‐phenylazoaniline)‐4‐phenylphenol, was synthesized and characterized by spectroscopic and computational analysis. An intramolecular hydrogen bonding (HB), O1H1···N1, involving the N1N2 group and the proton in a neighbor hydroxyl moiety, was identified. It was found responsible for a characteristic π‐conjugated H1O1C18C13N2N1 six‐membered cyclic fragment. It is worth noting that this azo group is involved in an azo‐hydrazo equilibrium, being the azo form the most stable one. This resonance‐assisted HB was characterized using the OH‐related infrared bands and the corresponding signals in 1H NMR. In addition, conformational studies and geometrical and electronic parameter calculations were performed using the density functional theory, at B3LYP/6‐311++G** level. Bond and ring critical points were identified using the atoms in molecules theory, which allowed confirming the intramolecular HB. The second azo‐group can...
Analytical Letters, 1993
Simple spectrophotometric methods a r e described for the determination of diclofenac sodium in p... more Simple spectrophotometric methods a r e described for the determination of diclofenac sodium in pharmaceutical preparations. The methods a r e based on the oxidation of the drug using reagents viz. c e r i c ammonium sulphate, dibromodimethylhydantoin , N-brornosuccinimide, and potassium bromate to yield coloured products with maximum absorbance at 450, 385, 385 and 495 nrn and linear calibration graphs in the range of 2-16, 4 0-400, 50-500 and 50-600 Mg.ml-' respectively. The methods a r e statistically validated and found to be accurate, sensitive and reproducible.
Analytical and Bioanalytical Chemistry, 2009
The capability of single-reflection near-IR (NIR) spectroscopy to differentiate, characterize and... more The capability of single-reflection near-IR (NIR) spectroscopy to differentiate, characterize and monitor the fate of a set of hydrocarbons spilled in the marine environment was compared with that of multiple-reflection horizontal attenuated total reflection mid-IR (ATR-MIR) spectroscopy. Multivariate pattern recognition techniques [principal component analysis (PCA), multivariate polynomial regression, cluster analysis and potential curves] were applied to unravel the major trends of the weathering processes of four generic types of crude oils and two heavy fuel oils spilled under controlled conditions for almost 4 months. A chemical interpretation of the NIR spectra related the weathering processes and the PCA loadings, which had not already been done in the literature. Weathering for both light and heavy products was characterized by a contrast among the linear aliphatic structures (more volatile and easy to degrade) and the branched and aromatic structures (more recalcitrant). Potential curves were applied to model each product and determine objectively whether unknown samples could be classified correctly. Polynomial regression on the PCA scores was employed to evaluate the time elapsed from the oil spillage to its sampling; this represents a new approach to assess the age of a hydrocarbon lump. In general, NIR spectroscopy yielded good results when light crude oils were studied, whereas ATR-MIR spectroscopy led to satisfactory results for both light and heavy products.
Acta crystallographica. Section C, Crystal structure communications, 2000
The crystal structure of the title compound, C(19)H(16)N(2)O(2), displays a trans configuration o... more The crystal structure of the title compound, C(19)H(16)N(2)O(2), displays a trans configuration of the azo moiety, which forms an intramolecular O-H.N=N hydrogen bond. The H.N and O.N distances are 1.81 (3) and 2.581 (4) A, respectively. The azobenzene moiety is approximately planar, and has a dihedral angle of ca 23 degrees with the substituted phenyl group.
Journal of Molecular Structure-theochem, 2001
AM1, PM3, HF/STO-3G, HF/3-21G∗, HF/6-31G∗, MP2/STO-3G//HF/STO-3G, MP2/3-21G∗//HF/3-21G∗ and MP2/6... more AM1, PM3, HF/STO-3G, HF/3-21G∗, HF/6-31G∗, MP2/STO-3G//HF/STO-3G, MP2/3-21G∗//HF/3-21G∗ and MP2/6-32G∗//HF/6-31G∗ calculations and the Boltzmann distribution law were used to establish a new model for the calculation of the tautomeric constant (KT) of 2-, 3- and 4-substituted pyridines in both gas and solution phase. The solvent effect was approximated with one water molecule around each tautomeric species. Three mathematical models were used
Journal of Molecular Structure: THEOCHEM, 2001
AM1, PM3, HF/STO-3G, HF/3-21G p , HF/6-31G p , MP2/STO-3G//HF/STO-3G, MP2/3-21G p //HF/3-21G p an... more AM1, PM3, HF/STO-3G, HF/3-21G p , HF/6-31G p , MP2/STO-3G//HF/STO-3G, MP2/3-21G p //HF/3-21G p and MP2/6-32G p // HF/6-31G p calculations and the Boltzmann distribution law were used to establish a new model for the calculation of the tautomeric constant (K T) of 2-, 3-and 4-substituted pyridines in both gas and solution phase. The solvent effect was approximated with one water molecule around each tautomeric species. Three mathematical models were used to calculate the K T values. A linear correlation was carried out to show that some results were similar to the experimental ones.
A mass spectrometric study of a set of six novel 2-(arylazo)-4-phenylphenols 1-6 was performed. T... more A mass spectrometric study of a set of six novel 2-(arylazo)-4-phenylphenols 1-6 was performed. The electron impact spectra were acquired and analyzed for five of the compounds in order to establish a fragmentation pattern. The suggested pathways were investigated and confirmed by means of tandem mass spectrometry (MS/MS) experiments together with high-resolution accurate mass data. However, the sixth molecule, a sodium sulfonate salt, was studied using fast atom bombardment (FAB) ionization in positive and negative modes. In addition, some electronic substituent effects were investigated by analyzing Hammett-McLafferty linear free energy correlations for some peaks derived from the corresponding molecular ions. Also, the role of the O-H...N hydrogen bond present in the target compounds was analyzed. The roles of these H-bonds were consistent with the corresponding acidity constant values obtained experimentally as well as by theoretical quantum chemistry calculations using HF/6-31 + G(d,p) and B3LYP/6-31G(d,p). Some spectrometric data were correlated with topological properties derived from the atoms-in-molecules (AIM) theory.
International Journal of Quantum Chemistry, 2012
A novel azocompound with two nonequivalents azo groups, 2‐(4‐phenylazoaniline)‐4‐phenylphenol, wa... more A novel azocompound with two nonequivalents azo groups, 2‐(4‐phenylazoaniline)‐4‐phenylphenol, was synthesized and characterized by spectroscopic and computational analysis. An intramolecular hydrogen bonding (HB), O1H1···N1, involving the N1N2 group and the proton in a neighbor hydroxyl moiety, was identified. It was found responsible for a characteristic π‐conjugated H1O1C18C13N2N1 six‐membered cyclic fragment. It is worth noting that this azo group is involved in an azo‐hydrazo equilibrium, being the azo form the most stable one. This resonance‐assisted HB was characterized using the OH‐related infrared bands and the corresponding signals in 1H NMR. In addition, conformational studies and geometrical and electronic parameter calculations were performed using the density functional theory, at B3LYP/6‐311++G** level. Bond and ring critical points were identified using the atoms in molecules theory, which allowed confirming the intramolecular HB. The second azo‐group can...
Analytical Letters, 1993
Simple spectrophotometric methods a r e described for the determination of diclofenac sodium in p... more Simple spectrophotometric methods a r e described for the determination of diclofenac sodium in pharmaceutical preparations. The methods a r e based on the oxidation of the drug using reagents viz. c e r i c ammonium sulphate, dibromodimethylhydantoin , N-brornosuccinimide, and potassium bromate to yield coloured products with maximum absorbance at 450, 385, 385 and 495 nrn and linear calibration graphs in the range of 2-16, 4 0-400, 50-500 and 50-600 Mg.ml-' respectively. The methods a r e statistically validated and found to be accurate, sensitive and reproducible.
Analytical and Bioanalytical Chemistry, 2009
The capability of single-reflection near-IR (NIR) spectroscopy to differentiate, characterize and... more The capability of single-reflection near-IR (NIR) spectroscopy to differentiate, characterize and monitor the fate of a set of hydrocarbons spilled in the marine environment was compared with that of multiple-reflection horizontal attenuated total reflection mid-IR (ATR-MIR) spectroscopy. Multivariate pattern recognition techniques [principal component analysis (PCA), multivariate polynomial regression, cluster analysis and potential curves] were applied to unravel the major trends of the weathering processes of four generic types of crude oils and two heavy fuel oils spilled under controlled conditions for almost 4 months. A chemical interpretation of the NIR spectra related the weathering processes and the PCA loadings, which had not already been done in the literature. Weathering for both light and heavy products was characterized by a contrast among the linear aliphatic structures (more volatile and easy to degrade) and the branched and aromatic structures (more recalcitrant). Potential curves were applied to model each product and determine objectively whether unknown samples could be classified correctly. Polynomial regression on the PCA scores was employed to evaluate the time elapsed from the oil spillage to its sampling; this represents a new approach to assess the age of a hydrocarbon lump. In general, NIR spectroscopy yielded good results when light crude oils were studied, whereas ATR-MIR spectroscopy led to satisfactory results for both light and heavy products.
Acta crystallographica. Section C, Crystal structure communications, 2000
The crystal structure of the title compound, C(19)H(16)N(2)O(2), displays a trans configuration o... more The crystal structure of the title compound, C(19)H(16)N(2)O(2), displays a trans configuration of the azo moiety, which forms an intramolecular O-H.N=N hydrogen bond. The H.N and O.N distances are 1.81 (3) and 2.581 (4) A, respectively. The azobenzene moiety is approximately planar, and has a dihedral angle of ca 23 degrees with the substituted phenyl group.
Journal of Molecular Structure-theochem, 2001
AM1, PM3, HF/STO-3G, HF/3-21G∗, HF/6-31G∗, MP2/STO-3G//HF/STO-3G, MP2/3-21G∗//HF/3-21G∗ and MP2/6... more AM1, PM3, HF/STO-3G, HF/3-21G∗, HF/6-31G∗, MP2/STO-3G//HF/STO-3G, MP2/3-21G∗//HF/3-21G∗ and MP2/6-32G∗//HF/6-31G∗ calculations and the Boltzmann distribution law were used to establish a new model for the calculation of the tautomeric constant (KT) of 2-, 3- and 4-substituted pyridines in both gas and solution phase. The solvent effect was approximated with one water molecule around each tautomeric species. Three mathematical models were used
Journal of Molecular Structure: THEOCHEM, 2001
AM1, PM3, HF/STO-3G, HF/3-21G p , HF/6-31G p , MP2/STO-3G//HF/STO-3G, MP2/3-21G p //HF/3-21G p an... more AM1, PM3, HF/STO-3G, HF/3-21G p , HF/6-31G p , MP2/STO-3G//HF/STO-3G, MP2/3-21G p //HF/3-21G p and MP2/6-32G p // HF/6-31G p calculations and the Boltzmann distribution law were used to establish a new model for the calculation of the tautomeric constant (K T) of 2-, 3-and 4-substituted pyridines in both gas and solution phase. The solvent effect was approximated with one water molecule around each tautomeric species. Three mathematical models were used to calculate the K T values. A linear correlation was carried out to show that some results were similar to the experimental ones.
A mass spectrometric study of a set of six novel 2-(arylazo)-4-phenylphenols 1-6 was performed. T... more A mass spectrometric study of a set of six novel 2-(arylazo)-4-phenylphenols 1-6 was performed. The electron impact spectra were acquired and analyzed for five of the compounds in order to establish a fragmentation pattern. The suggested pathways were investigated and confirmed by means of tandem mass spectrometry (MS/MS) experiments together with high-resolution accurate mass data. However, the sixth molecule, a sodium sulfonate salt, was studied using fast atom bombardment (FAB) ionization in positive and negative modes. In addition, some electronic substituent effects were investigated by analyzing Hammett-McLafferty linear free energy correlations for some peaks derived from the corresponding molecular ions. Also, the role of the O-H...N hydrogen bond present in the target compounds was analyzed. The roles of these H-bonds were consistent with the corresponding acidity constant values obtained experimentally as well as by theoretical quantum chemistry calculations using HF/6-31 + G(d,p) and B3LYP/6-31G(d,p). Some spectrometric data were correlated with topological properties derived from the atoms-in-molecules (AIM) theory.