Rodolfo Gómez-Balderas

Determination of pKa values of tenoxicam from 1H NMR chemical shifts and of oxicams from electrophoretic mobilities (CZE) with the aid of programs SQUAD and HYPNMR

In this work it is explained, by the first time, the application of programs SQUAD and HYPNMR to refine equilibrium constant values through the fit of electrophoretic mobilities determined by capillary zone electrophoresis experiments, due to the mathematical isomorphism of UV-vis absorptivity coefficients, NMR chemical shifts and electrophoretic mobilities as a function of pH. Then, the pK(a) values of tenoxicam in H(2)O/DMSO 1:4 (v/v) have been obtained from (1)H NMR chemical shifts, as well as of oxicams in aqueous solution from electrophoretic mobilities determined by CZE, at 25 degrees C. These values are in very good agreement with those reported by spectrophotometric and potentiometric measurements.

Theoretical analysis of hydrogen bonding in catechol–n(H2O) clusters (n = 0…3)

The electronic structure and hydrogen bonding of the stable isomers of catechol and its complexes with one to three water molecules is studied by means of theoretical methods. A conformational analysis based on a simulated annealing search on the potential energy surface of each complex was carried out previous to the quantum chemical energy minimization. Twenty three stable conformers were found including some involving a pi-interaction between the catechol moiety and a water molecule. The topological properties of the electron density reveal the presence of an intramolecular hydrogen bond only in the case of one complex with three water molecules. The infrared spectra of these molecules were computed and compared to available experimental results. An alternative assignment of the experimental vibrational spectrum within the range 3340-3750 cm(-1) of the catechol-3(H(2)O) complex (M. Gerhards, C. Unterberg, and K. Kleinermanns, Phys. Chem. Chem. Phys. 2000, 2, p. 5538) is proposed. The red-shift observed for the stretching vibrational frequency of the catechol hydrogen donor hydroxyl group in the presence of water molecules is rationalized in terms of the properties of the electron distribution and a Darwinian family tree is proposed to classify the diverse structural and energetic characteristics of the stable complexes found.

Promotional effect of Co or Ni impurity in the catalytic activity of MoS2: An electronic structure study

It has been observed that the catalytic activity of MoS2 crystals is enhanced when either Co or Ni atoms are added. The presence of these atoms leads to electronic rearrangements, which are considered the source of catalytic improvement. However, the relation between the electronic properties and the enhancement of the catalytic activity is not yet fully understood. In order to get insight into the electronic-level changes that affect the catalyst performance, a solid-state density functional study has been carried out for Mo, Co/Mo, and Ni/Mo sulfides, using bulk and surface models. The MoS2 crystallize in a well-known layered structure, which has been used together with the supercell model to simulate the (10N 10 ) edge surface of MoS 2. The binary sulfides were obtained substituting Co or Ni by Mo from the original MoS2 bulk model. The electronic structure in a nonmagnetic state is analyzed and, in particular, the density of states of metal and sulfur atoms for the surface and bulk are compared. Finally, we discuss the important role that these properties play in the hydrodesulfurization reaction and concluded that Mo at the surface remains the relevant reactive atomic center in the bimetallic systems, whereas Co and Ni are responsible for increasing the Mo reactivity at the surface. c 2000 John Wiley & Sons, Inc. Int J Quantum Chem 80: 406-415, 2000

Chemical Speciation of the System Cu(II)-Indomethacin in Ethanol and Water by UV-Vis Spectrophotometry

It has been proposed that the metal-drug complexes could be in fact the active agents displaying therapeutic effects of drugs. The characterization of the global formation equilibrium of complexes formed between metal ions and species with biological activity such as nonsteroidal anti-inflammatory drugs provides essential information to understand the mechanism of action of drugs. Since equilibrium constants determine the relative predominance of species, they provide crucial information to identify what complexes are more likely to be present in the system being responsible for the therapeutic effects of the drug. In this paper, the systems formed between copper and Indomethacin of different concentrations in ethanol or water were studied by UV-Vis spectrophotometry. The stoichiometry of the complexes Cu(II)–Indomethacin and their formation constants were investigated. Moreover, molecular structures of the Cu(II)–Indomethacin complexes were explored by means of the molecular modeling within the frame of the density functional theory.

Thermodynamic study of complexation of Zn(II)/L (L− = acetate, indomethacin and diclofenac anions) by isothermal titration calorimetry

In this work, a thermodynamic study of the Zn(II)/L systems (L− = acetate, AcO− or indomethacin anion, Indo− or diclofenac anion, Dic−) in ethanolic solution was carried out by isothermal titration calorimetry (ITC). Thermodynamic properties such as enthalpy (∆H), entropy (ΔS), Gibbs energy (ΔG) and formation constant (reported as logβi) associated with the complexation reactions were determined; the stoichiometry of the formed species was also found. Zn(II)/AcO− was used as a model system for the complexation of Zn(II) with indomethacin and diclofenac anions, because all of them coordinate through the carboxylate functional group. To determine the thermodynamic properties of each system under study, from the experimental results, a binding model has been devised to calculate the heat Qcalc that is released or absorbed in terms of the molar ratio

First-Principles Prediction of the pKas of Anti-inflammatory Oxicams

r_{{{\text{L/Zn}}\left( {\text{II}} \right)}}

A DFT study of the electronic structure of cobalt and nickel mono-substituted MoS2 triangular nanosized clusters

rL/ZnII in the complexation process between Zn(II) and L−. Calculated data (Qcalc) are adjusted to the ITC experimental results (Qexp), by means of MicroCal PEAQ-ITC analysis software to determine the enthalpy and formation constants of the MLj(2−j) formed complexes. Distribution diagrams of the fractions of the M and L species were obtained as a function of the molar ratio to discuss the predominance of the species in the systems as the titration was carried out.

Critical micelle concentration of an ammonium salt through DPD simulations using COSMO‐RS–based interaction parameters

Knowledge of coordination modes of metal and pharmaceuticals are crucial for gaining understanding of the chemical mechanisms underlying their biological activity, in particular for systems where there is a synergism based on the fact that complexes can provide enhanced activity of the drug with fewer side effects. Quantum chemistry calculations represent a unique and complementary approach to experimental methods to understand the thermodynamics of reactions in terms of structural details of the participating species. Here, the coordination modes between Cu(II) and piroxicam and their stability constants were studied, by means of DFT molecular modeling, in gas phase and in solution (water and ethanol) at the RevTPSS/def-SVP and (SMD- and CPCM-RevTPSS)/def-SVP levels of theory, respectively. Octahedral bidentate geometries are found to be the more stable, likely due to the chelate effect. Thermodynamic results on the stability of the formed complexes revealed that complexation is favored in ethanol. The calculated logKs with the (SMD-RevTPSS)/def-SVP level of theory are in better agreement to the experimental values than (CPCM-RevTPSS)/def-SVP results.