Centro de Química ICUAP

Cyanide ion has been utilized to probe the heme environment of the ferric states of horseradish peroxidase, lactoperoxidase and chloroperoxidase. The tSN-NMR signal for cyanide bound to these enzymes is located in the downfield region from 578 to 412 ppm (with respect to the nitrate ion reference). The corresponding signal for met-forms of hemoglobin, myoglobin and cytochrome c is much further downfield in the 1047-847 ppm region. The signal position for peroxidases is quite invariant with pH in the physiological ranges. The upfield bias for peroxidase chemical shifts must reflect unique trans iron(lll) ligand types and/or proximal-group hydrogen bonding or steric effects. Model compound studies reveal a significant upfield cyanide IS N shift with addition of agents capable of hydrogen-bonding to the coordinated cyanide ion. An even more striking upfield shift of 277 ppm is associated with deprotonation of a trans imidazole residue. The distinctive chemical shifts observed for the cyano ligand in peroxidases support the hypothesis that a distal hydrogen-bonding network and perhaps a polar, basic trans ligand are essential for O-O bond activation by peroxidases.

The acid constants of mangiferin (a natural xanthonoid) in aqueous solution were determined through an UV/vis spectroscopic study employing the SQUAD program as a computational tool. A NMR study complements the pK a values assignment and evidences a Hbridge presence on 1-C. The chemical model used was consistent with the experimental data obtained. The pK a values determined with this procedure were as follows: H 4 (MGF) = H 3 (MGF) − + H + , pK a 1 (6-H) = 6.52 ± 0.06; H 3 (MGF) − = H 2 (MGF) 2− + H + , pK a 2 (3-H) = 7.97 ± 0.06; H 2 (MGF) 2− = H(MGF) 3− + H + , pK a 3 (7-H) = 9.44 ± 0.04; H(MGF) 3− = (MGF) 4− + H + , pK a 4 (1-H) = 12.10 ± 0.01; where it has been considered mangiferin C 19 H 18 O 11 as H 4 (MGF). Mangiferin UV/vis spectral behavior, stability study in aqueous solution as well as NMR spectroscopy studies: one-dimensional 1 H, 13 C, 2D correlated 1 H/ 13 C performed by (g)-HSQC and (g)-HMBC methods; are also presented. pK a values determination of H 4 (MGF) in aqueous solution is a necessary contribution to subsequent pharmacokinetic study, and a step towards the understanding of its biological effects.

The stability of curcumin (H 3 Cur) in aqueous media is improved when the systems in which it is present are at high pH values (higher than 11.7), fitting a model describable by a pseudo-zero order with a rate constant k for the disappearance of the Cur 3− species of 1.39 (10 −9 ) M min −1 . There were three acidity constants measured for the curcumin as follows: pK A3 = 10.51 ± 0.01 corresponding to the equilibrium HCur 2− = Cur 3− + H + , a pK A2 = 9.88 ± 0.02 corresponding to the equilibrium H 2 Cur − = HCur −2 + H + . These pK A values were attributed to the hydrogen of the phenol part of the curcumin, while the pK A1 = 8.38 ± 0.04 corresponds to the equilibrium H 3 Cur = H 2 Cur − +H + and is attributed the acetylacetone type group. Formation of quinoid structures play an important role in the tautomeric forms of the curcumin in aqueous media, which makes the experimental values differ from the theoretically calculated ones, depending on the conditions adopted in the study.

The formation of complexes among the Curcumin, Fe(III) and Fe(II) was studied in aqueous media within the 5-11 pH range by means of UV-Vis spectrophotometry and cyclic voltammetry. When the reaction between the Curcumin and the ions present in basic media took place, the resulting spectra of the systems Curcumin-Fe(III) and Curcumin-Fe(II) presented a similar behaviour. The cyclic voltammograms in basic media indicated that a chemical reaction has taken place between the Curcumin and Fe(III) before that of the formation of complexes. Data processing with SQUAD permitted to calculate the formation constants of the complexes Curcumin-Fe(III), corresponding to the species FeCur (log β 1 1 0 = 22.25 ± 0.03) and FeCur(OH) − (log β 1 1-1 = 12.14 ± 0.03), while for the complexes Curcumin-Fe(II) the corresponding formation constants of the species FeCur − (log β 1 1 0 = 9.20±0.04), FeHCur (log β 1 1 1 = 19.76±0.03), FeH 2 Cur + (log β 1 1 2 = 28.11±0.02).

Combination of the nonsteroidal anti-inflammatory drugs (NSAIDs) aspirin (1), ibuprofen (2) and meclofenamic acid (3) with lead(II) nitrate gave metal complexes of the composition [Pb(C 9 H 7 O 4) 2 (H 2 O)] n (4), [Pb(C 13 H 17 O 2) 2 (H 2 O)] n (5) and [Pb(C 14 H 10 Cl 2 NO 2) 2 ] n (6). The compounds have been characterized by IR and NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction analysis. The complexes crystallized in the monoclinic and triclinic space groups P2 1 /n (4), P2 1 (5) and P 1 (6), respectively. All compounds are coordination polymers with a highly distorted coordination geometries. The polyhedra of the [PbO 7 ] (4 and 5) and [PbO 6 ] (6) cores are hemidirected as indicated by a vacant site, which can be attributed to an active inert pair of electrons.

Geometry, Symmetry and Chemistry: An Icosahedron Model made out with Plastic Straws) The construction of an icosahedron model made with drinking straws is described. This model is very useful for learning (and teaching) the geometry and symmetry of icosahedral species, such as, the closododecaborane ion, (B 12 H 12) 2- .

Immobilization of a peroxidase from chayote (Sechium edule (Jacq.) Sw) using an adequately functionalized and previously activated support which allows to preserve enzymatic activity is here presented. Studies were also carried out to show its potential for decontamination of artificial waste waters containing phenolic compounds. The peroxidase was successfully immo- bilized onto the organic support polystyrene-divinylbenzene copolymer functionalized with triglycine

Vanadium(IV/V) compounds have been studied as possible metallopharmaceutical drugs against diabetes mellitus. However, mechanisms of action and toxicological threshold have been tackled poorly so far. In this paper, our purposes were to evaluate the metabolic activity on dyslipidemia and dysglycemia, insulin signaling in liver and adipose tissue, and toxicology of the title compound. To do so, the previously reported bisammonium tetrakis 4-(,-dimethylamino)pyridinium decavanadate, the formula of which is [DMAPH](NH)[VO]·8HO (where DMAPH is 4-dimethylaminopyridinium ion), was synthesized, and its dose-response curve on hyperglycemic rats was evaluated. A Long-Evans rat model showing dyslipidemia and dysglycemia with parameters that reproduce metabolic syndrome and severe insulin resistance was generated. Two different dosages, 5 mol and 10 mol twice a week of the title compound (equivalent to 2.43 mg·V/kg/day and 4.86 mg·V/kg/day, resp.), were administered intraperitoneal (i.p.) for ...

A spectrophotometric method for the determination of glyphosate based on the monitoring of a complex formation between bis 5-phenyldipyrrinate of nickel (II) and the herbicide was developed. The method showed a short response time (10 s), high selectivity (very low interference from other pesticides and salts), and high sensitivity (LOD 2.07 × 10−7 mol/L, LOQ 9.87 × 10−7 mol/L, and a Kd from 1.75 × 10−6 to 6.95 × 10−6 mol/L). The Job plot showed that complex formation occurs with a 1:1 stoichiometry. The method was successfully applied in potable, urban, groundwater, and residual-treated water samples, showing high precision (0.34–2.9%) and accuracy (87.20–119.04%). The structure of the complex was elucidated through theoretical studies demonstrating that the nickel in the bis 5-phenyldipyrrinate forms a distorted octahedral molecular geometry by expanding its coordination number through one bond with the nitrogen and another with the oxygen of the glyphosate’ carboxyl group, at dis...

Cytosine, a DNA and RNA building-block, and Metformin, the most widely prescribed drug for the treatment of Type 2 Diabetes mellitus were made to react separately with ammonium or sodium metavanadates in acidic aqueous solutions to obtain two polyoxovanadate salts with a 6:1 ratio of cation-anion. Thus, compounds [HCyt] 6 [V 10 O 28 ]•4H 2 O, 1 and [HMetf] 6 [V 10 O 28 ]•6H 2 O, 2 (where HCyt = Cytosinium cation, [C 4 H 6 N 3 O] + and HMetf = Metforminium cation, [C 4 H 12 N 5 ] +) were obtained and characterized by elemental analysis, single crystal X-ray diffraction, vibrational spectroscopy (IR and Raman), solution 51 V-NMR, thermogravimetric analysis (TGA-DTGA), as well as, theoretical methods. Both compounds crystallized in P1 space group with Z' = 1/2, where the anionic charge of the centrosymmetric ion [V 10 O 28 ] 6− is balanced by six Cytosinium and six Metforminium counterions, respectively. Compound Sánchez-Lara et al. Cytosinine and Metformin Decavanadates Optimized structures were obtained and the main non-covalent interactions were characterized. Biological activities of these compounds are also under investigation. The combination of two therapeutic agents opens up a window toward the generation of potential metalopharmaceuticals with new and exciting pharmacological properties.

Un problema común en la enseñanza de la cristalografía está asociado con la representación bidimensional de estructuras tridimensionales. Es bien conocido que no todos los estudiantes son capaces de visualizar estructuras en tres dimensiones cuando éstas se representan en dos. Este problema podría resolverse mediante el uso de modelos de redes cristalinas; sin embargo, este recurso no es viable para la mayoría de los estudiantes debido al costo elevado de los mismos. Además, la producción en México de modelos para la enseñanza de la química es casi inexistente.