Fernando Mendizabal

Intercalation chemistry of molybdenum disulfide

Abstract Most relevant features of the fundamental and applied chemistry of MoS 2 are reviewed highlighting the importance of the layered nature of the solid on the optical and catalytic properties of the compounds. Experimental and theoretical aspects related to the 2H-1T-MoS 2 phase change induced by the insertion of lithium are discussed. The principal systems known until this moment, specifically those based on the intercalation of molecular and polymeric organic donors, organometallic species and cations into MoS 2 as well as the methods used for their synthesis, are described. The main characteristic of the products, principally their properties as mixed conductors and the diffusion of lithium inside the interlamellar spaces are discussed.

Complexation of morin with three kinds of cyclodextrin: A thermodynamic and reactivity study

Properties of inclusion complexes between morin (M) and beta-cyclodextrin (betaCD), 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD) and Heptakis (2,6-O-di methyl) beta-cyclodextrin (DMbetaCD) such as aqueous solubility and the association constants of this complex have been determined. The water solubility of morin was increased by inclusion with cyclodextrins. The phase-solubility diagrams drawn from UV spectral measurements are of the A(L)-type. Also ORAC(FL) studies were done. An increase in the antioxidant reactivity is observed when morin form inclusion complex with the three cyclodextrin studied. Finally, thermodynamics studies of cyclodextrin complexes indicated that for DMbetaCD the inclusion is primarily enthalpy-driven process meanwhile betaCD and HPbetaCD are entropy-driven processes. This is corroborated by the different inclusion geometries obtained by 2D-NMR.

Aurophilic attraction in binuclear complexes with Au(I) and Au(III). A theoretical study

Model compounds are used to study the aurophilic attraction among gold atoms in the different oxidation states Au(I)–Au(I), Au(I)–Au(III) and Au(III)–Au(III). An attraction is found for all models and there is a reasonable agreement between the experimental and theoretical geometries at the MP2 level. The dispersion, induction and electrostatic multipole components to this attraction are analyzed using intermolecular models.

ESR Spin Trapping Studies of Free Radicals Generated from Nitrofuran Derivative Analogues of Nifurtimox by Electrochemical and Trypanosoma cruzi Reduction

Electron spin resonance (ESR) spectra of radicals obtained from two analogues of the antiprotozoal drug nifurtimox by electrolytic and Trypanosoma cruzi reduction were analyzed. The electrochemistry of these compounds was studied using cyclic voltammetry. STO 3-21G ab initio and INDO molecular orbital calculations were performed to obtain the optimized geometries and spin distribution, respectively. The antioxidant effect of glutathione on the nitroheterocycle radical was evaluated. DMPO spin trapping was used to investigate the possible formation of free radicals in the trypanosome microsomal system. Nitro1 and Nitro2 nitrofuran analogues showed better antiparasitic activity than nifurtimox. Nitro2 produced oxygen redox cycling in T. cruzi epimastigotes. The ESR signal intensities were consistent with the trapping of either the hydroxyl radical or the Nitro2 analogue radicals. These results are in agreement with the biological observation that Nitro2 showed anti-Chagas activity by an oxidative stress mechanism.

Aurophilic attraction: the additivity and the combination with hydrogen bonds

Abstract The coexistence of gold–gold contacts and hydrogen bonding is studied in the model system [H 2 P(OH)AuCl] 2 and [H 2 P(OH)AuPH 2 (O)] 2 . The two interactions are found to be comparable. The possible non-additivity of the aurophilic, Au(I)–Au(I) interaction is studied at MP2 level for the pentagonal [Au(SH) 2 (AuSH) 5 )] − and hexagonal [Au(SH) 2 (AuSH) 6 ] − clusters. The possibilities of ‘mechanical cooperativity’ between different aurophilic attractions and of Au…S attractions are also considered.

CYCLIC VOLTAMMETRY AND ELECTRON PARAMAGNETIC RESONANCE STUDIES OF SOME ANALOGUES OF NIFURTIMOX

Abstract The EPR of radicals obtained by electrolytic reduction of some new analogues of the antiprotozoal drug nifurtimox were measured in DMSO and DMF. The electrochemistry of these compounds was studied using cyclic voltammetry AM1 and INDO semiempirical molecular orbital calculations were performed to obtain the optimized geometries and spin distribution, respectively. Density functional theory was used to rationalize the reduction potentials of these compounds.

Novel Benzo[1,2-c]1,2,5-Oxadiazole N-Oxide Derivatives as Antichagasic Agents: Chemical and Biological Studies

This research was supported by FONDECYT 1000834, 7040037, 1020095, CSIC (UdelaR), CLEMENTE ESTABLE and TWAS grants. We thank a scholarship for C. Rigol from RELACQ.

Electrochemical and microsomal production of free radicals from 1,2,5-oxadiazole N-oxide as potential antiprotozoal drugs

The electron spin resonance (ESR) spectra of free radicals obtained by electrolytic or microsomal reduction of several potential antiprotozoal 1,2,5-oxadiazoles were characterized and analyzed. Ab initio molecular orbital calculations were performed to obtain the optimized geometries and the theoretical hyperfine constant was carried out using ZINDO semiempirical methodology. Density functional theory was used to rationalize the reduction potentials of these compounds.

Theoretical insights into the adsorption of neutral, radical and anionic thiophenols on gold(111)

The interaction of thiol and thiolate containing molecules with gold (S-Au) has gained increasing interest because of its applications in molecular electronic devices and catalysis. In this context, the enhanced conductivity of thiophenol compared to alkanethiol represents an opportunity to develop more sensitive and selective gold-based devices by incorporating molecules with the aryl-thiol moiety into their structures. As has been proposed earlier, the thiol moiety is deprotonated after binding to gold, hence, we present here a comparative study of the S-Au bond strength between several neutral and deprotonated aromatic-sulfur systems in their anionic and radical forms with a detailed description of the nature of this interaction. The study was performed by means of computational chemistry methods, using a cluster of 42 Au atoms as a model of the Au(111) surface that allowed us to provide new chemical insights to control the S-Au interface interaction strength. Our results revealed that the thiophenols-gold interaction is mainly dispersive where the interaction energies range between 31 and 43 kcal mol(-1). The radical and anionic thiophenolates-gold interaction increases due to a strong charge transfer character, depicting interaction energies in the range of 50 to 55 kcal mol(-1) and 62 to 92 kcal mol(-1), respectively. These results suggest that for the anionic thiophenolate the binding strength can be tailored according to the electron-donor capabilities of the ligand which in turn can be finely tuned by several substituents. Our results are of possible impact for the design of new devices.

ESR, electrochemical, molecular modeling and biological evaluation of 4-substituted and 1,4-disubstituted 7-nitroquinoxalin-2-ones as potential anti-Trypanosoma cruzi agents

Electrochemical and ESR studies were carried out in this work with the aim of characterizing the reduction mechanisms of 4-substituted and 1,4-disubstituted 7-nitroquinoxalin-2-ones by means of cyclic voltammetry in DMSO as aprotic solvent. Two reduction mechanisms were found for these compounds: the first, for compounds bearing a labile hydrogen by following a self-protonation mechanism (ECE steps), and the second, for compounds without labile hydrogen, based on a purely electrochemical reduction mechanism (typical of nitroheterocycles). The electrochemical results were corroborated using ESR spectroscopy allowing us to propose the hyperfine splitting pattern of the nitro-radical, which was later corroborated by the ESR simulation spectra. All these compounds were assayed as growth inhibitors against Trypanosoma cruzi: first, on the non-proliferative (and infective) form of the parasite (trypomastigote stage), and then, the ones that displayed activity, were assayed on the non-infective form (epimastigote stage). Thus, we found four new compounds highly active against T. cruzi. Finally, molecular modeling studies suggest the inhibition of the trypanothione reductase like one of the possible mechanisms involved in the trypanocidal action.