Theoretical study of the electronic spectrum of binuclear gold(I) complexes

The electronic structure and the spectroscopic properties of [Au-2(CS3)(2)](-2), [Au-2(pym-2-S)(2)] (pym = pyrimidethiolate), [Au-2(dpm)(2)](+2) (dpm = bis(diphosphino)methane) were studied using density functional theory (DFT) at the B3LYP level. The absorption spectrum of these binuclear gold(l) complexes was calculated by single excitation time-dependent (TD) method. All complexes showed a (1)(5d sigma* -> 6p sigma) transition associated with a metal-metal charge transfer, which is strongly interrelated with the gold-gold distance. Furthermore, we have calculated the frequency of the gold-gold vibration (nu(Au2)) on the above complexes. The values obtained are theoretically in agreement with experimental range

Thermodynamic and geometric study of diasteroisomeric complexes formed by racemic flavanones and three cyclodextrins through NMR

Artículo de publicación ISIThe main purpose of this work was to study the chiral recognition thermodynamics of inclusion complexes formed by flavanones and b-cyclodextrins, and its relation with the inclusion geometries, through NMR experiments. By using the racemic mixtures of (±)-flavanone (FL) and (±)-20-hydroxyflavanone (20OHFL), diasteroisomeric complexes were formed employing b-cyclodextrin (bCD), (2- hydroxypropil)-b-cyclodextrin (HPbCD) and heptakis-(2, 6-O-dimethyl)-b-cyclodextrin (DMbCD). 1H NMR experiments of the complexes showed enantiodifferentiation for FL/bCD, FL/HPbCD, FL/DMbCD, 20OHFL/HPbCD and 20OHFL/DMbCDcomplexes, so they were able to be studied by obtaining the stoichiometry (1:1 for each complex), association constants (Ka), Ka ratios, and thermodynamics (DH, DS and DG). The results show that Ka values decrease with increasing temperature and that Ka ratio values removed from 1 not always reflect better enantiodiscrimination by NMR. Thermodynamics (DH and DG) show an exothermic and spontaneous formation of the complexes. Since the results were established for each couple of diasteroisomeric complexes separately, comparison of thermodynamics between them was possible, concluding that one half of the couples of diasteroisomeric complexes present chiral recognition due to enthalpic phenomena and the other half due to entropic phenomena. Additionally, ROESY experiments were performed to estimate the inclusion geometry of the complexes, which are in good agreement with the thermodynamic and Ka results

Complexes self-associate by hydrogen bonding and metallophilic attraction: Theoretical study

Hydrogen bonding and metallophilic attractions are studied in the model systems: [(AuNH3Cl)(2)], [(AuNH(CH3)(2)Cl)(2)], [{Au-2(mu-SH)(PH2O)(PH2OH}(2)], [(CuNH3Cl)(2)], and [{Cu(NH3)Cl}(4)] at the Hartree-Fock (HF) and second-order Moller-Plesset (MP2) levels. The two interactions are found to be comparable and prevailing in the final structure. It is determined that the aurophilic contact has a same magnitude that the hydrogen bonding, and is stronger than the cuprophilic interaction. The presence of hydrogen bond directs the growth of the crystal

Role of Superoxide Anions in the Redox Changes Affecting the Physiologically Occurring Cu(I)-Glutathione Complex

The physiologically occurring copper-glutathione complex, [Cu(I)-[GSH]2], has the ability to react continually with oxygen, generating superoxide anions (O2∙−). We addressed here the effects that superoxide removal has on the redox state of Cu(I) and GSH present in such complex and assessed the formation of Cu(II)-GSSG as a final oxidation product. In addition, we investigated the potential of a source of O2∙− external to the Cu(I)-[GSH]2 complex to prevent its oxidation. Removal of O2∙− from a Cu(I)-[GSH]2-containing solution, whether spontaneous or Tempol-induced, led to time-dependent losses in GSH that were greater than those affecting the metal. The losses in GSH were not accompanied by increments in GSSG but were largely accounted for by the cumulative formation of Cu(II)-GSSG molecules. Notably, the redox changes in Cu(I) and GSH were totally prevented when Cu(I)-[GSH]2 was coincubated with hypoxanthine/xanthine oxidase. Data suggest that the generation of O2∙− by Cu(I)-[GSH]2 implies the obliged formation of an intermediate whose subsequent oxidation into Cu(II)-GSSG or back reduction into Cu(I)-[GSH]2 is favoured by either the removal or the addition of O2∙−, respectively

Theoretical study of the d(10)-d(8) interaction between Au(I) and Au(III) on the cis/trans-[PH3Au(I)C(L)=C(L)Au(III)(R)(2)PH3] (R = -H -CH3; L = -H, -CH3) systems

We have carried out an ab initio study designed to shed some light on the aurophilic attractions between Au(I) and Au(III) in the [PH3Au(I)C(L)=C(L)Au(III)(R)(2)PH3] (where R = -H, -CH3; L = -H, -CH3) model. Calculations carried out at the MP2 level revealed important facts such as the presence of an intramolecular aurophilic interaction in the cis-complexes that stabilizes them with respect to the trans-isomers. Using two additional models to study the intermolecular interaction between Au(1) and Au(111) we were able to estimate an interaction energy between 21 and 25 kJ mol(-1) at the MP2 level of calculation

Insights into the antioxidant activity of phenolic compounds: Synthesis and electrochemical study of new series of hydroxycoumarins

The 15th International Electronic Conference on Synthetic Organic Chemistry session Bioorganic, Medicinal and Natural ProductsPhenolic compounds are bioactive substances widely distributed in the vegetable kingdom. They act as natural antioxidants, and their presence contributes to the color, flavor and aroma of food. This group of micronutrients is composed of one or more aromatic benzene rings with one or more hydroxyl groups and their redox properties are related with their chemical structure characteristics. The knowledge of their redox potentials may help the food industry, because when phenolic compounds are oxidized they could affect the quality of the wines, beers, grape juices, etc. Coumarins are a large family of compounds, of natural and synthetic origin, that show important biological activities. Therefore, they occupy an important place in the study of natural products and synthetic organic chemistry. Recent studies pay special attention to their antioxidative, anticarcinogenic and enzymatic inhibition properties. Their preparation, and the versatility of the synthetic methodology, allowed us obtaining a wide family of compounds with substituent in different positions in the molecule. The election of these derivatives has considered the later pharmacological evaluation. The investigation of the properties of these compounds, the study of the structural pattern and the elucidation of their biological role is of great interest for further development of coumarin-like antioxidant drugs. The electrochemical behaviour of a group of differently substituted hydroxycoumarins was investigated using cyclic, differential pulse and square wave voltammetry, in aqueous media at a glassy carbon electrode over the whole pH range. The antioxidant reactivity and capacity were also evaluated through a competition assay with hydroxyl radical (OH•) and DMPO like ORAC-FL methodology. Number and positions of the hydroxyl groups were important factors in the antioxidant activities against peroxyl radical of both types of coumarins derivativesWe are grateful to the Xunta de Galicia (PGIDIT09CSA030203PR) and Ministerio de Sanidad y Consumo (FIS PS09/00501) for the partial financial support. M.J.M. and A.G. also thank Fundação de Ciência e Tecnologia for the fellowship

Theoretical study on 5-nitrofuryl thiosemicarbazone radicals electronic properties

Theoretical studies of molecular conformations and electronic properties calculations of eight 5-nitrofuryl thiosemicarbazone free radicals, by means of ab initio (R/UHF), and DFT (R/UB3LYP) methods are presented and discussed in comparison with ESR and electrochemical experimental data. DFT calculated hyperfine coupling constants were used for the simulation of experimental spectra. We observed the molecules adopt mainly two conformations, both showing a pattern of spin density delocalization unusual for free radicals formed from aromatic nitrocompounds. Energy potential surfaces scaning through a determined dihedral angle were drawn to evaluate whether these conformations could coexist in equilibrium. Fukui and molecular orbital analysis were compared with ESR data as reactivity local indexes

Study of coumarin-resveratrol hybrids as potent antioxidant compounds

In the present work we synthesized a selected series of hydroxylated 3-phenylcoumarins 5–8, with the aim of evaluating in detail their antioxidant properties. From an in depth study of the antioxidant capacity data (ORAC-FL, ESR, CV and ROS inhibition) it was concluded that these derivatives are very good antioxidants, with very interesting profiles in all the performed assays. The study of the effect of the number and position of the hydroxyl groups on the antioxidant activity was the principal aim of this study. In particular, 7-hydroxy-3-(3'-hydroxy)phenylcoumarin (8) proved to be the most active and effective antioxidant of the selected series in four of the performed assays (ORAC-FL = 11.8, capacity of scavenging hydroxyl radicals = 54%, Trolox index = 2.33 and AI30 index = 0.18). However, the presence of two hydroxyl groups on this molecule did not increase greatly the activity profile. Theoretical evaluation of ADME properties of all the derivatives was also carried out. All the compounds can act as potential candidates for preventing or minimizing the free radical overproduction in oxidative-stress related diseases. OPEN ACCESS Molecules 2015, 20 3291 These preliminary findings encourage us to perform a future structural optimization of this family of compoundsThis project was partially supported by the FONDECYT (projects 1110029 and 1090078), PhD fellowship CONICYT, fellowship for operational expenses (N°21120376), Spanish researchers personal founds, University of Santiago de Compostela and Fundação para a Ciência e Tecnologia (FCT) for the Pest/C-QUI/UI0081/2013. MJ Matos was supported by the fellowship from Fundação para a Ciência e Tecnologia (FCT), POPH (Programa Operacional Potencial Humano) and QREN (Quadro de Referência Estratégica Nacional) (SFRH/BPD/95345/2013). S Vazquez-Rodriguez was supported by the Universidade de Porto postdoctoral grant NORTE-07-0124-FEDER-000065S

Nitrosobenzene: electrochemical, UV-visible and EPR spectroscopic studies on the nitrosobenzene free radical generation and its interaction with glutathione

This paper reports both the electrochemical characterization and the reactivity of the nitroso radical anion from nitrosobenzene with glutathione. The reduction of nitrosobenzene to the corresponding nitroso radical anion was kinetically characterized in acetonitrile. Free radicals exhibited a natural decay of second order, with a constant value of k(2) = 15 555 +/- 321 M-1 s(-1). Also, the radicals were characterized by UV-Visible and EPR spectroscopy. Data obtained with these two independent techniques clearly substantiated the formation of the nitrosobenzene radical under our experimental conditions. Furthermore, we have unambiguously demonstrated that glutathione (GSH) scavenged the nitroso radical anion electrochemically generated from nitrosobenzene. The scavenging effect of GSH is supported by the following experimental facts: 1. The parallel decrease of the anodic peak current in the cyclic voltammograms, corresponding to the nitroso radical anion concomitantly with the addition of GSH. 2. The significant decrease of the visible band at 560 nm corresponds to the radical after the addition of GSH. 3. The drop of the EPR signal intensity of the nitroso radical after the addition of GSH. By using a spin trapping technique, thiyl radical(GS) was detected during the reaction between the nitroso radical anion with GSH