Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The effect of intramolecular hydrogen bond (H-bond) interactions in the cis - trans isomerization of the amino acids such as, cysteine, serine, threonine and valine have been studied using density functional theory method. Our calculations have shown that the geometrical parameters are significantly changed during the isomerization process. This is due to the presence of intramolecular H-bonds within main chain or in between side chain and main chain. The barrier energies have been calculated for isomerization process in all the amino acids, which is more for cysteine and less for valine. The Fourier decomposition potential has been obtained for the above named amino acids which show that V2 potential has higher value. The vibrational frequency analysis has been carried out for the cis and trans forms of cysteine, serine, threonine and valine amino acids and the results are discussed.

The main pheromone component of Chilecomadia valdiviana has recently been reported to be (7Z,10Z)-7,10-hexadecadienal. The synthesis of a structural analog, (5Z,8Z)-5,8-tetradecadienyl formate is reported. The pheromone analog was not attractive to male C. valdiviana in the field, nor did it antagonize attraction of males to the pheromone compound.

The effect of the support on the formation of the Cu-CeO2 interface and its thermal stability after calcination at 500, 700 and 900 ºC is studied. The supports used are SiO2, because of its inert character, and Al2O3, because it can interact with the Cu and Ce species on the surface. The catalysts were characterized by BET, XRD, UV-vis DRS, and TPR with H2. The catalytic activity in the CO oxidation reactions with O2 at low temperature and the decomposition of N2O were selected to visualize the effect of temperature on the concentration of Cu-CeO2 interfacial sites. The results show that at a calcination temperature of 500 ºC the formation of the Cu-CeO2 interface is favored over the SiO2 support. However, the stability of the Cu-CeO2 interface on SiO2 is much lower than on Al2O3, causing a substantial decrease of the interfacial sites calcining at 700 ºC, and segregation of the Cu and Ce species on the surface of the silica, with complete loss of the catalytic activity in both reactions when calcining at 900 ºC. In contrast, on alumina the Cu-CeO2 interface is more stable and presents a significant catalytic activity in both reactions, even when calcining at 900 ºC. The characterization results show that the sintering process of Cu species and CeO2 particles is less on the alumina support due to the greater interaction of the Cu and Ce with this support.

Ozone is a strong oxidant used in the water treatment to remove organochloride compounds. Given that many processes of degradation generate chemical compounds that are more toxic than initial compounds, the development of optimized ozonation processes are required. In this study, pentachlorophenol (PCP) was used as a model of an organochlorine compound and the toxicity of its degradation products generated by both non-catalytic and catalytic ozonation processes were evaluated with a fresh-water Daphnia magna (ecotoxicity) and vegetables species Lactuca sativa and Panicum millaceum (Phytoxicity). The catalytic ozonation used MnO2/TiO2 as catalyst, which was characterized by X-ray diffraction analysis showing the presence of crystalline TiO2 phases, rutile and anatase. The specific BET surface area of MnO2/TiO2 was 43 m2/g. It was found that the use of ozone as an oxidant showed a first order degradation rate constant (kobs = 0.5 ± 0.1 min- 1). The uncatalyzed reaction showed several reaction intermediates like mono- and polychlorinated phenols, and quinones. The oxidation of these compounds led to low molecular weight organic acids. From these results, we proposed a pathway of PCP degradation using ozone. The catalyzed reaction showed a more potent effect in reducing the toxicity of the treated solution. Unlike the use of only ozone which does not decrease the toxicity. It was found that the treatment with catalytic ozonation decreases the toxicity of the solutions.

Homodinuclear (1) Co(II), (2) Ni(II), (3) Cu(II) and (4) Zn(II) metal complexes containing oxime group were tested for their catalase, catecholase and phenoxazinone synthase-like activity by volumetric and spectrophotometric procedures. Catalase-like activity of the complexes was studied by measuring the evolved dioxygen resulted from the disproportionation reaction of potentially harmful hydrogen peroxide. Catecholase and phenoxazinone synthase-like enzyme activities were followed by the increase in absorbance at 400 and 433 nm resulted from the oxidation reaction of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone and 2-aminophenol to 2-aminophenoxazine-3-one, respectively. Among the studied homodinuclear complexes, complex (3) showed the highest catalytic efficiency for three enzymes tested. Catalytic efficiency of the complexes was found 3>1>4=2 for catalase-like, 3>1>2>4 for catecholase-like and 3>1>4>2 for phenoxazinone synthase-like activity. Relatively higher catalytic activity of the Cu(II) complex is thought to be related to the lower redox potential of Cu(II) ion and better proximity of the chosen substrates with the complex (3).

Diethyl 2-((4-nitroanilino)methylene)malonate [4-NANM-E] is an important molecule owing to its role of precursor in the multistage synthesis of several quinoline derivatives possessing biological activities such as antiviral, immunosuppressive, anticancer and photoprotector. This molecule is usually synthesized by a nucleophilic vinyl substitution (SNV) between 4-nitroaniline and diethylethoxymethylene malonate (EMA). Although several procedures are available to synthesize 4-NANM-E in liquid phase, more convenient method is necessary to synthesize in less reaction time and at room temperature. In this study, it is demonstrated that equimolar amounts of EMA and 4-nitroaniline dissolved in alcoholic KOH react within a few seconds at room temperature to produce 4-NANM-E which is purified by simple filtration after acidification with aqueous HCl and washing with alcohol. The reaction has the yield varying at the range 45-53% when it occurs in ethanol, 2-propanol, 2-butanol or 2-pentanol. Therefore, this synthesis method is an excellent alternative to produce 4-NANM-E on an industrial scale.

Carboxylic acids have clearly been absent from the quantitative structure-property relationship literature. The studies of the quantitative structure–property relationships (QSPR) involve various chemometric methods in which the physico-chemical behavior of a compound is correlated with its structure represented by the structural indices. For example, QSPR methods are applied for the prediction of octanol-water partition coefficient of an organic compound. In this study, the relationship between the octanol/water coefficient partition and molecular descriptors was investigated. Also, the multiple linear-regression method based on QSPR methodology was applied to predict the Log P of saturated mono-carboxylic acids C1-C22. On the other hand, the relation [ Log P = - 0.426 ( Platt ) + 0.190 ( V/ A°3 ) - 0.155 ( Max.P.A/ A°2 ) - 1.914 ( X ) - 1.576 ; N = 22, R2 = 0.995 , F = 917.005, DW=1.391] was generated for selected mono-carboxylic acids. The results of study indicated that the Platt, Randic, Volume and Maximum-Projection-Area descriptors have an important role in predicting the octanol/water coefficient partition of saturated monocarboxylic acids (C1- C22).

In this paper we report the absolute configuration which has been determined from the refinement of the Flack parameter, x = 0.05(5), which indicate that the correct configuration had been assigned against 1353 (99%) CuKα Bijvoet pairs. On this basis the absolute configuration was assigned as C5R, C8S, C9R and C10S. The structure of 18-acetoxy-cis-cleroda-3,13E-dien-15-oic acid consists of a clerodane skeleton and the corresponding methyl groups are α-oriented (C8, C9) while C5 is β-oriented. The acidic lateral chain is β-oriented and the double bond between C13 and C14 has E isomeric. The ciclohexene, cyclohexane rings are cis fused, and in an sofa and chair conformation respectively. In the crystal the molecules are linked by one intermolecular OH⋅⋅⋅O hydrogen bond forming 1D-dimensional chain with distance donor-acceptor of 2.060(6)Å with graph-set notation C1 1 (15).

The electrochemical oxidation of hydroxyzine dihydrochloride at carbon paste electrode has been studied in 0.04 M Britton-Robinson buffer pH 6.2 using cyclic and differential pulse voltammetry. The oxidation process has been shown to irreversible and diffusion controlled with adsorption characterstics. Based on these studies, simple, rapid, and sensitive differential pulse anodic voltammetric method has been developed for the determination of the drug over the concentration range 0.45-5.36 μg/ml, with detection and quantification limits of 0.27 and 0.90 μg/ml hydroxyzine dihydrochloride, respectively. The proposed method was successfully used for quantification of hydroxyzine dihydrochloride in Atarax tablets and spiked human urine.

Phytochemical analysis of Azorella compacta resulted in the isolation of six known diterpenes and one unknown norditerpene using chromatographic meth­ods. The structure of this new compound was established by spectroscopic analysis. The bioactivity of the new compound was assessed against six oral bacteria using a drop test method. A high level of growth inhibition was observed against F. nucleatum and P. gingivalis; however, other species such as V. parvula and A. actinomycetemcomitans were not affected.