Chemical speciation of metal complexes from chemical shift calculations: the interaction of 2-amino-N-hydroxypropanamide with V(V) in aqueous solution.

The chemical speciation of 2-amino-N-hydroxypropanamide (ß-alaninohydroxamic acid, HL) and vanadium (V) in aqueous solution has been investigated through calculations of the thermodynamic properties and the (51)V nuclear magnetic resonance (NMR) chemical shifts of the species formed at equilibrium. The results have been compared directly with the experimental (51)V NMR data. The (51)V NMR chemical shifts have been calculated by using a density functional theory (DFT) approach accounting for relativistic corrections and solvent effects. All tautomers of the 1:1 and 1:2 VO2(+)/ß-ala complexes with different degrees of protonation have been calculated and thermodynamic and structural properties are presented for the most stable species. The system is better modeled as tautomeric equilibria, and species lying down in the range of 10 kcal·mol(-1) cannot be neglected at the BP/TZ2P/COSMO approach. In fact, the metal complex speciation in aqueous solution should not be investigated based solely on the thermodynamic analysis, but together with spectroscopic calculations such as NMR.

Design, structural and spectroscopic elucidation, and the in vitro biological activities of new diorganotin dithiocarbamates.

The reaction of 2,2-dimethoxy-N-methylethyllamine or 2-methyl-1,3-dioxolane with CS(2) in alkaline media produced two novel dithiocarbamate salts. Subsequent reactions with organotin halides yielded six new complexes: [SnMe(2){S(2)CNR(R(1))(2)}(2)] (1), [Sn(n-Bu)(2){S(2)CNR(R(1))(2)}(2)] (2), [SnPh(2){S(2)CNR(R(1))(2)}(2)] (3), [SnMe(2){S(2)CNR(R(2))(2)}(2)] (4), [Sn(n-Bu)(2){S(2)CNR(R(2))(2)}(2)] (5), [SnPh(2){S(2)CNR(R(2))(2)}(2)] (6), where R = methyl, R(1) = CH(2)CH(OMe)(2), and R(2) = 2-methyl-1,3-dioxolane. All compounds were identified in terms of infrared, (1)H and (13)C NMR, and the complexes were also characterized using (119)Sn NMR, (119)Sn Mössbauer and X-ray crystallography. The biological activity of all derivatives has been screened in terms of IC(90) and IC(50) against Aspergillus flavus, Aspergillus niger, Aspergillus parasiticus, Penicillium citrinum, Curvularia senegalensis, Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, Streptococcus sanguinis, Escherichia coli, Citrobacter freundii, Salmonella typhimurium, and Pseudomonas aeruginosa and the results correlated well with a performed study of structure-activity relationship (SAR). Complexes (3), (5) and (6) displayed the best IC(90) and IC(50) in the presence of the fungi, greater than that of miconazole, used as control drug.

Potentiometric, spectrophotometric and density functional study of the interaction of N-hydroxyacetamide with oxovanadium(IV): the influence of ligand to the V(IV)/V(V) oxi-reduction reaction.

The interaction of N-hydroxyacetamide (acetohydroxamic acid, HL) with V(IV) in aqueous solution has been investigated using potentiometric and spectrophotometric experiments. Density functional method (DFT) has been used aiming to understand the ligand chelation at a molecular level. Stability constants have been estimated for species with the metal/ligand ratios 1:1 and 1:2 from spectrophotometric and potentiometric measurements. The stability of these V(IV) species toward oxidation has been investigated. Experiments carried out in an oxygen atmosphere led to the displacement of the titration curves with respect to the one obtained under inert atmosphere. Spectrophotometric evidence of the V(IV)/V(V) oxidation in the presence of N-hydroxyacetamide is presented. It has been shown that V(IV)/V(V) oxidation in the presence of N-hydroxyacetamide by the oxygen can be simulated using the standard programs for simulating the equilibrium in a multiligand/multimetal system. In this approach, the oxygen is considered a ligand and the log beta estimated from the standard oxidation potential. The structure and respective tautomers of the species have been optimized from DFT calculations. Geometrical and thermodynamical properties have been estimated for the most stable complexes. The VOL-->VOL(2) equilibrium constant has been theoretically estimated with a less than 1.5 logarithmic unit of error with respect to the experimental estimate. The oxidation process has also been investigated and it is adequately described by the equation: 4[VOL(2)]+2H(2)O+O(2)-->4[VO(OH)L(2)]. The calculated value of DeltaG for this reaction is about -46.2 kcal mol(-1), in excellent agreement with the experimental estimates.

Avaliaçäo da presença de pesticidas N-Metilcarbamatos e seus produtos de degradaçäo nas águas da regiäo de Pará e Minas (MG) Brasil / Evaluation of the presence of N-Methylcarbamate pesticides and degradation products in waters of Pará de Minas (MG) region in Brazil

Os pesticidas N-metilcarbamatos e alguns de seus metabólitos säo altamente tóxicos para o homem e o meio ambiente. Por esta razäo desenvolveu-se método analítico utilizando extraçäo em fase sólida e cromatografia líquida de alta eficiência com detector de ultravioleta (CLAE/UV) para análise destes compostos em amostras de água. O método apresentou índice de recuperaçäo para 10 compostos de 57 a 99 por cento, com desvio padräo relativo (CV) de 5,67 a 7,67 por cento para n=6. A repetitividade do método forneceu CV entre 5,94 a 8,46 por cento para n=6. O limite de detecçäo do método (MDL) situou-se na faixa de 0,07 a 0,38 ug/L para 10 compostos. Este método foi aplicado na análise de amostras de águas coletadas na cidade de Pará de Minas - MG, Brasil e também em alguns pontos selecionados nas bacias dos Rios Paciência e Bom Sucesso, situadas no município de Pará de Minas. Os resultados das análises em amostras de água mostraram-se abaixo dos limites estabelecidos pela legislaçä brasileira

Acidos hidroxâmicos: aspectos químicos e atividade biológica / Hydroxamic acids: chemical aspects and biological activity

Foi feita uma revisäo extensiva da literatura recente relativa aos principais aspectos da química e das propriedades biológicas de ácidos hidroxâmicos. Foram enfatizados os métodos gerais de preparaçäo desses ácidos, porém outros aspectos como reatividade e estrutura também foram discutidos. Relativamente aos aspectos biológicos, foram abordados os seguintes: inibiçäo da enzima urease, propriedades anti-hipertensivas, inibiçäo da síntese do DNA, efeito carcinogênico, açäo contra tripanossomas, inibiçäo de zinco-metaloproteases, atividade fungicida etc