Electrochemical oxidation and electroanalytical determination of xylitol at a boron-doped diamond electrode

AbstractXylitol is a reduced sugar with anticariogenic properties used by insulin-dependent diabetics, and which has attracted great attention of the pharmaceutical, cosmetics, food and dental industries. The detection of xylitol in different matrices is generally based on separation techniques. Alternatively, in this paper, the application of a boron-doped diamond (BDD) electrode allied to differing voltammetric techniques is presented to study the electrochemical behavior of xylitol, and to develop an analytical methodology for its determination in mouthwash. Xylitol undergoes two oxidation steps in an irreversible diffusion-controlled process (D=5.05×10–5cm2s–1). Differential pulse voltammetry studies revealed that the oxidation mechanism for peaks P1 (3.4≤pH≤8.0), and P2 (6.0≤pH≤9.0) involves transfer of 1H+/1e−, and 1e− alone, respectively. The oxidation process P1 is mediated by the •OH generated at the BDD hydrogen-terminated surface. The maximum peak current was obtained at a pH of 7.0, and the electroanalytical method developed, (employing square wave voltammetry) yielded low detection (1.3×10–6molL–1), and quantification (4.5×10–6molL–1) limits, associated with good levels of repeatability (4.7%), and reproducibility (5.3%); thus demonstrating the viability of the methodology for detection of xylitol in biological samples containing low concentrations

Eficiência e diversidade fenotípica de bactérias diazotróficas que nodulam caupi [Vigna unguiculata (L.) Walp] e feijoeiro (Phaseolus vulgaris L.) em solos de mineração de bauxita em reabilitação Efficiency and phenotypic diversity among nitrogen-fixing bacteria that nodulate cowpea [Vigna unguiculata (L.) Walp] and common bean (Phaseolus vulgaris L.) in bauxite-mined soils under rehabilitation

A atividade de mineração provoca degradação ambiental em várias partes do mundo, e técnicas de revegetação, empregando diversas espécies vegetais, têm sido indicadas, com vistas em reabilitar essas áreas. A eficiência e a diversidade de grupos-chave de bactérias, como as que nodulam leguminosas e fixam N2 (BNLFN), são de extrema importância, uma vez que estas participam de processos de ciclagem de nutrientes e contribuem para a sustentabilidade dessas áreas. Com o objetivo de avaliar a eficiência e a diversidade de BNLFN, coletaram-se amostras de solo de áreas mineradas, sob diferentes estratégias e cronosseqüências de reabilitação, no verão de 1999, para instalação de ensaios, empregando feijoeiro e caupi como espécies de plantas-isca de BNLFN. Na floração, coletaram-se as plantas e avaliaram-se matéria seca da parte aérea, número, matéria fresca e atividade de nódulos. Não houve influência das diferentes estratégias de reabilitação na eficiência das populações de BNLFN no crescimento do feijoeiro. A diversidade fenotípica dos isolados de BNLFN foi avaliada por meio das características culturais destes em meio de cultivo 79. Após a caracterização fenotípica de 328 isolados de feijoeiro e 420 de caupi, verificou-se que este é mais indicado que o feijoeiro nos estudos de nodulação, eficiência e diversidade de BNLFN. O impacto negativo da mineração é maior na diversidade fenotípica cultural de BNLFN do que na nodulação das plantas-isca utilizadas. A revegetação contribuiu para aumentar a diversidade dessas bactérias em solos de áreas de mineração de bauxita, especialmente quando ocorreu a introdução de leguminosas.<br>Mining activities promote severe environmental degradation in many parts of the world, and revegetation techniques with diverse plant species have been used for rehabilitation of these areas. Studies on the occurrence, efficiency and diversity of key microbial groups such as leguminosae-nodulating, nitrogen fixing bacteria (LNNFB) are essential because they are involved in nutrient cycling processes and, therefore, to the sustainability of these areas. Aiming to evaluate the efficiency and phenotypic diversity of LNNFB, soil samples were collected from different bauxite mining areas with distinct rehabilitation strategies and chronosequences in the summer of 1999. With these materials we installed experiments using bean and cowpea as trap species under greenhouse conditions. At flowering, the plants were harvested and the shoot dry weight, nodule number, nodule weight, nitrogenase activity, and phenotypic diversity of LNNFB isolates evaluated by culture characterization on 79 medium. There was no influence of the different rehabilitation strategies on the efficiency of LNNFB populations in promoting bean growth. After phenotypic characterization of 328 bean and 420 cowpea LNNFB isolates, it was found that the latter is better suited than bean for studies evaluating LNNFB nodulation, efficiency and diversity in these areas. Mining strongly decreases the LNNFB diversity, while there is little effect on nodulation of trap plants. Rehabilitation strategies contribute to increase LNNFB diversity in bauxite mined soils, mainly when legume species were introduced