Electrochemical studies on small electron transfer proteins using membrane electrodes

Journal of Electroanalytical Chemistry 541 (2003) 153-162Membrane electrodes (ME) were constructed using gold, glassy carbon and pyrolytic graphite supports and a dialysis membrane, and used to study the electrochemical behavior of small size electron transfer proteins: monohemic cytochrome c522 from Pseudomonas nautica and cytochrome c533 as well as rubredoxin from Desulfovibrio vulgaris . Different electrochemical techniques were used including cyclic voltammetry (CV), square wave voltammetry (SW) and differential pulse voltammetry (DP). A direct electrochemical response was obtained in all cases except with rubredoxin where a facilitator was added to the protein solution entrapped between the membrane and the electrode surface. Formal potentials and heterogeneous charge transfer rate constants were determined from the voltammetric data. The influence of the ionic strength and the pH of the medium on the electrochemical response at the ME were analyzed. The benefits from the use of the ME in protein electrochemistry and its role in modulating the redox behavior are analyzed. A critical comparison is presented with data obtained at non-MEs. Finally, the interactions that must be established between the proteins and the electrode surfaces are discussed, thereby modeling molecular interactions that occur in biological systems

Adsorption of poly(ethylene glycol)s on mercury/aqueous solution interface. 2, Influence of the chain length

The adsorption on a mercury/aqueous solution interface of poly(ethylene glycol)s (PEGs) with molecular weights from 200 to 20 000 was studied by a.c. voltammetry in order to understand better the adsorption of linear components of fulvic acids on hydrophobic particles in natural waters, and the influence of their adsorption on voltammetric signals. As a general trend it was noted that the equilibrium adsorption constant increases with the molecular weight while the adsorption rate decreases. The values of the maximum surface concentration F. suggest a flat configuration for adsorbed molecules for all PEGs studied

Adsorption of poly(ethylene glycol)s on mercury/aqueous solution interface : 1. Kinetics of PEG 8000 adsorption

In order to study the influence of the adsorption of fulvic compounds on voltammetric signals and to understand better the adsorption of these compounds on hydrophobic natural water interfaces, adsorption studies of macromolecules such as poly(ethylene glycol) (HO(CH2CH2O)n) with molecular weight of 8000 were done on the mercury/water interface by a.c. voltammetry at the potential of zero charge. The maximum surface concentration, adsorption equilibrium constant and adsorption rate constant have been determined from the global adsorption mechanism, controlled by two determining steps: diffusion and kinetics of adsorption at the interface

Flow injection-assisted optical sensor for determination of iron (II) and iron (III) in natural water

An approach for speciation of iron (as Fe(II) and Fe(III)) based on integration of retention of the Fe(III)-SCN complex with detection using a conventional spectrophotometer is proposed here. The device (namely, a flow-cell packed with an exchange resin) has been coupled to a flow-injection manifold with inner-coupled injection valves which enables discrimination between Fe(III) and Fe(II) taking advantage of a redox minicolumn housed in the loop of one of the valves. The method thus proposed has good selectivity with a determination limit of 80 gl-1 and affords a determination range of 80-500 gl-1 for Fe(II) plus Fe(III). Application to synthetic and real samples containing both the oxidation states of iron lead to average recoveries of 103% and 101% for Fe(II) and total iron (Fe(II)+Fe(III)), respectively, thus showing the usefulness of the overall approach

Quantification of the diversity among common bean accessions using Ward-MLM strategy Quantificação da diversidade entre acessos de feijoeiro-comum com uso da estratégia Ward-MLM

The present work aimed at evaluating the divergence among common bean accessions by their agronomic, morphological and molecular traits, based on the Ward-MLM procedure. A collection of 57 accessions from the gene bank of Universidade Federal do Espírito Santo was used in this study, from which: 31 were landraces belonging to the community Fortaleza, in the municipality of Muqui, ES, Brazil; 20 accessions were provided by Embrapa Trigo; and 6 were commercial cultivars. Five agronomic traits (plant cycle, number of seeds per pod, number of pods per plant, weight of 100 seeds, and grain yield), five morphological traits (growth habit, plant size, seed shape, seed color, and commercial group) and 16 microsatellite primers were evaluated. High genetic variability was detected considering morphological, agronomic and molecular traits in the 57 common bean accessions studied. The Ward-MLM procedure showed that the ideal number of groups was five, according to the pseudo F and pseudo t² criteria. The accessions from Andean origin had heavier seeds than others and formed a cluster. The Ward-MLM statistical procedure is a useful technique to detect genetic divergence and to cluster genotypes by simultaneously using morphological, agronomic and molecular data.<br>O objetivo deste trabalho foi avaliar a divergência de acessos de feijoeiro-comum por suas características agronômicas, morfológicas e moleculares, com base no procedimento Ward-MLM. Uma coleção de 57 acessos do banco de germoplasma da Universidade Federal do Espírito Santo foi utilizada neste estudo, dos quais: 31 acessos locais, pertencentes à comunidade Fortaleza, no Município de Muqui, ES; 20 acessos fornecidos pela Embrapa Trigo; e 6 cultivares comerciais. Foram avaliados cinco caracteres agronômicos (ciclo da planta, número de sementes por vagem, número de vagens por planta, peso de 100 grãos e produtividade de grãos), cinco caracteres morfológicos (hábito de crescimento, porte da planta, formato da semente, cor da semente e grupo comercial) e 16 iniciadores microssatélites. Detectou-se ampla variabilidade genética pelos dados morfológicos, agronômicos e moleculares nos 57 acessos de feijão. O procedimento Ward-MLM mostrou que cinco foi o número ideal de grupos, de acordo com os critérios do pseudo F e pseudo t². Os acessos de origem andina tiveram sementes mais pesadas do que os outros e ficaram em um mesmo grupo. O procedimento Ward-MLM é uma técnica útil para detectar divergência genética e agrupar genótipos pelo uso simultâneo de descritores morfológicos, agronômicos e moleculares

Adubação mineral do angico-amarelo (Peltophorum dubium (Spreng.) Taub.) Mineral fertilization of Peltophorum dubium (Spreng.) Taub.

Com o objetivo de se estudar as exigências nutricionais no desenvolvimento inicial de mudas de Peltophorum dubium (Spreng.) Taub., foi realizado um experimento em casa de vegetação. Usou-se como substrato um latossolo vermelho-amarelo com baixa disponibilidade de nutrientes, utilizando-se 10 tratamentos, sob a técnica do elemento faltante. Foram aplicados um tratamento completo (com N, P, K, Ca, Mg, S, B e Zn), outros com omissão de um nutriente por vez (-N, -P, -K, -Ca, -Mg, -S, -B e -Zn) e uma testemunha (solo natural). Foram avaliadas as seguintes características: altura, diâmetro, peso de matéria seca da parte aérea e das raízes, e teor de nutrientes na matéria seca da parte aérea. Concluiu-se que as plantas do angico-amarelo apresentam elevada exigência nutricional; os nutrientes P, N, S e o Ca seguidos pelo Mg, K e pelo B são limitantes ao crescimento das plantas; as omissões de K, Ca e de Mg afetam a absorção de S pelas plantas.<br>A greenhouse experiment was carried out with seedlings of the tropical tree Peltophorum dubium (Spreng.) Taub. in order to study its nutritional requirements. As substrate an oxisol with low nutrient availability was used and distributed in 10 treatments: a complete one (N, P, K, Ca, Mg, S, B and Zn), the others lacking one element in each treatment (-N, -P, -K, -Ca, -Mg, -S, -B and -Zn) and a control (natural soil). The following characteristcs were assessed: plant height and diameter growth, dry matter production and levels of nutrient into dry matter of shoots. It was concluded that seedlings are affected by the omission of all nutrients in the following order: P > N > S > Ca > Mg > K > B. The omission of K, Ca and Mg affects S absorption by plants