Synthesis routes and parameters such as synthesis time, precursor molar ratio, pH, and temperature are critical for generating oxides of various sizes and morphological aspects. However, there is no information on how to prepare silver tungstate (Ag2WO4) crystals of different shapes and sizes under laboratory conditions and without using sulfating agents. In this study, we attempted to fill this gap by preparing α-Ag2WO4 crystals of various sizes and morphologies using the coprecipitation method in a 3 h interval at room temperature and without using sulfating agents. The powder X-ray diffraction analysis confirmed that all crystals had an orthorhombic structure, whereas Fourier-transform infrared spectroscopy revealed the degree of structural disorder in the bonds between the atoms in the materials. Scanning electron microscopy revealed that the α-Ag2WO4 crystals had different sizes (5.37-26.83 µm) and morphologies (tetragonal prism, rod, and cypress leave-like rod), whereas ultraviolet-visible diffuse reflectance spectroscopy analysis indicated the optical band gap energy (2.92-3.05 eV), calculated using the method proposed by Kubelka and Munk. Catalytic tests revealed that the synthesized samples with the smallest crystals (AW1) and a tetragonal prism morphology degraded dye more efficiently (apparent rate constant (k) = 5.86 × 10-3 min-1) than other samples.

O direcionamento por campo magnético tem sido aplicado em Bioeletroquímica, principalmente com intuito de transportar enzimas ou mediadores redox imobilizados em partículas de magnetita (Fe3O4) para a superfície de eletrodos, proporcionando o controle comutável das correntes faradaicas provenientes da biocatálise. Neste trabalho, relata-se um avanço no controle magnético de reações bioeletroquímicas por meio da construção de um sistema que contém simultaneamente partículas magnéticas (para transporte controlado), enzima redox (para biocatálise) e um mediador redox (para mediação da transferência eletrônica). Para isso, sintetizou-se um novo material que consiste em partículas de Fe3O4 modificadas com ferroceno insolúvel (Fc) e quitosana (Chi) entrecruzada com glicose oxidase (GOx). Quando esse material foi utilizado em suspensão em estudos eletroquímicos, observou-se um aumento de 70% da corrente catalítica de oxidação de glicose quando um campo de 0,24 T foi aplicado perpendicularmente ao plano do eletrodo. Esta é a primeira vez que um controle de processos bioeletrocatalíticos foi relatado utilizando enzima, mediador e magnetita em um sistema único controlado por campo magnético.

Magnetic fields have been used in Bioelectrochemistry to carry enzymes or redox mediators immobilized on magnetite (Fe3O4) to the electrodes surface, providing a switchable control of faradaic current from biocatalysis. In this work, it is reported an advance in the magnetic control of bioelectrochemical reactions, by construction of a system containing simultaneously a magnetic particle (for controlled driving), an enzyme (for biocatalysis) and a redox mediator (for mediation of electron transfer). The advance was attained by synthesis of a new material (Fe3O4-Chi-Fc/GOx) that consists of Fe3O4 particles modified with insoluble ferrocene (Fc) and chitosan (Chi) cross-linked with glucose oxidase (GOx). When this material was used in electrochemical studies, an increase of 70% was observed in the catalytic current of glucose oxidation when 0.24 T was applied perpendicularly to electrode plane. This is the first time that a control of the bioelectrocatalytic process was achieved using enzyme, mediator and magnetite in a unique system switched by a magnetic field.

Fatores estruturais que modulam a atividade das porfirinas englobam os ligantes equatoriais, o metal central e o número e estrutura dos seus ligantes axiais. A esses fatores se associam o microambiente fornecido por apoproteínas, solventes e membranas. Porfirinas são bastante utilizadas para a construção de estruturas supramoleculares com diferentes aplicações. A modulação da atividade das porfirinas tem sido freqüentemente obtida pela imitação da natureza, ou seja, fornecimento de diferentes microambientes. A associação das porfirinas a nanoestruturas lipídicas pode mudar a atividade destes compostos de tal forma a mimetizar diferentes enzimas como a SOD, citocromo P450, peroxidases e outros. As formas reativas das porfirinas são estados de alta valência: metal-oxo-πcátion e metal-oxo produzidos pela reação com peróxidos e perácidos. A modulação da atividade de porfirinas por nanoestruturas lipídicas também tem sido obtida para hemeproteínas uma vez que nanoestruturas lipídicas afetam a conformação das proteínas.

The structural factors modulating porphyrin activity encompass pyrrole and equatorial ligands, as well as the central metal and the number and structure of their axial ligands. Of equal importance is the microenvironment provided by apoproteins, solvents and membranes. Porphyrins are often used to construct supramolecular structures with different applications. The modulation of activity of the porphyrins has been frequently achieved by mimicking nature, i.e., by the provision of different microenvironments for these molecules. The association of porphyrins to surfactant- and lipid-containing nanostructures has changed the activity of these compounds to mimic different enzymes such as SOD, cytochrome P450, peroxidases and others. In determined conditions, the reactive forms of the porphyrins are high-valence states of oxo-metal-πcations and oxo-metal produced by the reaction with peroxides and peracids. The modulation of porphyrin activity by surfactant- and lipid-containing nanostructures has also been achieved for hemeproteins, as the lipid nanostructures affect the conformation of proteins.