Metallochlorophylls of magnesium, copper and zinc: evaluation of the influence of the first coordination sphere on their solvatochromism and aggregation properties

In this study the role of different metal centers (magnesium, zinc and copper) on the enhancement of the hydrophilic character of metallochlorophylls, was evaluated. The solvatochromism as well as the aggregation process for these compounds in water/ethanol mixtures at different volume ratios were evaluated using Fluorescence, and Resonant Light Scattering (RLS) measurements, aiming to characterize the behavior of these compounds. Independently on the studied metallochlorophyll, the presence of at least 60% of water results in a considerable increase in the fluorescence emission, probably a direct consequence of a lower aggregation of these compounds, which is confirmed by the results from RLS measurements. Additionally, the results suggest that magnesium and zinc chlorophyll should be promising phototherapeutic agents for Photodynamic Therapy.No presente estudo, o papel de diferentes centros metálicos (magnésio, zinco e cobre) sobre o caráter hidrofílico de metaloclorofilas foi avaliado. O solvatocromismo, assim como o processo de agregação para esses compostos, em misturas água/etanol foram avaliados usando medidas de fluorescência e de espalhamento de luz ressonante (ELR), visando caracterizar o comportamento desses compostos. Independente da metaloclorofila estudada, a presença de ao menos 60% de água resulta em incremento considerável na emissão de fluorescência apresentada por esses compostos. Isso, provavelmente, é uma conseqüência direta de uma menor agregação, o que é confirmado pelos resultados de ELR. Adicionalmente, os resultados sugerem que as clorofilas de magnésio e de zinco devem ser promissores agentes fototerapêuticos para emprego em Terapia Fotodinâmica.FAPESPFundação AraucáriaFAPEMIGCNPqNanobra

Electroanalytical determination of 4-nitrophenol by square wave voltammetry on diamond electrodes

The anodic voltammetric behavior of 4-Nitrophenol on a Boron-doped diamond electrode in aqueous solution has been studied using square wave voltammetry. After optimization of the experimental conditions, that model molecule was analyzed in pure water solutions using a Britton-Robinson buffer with pH 6.0 as the supporting electrolyte. Oxidation occurs at 1.0 V vs. Ag/AgCl in an irreversible two-electron process controlled by adsorption of the species. The detection limit (DL) obtained was 2.8 mug L-1. This result was comparable to that obtained from reduction of the molecule at -0.8 V vs. Ag/AgCl under the same experimental conditions (DL = 4.2 mug L-1). Both DL values are within the limits required by the legislation for drinking water (30 mug L-1). The combination of square wave voltammetry and diamond electrodes has proved to be an interesting and desirable alternative for the analytical determination of organic molecules

Screen-Printed Electrodes Based on Conductive Inks of Polyaniline/Graphene Hybrids and Their Application to Progesterone Detection

Screen-printed electrodes (SPEs) were produced using conductive inks based on hybrids of polyaniline (PAni) and reduced graphene oxide (rGO). Cyclic voltammetry (CV) showed peaks characteristic of the PAni redox behavior in acidic media for all the modified SPEs. Electrochemical impedance spectroscopy (EIS) showed a significant decrease in the charge-transfer resistances, from 930 Ω for SPE/G:PAni to 544 Ω for SPE/G:PAni-rGO1 and to 303 Ω for SPE/G:PAni-rGO2 with just 0.06% and 0.12% in mass of rGO, respectively, in the final mass composition of the conductive inks. The SPEs were evaluated in the determination of progesterone (P4) hormone in neutral medium (phosphate buffer solution, pH 7.0). The CV results showed higher current signals at SPE/G:PAni-rGO1 compared with SPE/G and SPE/G:PAni, indicating a synergistic effect of PAni-rGO1 in the determination of P4. EIS also showed significant changes in the electrochemical double-layer capacitances in the presence of P4. The limits of detection (LOD) and quantification (LOQ) were, respectively, 211 nmol l ^−1 and 703 nmol l ^−1 . This method is a simple, scalable and low-cost alternative for the fabrication of electrodes based on PAni-rGO hybrids, with synergic properties, aiming for future applications in sensors