Brazil has the greatest plant diversity on the planet, distributed in different types of biomes. These plants are important sources of biologically active natural products, which are derived from various drugs marketed worldwide. This paper presents an electrochemical study of three unusual dimeric flavonoids, pharmacologically active, isolated and identified for the first time by our research group, in a Brazilian plant (Fridericia platyphylla). The results showed that oxidation processes are favored at higher pH, and mass transport was controlled by diffusion. Brachydins derivatives, Bra-A was oxidized at the lowest potential value (0.48 V vs. Ag/AgCl, KCl(sat)) and Bra-B and Bra-C, presented the highest oxidation potentials (ca. 0.71 and ca. 0.57 V vs. Ag/AgCl, KCl(sat), respectively). This study shows that electrochemistry is one more tool that would help us focus on future bio-pharmacological investigations of these unusual compounds.

Neste trabalho, uma série de compostos nitro-heterocíclicos foi submetida a estudos químico-quânticos e de voltametria cíclica com a finalidade de determinar as propriedades físico-químicas que exercem influência sobre o potencial redox do grupo nitro. A otimização de estrutura, as propriedades e os mapas de superfícies estereoeletrônicas foram calculadas utilizando o método semi-empírico AM1. O potencial redox dos compostos, Ar-NO2/Ar-NO2•- , foi determinado em meio aprótico (DMSO e eletrólito de suporte Bu4NH4BF4 0,1 mol L-1), com o uso de eletrodos de trabalho de carbono vítreo, eletrodo auxiliar de fio de platina e eletrodo de referência de Ag/AgCl. A investigação dos confôrmeros de menor energia mínima demonstrou a ocorrência de quebra de planaridade estrutural entre o nitrogênio hidrazínico e o resíduo benzamídico. Não foi observada a ocorrência de correlação, avaliada através da análise de regressão de PLS, entre as propriedades estereoeletrônicas e o potencial redox, resultado, provavelmente, de quebra da estrutura co-planar no grupo de moléculas estudadas.

Stereoelectronic properties of nitro-heterocyclic bioisosteric congeners were investigated using theory-level quantum chemistry and cyclic voltammetry with the goal of determining physico-chemical properties that affect the redox potential of the nitro group. Molecular geometry, physicochemical properties and stereoelectronic surfaces, such as molecular electrostatic potential, and HOMO and LUMO orbitalar distributions, were calculated using the AM1 semiempirical method. The redox potential of nitro-heterocyclic compounds, which corresponds to the (Ar-NO2/Ar-NO2•- ) redox couple, was measured in aprotic media (DMSO and 0.1 mol L-1 Bu4NH4BF4) using glassy carbon as working electrode, Pt wire, Ag/AgCl, KCl(sat) as counter and reference electrodes, respectively. Analysis of minimal energy conformers of all derivatives indicated a break in structural planarity located between the hydrazine nitrogen and benzamide moiety. No statistical correlation was obtained using the PLS regression method, taking in account all physicochemical properties and the redox potential, which might result from the lack of coplanarity effect in the molecular structure of the compounds.

Filmes de azul da Prússia foram superficialmente depositados em eletrodos de pasta de carbono a partir de soluções contendo 2,0 x 10-3 mol L-1 de K3[Fe(CN)6], 3,0 x 10-3 mol L-1 FeCl3 e 1,0 x 10-2 mol L-1 HCl, usando dois potenciais controlados. Para aumentar a estabilidade do eletrodo modificado, efetuaram-se 50 ciclos em solução contendo 1,0 x 10-3 mol L-1 de RhCl3, 0,50 mol L-1 de KCl e 1,0 x 10-2 mol L-1 de HCl no intervalo de - 0,40 a + 0,60 V a 60 mVs-1. Estes eletrodos, denominados de Rh-PBMCPE, apresentaram boa estabilidade durante a determinação amperométrica de H2O2 a 0,040 V sem a interferência dos ácidos ascórbico e úrico. A corrente de redução variou linearmente com a concentração de H2O2 no intervalo de 5,0 x 10- 5 a 8,6 x 10-4 mol L-1. O limite de detecção foi de 2,8 x 10-5 mol L-1 com sensibilidade variando de 1,32 a 0,96 A mol-1 L cm-2 ao longo de cinco dias (180 determinações).

Prussian Blue was deposited at carbon paste electrode surface from a solution containing 2.0 x 10-3 mol L-1 K3[Fe(CN)6], 3.0 x 10-3 mol L-1 FeCl3 and 1.0 x 10-2 mol L-1 HCl using two controlled potentials. To improve the stability of the modified electrode it was 50 times cycled in a solution containing 1.0 x 10-3 mol L-1 RhCl3, 0.50 mol L-1 KCl and 0.010 mol L-1 HCl in the potential range from - 0.40 V to 0.60 V at 60 mV s-1. The Rh - Prussian Blue carbon paste modified electrode (Rh-PBMCPE) showed good stability during amperometric catalytic determination of H2O2 at 0.040 V, without ascorbic and uric acids interferences. The current changed linearly with H2O2 concentrations in the range of 5.0 x 10-5 - 8.6 x 10-4 mol L-1. The estimated detection limit was 2.8 x 10-5 mol L-1 with sensibility changing from 1.32 to 0.96 A mol-1 L cm-2 along five days (180 determinations).

The first studies about DNA electrochemistry appeared at the end of the fifties. The voltammetric techniques became important tool for the DNA conformational analysis, producing evidences about DNA double helix polimorphism. The new techniques based on electrodes modification with nucleic acid enlarged the use of the electrochemical methods on the DNA research. DNA electrochemical biosensors are able to detect specific sequences of DNA bases, becoming important alternative for the diagnosis of disease, as well as in the carcinogenic species determination. Besides, the use of DNA biosensors in the mechanism study of biological drug actions can be useful for drug design.