The photochemical behavior of nimodipine (NIMO) and felodipine (FELO), photolabile drugs widely used as antihypertensive calcium channel blockers, is studied in constrained media. Specifically, we are interested in the kinetic analysis of 4-aryl-1,4-dihydropyridine photodegradation processes when they are incorporated in biological-mimicking systems like micelles or liposomes. In order to establish if the nature of the head of surfactant (ionic or nonionic) could be important modulating the photo-reactivity of these drugs, we studied the photodegradation of NIMO and FELO incorporated in micelles formed with sodium dodecyl sulfate (SDS, anionic), dodecyl-pyridinium chloride (DPC, cationic) and mono lauryl sucrose ester (MLS, nonionic) as surfactants. Additionally, the results of the photodegradation of these compounds in liposomes were also included. The results clearly indicate that both dihydropyridines studied, NIMO and FELO, are located near to the interface, but the surface charge of micelles does not affect neither, the photodegradation rate constant nor the photodegradation products profile. The absence of singlet oxygen generation in micellar media is consistent with the proposition of these 4-aryl-1,4-dihidropyridines located near to the interface of the micelle, where a polar environment is sensed. In addition, the ethanol preferential location on membranes and dihydropyridine enhanced photodegradation by alcohol presence are interesting results to consider in future research.

1-Metil-4-nitro-2-bromometilimidazol (4-NimMeBr) foi eletroquimicamente reduzido em eletrodos de mercúrio, carbono vítreo e carbono vítreo modificado com nanotubos de carbono de parede múltipla (MWCNT). 4-NimMeBr adsorveu no eletrodo de carbono vítreo modificado com nanotubos de carbono, tornando possível a implementação de um método de quantificação por voltametria de redissolução adsortivo (ASV). 4-NimMeBr foi usado como protótipo de composto eletroativo para estudar o efeito do tamanho dos nanotubos e de sua funcionalização por oxidação, na resposta eletroquímica do eletrodo modificado. Nanotubos oxidados formaram melhores dispersões em água, produzindo uma superfície de eletrodo com alta densidade de MWCNT, como mostram os dados obtidos por microscopia de varredura eletroquímica (SECM). Sob as condições otimizadas, a corrente de pico foi proporcional à concentração de 4-NimMeBr no intervalo de 10-6 mol L-1 a 10-4 mol L-1 com limite de detecção e quantificação de 4,41×10-6 mol L-1 e 6,21×10-6 mol L-1, respectivamente. Além disso, a sensibilidade do eletrodo não modificado com nanotubos foi 0,01 µA per mmol L-1, consideravelmente menor que os valores de 5,34 e 6,97 µA per mmol L-1 obtidos usando nanotubos oxidados de carbono de parede múltipla (pequenos e longos), respectivamente.

1-Methyl-4-nitro-2-brominemethylimidazole (4-NimMeBr), was electrochemically reduced on mercury, glassy carbon and multiwalled carbon nanotubes (MWCNT) modified electrodes. 4-NimMeBr was adsorbed on the MWCNT modified electrode thus permitting the implementation of an adsorptive stripping voltammetric (ASV) method. We have used 4-NimMeBr as a prototype electroactive nitro compound to study the effect of both the size of the nanotubes and its functionalization by oxidation. The oxidized MWCNT forms better dispersions than the non-oxidized, producing electrode surface with higher density of MWCNT as was determined by electrochemical mapping using scanning electrochemical microscopy (SECM). Under the optimized conditions, the peak current was proportional to the concentration of 4-NimMeBr in the range of 10-6 mol L-1 to 10-4 mol L-1 with detection and quantification limits of 4.41×10-6 mol L-1 and 6.21×10-6 mol L-1, respectively. The sensibility of bare electrode was 0.01 µA per mmol L-1, which was lower than the value of 5.34 and 6.97 µA per mmol L-1 obtained using short and large oxidized MWCNT, respectively.

The electrochemistry of 2,2-dimethyl-(3H)-3-(N-3'-nitrophenylamino)naphtho[1,2- b]furan-4,5-dione ([Q]-PhNO2), on mercury was investigated. The first peak is consistent with a quasi-reversible one-electron reduction of the ortho-quinone, forming [Q•-]-PhNO2, while the second one, bielectronic, corresponds to the simultaneous reduction of the latter radical to a dianion and the nitro group to a nitro radical anion. The second order rate constant, k disp, for the decay of [Q•-]-PhNO2 is 15.188 x 10³ ± 827 mol"1 L s"1 and the t1/2 equals 0.06 s. E¹7Ic values for [Q]-PhNO2 and its precursor, nor-β-lapachone, are similar. The ease of semiquinone generation and its stability are parameters statistically relevant in the correlation biochemical/theoretical aspects.