PubMed · 3046419
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D C Johnson, M D Ryan, G S Wilson. 1988-06-15. Dynamic electrochemistry: methodology and application.. https://doi.org/10.1021/ac00163a011
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Described are studies directed at refining quantitative analysis of nitric oxide in solution using electrochemical techniques. The fabrication and behavior of several sensors based on modified carbon-based electrodes are reported. This technique has been used to resolve the vexing problem of determining the stoichiometry of the photochemical decomposition of the known antihypertension agent sodium nitroprusside, Na2[Fe(CN)5NO], as well as of two other metal nitrosyl complexes of biological interest, Roussin's black salt, NH4[Fe4S3(NO)7], and Roussin's red salt, Na2[Fe2S2(NO)4], in aqueous solutions. In this manner it was shown that the molar ratios of nitric oxide produced per starting complex photochemically decomposed were 0.95 +/- 0.03, 5.9 +/- 0.2, and 0.50 +/- 0.02 for Na2[Fe(C-N)5NO], NH4[Fe4S3(NO)7], and Na2[Fe2S2(NO)4], respectively.
Scavenging of singlet oxygen (1O2) by alpha-tocopherol (alpha-Toc) was investigated in liposomes. 1O2 was generated by photoirradiation in the presence of two photosensitizers, water-soluble methylene blue (MB) and lipid-soluble 12-(1-pyrene)dodecanoic acid (PDA). The rates of oxidation of alpha-Toc differed depending on the photosensitizing dye and the membrane charge: in the MB-system, alpha-Toc was oxidized fast in negatively charged dimyristoylphosphatidylcholine (DMPC) liposomes containing dicetylphosphate (DCP) and slowly in neutrally charged DMPC liposomes and positively charged DMPC liposomes containing stearylamine (SA), but in the PDA-system, the oxidation rate was independent of the membrane charge. The charge-dependent difference in the MB-system would be due to the site of 1O2 generation depending on the charge-dependent distribution of MB, because positively charged MB increased the zeta-potential of DCP-DMPC liposomes by its interaction with DCP at the membrane surface, but changed the zeta-potentials of DMPC and SA-DMPC liposomes less because of its location in the bulk water phase. The oxidation rate of alpha-Toc in liposomes was different from that in EtOH solution: in the MB system, the oxidation rate was faster in EtOH solution than in DMPC or SA-DMPC liposomes but the same as that in DCP-DMPC liposomes. However, in the PDA system, the oxidation rate was slower in EtOH solution than in DMPC liposomes with or without a charge. Membrane fluidity changed the rate of alpha-Toc oxidation in liposomes, the rate being higher in the liquid crystalline phase than the gel phase, as judged by the higher rate in DMPC liposomes than in dipalmitoylphosphatidylcholine (DPPC) liposomes at 30 degrees C. The rate constants of alpha-Toc for scavenging, the chemical reaction and physical quenching of 1O2 were determined in membranes using DCP-DMPC liposomes labeled with 1,3-diphenyl-isobenzofuran (DPBF), which traps 1O2. These constants differed in the two photosensitizing systems, being higher in the MB-system than in the PDA-system, and were lower than those in EtOH solution.
Immunoelectrochemical sensors in which the sensor surface functions as both analyte capture phase and electrochemical detector have recently been developed for bacteria analysis. The speed and sensitivity of these devices make them very attractive for applications such as the detection of pathogenic microorganisms in food and water. However, the development and optimization of assays utilizing these sensors can be complicated by undesired interactions between the capture and detection functions. Modification of the sensor to achieve improvements in one function can have deleterious effects on the other function, and such effects can be difficult to diagnose and correct. In the course of investigations on immunoelectrochemical detection of Salmonella, we developed a rapid, nondestructive epifluorescence microscopy method to determine bacteria capture efficiency. This method enabled us to study capture and detection functions independently and efficiently identify performance-limiting factors. Rapid-scan electrochemical methods were used to optimize detection sensitivity and to provide diagnostic information on detection performance.