The characterization of the sol-gel encapsulated curcumin as a possible sensor for small biologically important molecules.

Curcumin, a known phytochemical antioxidant was found to be useful as a potential sensor for some small biologically important molecules. Hydrogen peroxide, the sodium salt of nitrite (NO2-), hydroxide (OH-), bromide (Br-) and iodide (I-) were observed to quench the fluorescence of sol-gel encapsulated curcumin, which emits radiation at 530 nm when excited at 420 nm. The observed bimolecular quenching constant which is related to the Stern-Volmer quenching constant, KSV, for the species studied in this work was determined by a modified Stern-Volmer relation for molecular surface accessibility, was observed to be specific for each of these anions and correlates quite well with their half-wave potentials, E1/2. The extent of permeability of these molecules through the pores of the sol-gel matrix was determined and they, also, correlated with these molecules' charge densities and sizes. In all the species, the reaction was quite exergonic and the free energy change, DeltaGoET, obtained in each case, suggest an outer-sphere, long range electron transfer mechanism. These observations open up the possible use of curcumin as a sensor for probing and characterizing some relevant bio-molecules in biological systems.

Peroxynitrite interaction with curcumin solubilized in ethanolic solution.

Spectroscopic (fluorescence and absorptiometric) techniques were used to study the interaction between peroxynitrite, a known biological stressor, and curcumin, a potent biological antioxidant. In both techniques, the observed signals increased asymptotically until the concentration of peroxynitrite equals that of the curcumin, which was held constant at 1 x 10(-5) M. However, there was a shift in fluorescence wavelength after initial apparent oxidation of the hydroxyl group. This is perhaps due to nitration of the phenoxyl group of curcumin. The obtained data, using these techniques, suggest a second order reaction rate for the nitration of the curcumin by peroxynitrite. The biomolecular interaction or association constant obtained was 1.2 x 10(6)/M-s using the fluorescence technique and it was 3.6 x 10(6)/M-s using the absorptiometric technique. These values are in good agreement with literature values.

Electrooxidation of peroxynitrite in simulated body fluid at platinum electrode.

Peroxynitrite, a potent albeit deleterious biological oxidant, was electrooxidized at a bare platinum electrode in a medium of simulated body fluid (SBF) to nitrite anion and molecular oxygen. The SBF, prepared in accordance with literature procedure, has a pH of 7.4 and an ionic strength of 0.16. In this medium, peroxynitrite was observed to undergo a diffusion-controlled (D=1.63 x 10(-5) cm2/s) oxidation process at a bare platinum electrode with a heterogeneous rate constant, k(s), of 0.029 cm/sec. The formal redox potential, Eo', of this biological oxidant was determined as 1.18 V with respect to saturated calomel electrode (SCE) in a 2e- oxidation process. The electrochemical response of the oxidation process, measured in unit of current, is observed to be concentration dependent with a limit of detection of 1.6 x 10(-7) M. The linear dynamic range of the observed current-concentration plot extends over the entire concentration range studied. These observations make this electrochemical method a feasible technique for quantitative determination of peroxynitrite in vivo and in vitro.

Soybean oil as a possible solubilizing and vehicular medium for zinc phthalocyanine in photodynamic therapy.

Soybean oil (SBO) is used as a medium to solubilize zinc phthalocyanine (ZnPc), a known photosensitizer, which has been found to be of potential use in photodynamic therapy. It absorbs red light in this medium at 670 nm with good molar absorptivity comparable to its value in most organic solvents (2.45 x 10(5) M(-1) cm(-1)). The wavelength of the fluorescence emission band peaked at 700 nm when excited at 591 nm, and when excited at 560 nm, the emission band was observed at 680 nm. The characteristic emission band of ZnPc at the near end of the visible spectral region suggests that this compound exists in this medium in a monomeric form, a form most useful in photo therapeutic applications. Moreover, the excitation wavelength, observed in the far-red region, precludes minimal effect, if any, of skin photonecrosis if this medium is used in PDT. A fluorescence spectral analysis of the ZnPc-SBO solution carried out for thirty-eight days indicates that this solution is stable within this time frame. No toxicity was detected when this solution was seeded in human endothelial cells in a culture well for 36 hr and also when injected subcutaneously into the nude and Balb C mice. In both cases the ZnPc was observed to clear from the injected area in a reasonable time. This fact coupled with its good solubilizing property for ZnPc and its virtual nontoxicity may make soybean oil a possible vehicular medium for transporting useful photosensitizers to target cells in photodynamic therapy and related applications.

The fluorescence study of the binding of zinc phthalocyanine to breast cancer cells solubilized in synthetic liposomes.

Steady state fluorescence spectroscopy is used to study the binding characteristics of zinc phthalocyanine (ZnPc) to MCF-7 human breast cancer cells solubilized in a liposomal vesicle prepared with L-alpha-phosphatidic acid, dipalmitoyl. The observed apparent binding constant, K', of 1.14 x 10(7) together with the free energy of binding, deltaG, of -40.38 kJ/mole suggests a very strong affinity and spontaneous binding between the breast cancer cells and ZnPc. The wavelength of excitation of ZnPc in the liposomal vesicle (611 nm) is favorable to cytotoxic reactive singlet oxygen (1O2*) production necessary for photooxygenation reaction with the cancerous cells and is within the energy threshold that has good penetration to normal tissues without undue skin necrosis.

Bicontinuous microemulsions as media for electrochemical studies.

Biocontinuous microemulsions of didodecyldimethylammonium bromide (DDAB)/dodecane/water were explored as media for voltammetric reductions and oxidations of ruthenium(III) hexaammine, ferrocyanide, ferrocene, cob(II)alamin, and several polycyclic aromatic hydrocarbons (PAHs). These clear microemulsions are conductive and are believed to contain a dynamic extended network of interconnected water tubules. Agreement of simulated and experimental voltammetric data shows that electrochemical theory for homogeneous media is followed to a good approximation in DDAB microemulsions. Diffusion of electroactive solutes did not reflect the high bulk viscosities of the microemulsions. Non-polar molecules and ions diffuse as if they were in neat oil or aqueous media, respectively, and voltammograms with good signal to noise ratio are obtained. Reductions of PAHs in the microemulsions occurred by an ECE-type pathway, with nearly reversible one-electron reductions achieved at high scan rates.