Abstracts

Curcumin (CurcH) is a natural fluorescent dye, found in the rhizomes of turmeric, that has a bright yellow color, and the compound has attracted attention in recent years for exhibiting antibacterial, anti-inflammatory, hypoglycemic and antioxidant properties. Its photochemical properties and the fact that it is biocompatible give rise to a wide range of potential analytical applications, such as in fluorescence microscopy, the detection of hydrogen peroxide production sites in cells through chemiluminescence or its utilization as an activator (ACT) for the peroxyoxalate system. However, its low solubility in water reduces considerably its applicability in biological medium. The simplest way to use curcumin in analysis, is to dissolve it in organic solvents such as 1,2-dimethoxyethane (DME), ethyl acetate (EtOAc) or acetone (AC), except that the biocompatibility of the system is reduced due to the cytotoxicity of these solvents. To mitigate this problem, the use of binary water / organic solvents mixtures is an applicable and more sustainable approach, maintaining the curcumin soluble and lowering the toxicity of the system. The binary system also increases the efficiency of the peroxyoxalate system since faster reactions and lower emission intensities are observed for this reaction in aqueous medium. In this communication, we report our initial experimental results of a kinetic study of the peroxyoxalate reaction using bis(2,4,6-drichlorophenyl) oxalate (TCPO) as oxalic ester and curcumin as well as 9,10-diphenylanthracene (DPA) for comparison, as activators in different binary mixtures of water and DME as reaction medium. The kinetic studies give rise to observed rate-constants (kobs) in different experimental conditions, thereby characterizing the slow reaction steps and the molecularity of each reactant. The chemiluminescence emission (FCL) and singlet excitation (FS) quantum yields were determined from the integrated emission intensity versus time curves, using luminol standard. The singlet excitation quantum yields at infinite ACT concentrations (FS¥) was determined from the ACT concentration dependence, using a double-reciprocal plot. The reaction kinetics are not altered by the nature and concentration of the ACT and the FS¥ are higher for curcumin as compared to DPA in anhydrous organic medium, although the FCL are higher for DPA due to its higher fluorescence quantum yield. These results clearly demonstrate that the natural product curcumin can be utilized as ACT in the peroxyoxalate reaction in partially aqueous media, thereby contributing to more sustainable assay conditions. Currently, the toxic oxalic ester TCPO is being substituted by less toxic oxalate derivatives containing as phenolic components vanillin and other natural phenols.