A cafeína vista sob nova abordagem: degradação do contaminante emergente e precursor de moléculas de interesse via reação de N-desmetilação

Abstract

Methylxanthines are alkaloids derived from the secondary metabolism of plants, represented by caffeine, theobromine and theophylline, whose biosynthesis depends on the plant species, thus caffeine is preferably formed in coffee, and theobromine in cocoa. They are purine derivatives with fused pyrimidine and imidazole rings whose structural difference is due to the absence of a methyl group at different positions. Caffeine is the chemical substance with psychoactive activity most consumed by the population, being incorporated in industrialized products such as stimulant drinks, dietary supplements and medicines. In the human body, it is metabolized generating dimethylxanthines: paraxanthine, theobromine and theophylline. Due to its high consumption and stability, caffeine has been found in wastewater and considered an emerging micropollutant. Thus, conditions were studied to promote the degradation of caffeine in an aqueous solution simulated by contamination, applying the Fenton, Fenton-type and ascorbic acid conditions, which allowed evaluating the influence of Fenton H2O2/Fe2+ reagents, in addition to pH and catalysts (Fe3+, iron oxides/hydroxides). The application of catalytic reactions aimed at converting caffeine into dimethylxanthines was also investigated. The work comprised the reactional monitoring with evaluation of caffeine transformation products, monitored by HPLC. In addition, the application of analytical techniques paper chromatography, UV-Vis and FTIR to detect caffeine in samples was evaluated, obtaining better results with FTIR associated with the deconvolution technique or principal component analysis, which made the semiquantification of caffeine possible, even in the presence of theobromine. At the same time, an analytical method suitable for reaction monitoring aimed at quantifying caffeine and its transformation products was sought. The HPLC method, consisting of a mixture of water and acetonitrile (9:1) as mobile phase, flow 1.0 mL.min-1, C18 column 150 x 4.6 mm and 5μm particle size, detection at 272 nm using DAD, run time of 14 minutes, allowed the verification of 10 transformation products, with the identification of theobromine (3,7-dimethylxanthine) and the inference of other products such as paraxanthine, theophylline and uric acid derivatives. A fraction of the sample was also evaluated by mass spectrometry showing ion m/z 181, compatible with dimethylxanthines. The mechanisms of the Ndemethylation and C-hydroxylation reactions were proposed, with a molar ratio caffeine/HO˙ of 1:2, via hydroxyl radicals, or caffeine/H2O2 1:1, mediated by H2O2. The observation of the N-demethylation reaction in the formation of dimethylxanthines is interesting, since caffeine is an important precursor of new molecules.