Purification, characterization and study of blue fluorescent substance in caffeine

Abstract

AbstractBackgroundCaffeine, a xanthine alkaloid compound, is a stimulant of the central nervous system and is mainly used in the pharmaceutical and food industries. Because caffeine is directly absorbed into the body, Chinese pharmacopeia has high requirements on the quality of caffeine products, and fluorescence has always been an important indicator to measure the quality of caffeine. In this study, a major fluorescent impurity affecting the appearance and purity of caffeine products was isolated for the first time, and the solubility, thermodynamic properties and dissociation constants of this impurity were studied.Results(i) The fluorescent impurity affecting the appearance and purity of the product was successfully isolated from crude caffeine and theophylline sodium salt, and named as a blue fluorescent substance. The mass purity of the substance was 96.27%, and its structure was determined based on a comprehensive analysis of high‐resolution mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy [hydrogen 1 (1H) NMR, carbon‐13 (13C) NMR, COSY, NOESY, HSQC, HMBC]. (ii) The solubility of blue fluorescent substance in four pure solvents was determined and the thermodynamic properties were calculated. (iii) The dissociation constants of the blue fluorescent substance in water at 298.15 K were determined by UV spectrophotometry.ConclusionThe results provide a theoretical basis for the crystallization separation of the blue fluorescent substance during the industrial production of caffeine, as well as basic data for the green synthesis process of caffeine. © 2024 Society of Chemical Industry (SCI).