FTIR, 2D IR, and computational studies of two coupled C=O stretching modes of xanthine and its derivatives in aqueous solution

Xanthine can be obtained during the purine metabolism reaction, and a large amount of xanthine in the human body may cause kidney stones. Xanthine derivatives are easily observed in coffee or chocolates, which are heavily consumed in the human body. Therefore, the molecular property and dynamics of xanthine and its derivatives in an aqueous solution is a topic of considerable interest. Xanthine and xanthine derivatives (theobromine, theophylline, paraxanthine, and caffeine) have two adjacent carbonyl groups, making them good candidates to study by infrared spectroscopy. However, infrared studies of xanthine in an aqueous solution have not been reported because of the low water solubility of xanthine. In this regard, two-dimensional infrared (2D IR) spectroscopy, which has the effect of suppressing the background signal, was used to detect a weak sample signal. In parallel, ab initio calculation was also performed for the xanthine in an aqueous solution. FTIR, 2D IR, and computational studies of xanthine and xanthine derivatives in D2O solutions are presented in this work