Abstract
The interactions of calcium and magnesium ions with caffeine and theophylline have been investigated in aqueous solution at physiological pH. Fourier Transform infrared (FTIR) spectroscopy and absorption spectra were used to determine the cation binding mode and the association constants. Our spectroscopic results showed that calcium and magnesium ions do not complex with caffeine strongly and the weak interactions between caffeine and Mg 2+ and Ca 2+ might be via O6 atom. In Ca 2+–theophylline complex, binding between Ca 2+ with CO and N7 is observed, however in Mg 2+–theophylline complex, binding between Mg 2+ and N7 is more likely. The k values of these complexes are as follows: k(caffeine–Ca)=29.8 M −1, k(caffeine–Mg)=22.4 M −1, k(theophylline–Ca)=59.8 M −1 and k(theophylline–Mg)=33.8 M −1. These values are evidence for a weak cation interaction in these metal complexes.
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