Interaction of metal ions with caffeine and theophylline: stability and structural features.
The interactions of caffeine and theophylline with divalent cadmium, mercury, strontium and barium ions were studied in aqueous solution and physiological pH. Fourier transform infrared spectroscopy (FTIR) and absorption spectra were used to determine the cation binding mode and association constants. Spectroscopic results showed that Cd(2+), Hg(2+), Sr(2+) and Ba(2+) bind strongly to caffeine and theophylline. Direct and indirect (through metal hydration shell) interactions were observed for caffeine and theophylline with Cd(2+), Hg(2+), Sr(2+) and Ba(2+) through O6 and N9 (caffeine) and O6, N9 and N7 atoms (theophylline). The overall binding constants are:k(Cd-caffeine) = 1.24 x 10(5) M(-1), k(Hg-caffeine) = 1.74 x 10(5) M(-1), k(Sr- caffeine) = 3.3 x 10(4) M(-1), k(Ba-caffeine) = 1.8 x 10(4) M(-1), k(Cd-theophylline) = 5.75 x 10(5) M(-1), k(Hg-theophylline) = 2.14 x 10(5) M(-1), k(Sr-theophylline) = 4.6 x 10(4) M(-1), k(Ba-theophylline) = 3 x 10(4) M(-1). These k values are evidence for weak and strong cation interactions in these metal complexes.
Nafisi
Shohreh
S
Department of Chemistry, Azad University, Tehran Central Branch, South Felestine Str, Below the Felestine Square, Tehran, 14169 63316, Iran. drshohreh@yahoo.com
Sadjadi
Abolfazl Seyed
AS
Zadeh
Sakine Shokrollah
SS
Damerchelli
Maryam
M
D002110:Caffeine / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D015394:Molecular Structure; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D013806:Theophylline / Q000737:chemistry*
D007477:Ions; D008670:Metals; D012996:Solutions; D002110:Caffeine; D013806:Theophylline