Cation binding characteristics of tetrandrine studied by UV-Vis absorption and fluorescence spectroscopies

摘要

The binding of monovalent (Li~+, Na~+, K~+) and bivalent (Mg~(2+), Ca~(2+)) metal cations to a macrocyclic alkaloid tetrandrine has been studied by UV-Vis absorption and fluorescence spectroscopies. The calculated binding constants are between 3654 and 282 613 dm~3 mol~(-1) and the corresponding free energies from 4.777 to 7.308 kcal mol~(-1). The effect of the solvent on the complexation strength as well as the role of the counter-ion are discussed. Small changes are observed in the UV-Vis spectrum after complexation in respect to free ligand. The fluorescence response increases significantly in intensity and a blue shift appears by adding of calcium perchlorate to tetrandrine (6, 6', 7, 12-tetramethoxy-2, 2'-dimethyl-berbaman; TET) as a consequence of conformational restriction induced by cation binding.