Investigation of the effects of Zn2+, Ca2+ and Na+ ions on the interaction between zonisamide and human serum albumin (HSA) by spectroscopic methods.

In this work, The effect of three metal ions Zn(2+), Ca(2+) and Na(1+) on the interaction between human serum albumin (HSA) and zonisamide (ZNS) was investigated employing fluorescence, ultraviolet-visible (UV-Vis) absorption and circular dichroism (CD) under simulated physiological conditions. Fluorescence spectroscopy revealed that these metallic ions and ZNS can quench the HSA fluorescence, and this quenching effect became more significant when both ion and drug are present together. It was found that the quenching mechanism is a combination of static quenching with nonradiative energy transfer. The binding sites number (n), the binding constant (Kb) and the spatial-distance (r) of ZNS with HSA without or with Zn(2+), Ca(2+) and Na(1+) ions were calculated. The presence of Ca(2+) and Na(+) ions decreased the binding constants (Kb) and the number of binding sites (n) of ZNS-HSA complex. However, the presence of Zn(2+) increased the affinity of ZNS for HSA largely. Changes in UV-Vis absorption and CD data are due to the microenvironment of amide moieties in HSA molecules.