Spectroscopic studies on the interaction of chromium (VI) and chromium (III) with keyhole limpet hemocyanin

The interactions of keyhole limpet hemocyanin (KLH) with chromium nitrate, potassium dichromate, and chromate were investigated using fluorescence, UV–vis absorption and circular dichroism (CD) spectroscopy under simulated physiological conditions. The experimental results showed that the different forms of chromium could quench the intrinsic fluorescence of KLH following a static quenching mechanism rather than by dynamic collision, which indicated that a Cr–KLH complex was formed. The Stern–Volmer quenching constants for the interaction indicated that the binding reaction of KLH with Cr(VI) was stronger the binding of KLH with Cr(III). The thermodynamic values for binding of Cr(VI) to KLH are ΔH > 0 and ΔS > 0. By contrast, the values for the interaction of Cr(III) with KLH are ΔH < 0 and ΔS < 0. The results of synchronous fluorescence, UV–vis absorption and CD spectroscopy showed that the α‐helical secondary structure and conformation of KLH were altered by different forms of chromium. Copyright © 2016 John Wiley & Sons, Ltd.