Static and Dynamic Quenching of Tryptophan Fluorescence in Various Proteins by a Chromium (III) Complex

ABSTRACT

The interaction of a chromium (III) complex, (R,R)-N,N′-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diaminochromium (III), with human serum albumin, bovine serum albumin, lysozyme, and free tryptophan was studied using steady-state fluorescence spectroscopy. Dynamic and static quenching constants were calculated using Stern-Volmer kinetics. The complex bound more tightly to the serum albumins than to lysozyme or free tryptophan, but only one binding site was determined in all systems. The interaction was also determined to be thermodynamically favorable, and the binding constants were on the order of 10³–10⁶. The fluorescence quenching was static in nature with Forster distances in the 1.8–2.0 nm range.

KEYWORDS:

• Cr (III) complex
• fluorescence
• static and dynamic quenching
• Stern-Volmer
• tryptophan

ACKNOWLEDGMENTS

The authors thank Susquehanna University for financial support for this project. They also thank the Chemistry Department at Bryn Mawr College for supporting the initial part of the project.