Static quenching of tryptophan fluorescence in proteins by a dioxomolybdenum(VI) thiolate complex

• Fluorescence quenching of proteins and tryptophan.
• Non-aromatic cis-dioxobis(dithiocarbamato) molybdenum(VI) complex.
• Static quenching via H-bond and other forces.
• Non-fluorescence complex formation that is exothermic with a negative entropy change.
• Binding constants on the order of 104–105 M−1.

The binding of cis-dioxobis(dithiocarbamato) molybdenum(VI) with the proteins bovine serum albumin, human serum albumin, lysozyme, and free tryptophan was studied using fluorescence spectroscopy and Stern–Volmer kinetics. The quenching of tryptophan fluorescence was determined to be static with binding constants on the order of 104–105 M−1, and with a binding site number of one. The interaction was studied over a range of temperatures, and the binding was found to be exothermic with a negative change in entropy. Quantum chemical calculations were also conducted to identify optimal spatial contacts and the resulting energetic contributions between the complex and free tryptophan.

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