Spectroscopic investigation of the interaction between thiourea-zinc complex and serum albumin

The interaction between 1-Zn (N-p-(dimethylamino)benzamido-N′-phenylthiourea-zinc) complex and serum albumins was studied. In the presence of proteins such as BSA or HSA, the fluorescence spectrum of 1 did not change. However, the fluorescence intensity of its zinc complex (1-Zn) was greatly enhanced. It was ascribed to the fact that zinc ion promoted the interaction between 1 and proteins. Therefore, it was concluded that zinc ion could facilitate bioactivity of thiourea derivative drugs. Energy transfer occurred between 1-Zn and the proteins, which led to decrease of proteins' emission and increase of 1-Zn's emission. The fluorescence quenching of serum albumins by 1-Zn was considered as a static quenching process. The binding constants between 1-Zn and serum albumins were estimated as 1.02×1012 mol−1 L for BSA and 1.32×1010 mol−1 L for HSA, respectively, and the number of binding sites was 2 for both. The effect of 1-Zn on the conformation of serum albumins was further investigated using synchronous fluorescence spectrometry and the results implied that tyrosine residues of proteins were closer to 1-Zn than tryptophan residues.