Indole Schiff Base Complex: Synthesis and Optical Binding Investigation with Biogenic Amines

Biogenic amines, produced by bacterial enzymatic reactions in food storage or processing, serve as indicators in food processing industries to assess food quality and freshness. Biogenic amines also often associated with various health problems, including abnormal immune responses and gastrointestinal disease. Previously, salphen base complexes have been reported but still exhibited low fluorescence enhancement upon biogenic amines. This research focused on synthesizing and characterizing new Zn(II) Schiff base complex with indole sidechain to enhance the fluorescence property and exploring their binding behaviour with the biogenic amines, which were phenylethylamine and cadaverine. The Zn(II) indole Schiff base complex's structure was verified by diverse spectroscopic techniques. Then, the binding behaviours between the Zn(II) indole Schiff base complex with the biogenic amines were analyzed using UV-Vis, fluorescence spectroscopy, and Job's plot analysis. UV-Vis binding study results indicated that the synthesized complexes could bind stronger with phenylethylamine than cadaverine, with binding constant, K_b= (8.21 ± 0.58) × 10⁴ M^- 1 and (2.506 ± 0.004) × 10⁴ M^- 1 respectively. Moreover, Zn(II) indole Schiff base complex-phenylethylamine binding also generated higher fluorescence enhancement than cadaverine, which were 54% and 51% respectively. Based on Job's plot analysis, the complex and biogenic amines were bound in the ratio of 1:1. To conclude, the synthesized complex has promising potential as a sensing material for biogenic amines detection in food. The complex is recommended to be deployed in the development of solid-state fluorescence sensor for biogenic amines detection for monitoring the food spoilage in the food industry in the future.