Synthesis, spectroscopic characterization, DFT studies, and initial antibacterial assays in vitro of a new palladium(II) complex with tryptophan

Abstract

A new palladium(II) complex with the amino acid L-tryptophan (Pd-TRP) was synthesized in aqueous solution and characterized by chemical and spectroscopic methods. Elemental, ESI-QTOF mass spectrometric, and thermal analyses of the solid compound permitted proposing the [Pd(C₁₁H₁₁N₂O₂)₂] · 2H₂O composition. Infrared, Raman, and UV-Vis spectroscopic data indicate the coordination of the ligand to Pd(II) through monodentate oxygen of carboxylate and through nitrogen of the amino group. The ¹H and ¹³C NMR spectroscopic data confirm coordination through the carboxylate, while ¹⁵N NMR data confirm coordination of nitrogen of NH₂. Density functional theory studies confirmed nitrogen and oxygen coordination to palladium(II) as a minimum of the potential energy surface with calculations of the hessians showing no imaginary frequencies. Biological studies were performed to provide information concerning the antibacterial activities of the compound. The Pd-TRP complex was shown to be active against Gram-positive and Gram-negative pathogenic bacterial strains.

Keywords:

• Palladium(II)
• L-Tryptophan
• ESI-QTOF-MS
• Molecular modeling
• Infrared
• Antibacterial agent

Acknowledgments

This study was supported by grants from the Brazilian Agencies FAPESP (São Paulo State Research Foundation, proc. 2006/55367-2, 2008/57805-2) and CNPq (proc. 479415/2009-9, 472468/2010-3, and 573672/2008-3) and by the Laboratory of Advanced Optical Spectroscopy (LMEOA/IQ-UNICAMP/FAPESP 2009/54066-7). The authors are grateful to Professor Claudio Airoldi for his assistance and also to Professor Carol H. Collins for English revision of the article.