A Joint Study on Juglone Metal Complexes by Infrared Spectroscopy and Density Functional Theory Calculations

Juglone [=5-hydroxy-1,4-naphthalenedione] is a natural product obtained from plants belonging to Juglandaceae genus (e.g. walnut). Past folk medicine used extract of walnut for antimicrobial, anti-inflammatory and antioxidant treatments. Recently juglone has shown a cytotoxic activity on (HL-60, HL-60R, A549 and SCG-7901) human tumor cells by inducing apoptosis, and its complexes with transition metal ions were proved antibacterial activity.2 From here our interest in the structural analysis of Cu(II) and Ni(II) complexes of juglone. Over the last decades, infrared spectroscopy (IR) has experienced a renewed role in the molecular structure elucidation of organic compounds, due to the availability of simulated spectra by density functional theory (DFT) calculations able to assign the frequencies associated to vibrational modes obtained by experimental spectra. The juglone metal complexes, whose stoichiometry was supported by ESI-MS/MS experiments were analyzed by FT-IR spectroscopy equipped with the attenuated total reflectance (ATR) technique and the frequencies assigned by DFT calculated spectra using a B3LYP/6-311G(d) basis set. The changes induced by metal chelation are discussed also in comparison with the ion-dipole interactions observed for Na and Cs salts of juglone. Keywords: DFT calculations, IR Spectroscopy, Juglone, Metal complexes