DPPH Free Radical Scavenging Activity, and their Synthetic, Structural, Electronic and Magnetic Studies of Two [CuII2(thb)] Compounds, (thb= N,N,Nô,Nô-tetrakis-{3-[(2-hydroxibenzyliden)-amine]propyl}-1,4-butanodiamine)]

Abstract

Synthesis, structural, electronic, and magnetic characterization of two [CuII 2(thb)] (thb = N,N,N’,N’- tetrakis-{3-[(2- hydroxibenzyliden)-amine]propyl}-1,4-butanodiamine)]) crystalline phases (1a and 1b) are reported. Both, 1a and 1b, showed free radical scavenging activity, which was quantified by the DPPH free radical scavenging activity assay. 1b crystallized in a P21/c space group. In 1b each molecule contains two CuII-(hidroxibenzyliden) groups bonded in the extremes of the organic DAB-Am nucleus. The CuII-(hidroxibenzyliden) groups of each extreme, form 1D chains along of the b-axis. IR and UV-Vis spectra showed d-d transitions and νCu-O, νCu-N vibrations respectively, confirming the formation of the compound. 1H-NMR spectra of 1a and 1b showed similar spectra, being characteristics of paramagnetic compounds. Bulk magnetization of 1a and 1b from 2 K to 300 K showed paramagnetic behaviour. The best fit for the susceptibility data was obtained using Curie-Weiss and modified Curie-Weiss equations with θ and C values of θ1a/1b C-W = 0 ± 1K, C1a/1b C-W = 0.82/0.66 cm3 K mol-1, and θ1a/1b modified C-W = 0.6 ± 1K and C1a/1b modified C-W = 0.80/0.70 cm3 K mol-1. The X-band ESR spectra of 1a and 1b in solid samples showed a single and a rhombic signals, respectively, with g values around 2.1 at 77 K and 300 K, however, in CH2Cl2 solutions at 77 K the spectra were similar. The spectroscopic and magnetic results allowed us to conclude that 1a and 1b are two different crystalline phases which were proven to act as effective antioxidants showing both an IC50 = 16.5 μM, in contrast with Trolox, IC50 = 39.3 μM, normally used as a vitamin E analog and a strong antioxidant. Additionaly the DPPH free radical is scavened by reduction mechanism of CuII to CuI. The overall electronic, magnetic and structural information about 1a and 1b provide us some characteristics of this kind of transitional metal ionic coordination compounds.