Copper(II) Thiosemicarbazone Complexes and Their Proligands upon UVA Irradiation: An EPR and Spectrophotometric Steady-State Study

Abstract

X-and Q-band electron paramagnetic resonance (EPR) spectroscopy was used to characterize polycrystalline Cu(II) complexes that contained sodium 5-sulfonate salicylaldehyde thiosemicarbazones possessing a hydrogen, methyl, ethyl, or phenyl substituent at the terminal nitrogen. The ability of thiosemicarbazone proligands to generate superoxide radical anions and hydroxyl radicals upon their exposure to UVA irradiation in aerated aqueous solutions was evidenced by the EPR spin trapping technique. The UVA irradiation of proligands in neutral or alkaline solutions and dimethylsulfoxide (DMSO) caused a significant decrease in the absorption bands of aldimine and phenolic chromophores. Mixing of proligand solutions with the equimolar amount of copper(II) ions resulted in the formation of 1:1 Cu(II)-to-ligand complex, with the EPR and UV-Vis spectra fully compatible with those obtained for the dissolved Cu(II) thiosemicarbazone complexes. The formation of the complexes fully inhibited the photoinduced generation of reactive oxygen species, and only subtle changes were found in the electronic absorption spectra of the complexes in aqueous and DMSO solutions upon UVA steady-state irradiation. The dark redox activity of copper(II) complexes and proligand/Cu(II) aqueous solutions towards hydrogen peroxide which resulted in the generation of hydroxyl radicals, was confirmed by spin trapping experiments.

Antioxidant vs. Prooxidant Properties of the Flavonoid, Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity, Fenton Reaction and DNA Damage Study

“…In addition to the • DMPO-OH spin adduct, the EPR spectra obtained also revealed low intensity EPR signals which, based on a simulation analysis were attributed to superoxide radical anions, detected as the • DMPO-O 2 – spin adduct ( a N = 1.464 mT, a H β = 1.138 mT, a H γ = 0.193 mT; g = 2.0057), and methyl radicals, detected as the • DMPO-CH 3 spin adduct ( a N = 1.558 mT, a H β = 2.232 mT; g = 2.0056). The formation of several different kinds of ROS provides evidence for the complex reactions that occur when Cu(II) ions interact with hydrogen peroxide [ 35 , 36 ] and the consecutive reactions of the reactive radicals generated with the solvent molecule (rate of the reaction between dimethyl sulfoxide and hydroxyl radicals 6.6 × 10 9 dm 3 mol –1 s –1 [ 37 , 38 ].…”

Understanding the bactericidal mechanism of Cu(OH)2 nanorods in water through Mg-substitution: high production of toxic hydroxyl radicals by non-soluble particles

“…5a). Each experimental EPR spectrum can be satisfactorily fitted with two superimposed signals characterized by the spin-Hamiltonian parameters typical for two DMPO-adducts of oxygen-centered radicals, namely ˙DMPO-O 2 − /O 2 H (12-line signal; a N = 1.427 ± 0.017 mT, a β H = 1.141 ± 0.011 mT, a H γ = 0.140 ± 0.010 mT, g = 2.0058) and ˙DMPO-OH (4-line signal; a N = 1.507 ± 0.004 mT, a β H = 1.477 ± 0.007 mT, g = 2.0057) 54,55 (Fig. 5a).…”

“…5a). Each experimental EPR spectrum can be satisfactorily fitted with two superimposed signals characterized by the spin-Hamiltonian parameters typical for two DMPOadducts of oxygen-centered radicals, namely DMPO-O 54,55 (Fig. 5a).…”

“…S3 in Section S5, ESI †). Each experimental EPR spectrum can be satisfactorily fitted with three superimposed signals: (i) four-line signal of DMPO-OH spin adduct (a N = 1.507 AE 0.004 mT, a b H = 1.477 AE 0.007 mT, g = 2.0057), 54,55 (ii) six-line signal with parameters typical for DMPO-adduct with carbon-centered radical (a N = 1.602 AE 0.005 mT, a b H = 2.331 AE 0.008 mT, g = 2.0055) and (iii) six-line signal compatible with DMPO-C(O)R spin adduct (a N = 1.493 AE 0.004 mT, a b H = 1.843 AE 0.004 mT, g = 2.0059). 56 As shown in Fig.…”

Aspergillus flavus NRRL 3251 Growth, Oxidative Status, and Aflatoxins Production Ability In Vitro under Different Illumination Regimes

“…Thus, identifying compounds that can decrease contamination will increase the production of safe food, reduce human and animal exposure, and ensure public health. However, some of such compounds can be photosensitive [22] while A. flavus has been suggested to be a light-responsive fungus, response varying with fungal strain type [23,24,25]. Aflatoxins have also been reported to be light sensitive compounds [26], giving very dynamic and comprehensive response to the VIS light.…”