Reactivity of substituted copper(II) salicylates with tert‐butylperoxyl radical: Structure–reactivity relationships

Abstract

Absolute rate constants (k eff ) for the chemical reactions of Cu(II) 2 (3,5-di-iso-propylsalicylate) 4 (H 2 O) 3 , Cu(II) 2 (3,5-di-tert-butylsalicylate) 4 , Cu(II) 2 (3,5-di-tert-butylsalicylate) 4 (H 2 O) 4 , Cu(II) 2 (3,5-dimethylsalicylate) 4 (H 2 O) 3 , Cu(II) 2 (3-ethylsalicylate) 4 (H 2 O), Cu(II) 2 (3-phenylsalicylate) 4 , and Cu(II)(3,5-di-iso-propylsalicylate) 2 (pyridine) 2 with tertbutylperoxyl radical were determined using kinetic electron paramagnetic resonance measurements in 10% toluene in the hexane medium at temperatures ranging from −63 • C to 2 • C. These antioxidant (AO) chelates were ranked by their reactivity as follows:Cu(II)(3,5-di-isopropylsalicylate) 2 (pyridine) 2 at 20 • C. Differential pulse voltammetry was used to determine redox behavior of these chelates in CH 2 Cl 2 . Two types of salicylic OH groups were detected in these Cu(II) salicylates, characterized by the presence or absence of AO reactivity. One of them REACTIVITY OF SUBSTITUTED COPPER(II) SALICYLATES WITH TERT-BUTYLPEROXYL RADICAL 57was coordinate covalently bonded to Cu(II) via the oxygen atoms of the salicylic OH groups, displaying oxidation peak potentials in the range from +650 to 970 mV versus Ag/Ag + . The second type was intramolecularly hydrogen bonded to carboxylate oxygens, with an oxidation peak potential in the range from +1100 to 1200 mV versus Ag/Ag + . It was concluded that nonhydrogen-bonded salicylic OH groups are responsible for the antiperoxyl radical reactivity of these chelates, while neither Cu(II) nor salicylate ligands displayed reactivity with peroxyl radical. It has been established in this research that axially bonded electron pair donors such as pyridine and water decrease H-donating reactivity of Cu(II) salicylates by promoting the formation of intramolecular hydrogen bonding between the salicylic OH hydrogen atoms and carboxylate oxygen atoms in the salicylic ligands. Dependences of log k eff at 20 • C and the anodic oxidation potential (E pa ) for the salicylic OH group on the difference between symmetric and asymmetric stretching frequencies of carboxylate groups (in Fourier transform infrared spectra) for the substituted Cu(II) salicylates were determined. C 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: [56][57][58][59][60][61][62][63][64][65][66][67] 2010

Mononuclear copper (II) salicylate complexes with 1,2-dimethylimidazole and 2-methylimidazole: Synthesis, spectroscopic and crystal structure characterization and their superoxide scavenging activities

“…An excess of 2-methylimidazole (1 g = 12 mmol) in a 10 mL of chloroform was added to 0.5 g (0.59 mmol) of copper (II) aspirinate [Cu 2 (asp) 4 ]. The mixture was stirred in an ice bath for 10 h. Anhydrous diethyl ether was added to the mixture and stirring was continued at room temperature until a green precipitate formed.…”

“…Salicylic acid (a) and its derivatives have been used for many years as anti-inflammatory, antipyretic and analgesic drugs. Binary and ternary Cu (II) complexes of salicylic acid and its derivatives with basic ligands have been found to exhibit several pharmacological effects suggesting treatment of many pathological disease states [3][4][5][6][7][8][9][10]. These disease states include many inflammations, seizures, gastric and intestinal ulcers, diabetes, neoplasias carcinogenesis, convulsion, mutagenesis, ischemia-reperfusion injury, and radiation injury.…”

Reactivity of tert‐butylperoxyl radical with some phenylthiazolidine derivatives and probucol

“…Kinetic-EPR measurements with pulse reactant injection were carried out applying the experimental setup described in a series of work. [22][23][24][25] Measurements of absolute rate constants for the reaction of t-BuOO • with test compounds were performed in the temperature range of −63 to 0 • C. The upper temperature limit was determined by the value of the rate constant for the selfreaction t-BuOO • radicals, as well as by the sensitivity of apparatus. 22 T-BuOO • radicals were formed by photolytic irradiation (300-850 nm) of a 10 −3 to 10 −1 M di-tert-butyldiazene solution in the quartz EPR cavity at an air-saturated with a 500 W high-pressure mercury lamp.…”

“…Precise kinetic studies of alkylperoxyl radical reactions with the test compounds by kinetic electron paramagnetic resonance (EPR) technique in biologically relevant lipid media were performed in a series of work. [19][20][21][22][23][24][25][26] The main objective of the present work is to study the tert-butylperoxyl radical (t-BuOO • ) radical reactivity with selected hybrid molecules phenylthiazolidine and its derivatives and hybrid AO, probucol. This task was solved by direct kinetic measurements using EPR spectroscopy for the reactions of t-BuOO • with these compounds in lipophilic organic media.…”

“…Precise kinetic studies of alkylperoxyl radical reactions with the test compounds by kinetic electron paramagnetic resonance (EPR) technique in biologically relevant lipid media were performed in a series of work 19–26 …”