Simultaneous In Situ Infrared Reflection Absorption Spectroscopy and Kelvin Probe Measurements during Atmospheric Corrosion

Abstract

The electrochemical behavior of benznidazole has been investigated in dimethylsulfoxide by cyclic voltammetry and controlled-potential electrolysis. The reduction occurs in two one-electron steps, where the first electron transfer corresponds to the reversible formation of the radical anion followed by a slow chemical reaction. The second electron transfer is attributed to the reduction of the radical anion to a dianion by an electrodic process involving a very fast cleavage of the dianion with the formation of a lactam derivative as the principal product of reduction in aprotic medium. Nitroimidazoles are compounds with a wide range of biological effects, some of which have particular therapeutic value in human and animal treatment. These compounds have exhibited chemothera-peutic effects against protozoal and bacterial infection and tumorous regions. 1 Benznidazole, N-benzil-2-nitroimidazolyl acetamide 1 is one of the most effective drugs for the treatment of Trypanosoma cruzi infection in the chronic phase as well as in the acute phase. 2 Cha-gas's disease is common in countries of Latin America, where it is a social and economic question. 3 However, little is known about benznidazole metabolism in the human body. Most of the studies on the pharmacological action of nitroimidazole suggest that the mechanism of cytotoxicity in protozoa is related to the enzymatic reduction of the nitro group and the affinity of the anion radicals to biomolecules. 4 The nitroimidazoles have been studied by electrochemical methods with success in diverse purposes such as the analytical determination in pharmaceutical formulations 5,6 and the determination on the degree of interaction of these drugs with biomolecules, because it is known that many drugs exert part of their activity via an electron-transfer process. The intention of this work is to investigate the electrochemical behavior of benznidazole in an aprotic medium using cyclic voltam-metry and controlled-potential electrolysis in order to gain insight regarding the kinetic and the electrodic mechanism for benznidazole reduction in dimethylsulfoxide. Materials and Methods Benznidazole was kindly provided by Hoffmann-La Roche & Co. The supporting electrolyte was tetrabutylammonium tetrafluor-borate (Bu 4 NBF 4 , Aldrich. The solvent was dimethylsulfoxide DMSO, Merck. Electrochemical measurements were carried out using a poten-tiostat EG&G PAR model 273, a function generator EG&G PAR model 175, and an X-Y recorder EG&G PAR model RE0089. The cell used for cyclic voltammetric experiments was of the three-electrode type, with two compartments. The working electrode was of vitreous carbon Tokai Carbon Co, type GC30 with a disk area of 0.07 cm 2 , sealed in glass. The counter electrode was a Pt ring placed below the working electrode, and the reference was a saturated calomel electrode SCE. The test solution was continuously blanketed with nitrogen for approximately 15 min before each measurement , and the working electrode surface was renewed by polishing with 0.05 m alumina f...

In situ studies of the corrosion during drying of confined zinc surfaces

“…The spectra of the reference compounds are usually obtained from the pure compounds measured with transmission measurements using the KBr pellet method. These spectra are different from the spectra of the samples obtained by the methods mentioned above, especially for stronger IR bands such as oxides [12,14]. The simulated spectra can be used as basis for the interpretation of the experimental spectra.…”

“…14 shows reference spectra of ZnO, Zn 5 (OH) 6 (CO 3 ) 2 , Zn 5 (OH) 8 Cl 2 Á H 2 O and Na 2 CO 3 Á 10H 2 O. The reference spectra of the zinc compounds were obtained by simulating reflection absorption spectra from transmission spectra of these compounds [14]. The characteristic peak of ZnO is found Fig.…”

Vibrational Spectroscopy in Studies of Atmospheric Corrosion

“…In order to obtain information about both the nature of the corrosion products formed and the changes in Volta potential, IRRAS was combined with Kelvin probe measurements by Person et al, [ 59 ]. Zinc was exposed to humid air and by IRRAS ZnO, Zn 5 (OH) 8 Cl 2 ·H 2 O and zinc hydroxy carbonate were observed as the corrosion products.…”

Monitoring Corrosion Using Vibrational Spectroscopic Techniques

“…[113][114][115][116][117] Zinc acetate was detected as the major corrosion products in humid environments with sub-ppm concentration of acetic acid and acetaldehyde, 113,114 while zinc formate formed on zinc exposed to environments containing formic acid. NaCl particleinduced atmospheric corrosion has been studied using in situ IRAS for Zn, 118,119 Al, 120 Fe, 121 Cu, 122,123 and Mg. 124 For Zn with predeposited NaCl particles and then exposed to high humidity (>90%), a surface film containing ZnO, Zn 5 (OH) 8 Cl 2 ·H 2 O, and zinc Zn 5 (OH) 6 (CO 3 ) 2 was detected by in situ IRAS. NaCl particleinduced atmospheric corrosion has been studied using in situ IRAS for Zn, 118,119 Al, 120 Fe, 121 Cu, 122,123 and Mg. 124 For Zn with predeposited NaCl particles and then exposed to high humidity (>90%), a surface film containing ZnO, Zn 5 (OH) 8 Cl 2 ·H 2 O, and zinc Zn 5 (OH) 6 (CO 3 ) 2 was detected by in situ IRAS.…”

“…115 Atmospheric corrosion of metals is greatly enhanced by NaCl deposition, which can originate from either airborne sea salt particles or deicing salts. 118 The rate of the corrosion process could also be evaluated from the rate of surface film formation obtained from the IRAS measurements. 118 The rate of the corrosion process could also be evaluated from the rate of surface film formation obtained from the IRAS measurements.…”