Electrochemical oxidation of histidine at an anodic oxidized boron-doped diamond electrode in neutral solution
Introduction
Histidine (His) is one of the necessary amino acids existing widely in muscular and nervous tissue. His constitutes the active center of many enzymes and brain nervous peptide and controls the transmission of metal elements in biological bases [1], [2]. Based on electron transfer communication, poly-His with different metals as the active center for electrode modification to mimic biological reactions has been utilized for oxygen reduction [3], [4], [5]. The main intermediates and products [6], [7], [8], such as histamine, imidazole acetic acid and methyl imidazole acetic acid, play important roles in the metabolism of His. For example, histamine, one of the products, is a major factor that causes allergenic reactions. The electrochemical behavior of His becomes necessary for advanced investigation. However, little attention has been paid to the electrochemical reaction of His because it is electrochemically inactive in water. The adsorption and electrochemical reaction mechanism of His has been reported [9], [10], requiring efficient and environmental friendly anode materials.
Recently, boron-doped diamond (BDD) thin films have been used as a promising electrode material to detect electro-active species oxidation at high positive potentials, because of its specific physical and chemical properties such as hardness, chemical inertness, thermal conductivity and electrical conductivity [11], [12]. BDD electrodes show a wide potential window in aqueous electrolytes (about −1.35 to 2.3 V/NHE) with low and stable voltametric background current density, permitting the detection of species that have been masked by the electrochemical decomposition of the solvent used or by surface reactions on classic carbon electrodes. Relative to other materials, the superiority of BDD has attracted considerable interest in various fields, including electroanalytical applications on different biomolecules [13], [14], [15], [16], [17], [18], [19], [20], [21]. Although the electrochemical reactions of some amino acids, including glycine, cysteine, tryptophan, and tyrosine, at the BDD electrode have been reported [14], [22], there are relative few reports on His.
The purpose of this work is to study the electrochemical behavior of His at an anodic oxidized BDD electrode. The adsorbed film characteristics of His-oxidized product was identified by studying the electrochemical behavior of the redox probe (Fe(CN)64−) using cyclic voltammetry and electrochemical impedance spectroscopy. The scanning electron microscopy, Raman and X-ray photoelectron spectroscopy measurements were used to examine the His-oxidized product. Fast and simple removal of the adsorbed film using anodic polarization is also confirmed.
Section snippets
Experimental
l-Histidine (His) was purchased from Sigma and used without further purification. The electrolyte is 0.5 M K2SO4 (Merck) solution (pH 6.8). All solutions were prepared with pure water purified through a Millipore ultra-purification system. All other chemicals were reagent grade and used without further purification. All experiments were performed at 25 oC. This temperature was controlled (accuracy of 0.05 oC) using a water thermostat (HAAKE D8 and G).
The as-deposited BDD electrodes, grown using
Electrochemical reaction of histidine (His) at anodic oxidized boron-doped diamond electrode (AOBDDE)
Fig. 1 shows the cyclic voltammograms of the AOBDDE in 0.5 M K2SO4 solution with and without 2 mM His. An examination of Fig. 1(a) indicates that a significant peak can be observed in the first scan cycle at about 1.5 V after the addition of 2 mM His, which is attributed to the oxidation of His at the AOBDDE. Two amino acids with different residual groups, glycine and glutamic acid, were chosen to compare the electrochemical properties with His. Interestingly, no discernible oxidation peak was
Conclusion
In this study, a well-defined His oxidation signal can be found at about 1.5 V vs. Ag/AgCl in 0.5 M K2SO4 at AOBDDE. Experiments confirmed the adsorption of a non-conductive film from His-oxidized product at the AOBDD electrode surface. This film reduces the electrode electrochemical activity. SEM images show the adsorbed materials clearly at the low-lying regions of the polycrystallite AOBDD surface, which are considered the most possible active sites of His oxidation. Raman spectrograms show
Acknowledgements
The authors thank the Center for Micro/Nano Technology Research and the Center for Bioscience and Biotechnology, National Cheng Kung University, Tainan, Taiwan, for equipment access and technical support.
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2014, Biosensors and BioelectronicsCitation Excerpt :Amino acids oxidation is an irreversible electrochemical process. Schemes of electrochemical oxidation reactions for tyrosine (Brabec and Mornstein, 1980a; Brabec and Mornstein, 1980b; Reynaud et al., 1980) tryptophan (Malfoy and Reynaud, 1980; Nguen et al., 1986), cysteine (Reynaud et al., 1980a; Devis and Bianco, 1966), histidine (Chen et al., 2008), cystine (Reynaud et al., 1980a; Reynaud et al., 1980b) and methionine (Brabec and Mornstein, 1980a; Reynaud et al., 1980b; Gómez-Mingot et al., 2011; Enache and Oliveira-Brett, 2011) are presented in Fig. 2. Chemically modified electrodes are extensively researched in recent years for electrocatalytic oxidation of amino acids (Yu et al., 2008; Huang et al., 2008; Swetha and Kumar, 2013; Sharifi et al., 2012; Hasanzadeh et al., 2009, Saghatforousha et al., 2011; Hosseini et al., 2014; Sandoval et al., 2013; Beitollahi et al., 2013).
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