Elsevier

Electrochimica Acta

Volume 53, Issue 6, 15 February 2008, Pages 2883-2889
Electrochimica Acta

Electrochemical oxidation of histidine at an anodic oxidized boron-doped diamond electrode in neutral solution

https://doi.org/10.1016/j.electacta.2007.10.071Get rights and content

Abstract

Electrochemical oxidation of histidine (His) at an anodic oxidized boron-doped diamond electrode (AOBDDE) was performed. A significant peak of His oxidation is observed at about +1.5 V vs. Ag/AgCl, however, the response current was inhibited due to strong His-oxidized product adsorption onto the electrode surface. The characteristics of the His-oxidized product adsorbed onto the electrode surface were investigated by studying the electrochemical behavior of the Fe(CN)64− redox reaction using cycle voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Both CV and EIS results showed a decrease in the sum of transfer coefficients and an increase in the electron transfer resistance, which indicate that the adsorption film is a non-conductive film. The most possible active site locations for the AOBDDE for His oxidation are within these low-lying polycrystallite AOBDDE surface regions. The results from Raman and X-ray photoelectron spectroscopy offer strong evidence of the imidazole ring reaction from His. Experiments confirmed that the adsorbed film can be removed and the electrode surface reactivated using brief polarization at +2.5 V.

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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