Electrocatalytic activity of [Ru(bpy)3]2+ for hypoxanthine oxidation studied by rotating electrode methods
Introduction
Purines are the most integral part of living system and play various important roles in life process such as cellar metabolism and heredity, etc. [1], [2]. Several drugs based on purines have also been developed in treating cancer, virus infection and vascular diseases [3]. Apparently, gross uric acid in the blood is overproduced by the rapid catabolism of the bases due to the difficult recycle of hypoxanthine (Hx), it is deposited around joints and further leads to acute gout [4]. On the other hand, Hx may be formed in the degradation processes of foodstuffs and accumulated mostly in the animal muscle [5], [6], [7]. Thus, the Hx levels may be used as indicators of foodstuff freshness in the food industry as well as acute gout symptom [8], [9].
Various methodologies including high performance liquid chromatography (HPLC) and capillary electrophoresis have been incorporated to detect Hx in the blood [10], [11], [12]. Recently, in order to improve its detection, some coupled methods have been used to monitor the Hx concentration such as HPLC with photodiode array detection [13], or diode array detector-mass spectrometry [14]. However, some of them have been involved more complicated extraction or derivative procedures. Similarly, the redox reaction of Hx and its derivates on the modified electrodes [15], [16], [17] have extensively been reported as well as Hg [18], Ag [19], Pt [20], and C [21], [22], [23] electrodes. The amperometric biosensors have been developed for the special applications based on the catalytic reaction of enzymes such as xanthine oxidase [24], [25], [26], [27], [28], [29].
It is known that some Ru(II) and Ru(III) complexes exhibit the rich mixed-valence chemistry [30], catalytic properties [31], and excellent photodynamic activity to therapy [32]. Therefore, combined the performances of the ruthenium complexes with purine derivatives, several ruthenium complexes with Hx show the excellent anticancer activity reported in the literature [33], [34]. The ruthenium (III) or/and oxoruthenium (IV) complexes and their para-substituted derivatives also indicate the electrocatalytic activity for the oxidation of purine derivates and DNA [35]. However, rotating ring-disk electrode methods used as electrochemical studies of Hx have so far received little attention, especially, depending on the indirect electrocatalytic oxidation of polypyridyl ruthenium (II) compounds.
In this work, we further extend the electrochemical techniques by incorporating rotating ring-disk electrode measurement to the electrochemical studies for Hx oxidation catalyzed by [Ru(bpy)3]3+/2+ reaction. The results are significant for better understanding the electrocatalytic mechanism of redox mediator to biomolecules.
Section snippets
Chemicals and materials
[Ru(bpy)3]Cl2·6H2O and Tris (where Tris is tris(hydroxy methyl)amino-methane) was purchased from Aldrich and Shanghai Boao Chemical Company, respectively. Hypoxanthine (Hx) was obtained from Shanghai Guoyao Chemistry Co. Ltd. All other reagents and solvents were analytical grade reagents and used as received unless otherwise noted. The electrolyte solution prepared with double distilled water was 10 mmol/L Tris–HCl/50 mmol/L NaCl at pH of 7.2.
Apparatus
All experiments were performed with an Autolab
Voltammetric behavior of Ru(bpy)33+/2+ on the rotating Pt–Pt electrode
As shown in Fig. 1, the voltammetric curves of 2.0 mmol/L [Ru(bpy)3]2+ exhibit obvious limiting current plateaus on the rotating Pt disk electrode. The limiting current values increase with the rise of rotating angular velocity (ω) and are linear with the square root of ω (See the inset of Fig. 1). The results conform to the Levich equation and the diffusion coefficient is 5.6 × 10− 6 cm2/s, suggesting that [Ru(bpy)3]3+/2+ reaction on the rotating Pt electrode undergoes a diffusion-controlled
Acknowledgement
We are grateful to the Natural Science Foundation of Guangzhou and Guangdong Province for their financial support.
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