NADH Electrooxidation Using Bis(1,10-phenanthroline-5,6-dione) (2,2'-bipyridine)ruthenium(II)-Exchanged Zirconium Phosphate Modified Carbon Paste Electrodes

Abstract

We present a carbon paste electrode (CPE) modified using the electron mediator bis(1,10-phenanthroline-5,6-dione) (2,2'-bipyridine)ruthenium(II) ([Ru(phend)(2)bpy](2+)) exchanged into the inorganic layered material zirconium phosphate (ZrP). X-Ray powder diffraction showed that the interlayer distance of ZrP increases upon [Ru(phend)(2)bpy](2+) intercalation from 10.3 Å to 14.2 Å. The UV-vis and IR spectroscopies results showed the characteristic peaks expected for [Ru(phend)(2)bpy](2+). The UV-vis spectrophotometric results indicate that the [Ru(phend)(2)bpy](2+) concentration inside the ZrP layers increased as a function of the loading level. The exchanged [Ru(phend)(2)bpy](2+) exhibited luminescence even at low concentration. Modified CPEs were constructed and analyzed using cyclic voltammetry. The intercalated mediator remained electroactive within the layers (E°' = -38.5 mV vs. Ag/AgCl, 3.5 M NaCl) and electrocatalysis of NADH oxidation was observed. The kinetics of the modified CPE shows a Michaelis -Menten behavior. This CPE was used for the oxidation of NADH in the presence of Bakers' yeast alcohol dehydrogenase. A calibration plot for ethanol is presented.

Fig. 1

XRPD patterns of the 10.3 Å phase of ZrP and of [Ru(phend)₂bpy]²⁺-exchanged ZrP materials at various loading levels. The interlayer distance is indicated next to the first order diffraction peak.

Fig. 2

Formal potential of Ru-ZrP as a function of pH. The measurements were made in PBS, μ = 0.1 at 100 mV/s.

Fig. 3

Randles – Sêvcik plot for the modified CPE at different scan rates.

Fig. 4

a) Cyclic voltammogram at 5 mV/s of Ru-ZrP modified CPE (1:2.3 Ru-ZrP loading level) in PBS (μ = 0.1, pH 8.0). b) Cyclic voltammogram at 5 mV/s showing electrocatalysis of 0.69 mM NADH using the Ru-ZrP modified CPE (1:1 Ru-ZrP loading level) in PBS (μ = 0.1, pH 8.0).

Fig. 5

Variation of 1/i_cat as a function of 1/[NADH] at pH 8.0 (PBS μ = 0.1, rpm = 200, scan rate = 5.0 mV/s).

Fig. 6

Calibration plot for ethanol sensing using [Ru(phend)₂bpy]²⁺-exchanged ZrP modified CPE in the presence of 7.5 U/mL y-ADH and 10 mM of NAD⁺ in PBS (μ = 0.1), at pH 8.0, 1 mV/s.

Scheme 1

EC scheme for the reaction between NADH and [Ru(phend)₂bpy]²⁺-exchanged ZrP.

Scheme 2

Proposed Michaelis – Menten-like mechanism for the electrochemical reaction that occurs in the electrode surface.

Scheme 3

A monoenzymatic reaction cycle for ethanol sensing.