DFT study and determination of metronidazole based on ionic liquid mediated carbon nanotube modified carbon paste electrode

In this work, we prepared a new high sensitive sensor for metronidazole (MNZ) by Single-walled carbon nanotube (SWCNT) and ionic liquid (IL). The use of SWCNT-IL nano composite in the paste increased the response of the electrode, significantly. The performance of the proposed carbon paste electrode was investigated by differential pulse voltammetry (DPV). The sensor prepared based on methods that have been previously reported [1-3]. Various factors such as electrode composition, types of supporting electrolyte, pH, stirring rate, scan rate were studied and optimized. The best performance of the electrode was obtained with composition of 76 % graphite powder, 20% ionic liquid and 4% SWCNT. In the optimum experimental conditions (pH=7 Britton-Robinson (B-R) buffer, stirring rate = 400 rpm, scan rate= 50 mV/s) , the current response of the electrochemical sensor studied for metronidazole solution and linearity was obtained in the range from 5.00 × 10-5 to 5.00 × 10-3mgL-1, with the detection limit of 1.238 × 10- 5 mgL-1. The interference study was performed for some drugs and cations that do not show any significant interference. This method was successfully applied to the analysis of MNZ in the milk and egg samples with acceptable recoveries of 90.33–108.0% with RSD ≈ 4.41 %. Also, the non-covalent interactions of the metronidazole with the SWCNT in four different manners were investigated by using the density functional theory (DFT) Methods[4] with the M062X and B3LYP functional. Geometries of the investigated species were fully optimized at 6- 31+G (d, p) basis sets and Polarizable-Continuum Model (PCM)[5] for investigation of solutesolvent interactions in aqueous solution. The order of the DFT-calculated binding energy of the optimized geometries is SD2 SD1 SD3 SD4. The most stable form (SD2) of them involves the interaction of the Metronidazole with the SWCNT via the nitrogen atom of the nitro group.(Fig. 1) that confirms catalytic reduction nitro group in experimental study[6, 7].