Modelling the Bi-based clusters effect on the electron transfer to Paracetamol: from physics to computation

Theoretical model and computational analysis are exploited to estimate the electron transfer (ET) due to Paracetamol oxidation. Functionalized electrode surface through HO-BiONO3 based nanocomposite have shown to improve the electrochemical sensor performance from previous experiments. The main aim is to build up an hypothetical transistion state (HTS) model to look at the Bismuth cluster effects on electron transfer rate constant. First, the HTS model based on two Bi atoms cluster is studied as a minimum unit to have a two-electron oxidation process as the Paracetamol one. Then, three Bi atoms cluser based model is drawn to examine a situation in which a free site is close to two reacting sites. For both the two cases, simulations are performed on several clusters that differ in the functional groups bondend with Bi atoms. The presence of probable contaminants after a pretreatment in H2SO4 are studied in this way. HTS molecular structures from simulations shows how orientation in space and relative position of Paracetamol and Bismuth functional groups lead to steric hindrance due to electron clouds repulsion. This and the atoms electrostatic interactions define the HTS conformation and provide the interacting distance and the electronic properties affecting the ET rate constant. It is observed how some functional groups could be preferable resulting in less distorted structure: huge atoms hindrance can hardly influence length bonds and angles due to large functional groups approach. Molecular mechanics method based on MM+ forces field and quantum mechanics semiempirical method are used to perform the computational simulations. MM+ treats the system as made by springs and exploits Hook's law based equations. Indeed, it is useful to perform a first geometry optimization of the molecular structure but it is not suitable to provide electronic properties informations. The many body system is further optimized with a quantum mechanics simulation. In that case, Schrodinger equation is solved according to the semiempirical method and the basis set choosen: PM3 in that case. The method is Hartree Fock (HF) based and the basis set parameters defining the electron wavefunctions: s and p orbitals formed this basis set. Moreover, PM3 also introduces some approximations to reduce the number of integral to be solved according to the neglect differential of diatomic overlap (NDDO) assumptions: too iterations will results in a time consuming process not suitable for large system. Finally, the ET rate constant values is determined by using the computational data within a physical theoretical model. It comes from Marcus model and differ from it in some assumptions regarding the solvation effect of the electrolyte solution. To have a complete description of the ET between the electrode and the organic compound, differential equations (PDE) problem based on Fick’s laws are used as well to analyse spontaneous diffusion and define the reacting specie concentrations at the surface.