Design and Prediction of Corrosion Inhibitors from Quantum Chemistry: I. Can Effective Partition Coefficients for Organic Corrosion Inhibitors be Determined from First-Principles?

Abstract

Quantum chemistry is a powerful tool for computing the properties of molecules and their interactions with one another in a variety of environments. In this first paper of a two-part series, the technique is applied to investigate the capabilities for different quantum chemical techniques to compute the partition coefficients for chemical inhibitors relevant to corrosion management from first-principles. Density functional theory calculations using the exchange-correlation functionals B3LYP and M05-2X, with either 6-31+g(d,p) or the pc-3 basis set, as well as the semi-empirical AM1 method and two separate solvation methods (PCM and SMD) were used to calculate the effective partition coefficients for benzimidazole and 1,2-dimethylimidazole for the n-octanol/water system. The equation for the effective partition coefficient (log P) was developed taking into account the possible protonation of the solute molecules, according to the computed acid dissociation constant (pKa) obtained using the isodesmic method with ethylamine as a reference. The variation in log P computed using the different theoretical methods was presented along with a discussion of how to apply theoretical calculations of observable quantities, such as the partition coefficient, in an engineering context.