Study of the direct method for calculating pKa for different multiprotic species from quantum calculations

• Grant number: 21/03201-3
• Support type: Scholarships in Brazil - Doctorate
• Effective date (Start): August 01, 2021
• Effective date (End): May 31, 2025
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Physical-Chemistry
• Principal researcher: Rogério Custodio
• Grantee: Felipe Ribeiro Dutra
• Home Institution: Instituto de Química (IQ). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil

Abstract

A preliminary alternative for the calculation of pKa of monoprotic acids based on the direct aqueous reaction was developed by the authors, showing an excellent agreement between values calculated with electronic structure methods and experimental data. The methodology is simple and is based on a selective adjustment of Gibbs energy for the solvated proton (Gaq(H+)). The present study intends to evaluate the applicability and generalized nature for different direct schemes and other classes of molecules, in addition to monocarboxylic acids, such as: polyprotic acids, amines, amides, alcohols, thiols, among others. It is intended to analyze the electronic and structural effects at different levels of theory involving conventional quantum methods: Hartree-Fock, semi-empirical (e.g. AM1, PM6), density functional theory, composite methods (e.g. CBS-QB3, G3 (MP2)//B3-CEP), correlated conventional (e.g. CI, CCSD) and unconventional (e.g. Quantum Monte Carlo) methods. Solvent effect will be assessed using implicit (e.g. SMD, COSMO), explicit (e.g. Classic Monte Carlo) solvation models and a combination of implicit models and explicit molecules. Statistical analyzes will be conducted in order to establish the best relationships between the characteristics of the chosen molecules and the training set to estimate the most appropriate Gaq(H+) value for different classes of molecules, as well as the adjustment of other conditions to reduce to the maximum the pKas error calculated in relation to experimental ones. (AU)