pK_a Calculation

• 1. Input compounds
• 2. Parameters
• 3. Review & submit
• 4. Results & download

• Calculate from outputs

• 1. Upload the output files

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Proton dissociation constant (pK_a) calculation

Proton dissociation constant (pK_a) is an equilibrium constant for the dissociation of an acid in solution. It is a quantitative measure of the strength of an acid in solution. pK_a provides the information required to calculate the concentration(s) of the proton, acid, and the conjugate base in solution. It can be measured by titrations combined with different measurements, such as absorbance spectra, fluorescence spectra, and NMR spectra. However, due to the practical reasons, experimental measurements of pK_a are not always possible. Therefore, theoretical calculations with quantum mechanics (QM) methods provide a feasible option to evaluate it. This module aims to design an user-friendly interface for researchers to perform the calculation with QM methods.

Theoretical model

QM calculation of pK_a based on the following equation,

HA ----> A^- + H⁺    K_a = [A^-][H⁺]/[HA]    

pK_a = -log K_a

. Therefore, it requires the user to provide both the deprotonated (A^-) and the protonated (HA) forms of the compound.

Flowchart of the pK_a calculation module

Start from "Step 1. Input compounds"