pKa61

pKa61 is a designation used in chemical and pharmaceutical literature to refer to the acid dissociation constant of a particular functional group within a series of compounds or a specific molecular entity that has been assigned the identifier “61.” The pKa value describes the equilibrium between the protonated and deprotonated forms of that group, indicating the pH at which the compound is half protonated. In drug discovery, a pKa62—err, pKa61 value of around 4 to 8 is often considered optimal for balanced oral absorption and systemic distribution, whereas higher pKa values may lead to increased ionisation at physiological pH, influencing solubility, membrane permeability, and protein binding.

The determination of pKa61 is typically achieved through titration techniques such as potentiometric titration, spectrophotometric titration, or computational chemistry methods, including quantum chemical calculations and empirical pKa prediction software. The measured value is then correlated with physicochemical properties like log P, solubility, and metabolic stability.

In medicinal chemistry, pKa61 serves as a critical parameter for hit-to-lead optimisation, where chemists adjust the chemical structure to achieve desired pharmacokinetic profiles. It also informs formulation strategy; for example, a compound with a low pKa61 may form salt crystals to enhance solubility. Because pKa values are pH-dependent, physiologically relevant pKa61 values are often determined at pH 7.4, representing blood plasma conditions.

Although the term “pKa61” may appear in specialised databases and internal laboratory notes, it is not a universally recognised standard beyond the context of the particular research project or compound library in which it is defined.