logPnin

logPnin is a descriptor used in cheminformatics to denote the lipophilicity of a compound in its neutral form. The term combines logP, the octanol–water partition coefficient, with "nin" to indicate neutral, non-ionized status. logPnin therefore represents the predicted or calculated logP value assuming the molecule exists without ionizable groups turned on or off by pH, and is distinct from pH-dependent measures such as logD.

Calculation methods: It is typically derived by fragment-based approaches that assign hydrophobic fragments to molecular components and sum their contributions, or by machine learning models trained on neutral species. Different software packages may implement slightly different fragment sets or training data, so reported logPnin values can vary between tools.

Applications and interpretation: logPnin helps researchers compare intrinsic lipophilicity of different scaffolds independent of ionization state, supporting early-stage screening, lead optimization, and QSAR modeling. It complements pKa and logD values, which capture ionization effects at a given pH and solvent system.

Limitations and caveats: As with logP, logPnin is a model-dependent quantity and may not correspond to a measurable experimental parameter. It does not account for ionization, tautomerism, or specific interactions with solvents. When evaluating pharmacokinetic properties, logD or experimental logP data should be consulted alongside logPnin. See also logP, logD, and lipophilicity.