protonate

Protonate means to add a proton (H+) to a molecule or ion, forming its conjugate acid. It is a fundamental process in acid–base chemistry, typically driven by the relative acidity of the species involved and the availability of a proton donor.

Common protonation targets include amines, which become ammonium salts (R3N + H+ → R3NH+); carbonyl compounds, where the oxygen can be protonated to give a reactive oxonium-like species (R2C=O + H+ → R2C(OH)+); and alkenes, which can protonate to form carbocation intermediates in electrophilic addition reactions. Protonation can occur in solution, in the gas phase, or on solid supports, and the site and outcome depend on the molecule’s structure and the solvent or medium.

In biology and biochemistry, protonation states of amino acid residues and other functional groups depend on pH and influence protein folding, enzyme catalysis, and ligand binding. Protonation is a dynamic feature of biomolecules, often shifting as environments or conditions change.

In analytical chemistry and mass spectrometry, protonation is exploited to generate positively charged species, such as [M+H]+ ions in positive-mode electrospray ionization, enabling detection and characterization of many compounds.

Protonation is distinct from deprotonation (loss of a proton) and from hydrogenation (addition of hydrogen atoms to a bond). The extent of protonation is governed by pH, pKa values of the conjugate acids, and the strength of the proton source.