In view of the widespread use in biochemistry of labelling with hydrogen isotopes, recent IUPAC recommendations [2] for unambiguous naming of these isotopes may interest biochernists. There is often little harm in current practice of using the name 'proton' both for 1H+ and for H+ in its natural abundance of isotopes, but there are contexts in discussing isotope effects where distinction is necessary. The names listed in Table 1 allow the ambiguities to be avoided. Thus the general terms allow description of experiments on reaction mechanism, e.g. where hydronation is specifically with 2H+ or with 3H+, where the term 'protonation' would be misleading. The use of the recommendations may be illustrated by the following example: 'The observation of a protium/deuterium kinetic isotope effect may be interpreted in terms of the extent of hydron transfer in the transition state'.
Table 1. Names for hydrogen species
| General | 1H | 2H | 3H | |
| Atom (H) | hydrogen | protium | deuterium | tritium |
| Cation (H+) | hydron | proton | deuteron | triton |
| Anion (H-) | hydride | protide | deuteride | tritide |
| Group (-H) | hydro | protio | deuterio | tritio |
| Transfer of cation to substrate | hydronation | protonation | deuteronation | tritonation |
| Replacement of hydrogen by a specific isotope | protiation | deuteriation (or deuteration) | tritiation |
2. IUPAC Corninission on Physical Organic Chemistry (CPOC) Narnes for hydrogen atoms, ions, and groups, and for reactions involving them, Pure Appl. Chem. 1988, 60, 1115-1116.