Isotope labelling

Introducing selected isotopes into molecules to support detection or assignment. In nuclear magnetic resonance, labelling can add observable spins or suppress unwanted relaxation pathways.

Isotopic labelling of selected methyl groups to provide sensitive NMR probes in a relatively sparse spin network.

Methyl groups provide several equivalent hydrogen nuclei and can remain useful reporters in large molecular assemblies. Selecting a subset reduces spectral crowding, while isotope substitution elsewhere can reduce unwanted interactions. The observed signal identifies labelled sites rather than every part of the protein equally. ^[ref]

Replacement of hydrogen with deuterium. In protein NMR, suitable deuteration reduces proton dipolar relaxation but also removes directly observable proton signals unless selected sites are retained or reintroduced.