Binding of aromatic isonitriles to haemoglobin and myoglobin.

A series of aromatic isonitriles were synthesized and their binding to sheep haemoglobin and horse heart myoglobin was investigated. The disubstituted ligands 2,6-dimethylphenylisonitrile and 2,6-diethylphenylisonitrile were found to bind to horse-heart myoglobin with affinities ranging from 500 to 5000 times greater than that of ethylisonitrile (4.6 x 10(-6) M) which has been the tightest binding isonitrile ligand for myoglobin thus far reported. The tight binding was not found to vary significantly with pH or temperature. An explanation for the unexpectedly high affinity is offered in terms of the electronic structure of aromatic isonitriles.