Nuclear magnetic resonance studies of the binding of 15N-labelled ligands to haemins and haemoproteins. Solvent effects on the 15N paramagnetic shifts of iron–bound C15N– in low–spin haemin cyanide complexes and cyano haemoproteins

Abstract

¹⁵ N n.m.r. isotropic shifts for the iron-bound ¹⁵N labelled cyanide of the low spin ferric mono- and dicyano complexes of natural porphyrins are shown to be very sensitive to the solvent; protic solvents were most effective in causing upfield bias of the C¹⁵N shift and the sizable ¹⁵N shift induced by pH variation for cyano myoglobin was interpreted in terms of possible involvement of hydrogen bonding between distal histidine and haem-bound cyanide.