The paper reports synthesis and physical characterisation of a new iron(III) porphyrin which shows unusual features of quantum mechanically mixed ground state in its magnetic properties. Magnetic susceptibility (300−3·6 K) and Mössbauer spectroscopy (300−77 K) studies of the compound are described and discussed with reference to some bacterial ferricytochromeC' exhibiting similar spin-mixed ground state.

Carbon-13 NMR studies on a series of high spin iron(III) porphyrins, namely tetraphenylporphyrin iron(III) halides [Fe(TPP) X, X=Cl, Br, I] in CDCl₃ solution are reported. As expected the¹³C shifts are found to be an order of magnitude larger than the corresponding proton shifts. The dipolar contribution, which is quite important for the proton NMR, becomes much less significant for the¹³C shifts. No systematic variation in the¹³C shift across the series is observed, except for the meso-carbon which shows a small but gradual decrease in going from the chloro to the iodo complex. The¹³C shift for the various carbon atoms of the porphyrin ligand shows interesting pattern which is discussed in terms of spin delocalisation mechanisms.

Acid⇌alkaline transition in horseradish peroxidase and lactoperoxidase has been investigated by use of circular dichroism and nuclear magnetic resonance spectroscopy. The conformational changes associated with this transition in these hemeproteins have been monitored and pK of the transition determined.