What is the crucial factor for vibrational circular dichroism in hemoprotein ligands?

Anisotropy values of a certain range is shown to result in intense vibrational circular dichroism (VCD) bands for the azide antisymmetric stretching vibration in the azide complex of a C2-chiral strapped iron porphyrin, the first time that an extremely strong VCD band has been measured for the ligand vibration of iron porphyrin without an apo-protein. The generation of the intense VCD bands in hemoproteins can be attributed to a chiral environment produced by the peripheral substituents on the porphyrin ring.