Magnetic circular dichroism of protoporphyrin derivatives in the ultraviolet region.

The MCD spectra of ferri- and ferro-heme in high and low spin states and zinc porphyrin for reference have been measured in the ultraviolet region. Zinc porphyrin offered an A term at 325 nm attributable to the N transition. A ferrous low-spin complex with CO or CN exhibited MCD spectra composed of B terms around 325 nm. This striking difference from that of zinc porphyrin in the ultraviolet region is noted from the fact that their Soret and visible MCD's gave A terms similar to those of zinc porphyrin. A ferric complex with high spin had MCD spectrum different from that of low spin, the former showing a negative C term at 287 nm and a B term at 339 nm, but the latter positive C terms at 275 nm and 320 nm. Some of these Faraday parameters were ascribed to charge-transfer transitions.