Principles of MCD Spectroscopy Applied to Hemes

The MCD spectrum is a measure of the difference between the absorption of right- and left-circularly polarized light as a function of the 

The absorption spectrum of a diamagnetic metalloporphyrin consists of two electronic transitions, the Q-band (or a-band) in the region 550-600 nm, of lower intensity, corresponding to the mixture of one-electron transitions that involve partial cancallation of the dipole moments, and the other, the B-band (or Soret band), between —380 and 450 nm, of high intensity, which comprises the one-electron transition 

The realization that measurements of the intensity of an MCD spectrum into the region where it is nonlinear in field and temperature could be analyzed to yield ground-state g values enabled the magnetic properties of individual paramagnetic centers in a multicentered me-talloprotein to be probed for the first time (iO). The detailed analysis of the temperature dependence of the MCD spectrum at magnetic field strengths that are within the linear limit enable the zero-field splitting 

Optical and MOD Spectra of Ferrous and Ferric Hemes A. Introduction 

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