Singlehyphen;Crystal Spectra of Ferrimyoglobin Complexes in Polarized Light

摘要

The polarized absorption spectra of ferrimyoglobin cyanide, ammonia, azide, fluoride, formate, and water (acid ferrimyoglobin) complexes in single crystals are described. Special emphasis is placed on the polarizationhyphen;ratio (PR) spectrummdash;the spectrum of the intensity ratio for light absorbed along and perpendicular to the crystal symmetry axis. It is shown that the PR spectrum magnifies spectral effects that are otherwise obscured by wide absorption bands, and it is shown to be a most useful parameter for studying the spectra of those systems that are intrinsically broad and whose spectra do not show any sharpening at low temperature. The results confirm many general features of porphyrin spectra such as the polarization of theBandQstates, the vibronic nature of theQvstate, and the intensity imbalance in theQ0state. The substances studied span a variety of spectral types, from lowhyphen;spin, through mixedhyphen;spin, to highhyphen;spin iron complexes. The highhyphen;spin spectra show, in addition to porphyrin bands, chargehyphen;transfer bands that are associated with irondxzanddyzorbitals. The spectra manifest the splitting of these irondpgr;orbitals, and some reasons for this are discussed. The Soretlpar;Brpar;bands are also shown to be split. The PR spectrum of the lowhyphen;spin azide complex uncovered a new excited state, transitions to which were shown to be polarized out of plane. Possible mechanisms for this transition are discussed. The absolute intensity of myoglobin crystal absorption spectra are shown to be unchanged from the solution values, indicating that the heme environment is comparable in the two media. The heme orientation is shown to be identical, within the precision of the subtle variations of the PR spectrum, for all the derivatives studied, with the possible exception of the azide.