Haem electronic structure

Protein-induced perturbation on the haem electronic structure... 

Haem electronic structure in deoxy myoglobin Acid-alkaline transition in ferric myoglobin Oxy and carbonmonoxy myoglobins F relaxation mechanism... 

The electronic structures of the porphyrins were compared through the analysis of the H NMR spectra of their dimethyl ester derivatives (Fig. 4). The fluorinated porphyrins exhibited typical spectral patterns similar to those of protoporphyrin and mesoporphyrin. In general, the shifts of the signals are affected by the ring current of the porphyrin macrocycle and the electronic inductive effect of nearby substituents and the ring-current shift is also modulated by the electronic contribution of the substituents. Since four meso protons, namely, protons bound to carbons at the 5, 10, 15, and 20 positions occupy the same orientation relative to the porphyrin macrocycle, in-plane asymmetry of the haem electronic structure is reflected directly... 

The spread of the two signals in the spectra of MbCO and met-cyano Mb are compared with those of 7-PFP, 3,7-DFP, and 2-MFP in Figs. 20-22. Due to the dpara valuc, thc sprcads of the signals in the spectra of met-cyano Mbs are increased considerably, compared with those in the spectra of MbCOs. In the case of met-cyano Mb, the orientation of His F8 imidazole, relative to the haem, modulates the haem electronic structure through the interaction of the /, j-orbital of imidazole with the highest energy unpaired electron resides (Fig. 23). ... 

Rhombic perturbation of haem electronic structure induced by asymmetric interaction of haem with the protein matrix has been thought to be relevant to the... 

Fig. 23. Delocalisation of unpaired electron in haem (A) and the effect of the proximal histidine imidazole orientation on the haem electronic structure (B).

Mb(7-PF), the signals of Mb(3,7-DF) and Mb(2-MF) exhibited similarly large values of 250 ppm, demonstrating the predominant contribution of 62 state to their haem electronic structures. 

In the absence of detailed structural information on the haem active sites in these reconstituted Mbs, the observed F shifts could not be interpreted quantitatively in terms of the haem electronic structure. However, the electron density of a pyrrole carbon atom bearing a fluorine atom could be inferred from the observed F shift. ° A comparison of the F shifts indicates that the signals for Mb02(3,7-DF) are low-frequency-shifted relative to the corresponding signals for MbCO(3,7-DF), indicating that the electron density in the porphyrin 7t-system of MbCO(3,7-DF) is lower than that of Mb02(3,7-DF). Thus, the effect of Fe n back-donation ° °... 

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