The Crystal Structure and Molecular Stereochemistry of Methoxyiron (III) Mesoporphyrin-IX Dimethyl Ester¹

The crystal and molecular structure of vanadyldeoxophylloerythroetioporphyrin-1,2-dichloroethane solvate: an analogue of chlorophyll

“…Table 4 is a list of the C-H bond distances, but they should not be considered as accurate in relation to the heavy atom portion of the structure. Although the accuracy of the structure is low, the results indicate that there is a distortion in the fourfold symmetry normally found in porphyrin and porphine structures (Hoard, Hamor, Hamor & Caughey, 1965;Koenig, 1965;Fleischer, 1963;Webb & Fleischer, 1965). The distortion is presumably due to the introduction of the isocyclic ring E, which distinguishes this structure from the other porphyrin and porphine structures studied to date.…”

The crystal structure of octaethylporphinato(methyl)rhodium(III). An unusually short Rh–CH3 distance

“…It should be noted that the deviation of Rh is only 0.051 A from the mean plane toward the apex. In the usual square pyramid of Co-, Zn-, and Fe-porphyrins (Scheidt, 1974;Little & Ibers, 1974b;Dwyer, Madura & Scheidt, 1974;Collins & Hoard, 1970;Spaulding, Eller, Bertrand & Felton, 1974;Koenig, 1965;Hoard, Hamor, Hamor & Caughey, 1965;Hoffman, Collins, Day, Fleischer, Srivastava & Hoard, 1972;Hoard & Scheidt, 1973), the metal deviation increases with the bond radius of the metal. If this relation were applicable to the present complex, the Rh atom would have a deviation of 0-23-0.37 .~.…”

Stereochemical Trigger for Initiating Cooperative Interaction of the Subunits During the Oxygenation of Cobaltohemoglobin

“…It then appears that moderate doming of the porphinato core in combination with modest stretch in the Co-N, bond can readily lead to an N. -* P, distance approaching 2.90 A in deoxycobaltohemoglobin and, consequently, to compatibility with Perutz's postulated trigger for the initiation of cooperative interaction of the subunits during the reversible oxygenation of hemoglobin. In Perutz's stereochemical mechanism (1, 2) for the reversible oxygenation of hemoglobin (Hb), the primary trigger for initiating cooperative interaction of the subunits is the large alteration in the stereochemistry of the coordination group of a protoheme that is concomitant with the transformation of any iron porphyrin from high-spin five-coordination to low-spin six-coordination (3)(4)(5)(6)(7)(8). The protoheme is linked to the globin framework through the axial complexing bond formed by the iron(II) atom with the imidazole-nitrogen atom (Nj) of the proximal histidine residue.…”