Iron Porphyrin Phenoxides: Models for Some Hemoglobin Mutants

Variously substituted phenoxides (L) react with [Fe(PPIXDBE)]2O (PPIXDBE is protoporphyrin IX di-tert-Bu ester dianion) to produce 5-coordinate high-spin complexes Fe(PPIXDBE)L which display spectroscopic properties similar to those of the Met form of the ╬▒ mutant chain of Hb M Boston. The addition of pyridine or 1-methylimidazole (L') to Fe(PPIXDBE)L at 77 oK produced low-spin 6-coordinate complexes Fe(PPIXDBE)LL' which were studied spectroscopically. With the strongly basic 2,6-dimethoxyphenoxide (L), the above reaction was studied at 298 oK, where for L' = 1-methylimidazole the binding constant was approximately 100 M-1 in CH2Cl2. The Fe(PPIXDBE)LL' complexes were made in an attempt to mimic the Fe(III) in the ╬▒chain of Met Hb M Iwate; however, the latter is high spin. With excess p-nitrophenoxide in CH2Cl2, Fe(PPIXDBE)(OC6H4-4-NO2) forms Fe(PPIXDBE)(OC6H4 -4-NO2)2-, which exhibits a high-spin EPR spectrum at 77 oK. Addition of phenoxides or F- to Fe(II)