IRON PORPHYRIN PHENOXIDES - MODELS FOR SOME HEMOGLOBIN MUTANTS

Variously substituted phenoxides (L) reacted with [Fe(PPIXDBE)]20 (PPIXDBE is the protoporphyrin IX di-tert-butyl ester dianion) to produce 5-coordinate high-spin complexes Fe(PPIXDBE)L which displayed spectroscopic properties similar to those of the Met form of the .alpha. mutant chain of [human] HbM Boston. The addition of pyridine or 1-methylimidazole (L'') to Fe(PPIXDBE)L at 77.degree. K 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.degree. K, 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 .alpha. chain of Met HbM Iwate. The latter was high spin. With excess p-nitrophenoxide in CH2Cl2, Fe(PPIXDBE) (OC6H4-4-NO2) formed Fe (PPIXDBE) (OC6H4-4-NO2)2-, which exhibited a high-spin EPR spectrum at 77.degree. K. Addition of phenoxides or fluoride to Fe(II) protoporphyrin ester systems produced species such as Fe(PPIXDBE)X22- (X = OR or F), similar to those found previously with methoxide and hydroxide ions. The addition of CO to a bisphenoxy species, in Me2SO, resulted in a splitting of the Soret Band at 438 nm into 2 bands at 434 and 413 nm, which were attributed, respectively, to a carbonyl (phenoxide) species and a carbonyl species which contains no phenoxide. The visible spectral data supported the view expressed by others that upon reduction of HbM Iwate at pH 6.5 by Na2S2O4 the iron-tyrosine bond was broken.