Protoporphyrin resonance

Fio. 28. Paramagnetic resonance of copper protoporphyrin in a high viscosity oil at 9.47 kmc./second. Broad humps are due to Cu hyperfine structure sharp lines at high field are due to nitrogen hyperfine structure 164). 

Figure 1 shows the Raman spectrum of Hb obtained with 406.7-and 413.1-nm excitation and the spectrum of monomeric, four-coordinate Ni protoporphyrin in aqueous micellar solution (9). Excitation at 413.1 nm is at resonance with the red component of the split Soret band of Ni-reconstituted hemoglobin at 406.7 nm the blue component of the Soret band is selectively probed. Comparison of the spectra shows that two sets of marker line frequencies exist. One set (labeled 4 in Figure 1) is enhanced by resonance with the blue Soret component the other set (labeled 5) is enhanced by excitation of the red Soret component. Thus, the shifts in the core-size lines in going from set 4 - 5 are -39 cm (i/-q at 1657 cm ), -20 cm cm ), and -34 cm 1 19 cm ). 

The NMR of ferrous complexes of MPll and MP8 in aqueous SDS solutions has been studied the spectra are very broad and ill-resolved [23]. The heme proton resonances appear in the range 15 to 30 ppm and resemble those of ferrous hemoproteins. The similarity in the linewidths and spectral range of the heme protons in these ferrous peptide complexes with the ferrous hemoproteins suggests that the larger size of the heme peptide restricts the mobility of the molecule inside the micelles compared to that in case of the protoporphyrin complex in micellar solutions, where the spectrum is better resolved. 

The micelle-encapsulated six coordinated bis(pyridinato) iron(II) complexes of protoporphyrin and OEP have been reported by addition of pyridine to the four coordinate ferrous complex in aqueous micellar solution. The optical spectrum of [Fe(II)(PP)(Py)2] in micelle (Fig. 10) is identical to S = 0 six-coordinate bis(pyridinato) iron(II) porphyrin complex [3]. The magnetic moment measurements in solution confirm their diamagnetic nature. The HNMR spectra are also characteristic low-spin iron(II) resonances (S = 0) with shifts lying in the diamagnetic region (Table 2). 

Fig. 9. Proton NMR spectra at 220 Me of solutions in d5-pyridine of the Zn(II)-complexes with porphin, and the dimethylesters of mesoporphyrin IX, deuteropor-phyrin IX, and protoporphyrin IX. The resonance assignments were based on the relative resonance intensities and the observed fine-structure from spin-spin coupling they agree with previously published data by Caughey and Koski (17 a = ring methyls (for porphin protons at positions 1 to 8), b = mesoprotons, c and d = methylene protons of the propionates, e = methylesters, / and g = resonances of the substituents at positions 2 and 4. Three strong resonances between —7 and —9 ppm come from d5-pyridine, the line at ca. —4.9 ppm from HDO. T = 25 °C...

Kurland et al. (64) observed hyperfine-shifted resonances of ferrimyoglobin between —20 and —90 ppm. Comparison with the spectra of the iron(III)-complexes with protoporphyrin IX, deuteroporphyrin IX, and mesoporphyrin IX seems to indicate that four of the low field resonances correspond to the four ring methyl groups. Additional lines at high fields from DSS were observed in ferrimyoglobin (116), and in high spin porphyrin-iron(III) complexes (Caughey et al. (19)). The observation... 

Berthomieu C, Boussac A, Mantele W, Breton J, Nabedryk E. (1992) Molecular changes following oxidoreduction of cytochrome b559 characterized by Fourier transform infrared difference spectroscopy and electron paramagnetic resonance Photooxidation in photosystem II and electrochemistry of isolated cytochrome b559 and iron protoporphyrin IX-bisimidazole model compounds. Biochemistry 31 11460-11471. 

High-temperature solution decomposition of Fe(TPP)N3 (TPP = tetraphenyl-porphyrin) in the absence of added base or oxygen has been examined. The only reaction product observed is formulated as (TPP)FeNFe(TPP), analogous to [Fe(TPP)]20.258 The structure of Fe(l-methylimidazole)2(PPIX),CH30H,H20 (PPIX = protoporphyrin IX) has been reported. The porphyrin has a distinctly ruffled inner core. Magnetic resonance studies of the autoreduction of ferric porphyrins in the presence of piperidine or cyanide demonstrate that reduction to iron(ii) is accompanied by one-electron oxidation of the substrate. ... 

Several haemin type compounds have been examined [1, 3, 4], and selected Mossbauer parameters are given in Table 13.1. The haemin chlorides of protoporphyrin IX, 2,4-diacetyldeuteroporphyrin IX dimethyl ester, and mesoporphyrin IX, and haematin all show a characteristic broadening of one of the resonance lines with rising temperature. This is dramatically illustrated in Fig. 13.2 for the deuterohaemin compound. In all cases they are Fe(III) 5 = f compounds. 

Figure 6.2.5 The P-vinyl groups of protoporphyrin derivatives are conjugated with the porphyrin 7C-system and tend to lie parallel to the ring. Two conformations dominate and show characteristic Raman resonance bands. (From Kalsbeck et al, 1995.)...

Janson, T. R., Katz, J. J. (1972). An Examination of the 220 MHz NMR Spectra of Meso-porphyrin IX Dimethyl Ester, Deuteroporphyrin IX Dimethyl Ester, and Protoporphyrin IX Dimethyl Ester, J. Magn. Resonance, 6 209. 

Figure 14, Proton magnetic resonance spectrum at 100 MHz of fx oxo bis(protoporphyrin IX dimethyl ester iron(lIl)) in CDCI3 at 35°C...

Ferroheme is easily oxidized to ferriheme, containing iron(lll). Ferriheme chloride (old name hemin chloride) forms black crystals. Protoporphyrin is purple its color, the black color of hemin salts, and the red color of blood are related to the system of resonating double bonds in the porphyrin structure. 

Comparing these measurements with embedded reference molecules consisting of protoporphyrin molecules without metal ion, it was demonstrated that ET is mediated by the Fe ion in this case. These results demonstrated resonant tunneling as the mechanism for ET in this system [83]. 

When ferrous iron is inserted into protoporphyrin, the ubiquitous iron porphyrin or heme is formed. Because of the resonating structure, an electron donor or acceptor molecule need not come in contact with the iron atom directly to oxidize or reduce the iron atom it is probably sufficient that contact be made with any portion of the resonating molecule for the iron atom to be oxidized or reduced. The oxidative properties of the iron atom in heme are modified by the iron being held in this ring and are further modified by the heme being attached to specific proteins. In nature the other metal that complexes with protoporphyrin is magnesium Mg protoporphyrin is an intermediate compound in the biosynthetic chain of chlorophyll synthesis. The movements of the ir electrons in the porphyrin are undoubtedly intimately connected with the functioning of the heme and chlorophyll structures, but of this we know very little. 

---