Porphyrins spectral properties

The positions of the absorption peaks of protopoqtlQrnn IX vaiy with the nature of the solvent. When dissolved in water, aggregatim of poiphyrins occurs very ea y (more details on porphyrin spectral properties are ven in chapter 9). 

Columns 3—5 of Table 9 show a comparison of the wavelength or wavenumber of the a-band and the chemical shift of the meso protons of the porphyrin ring. There is a correlation between these data the energy (expressed as va) of the a-band and the shielding of the meso protons increase in the series [29a] < [29b] < [29c] < [29d] < [29e] < [29f] < [ 29i]. The absorption spectra are of a Ayper-disturbed hypso type (Fig. 7), and the latter type allows the application of transmission modes A, D, or E (Fig. 1) for an interpretation of the observed cis effect of the axial ligands L on the spectral properties of the porphinato ligand (OEP). 

Absorption studies of the model compound in polar and nonpolar solvents support the finding that the dimer is present in a form which allows for close proximity between the two porphyrin rings. The absorption spectra of the dimer and the monomer are shown in Fig. 9. The spectra in methanol show a significant blue-shift of the Soret peak and a small red-shift in the visible bands for the diporphyrin, consistent with the spectral properties of previously synthesized cofacial diporphyrins(16,17) wherein exciton interactions can take place. ( 18) In methylene chloride, the Soret blue shift appears to be much less (<5 nm with reference to 4). 

Fan, J.,Whitehold, J.A., Olenyuk, B., Levin, M.D., Stang, P.J. and Fleischer, E.B. (1999) Self assembly of porphyrin arrays via coordination to transition metal bisphosphine complexes and the unique spectral properties of the product metallacyclic ensembles. J. Am. Chem. Soc., 121 (12), 2741-2752. 

Carbon monoxide binds readily to iron(II), but not iron(III), porphyrins to form complexes that are quite distinctive in terms of the spectral properties both of the heme and of the bound CO. Thus, CO has been widely used as a probe of the active site of heme proteins (113,... 

Generally speaking, the spectral properties of the heterosapphyrins resemble those of the pentaaza parents . That is to say, each of these species displays intense Soret- and Q-bands that are red-shifted relative to those of the porphyrins. For instance, when one, two, or even three of the pyrrolic subunits of sapphyrin is formally replaced by a 3,4-dialkyl furan (as in 5.74-5.76), the absorption spectrum is relatively unaffected (Xmax for the free-base form is ca. 450 nm as compared to the max value of 445 nm for typical decaalkyl sapphyrins such as 5.21). Treatment of these oxasapphyrins with an acid such as HCl or HBr has only a minimal effect on the location of the Soret band it is also found at ca. 450 nm in the case of these protonated systems. 

The zinc(II) porphyrin of 1 is particularly suitable for electron transfer studies because it is a photoactivated electron donor with easily monitored spectral properties. Forward and back electron transfer rate constants for la ( f = 5.0 x lO ... 

Metalloporphyrins and related compounds continue to attract attention as photosensitizers and as building blocks for construction of artificial lightharvesting arrays. The photophysical properties of several structurally modified porphyrins have been measured with a view to identifying new sensitizers for use in photodynamic therapy. The triplet state properties of porphyrins adsorbed onto the outer surface of vesicles have been describedand the fluorescence spectral properties of some amphiphilic porphyrins have been recorded. Similar studies have been carried out with halogenated tetraar-... 

Very recently the synthesis of a covalently bound chlorophyll-a-dimer analogue has been reported703). It was shown that bis-(chlorophyllide-a)ethylene glycol diester with porphyrin rings held together via nucleophilic hydrogen bridging closely resembles in its spectral properties, photochemical activity and redox potential to Chl-aj and therefore can serve as an in vitro model for the native Chl-ai-dimer-protein complex. 

Third-row metallocorrole complexes are scarce in the literature. The synthesis of (oxo)Re(tfmc) (tfmc = 5,10,15-(tris)trifluoromethylcorrolate), procured via a porphyrin ring contraction in the presence of Re2(CO)io, was reported in 1988 [69], and the synthesis, electrochemistry, and spectral properties of a number of Au... 

Recently, several papers have appeared on various aspects of sterically crowded porphyrins. Nonplanarity in these systems has been induced either by substituting bulky groups on (3-pyrrole and/or meso-carbons or by attaching a short bridging chain across the porphyrin periphery in the so-called basket handle porphyrins [169-171]. Some typical examples of sterically crowded porphyrins are depicted in Fig. 17. An analysis of the crystal structure and the various spectral properties clearly reveal the effect of nonplanarity of the porphyrin rings. The details of these results are highlighted in this section. 

Spectral properties of porphyrines, their precursors, and derivatives 01UK656. 

Cytochrome c oxidase is the terminal member of the respiratory chain in all animals and plants, aerobic yeasts, and some bacteria." " This enzyme is always found associated with a membrane the inner mitochondrial membrane in higher organisms or the cell membrane in bacteria. It is a large, complex, multisubunit enzyme whose characterization has been complicated by its size, by the fact that it is membrane-bound, and by the diversity of the four redox metal sites, i.e., two copper ions and two heme iron units, each of which is found in a different type of environment within the protein. Because of the complexity of this system and the absence of detailed structural information, spectroscopic studies of this enzyme and comparisons of spectral properties with 02-binding proteins (see Chapter 4) and with model iron-porphyrin and copper complexes have been invaluable in its characterization. 

An early report described the preparation in low yield of two isomeric meso-monofluorinated derivatives of porphyrins using the Schiemann reaction. Electrophilic fluorinating agents have been a more effective way to carry out direct fluorination of the porphyrin system. For example, reaction of octaethylporphyrin with A-fluoropyridinium salts such as A-fluoro-2,3,4,5,6-pentachloropyridinium triflate gave a mixture of mono, di, tri, and tetrafluoro derivatives 88 (Fig. 3.41). The perfluorinated derivative was formed in 20% yield. mew-Fluorination of octaethylporphyrin had minimal effects on oxidation potential and spectral properties. 

Partially fluorinated porphyrins were made by a similar Lindsey cyclization. Condensation of benzaldehyde with mixtures of 3,4-difluoropyrrole and pyrrole gave mixtures of di-, tetra-, and hexafluoro me.so-tetraphenylporphyrin with fluorine atoms in pairs per pyrrole. On the other hand, condensation of 3-fluoropyrrole with benzaldehyde gave a mixture of tetrafluoro-we o-tetraphenylporphyrin with one fluorine atom per pyrrole." These partially [3-fluorinated porphyrins were used to study the differential effects of fluorine substituents on spectral properties and core deformations of the porphyrin system. 

The kinetic products they obtained contained covalently bound chromium with Cr(III) to protein ratios of 1.0 for myoglobin and 4.0 for hemoglobin. These Cr(III)-protein complexes retained spectral properties and oxygen and CO binding properties identical to the untreated protein. They concluded that the Cr(III) was not bound at or near the sixth axial position and that the Cr(II) probably passed one electron to the Fe(III) via an exposed porphyrin edge. It was concluded that the chromium(III) was attached to amino acids 32-42 and/or 57-63 which contain close or adjacent aspartic acid and glutamic acid residues. 

Because of the dual spectral properties of Fe and a porphyrin Fe anion radical, it was suggested that the reduction product of Eq. (7) could be described by the resonance hybrid shown below ... 

Boucher and Katz (1967a) have investigated manganese protoporphyrin IX dimethyl ester complexes with anionic ligands F , Cl , Br , I", CN , and SCN. Elemental analyses and physical and spectral properties were consistent with the formulation, [Mn(III)porphyrin X]. Infrared spectra of the complexes, in the solid state and in nonpolar solvents, gave evidence for coordination of the anions to an axial position of the metal. Visible spectra also supported this conclusion. 

Kariya. N. Imamura. T. Sasaki, Y. Synthesis, characterization, and spectral properties of new perpendicularly linked osmium(III) porphyrin. Inorg. Chem. 1997,36. 833. 

Three series of /I-pyrrole brominated porphyrins have been reported in the literature . The first type-1 is represented as (TPPBr c)M where TPPBr c is the dianion of / -pyrrole brominated tetraphenylporphyrin, x = 0-8 and M = 2H, Mn, Fe, Co, Ni, Cu, or Zn - (Figure 9.1). The TPPBr derivatives have been studied in order to ascertain how distortion of the porphyrin ring will quantitatively affect the redox and spectral properties of the porphyrin as a function of the number of halogen substituents at the yS-pyrrole positions which can be varied from 0 to 8. 

The above discussions clearly demonstrates the importance of 6-pyrrole brominated porphyrins in both fundamental and applied fields of porphyrin chemistry. While one aim of these studies has been to gain insights into the role of macrocycle distortion in relation to biological systems containing porphyrins or related macrocycles , another has been to determine which factors influence the robustness of such catalysts in the oxidation of organic substrates ". Both measurements of electrochemical redox potentials and spectral properties of the porphyrins are needed to understand these properties and both are reviewed in this chapter on yS-pyrrole brominated porphyrins. 

---