Metalloporphyrins

There have been a number of studies of the important class of proteins that have metalloporphyrin active sites. Models for the metalloporphyrin and corphinoid sites have been derived by modeling small molecules and extending the AMBER 451 and lMiu [6. 196,398] slightly modified version of the AMBER force field 

The geometry of metalloporphyrins and other tetrapyrroles have been studied in detail by molecular mechanics. The effect of (i) the size of the metal ion, (ii) axial ligation by planar ligands, such as imidazoles, (iii) the phenyl group orientation in tet-raphenyl porphinato complexes, and (iv) the flexibility of the porphyrin macrocycle, 

The solution structures of a number of metalloproteins with paramagnetic metal centers were determined with molecular mechanics and dynamics in combination with NMR spectroscopy (see also Chapter 9)1124-126,189]. Due to the complexity of the molecules, for metalloproteins a crystal structure of the compound or a derivative is often needed for the definition of the starting geometry. Molecular dynamics is then used to find low-eneigy conformers. The dynamics calculations also allow the visualization of areas of large flexibility, and this may lead to some understanding of the enzyme mechanism11891. 

The last step of methanogenesis by archaebacteria is catalyzed by coenzyme F430 which contains nickel coordinated to the most reduced tetrapyrrolic macrocycle 

Aluminum porphyrins have been used to prepare block copolymers by sequential monomer addition of two oxiranes [68, 318], of two )8-lactones [319], of a j5-lactone and an oxirane [319], of ethylene oxide and e-caprolactone [74] of propylene oxide and D-lactide [75], and of two methacrylates [76]. In the one example involving monomer pairs (j3-lactone and oxirane) which generate two different types of propagating species, the )8-lactone had to be polymerized 

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Hill J R ef a/1995 Vibrational relaxation of oarbon monoxide in model heme oompounds 6-ooordinate metalloporphyrins (M = Fe, Ru, Os) Chem. Phys. Lett. 224 218-23... 

Hill J R, Ziegler C J, Susliok K S, DIott D D, Rella C W and Payer M D 1996 Tuning the vibrational relaxation of CO bound to heme and metalloporphyrin oomplexes J. Phys. Chem. 100 18023-32... 

Metallacyclopentanes, 3,4-dimethylene-synthesis, 1, 669 Metallacyclopentan-2-ones synthesis, 1, 669 Metallacyclopentenes synthesis, 1, 670 Metallafluorenes synthesis, 1, 671 Metallaindanes synthesis, 1, 670 Metallaindenes synthesis, 1, 670, 671 Metallaxanthenes synthesis, 1, 671 Metalloporphyrins anions, 4, 398 demetallation, 4, 389... 

Eullerene-based donor-acceptor complexes and ion-radical salts with tetrathia-fulvalenes, metalloporphyrins, and cyclic amines as donors 99UK23. 

Binding of organic nitroso compounds to metalloporphyrins 99ACR529. Design and applications of chiral porphyrins 98YGK201. 

Metalloporphyrins and their analogs as photo- andradiosensitizers 99CRV2379. 

Oxo-hydroxo tautomerism as a useful tool in oxygenation reactions catalyzed by water-soluble metalloporphyrins 98CC2167. 

Photoinduced electron transfer reactions in supramolecularmodel systems based on metalloporphyrins 97YGK557. 

Solvation effects and coordination properties of porphyrins and metalloporphyrins in solutions 98MI19. 

The metalloporphyrin-catalyzed decomposition of ethyl azidoformate in the presence of an arene has been investigated but with little success in improving the yields of the 1 //-azepines.151 The nickel and copper complexes had no effect, whereas the cobalt-tetraphenylporphyrin complex accelerated the decomposition rate of the azido ester but produced more A-arylurethane rather than 1//-azepine. 

The high stability of porphyrins and metalloporphyrins is based on their aromaticity, so that porphyrins are not only most widespread in biological systems but also are found as geoporphyrins in sediments and have even been detected in interstellar space. The stability of the porphyrin ring system can be demonstrated by treatment with strong acids, which leave the macrocycle untouched. The instability of porphyrins occurs in reduction and oxidation reactions especially in the presence of light. The most common chemical reactivity of the porphyrin nucleus is electrophilic substitution which is typical for aromatic compounds. 

Chlorins are also accessible by carbene additions to C-C double bonds on the periphery of metalloporphyrins. The most effective reaction on a preparative scale is the addition of ethyl diazoacetate in refluxing benzene to copper octaethylporphyrin (4) or meso-tetraphenylpor-phyrin in the presence of copper(I) iodide,100108b 110 which gives a diastereomcric mixture of chlorins, e.g. 5. 

Isobacteriochlorins, since they are tetrahydroporphyrins, can be obtained by tetrahydrogena-tion of porphyrins and dihydrogenation of chlorins. However, alkali-metal reduction of porphyrins and metalloporphyrins always gives a mixture of chlorins, bacteriochlorins or isobacteriochlorins.14 The method of choice for the preparation of pure isobacteriochlorins, e.g. 2, is the diimide reduction of zinc(II) chlorins, e.g. l.15a,b... 

Metalloporphyrin redox reactions. L. E. Bennett, Prog. Inorg. Chem., 1973,18,1-176 (750). 

Kinetics and mechanism of metalloporphyrin formation. W. Schneider, Struct. Bonding (Berlin), 1975,23, 123-166 (65). 

Recent developments in the studies of titanium and vanadium porphyrins with special emphasis on oxygen adducts, low valent metalloporphyrins and related systems of sulphur and selenium. R. Gui-lard and C. Lecomte, Coord. Chem. Rev., 1985, 65, 87 (76). 

Metalloporphyrins as catalysts of chain transfer in radical polymerisation and stereoselective oxidation. L. Karmilova, G. V. Ponomarev, B. R. Smirnov and I. M. Bel yovskii, Russ. Chem. Rev. (Engl. Transl), 1984, 53,132 (44). 

Catalysis by metalloporphyrins of reactions involving oxidation by molecular oxygen and oxygen-containing compounds. N. S. Enikolopyan, K. A. Bogdanova, L. V. Karmilova and K. A. Askarov, Russ. Chem. Rev. (Engl. Transl.), 1985,54,215 (188). 

It was shown that dibenzothiophene oxide 17 is inert to 1-benzyl-l,4-dihydro nicotinamide (BNAH) but that, in the presence of catalytic amounts of metalloporphyrin, 17 is reduced quantitatively by BNAH. From experimental results with different catalysts [meso-tetraphenylporphinato iron(III) chloride (TPPFeCl) being the best] and a series of substituted sulfoxides, Oae and coworkers80 suggest an initial SET from BNAH to Fe1 followed by a second SET from the catalyst to the sulfoxide. The results are also consistent with an initial coordination of the substrate to Fem, thus weakening the sulfur-oxygen bond in a way reminiscent of the reduction of sulfoxides with sodium borohydride in the presence of catalytic amounts of cobalt chloride81. 

Cohen lA (1980) Metal-Metal Interactions in the Metalloporphyrins, Metalloproteins and Metalloenzymes. 40 1-37... 

Schmidtke H-H, Degan J (1989) A Dynamic Ligand Field Theory for Vibronic Structures Rationalizing Electronic Spectra of Transition Metal Complex Compounds. 71 99-124 Schneider W (1975) Kinetics and Mechanism of Metalloporphyrin Formation. 23 123-166... 

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