Imidazole porphyrins

Iron, Fe2+ (d6) 6, octahedral A-Imidazole, porphyrin Dioxygen transport in hemoglobin and myoglobin... 

Nitrogen ligands are the most donor functions in enzymes, the oldest homogeneous catalysts. Here they occur in imidazoles, porphyrins, binding to metals such as copper and iron, and they are involved in many oxidation reactions. Numerous mimics of these complexes are used in homogeneous... 

Two amphiphilic molecules were synthesized the porphyrin P = Co (II) 5, 10, 15, 20-tetra-(4-oxy-(2 -docosanoic acid)phenyl)porphyrin, and the imidazole Im = N-octadecylimidazole. These two molecules interlock, to produce the planned architecture with the same activity toward dioxygen. The geometry is controlled by the combination of mixed and alternated layers, obtained by the LB technique, and by the chemical reactivity, which allows the long-chain imidazole to insert in the macro ring, and stand above the Co atom. The mixed monolayers of the set imidazole-porphyrin are homogeneous, (area per mole = area of P alone, and not area of P + area Im) because an efficient chemical interaction is involved between P and Im. To avoid dimerization, alternate layers were built (with the help of an automatic trough) of either behenic acid interspersed with mixed layers of P + Im, or else layers of P alternated with layers of Im, as shown in Fig. 5. 

When a phthalocyanine macrocycle is grafted onto the imidazole-porphyrin (34, Figure 22), no change is observed in the binding geometry, indicating that the imidazole-zinc porphyrin interaction is much stronger than the imidazol-zinc phthalocyanine one." ... 

Fig. 7 Imidazole porphyrin derivatives that self-assemble via n-n interactions and hydrogen bonding...

Classic A/-heterocychc ligands, eg, bipyridyl (bipy), terpyridyl, imidazole, pyrazine, phenanthroline, piperazine (including alkyl- and aryl-substituted derivatives), and polypyrazol-l-yl-borates (bis, tris, and tetra), have all been found to coordinate Th(IV) chlorides, perchlorates, and nitrates. The tripodal hydrotris(pyrazolyl)borates, HBPz, have been used to stabilize organometaHic complexes (31). Bis-porphyrin Th(IV) "sandwich" complexes have been... 

The structure of the diamagnetic, cherry-red vitamin B12 is shown in Fig. 26.6 and it can be seen that the coordination sphere of the cobalt has many similarities with that of iron in haem (see Fig. 25.7). In both cases the metal is coordinated to 4 nitrogen atoms of an unsaturated macrocycle (in this case part of a corrin ring which is less symmetrical and not so unsaturated as the porphyrin in haem) with an imidazole nitrogen in the fifth position. A major... 

The introduction of chlorinated porphyrins (10) allowed for hydrogen peroxide to be used as terminal oxidant [62], These catalysts, discovered by Mansuy and coworkers, were demonstrated to resist decomposition, and efficient epoxidations of olefins were achieved when they were used together with imidazole or imidazo-lium carboxylates as additives, (Table 6.6, Entries 1 and 2). 

The observation that addition of imidazoles and carboxylic acids significantly improved the epoxidation reaction resulted in the development of Mn-porphyrin complexes containing these groups covalently linked to the porphyrin platform as attached pendant arms (11) [63]. When these catalysts were employed in the epoxidation of simple olefins with hydrogen peroxide, enhanced oxidation rates were obtained in combination with perfect product selectivity (Table 6.6, Entry 3). In contrast with epoxidations catalyzed by other metals, the Mn-porphyrin system yields products with scrambled stereochemistry the epoxidation of cis-stilbene with Mn(TPP)Cl (TPP = tetraphenylporphyrin) and iodosylbenzene, for example, generated cis- and trans-stilbene oxide in a ratio of 35 65. The low stereospecificity was improved by use of heterocyclic additives such as pyridines or imidazoles. The epoxidation system, with hydrogen peroxide as terminal oxidant, was reported to be stereospecific for ris-olefins, whereas trans-olefins are poor substrates with these catalysts. 

More recently 233) it has been reported that cross-linked polystyrene containing imidazole ligands did not provide a support rigid enough to prevent dimerization, and that the p-oxo dimer was benzene extracted from oxygenated tetraphenyl porphyrin iron(ll), Fe(TPP), which had been attached to the modified polystyrene. A discussion of model synthetic porphyrins, from which definitive structural and other physical data are obtained, is given in section V.C. 

A silica gel containing 3-imidazole propyl groups bonded to surface atoms of silicon has been prepared (253), and was treated 254) with a solution of Fe(TPP)L2, where L = py or pip, where upon the iron(II) porphyrin became attached to the imidazole groups on the surface of the gel,... 

Heme complexes and heme proteins have also been the subject of NIS studies. Of specific interest have been three features the in-plane vibrations of iron, which have not been reported by Resonance Raman studies [108], the iron-imidazole stretch, which has not been identified in six-coordinated porphyrins before, and the heme-doming mode, which was assumed to be a soft mode. 

Fig. 13. Cooperative closed dimers assembled from imidazole-functionalized porphyrins.

Reduction of both nickel porphyrins and thiaporphyrins to Ni1 species has been studied by EPR and 2H NMR spectroscopy.179, 2 58 The Ni1 complex of 5,10,15,20-tetraphenyl-21-thiaporphyrin has been isolated and characterized. Reaction of this complex with sulfur dioxide produced a paramagnetic five-coordinated Ni1 S02 adduct, while reaction with nitrogenous base ligands (amines, pyridines, imidazoles) yielded five- and six-coordinate complexes. In addition, the crystal structure of Ni1 diphenyldi-p-tolyl-21-thiaporphyrin has been determined. The coordination geometry about the nickel center is essentially square planar with extremely short Ni—N and Ni—S bonds (Ni—N = 2.015(2) A, 2.014(12) A, and 1.910(14) A and Ni—S = 2.143(6) A).2359... 

A trianionic zinc porphyrin anchored to a membrane by an imidazole link has been used to bind cytochrome c at the membrane surface. UV spectra confirmed the insertion of the zinc porphyrin into the phospholipid vesicle and was used to study surface association of cytochrome c. 

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