Tetra porphyrins structure

The reduction electrochemistry of ECP porphyrin films furthermore responds to added axial ligands in the expected ways. We have tested this (2,6) for the ECP form of the iron complex of tetra(o-amino)phenyl)porphyrin by adding chloride and various nitrogeneous bases to the contacting solutions, observing the Fe(III/II) wave shift to expected potentials based on the monomer behavior in solution. This is additional evidence that the essential porphyrin structure is preserved during the oxidation of the monomer and its incorporation into a polymeric film. 

Fig. 1 Basic structure (left side) and the absorption spectra (right side) of some photosensitizers. The absorption spectra of porphyrins (derived from porphins) consists of a Soret band (around 400 nm) and four Q-bands. Upon reduction of one or two double-bonds of the tetra-pyrrole structure or by expanding the number of 7i-electrons (by expanding the ring structure), the outermost Q-band becomes bathochromically shifted and the absorption coefficient increased as indicated on the figure. As described in the text, such chemical modifications are important for improving the therapeutic effect in deeper tissue layers...

An unusual porphyrin-supported hafnium guanidinate was obtained from the reaction of (TTP)Hf=NAr (TTP = meso-tetra-p-tolylporphyrinato dianion, Ar = 2.6-diisopropylphenyl) with 1,3-diisopropylcarbodiimide. The molecular structure of the product, (TTP)Hf[Pr NC(NPr )(NAr)] is shown in Figure 24. ° ... 

Dloxygen reduction electrocatalysis by metal macrocycles adsorbed on or bound to electrodes has been an Important area of Investigation (23 ) and has achieved a substantial molecular sophistication in terms of structured design of the macrocyclic catalysts (2A). Since there have been few other electrochemical studies of polymeric porphyrin films, we elected to inspect the dloxygen electrocatalytic efficacy of films of electropolymerized cobalt tetraphenylporphyrins. All the films exhibited some activity, to differing extents, with films of the cobalt tetra(o-aminophenylporphyrin) being the most active (2-4). Curiously, this compound, both as a monomer In solution and as an electropolymerized film, also exhibited two electrochemical waves... 

Interpreting these results on a detailed molecular basis is difficult because we have at present no direct structural data proving the nature of the split Co(IIl/lI) voltammetry (which seems critical to the electrocatalytic efficacy). Experiments on the dissolved monomeric porphyrin, in CH-C solvent, reveal a strong tendency for association, especially for the tetra(o-aminophenyl)porphyrin. From this observation, we have speculated (3) that the split Co(III/II) wave may represent reactivity of non-associated (dimer ) and associated forms of the cobalt tetra(o-aminophenyl)porphyrins, and that these states play different roles in the dioxygen reduction chemistry. That dimeric cobalt porphyrins in particular can yield more efficient four electron dioxygen reduction pathways is well known (24). Our results suggest that efforts to incorporate more structurally well defined dimeric porphyrins into polymer films may be a worthwhile line of future research. 

The functionalization of zinc porphyrin complexes has been studied with respect to the variation in properties. The structure and photophysics of octafluorotetraphenylporphyrin zinc complexes were studied.762 Octabromoporphyrin zinc complexes have been synthesized and the effects on the 11 NMR and redox potential of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraarylporphyrin were observed.763 The chiral nonplanar porphyrin zinc 3,7,8,12,13,17,18-heptabromo-2-(2-methoxyphenyl)-5,10,15,20-tetraphenylporphyrin was synthesized and characterized.764 X-ray structures for cation radical zinc 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin and the iodinated product that results from reaction with iodine and silver(I) have been reported.765 Molecular mechanics calculations, X-ray structures, and resonance Raman spectroscopy compared the distortion due to zinc and other metal incorporation into meso dialkyl-substituted porphyrins. Zinc disfavors ruffling over doming with the total amount of nonplanar distortion reduced relative to smaller metals.766 Resonance Raman spectroscopy has also been used to study the lowest-energy triplet state of zinc tetraphenylporphyrin.767... 

Other supramolecular structures such as dendrimers have also been synthesized with zinc-containing porphyrins. Sixteen free base and sixteen zinc porphyrin units were added at the fifth generation of dendritic poly(L-lysine) and intramolecular fluorescence energy transfer was observed.823 Assembly of supramolecular arrays in the solid state has been achieved with the incorporation of an amide group for hydrogen bonding. Zinc meso-tetra(4-amidophenyl)porphyrin... 

Fig. 17. The structures of CB[10] and its inclusion complexes 20a-d with the corresponding free base and metalated tetra(N-methylpyr-idinium)porphyrins 19a-d (126).

Manganese nitrosyl porphyrins [215] are considered good models for the iron-nitric oxide analogs, which are relatively unstable but very vital to many biological operations. A six-coordinate manganese nitrosyl porphyrin of the form (por)Mn(NO)(L), where por can be TTP (TTP = tetra(4-methylphenyl)porphine) and L = piperidine, methanol, 1-methyhmidazole, has been prepared [216] in moderate yields by the reductive nitrosylation of the (por)MnCl complex with NO in piperidine. The crystal structures of these compounds give indication of a linear Mn-NO bond [215]. 

Fig. 6. Molecular structures of selected Group 14 organometallic porphyrin complexes (a) Si(TPP)(C6H5)2, (b) Si(TPP)(CH2SiMe3)2, (c) cis-SnCTBPPKCeHjlz (TBPP = tetra(4- Bu-phenyl)porphyrin), (d) rranr-Sn(TPP)(C6H5)2, (e) Sn(OEC)(C6H5)." ...

The examples cited above represent part of an increasing body of structural information on chlorophylls, chlorins, bacteriochlorins and isobacteriochlorins (10-14 and references therein) that points to the remarkable flexibility of these molecules This ability of the macrocycle to adjust is not limited to hydroporphyrins but is also observed in porphyrins 5,10,15,20-tetra-n-propylporphinato lead (II) assumes a "roof" shape by folding along an axis defined by two opposite methine carbons with the two planes of the "roof" inclined at 22 to one another (15) In contrast, triclinic 5,10,15, 20-tetraphenylporphinato cobalt (II) is distinctly saddle shaped with the 3 carbons of adjacent pyrrole rings lying 40 66 and -0 66A above and below the plane of the four nitrogens (16) ... 

The carotenoids, trans-3 carotene (Sigma), I canthaxanthin (Fluka), II 3-8 -apocarotenal (Fluka), III and crocetin (Sigma), IV were used in this study (see structure). Of the above four carotenoids, only crocetin is water soluble. The porphyrins 5,10,15,20-tetra-phenyl-21H,23H-porphine (TPP) and 5,10,15,20-tetra-(4-sodiumsulfonato-phenyl)-21H,23H-porphine, TPPS were obtained from Aldrich, TPPS is a water soluble porphyrin. Carotenoids I-III were used as supplied, however crocetin was purified according to published methods (15) just prior to use. 

The molecules of interest are tetra(benzo-lS-crown-S)porphyrin (TCP, I), tetra(4-sulfonatophenyl)porphyrin (TPPS, II), and tetra(4-trimethylammoniumphenyl)porphyrin (ITAP, III).(See Structure.)... 

Porphycenes (150) and corrphycenes (151) are porphyrin isomers, several of whose iron(III) complexes have been characterized. Examples include distorted square-pyramidal (12,17-diethox-ycarbonyl-2,3,6,7,1 l,18-hexamethylcorrphycenato)iodo-iron(III), [Fe(tprpc)X] (where tprpc = 2,7, 12,17-tetra-u-propylporphycene) with X = C1, Br, N3, 02CMe, or OPh and [Fe(tprpc)2]0. " Iron(II)- and iron(IV)-tproc complexes also exist, as established in an examination of oxygenation of iron(II) porphycene.The structure of chloro(3,6,13,16-tetraethyl-2,7,12,17-tetramethylpor-phycenato)iron(III), also distorted square-pyramidal, has been compared with those of chloro-iron(III) porphyrin complexes. ... 

Complexes with tetradentate ligands L (L = (salen)2-, (acacen)2-), of the form [MoCl2L], have been prepared by reaction of [MoCl4(NCMe)2] or [MoCl3(py)3] with H2L.159 The reaction of HC1 with [MoO(TPP)] (TPP = dianion of 5,10,15,20-tetra-4-tolylporphyrin) forms [MoCl2(TPP)] the structure of the latter involves a planar porphyrin ring with the tram chlorides at distances from the molybdenum of 2.347(4) and 2.276(4) A, although they appear to be chemically equivalent.113... 

Hydrodemetallation pathways for Ni-etioporphyrin and Ni-tetra(3-methylphenyl)porphyrin are shown in Fig. 20. Both are characterized by a sequential hydrogenation-hydrogenolysis global mechanism, but important differences are apparent. Ware and Wei (1985a) rationalized the differences in porphyrin reactivity on the basis of porphyrin molecular structure. Structural differences on the periphery of the metalloporphyrin, in particular the substituent groups at the /3-pyrrolic and methine bridge... 

In a later article, complexes of Ni(II), Cu(II), Pd(II), and V02+ ions with the same tetra-substituted porphyrin were reported. Stepwise oxidation of these complexes gave products for which the authors proposed quinonoid, monoradical, and diradical structures. The most prolonged oxidations yielded the diradical products, which were isolated as dark purple crystals, relatively stable in air (40). The monoradical vanadyl complex was observed to be diamagnetic, suggesting antiferromagnetic coupling between the phenoxyl radical and unpaired electron on vanadium, whereas in the copper complex no such coupling was observed. More detailed studies of these systems seem warranted. 

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