Porphins ring structure

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...

Quadridentate ligands can be obtained by condensing suitably substituted aldehydes and ketones with bidentate primary amines, and the resulting Schiff bases closely resemble the porphin ring system. Generally, one of the structural units—N=C—C=N—,—N=C—NHC=N—, N=C—NH—N=C—, —C=N—CH=CH—N=C—, or —C=N— CH2—CH2—N=C—is incorporated into the structure for maximum stability. For example, if or /io-aminobenzaldehyde is condensed with ortho-... 

FIGURE 8.22 Structures of (a) porphine, (b) heme, and (c) bacteriochlorophyll. The porphine ring common to the three structures is highlighted in blue. 

Name coined by Eschenmoser for a heterocyclic ring system with a structure between that of 001110 and that of porphine. C. structures have been detected as intermediates in vitamin B 2 biosynthesis. The participating enzymes are also able to convert unnatural substrates such as uroporphyrinogen I in vitro to C. compounds The basic skeleton of factor F 430, in-... 

The structure in Figure 24-24 is commonly found in both plant and animal matter. If the eight R groups are all H atoms, the molecule is called porphin. The central N atoms can give up their H atoms, and a metal atom can coordinate simultaneously with all four N atoms. The porphin is a tetradentate ligand for the central metal, and the metal-porphin complex is called a porphyrin. Specific porph Tins differ in their central metals and in the R groups on the porphin rings. 

Examine the geometry of porphin. Is the molecule planar Does the molecule incorporate explicit single and double bonds (as in the structure above) or bonds of intermediate length How many % electrons are involved in porphin s central ring Is poiphin aromatic Elaborate. 

It has been recently demonstrated that the simplest of the cobalt porphyrins (Co porphine) adsorbed on a pyrolytic graphite electrode is also an efficient electrocatalyst for reduction of 02 into 1120.376 The catalytic activity was attributed to the spontaneous aggregation of the complex on the electrode surface to produce a structure in which the cobalt-cobalt separation is small enough to bridge and activate 02 molecules. The stability of the catalyst is quite poor and largely improved by using porphyrin rings with mew-substitu-tion.377-380 Flowever, as the size of the mew-substituents increases the four-electron reduction efficiency decreases. 

Copper Phthalocyanine Blue is the copper(II) complex of tetraazatetrabenzo-porphine. As shown below, the mesomeric structures indicate that all of the pyrrole rings simultaneously contribute to the aromatic system ... 

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...

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