Porphyrin disulfides

Figure 5.44 (a) General molecular structure of the porphyrin disulfides, PDSn, described by Ishida and Majima [76]. (b) Changes in the surface plasmon enhanced fluorescence spectra for the exchange reaction of a decane thiol SAM with a 50 mmol dm-31,2-dichloroethane solution of PDS10 (Xem = 725 nm Xex = 425 nm). From A. Ishida and T. Majima, /. Chem. Soc., Chem. Commun., 1299-1300 (1999). Reproduced by permission of The Royal Society of Chemistry... 

Fig. 17 Gold electrodes modified with self-assembled monolayers of porphyrin disulfide dimers with different chain length of spacers [142,241-243]...

The use of disulfide linked di-a-helical peptides for the self-assembly of a heme-peptide model compounds has also been explored by Benson et al. (109). Conceptually analogous to the larger heme-protein systems utilized by Dutton and co-workers, to be detailed later, the incorporation of C4 S5mimetric Co(III)-porphyrins, based on coproporphyrin and octaethylporphyrin, resulted in helical induction comparable to that observed in the covalent PSM systems. 

Scheme 55 Intrahelical Disulfide Porphyrin Bridged Peptide 196[1051...

Aromatic and aliphatic thioles RSH (R = 2-, 3-, or 4-tolyl, 2-hydroxyethyl, 2-ethoxyethyl, 4-chlorphenyl, etc.) in the presence of a base yield anionic dithiolatorhodium(III) porphyrins (path j) which show the so-called hyperporphyrin spectra and are susceptible to autoxidation yielding hyperoxide ions. Although the formation of the latter ones is formulated via a nucleophilic exchange of coordinated OJ with thiolate, it could well be that an outer-sphere electron transfer between he anionic bis(thiolato) complex and molecular dioxygen initiates the observed formation of disulfides RSSR. 

Structural model systems are difficult to construct for cytochrome P-450 because thiolates do not bind strongly to Fe (III) porphyrin units, and oxidation of the thiolate to disulfides accompanied by reduction to Fe(II) is common (Equation 12.5). A range of models for the Fe(III) resting state have been prepared using open iron (III) porphyrins with alkyl or aryl thiolates, however. 

Figure 5.33 Structures of disulfide-terminated (a) pyrene (Pyr) and (b) porphyrin (Por), and thiol-terminated (c) boron-dipyrin (BoDy), (d) porphyrin (ThPor), and (e) the ferrocene-porphyrin-fullerene triad (Fc-P-C60)...

Imahori et al. reported on the energy transfer in mixed self-assembled monolayers of pyrene and porphyrin [83]. The molecular structures of the disulfide-terminated chromophores are illustrated in Figure 5.53. Porphyrin and pyrene dimers were coadsorbed onto Au(lll) mica substrates in different ratios. The ratios of pyrene to porphyrin were experimentally determined from absorption spectroscopy and the pyrene dimer was observed to adsorb preferentially, possibly due to its strong... 

Pantothenic acid has a central role in energy-yielding metabolism as the functional moiety of coenzyme A (CoA), in the biosynthesis of fatty acids as the prosthetic group of acyl carrier protein, and through its role in CoA in the mitochondrial elongation of fatty acids the biosynthesis of steroids, porphyrins, and acetylcholine and other acyl transfer reactions, including postsynthetic acylation of proteins. Perhaps 4% of all known enzymes utilize CoA derivatives. CoA is also bound by disulfide links to protein cysteine residues in sporulating bacteria, where it may be involved with heat resistance of the spores, and in mitochondrial proteins, where it seems to be involved in the assembly of active cytochrome c oxidase and ATP synthetase complexes. 

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