Porphyrin design

Biomimetic ORR catalysts are highly elaborate porphyrins designed to replicate the stereoelectronic properties of the O2 reducing site of heme/Cu oxidases (see... 

The prevalence of the heme in O2 metabolism and the discovery in the 1960s that metallophthalocyanines adsorbed on graphite catalyze four-electron reduction of O2 have prompted intense interest in metaUoporphyrins as molecular electrocatalysts for the ORR. The technological motivation behind this work is the desire for a Pt-ffee cathodic catalyst for low temperature fuel cells. To date, three types of metaUoporphyrins have attracted most attention (i) simple porphyrins that are accessible within one or two steps and are typically available commercially (ii) cofacial porphyrins in which two porphyrin macrocycles are confined in an approximately stacked (face-to-face) geometry and (iii) biomimetic catalysts, which are highly elaborate porphyrins designed to reproduce the stereoelectronic properties of the 02-reducing site of cytochrome oxidase. 

Figure 1. Schematic view of chiral porphyrins designed to recognize alkyl residues of different sizes attached to a common oxidizable functional group.

FIGURE 4.9 Representative sterically constrained porphyrins designed for reversible dioxygen binding to their Fe(II) or Co(II) complexes.31... 

C32H34N4O4, Mr 538.65 uv ,jj (dimethyl ester in CHCI3) 400,498,538,565, and 618 nm. C. A is one of the few naturally occurring, metal-fiee porphyrins. Occurrence C. A is isolated from the New Caledonian marine sponge Corallistes sp. which contains further porphyrins designated as C. B-E in addition to the main component C.A. Their substitution patterns differ slightly firom that of C. A. 

Following successfid push-pull porphyrin design for application in DSSCs, a study focused on enhancement of the pull properties of the anchoring moiety of... 

Improvement of the YD2 and YD-0-C8 Zinc Porphyrin Design by Broadening Absorbance Wavelength Range for Push-Pull Porphyrins Through Modification of Their Donor and Acceptor Moieties... 

In other sections in this chapter, we have referred to a variety of macropolycyclic structures which are more elaborate than the simple three-stranded bicyclic cryptands. This includes bridged double-macrocycles " , in-out bicyclic amines and the macrotricyclic quaternary ammonium salts of Schmidtchen. In addition to these, there are two other types of compounds which deserve special note. The first of these is a stacked twin-ring cryptand, but it is a hybrid molecule rather than a double-cryptand . The species shown below as 20 is a crowned porphyrin, and was designed to provide a pair of metal cation binding sites similar to those which might be available in natural biological systems . 

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

Porphyrins are formally derived from the porphin (1) nucleus by substitution of some or all peripheral positions with various side chains. In the classical system of nomenclature T, introduced by H. Fischer,Sc the peripheral /5-pyrrolic positions are numbered front 1 to 8 and the methine positions (also named meso positions) between the pyrrole rings are designated a, //, y, and 5. The rings are lettered clockwise A, B, C, and D. The classical nomenclature was in the past more and more displaced by a nomenclature which numbers all the carbon... 

The tetramerization of suitable monopyrroles is one of the simplest and most effective approaches to prepare porphyrins (see Section 1.1.1.1.). This approach, which is best carried out with a-(hydroxymethyl)- or ot-(aminomethyl)pyrroles, can be designated as a biomimetic synthesis because nature also uses the x-(aminomethyl)pyrrole porphobilinogen to produce uroporphyrinogen III. the key intermediate in the biosynthesis of all kinds of naturally occurring porphyrins, hydroporphyrins and corrins. The only restriction of this tetramerization method is the fact that tnonopyrroles with different -substituents form a mixture of four constitutionally isomeric porphyrins named as porphyrins I, II, III, and IV. In the porphyrin biosynthesis starting from porphobilinogen, which has an acetic acid and a propionic acid side chain in the y6-positions, this tetramerization is enzymatically controlled so that only the type III constitutional isomer is formed. 

FIGURE 5-14 Structures of some chemical species useful for designing anion-selective electrodes (a) Mn(III) porphyrin (b) vitamin Bi2 derivative (c) tri-n-octyltin chloride (d) lipophilic polyamine macrocyclic compound. 

The scientific interest in porphyrin ligands (Fig. 5) derives in part from their ability to accommodate a large series of different elements, often in various oxidation states. On the other hand porphyrins are planar molecules with a delocalized 18 Ti-electron system and a diatropic ring current [25], which makes them interesting for the design of new materials with applications in photochemistry [25-27]. 

Sugiura K (2003) An Adventure in Macromolecular Chemistry Based on the Achievements of Dendrimer Science Molecular Design, Synthesis, and Some Basic Properties of Cyclic Porphyrin Oligomers to Create a Functional Nano-Sized Space. 228 65-85 Sun J-Q, Bartlett RJ (1999) Modern Correlation Theories for Extended, Periodic Systems. 203 121-145... 

The processes that govern the formation of ash particles are complex and only partially understood (Figure 7.12). The mineral matter in pulverized coal is distributed in various forms some is essentially carbon-free and is designated as extraneous some occurs as mineral inclusions, typically 2-5 pm in size, dispersed in the coal matrix and some is atomically dispersed in the coal either as cations on carboxylic acid side chains or in porphyrin-type stmctures. The behavior of the mineral matter during combustion depends strongly on the chemical and physical state of the mineral inclusions. 

Much effort has also been directed toward mimicking electron transfer on natural photosynthetic systems. Recently, the group of Harada has been able to prepare monoclonal antibodies against metallo porphyrins and show that the biological edifice can control photoinduced electron transfer from the porphyrin to organic acceptor molecules in solution. As it was important to design a biomolecule able to accommodate not only the metalloporphyrin unit but also organic substrates, Harada recently used a hexacoordinated phosphorus... 

Heme and its immediate precursor, protoporphyrin IX (Figure 32-4), are both type III porphyrins (ie, the methyl groups are asymmetrically distributed, as in type III coproporphyrin). However, they are sometimes identified as belonging to series IX, because they were designated ninth in a series of isomers posmlated by Hans Fischer, the pioneer worker in the field of porphyrin chemistry. 

To reveal the light-harvesting process, synthetic studies on cyclic porphyrin oligomers, designed based on the information of the protein structure, are considered. Nature adopted the cyclic alignment of chlorophyll. Is the closed cyclic... 

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