Porphyrin-based compounds

Tomita, F. Yokota, A. Saito, K., and Abe, A., Method for Decomposing Porphyrin-Based Compound. Patent No. JP11187890. 1999, July 13. 

Initial work in biomimetic O2 reduction was aimed almost exclusively at designing Fe porphyrin-based compounds that, when immobilized on an electrode, would catalyze electrochemical O2 reduction mainly to H2O (as opposed to H2O2) regardless of the electrochemical potential or the lifetime of the cat-aiyst28,32 objective is problematic in several aspects, as discussed be-... 

Electronic Transitions and Lifetime of Excited States in Porphyrin-Based Compounds... 

The first step in the catalytic cycle is the reaction between H2O2 and the Fe(ni) resting state of the enzyme to generate compound I, a high-oxidation-state intermediate comprising an Fe(IV) oxoferryl center and a porphyrin-based cation radical... 

Metalated container molecules can be viewed as a class of compounds that have one or more active metal coordination sites anchored within or next to a molecular cavity (Fig. 2). A range of host systems is capable of forming such structures. The majority of these compounds represent macrocyclic molecules and steri-cally demanding tripod ligands, as for instance calixarenes (42), cyclodextrins (43,44), and trispyrazolylborates (45-48), respectively. In the following, selected types of metalated container molecules and their properties are briefly discussed and where appropriate the foundation papers from relevant earlier work are included. Porphyrin-based hosts and coordination cages with encapsulated metal complexes have been reviewed previously (49-53) and, therefore, only the most recent examples will be described. Thereafter, our work in this field is reported. 

C.DiNatale, D.Salimbeni, R.Paolesse, A.Macagnano, A.D Amico. Porphyrins-based opto-electronic nose for volatile compounds detection, Sensors and Actuators B 65 (2000) 220-6. 

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. 

A simple method has been developed to construct a variety of molecular architectures containing free base-magnesium or magnesium-metalloporphyrin systems consisting of two to nine porphyrin units. Compound 25 is a typical example for such a compound that are important for studying the electronic communication in multichromophoric... 

Based on elemental analyses and microprobe tracing (Dautzenberg et al., 1978), metal deposits appear to be present in sulfide forms and not as adsorbed porphyrin-type compounds or as metals in the elemental or metallic state. Takatsuka et al. (1979) and Rankel and Rollmann (1983) have reported direct linear correlations of the spent catalyst sulfur content with the deposited metal content. The sulfide forms of nickel and vanadium are consistent with expectations based on thermodynamics for the conditions typically encountered in residuum hydroprocessing units (600-800°F, 1000-2200 psig, H2/H2S environment). 

The first of this class of receptor reported was a cobalticenium-based macrocycle that complexed bromide ions, with shifts of up to 45 mV in the position of the redox peaks of the cobalt moieties [96]. Other species have been used as active receptors including calixarene-based compounds [97] and porphyrins [98]. 

To construct such a porphyrin-based positive allosteric system, we chose a cerium(iv) bis(porphyrinate) double decker compound 184-861 namely the tetrakis(4-pyridyl)porphyrin derivative 38.[871 This molecule satisfies the aforementioned requirements firstly, slow rotation of the two porphyrin planes with respect to one another should be possible at room temperature,1881 in analogy to similar cerium(iv) bis(diarylporphyrin) and bis(tetraarylporphyrin) complexes studied by Aida et al/861 Secondly, tilting of two porphyrin planes is more difficult than in 37, and thirdly, four pairs of 4-pyridyl groups are available as hydrogen bond acceptor sites for diols, hydroxycarboxylic acids, and dicarboxylic acids. Compound 39, which has only one pair of pyridyl groups, was used as a reference. 

Di Natale C, Salimbeni D, Paolesse R, Macagnano A, D Amico A. Porphyrins-based optoelectronic nose for volatile compounds detection. Sens Actuators 2000 B65 220-6. 

Emission. The fluorescence properties of metalloporphyrin and porphyrin-like compounds depend on the character of central metal ion. Fluorescence of porphyrins is generally observed from the free-base or closed-shell metal complexes. The... 

Extensive investigations on the catalytic mechanism of classical peroxidases resulted in a consensus model involving five different iron species [30, 31], These species are ferrous, ferric, Compound I, Compound II, and Compound III (Fig. 11.1). As discussed in Chap. 5, after the reaction of ground state (GS) Femporphyrin with H202, Compound I (Cl) is formed, a cationic oxob e,vpor-phyrin-based Ji-free radical. Electron paramagnetic resonance (EPR) studies established that, in peroxidases of classes I and III, the second oxidation equivalent in Cl is present as a porphyrin-based free radical [32, 33]. In peroxidases from fungal sources, electron abstraction from the protein results in the formation of a different species with the free radical based in a residue close to the porphyrin. 

The catalytic cycle proposed for the rhodium-porphyrin-based catalyst is shown in Fig. 7.18. In the presence of alkene the rhodium-porphyrin precatalyst is converted to 7.69. Formations of 7.70 and 7.71 are inferred on the basis of NMR and other spectroscopic data. Reaction of alkene with 7.71 gives the cyclopropanated product and regenerates 7.69. As in metathesis reactions, the last step probably involves a metallocyclobutane intermediate that collapses to give the cyclopropane ring and free rhodium-porphyrin complex. This is assumed to be the case for all metal-catalyzed diazo compound-based cyclo-propanation reactions. 

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