Water-soluble metalloporphyrins

Oxo-hydroxo tautomerism as a useful tool in oxygenation reactions catalyzed by water-soluble metalloporphyrins 98CC2167. 

An interesting, pH-dependent mechanistic changeover was reported in the H2A-02-[Fem(TPPS)] (TPPS = 5,10,15,20-tetrakis(p-sulfonatophe-nyl)porphyrinate) system in aqueous solution (23). This water-soluble metalloporphyrin exists as a monomer under slightly acidic conditions and reacts with ascorbic acid on the time-scale of several hours to produce [Fen(TPPS)] in the absence of dioxygen. The formation of the [Fem(TPPS +)] radical was also reported at pH 5, but it is not clear how... 

Scheme I. Structures of sulfonated robust metalloporphyrin complexes. The axial ligand of these water-soluble metalloporphyrins depend on the pH value, at acidic pH an hydroxo ligand occupies the axial position whereas it is a water molecule at basic pH values.

The second and third steps involve successive additions of the pyrazine and non-surfactant water soluble metalloporphyrin complexes to the template submerged in the aqueous phase (Steps 2 and 3, respectively). The two-layered assembly is then removed from the water through a protective monolayer of stearic acid to prevent disruption of the film structure (Step 4). If instead of removing the assembly in Step 4, Steps 2 and 3 were successively repeated, multi-layered assemblies having the essential features described in Figure 1 might be realized. 

Radiative and Nonradiative Decay Processes - Due to the potential application of these compounds as photosensitizers for photodynamic therapy" the photophysical properties of porphyrins and phthalocyanines, and their corresponding metal complexes, have been investigated extensively over the past decade. The photophysical properties of water-soluble metalloporphyrins, and especially the tetraphenylsulfonates," have been re-examined but nothing new has been found. The disulfonated metallophthalocyanines (MPcS2, where M = Al ", Ga" , or Zn") form complexes with fluoride ions for which the fluorescence yields and lifetimes are decreased with respect to the parent dyes while there are... 

J. Bernadou, A. Fabiano, A. Robert, B. Meunier, Redox tautomerism in high-valent metal-oxo-aquo complexes.Origin of the oxygen atom in epoxidation reactions catalyzed by water-soluble metalloporphyrins,/. Am. Chem. Soc. 116 (1994) 9375. 

Hydrated electrons react with certain water-soluble metalloporphyrin complexes, reducing the porphyrin ligands to pi-radical species. When the metal centers are Zn(II), Pd(II), Ag(II), Cd(II), Cu(II), Sn(IV), and Pb(II), the radical complexes are produced at diffusion-controlled rates and decay with second-order kinetics.188 Fe(III) porphyrins, on the other hand, yield Fe(II) porphyrins.189 Rather different behavior is seen in the reaction of e (aq) with [Ru(bpy)3]3 + here, parallel paths generate the well-known luminescent excited-state [ Ru(bpy)3]2 + and another reduced intermediate, both of which decay to the ground-state [Ru(bpy)3]2+, 190 In a direct demonstration of the chemical mechanism of inner-sphere electron transfer, [Coni(NH3)5L]2+ complexes where L = nitrobenzoate and dinitrobenzoate react with e (aq) to form Co(III)-ligand radical intermediates, which then undergo intramolecular electron transfer to yield Co(II) and L.191... 

Balahura, R.J., A. Sorokin, J. Bernadou, and B. Meunier (1997). Origin of the oxygen atom in C-H bond oxidations catalyzed by a water-soluble metalloporphyrin. Inorg. Chem. 36, 3488-3492. 

SWCNTs were modified with several water-soluble pyrene derivatives (1-pyreneacetic acid, 1-pyrenecarboxylic acid, 1-pyrenebutyric acid, and 8-hydroxy-l,3,6-pyrenetrisulfonic acid) bearing negatively charged ionic head-groups, to act as anchors to several pyridium headgroups present in a series of water-soluble metalloporphyrins [MP] + (M = Zn, Co, and Fe) [60a]. Interactions between the metalloporphyrins and SWCNTs proceeded through a combination of associative van der Waals (spacer-CNT) and electrostatic interactions (metalloporphyrins-spacer-CNT), as demonstrated by the combination of spectroscopic and surface techniques. 

Extending the studies on the reductive electron transfer from reduced metalloporphyrin states to [60]fullerene into aqueous media requires employment of a water-soluble form of [60]fullerene. Therefore, a micellar assembly consisting of the fullerene incorporated into Triton X-100 was investigated. The electron transfer does indeed occur across the interface of the micellar assembly. The rates exhibit a considerable slow-down compared to the homogeneous systems but, on the other hand, show a clear dependence on the reduction potential of the water-soluble metalloporphyrin. 

The azide and dichloride radicals react more rapidly and the organic radicals shown above react more slowly. Many water-soluble metalloporphyrins were oxidized by these reactions, and radical cations were generated from Zn", Cd", Cu", Pd" and Sn -porphyrins. Other metalloporphyrins were subsequently studied. 

This survey is limited to model systems based on synthetic water-soluble metalloporphyrins. The activity of KHSOs/sulfonated metalloporphyrin models has been checked with the usual... 

Figure 11.2. Schematic representation of the heterogeneous photo-oxidation of ferrocene by specifically adsorbed water-soluble metalloporphyrin at the water/EKlE interface. It is postulated that the distance of closest approach is determined by the onset of the solvent density profiles generated by capillary wave fluctuations.

As illustrated by Figure 11.3, the potential profile is distributed between both electrolyte phases. Depending on the charge of the porphyrin molecule, the Gibbs free energy of adsorption (A Gads) of water-soluble metalloporphyrins can be affected by the fraction of the potential drop in the aqueous phase A" ,... 

Active Iron-Oxo and Iron-Peroxo Species in Cytochromes P450 and Peroxidases Oxo-Hydroxo Tautomerism with Water-Soluble Metalloporphyrins... 

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