Porphyrin surface

Porphyrin monomers and organized monolayers on conducting or semiconducting surfaces provide the unique possibility to convert the energy of the excited state directly into photocurrents. Furthermore, the large porphyrin surface allows... 

The association of porphyrin and fullerene electron acceptors in LB films can also proceed via a stepwise, noncovalent formation of the assembly, as demonstrated by Shinkai and Ikeda (Figure 13.88). The host-guest interaction of Ceo with homooxa-calix[3]arene is the noncovalent interaction that assists film formation The fullerene absorption in the host-guest complex is used to determine a surface concentration of 1.4 x 10 ° molcrn" in the Ceo layer, which is then further covered with the polymer-sustained porphyrins 165 or 166. Porphyrin surface concentrations are then controlled by UV-visible absorption and are found to be 7.6 X 10 and 5.5 x 10 for 165 and 166, respectively. Photocurrent measurements performed under irradiation at 420 nm, with a 1.36 mW cm for a coating of 165, and at 430 nm, with a 1.53mWcm for a coating of 166, in... 

Akiyama T, Imahori H, Ajawakom A and Sakata Y 1996 Synthesis and self assembly of porphyrin-linked fullerene on gold surface using S-Au linkage Chem. Lett. 907-8... 

In (87BBPC941), Limbach made a major contribution to understanding crystalline and amorphous environments using compounds that in the gas phase show symmetric double minimum potentials. Several compounds were used to illustrate the periodic (crystal) and random (glass) distortions of the potential surface, among them H2P and porphycene. Tlie seminal paper on the tautomerism of porphyrins in the solid state is that of Limbach... 

Mechanisms of micellar reactions have been studied by a kinetic study of the state of the proton at the surface of dodecyl sulfate micelles [191]. Surface diffusion constants of Ni(II) on a sodium dodecyl sulfate micelle were studied by electron spin resonance (ESR). The lateral diffusion constant of Ni(II) was found to be three orders of magnitude less than that in ordinary aqueous solutions [192]. Migration and self-diffusion coefficients of divalent counterions in micellar solutions containing monovalent counterions were studied for solutions of Be2+ in lithium dodecyl sulfate and for solutions of Ca2+ in sodium dodecyl sulfate [193]. The structural disposition of the porphyrin complex and the conformation of the surfactant molecules inside the micellar cavity was studied by NMR on aqueous sodium dodecyl sulfate micelles [194]. 

It is not surprising then that the first reported surface mediated reaction made use of vicinal dihalides. In addition to poly-p-nitrostyrene immobilized metallo-porphyrins and viologens were found to be catalytically active. Recently,... 

Fig. 12a,b. The sensorgrams for the binding of the antibody dendrimer (a) or IgG (b) to the anionic porphyrin immobilized onto the surface of the sensor chip. Phosphate borate buffer (0.1 M, pH 9.0) was used. TCPP was immobilized via hexamethylenediamine spacer onto the sensor chip and then a solution of IgG or the dendrimer was injected to the flow cell. After 60 s from the injection of the antibody solutions, flow ceU was filled with buffer... 

Carotenoid/ curcumin/porphyrin Water dispersion without using compositions surface-active substance... 

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

Considerable progress has been made recently In the development of In situ spectroscopic techniques applicable to the study of transition metal macrocycles adsorbed at submonolayer coverages onto electrode surfaces. These have been aimed at gaining Insight into the nature of the Interactions of these compounds with the surface and with 02 Most of the attention In the authors laboratory has been focused on Fe- and Co-TsPc, although some preliminary results have already been obtained for some Iron and cobalt porphyrins. The main conclusions obtained from these Investigations will be outlined In the following sections. 

Achieving fast electron transfer to enzyme active sites need not be complicated. As mentioned above, many redox enzymes incorporate a relay of electron transfer centers that facilitate fast electron transfer between the protein surface and the buried active site. These may be iron-sulfur clusters, heme porphyrin centers, or mononuclear... 

ORR catalysis by Fe or Co porphyrins in Nation [Shi and Anson, 1990 Anson et al., 1985 Buttry and Anson, 1984], polyp5rrolidone [Wan et al., 1984], a surfactant [Shi et al., 1995] or lipid films [CoUman and Boulatov, 2002] on electrode surfaces has been studied. The major advantages of diluting a metalloporphyrin in an inert film include the abUity to study the catalytic properties of isolated molecules and the potentially higher surface loading of the catalyst without mass transport Umit-ations. StabUity of catalysts may also improve upon incorporating them into a polymer. However, this setup requires that the catalyst have a reasonable mobUity in the matrix, and/or that a mobile electron carrier be incorporated in the film [Andrieux and Saveant, 1992]. The latter limits the accessible electrochemical potentials to that of the electron carrier. 

Simple Fe porphyrins whose catalytic behavior in the ORR has been smdied fairly extensively are shown in Fig. 18.9. Literature reports disagree substantially in quantitative characterization of the catalytic behavior overpotential, stability of the catalysts, pH dependence, etc.). It seems plausible that in different studies the same Fe porphyrin possesses different axial hgation, which depends on the electrolyte and possibly specific residues on the electrode surface the thicknesses and morphologies of catalytic films may also differ among studies. AU of these factors may contribute to the variabUity of quantitative characteristics. The effect of the supporting surface on... 

The apparent redox stoichiometry of O2 reduction catalysis [ av. Reaction (18.8)] is pH-independent, but for many catalysts depends strongly on the applied potential (Fig. 18.10). The apparent selectivity of Fe porphyrins deposited on the electrode surface typically increases with the amount of deposited catalyst. 

Figure 18.11 Plausible catalytic cycle for the ORR by simple Fe porphyrins adsorbed on the electrode surface and side Reactions (18.15)-(18.18). At pH < 3, the resting state of the catalyst is assumed to be ferric-aqua.

A silica gel containing 3-imidazole propyl groups bonded to surface atoms of silicon has been prepared (253), and was treated 254) with a solution of Fe(TPP)L2, where L = py or pip, where upon the iron(II) porphyrin became attached to the imidazole groups on the surface of the gel,... 

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