Porphyrin-based membranes

This biological membrane system is ideal for porphyrin-based energy conversion systems. For energy storage by photoinduced vectorial charge separation, the elecfron must be removed faster from the excited porphyrin than about IG ps in order to avoid deactivation. Thereafter, the electron should be kept at a... 

The X-ray structural studies of the photosystem II reaction center of Rhodo-pseudomonas viridis and related aspects of plant membrane structure have been reviewed/ Photoinduced charge separation in synthetic, porphyrin-based molecules which mimic aspects of the natural photosystems have also been reviwed/ ... 

Metalloporphyrins, one carbon larger but structurally analogous to the corrin ring of vitamin B12, exhibited unique anion ionophore properties when incorporated into a polymer membrane. Mn(III), Co(III), Ru(II), and Sn(IV) porphyrin-based ion-selective sensors exhibit high selectivity for thiocyanate, nitrite/thiocyanate, thiocyanate and siicylate, respectively. doo-io7,i 10-114 nature of the... 

Table 4. Typical Selectivity Coefficients, Log y for the Uquid-Membrane Electrodes Based on Porphyrins and Quarternary Ammonium Salts (QAS)...

Meng H, Larouche N, Lefevre M, Jaouen F, Stansfield B, Dodelet J-P (2010) Iron porphyrin-based cathode catalysts for polymer electrolyte membrane fuel cells effect of NH3 and Ar mixtures as pyrolysis gases on catalytic activity and stability. Electrochim Acta 55 6450-6461... 

Based on the oxidation of AA by periodate. A new potentiometric periodate sensor is constructed to monitor this reaction. The selective membranes are of PVC with porphyrin-based sensing systems and a lipophilic cation as additive... 

Ruhlmann, L., Zimmermann, J., Fudicker, w., Roeder, B. and Fuhrhop, J.-H., Hydrophobic Membrane Gaps on Gold with a Fluorescing Porphyrin Base, J. Am. Chem. Soc.y submitted for publication. 

Brown DV, ChaniotaMs NA, Lee IH, Ma SC, Park SB, Meyerhoff ME et al (1989) Mn(III)— porphyrin-based thioeyanate-selective membrane electrodes characterization and application in flow injection detrmninatirai of thiocyanate in saliva. Electroanalysis 1 477-484... 

The anion optical sensor can also be fabricated with metalloporphyr-ins. For example, polymeric membranes doped with indium porphyrins and a lipophilic dichlorofluorescein derivative were shown to be very selective to chloride and acetate anions. The response mechanism is based on extraction of anions into the bulk organic film by indium porphyrins and a simultaneous coextraction of hydrogen ions. This results in protonation of the pH chromophore, and hence a change in the optical absorbance of the polymeric film. 

Most of the catalysts employed in PEM and direct methanol fuel cells, DMFCs, are based on Pt, as discussed above. However, when used as cathode catalysts in DMFCs, Pt containing catalysts can become poisoned by methanol that crosses over from the anode. Thus, considerable effort has been invested in the search for both methanol resistant membranes and cathode catalysts that are tolerant to methanol. Two classes of catalysts have been shown to exhibit oxygen reduction catalysis and methanol resistance, ruthenium chalcogen based catalysts " " and metal macrocycle complexes, such as porphyrins or phthalocyanines. ... 

Using a typical poly (vinyl chloride) (PVC)-based membrane with different ionophores - Zn-bis(2,4,4-trimethylpen-tyl) dithiophosphinic acid complex [450], protoporphyrin IX dimethyl ester [451], porphyrin derivative [452] and hemato-porphyrin IX [453], tetra(2-aminophenyl) porphyrin [454], cryptands [455, 456], 12-crown-4 [457], benzo-substituted macro-cyclic diamide [458], 5,6,14,15-dibenzo-l, 4-dioxa-8,l 2, diazacyclopentadecane-5,14-diene [459], and (A-[(ethyl-l-pyrrolidinyl-2 -methyl) ] methoxy-2-sulfamoyl-5 -benza-mide [460] - the sensors for zinc ions were prepared and investigated. The armed macrocycle, 5,7,7,12,14,14-hexamethyl-1,4,8,11 -tetraazacyclo tetradeca-4,11 -diene dihydrogen perchlorate was used for the preparation of polystyrene-based Zn(II)-sensitive electrode [461]. 

It was reported that cobalt-tetraphenylporphyrin complex (CoTPP) coated on an electrode catalyzes electrocatalytic proton reduction,215 but the activity was not very high. We have found that metal porphyrins and metal phtahlocyanines when incorporated into a polymer membrane coated on an electrode show high activity in electrocatalytic proton reduction to produce H2.22,235 Some data are summarized in Table 19.2. It was shown that this catalyst is more active than a conventional platinum base electrode. 

A tetraruthenated porphyrin was electropolymerised onto glassy carbon and used to catalyse the oxidation of nitrite to nitrate, with the resultant current giving a selective measure of the concentration of nitrite ion [81]. As an alternative method, soluble poly(3-octyl thiophene) [82] was cast along with tridodecylmethylammonium chloride onto glassy carbon, to give electrodes with superior selectivity over PVC-based membranes to lipophilic ions such as bromide or nitrate. 

Another mechanism of the transmembrane electron transfer in the system under discussion has been proposed by Khairutdinov and co-workers [60]. This mechanism assumes the two-quantum ionization of porphyrin dimer located in the inner membrane monolayer with the capture of the electron by MV2+ dication to be the primary redox photochemical process. However, this interpretation is based on the data obtained when studying vitreous suspensions of vesicles at 77 K, and further experiments seem to be needed to justify their applicability to liquid suspensions at ambient temperatures. 

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