Metalloporphyrin films

While much work has been done for the detection of nonligating organic odorants, detection of metal-ligating vapors via array-based sensing has been less explored. Included in this class of analytes are noxious ligands such as amines, phosphines and thiols, as well as more toxic substances, for example, nerve toxins such as Tabun. Due to their synthetic versatility and excellent chemical and thermal stability, metalloporphyrins are a natural choice for the detection of such species. Natale and coworkers have utilized metalloporphyrin films in piezoelectric-sensing arrays, where they have shown some success in detection of ligating vapors and determination of food quality. 

Macor, K.A. and T.G. Spiro (1984). Oxidative electrochemistry of electropolymerized metalloporphyrin films. J. Electroanal. Chenu 163, 223-236. 

Several authors have also reported the potential use of electropolyme-rized metalloporphyrin films as new electrode materials for anion detection and pH measurements. For example, Daunert et al reported that anion-selective membrane electrodes can be prepared by electropolymerizing aniline-substituted cobalt tetraphenylporphyrin complexes onto a glassy carbon surface. It was shown that the resulting electrodes are highly selective towards the detection of thiocyanate and nitrite anions. The mechanism by which these metalloporphyrin electrode sensors operate is probably related to the well-known axial complexation capability of the central metal cation of the porphyrin towards different kind of anions and bases. The same authors also reported a detection limit of 5 x 10 M for these ion-selective electrodes which have lifetimes of more than 2 months... 

Electrochemical oxidation of NO at the surfaces of novel electrode materials (e.g., platinum, gold, glassy carbon, carbon fiber) is known to be kinetically slow. However, accelerated electron-transfer kinetics of NO oxidation have been reported for a variety of chemically modified electrodes with polymeric metalloporphyrin films (11,12) and platinized Pt (13). These electrodes require less positive potentials for NO oxidation to nitrate ( 0.65-0.75 V vs. Ag/AgCl) and generate higher current (5-10 fold) than bare metal electrodes. 

Yeh CY, Cheng SH (2003) Electropolymerization of metalloporphyrin films for catalytic reduction of dioxygen. Tamkang J Sci Eng 6 81-86... 

Di Natale C, Buchholt K, Martinelli E, Paolesse R, Pomarico G, D Amico A, Lundstrom I, Lloyd Spetz A (2009) Investigation of quartz microbalance and ChemFET transduction of molecular recognition events in a metalloporphyrin film. Sens Actuators B 135 560-567... 

METALLOPORPHYRIN FILMS ON SOLID ELECTRODES REFLECTANCE SPECTROSCOPY AND AC IMPEDANCE STUDIES IN AQUEOUS AND NONAQUEOUS MEDIA... 

Electrochemical polymerization offers particular advantages in that polymerized porphyrins can form electroactive, adherent and stable films on solid electrodes. Oxidative electropolymerization of several porphyrins and metalloporphyrins have been reported . Special focus has been placed on amino-substituted porphyrins due to the propensity of aniline to form electroactive polymers. Murray et al. reported on the electropolymerization of tetrakis(o-aminophenyl)porphyrin and several para-, ortho-, and meta-substituted tetrakis(aminophenyl)porphyrins with Co as a central metal s. They found that poly-Co(o-NH2)TPP films are effective catalysts for the electroreduction of oxygen in aqueous solution. Metalloporphyrin films on solid electrodes have been mainly characterized by voltammetry and resonsance Raman spectroscopy. The electrochemistry of ruthenium paradiethylamino substituted tetraphenylporphyrins recently have been investigated . This study reports the ac impedance and UV-visible reflectance spectroscopic studies of paradiethylamino substituted tetra-phenylporphyrin films formed via an oxidative electropolymerization process. 

Table 2. Peak Potentials for Electroreduction of Dioxygen (O2 Saturated Solution of 0.5 M H2SO4 or 1 M NaOH) on Various Metalloporphyrin Films... 

This study presents evidence to show that M(p-Et2N)TPP and MT([2.2]PCP)P can undergo oxidative polymerization leading to film formation on platinum electrodes. Stable adherent metalloporphyrin films thus formed show good electroactivity over substantial thicknesses (over 800 monlayer equivalents) and are stable in most common nonaqueous solvents as well as in aqueous solution. UV-visible diffuse reflectance spectroscopy shows M(p-Et2N)TPP polymeric films can be reversibly reduced to form dications and cation radicals. 

Metalloporphyrin Films on Solid Electrodes Reflectance Spectroscopy and AC Impedance Studies in Aqueous and Nonaqueous Media... 

Most studies of ORR catalysis by metalloporphyrins have been carried out using water-insoluble catalysts absorbed on a graphite electrode in contact with aqueous solution. In a limited number of cases, four other approaches have been used catalysts imbedded in an inert film (i.e., Nafion or lipid) on the electrode surface self-assembled monolayers of catalysts catalysts in aqueous or mixed organic/aqueous solutions in contact with an electrode and catalysis in mixed aqueous/organic medium using... 

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. 

Relatively little work has been done on ORR catalysis by self-assembled mono-layers (SAMs) of metalloporphyrins. The advantages of this approach include a much better defined morphology, structure, and composition of the catalytic film, and the surface coverage, and the capacity to control the rate at which the electrons ate transferred from the electrode to the catalysts [CoUman et al., 2007b Hutchison et al., 1993]. These attributes are important for deriving the catal5d ic mechatfism. The use of optically transparent electrodes aUows characterization of the chemical... 

So far, certain biomimetic catalysts (1 and 2b in Fig. 18.17) have been shown to reduce O2 to H2O under a slow electron flux at physiologically relevant conditions (pH 7,0.2-0.05 V potential vs. NHE) and retain their catalytic activity for >10" turnovers. Probably, only the increased stability of the turning-over catalyst is of relevance to the development of practical ORR catalysts for fuel cells. In addition, biomimetic catalysts of series 1,2,3, and 5, and catalyst 4b are the only metalloporphyrins studied in ORR catalysis with well-defined proximal and distal environments. For series 2, which is by far the most thoroughly studied series of biomimetic ORR catalysts, these well-defined environments result in an effective catalysis that seems to be the least sensitive among all metalloporphyrins to the electrode material (whether the catalyst is adsorbed or in the film) and to chemicals present in the electrolyte or in the O2 stream, including typical catalyst poisons (CO and CN ). 

Wang E., Meyerhoff M.E., Anion selective optical sensing with metalloporphyrin-doped polymeric films, Anal. Chim. Acta 1993, 283 673. 

Porphyrin-based self-assembled molecular squares 389 can form mesoporous thin films in which the edge of a square, thus the size of the cavity, can be adjusted by appropriate choice of substituents [8]. Fibers that form coil-coiled aggregates with distinct, tunable helicity are built from crown ethers bearing porphyrins 390 [9]. In addition to the porphyrin applications discussed in Sections 6.3.2.2 and 6.4, dendrimer metalloporphyrins 391 to be applied in catalysis [10] and the water-soluble dendritic iron porphyrin 319 modelling globular heme proteins [11] can be mentioned. 

Zinc-5,10,15,20-tetraphenylporphyrin (ZnTPP) has been used as a coating material in ammonia sensors by immobilizing it on the surface of silicone rubber. Absorbance and fluorescence emission were the modes of detection. A spectral change is caused by the coordination of NH3 molecules to the Zn11 ion in the immobilized metalloporphyrins. Sensing films made from the ZnTPP immobilized in silicone rubber were found to be the most sensitive for NH3 sensing (20). 

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. 

In the most important series of polymers of this type, the metallotetraphenylporphyrins, a metalloporphyrin ring bears four substituted phenylene groups X, as is shown in 7.19. The metals M in the structure are typically iron, cobalt, or nickel cations, and the substituents on the phenylene groups include -NH2, -NR2, and -OH. These polymers are generally insoluble. Some have been prepared by electro-oxidative polymerizations in the form of electroactive films on electrode surfaces.79 The cobalt-metallated polymer is of particular interest since it is an electrocatalyst for the reduction of dioxygen. Films of poly(trisbipyridine)-metal complexes also have interesting electrochemical properties, in particular electrochromism and electrical conductivity.78 The closely related polymer, poly(2-vinylpyridine), also forms metal complexes, for example with copper(II) chloride.80... 

Abstract Pressure-sensitive paint (PSP) is applied to the areodynamics measurement. PSP is optical sensor based on the luminescence of dye probe molecules quenching by oxygen gas. Many PSPs are composed of probe dye molecules, such as polycyclic aromatic hydrocarbons (pyrene, pyrene derivative etc.), transition metal complexes (ruthenium(II), osumium(II), iridium(III) etc.), and metalloporphyrins (platinum (II), palladium(II), etc.) immobilized in oxygen permeable polymer (silicone, polystyrene, fluorinated polymer, cellulose derivative, etc.) film. Dye probe molecules adsorbed layer based PSPs such as pyrene derivative and porphyrins directly adsorbed onto anodic oxidised aluminium plat substrate also developed. In this section the properties of various oxygen permeable polymer for matrix and various dye probes for PSP are described. 

PtOEP is widely used as a PSP probe among the metalloporphyrins. The absorption and emission maximum of PtOEP are 381 and 535, and 646 nm, respectively. For examples of PSPs based on the OEP metal complexes in silicone polymer films, PSPs based on the platinum or palladium OEP immobilized in poly(TMSP) film have been reported. Oxygen permeability of poly(l-trimethylsily-l-propyne) (poly(TMSP)) film is about ten times larger than that of poly(dimethylsiloxane) (poly(DMS)) film, and provides a tough and thin film [14,15]. The poly(TMSP) film is a porous polymer matrix with a high oxygen permeability and diffusion, indicating that the probe... 

The incorporation of vitamin B12 derivatives into plasticized poly(vinyl chloride) membranes has resulted in the development of several ion-selective electrodes (ISEs). The response of the electrodes has been related to principles of molecular recognition chemistry. In addition, ISEs have been prepared by electropolymerization of a cobalt porphyrin. These electrodes have selectivity properties that are controlled by both the intrinsic selectivity of the metalloporphyrin and the characteristics of the polymer film (e.g., pore size). 

Amao Y, Miyashita T, Okura I. Optical oxygen detection based on luminescence change of metalloporphyrins immobilized in poly(isobutylmetacrylate-co-trifluoroethylmeth-acrylate) film. Anal Chirn Acta 2000 421 167-74. 

SERS Studies on Metalloporphyrin Self-Assembled Films on Organic-Monolayer-Modified Substrates... 

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