Anion sensing porphyrin

Figure 11.5 Schematic of anion sensing porphyrin Au MMPC. Reprinted with permission from Ref. 26.

E. Wang, C. Romero, D. Santiago and V. Syntilas, Optical anion sensing characteristics of indium-porphyrin and lipophilic dichlorofluorescein doped polymer films, Anal. Chim. Acta, 433 (2001) 89-95. 

A = 430, 440 nm) with HS04. Electrochemical studies displayed cathodic shifts in the [Cp2Co]/[Cp2Co] redox couple of 35-75 mV on addition of Gl or HS04, and 225 mV for H2P04. Smaller shifts were seen in the porphyrin oxidation wave. It should be noted that these anion-sensing effects are specific to the m-a,a,a,a-atropisomer. 

Beer. P.D. Drew, M.G.B. Hesek. D. Jagessar. R. Spectral and electrochemical anion sensing by a novel 5,10,15,20-tetrakis(R-substituted) porphyrin receptor (R-C6H4NHC(0)C5H4CoC5H5+PF6 ). Chem. Commun. 1995, 11, 1187. 

While detection of cations via porphyrin-ba.sed materials has been explored less than anion sensing, the ability of a porphyrin to coordinate different metals and the unique spectral signatures that result form the basis for metal ion detection. Use of free-base porphyrins in polymer matrices has allowed for the detection of heavy metal ions by Ache et Immobilization of 5,10,15,20-tetrakis(4-N-methylpyridyOporphyrin on Nafion membranes pennitted detection of cadmium and mercury in solution with detection limits of 5 X 10 M and 2 x 10 M, respectively over a 20-minute measuring period. The method is subject to interferences from other metal ions, but the researchers were able to detect several ions simultaneously using pattern-recognition techniques such as principal component analysis. Sol-gel films doped with 5,l0,l5,20-tetra(p-sulfonatophenyDporphyrin have also been used by Ache and coworkers for the fluorimetric determination of mercury in solution, with a detection limit of approximately 7 X 10... 

Structural types for organometallic rhodium and iridium porphyrins mostly comprise five- or six-coordinate complexes (Por)M(R) or (Por)M(R)(L), where R is a (T-bonded alkyl, aryl, or other organic fragment, and Lisa neutral donor. Most examples contain rhodium, and the chemistry of the corresponding iridium porphyrins is much more scarce. The classical methods of preparation of these complexes involves either reaction of Rh(III) halides Rh(Por)X with organolithium or Grignard reagents, or reaction of Rh(I) anions [Rh(Por)] with alkyl or aryl halides. In this sense the chemistry parallels that of iron and cobalt porphyrins. 

A tetra-cobaltocenium receptor 4 has been synthesised that is supported by a porphyrin skeleton [9]. This exhibits parallel photo- and electrochemical sensing of anions with a trend in selectivity of Cl >Br NOg. Proton NMR titrations in CD3CN showed chloride and bromide to be bound in 1 1 stoichiometry with stability constants of 860 and 820 M"1, respectively, whereas nitrate exhibited weaker binding with K=190 M"1. In the UV-vis spectrum of 4 in acetonitrile solution the Soret band (Amax=425 nm) of the porphyrin was signif-... 

Compared to systems based on a single interaction, cooperative sensors based on multiple, concerted, inter-molecular interactions between the components exhibit higher discrimination capabilities and enhanced functions. As examples for this class of sensors, two systems, both based on the absorption/luminescence properties of the porphyrin nucleus are illustrated in Fig. 5. Structure (a) represents a ditopic receptor where cooperative binding of a cation by the amide-appended calixarene and of an anion by the Zn-porphyrin allows recognition of complete binary metal salts. Structure (b) incorporates two cyclodextrin cavities and relies on the modification of the Fe(III) complex spectroscopic properties by inclusion of guests in these hydrophobic sites.This species is able to sense the presence of benzylmercaptane and 1-adamantanecarboxylate in four... 

A new class of ferrocene (also cobaltocenium) receptors which sense anions both spectrally and electrochemically, is based upon attachment of metallocene moieties to a porphyrin skeleton. The porphyrin fragment can be simultaneously complexed by zinc [120]. 

Combined physical/supramolecular methods have also been applied for the organization of porphyrins. The layer-by-layer method,based on alternating electrostatic assembly of materials, has been used to assemble porphyrins (Figure 7), and their potential as sensing elements was assessed. Also, porphyrinoids such as N-confused porphyrins have been incorporated in LB films and used as a selective sensor for iodide anions based on the incorporation of these anions in the LB films upon their transfer to a substrate. In that work, only iodide anions formed a stable... 

As noted earlier, reduced zinc(II) and copper(Il) porphyrins behave as aromatic anion radicals in the sense that the representative pdnts follow the same activation vs. driving force line as the aromatic anicm radicals. 

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