Ionic porphyrin

Ion-association adsorption of water-soluble porphyrin was studied using time-resolved TIR fluorometry. Interfacial adsorption of anionic or cationic surfactants succeeded in attracting the oppositely charged porphyrin from the mixture of cationic and anionic porphyrins in the aqueous phase, tetrakis(sulphonatophenyl)porphyiin (TPPS) adsorbed with the hexadecyltrimethylammonium ion and tetrakis(iV-methylpyridyl)porphyrin (TMPyP) with the hexadecanesulfonate [44], In addition, it was found that the application of an external electric field across the interface enabled to control the interfacial ion-association adsorption of ionic porphyrin [45]. Furthermore, TIR Raman microspectroscopy revealed the interfacial concentration of meso-tetrakis(A -methylpyridyl) porphyrinato-manganese(III) (Mn(tmpyp) +) adsorbed with dihexadecyl hydrogenphosphate (DHP) at the toluene/water interface and also revealed that the orientation of the tilt angle was 65° from the interface normal [46]. 

As discussed in Section 4.1, the specific adsorption of the ionic porphyrins at the liquid/liquid interface manifests itself by changes in the distribution of ions at the interface as well as in the interfacial tension. However, these two parameters do not provide direct information on the organisation of the adsorbed species in terms of lateral interactions and average molecular orientation. These aspects will be reviewed in Section 4.2 based on SHG and photocurrent Ught polarisation anisotropy studies of metalloporphyrins at the polarised water/IX2E interface. 

Excess Charge Associated with the Specific Adsorption of Ionic Porphyrins... 

Figure 24 Tetrasulfonated porphyrin a water-soluble tetraan-ionic porphyrin.

Y. Saitoh and H. Watarai, Total internal reflection fluorometric study on the ion-association adsorption of ionic porphyrins at liquid-liquid interface. Bull. Chem. Soc. Jpn., 70, 351-358 (1997). 

The corresponding reactions of transient Co(OEP)H with alkyl halides and epoxides in DMF has been proposed to proceed by an ionic rather than a radical mechanism, with loss of from Co(OEP)H to give [Co(TAP), and products arising from nucleophilic attack on the substrates. " " Overall, a general kinetic model for the reaction of cobalt porphyrins with alkenes under free radical conditions has been developed." Cobalt porphyrin hydride complexes are also important as intermediates in the cobalt porphyrin-catalyzed chain transfer polymerization of alkenes (see below). 

Another iron porphyrin complex with 5,10,15,20-tetrakis(2, 6 -dichloro-3 -sulfonatophenyl)porphyrin was applied in ionic liquids and oxidized veratryl alcohol (3,4-dimethoxybenzyl alcohol) with hydrogen peroxide in yields up to 83% to the aldehyde as the major product [145]. In addition, TEMPO was incorporated via... 

Although the correlation between ket and the driving force determined by Eq. (14) has been confirmed by various experimental approaches, the effect of the Galvani potential difference remains to be fully understood. The elegant theoretical description by Schmickler seems to be in conflict with a great deal of experimental results. Even clearer evidence of the k t dependence on A 0 has been presented by Fermin et al. for photo-induced electron-transfer processes involving water-soluble porphyrins [50,83]. As discussed in the next section, the rationalization of the potential dependence of ket iti these systems is complicated by perturbations of the interfacial potential associated with the specific adsorption of the ionic dye. 

Because of its ionic size, cadmium(II) does not fit well into the coordination site of the porphyrin nucleus (N-centre distance 200 pm), and the complexes are readily demetalated (stability group IV, Tables land 2). The complexes can be prepared, of course, but zinc(II) compounds have been overwhelmingly favored for PDT purposes. 

A second example has been addressed in which the synthesis and potential application of a series of neutral O-glycosylated porphyrin dimers and two original O-glycosyl cationic dimers were examined in PDT. In order to understand the influence of the number of glycosyl moieties, the spatial geometry and the ionic character on their photodynamic activity was evaluated.144 The in vitro results... 

The method for electrosynthetic generation of (P)Rh(R) involves an initial formation of (P)Rh and is accomplished by the one electron reduction of an ionic Rh(III) porphyrin species(l4). The generated Rh(II) porphyrin can dimerize as shown in Equation 1 but, in the presence of an alkyl halide RX, will react to form (P)Rh(R). The overall reaction between RX and (P)Rh11 is given by Equation 3, where S is an electron source other than the electrode. 

The highly evolved catalyst 20 combines several features that have proved successful in simpler cases. The ionic sulfonate groups make the substrate sufficiently soluble for the reaction to be run in water. (The four hydrophilic cyclodextrins perform the same service for the catalyst.) The target reaction, the seledive oxidation of the steroid skeleton, goes back to the early days of enzyme models,1711 and the choice of porphyrin and of manganese as the metal cation are based on many years experience. The aryl groups are perfluorinated because an earlier version of the catalyst suffered self-oxidation. 

The precursor model of FAB applies well to ionic analytes and samples that are easily converted to ionic species within the liquid matrix, e.g., by protonation or deprotonation or due to cationization. Those preformed ions would simply have to be desorbed into the gas phase (Fig. 9.6). The promoting effect of decreasing pH (added acid) on [M+H] ion yield of porphyrins and other analytes supports the precursor ion model. [55,56] The relative intensities of [Mh-H] ions in FAB spectra of aliphatic amine mixtures also do not depend on the partial pressure of the amines in the gas phase, but are sensitive on the acidity of the matrix. [57] Furthermore, incomplete desolvation of preformed ions nicely explains the observation of matrix (Ma) adducts such as [M+Ma+H] ions. The precursor model bears some similarities to ion evaporation in field desorption (Chap. 8.5.1). 

Fe(edta) is sensitive to O2 but is a useful gentle reductant which, for example, unlike many reductants, does not attack the porphyrin ring in metal-porphyrin complexes. For the reactions of Co(tpps) and Co(tap) + with (excess) Fe(edta) , predict the rate vs [Fe(edta) ] profile, and the effect of ionic strength on any second-order rate constants for the two reactions. 

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