Water-Soluble Porphyrin Complexes

The syntheses, and especially the purification, of water-soluble porphyrin complexes are often different from the above-mentioned methods, and experimentally more difficult, because of the salt-like character of the compounds. Thus, besides the reaction conditions, some notes on the workup are given. Some papers do not specify the counter ions neutralizing the charge of the respective metalloporphyrin. In such cases, just the respective ion of the porphyrin complex is noted. The porphyrin systems involved are specified in Table 1. 

For the preparation of an uroporphyrin-I derivative of the composition RuCO(Uro-I)H20, Uro-I octamethylester was metallated with Ru3(CO)12 in xylene and saponified with NaOH [128]. 

Iridium - The authors are not aware of any water-soluble iridium porphyrin. 

Silver - Na4[Ag(TPPS4)] was obtained by stirring a suspension of Ag20 in a solution of Na4[H2(TPPS4)] in water at room temperature. The excess metal carrier was separated from the product by filtration [139], Using AgOAc for the 

Gold - Water-soluble gold porphyrin ions, [Au(TPPS4)]3 and [Au(TMPyP)]5+ (as the 3- and 4-pyridyl isomers), were obtained from the respective free-base porphyrins in a mixture of water/pyridine/lithium chloride containing KAuCl4 [142]. The products were purified by extraction with acetone and methanol and subsequent HPLC, however, the counterions were not determined. 

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This chapter deals with the provision of suitable starting materials for investigations in the noble metal porphyrin field (Sects. 2.1-2.4) and the establishment of their structures (Sect. 2.5). Most of these investigations are devoted to complexes with synthetic porphyrin ligands which are soluble in organic solvents [e.g. (OEP)- or (TPP) complexes Sect. 2.1]. Special mention is made to some novel porphycene derivatives (Sect. 2.2), to phthalocyanine systems (Sect. 2.3), and to water-soluble porphyrin complexes (Sect. 2.4). 

Photophysics and photochemistry of kinetically labile, water-soluble porphyrin complexes 06CCR(250)1792. 

Anation of the water-soluble porphyrin complex [Co(P)(OH2)2l [H2P = 5,10,15,20-tetrakis-(A -methylpyridyl)porphine] is very fast for a substitution reaction at cobalt(ra). Rate data are also reported for the anation of the [Co(P)(NCS)-(0H2)] + and [Cb(P)(NCS)(OH)] + ions, and thiocyanate ion is shown to have a strong trans effect (> 10 ) upon the remaining co-ordinated water molecule. Omitting charges for convenience, rate data for the following reactions were as shown ... 

Cobalt(II) complexes of three water-soluble porphyrins are catalysts for the controlled potential electrolytic reduction of H O to Hi in aqueous acid solution. The porphyrin complexes were either directly adsorbed on glassy carbon, or were deposited as films using a variety of methods. Reduction to [Co(Por) was followed by a nucleophilic reaction with water to give the hydride intermediate. Hydrogen production then occurs either by attack of H on Co(Por)H, or by a disproportionation reaction requiring two Co(Por)H units. Although the overall I easibility of this process was demonstrated, practical problems including the rate of electron transfer still need to be overcome. " " ... 

While the control resins were deep red in color due to the presence of soluble porphyrin complexes, the methacrylate resins obtained after removal of the polyethylene-supported catalysts varied from light yellow to nearly water-white (APHA < 25). UV-Vis spectrophotometric analysis of the yellow resins indicated an absorption signal for the cobalt porphyrin complex Soret band (wavelength of cobalt(ll) porphyrin species appears at -415 nm free porphyrin ligand is formd at -423 tun). Resin samples that visttally appear as water-white show little or no porphyrin species present in the spectrum. Measured catalyst activity and PDl of the polyethylene-supported porphyrin complexes are in the expected range for soluble porphyrin CCT catalysts (PDl = M /Mn - 1.2- 2.0)." The screening resrrlts clearly... 

Laverman and coworkers have reported activation parameters for the aqueous solution reactions of NO with the iron(II) and iron(III) complexes of the water soluble porphyrins TPPS andTMPS (21). These studies involved systematic measurements to determine on and kQ as functions of temperature (298—318 K) and hydrostatic pressure (0.1—250 MPa) to determine values of AH, AS and AV for the on and off reactions of the ferri-heme models and for the on reactions of the ferro-heme models (Table II). Figure 2 illustrates hydrostatic pressure effects on kOTL and kQff for Fem(TPPS). 

With regard to the pressure effects, we have, as usual, been interested in systems that are not simple. One system we have been looking at involves water-soluble porphyrins. Actually, the only reactions we have studied thus far involve the iron(III) and manganese(III) tetra(4-N-methylpyridyl)porphyrin complexes. These complexes are in the form of tosylate salts, which causes some problems. The rate constants are on the order... 

The combination of cationic (TTAP) and anionic (TPPS) water soluble porphyrins also leads to the formation of a stable 1 1 complex [TIAP/TPPS] ( ) It is evident that dimerization is promoted by electrostatic interaction between the oppositely charged substituents. It is likely, therefore, that a face-to-face dimer is formed. EPR spectra of the [CuTTAP/CuTPPS] dimer indicate that the Cu-Cu distance is larger than 0.6 nm. 

Ligand substitution kinetics on water-soluble porphyrins have been measured.18,105 106 The Co111 ion of the porphyrin exchanges axial ligands several orders of magnitude more readily than do simple amine or aqua complexes. Relatively low ligand discrimination ratios and positive activation entropies support a dissociative mechanism (equation 18, Table 7). 

Implementation of a crown ether unit in water-soluble pyridinium-substituted porphyrins leads to new peptide receptors of hitherto unknown sensitivities. The Soret bands in these complexes provide for a conveniently measurable and highly sensitive optical signal, which can be of importance for the development of new sensors. A series of water-soluble porphyrins were synthesized in order to test their... 

Hydrated electrons react with certain water-soluble metalloporphyrin complexes, reducing the porphyrin ligands to pi-radical species. When the metal centers are Zn(II), Pd(II), Ag(II), Cd(II), Cu(II), Sn(IV), and Pb(II), the radical complexes are produced at diffusion-controlled rates and decay with second-order kinetics.188 Fe(III) porphyrins, on the other hand, yield Fe(II) porphyrins.189 Rather different behavior is seen in the reaction of e (aq) with [Ru(bpy)3]3 + here, parallel paths generate the well-known luminescent excited-state [ Ru(bpy)3]2 + and another reduced intermediate, both of which decay to the ground-state [Ru(bpy)3]2+, 190 In a direct demonstration of the chemical mechanism of inner-sphere electron transfer, [Coni(NH3)5L]2+ complexes where L = nitrobenzoate and dinitrobenzoate react with e (aq) to form Co(III)-ligand radical intermediates, which then undergo intramolecular electron transfer to yield Co(II) and L.191... 

The following topics have not been considered in this section metal complexes of sulfonated 2,2 -bipyridine [43] and alizarin [44], water-soluble porphyrins and cy-dopentadienyl ligands [45], and metal complexes of sulfonated phenanthroline derivatives [46], Also P,N-bidentate phosphines [47], of which coordination properties await further study, have not been discussed here. 

Much of the research devoted to catalytic oxidations mediated by metal complexes of water-soluble ligands falls into the category of biomimetic oxidations. Hence, water-soluble porphyrins and the structurally related phthalocyanines have been... 

Martin, M. T Prieto, 1.. Camacho, L Miibius, D. (1996). Partial stacking of a water soluble porphyrin in complex monolayers with insoluble lipid, Lanfimuir, 12 6554. 

M. Faraggi, P. Peretz, and D. Weintraub, Chemical Properties of Water-Soluble Porphyrins. 4. The Reaction of a Picket-Fence-Like Iron(IIl) complex with the Superoxide Oxygen Couple, Int. J. Radiat. Biol., 49 (1986) 951. 

BW Gregory, D Vaknin, TM Cotton, WS Struve. Interfacial complexation of phospholipid Langmuir monolayers with water-soluble porphyrins and phthalocyanines an X-ray reflectivity study. Proceedings of Seventh International Conference on Organized Molecular Films, Numana, Italy, 1996, pp 849-853. 

Encounter Complexes. A major part of the data to be discussed refers to water soluble porphyrins with peripheral charges. In TMPyP and TPPS4 the charged groups are unable to form inner-sphere complexes with M(z). On the other hand, TPyP and uroporphyrin carry pyridyl and carboxylic groups, respectively. 

With fully water-soluble porphyrins, the metal-incorporation rate has been found to be first order in free base, metal, and anion. However, it has been suggested that during incorporation of metals in poorly soluble porphyrins, which would correspond to the situation of polymeric porphyrins, intermediate ( sitting-atop complexes) can be formed. Incorporation kinetics were suggested to be second order in metal and first order in porphyrin. The number of monolayers of polymeric porphyrins occupied by Ni(II) increases with its initial concentration. At trace concentration levels, film thickness is not important because only the first few layers are occupied, and the analyte signal does not depend on film thickness. The concentration levels (10 -10 M) and preconcentration times (40-100 seconds) are not sufficient to exceed the film capacity of monolayer film to incorporate Ni(II). However, for high Ni(II) concentra-... 

Supramolecular spherical assemblies of NPs with photoresponsive adhesion/dispersal behaviour were also obtained in a ternary system hierarchically combining the host-guest interaction of different types of CDs toward porphyrin and azobenzene. The inclusion complexation of an azobenzene modified water soluble porphyrin (1) with phthalo-cyanine-grafted permethyl (3-CDs (2) could be reversibly cross-linked to relatively larger nanospheres with naphthyl bridged bis(a-CD)s (3). The large spheres (12 -3) turned reversibly to small-sized particles (1 2) upon photoisomerization of the azoaromatic group in 1 (Fig. 13). 

The interfacial reactivity of metalloporphyrins and chlorins is critically determined by their specific adsorption at the liquid/liquid junctions. The affinity of the water-soluble porphyrins for these interfaces is associated with their complex solvation structure arising from the hydrophobic central ring and peripheral ionisable groups. This chapter will also feature a brief overview on recent studies of the molecular organisation of water-soluble porphyrins as probed by a variety... 

Kostas, I.D., Coutsolelos, A.G., Charalambidis, G. and Skondra, A. (2007) The first use of porphyrins as catalysts in cross-couphng reactions a water-soluble palladium complex with a porphyrin ligand as an efficient catalyst precursor for the Suzuki-Miyaura reaction in aqueous media under aerobic conditions. Tetrahedron Lett., 48, 6688-91. 

Reduction of the water-soluble porphyrin tetrakis-(4-iV-methylpyridyl)porphine-cobaIt(m), Co(TMpyP), is achieved with dithionite at pH 8. Addition of an excess of dithionite initially causes a reversible shift in the Soret band followed by its irreversible disappearance, implying that the first reduction step occurs at the metal site and that the metalloporphyrin remains intact but that, in a subsequent step, the porphyrin ring system itself is reduced. This is consistent with the kinetic results which have a half-order dependence on dithionite, suggesting that the reactive reductant might be the SOg" radical, a one-electron reducing agent. This is the sole reaction with the diaquo and bis(pyridine) complexes of Co(TMpyP), with rate constants 3.1 x 10 and 2.9 x 10 1 mol s (T = 25 °C, I = 0.5 mol 1 ) respectively, whereas for the aquohydroxo-derivative direct reaction with dithionite is also observed,... 

Miscellaneous Metal Ions.—Mention has been made already of a relatively slow formation reaction for the normally labile manganese(ii) ion. Incorporations of the labile bivalent metal ions zinc(ii), copper(ii), manganese(n), cobalt(ii), and nickel(n) into water-soluble porphyrin molecules such as tetrakis-(4-N-methyI-pyridyl)porphine, tetrasulphonated tetraphenylporphine, and uroporphine are also relatively slow reactions. However, by taking into account the porphyrin deformation which is necessary, an Id mechanism can be fitted to these reactions. The rates of formation and dissociation of nickel(ii), copper(n), cobalt(ii), and zinc(ii) complexes of the sterically hindered ligand 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetra-decane (Meicyclam) are also 10 —10 smaller than is normal for these metal ions. ... 

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