Coordinative binding phthalocyanine

Electrochemical NO sensors based on platinized or electrocatalyst-modified electrodes often in combination with a permselective and charged membrane for interference elimination were proposed. Although the catalytic mechanism is still unknown, it can be assumed that NO is co or dinative ly bound to the metal center of porphyrin or phthalocyanine moieties immobilized at the electrode surface. The coordinative binding obviously stabilizes the transition state for NO oxidation under formation of NO+. Typically, sub-pM concentrations of NO can be quantified using NO sensors enabling the detection of NO release from individual cells. 

Soluble, swellable and macroporous chelate polymers with coordinative and covalent bonds (Chaps. 2, 3) may be prepared. Structure investigations are in most cases possible with conventional methods. The advantage of coordinative binding is the ease of preparation. But on the other side such a bond is not so strong when compared with a covalent one. So the application must decide between coordinative or covalent bond. Reversible binding of small molecules, catalysis and photoredox reactions may be important. Cheaper, easier to prepare and more stable phthalocyanines, oximes and Schiffbase chelates will find higher practical interest then porphyrins. 

The coordinative binding of cobalt phthalocyanines 48 with R = -COOH or R = -SO3H taking polymer ligands such as poly(ethyleneimine), poly(vi-nylamine), amino group-modified poly(acrylamide) or modified silica gel was reviewed some years ago [125,126]. 

For the coordinative binding of phthalocyanines at inorganic carriers, the surface has to be modified. In a one-step-procedure for the preparation of silica modified on the surface with imidazoyl-groups, different silica materials as mentioned before were treated with a mixture of 3-chloropropyltriethoxysilane and an excess of imidazole in m-xylene [equation (20)]. Following treatment with different kind of substituted cobalt phthalocyanines, naphthalocyanines and porphyrins 20-22 in DMF led to the modified silica as exemplarily shown with 20 (R = -H) for 31. The silica contains 0.8-12 imolg metal... 

The last category was concerned with miscellaneous subjects, while citing some chirogenic porphyrin-based systems. Representative reviews include chiral lanthanide complexes by Aspinall [41], coordination chemistry of tin porphyrins by Arnold and Blok [42], photoprocesses of copper complexes that bind to DNA by McMillin and McNett [43], nonplanar porphyrins and their significance in proteins by Shelnutt et al. [44], cytochrome P450 biomimetic systems by Feiters, Rowan, and Nolte [45] and phthalocyanines by Kobayashi [46,47]. 

A related imidazole-appended zinc(II) porphyrin linked via an ethynylphenyl unit to a magnesium(II) phthalocyanine has recently been reported [38], The imidazole group binds to the magnesium center to form a stacked dimer in noncoordinating solvents such as chloroform even at submicromolar concentration (<10-6M). Upon addition of dimethyl sulfoxide, the stacked dimer transforms to an extended dimer in which the imidazole group binds to the zinc center on the basis of the hard and soft acid and base principle. The extended dimer exhibits a much stronger fluorescence (by a factor of 28) compared with the stacked dimer, and this coordination-induced sliding motion has been found to be reversible. 

Similarly, the dipyridyl perylenediimide 45 also axially binds to zinc(II) 1,8, 15,22-tetrakis(2,4-dimethyl-3-pentoxy)phthalocyanine (25) to form the corresponding 1 1 and 1 2 supramolecular complexes [48], The coordination of these two compounds has been monitored by UV-Vis, fluorescence, and 1H NMR spectroscopic methods. It has been found that the ligation of pyridyl ligand to zinc phthalocyanine is relatively weak and labile with a binding constant of 2,080 M-1 in CDCI3. The two components can mutually quench the fluorescence of their partner through an electron transfer process. 

For the construction of artificial metalloproteins, protein scaffolds should be stable, both over a wide range of pH and organic solvents, and at high temperature. In addition, crystal structures of protein scaffolds are crucial for their rational design. The proteins reported so far for the conjugation of metal complexes are listed in Fig. 1. Lysozyme (Ly) is a small enzyme that catalyzes hydrolysis of polysaccharides and is well known as a protein easily crystallized (Fig. la). Thus, lysozyme has been used as a model protein for studying interactions between metal compounds and proteins [13,14,42,43]. For example, [Ru(p-cymene)] L [Mn(CO)3l, and cisplatin are regiospecificaUy coordinated to the N = atom of His 15 in hen egg white lysozyme [14, 42, 43]. Serum albumin (SA) is one of the most abundant blood proteins, and exhibits an ability to accommodate a variety of hydrophobic compounds such as fatty acids, bilirubin, and hemin (Fig. lb). Thus, SA has been used to bind several metal complexes such as Rh(acac)(CO)2, Fe- and Mn-corroles, and Cu-phthalocyanine and the composites applied to asymmetric catalytic reactions [20, 28-30]. 

Various fullerenes and C70) were coordinated to zinc(II) and mag-nesium(II) porphyrins via functionalized pyridines or imidazoles (Fig. 7) by D Souza and Ito [10-22]. Both single-point [10,11] and two-point [12-14] binding strategies were employed, together with additional covalent functionalization of the porphyrins with ferrocene (Fc) [10] or boron dipyrrin (BDP) [16]. Similar systems were also studied by Guldi, Diederich, Nieren-garten and Schuster, and the results on the intermolecular and supramolecu-lar photoinduced electron transfer (PET) processes of fullerene-porphyrin and phthalocyanine systems were reviewed recently [23,24]. Since PET is... 

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