Encapsulated porphyrin

Figure 4.15 Encapsulated porphyrins in clay and zeolite structures.

Polymer vesicles are also suitable to transport and target imaging agents such as fluorescent dyes and paramagnetic contrast agents. Hammer and coworkers encapsulated porphyrin-based near-infrared (NIR) fluorophores into PBD-PEO... 

Future sensitisers for the brain must be tailored for cerebral lesions. The absorption must be, ideally, in the near-infrared range around 700 to 800 nm, which allows a penetration of up to 4 cm into the surrounding brain [21,33,40,81]. The use of carrier systems such as liposome-encapsulated porphyrins or phthalocya-nines or combination of AB conjugates with second or third generation sensitisers... 

Another promising example of a metal-based sensor can be seen in the work of Lee and Okura (239) who used entrapped platinum octaethylporphyrin complexes to form photostable devices. In their study, they found by adding the surfactant Triton X-100 to the sol-gel mixture, they could improve homogeneity and phosphorescence of the dye-containing glass. Encapsulated porphyrin molecules have also been used successfully in the sensing of nitrogen dioxide (240) and, as will be discussed below, can be used to sense metal ions. 

Deda DK, Budu A, Cruz EN, AraM K, Garcia CRS (2015) Strategies for development of antimalarials based on encapsulated porphyrin derivatives. Mini-Rev Med Chem 141055-1071... 

One example has used a manganese porphyrin and iodobenzene encapsulated within a dendrimer to bring about shape-selective epox-idation of alkenes. The important aspect of catalysts is that the reactants can move rapidly to the active site, and that the products can be removed rapidly from the active site and expelled from the dendrimer. 

Very few examples have been described for the non-covalent immobilization of chiral porphyrin complexes (Fig. 26). In the first case, the porphyrin-dichlororutheninm complex was encapsulated in silica, which was prepared around the complex by a sol-gel method [78], in an attempt to prevent deactivation observed in solution in the epoxidation of different alkenes with 2,6-dichloropyridine N-oxide. In fact, the heterogeneous catalyst is much more active, with TON up to 10 800 in the case of styrene compared to a maximum of 2190 in solution. Enantioselectivities were about the same imder both sets of conditions, with values aroimd 70% ee. 

Aida and Jiang recently reported an iron(II) porphyrin 1-methylimidazole complex covalently encapsulated within a large aryl ethereal dendrimer cage, as... 

Metalated container molecules can be viewed as a class of compounds that have one or more active metal coordination sites anchored within or next to a molecular cavity (Fig. 2). A range of host systems is capable of forming such structures. The majority of these compounds represent macrocyclic molecules and steri-cally demanding tripod ligands, as for instance calixarenes (42), cyclodextrins (43,44), and trispyrazolylborates (45-48), respectively. In the following, selected types of metalated container molecules and their properties are briefly discussed and where appropriate the foundation papers from relevant earlier work are included. Porphyrin-based hosts and coordination cages with encapsulated metal complexes have been reviewed previously (49-53) and, therefore, only the most recent examples will be described. Thereafter, our work in this field is reported. 

Fujita and coworkers have also reported the encapsulation of multimeric porphyrin assemblies in the box-shaped cavities of ternary Pd6 coordination cages. Two types of cofacial porphine dimers A and B could be stabilized (133). In the smaller [Pd6(L14)2(L15)6]12+ cage 29, whose diameter is 10.4 A (Fig. 21), two porphyrin molecules can be stackedo directly on top of each other with an interplane distance of 3.4 A. In the larger cage 30, an additional molecule of L14 is intercalated between the two porphyrin bases. All complexes were found to be water-soluble in contrast to other 7i-stacked porphyrin dimers. The encapsulation... 

One can conclude that PVA hydrogels represent an efficient encapsulation vehicle for the studied porphyrins, both water soluble and non-water soluble. Their biocompatible, biodegradable, non-toxic, and non-carcinogenic nature makes them especially effective for pharmaceutical applications, but also for environmental uses, such as advanced wastewater... 

B. T. Holland, C. Walkup, and A. Stein, Encapsulation, stabilization and catalytic properties of flexible metal porphyrin complexes in MCM-41 with minimal electronic perturbation by the... 

Recently, Kimura et al. have reported the encapsulation of electro chemically and photo chemically active groups such as a porphyrin unit (51) or a ruthe-nium(II) bis(terpyridyl) (52) unit in the interior of a 1,3,5-polyphenylene-based dendritic structure (Scheme 21). The dendritic porphyrins have been synthesiz-... 

The energetics of peptide-porphyrin interactions and peptide ligand-metal binding have also been observed in another self-assembly system constructed by Huffman et al. (125). Using monomeric helices binding to iron(III) coproporphyrin I, a fourfold symmetric tetracarboxylate porphyrin, these authors demonstrate a correlation between the hydropho-bicity of the peptide and the affinity for heme as well as the reduction potential of the encapsulated ferric ion, as shown in Fig. 12. These data clearly demonstrate that heme macrocycle-peptide hydrophobic interactions are important for both the stability of ferric heme proteins and the resultant electrochemistry. 

The most elegant example which demonstrates this aspect of proton transfer equilibrium of heme proteins is the study reported on six coordinated aqua (pyridine) iron(III) porphyrin complexes encapsulated in aqueous micelles [27]. The ferric ion in these complexes is axially co-ordinated to a water and a pyridine molecule, thus having a coordination geometry similar to that of the heme in metmyoglobin. The pH dependence of the absorption spectra of the... 

The diaqua and aqua (hydroxo) hemin complexes encapsulated in the micelles [20] are found to be high-spin (peff = 5.7 — S.Sps). Their high-spin nature is further confirmed from the ESR spectra at 4.2 K (Fig. 4). The spectra are characteristic of high-spin ferric porphyrins with a large zero-field-split Ai ground state with Mg = 1/2 lying lowest. The spectra are axially symmetric (gf = 2.05, = 6.0) for the diaqua complex, while for the aqua (hydroxo)... 

The HNMR spectra of the diaqua and aqua (hydroxo) hemin complexes encapsulated in micelles have been reported [20] (Fig. 5). The heme methyl resonances in the diaqua species lie in the same region as those of the high-spin bis(dimethyl sulphoxide) iron (III) porphyrin complex [37-39], while those of the aqua (hydroxo) complex appear in a more upheld region. The positions and linewidths of the heme methyl resonances in these complexes are similar to those observed in the aqua and hydroxo hemoproteins [19,40]. The broadness of the ring methyl resonances of both the diaqua and aqua (hydroxo) species in micelles has been ascribed to arise from the hindered rotational tumbling motion of the heme inside the micelles. The spread and linewidth of these resonances are much larger than those of similar high-spin model heme complexes in simple solution [3]. 

The dithionite reduction of the micelle encapsulated aqua (hydroxo) ferric hemes at pH 10 (in inert atmosphere) gives an iron (II) porphyrin complex whose optical spectrum [21] shows two well-defined visible bands at 524 and 567 nm and a Soret band split into four bands (Fig. 10). Such spectral features are typical of four-coordinate iron (II) porphyrins. The magnetic moment (p = 3.8 + 0.2 Pb) of this sample in the micellar solution is also typical of intermediate spin iron(II) system and is similar to that reported for four-coordinate S = 1 iron(II) porphyrins and phthalocyanine [54-56]. The large orbital-contribution (ps.o. = 2.83 p for S = 1) observed in this iron(II) porphyrin... 

The micelle-encapsulated six coordinated bis(pyridinato) iron(II) complexes of protoporphyrin and OEP have been reported by addition of pyridine to the four coordinate ferrous complex in aqueous micellar solution. The optical spectrum of [Fe(II)(PP)(Py)2] in micelle (Fig. 10) is identical to S = 0 six-coordinate bis(pyridinato) iron(II) porphyrin complex [3]. The magnetic moment measurements in solution confirm their diamagnetic nature. The HNMR spectra are also characteristic low-spin iron(II) resonances (S = 0) with shifts lying in the diamagnetic region (Table 2). 

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