Porphyrin-based Receptors

This strong binding ofaxial ligands was beneficially used in the epoxidation of alkenes with porphyrin clip Mnll as a catalyst, since only one equivalent of added pyridine sufficed to give a fully ( 99+%) coordinated Mnll-pyridine complex The resulting catalyst appeared to be highly active in the epoxidation of alkenes in a biphasic system 

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Use of porphyrin-based receptors for sugar recognition provides some advantages because the sensitive probing ability of porphyrins greatly helps in the detection of interaction with carbohydrates, which are, in general, spectroscopically poor substrates. 

Recognition of quinones by porphyrin-based receptors has attracted interest since poiphyrins and quinones form an electron-transfer redox pair in metabolic processes. Particularly interesting is the binding of quinone to poiphyrin via noncovalent forces to regulate electron-transfer reactions. Table 5 lists the binding constants of quinones. 

Recently, Takeuchi and coworkers [37] reported the use of molecular imprinting for constructing a highly specific porphyrin-based receptor site. 9-Ethyladenine [37] was chosen as the imprint molecule. Two different functional monomers were utilized to bind 58 during the polymerization process, methacrylic acid (MAA) and a polymerizable zinc-porphorin derivative, 59 (P-53), as shown in Fig. 20. Reference polymers imprinted with 56 were fabricated using either 59 or MAA (P-54 and P-55, respectively) and corresponding nonimprinted, blank polymers were prepared using MAA and 59, MAA, or 57 as functional monomers to form polymers P-56, P-57, and P-58, respectively (Fig. 21). 

Porphyrins and expanded porphyrins as receptors for carbon nanostructures. Here, specific emphasis is placed on the design of porphyrin-based receptors that are optimized for interaction with carbon-rich surfaces and the tools that are used for the analysis of the resulting complexes. As is true throughout the chapter, key concepts are illustrated through the use of recently published, notable examples. 

Another tripod-type, porphyrin-based receptor is 10. This system, characterized by flexible linkers, was readily synthesized through a one-step click reaction of an azide-functionalized porphyrin with a tertiary amine functionalized with three alkynyl groups. The resulting tripod system can capture a pyridine-functionalized fullerene with 1 1 stoichiometry. The corresponding association constant, K, was found to be 9.4 x 1(1 in o-dichlorobenzene as determined from UV-vis spectroscopic titrations. The supramolecular dyad formed via this capture event was then found capable of undergoing photoinduced ET from the zinc porphyrin to the fullerene with a charge-separated lifetime of 0.5 ns. ... 

GUday LC, White NG, Beta- PD (2013) Halogen- and hydrogen-bonding triazole-functionalised porphyrin-based receptors fin anion recognition. Dalfim Trans 42 15766... 

Porphyrin-based diboronic acids as artificial receptors for saccharides 98YGK831. 

Porphyrin-based synthetic receptors for ubiquinone and cytochrome C 98YGK745. 

Addition of cytochrome c to solutions containing some of our TPP-based receptors resulted in quenching of porphyrin fluorescence emission (Ex = 420, Em = 650 mn). In contrast, titrations with tetracationic /w-tetrakis-(4-trimethylaminophenyl) porphyrin (11,TTMAPP) and cationic TPP-based receptor 10 showed no quenching even at high concentrations. This demonstrates the clear preference for anionic species by the cationic cytochrome c recognition surface, in agreement with previously reported studies. 

Bipyridine- and porphyrin-based metal complexes as receptors for anions 03CCR(240)77. 

Figure 24. Structures of the water-soluble porphyrin-based peptide receptors.

Kuroda Y, Kato Y. Chiral amino acid recognition by a porphyrin-based artificial receptor. J Am Chem Soc 1995 117 10950-8. 

Kuroda. Y. Kato, Y. Higashioji, T. Hasegawa, J. Kawanami, S. Takahashi, M. Shiraishi, N. Tanabe, K. Ogoshi. H. Chiral amino acid recognition by a porphyrin based artificial receptor. J. Am. Chem. Soc. 1995, 117. 10950. 

Fig. 5 Two examples of porphyrin-based cooperative optical sensors, (a) A ditopic receptor for binary metal salts. (h) A cyclodextrin-capped porphyrin system able to sense and report in four distinguishable association modes. ...

Because of their inherent stability, unique optical properties, and synthetic versatility, porphyrins and metalloporphyrins are excellent candidates for a variety of sensing-materials applications. Research in this area has focused on incorporation of synthetic porphyrins and metalloporphyrins into a variety of material matrices, such as polymers, glasses, and LB films. Substantial work has been done in the areas of solution and gas-phase. sensing, and highlights of both areas will be di.scussed. We will al.so briefly examine molecular recognition and receptor studies, becuase developments in these areas will further the development of porphyrin-based sensing materials. 

Studies of synthetic porphyrin-based anion receptors should form the basis for more effective sensors. Metallocene-substituted porphyrins examined by Beer and coworkers have proven successful in the solution-phase binding of ions such as chloride, bromide and nitrate." The cobaltocenium-substituted and ferrocene-substituted porphyrins (Figure 134) bind ions in solution, as shown by H NMR and electrochemical studies. The latter measurements reveal that the porphyrin and ferrocene redox... 

Matsui, J. Higashi, M. Takeuchi, T. Molecularly imprinted polymer as 9-ethyladenine receptor having a porphyrin-based recognition center. J. Am. Chem. Soc. 2000, 122,... 

Because of limited space, this chapter covers porphyrins and expanded porphyrins as receptors through mostly non-covalent or supramolecular interactions. As a general rule, examples wherein the porphyrin acts as a receptor via metal coordination are excluded. For a further reading on this latter topic, the reader is referred to a recent Chemistry Review article entitled Supramolecular Chemistry of Metallopor-phyrins. On the other hand, inspired by a recent review by Anslyn entitled Supramolecular Analytical Chemistry, we expand our definition of receptor-substrate interactions to include certain boronic acid binding motifs and several representative examples of metalated porphyrins that are applied to sensing applications, wherein the proposed mode involves metal complexation. Thus, included in this chapter is a brief summary of the seminal work carried out by Suslick and his group, where porphyrins are used to create the so-called artificial nose, that is, an array-based sensing device for various vapors. Also included are... 

One of the first reports of porphyrin-based fullerene recognition that included crystallographic evidence for encapsulation in a cyclic structure came from the Aida group. Here, the receptor, 7, is a cyclic dimer of zinc porphyrins (Figure 8). At the time of publication in 2001, system 7 held the record for the largest host-Ceo association constant (K = 6.7 x 10 M in benzene). The crystal structure also provided support for the presence of 7T interactions, as evidenced by separations of 2.765 and 2.918 A between the Zn atom and fullerene carbon atoms. 

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