Supramolecular Chemistry Composed of Porphyrins and Cyclodextrins

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1) Porphyrin Permethylated Cyclodextrin Complexes : We found that some water-soluble tetraarylporphyrins form extremely stable 1:2 inclusion complexes with per-O-methylated β-cyclodextrin (TMe-β-CD). The complexes were formed quantitatively in aqueous solutions even when the concentrations of both host and guest were 10-6 M. The results strongly suggest the possibility of this system to be utilized for preparing various supramolecular systems2) Mechanism for Formation of Porphyrin-TMe-β-CD Complexes : Mechanism for formation of extremely stable porphyrin-TMe-β-CD complexes was studied. As a result, it was clarified that TMe-β-CD can alter its shape according to the shape of a guest resulting in "induced-fit type complexation" as is found in biological systems. The optimum van der Waals contacts between the host and the guest are achieved by the induced-fit type inclusion.3) Formation of Heteroporphyrin Arrays : A very convenient method to prepare heteroporphyrin arrays was developed by … More applying the results on complexation of water-soluble porphyrins and TMe-β-CD. A scaffold is the tetraphenylporphyrin whose para-positions of the peripheral phenyl groups are attached by per-O-methylated β-cyclodextrin moieties. Such a porphyrin-cyclodextrin conjugate can form heteroporphyrin array just by mixing with another porphyrin solution. Very efficient energy transfer from zinc complex of water-soluble anionic porphyrin (ZnTPPS) to the free base porphyrin of the conjugate was achieved just by mixing the solution of the conjugate with that of ZnTPPS.4) Met-Myogbbin Model : Fe(III) complex of the anionic porphyrin (Fe(III)TPPS) forms a very stable 1:2 inclusion complex with TMe-β-CD. Such a complex can act as a met-myoglobin model whose Fe(III) center is bound to various anions in aqueous media. The fact that no anion binding to Fe(III)TPPS occurs in aqueous solution in the absence of TMe-β-CD, TMe-β-CD seems to show the function similar to proteins in biological system. High selectivity was found in anion binding to Fe(III)TPPS/FMe-β-CD complex; namely N3- is selectively bound to the complex. Hydrophilicity, basicity, and shape of an anion are the factors to determine the stability of the anion-bound Fe(III)TPPS/TMe-β-CD complex.5) Myogbbin Model and Reversible O2 Binding : A met-myoglobin model was constructed by Fe(III)TPPS and a per-O-methylated β-cyclodextrin dimer where two cyclodextrin moieties were linked with a bridge containing a pyridine moiety as a proximal base. We call such a model "met-hemoCD". Met-hemoCD was reduced by dithionite to form hemoCD (Fe(II)TPPS/cyclodextrin dimer), which bound dioxygen reversibly. The half life time of oxy-hemoCD was 30h in pH 6.0 phosphate buffer. The dioxygen affinity was determined to be 17 Torr. HemoCD shows the functions similar to myoglobin. The present system is the first example of the model of myoglobin or hemoglobin that works in aqueous solution. Less