1) met-Myoglobin model was prepared by complexing Fe(III)TPPS with per-methylated b-cyclodextrin (TMe-b-CD) in aqueous solution.

TPPS is 5,10,15,20-tetrakis(p-sulfonatophenylporphyrin, whose Fe(III) complex was included by two TMe-b-CD to form a trans-type 1:2 inclusion complex. The iron center is located at a creft of the cyclodextrin cavities from which most of water molecules are extruded. Such a circumstance is similar to that of Mb. Our model metMb shows the behavior similar to that of native Mb.

K. Kano, H. Kitagishi, S. Tamura, A. Yamada, J. Am. Chem. Soc. in press.

2) Mb model that works in aqueous solution

In 1974, Collman and co-workers reported a first example of myoglobin (Mb) model using a picket-fence porphyrin.1 After that, various Mb models have been designed and prepared to protect formation of m-oxo dimers and six coordinate Fe(II)porphyrins.2 Most of these studies were carried out in organic solvents and very few examples have been reported with O2 binding to Mb models in protic solvents. Recently, Zhou and Groves synthesized a hemoprotein model involving a cyclodextrin substructure that works in aqueous solution.3 Their model compound, however, is so complex that there is a problem of versatility. In the present study, we found that a per-O-methylated b-cyclodextrin dimer containing a pyridine bridge (I) forms an inclusion complex of Fe(III)TPPS (TPPS = meso-tetrakis(p-sulfonatophenyl)porphyrin) (II) whose Fe(II) form binds O2 reversibly in aqueous solution.
Compound I incorporated Fe(III)TPPS into its cavities to form II that was extremely stable in aqueous solution. UV-vis absorption spectral changes of Fe(III)TPPS was halted upon addition of an equimolar amount of I, indicating the formation of a stable 1:1 complex. 1H NMR spectrum of II in D2O showed the signals due to the pyrrole b-protons at 51, 53, and 55 ppm (standard: TSP) at pD 4.4. These chemical shifts indicate the generation of a five coordinate admixed spin state. At pD 8.7, the pyrrole b-protons showed the broad signals at ca. 84 ppm, suggesting the formation of a high spin mono-hydroxo Fe(III) complex.

Complex II in aqueous solution at pH 4.5 was reduced by Na2S2O4 under Ar atmosphere. The reduction product had a Soret band at 434 nm, which was ascribed to Fe(II)TPPS. Introducing O2 into the solution of the Fe(II) form of II caused the blue shift of the Soret band (423 nm), which shifted again to 422 nm by replacing the atmosphere of O2 with CO (Figure 1). These absorption spectral data strongly suggest that the O2 molecule is bound to the five coordinate Fe(II) complex of II to yield a six coordinate O2 adduct, from which the O2 molecule was removed by introducing a stronger ligand CO into the system. The formation of the six coordinate Fe(II)(O2) complex was supported by 1H NMR spectrum. Namely, the pyrrole b-protons of the O2 adduct appeared at ca. 8-9 ppm. Such upfield shifts suggest the formation of a six coordinate low spin state. In addition, a Fe-O stretching band was observed at 569 cm-1 that shifted to 546 cm-1 by replacing 16O2 with 18O2 in the resonance Raman spectrum of the O2 adduct of reduced II.
The half-lifetimes (t1/2) of the O2 adduct of the Fe(II) complex of II under air were measured by means of absorption spectroscopy. At pH 4.5 (succinic acid buffer), t1/2 was 12.0 h, while it was elongated to 16.9 h at pH 6.0 (succinic acid buffer). Although reason has not been clarified yet, t1/2 became longer when the phosphate buffer was used. Presumably, a CO2- group of succinate ion is weakly bound to Fe(II) to cause the release of O2.
The dioxygen was removed from the Fe(II)(O2) complex when the atmosphere of the system was replaced by Ar, indicating the occurrence of reversible O2 uptake. The O2 uptake-release cycles were possible to repeat several times.
The present results show that the compound II and its Fe(II) complex are excellent metMb and Mb functional models, respectively.

Acknowledgement: The authors acknowledge Professor T. Kitagawa at Institute of Molecular Science and Technology for his wonderful discussion on resonance Raman spectroscopy.

REFERENCES
1. Collman J. P., Gagne R. R., Reed, C. A., Robinson W. T., Rodley G. A.: Proc. Nat. Acad. Sci. U.S.A. 71, 1326 (1974).
2. Collman J. P., Boulatov R., Sunderland C. J., Fu L.: Chem. Rev. 104, 561 (2004).
3. Zhou H., Groves J. T.: Biophys. Chem. 105, 639 (2003).

K. Kano, H. Kitagishi, M. Kodera, S. Hirota, Angew. Chem. Int. Ed. in press.

3) Flip-flop of glucopyranose units in per-O-methylated b-cyclodextrin

Purpose: Clarification of somersault of two glucopyranose units in a permethylated b-cyclodextrin-bearing porphyrin 1 to form a self-inclusion complex 2.

Methods: Compound 1 was prepared and analysed in aqueous media by means of UV-vis, fluorescence, and NMR spectroscopy.

Results: UV-vis absorption spectrum of 1 clearly suggests the self-inclusion of 1 where two phenyl groups of 1 at the 5 and 15 positions of the porphyrin are completely included by the permethylated b-cyclodextrin cavities. The pKa value of compound 1 for the protonation-deprotonation equilibrium at the pyrrole nitrogens is also support the self-inclusion. 2D NMR spectra definitely show the formation of the self-inclusion complex 2. The self-inclusion complex resists the attack by anthraquinone-2-sulfonate (AQS) resulting in poor fluorescence quenching of excited 1 by AQS.
Conclusion: The ability of permedthylated b-cyclodextrin to include the phenyl groups at the meso positions of porphyrins is so strong that the glucopyranose units of compound 1 tumble to form self-inclusion complex 2. This is the second example of the somersault of the glucopuranose unit in permethylated b-cyclodextrin. The first example was reported by Kaneda et al. (Chem. Lett. 2003, 534.).

R. Nishiyabu, K. Kano, Eur. J. Org. Chem. in press.

4) Professor Koji Kano was awarded a proze from the Cyclodextrin Society, Japan, on September 16, 2004 at Kumamoto.