The reaction between H(2)O(2) and a pyridine-coordinated ferric porphyrin encapsulated by a cyclodextrin dimer yielded a hydroperoxoferric porphyrin intermediate, PFe(III)-OOH, which rapidly decomposed to oxoferryl porphyrin (PFe(IV)═O). Upon reaction with H(2)O(2), PFe(IV)═O reverted to PFe(III)-OOH, which was converted to carbon monoxide-coordinated ferrous porphyrin under a CO atmosphere. PFe(IV)═O in the presence of excess H(2)O(2) behaves as PFe(III)-OOH.

A synthetic oxygen (O(2)) and carbon monoxide (CO) receptor (hemoCD) composed of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphinatoiron(ii) and a per-O-methylated β-cyclodextrin dimer with a pyridine linker (Py3CD) was functionalised with poly(ethylene glycol) (PEG) to elongate the circulation time of the receptor in the bloodstream. α-PEG monocarboxylic acid (HOOC(CH(2))(3)(CO)O-PEG(mw)-OCH(3); mw = 750 or 5k) or α,ω-PEG dicarboxylic acid (HOOC(CH(2))(3)(CO)O-PEG(mw)-O(CO)(CH(2))(3)COOH; mw = 10k or 20k) was reacted with the amino group of 5-(4-aminophenyl)-10,15,20-tris(4-sulfonatophenyl)porphyrin to afford a porphyrin monomer having a PEG chain or a porphyrin dimer having a PEG linker, respectively. The ferrous complexes of these PEGylated porphyrins (PEG750-, PEG5k-, PEG10k- and PEG20k-hemoCDs) bound O(2) in aqueous solution, P(1/2) values being 6.5-8.1 Torr at pH 7.0 and 25 °C. Each PEG(mw)-hemoCD was infused into the femoral vein of a Wistar male rat. After 6 h of the infusions, 67, 82, 86 and 42% of PEG750-, PEG5k-, PEG10k- and PEG20k-hemoCD were excreted in the urine. PEG750-hemoCD with a hydrodynamic diameter (D(h)) of 3.4 nm seemed to partly leak from the blood vessels (pore size: 2-6 nm) before renal filtration (pore size: 4-14 nm). PEG5k- (D(h) = 6.2 nm) and PEG10k-hemoCDs (9.0 nm) hardly passed through the blood vessels but were fully filtered by the kidney, resulting in high excretion rates. A considerable amount of PEG20k-hemoCD (D(h) = 12.0 nm) was retained in the blood even at 6 h after administration. The present study demonstrates that the behaviour of hemoCD in blood after administration can be controlled by modification of hemoCD with PEG having an appropriate molecular weight.

A 1:1 supramolecular complex (met-hemoCD) of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinatoiron(III) (Fe(III)TPPS) with a per-O-methylated β-cyclodextrin dimer having a -SCH2PyCH2S- (Py = pyridin-3,5-diyl) linker (Py3CD) reacted rapidly with hydrogen peroxide or cumene hydroperoxide in an aqueous solution forming two types of hydroperoxo or alkylperoxo intermediates, ROO-Fe(III)(OH(-))PCD and ROO-Fe(III)(Py)PCD, which underwent rapid homolysis to the corresponding ferryloxo species, namely, O═Fe(IV)(OH(-))PCD and O═Fe(IV)(Py)PCD, respectively. For the O═Fe(IV)(OH(-))PCD species, the iron-oxo oxygen facing the linker gradually transferred to the nearby sulfide bond on the linker, forming the sulfoxidized Py3CD (Py3CD-O)/Fe(II)TPPS complex, which then bound dioxygen in air forming an oxy-ferrous complex, O2-Fe(II)TPPS/Py3CD-O. In contrast, the O═Fe(IV)(Py)PCD species, in which the iron-oxo oxygen was located on the opposite side of the sulfide bond on the linker across the porphyrin ring, was reduced to the resting state (met-hemoCD) by the surroundings without any oxidation of the Py3CD linker.