Eishin Kyuno

Synthesis and Effectively Reversible Oxygenation of Some “Picket Fence” Type Porphyrinatocobalt(II) Complexes

Abstract Some “picket fence” type meso-tetrakis(2-substitu-ted phenyl)porphyrinatocobalt(II) complexes were newly synthesized, which had different peripheral substituents in their numbers and/or geometrical dispositions to form “cavity” on the porphyrin plane. Their O2 affinities were determined with 1-methylimidazole as an axial base at various temperatures in solution, by visible spectral measurements. On the basis of thermodynamic quantities, four neopentylcarbonylamino groups were the most effective as a picket fence, and the thermodynamic values of the complex were nearly comparable to those of cobalt(II)myoglobin. It was found that O2 affinity decreased with an increase in ΔH°, regardless of ΔS°. In the case of using various amines as an axial base, imidazoles were effective to enhance O2 affinity rather than pyridines.

Thermodynamics for base binding to four atropisomers cobalt(II) picket fence porphyrin. Intramolecular ligand–ligand interactions

Thermodynamic parameters for base binding to four atropisomers of meso-tetrakis(o-pivalamidophenyl)porphyrinatocobalt(II) were determined by spectrophotometry in toluene. The order of the affinities of the four isomers with 1-methylimidazole and pyridine is α4<α3<cis-α2<trans-α2. The higher base affinities of the trans-α2 complex compared with the α4 complex are due to an increase in the binding energies of the bases, although a substantial decrease of entropy changes also occurs; the differences of thermodynamic values on both complexes are −ΔΔG = 1.49 and 1.36 kcal/mol, −ΔΔH = 3.4 and 3.1 kcal/mol and −ΔΔS = 6.4 and 6.1 eu, with 1-methylimidazole and pyridine, respectively. With saturated bases pyrrolidine and piperidine, the affinities of the trans-α2 complex are comparable to those of the α4 complex, and those of the cis-α2 complex are the lowest. The increased steric repulsion between the pickets and ligated pyrrolidine or piperidine may cancel out the stabilizing effect on the base binding to the α2 complexes. Proton NMR study suggests the preferential solvation of the four-coordinate species of the trans-α2 complex to that of the α4 complex. It could be concluded that the stabilization of the base binding by the pickets is attributed to an intramolecular ligand–ligand interaction between the ligated base and the pickets rather than to the inhibition of the undesirable solvation on the active sites.

Effects of polarity on dioxygen binding to cobalt(II) porphyrins

Abstract Some picket fence porphyrinatocobalt(II) complexes which contain a replaced polar or non-polar group in their fences were newly prepared and characterized, and their oxygen affinities were measured spectrophotometrically. The O 2 affinities of the complexes containing a replaced polar group other than amido linkages are appreciably reduced as compared with those of the complexes with a similar non-polar group, regardless of the charge sign of the polarity in the cavity. On the other hand, solvent polarity affects the O 2 affinity of the complex with a polar group which is accessible to the coordinated dioxygen molecule, while solvation effects of the corresponding complex without such a group are little. On the basis of these results the relationships between O 2 affinity and pocket polarity or solvent polarity are discussed.

Phase transition and electrical properties of mono-, di-, tri- and tetraalkyl (or aryl) ammonium tetrahalogenocuprates(II)

Abstract The following four series of organoammonium tetrahalogenocuprates(II) were systematically prepared: (RNH 3 ) 2 CuX 4 , (R 2 NH 2 ) 2 CuX 4 , (R 3 NH) 2 CuX 4 and (R 4 N) 2 CuX 4 (where R = alkyl or aryl group; X = bromide or chloride ion). Their phase transitions and electrical properties were investigated by means of DTA, DSC, electrical conductivity measurements, and IR and UV spectrophotometries.

Cooperative dioxygen binding to the bi-bridged dimeric porphyrinatocobalt(II) complexes

Abstract Two types of bi-bridged dimeric porphyrinatocobalt(II) complexes, ‘picket fence’ type and ‘strapped’ type as a hemoglobin model, and the corresponding monomeric complexes were designed and synthesized. Their equilibrium constants for monodentate or bidentate axial ligands and their dioxygen affinities were measured in DMF. A strapped type dimer complex binds 1,2-bis(4-pyridyl)ethane to form a ‘sandwich’ structure and reveals the cooperative effect upon dioxygen binding. To explain such hemoglobin-like cooperativity, an intramolecular mechanism is postulated in keeping with the proposal of Perutzs stereochemical trigger mechanism.

Effect of aromatic-aromatic interaction on ligand binding to zinc porphyrins

Abstract Two zinc porphyrins with a superstructure around the ligand binding sites have been prepared and characterized by 1 H NMR spectroscopy. The binding properties of amine ligands to the zinc porphyrins were analyzed by UV-Vis and 1 H NMR spectroscopy. The thermodynamic parameters for ligand binding to the zinc porphyrins were estimated and compared to those of zinc porphyrins with and without the superstructure. The binding of aromatic amines to the superstructured zinc porphyrins bearing phenyl groups was found to be strong compared to the binding of butylamine to the zinc porphyrins. The enhanced binding of aromatic ligands to the zinc porphyrins was discussed in terms of the relation between ligand geometries and the superstructure.

Syntheses and characterization of cobalt(II) complexes of dimeric ‘picket fence’ porphyrins

Abstract A series of dimeric picket fence porphyrinatocobalt(II) complexeses in which the length of the bridging chain controls the dioxygen affinity was newly derived from the coupling of two meso -mono- (β-o-aminophenyl)-tris-(α,α,α-o-pivaloylamidophenyl)- porphyrins with (CH 2 ) n (COCl) 2 ( n = 1, 3, 5 or 7). Some of the dimeric complexes form a unique ‘sandwich structure’ upon binding with certain bidentate ligands, and their dioxygen affinities are greatly increased compared with those for corresponding monomeric complexes. The relationship observed between the length of the bridging chain and the dioxygen affinity of the dimer complex having a sandwich structure is interpreted in terms of the displacement mechanism of the metal atom from a porphyrin plane.

Modified picket fence porphyrin Fe(III) and Zn(II) complexes as a model for hemoglobin mutants

Abstract Zinc(II) and iron(III) complexes of three modified picket fence porphyrins in which one of the four pivalamido pickets was replaced by a meta -methyl, -amino, or -hydroxy benzoylamino picket were synthesized. The iron complex containing the phenolic OH on the picket fence mimics the abnormal active sites for a type of hemoglobin mutant, Hb M. Proton NMR and visible spectra for the zinc complexes have shown that the NH 2 or OH group on the picket fence does not coordinate to the central metal ion in CH 2 Cl 2 at room temperature. Contrary to this, coordination of the phenolic OH (or O − ) on the picket fence to form OFeO axial geometry was found for the iron complex by ESR measurements in CH 2 Cl 2 at 77 K. On the other hand, the ESR spectra for the three iron complexes with 1-methylimidazole under basic conditions have shown the presence of two regioisomers in OFeN axial geometry, because of the unsymmetrical distribution of the picket fences on the porphyrin plane.

Synthesis of Some Protic Picket Fence Porphyrinatocobalt(II) Complexes and Their Reactions with Dioxygen as Hydrogen-Bond Models in Oxy Hemoproteins

Abstract Some specific picket fence porphyrinatocobalt(II) complexes were newly synthesized and characterized. The complexes contain one protic substituent capable of forming intramolecular hydrogen bond with the dioxygen molecule coordinated to the central metal ion. Their reactions with dioxygen molecule were measured spectrometrically in solution containing an axial base, and the thermodynamic functions were determined. The results indicate that the protic groups promote the irreversible oxidation of Co(II) to Co(III). This effect may be ascribed to decreased electron density at the central Co(II) ion, which is resulted from shifted electron density toward the hydrogen atom of the protic group through the coordinated O2 molecule by hydrogenbond formation or the like. It is also found that the complexes prepared have lower O2 affinity than the corresponding complexes with no protic substituent and that the decreased binding energy −ΔH° of the dioxygen molecule to the complexes brings about the increased...

Discrimination reaction of O2 and CO to ‘cross-strapped’ type iron(II) porphyrins

Abstract The syntheses and characterization of cross- strapped type iron(II) porphyrins with sterically protected cavities on one face are described. The porphyrins, in which one set of two amino groups in the trans position was bridged by heptamethylenedicarbonyl and the other by tetradecamethylenedicarbonyl or octadecamethylenedicarbonyl, were derived from the α,α,α,α-isomer of meso-tetra(o- aminophenyl)porphyrin. The heptamethylene chain was found to be crushed by the steric interaction with the tetradecamethylene chain bridged over the heptamethylene chain. The iron(II) complexes bind O2 and CO reversibly in toluene containing 1,2- dimethylimidazole at 20 °C, and their O2 and CO affinities have been determined. The O2 and CO adducts of the iron(II) complexes have been characterized by 1H NMR and IR spectra. The changes of the O2 and CO affinities of the iron(II) complexes are discussed in terms of the polar effect of amide groups, the H-bonding of amide groups with O2, and the steric effects of cavities.