The First Oxovanadium Ring in [{OV(salen)}₂(μ-F)][VO(salen)][BF₄]·(CH₂Cl₂)<i>_x</i> Crystals

The crystal structure of [{OVV(salen)}2(μ-F)][VIVO(salen)][BF4]·(CH2Cl2)x revealed a hollow cavity with a diameter of 5.3 Å that penetrates through the crystal, and a remarkable cyclic chain of the [VO(salen)] unit, a motif that has never been fashioned from oxometal building blocks. These features endow the crystal with a molecular sievelike property for the rapid, reversible, and size-selective absorption of guest CH2Cl2 molecules

A Novel Decavanadium(V) Cluster with a Chiral Framework: [(OV)₁₀(μ₂-O)₉(μ₃-O)₃(C₅H₇O₂)₆] Having an Approximate <i>C</i>₃ Symmetry

A Novel Decavanadium(V) Cluster with a Chiral Framework:  [(OV)10(μ2-O)9(μ3-O)3(C5H7O2)6] Having an Approximate C3 Symmetr

Highly Selective Oxygen Permeation through a Poly(vinylidene dichloride)−Cobalt Porphyrin Membrane: Hopping Transport of Oxygen via the Fixed Cobalt Porphyrin Carrier

A combination membrane having both gas barrier properties and selective oxygen-absorbing and -carrying capability was prepared by complexing poly(vinylidene dichloride-co-vinylimidazole) and meso-tetrakis(α,α,α,α-o-pivalamidophenyl)porphyrinatocobalt (CoP). The vinylidene dichloride copolymer was selected because of its low physical gas permeability and its dense and tough thin-membrane formability even after the CoP complexation. Oxygen permeation was selectively facilitated with the CoP carrier fixed in the membrane, and high oxygen permselectivity (facilitation factor > 25, oxygen/nitrogen permselectivity > 100, permeability 10-10 cm3 (STP) cm cm-2 s-1 cmHg-1) was observed, e.g., for the membrane containing > 20 wt % CoP at an upstream oxygen partial pressure of 0.5 cmHg. The facilitated oxygen transport was properly analyzed by a dual-mode model to give permeation parameters of the membrane such as the postulated diffusion coefficient of oxygen hopping via the fixed CoP carrier (DC). DC was inversely proportional to the average distance between the CoP carrier sites

Catalytic Cycle of a Divanadium Complex with Salen Ligands in O₂ Reduction: Two-Electron Redox Process of the Dinuclear Center (salen = <i>N,N‘</i>-Ethylenebis(salicylideneamine))

In an attempt to provide confirmation for the postulated mechanism of O2 reduction in vanadium-mediated oxidative polymerization of diphenyl disulfide, a series of divanadium complexes containing salen ligand (salen = N,N‘-ethylenebis(salicylideneamine)) were prepared, characterized, and subjected to reactivity studies toward dioxygen. A divanadium(III, IV) complex, [(salen)VOV(salen)][I3] (II), was yielded both by treatments of solutions of [(salen)VOV(salen)][BF4]2 (I) in acetonitrile with excess tetrabutylammonium iodide and by electroreduction of I followed by anion exchange with tetrabutylammonium triiodide. The complex II was characterized by a near-infrared absorption at 7.2 × 103 cm-1 (ε = 60.1 M-1 cm-1 in acetonitrile) assigned to an intervalence transfer band. A crystallographically determined V(III)−V(IV) distance of 3.569(4) Å is consonant with the classification of II as a weakly coupled Type II mixed-valence vanadium (α = 3.0 × 10-2). Oxidation of the cation [(salen)VOV(salen)]+ with O2 in dichloromethane yielded spontaneously the deep blue, mixed valent, divanadium(IV, V) species [(salen)VOVO(salen)]+ which was structurally characterized both as its triiodide (III) and perchlorate (IV) salts. Crystal data for III:  triclinic space group P1̄ (no. 2), a = 14.973(2) Å, b = 19.481(2) Å, c = 14.168(2) Å, α = 107.00 (1)°, β = 115.56(1)°, γ = 80.35(1)°, V = 3561.3(9) Å3, Z = 4, Dcalc = 1.953 g/cm3, μ (MoKα) = 31.74 cm-1, final R = 0.057 and Rw = 0.065. Crystal data for IV:  triclinic space group P1̄ (no. 2), a = 11.923(3) Å, b = 14.25(1) Å, c = 11.368(7) Å, α = 112.92(5)°, β = 92.76(4)°, γ = 99.13(4)°, V = 1743(1) Å3, Z = 2, Dcalc = 1.537 g/cm3, μ (CuKα) = 57.69 cm-1, final R = 0.042 and Rw = 0.061. The complexes III and IV were deoxygenated in strongly acidic nonaqueous media to produce [(salen)VOV(salen)]3+ as a high-valent complex whose reversible two-electron redox couple (VOV3+/VOV+) at 0.44V vs Ag/AgCl has been confirmed. Its ability to serve as a two-electron oxidant provided a unique model of a multielectron redox cycle in oxidative polymerization

Effect of Heme Structure on O₂-Binding Properties of Human Serum Albumin−Heme Hybrids: Intramolecular Histidine Coordination Provides a Stable O₂−Adduct Complex

5,10,15,20-Tetrakis[(α,α,α,α-o-pivaloylamino)phenyl]porphinatoiron(II) and 5,10,15,20-tetrakis{[α,α,α,α-o-(1-methylcyclohexanoylamino)]phenyl}porphinatoiron(II) complexes bearing a covalently bound 8-(2-methyl-1-imidazolyl)octanoyloxymethyl or 4-(methyl-l-histidinamido)butanoyloxymethyl side-chain [FeRP(B) series:  R = piv or cyc, B = Im or His] have been synthesized. The histidine-bound derivatives [FepivP(His), FecycP(His)] formed five N-coordinated high-spin iron(II) complexes in organic solvents under an N2 atmosphere and showed large O2-binding affinities in comparison to those of the 2-methylimidazole-bound analogues [FepivP(Im), FecycP(Im)] due to the low O2-dissociation rate constants. On the contrary, the difference in the fence groups around the O2-coordination site (pivaloyl or 1-methylhexanoyl) did not significantly influence to the O2-binding parameters. These four porphinatoiron(II)s were efficiently incorporated into recombinant human serum albumin (rHSA), thus providing the synthetic hemoprotein, the albumin−heme hybrid [rHSA−FeRP(B)]. An rHSA host absorbs a maximum of eight FeRP(B) molecules in each case. The obtained rHSA−FeRP(B) can reversibly bind and release O2 under physiological conditions (in aqueous media, pH 7.3, 37 °C) like hemoglobin and myoglobin. As in organic solutions, the difference in the fence groups did not affect their O2-binding parameters, but the axial histidine coordination significantly increased the O2-binding affinity, which is again ascribed to the low O2-dissociation rates. The most remarkable effect of the heme structure appeared in the half-life (τ1/2) of the O2−adduct complex. The dioxygenated rHSA−FecycP(His) showed an unusually long lifetime (τ1/2:  25 h at 37 °C) which is ca. 13-fold longer than that of rHSA−FepivP(Im)

Coordination of BF₄^- to Oxovanadium(V) Complexes, Evidenced by the Redox Potential of Oxovanadium(IV/V) Couples in CH₂Cl₂

The oxidation of oxovanadium(IV) complexes [LVIVO] (L = tetradentate Schiff-base ligands such as N,N‘-ethylenebis(salicylideneaminate)(2−) (salen) and N,N‘-2,2-dimethylpropylenebis(salicylideneaminate)(2−) (salpn)) to [LVVO]+, believed to be responsible for the voltammetric response near 0.6 V vs Ag/AgCl in CH2Cl2 in the presence of tetrabutylammonium tetrafluoroborate as a supporting electrolyte, is in fact coupled to a homogeneous process where [LVO]+ coordinates BF4- to form a neutral complex formulated as [LVOBF4]. The formation constants for [VO(salen)BF4] and [VO(salpn)BF4] are evaluated to be Ksalen-1 = 1.1 × 102 M-1 and Ksalpn-1 = 1.4 × 10 M-1, respectively. Crystal structure of [VO(salen)BF4] reveals that one of the fluorine atoms in BF4- is so close to the vanadium(V) atom as to be practically bound in the solid state

Coordination of BF₄^- to Oxovanadium(V) Complexes, Evidenced by the Redox Potential of Oxovanadium(IV/V) Couples in CH₂Cl₂

The oxidation of oxovanadium(IV) complexes [LVIVO] (L = tetradentate Schiff-base ligands such as N,N‘-ethylenebis(salicylideneaminate)(2−) (salen) and N,N‘-2,2-dimethylpropylenebis(salicylideneaminate)(2−) (salpn)) to [LVVO]+, believed to be responsible for the voltammetric response near 0.6 V vs Ag/AgCl in CH2Cl2 in the presence of tetrabutylammonium tetrafluoroborate as a supporting electrolyte, is in fact coupled to a homogeneous process where [LVO]+ coordinates BF4- to form a neutral complex formulated as [LVOBF4]. The formation constants for [VO(salen)BF4] and [VO(salpn)BF4] are evaluated to be Ksalen-1 = 1.1 × 102 M-1 and Ksalpn-1 = 1.4 × 10 M-1, respectively. Crystal structure of [VO(salen)BF4] reveals that one of the fluorine atoms in BF4- is so close to the vanadium(V) atom as to be practically bound in the solid state

Rheological Properties of Hemoglobin Vesicles (Artificial Oxygen Carriers) Suspended in a Series of Plasma-Substitute Solutions

Hemoglobin vesicles (HbV) or liposome-encapsulated Hbs are artificial oxygen carriers that have been developed for use as transfusion alternatives. The extremely high concentration of the HbV suspension (solutes, ca. 16 g/dL; volume fraction, ca. 40 vol %) gives it an oxygen-carrying capacity that is comparable to that of blood. The HbV suspension does not possess a colloid osmotic pressure. Therefore, HbV must be suspended in or co-injected with an aqueous solution of a plasma substitute (water-soluble polymer), which might interact with HbV. This article describes our study of the rheological properties of HbV suspended in a series of plasma substitute solutions of various molecular weights:  recombinant human serum albumin (rHSA), dextran (DEX), modified fluid gelatin (MFG), and hydroxylethyl starch (HES). The HbV suspended in rHSA was nearly Newtonian. Other polymersHES, DEX, and MFGinduced HbV flocculation, possibly by depletion interaction, and rendered the suspensions as non-Newtonian with a shear-thinning profile (10-4−103 s-1). These HbV suspensions showed a high storage modulus (G‘) because of the presence of flocculated HbV. However, HbV suspended in rHSA exhibited a very low G‘. The viscosities of HbV suspended in DEX, MFG, and high-molecular-weight HES solutions responded quickly to rapid step changes in shear rates of 0.1−100 s-1 and a return to 0.1 s-1, indicating that flocculation is both rapid and reversible. Microscopically, the flow pattern of the flocculated HbV that perfused through microchannels (4.5 μm deep, 7 μm wide, 20 cmH2O applied pressure) showed no plugging. Furthermore, the time required for passage was simply proportional to the viscosity. Collectively, the HbV suspension viscosity was influenced by the presence of plasma substitutes. The HbV suspension provides a unique opportunity to manipulate rheological properties for various clinical applications in addition to its use as a transfusion alternative

Molecular Assembly of Cholesterol-Bearing Poly(allylamine) for Binding Bile Salts in Water

Molecular Assembly of Cholesterol-Bearing Poly(allylamine) for Binding Bile Salts in Wate

Synthetic Routes to Polyheteroacenes: Characterization of a Heterocyclic Ladder Polymer Containing Phenoxathiinium-type Building Blocks

The synthetic routes to ladder polymers that consist of benzenetetrayl subunits with oxo and methylsulfonio linkages are described. As the key intermediate, poly(phenylene oxide)s having pendant methylsulfenyl groups are prepared by copper-catalyzed oxidative polymerization of the corresponding phenols with O2. The oxidation of the polymer with an equimolar amount of H2O2 in the presence of acetic acid effects the high-yielding conversion of methylsulfenyl to methylsulfinyl groups without the formation of the undesired methylsulfonyl groups. The superacidified condensation of the resulting polymer (Swern reaction of aryl sulfoxides) under dilution conditions induces the polymer-analogous intramolecular electrophilic ring-closing reaction of the hydroxymethylphenylsulfonium cation onto the adjacent benzene ring to yield the required ladder polymer, which has proved to be a semiconductor with an intrinsic electric conductivity of 2 × 10-5 S/cm. A comparison of the spectroscopic properties of the ladder polymer with those of the model compounds such as 5-methylphenoxathiinium triflate and phenoxathiin discloses π-electron delocalization over the methylsulfonio linkages, demonstrating the efficacy of the ladderization for p−π/d−π interactions in arylsulfonium moieties. This synthetic approach permits the thio and alkylsulfonio ladder linkages for a variety of phenyl ethers to form in high yields