Synthesis of Bioactive and Porous Organic-Inorganic Hybrids for Biomedical Applications

Bioactivity has been exhibited by a limited range of ceramics since the invention of Bioglass®. Recently, some bioactive polymeric organic-inorganic hybrids were introduced, including not only organically modified silicates (Ormosils) synthesized from polydimethylsiloxane (PDMS) and tetraethoxysilane but also those with gelatin and 3-glycidoxypropyl-tremethoxysilane. Preparation of the bulk and porous hybrids and their polymeric structures analyzed by Si NMR spectroscopy were presented. In vitro bioactivity or apatite deposition in a simulated body fluid of the Kokubo recipe were also described for those hybrids. Freeze-drying techniques introduced porosity (up to 90%) and pores extending in a preferred direction.     

Effect of cationic surfactant on the formation of ferron complexes

In the spectrophotometric determination of aluminium and iron with ferron (7-iodo-8-quinolinol-5-sulphonic acid, H(2)L), the addition of cationic surfactants greatly improves the linearity of the calibration curve and widens the useful pH range. The effect of cetyltrimethylammonium chloride (CTMAC) on the stepwise stability constants (K(1),K(2) and K(3)) of the ferron complexes of aluminium and iron (ML(+), ML(-)(2) and ML(3-)(3)) and on the acid-dissociation constants (K(a1) and K(a2)) of ferron has been studied in connection with the role of the surfactant. CTMAC greatly increases the value of K(3) while exerting little effect on K(1) and K(2), thus rendering ML(3-)(3) the predominant species even at very low concentration of free L(2-). It also has some effect on the acid-dissociation constants of ferron, but sometimes it acts to decrease the free L(2-) concentration. At is therefore concluded that the improvements due to addition of surfactant should be attributed to the increased K(3) value. The presence of surfactant micelles is not essential, because the surfactant has a favourable effect when present at well below its critical micelle concentration, and because the continuous variations plots show a peak at a point corresponding to the composition M: L: Q (Q = cationic surfactant) = 1:3:3.     

Regioselectivity in palladium-indium iodide-mediated allylation reaction of glyoxylic oxime ether and N-sulfonylimine

Allylation reaction of electron-deficient imines with allylic alcohol derivatives in the presence of a catalytic amount of palladium(0) complex and indium(I) iodide was studied. The reversibility of allylation was observed in the reaction of glyoxylic oxime ether having camphorsultam. As the important effect of water on regioselectivity, the gamma-adducts were kinetically formed from monosubstituted allylic reagents in the presence of water. The selective formation of thermodynamically stable alpha-adducts was observed in anhydrous THF. In contrast, the allylation of N-sulfonylimine gave the gamma-adducts with high regioselectivities even under anhydrous reaction conditions.     

Surface diffusion in reversed-phase liquid chromatography using silica gels bonded with C1 and C18 ligands of different densities

Surface diffusion in reversed-phase liquid chromatography (RPLC) using silica gels bonded with C₁ and C₁₈ alkyl ligands of different densities was studied from the viewpoints of two extrathermodynamic relationships, i.e., enthalpy-entropy compensation (EEC) and linear free energy relationship (LFER). First, according to the four methods proposed by Krug et al., the values of surface diffusion coefficient (D_s) were analyzed to confirm that an actual EEC resulting from substantial physico-chemical effects takes place for surface diffusion. Then, it was also demonstrated that a LFER is observed between surface diffusion and the retention equilibrium. The establishment of EEC and LFER suggests a mechanistic similarity of molecular migration by surface diffusion, irrespective of the alkyl chain length and the densities of C₁ and C₁₈ ligands. Finally, a thermodynamic model for the LFER based on the real EEC was used to estimate D_s values under various RPLC conditions. The D_s values can be estimated with a mean square deviation of about 25–30%. The agreement between the D_s values estimated and those experimentally measured suggests that the total mass flux by surface diffusion consists of the two contributions due to C₁ and C₁₈ ligands and that the contribution of each ligand is proportional to the ligand density.     

Asymmetric synthesis of alpha-amino acids: indium-mediated reactions of glyoxylic oxime ether in aqueous media

The indium-mediated allylation and alkylation reactions of the Oppolzer camphorsultam derivative of glyoxylic oxime ether proceeded with excellent diastereoselectivity in aqueous media, providing a variety of enantiomerically pure alpha-amino acids.     

Stannyl radical addition-cyclization of oxime ethers connected with olefins

Stannyl radical addition-cyclization of oxime ethers connected with olefin moieties was studied. The radical reactions proceeded effectively by the use of triethylborane as a radical initiator to provide the functionalized pyrrolidines via a carbon-carbon bond-forming process.     

THE ROLE OF DIOXYGEN SPECIES IN THE BASE- AND COBALT-CATALYZED OXYGENATION OF HINDERED PHENOLS

Abstract— The mechanisms by which 4-substituted 2,6-di- t -butylphenols are oxygenated by base- and Co(II) Schiff base complex-catalysis into o - or p -peroxyquinols and their Co(III) complexes, respectively, have been investigated. For the base-catalyzed oxygenation, a one-step ionic mechanism involving no radical species is suggested to be the most probable one. For the formation of the peroxycobalt(III) complexes, the following stoichiometry is concluded: ArOH + Co(II) + 5/4 O₂→ peroxycobalt(III) complex + 1/2 H₂O. A mechanism involving an electron transfer between the phenols and the Co(II)-O₂ complex followed by further electron transfer between the formed phenoxy radicals and the Co(II) complex to give the corresponding phenolate anions is proposed.     

Extrathermodynamic study of surface diffusion in reversed-phase liquid chromatography with silica gels bonded with alkyl ligands of different chain lengths

Surface diffusion on adsorbents made of silica gels bonded to C1, C4, C8, and C18 alkyl ligands was studied in reversed-phase liquid chromatography (RPLC) from the viewpoints of two extrathermodynamic relationships: enthalpy-entropy compensation (EEC) and linear free-energy relationship (LFER). First, the values of the surface diffusion coefficient (D(s)), normalized by the density of the alkyl ligands, were analyzed with the modified Arrhenius equation, following the four approaches proposed in earlier research. This showed that an actual EEC resulting from substantial physicochemical effects occurs for surface diffusion and suggested a mechanistic similarity of molecular migration by surface diffusion, irrespective of the alkyl chain length. Second, a new model based on EEC was derived to explain the LFER between the logarithms of D(s) measured under different RPLC conditions. This showed that the changes of free energy, enthalpy, and entropy of surface diffusion are linearly correlated with the carbon number in the alkyl ligands of the bonded phases and that the contribution of the C18 ligand to the changes of the thermodynamic parameters corresponds to that of the C10 ligand. The new LFER model correlates the slope and intercept of the LFER to the compensation temperatures derived from the EEC analyses and to several parameters characterizing the molecular contributions to the changes in enthalpy and entropy. Finally, the new model was used to estimate D(s) under various RPLC conditions. The values of D(s) that were estimated from only two original experimental D(s) data were in agreement with corresponding experimental D(s) values, with relative errors of approximately 20%, irrespective of some RPLC conditions.