Immobilization of ethylene bis-indenyl ligands on functionalized silica gel

Four ethylene bis-indenyl ligands containing tethers of various lengths were successfully immobilized on the surface of functionalized silica gel. The strategy of immobilization was based on catalytic thiol-ene coupling of terminal alkene groups in the tethers with surface thiol groups. Obtained materials have high BET surface area and pore volume. The method developed can be used for immobilization of catalytically active bis-indenyl metallocene complexes, thus preventing their dimerization and deactivation.     

Diffusion coefficients of tungsten heteropolyacids

Controlled hydrodynamics at rotating platinum and amalgamated copper electrodes were used to measure diffusion coefficients for 12-phosphotungstic and polyphosphotungstic acids in 1 M phosphoric acid, D_112-PTA=2.48 · 10^-6; D_polymer= 2.68 · 10^-7 cm²/sec, assuming only 1 tungsten atom in 12 is reduced at each diffusing entity. The phosphotungstic acids in phosphoric acid probably exist as polymers on initial formation, not greater than tetramers, rearranging to give monomers from calculations based on one reduced tungsten atom to each complex ion. Diffusion parameters of the phosphotungstic acids are compared with diffusion results of tungsten compounds from the literature obtained with dropping mercury electrodes. In all instances, low diffusion values are obtained indicating large diffusing entities.     

Immobilization of phosphomolybdic acid on the surface of mesoporous silica functionalized with alkylammonium groups

Silica containing protonated 3-aminopropyl groups has been synthesized by a template method using Pluronic 123 as a surfactant in an acidic medium at a hydrochloric acid concentration of 1.72 M. The X-ray diffraction data have indicated that the obtained sample has a highly ordered hexagonal structure, which agrees with the large specific surface area and sorption pore volume (S _sp = 880 m²/g, V _s = 1.28 cm³/g) typical of SBA-15 materials. However, transmission electron microscopy data show that this material contains two phases, with one of them being similar to SBA-15 mesoporous silica and the other belonging to socalled “honeycomb foams.” An ion-exchange reaction has been employed to immobilize phosphomolybdic acid H₃[P(Mo₃O₁₀)₄] on the pore surface, and the fact of immobilization has been confirmed by IR and TGA data. This functionalization significantly reduces the S _sp and V _s values of the sample but has no effect on isotherm pattern, thereby attesting to retaining the silica structure after the modification.     

Immobilization of the [RuII(edta)NO+] Ion on the surface of functionalized silica gel

The reaction of NO and the immobilized dimer complex (edta)(2)Ru(2)(III(1/2),III(1/2)) on silica gel chemically modified with [3-(2-aminoethyl)aminopropyl]trimethoxysilane (AEATS) produces the corresponding immobilized nitrosyl complex AEATS/Ru(II)NO(+). This compound, a monomer, was obtained by reducing the immobilized ruthenium dimer either electrochemically or with Eu(II) and reacting this species with NO(2)(-) ions. The properties of [Ru(edta)NO](-) in solution and anchored (AEATS/Ru(II)NO(+)) on silica were compared using electrochemical (DPV, CV) and spectroscopic (IR, UV-vis, and ESR) techniques. The results indicate that immobilization does not alter the reactivity of the ruthenium complex and confirm that [Ru(edta)(H(2)O)](2)(-) may be used, either in solution or immobilized, as a catalyst for the conversion of NO(2)(-) to NO(+). Both the anchored nitrosyl complex AEATS/Ru(II)NO(+) and the [Ru(edta)NO](-) species in solution, upon one-electron reduction, liberate NO at comparable rates.     

Immobilization of proteins on carboxylic acid functionalized nanopatterns

The immobilization of proteins on nanopatterned surfaces was investigated using in situ atomic force microscopy (AFM) and ex situ infrared reflectance–absorption spectroscopy (IRAS). The AFM-based lithography technique of nanografting provided control of the size, geometry, and spatial placement of nanopatterns within self-assembled monolayers (SAMs). Square nanopatterns of carboxylate-terminated SAMs were inscribed within methyl-terminated octadecanethiolate SAMs and activated using carbodiimide/succinimide coupling chemistry. Staphylococcal protein A was immobilized on the activated nanopatterns before exposure to rabbit immunoglobulin G. In situ AFM was used to monitor changes in the topography and friction of the nanopatterns in solution upon protein immobilization. Complementary studies with ex situ IRAS confirmed the surface chemistry that occurred during the steps of SAM activation and subsequent protein immobilization on unpatterned samples. Since carbodiimide/succinimide coupling chemistry can be used for surface attachment of different biomolecules, this protocol shows promise for development of other aqueous-based studies for nanopatterned protein immobilization.     

Synthesis and polypyrrole-loading study of antifungal medicine fluconazole functionalized Keggin polyoxotungstates

To rich the coordination polymer and polyoxometalate (POM) chemistry, two new hybrid compounds based on Keggin POMs with antifungal medicine fluconazole (Hfkz = [1-(2,4-difluorophenyl)-1,1-bis [(1H-1,2,4-triazol-1-yl)-methyl]methanol]), [Ag₄(Hfkz)₂][PW₁₂O₄₀] (AgFkzPW₁₂) and [Ag₄(Hfkz)₂][SiW₁₂O₄₀] (AgFkzSiW₁₂), have been successfully synthesized and structurally characterized. Moreover, to improve the photogenerated electron-hole pair separation properties, the surface of hybrid compounds was loaded by polypyrrole (PPy) through a chemical oxidation polymerization process in situ fabricating hybrid nanocomposites AgFkzPW₁₂@PPy and AgFkzSiW₁₂@PPy. As a result, the Hfkz molecules were successfully grafted onto the surface of the Keggin polyoxoanions, and their nanocomposites exhibit better photocatalytic activity than the respective matrix compounds under the irradiation of visible light.     

Heterocyclic amine salts of Keggin heteropolyacids used as catalyst for the selective oxidation of sulfides to sulfoxides

A range of sulfides can be selectively oxidized to the corresponding sulfoxides in good yields using catalytic quantities of heterocyclic amine salts (quinoline, cinchonine, and cinchonidine) of Keggin heteropolyacids with different green oxidants. The cinchonine heteropolyacid catalyst is easily recoverable and reusable without loss of its catalytic activity, and an enantiomeric excess can be obtained.     

Electro-assisted generation of functionalized silica films on gold

Electrochemical tuning of pH at electrode/solution interfaces is exploited for preparing thiol-functionalized silica films on gold surfaces by the sol–gel process. Film formation is carried out from a sol solution containing various ratios of prehydrolyzed mercaptopropyltrimethoxysilane and tetraethoxysilane precursors. This mixture is allowed to gelify only on the electrode surface by maintaining a negative potential value (to reduce protons and water and to generate hydroxyl species) to increase the local pH, which is known to catalyze polycondensation of the precursors. High mechanical stability of the resulting films is ensured by the strong interactions between thiol functions and the gold surface. Film porosity is very dependent on the amount of mercaptopropyl groups in the composite layer as pointed out by cyclic voltammetry of a redox probe (Fe(CN)₆³⁻). The organic group content is also a key factor influencing the sensitivity of Hg^(II) detection by anodic stripping voltammetry after accumulation at open-circuit. The preparation method can be extended to the deposition of other silica-based films on gold electrodes.     

Immobilization of multifunctional silsesquioxane cage on precipitated silica supports

Synthesis of octakis({3-glycidoxypropyl}dimethylsiloxy) octasilsesquioxane (G-POSS) was carried out based on a reaction involving the hydrosilylation of allyl glycidyl ether with octakis(dimethylsiloxy) octasilsesquioxane, using Karstedt’s catalyst and toluene. SiO₂/POSS hybrid systems were obtained via a method of immobilization by evaporation of the solvent, using hydrated or spherical silica obtained by precipitation in an aqueous or emulsion environment. The surface of the SiO₂ was modified using octakis({3-glycidoxypropyl}dimethylsiloxy) octasilsesquioxane (G-POSS). The effectiveness of the modification of the obtained hybrid materials was verified using Fourier transform infrared spectroscopy and nuclear magnetic resonance (²⁹Si and ¹³C CP MAS NMR). The tests showed that the interactions between the silica support and the modifier are of the nature of chemical adsorption. In addition a mechanism was proposed for the interactions between silica and oligosilsesquioxane. To test the final effect, the hybrid systems were subjected to morphological evaluation (transmission electron microscopy). Parameters of porous structure of the products were also determined: the specific surface area, pore diameter and pore volume. Thermal stability was tested for the pure silsesquioxane cage, the initial silica supports and the resulting systems. Elemental analysis was also carried out to determine the effect of surface modification on the degree of coverage with a particular POSS compound.     

Immobilization of papain on mesoporous silica: pH effect

The enzyme papain was adsorbed on mesoporous silica at 4°C and pH values between 3 and 11. From the adsorption kinetic data, the rate constant for the process was evaluated. The concentration of the enzyme in solution was calculated by monitoring the absorbance at 280 nm, and the quantity of papain bound to the solid was evaluated from the initial and residual soluble enzyme concentrations. The best results were observed for papain adsorption at pH 5.0; under these conditions, the desorption of the enzyme was <5%.     

Route for the elaboration of functionalized hybrid 3d-substituted trivacant Keggin anions

On the basis of four examples involving various transition-metal cations and various carboxylic acid derivatives, we have shown that hybrid 3d metal-containing polyoxometalate systems can be easily built under mild conditions.     

Surface acidity and basicity of functionalized silica particles

Tetraethoxysilane has been co-hydrolyzed with functionalized organosilanes in a modified Stöber process to produce silica particles with amino, carboxylate or dihydroimidazole groups on the surface. The effects of reaction conditions and the loading of the functionalized organosilane on particle size was examined by TEM. Fluorescence spectroscopy of the surface amino groups covalently modified with fluorescamine, and the surface carboxylate groups with 4-bromomethyl-6,7-dimethoxycoumarin, demonstrated that these functional groups were accessible for further reaction. Changes in surface acidity and basicity caused by the presence of functional groups (amine, dihydroimidazole, carboxylate) on the particle surface were determined using an indicator titration technique. Particles with surface imidazole and amine groups and particles with surface carboxylate groups have enhanced basicity and acidity, respectively. Dihydroimidazole-modified silica had greater surface basicity than the amine-modified silica. The effect on basicity and acidity increases as the amount of added functionalized silane increases. However, this increase is nonlinear with respect to the increase in added functionalized silane. Particles with both surface dihydroimidazole and carboxylate groups demonstrated reduced surface basicity and acidity.     

Adsorption of hydrogen peroxide on functionalized mesoporous silica surfaces

MCM-41 and MSU-H mesoporous silicas were successfully functionalized with hydrogen bonds forming organic moieties, which have been proven by elemental analysis. Both moieties, based on oxygen and nitrogen containing groups, were introduced with high efficiency—the amount of carbon in all cases exceeded 10 % and the elemental ratios suggest binding to the surface through two or three Si–O–Si bonds. Hydrogen peroxide adsorption was conducted in its aqueous solutions and the amount adsorbed was determined using the ferric thiocyanate method. Results are presented as a function of hydrogen peroxide concentration in aqueous solution from 5 to 30 %. Both functionalized silicas show increased adsorption capacity when compared with that of their unfunctionalized analogues. The surface modified with nitrogen-based organic moiety revealed better adsorption properties as well as higher resistance against oxidation. MSU-H silica, due to its larger pore diameter, provides more space to bind hydrogen peroxide molecules and thus was found to have higher adsorption capacity: it adsorbed up to four times more hydrogen peroxide than MCM-41.     

Immobilization of Ru — TsDPEN catalyst on functionalized MCM — 41

A Ru — TsDPEN (RuCl[(1S,2S)-N-p-tosyl-1,2-diphenylethylendiamine]p-cymene) catalyst of the Noyori type was immobilized in the channels of MCM — 41 molecular sieve functionalized by (3 — aminopropyl)triethoxysilane (APTES). The resulting compound was tested as a catalyst for the hydrogenation of 1-methyl-3,4-dihydroisoquinoline (MIQ) under laboratory conditions using an azeotropic mixture of formic acid and triethylamine (5:2) as the source of hydrogen and compared to the results acquired in the corresponding system.     

巯基功能化介孔材料高效锚定钯负载型催化剂的制备及其苯酚加氢催化性能

以含巯基官能团有机硅烷修饰的介孔材料MCM-41和SBA-15为载体, 采用浸渍-氢气还原法制备了高分散和高活性的负载型Pd催化剂. X射线衍射、N₂吸附-脱附和透射电子显微镜表征结果显示, 所制Pd催化剂Pd-SH-MCM-41和Pd-SH-SBA-15具有很好的长程有序结构、分布均匀的孔径、高比表面积及高度分散的Pd颗粒. 苯酚加氢反应结果表明, 以Pd-SH-MCM-41和Pd-SH-SBA-15为催化剂时, 在80℃, 1.0MPa反应1h, 苯酚转化率达99%以上, 环己酮选择性为98%. 它们的催化活性为商业Pd/C催化剂的5倍, Pd/MCM-41和Pd/SBA-15催化剂的3倍. 这可归因于介孔材料表面修饰的巯基官能团对Pd的锚定作用, 避免了Pd颗粒的团聚, 使其高度分散在介孔材料上.     

Immobilization of stationary liquids on silica particles by γ-radiation

Summary Continuing our work on new silanization reagents for producing chemically-modified small-particle, silica support material exhibiting improved chromatographic performance and especially good shielding of silanol groups in respect of solute-stationary phase interaction, we have developed new silica-based polymer phases with different polarities by crosslinking or polymerization reactions induced by -radiation.Polybutadienes or polysiloxanes were immobilized on non-, or specially presilanized, 5m silica particles by using different dose-rates of -radiation and by addition of different amounts of allylmethacrylate as a radical stabilizer.The materials obtained were tested by elemental analysis, scanning electron microscopy, ESCA and IR-reflexion measurements as well as by chemical Si–OH determinations. Chromatographic testing has been carried out with different, especially strongly basic solutes, under normal and reversed phase conditions.The dual retention mechanism model of Nahum and Horvath [1] was applied to the usual commercially available phases and those phases produced by ourselves. The influences of mobile phase additives such as acetonitrile or tetrahydrofuran were also investigated following the chromatographic test procedures for characterization of the support materials synthesized. The silicas obtained show excellent long term stability to all types of HPLC solvents. Their inertness with respect to irreversible adsorption of polar, especially basic, compounds can only be compared with that of reticular bulk polymer stationary phases without any silica skeleton. Unlike pure polymer particles these materials exhibit high pressure stability, only moderate shrinking and swelling effects, and most importantly, high plate numbers, comparable with normal brushtype stationary phases.Dedicated to Professor A. Zlatkis on the occasion of his 60th birthday.     

Preparation and electronic properties of monolayer tungsten oxide on silica particles

Monolayer tungsten oxide on silica particles was prepared by a controlled hydrolysis technique. The material displays a bandgap which is 0.3 eV higher in energy than that for bulk WO₃. The quasi-Fermi level for electrons, in this material, as determined by electrochemical measurements, is 170 mV more negative for SiO₂/WO₃ than that for particulate WO₃.     

Thermoanalytical studies on the curing of epoxy resin under the action of aqueous solutions of heteropolyacids of tungsten and molybdenum

By means of DSC, DTA, TG and NMR it was established that the process of cure of epoxy resins induced by aqueous solutions of heteropolyacids consists of two stages, the first one being connected with a catalytic interaction between oligomer and water, and the second one with epoxy-hydroxyl etherification. Analysis of kinetic data shows that the first reaction is diffusion controlled, the second process can be described by pseudo-first order kinetics with activation energy about 40 kJ/M.The authors thank Dr. A. E. Chalykh for the help in our work.