Supramolecular Templating of Mesopores in Phase-Separating Silica Sol-Gels Incorporated with Cationic Surfactant

Silica gels with hierarchical macropores and mesopores have been prepared by inducing phase separation in the alkoxide-based sol-gel system with an addition of alkyltrimethylammonium salt. Narrowly distributed mesopores were observed in the heat-treated gel samples possibly as a result of supramolecular templating of silica oligomers in the reacting solution. The ionic attractive interaction and hydrophobicity of the attached alkyl group cooperatively determined the phase separation tendency. No indication of long-range order of the mesopores was obtained.     

Dependence of selective enclathration on types of cholic acid crystals

Competitive recrystallizations of cholic acid (CA) from 1:1 binary mixtures of seven mono-substituted benzenes are demonstrated. The order of preference for guests to be incorporated into the cholic acid crystals are as follows: benzene, toluene > n-amylbenzene, n-hexylbenzene > ethylbenzene, n-propylbenzene, n-butylbenzene. These seven compounds afford bilayer type inclusion crystals that are classified into four types based on the host frameworks and host-guest stoichiometries. The order of selective enclathration corresponds to the four types as follows: 1:1 alpha G > 2:1 alpha G > 1:1 beta T or 2:1 alpha T. The preference for the alpha G type was also confirmed by investigating the host frameworks of the crystals obtained from binary mixtures. The dependence of the selectivity on the different types of CA crystals can be understood in terms of the fit of the guest molecule in the host cavity.     

Highly Selective Separation of Rhodopsin from Bovine Rod Outer Segment Membranes Using Combination of Divalent Cation and Alkyl(thio)glucoside

The micellization process of bovine rod outer segment (ROS) membranes is investigated utilizing a series of neutral detergents. It is found that when alkyl(thio)glucosides with an appropriate hydrophilic–lipophilic balance (e.g. octylthioglucoside) are used in combination with a divalent cation, rhodopsin is selectively extracted from ROS membranes at a specific detergent-to-membrane ratio. This allows remarkable purification of rhodopsin by a single-step solubilization, because the residual membranes are heavily aggregated in the presence of divalent cation and are therefore easily sedimented by low-speed centrifugation. The absorption spectrum of the supernatant reproducibly exhibits an A₂₈₀/A₅₀₀ value of 1.6, an excellent value that could rarely be obtained by chromatographic purification. The degree of purification also depends on the type of divalent cation included in the solubilization solution; specific binding of IIB-series cations (Zn²⁺ and Cd²⁺) to ROS membranes is suggested to play an important role in the solubilization process. The present result represents a unique example of selective solubilization of a specific membrane protein from highly aggregated membranes.     

Coating and water permeation properties of SiO2 thin films prepared by the sol-gel method on nylon-6 substrates

Nylon-6 substrates were coated with SiO₂ thin films by the sol-gel method and their water permeability coefficient was evaluated. Methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) were used as starting materials. The addition of MTES to TEOS has enabled the formation of crack-free thin films on the substrates. The thin films strongly adhered to the substrates. The water permeability coefficients of nylon-6 substrates coated with these thin films decreased with the increase in the ratio of TEOS to the total alkoxides. The pretreatment of the nylon-6 substrates with -aminopropyltriethoxysilane was found to be effective to suppress the water permeability. The water permeability was suppressed by about 40% under the optimal condition.     

Selective foam separation of binary protein solution by SDS complexation method

A fundamental study about the selective foam separation of protein mixture was carried out. A solution containing two proteins, ovalbumin (OA) and lysozyme (LZ), and an anionic surfactant, sodium dodecyl sulfate (SDS), was adjusted to pH 6.0, which referred to an intermediate state between the isoelectric points of the proteins. The solution was processed by continuous foam separation. The results showed that a proper addition of SDS greatly improved the selective recovery of LZ to OA. The experimental data were well explained by a simple model that most of cationic protein molecules (LZ) are associated with SDS and the adsorption of all the species including LZ-SDS complexes are subjected to Langmuir adsorption isotherm. The results also showed that one of the Langmuir parameters, which means a kind of lyophillic property of adsorbed material, of LZ-SDS complexes was extremely large as compared with that of primary protein.     

Phase Separation in Sol-Gel System Containing Mixture of 3- and 4-Functional Alkoxysilanes

The phase separation behavior of gelling systems containing the mixture of 3-functional and 4-functional alkoxysilanes has been investigated. The relation between the starting composition and resultant macroporous morphology was examined using tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) as starting alkoxysilanes, formamide (FA) as an additive, under an acidic condition. Up to TMOS:VTMS molar ratio of 0.5:0.5, the phase relation remained almost unchanged from that of pure TMOS system which exhibits morphology with well-defined co-continuous macropores in a very limited concentration region. On the VTMS-rich side typically TMOS:VTMS = 0.2:0.8, however, the co-continuous macroporous morphology was obtained in a broader composition range than those of either pure TMOS or VTMS system. A dome-like pseudo binary region was obtained with the two-phase region extending toward FA-rich direction. The domain size and pore volume of the gels with macroporous morphology could be controlled by alkoxide:water ratio and total solvent fraction, respectively.     

Crystal structures and topochemical polymerizations of 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes

Highly conjugated monomers, 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes (methoxy (1a), ethoxy (1b), isopropoxy (1c), benzyloxy (1d), chloroethoxy (1e), and bromoethoxy (1f)), were synthesized. Recrystallizations of 1a, 1c, 1e, and 1f yielded two crystal forms (prisms (1a-A) and needles (1a-B), needles (1c-A) and plates (1c-B), prisms (1e-A) and plates (1e-B), and prisms (1f-A) and needles (1f-B)), which have different molecular packing modes by X-ray crystal structure analysis, indicating that the crystals are polymorphic. In the photopolymerizations of these monomer crystals in the solid state, 1a-A, 1e-A, and 1f-A polymerized topochemically to give crystalline polymers. For their thermal polymerizations in the solid state, in addition to 1a-A, 1e-A, and 1f-A, 1e-B and 1f-B polymerized, but polymers formed from the 1e-B and 1f-B were amorphous. The packing of quinodimethane molecules in the crystals was defined by four kinds of parameters, stacking distance (d(s)), the distance between the reacting exomethylene carbon atoms (d(cc)), the angles formed between the stacking axis and longer axis of the monomer molecule (theta(1)), and the shorter axis of the monomer molecule (theta(2)), and then the polymerization reactivity of these quinodimethanes in the solid state was discussed on the basis of these parameters.     

Monolithic silica columns with various skeleton sizes and through-pore sizes for capillary liquid chromatography

Reduction of through-pore size and skeleton size of a monolithic silica column was attempted to provide high separation efficiency in a short time. Monolithic silica columns were prepared to have various sizes of skeletons (approximately 1-2 microm) and through-pores (approximately 2-8 microm) in a fused-silica capillary (50-200 microm I.D.). The columns were evaluated in HPLC after derivatization to C18 phase. It was possible to prepare monolithic silica structures in capillaries of up to 200 microm I.D. from a mixture of tetramethoxysilane and methyltrimethoxysilane. As expected, a monolithic silica column with smaller domain size showed higher column efficiency and higher pressure drop. High external porosity (> 80%) and large through-pores resulted in high permeability (K = 8 x 10(-14) -1.3 x 10(-12) m2) that was 2-30 times higher than that of a column packed with 5-mirom silica particles. The monolithic silica columns prepared in capillaries produced a plate height of about 8-12 microm with an 80% aqueous acetonitrile mobile phase at a linear velocity of 1 mm/s. Separation impedance, E, was found to be as low as 100 under optimum conditions, a value about an order of magnitude lower than reported for conventional columns packed with 5-microm particles. Although a column with smaller domain size generally resulted in higher separation impedance and the lower total performance, the monolithic silica columns showed performance beyond the limit of conventional particle-packed columns under pressure-driven conditions.     

Preparation of Silicalite-1 Within Macroporous Silica Glass

Microcrystalline silicalite-1 was formed on the inner surface of macroporus silica glasses prepared by the sol-gel process. By heating a homogeneous precursor solution at 100°C under a hydrothermal condition, 2–5 m of plate-like particles of silicalite-1 were deposited. With an increase of mixing time of the precursor solution, the number of silicalite-1 particles increased, accompanied by the relative decrease of the particle size. Depending on the temperature and the duration of the heat-treatment of the macroporous silica, the amount of deposited silicalite-1 varied. Below 1000°C, the amount increased with the heat-treatment temperature, as a result of the competition between the precipitation of silicalite-1 and the dissolution of silica from the macroporous silica glass under a strongly basic condition. On the other hand, above 1000°C the amount of deposited silicalite-1 decreased in accordance with the decrease of the macropore diameter by the heat-treatment, because of the limited transport of the dissolved silicate species through the smaller macropores.