Modeling of the Permeate Flux during Microfiltration of BSA-Adsorbed Microspheres in a Stirred Cell

A study on the variation of the permeate flux was performed in a stirred cell charged with microspheres, to investigate the effects of the stirrer speeds (300, 400, and 600 rpm) and the BSA concentration (0.1, 0.2, 0.4, and 0.8 g/L) under constant pressure. The permeate flux increased over time before the saturation point, but it began to decrease after that point. An increase of the BSA concentration and the stirrer speed resulted in the rapid increase of the permeate flux. This is contrary to the observation of the conventional filtration experiments using a stirred cell. A resistance-in-series model was employed for the modeling of the permeate flux. The cake resistance (R(c), induced by the concentration polarization of microspheres) and the fouling resistance (R(f), induced by the adsorption of BSA inside the membrane pore) must be considered simultaneously for the modeling. These modeling results were in good agreement with the experimental data. These can be applied to the special system considering both R(c) and R(f) as well as the general filtration systems using a stirred cell. Copyright 2000 Academic Press.     

Synthesis and Structures of Titanosiloxane Cage Compounds

Reaction of (triphenylmethyl)silanetriol (1) with cyclopentadienyltitanium trichloride (CpTiCl₃) in the presence of triethylamine as a HCl scavenger gave both compounds of a partial open-cage type {[Ph₃CSiO(OH)]₃(Ph₃CSiO_3/2)(CpTiO_3/2)₄} (2) and cube type (Ph₃CSiO_3/2CpTiO_3/2)₄ (3). The 1:1 reaction of 1 and CpTiCl₃ in toluene solvent at reflux temperature for 3 d afforded compounds 2 (22%) and 3 (36%). When 1 is reacted with a 1.5 fold excess of CpTiCl₃ under the same conditions, compound 3 was obtained in high yield (81%) along with 2 in trace quantities. Compounds 2 and 3 were fully characterized by the analyses of ¹H, ¹³C, ²⁹Si NMR, IR, and FAB MS data. The solid-state structure of 3 was determined by a single crystal X-ray diffraction study. Compound 3 had shown to have catalytic activity for the oxidation of alkenes such as 1-octene, cyclooctene, and norbornene with t-butyl hydrogen peroxide. The effect of solvent was observed in this epoxidation reaction. The order of reactivity were decreased as follows: CHCl₃ > hexane THF.     

Anomalies in the asymmetric hydroboration of olefins with the 11 adduct of (+)-α-pinene and BH3 · THF

The hydroboration of cis-2-butene and cis-3-hexene with pure diisopinocampheylborane (IPC₂BH) and monoisopinocampheylborane (IPCBH₂), both prepared from (+)-α-pinene, were studied. In contrast to IPC₂BH, which yielded R-(?)-2-butanol and R-(?)-3-hexanol in 98.4 and 94.5% optical purities, IPCBH₂ yielded S-(+)-2-butanol and S-(+)-3-hexanol in 23.6 and 19.7% optical purifies respectively. PMR examination of the methanolyzed products were utilized to establish the species present in the freshly prepared and aged $\text{1}\text{1}$ adduct from (+)-α-pinene and BH₃ · THF. The results confirm the interpretation previously advanced for the major differences realized in asymmetric hydroboration with the fresh and aged $\text{1}\text{1}$ adducts.     

A boundary element method for molecular electrostatics with electrolyte effects

A boundary element method is developed to compute the electrostatic potential inside and around molecules in an electrolyte solution. A set of boundary integral equations are derived based on the integral formulations of the Poisson equation and the linearized Poisson-Boltzmann equation. The boundary integral equations are then solved numerically after discretizing the molecular surface into a number of flat triangular elements. The method is applied to a spherical molecule for which analytical solutions are available. Use is made of both constant and linearly varying unknowns over the boundary elements, and the method is tested for various values of parameters such as the dielectric constant of the molecule, ionic strength, and the location of the interior point charge. The use of the boundary integral method incorporating the nonlinear Poisson-Boltzmann equation is also briefly discussed.     

Pd(II)-Catalyzed cyclogeneration of carbocations: subsequent rearrangement and trapping under oxidative conditions

A catalytic oxidative polycyclization reaction initiated by the carbocyclization of 1,5-dienes with Pd(II) is reported. Trapping of a putative carbocation with suitable functional groups (phenols, alkenes, alcohols, sulfonamide), or rearrangement protocols (Pinacol) yields poly-cyclic products in good yields and in excellent diastereoselectivities. Turnover of the intermediate Pd-C bond is via β-H elimination.     

Direct determination of estriol 3- and 16-glucuronides in pregnancy urine by column-switching liquid chromatography with electrospray tandem mass spectrometry

Using column-switching liquid chromatography/tandem mass spectrometry (LC-MS/MS), we developed an improved analytical method of urinary estriol glucuronides. This new method is derived predominantly from maternal and fetal precursors in pregnancy. We used in the following procedure: first, we filtered urine samples with a membrane filter. Next, we directly injected the 50 microL aliquot of urine samples onto a pre-column. Then, after activating the column-switching valve, we backflushed the loaded samples onto the C(18) analytical column. Urine samples can be assayed within 20 min without any sample preparation steps. We monitored separated estriol glucuronides by negative electrospray ionization (ESI) and selected-reaction monitoring (SRM). The calibration range of estriol-3-glucuronide (E3-3G) and estriol-16-glucuronide (E3-16G) was 0.1-20 microg/mL and the linearity of the method was 0.9984 for E3-3G and 0.9987 for E3-16G. The limits of detection at a signal-to-noise (S/N) ratio of 3 were 10 ng/mL (E3-3G) and 5 ng/mL (E3-16G). The analytical recovery was over 85% and, in general, inter-day and intra-day variability for precision and accuracy were less than 10%. When applied to a pregnancy urine sample to biomedical monitoring of the function of the maternal/fetal unit, the proposed method allowed rapid and sensitive screening for the detection of E3-3G and E3-16G.     

Synthesis and Characterization of Fluoro- and Chloro- bimetallic Alkoxides as Precursors for Luminescent Metal Oxide Materials via Sol-Gel Technique

Heterobimetallic alkoxides are broadly recognized as versatile precursors for luminescence materials, and efforts are being made to develop novel routes by applying the concept of geometrical molecular design, for their synthesis and to design a single source precursor suited to photoluminescent materials. Novel and new series of bimetallic alkoxides has been prepared by metathesis route. They exhibit a lower sensitivity towards hydrolysis and so they are easier to handle as compared to other alkoxides. All the compounds were characterized by elemental analysis, FT-IR and multinuclear NMR spectroscopies. FT-IR revealed that the molecular structure of these metal alkoxides was retained to a large extent in 4 ： 1 halogenated alcohol-benzene solution. The heteronuclear NMR spectroscopy provided useful information about chemical shifts for better understanding the likely structure based on interactions with their coordinate metals. The mass spectra show similar types of fragmentation pattern. SEM-EDS analyses showed consistency with the formulation. XRD patterns show an enhanced homogeneity at high temperature. TGA measurements show that thermal decomposition occured in steps that depended entirely on the chemical compositions and the synthesis routes. SEM observation reveals that the morphology and particle size strongly depend on synthesis routes for their precursors.     

Highly stereoselective synthesis of 2,5-disubstituted 3-vinylidene tetetrahydrofurans via Prins-type cyclization

[reaction: see text]. A novel synthetic methodology for 2,5-disubstituted tetrahydrofurans having an allenyl group at the 3-position via Prins-type cyclization was developed. The reaction led to excellent selectivity and moderate to high yields.     

Controlled peak wavelength shift of Ca1−xSrx(SySe1−y):Eu phosphor for LED application

The highly efficient red-orange-yellow-emitting phosphor (Ca_1−xSr_x)(S_1−ySe_y):Eu²⁺ in combination with commercial green phosphor SrGa₂S₄:Eu²⁺ and blue LED are proposed for a three-band white LED. The luminescence mechanism and optimization parameters are discussed on the basis of proposed peak wavelength diagram.     

Dispersion of silica nano-particles in sol-gel hybrid resins for fabrication of multi-scale hybrid nanocomposite

Multi-scale hybrid nanocomposites containing both ∼15 nm silica colloids and ∼2 nm oligosiloxanes in a methacryl polymer matrix were newly designed and fabricated. Colloidal silica sols were dispersed in methacryl oligosiloxanes nano-hybrid resins synthesized by sol-gel reaction of methacryloxypropylmethoxysilane and diphenylsilanediol. On the basis of TEM and SANS analyses, it was confirmed that the silica colloids were compatibly dispersed and different sizes of colloidal silica and oligosiloxanes co-exist in the solutions. Multi-scale hybrid nanocomposites fabricated by UV and thermal curing with incorporation of silica colloids in the nano-hybrid materials show enhanced mechanical and thermal characteristics.