Mechanism and nanosize products of the sol-gel reaction using diphenylsilanediol and 3-methacryloxypropyltrimethoxysilane as precursors

We use a first-principles calculation and small-angle neutron scattering (SANS) to investigate the mechanism and the nanosize products of the sol-gel reaction with diphenylsilanediol (DPD) and 3-methacryloxypropyltrimethoxysilane (MEMO) precursors in synthesizing a hybrid waveguide material. It is predicted that switching between a DPD hydroxyl and a MEMO methoxy with a reaction rate of 6.8 x 10(-6) s(-1) at 300 K is the fastest process for the first reaction step, thus generating diphenylmethoxysilanol (DPM) and 3-methacryloxypropyldimethoxysilanol (MEDO) as products. However, we determine that this reaction pathway could be modified by the presence of the H2O released from a catalyst such as Ba(OH)2.H2O. Next, switching between the DPM hydroxyl and the MEDO methoxy is followed to generate diphenyldimethoxysilane (DPDM) and 3-methacryloxypropylmethoxysilanediol (MEMDO). However, condensation between a MEMDO hydroxyl and a DPDM methoxy is found to be most favorable for the third reaction step, which generates the DPDM-MEMDO dimer and CH3OH molecule as products. In a similar fashion, a DPDM methoxy of the DPDM-MEMDO dimer can condense with a MEMDO hydroxyl of the second DPDM-MEMDO dimer to increase the chain, but its reaction rate of 2.8 x 10(-11) s(-1) is predicted to be about 5 times smaller than that between a DPDM methoxy and a MEMDO hydroxyl. This implies that the reaction rate for the larger nanostructures becomes smaller. Additionally, our SANS measurements determine that the final products from our sol-gel reaction are on the nanometer scale, at sizes from 1.76 to 2.36 nm.     

Chirality exchange from sp3 central chirality to axial chirality: benzannulation of optically active diaryl-2,2-dichlorocyclopropylmethanols to axially chiral alpha-arylnaphthalenes

Chirality exchange benzannulation of optically active (1S)-aryl(aryl')-2,2-dichlorocyclopropylmethanols (>99% ee) using TiCl4 successfully proceeded to give axially chiral (M)-alpha-arylnaphthalenes with excellent levels of stereo induction (>99% ee). This unique transformation involves the single-step chirality exchange from sp3 central chirality to axial chirality, that is, a type of excellent memory effect.     

A polymer-based microfluidic device for immunosensing biochips

This paper describes the design, fabrication, and test of a PDMS/PMMA-laminated microfluidic device for an immunosensing biochip. A poly(dimethyl siloxane)(PDMS) top substrate molded by polymer casting and a poly(methyl methacrylate)(PMMA) bottom substrate fabricated by hot embossing are bonded with pressure and hermetically sealed. Two inlet ports and an air vent are opened through the PDMS top substrate, while gold electrodes for electrochemical biosensing are patterned onto the PMMA bottom substrate. The analyte sample is loaded from the sample inlet port to the detection chamber by capillary force, without any external intervening forces. For this and to control the time duration of sample fluid in each compartment of the device, including the inlet port, diffusion barrier, reaction chamber, flow-delay neck, and detection chamber, the fluid conduit has been designed with various geometries of channel width, depth, and shape. Especially, the fluid path has been designed so that the sample flow naturally stops after filling the detection chamber to allow sufficient time for biochemical reaction and subsequent washing steps. As model immunosensing tests for the microfluidic device, functionalizations of ferritin and biotin to the sensing surfaces on gold electrodes and their biospecific interactions with antiferritin antiserum and streptavidin have been investigated. An electrochemical detection method for immunosensing by biocatalyzed precipitation has been developed and applied for signal registration. With the biochip, the whole immunosensing processes could be completed within 30 min.     

Synthesis of end‐functionalized poly(methyl methacrylate) by ruthenium‐catalyzed living radical polymerization with functionalized initiators

A series of functionalized 2‐bromoisobutyrates and 2‐chloro‐2‐phenylacetates led to α‐end‐functionalized poly(methyl methacrylate)s in Ru(II)‐catalyzed living radical polymerization; the terminal functions included amine, hydroxyl, and amide. These initiators were effective in the presence of additives such as Al(Oi‐Pr)₃ and n‐Bu₃N. The chlorophenylacetate initiators especially coupled with the amine additive gave polymers with well‐controlled molecular weights (M_w/M_n = 1.2–1.3) and high end functionality (F_n ～ 1.0). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1937–1944, 2002     

Iron‐catalyzed living radical polymerization of acrylates: Iodide‐based initiating systems and block and random copolymerizations

A half‐metallocene iron iodide complex [Fe(Cp)I(CO)₂] induced living radical polymerization of methyl acrylate (MA) in conjunction with an iodide initiator [(CH₃)₂C(CO₂Et)I, 1 ] and Al(Oi‐Pr)₃ to give polymers of controlled molecular weights and narrow molecular weight distributions (MWDs) (M_w/M_n < 1.2). With the use of chloride and bromide initiators, the MWDs were broader, whereas the molecular weights were similarly controlled. Other acrylates such as n‐butyl acrylate (nBA) and tert‐butyl acrylate (tBA) can be polymerized with 1 /Fe(Cp)I(CO)₂ in the presence of Ti(Oi‐Pr)₄ and Al(Oi‐Pr)₃, respectively, to give living polymers. The 1 /Fe(Cp)I(CO)₂ initiating system is applicable for the synthesis of block and random copolymers of acrylates (MA, nBA, and tBA) and styrene of controlled molecular weights and narrow MWDs (M_w/M_n = 1.2–1.3). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2033–2043, 2002     

Capillary electrophoresis of trace metals in highly saline physiological sample matrices

Trace metal ions in highly saline samples such as urine were determined with capillary electrophoresis (CE) without desalting or off-line preconcentration. By mixing with a dye, 4-(2-pyridylazo) resorcinol (PAR), the metal ions were converted into anionic complexes having strong absorbance near 500 nm. A large volume of the metal-PAR complex sample solution injected into a coated capillary was stacked isotachophoretically and separated under a reverse potential. The salt anion (chloride) and PAR in the sample matrix acted as the leading and terminating electrolytes, respectively. In a sample containing a 250 mM NaCl matrix, more than 400-fold enhancement in the absorbance detector response was realized compared to the normal CE injection mode. Combination of the dye complexation and isotachophoretic stacking provided excellent detection limits (S/N = 3) for three trace metal ions in the low ppb range (Fe(2+), 0.7 ppb, Ni(2+), 0.4 ppb; Zn(2+), 1.2 ppb) with absorbance detection. The migration time reproducibility was excellent (relative standard deviations: standard samples < 1%, urine samples approximately 1%). The proposed method is convenient and fast, and the sample analysis can be completed within 20 min.     

Effect of plant matrix and fluid ethanol concentration on supercritical fluid extraction efficiency of schisandrin derivatives

An investigation of the effect of plant matrix on the supercritical fluid extraction efficiency of five schisandrin derivatives is reported, exhibiting a great difference with respect to extraction efficiency depending on the matrix. Pure supercritical CO2 at 60 degrees C and 34.0 MPa cannot fully recover schisandrin derivatives from the leaves as much as from the other matrices. Only 36.9% of these compounds are extracted from leaves of Schisandra chinensis by supercritical CO2 in comparison with organic solvent extraction. However, more than 80% of schisandrin derivatives are obtained from both stem and fruit parts. Ethanol addition also shows a different effect depending on plant matrix; that is, CO2 modified with 10% ethanol could enhance the yield of schisandrin derivatives from leaves by four times when compared with that of pure CO2, but it has little effect on both stems and fruits.     

Colorimetric anion chemosensor based on 2-aminobenzimidazole: naked-eye detection of biologically important anions

We synthesized a novel colorimetric anion chemosensor bearing benzimidazole motifs as recognition sites in the pods of the receptor. The addition of tetrabutylammonium salts of F⁻ or AcO⁻ to the solution of receptor caused dramatic color changes from colorless to yellow, which was clearly visible to the naked eye. The receptor showed no significant changes on addition of other anions such as Cl⁻, Br⁻, I⁻, NO₃⁻, and H₂PO₄⁻.     

Adsorption of atomic hydrogen on single-walled carbon nanotubes

We have investigated atomic and electronic structures of hydrogen-chemisorbed single-walled carbon nanotubes (SWCNTs) by density functional calculations. We have searched for relative stability of various hydrogen adsorption geometries with coverage. The hydrogenated SWCNTs are stable with coverage of H/C, theta >/= 0.3. The circular cross sections of nanotubes are transformed to polygonal shapes with different symmetries upon hydrogen adsorption. We find that the band gap in carbon nanotubes can be engineered by varying hydrogen coverage, independent of the metallicity of carbon nanotubes. This is explained by the degree of sp(3) hybridization.