Tandem Blaise-Nenitzescu reaction: one-pot synthesis of 5-hydroxy-α-(aminomethylene)benzofuran-2(3H)-ones from nitriles

In contrast to the reaction of benzoquinones with β-enaminoesters providing indoles (Nenitzescu reaction), the tandem one-pot reaction of the Blaise reaction intermediate, zinc bromide complex of β-enaminoesters, with benzoquinone affords 5-hydroxy-α-(aminomethylene)benzofuran-2(3H)-ones in good to excellent yields (tandem Blaise-Nenitzescu reaction).     

Investigation of the signaling mechanism and verification of the performance of an electrochemical real-time PCR system based on the interaction of methylene blue with DNA

The operation of an electrochemical real-time PCR system, based on intercalative binding of methylene blue (MB) with dsDNA, has been demonstrated. PCR was performed on a fabricated electrode-patterned glass chip containing MB while recording the cathodic current peak by measuring the square wave voltammogram (SWV). The current peak signal was found to decrease with an increase in the PCR cycle number. This phenomenon was found to be mainly a consequence of the lower apparent diffusion rate of the MB-DNA complex (D(b) = 6.82 × 10(-6) cm(2) s(-1) with 612 bp dsDNA) as compared to that of free MB (D(f) = 5.06 × 10(-5) cm(2) s(-1)). Utilizing this signal changing mechanism, we successfully demonstrated the feasibility of an electrochemical real-time PCR system by accurately quantifying initial copy numbers of Chlamydia trachomatis DNA templates on a direct electrode chip. A standard calibration plot of the threshold cycle (C(t)) value versus the log of the input template quantity demonstrated reliable linearity and a good PCR efficiency (106%) that is comparable to that of a conventional TaqMan probe-based real time PCR. Finally, the system developed in this effort can be employed as a key technology for the achievement of point-of-care genetic diagnosis based on the electrochemical real-time PCR.     

Immobilization of Tyrosinase on Chitosan — An Optimal Approach to Enhance the Productivity of L‐DOPA from L‐Tyrosine

Tyrosinase was immobilized on Chitosan (CTS) beads to produce 3,4‐dihydroxy‐L‐phenylalanine (L ‐DOPA) from L ‐tyrosine. Epichlorohydrin (ECH), ethylene glycol diglycidyl ether (EGDE), and glutaraldehyde (GLU) were used as coupling agents, respectively. Ultraviolet/visible measurements on CTS films showed that the reaction intermediate (L ‐dopaquinone) attacked the amino groups on CTS, so the amine residues on chitosan were capped by acetic acid anhydride (Ac) or formaldehyde (Fm) to avoid the deactivation of the immobilized tyrosinase. The pH and temperature of the maximal rate to produce L‐DOPA were investigated. GLU (coupling agent) and Ac (capping agent) were selected for practical utility. A 7.5% (w/v) concentration of GLU was found to attain maximal activity of the immobilized enzyme. The thermal stability of tyrosinase immobilized on CTS‐GLU‐Ac, and after treatment with sodium borohydride, was enhanced to a great extent. The L ‐DOPA converting efficiency in the environmental conditions of this study decreased from 45.1% to 39.9% (between 1^st and 30^th batch). This immobilized tyrosinase can be used practically in the production of L‐DOPA from L‐tyrosine.     

Synthesis and characterization of fully rodlike poly(4,4′‐biphenylene pyromellitimide)s with various short side groups

Fully rodlike poly(4,4‐biphenylene pyromellitimide) (PMDA–BZ) is so brittle in spite of its extremely high modulus. In this study, the brittleness was attempted to be improved without a significant sacrifice of the high modulus by incorporating short side groups. For this, benzidine monomers, which contain methyl, methoxy, fluoro, and trifluoromethyl at the 2,2′‐positions, were synthesized and then used for polycondensation reactions with pyromellitic dianhydride in N‐methyl‐2‐pyrrolidone, producing soluble poly(amic acids)s. The synthesized poly(amic acid)s were converted to the fully rodlike polyimides in films by a conventional spin‐coating on substrates, soft bake, and thermal imidization. The brittleness of PMDA–BZ was successfully healed with a small portion of sacrifice in the modulus by incorporating methyl, methoxy, and trifluoromethyl groups but could not be healed by the fluoro side group. The improvement in the brittleness might be contributed from the chain mobility and lateral chain packing order enhanced by the incorporation of the side groups, which are evident on the measured structures and properties. The structure and other properties were detected to be influenced by the incorporated side groups. The detailed structures and properties were interpreted by considering roles of side groups and the correlation between structure and properties, respectively. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 937–957, 1999     

Effect of nanoscaled SnO2 coating on ZnS:Mn phosphors under electron irradiation

The luminescence properties of SnO₂-coated ZnS:Mn phosphors are investigated. In the case of photoluminescence, emission intensities show little change when SnO₂ is coated on the surface of ZnS:Mn, while in the case of cathodoluminescence (CL), emission intensities vary depending on excitation energies. In order to determine the luminescence behaviors, surface analyses of the phosphors were performed. Auger electron spectroscopy showed that the width of the SnO₂ layer on the ZnS:Mn phosphor was saturated at approximately 120 nm. Also, X-ray photoelectron spectroscopy indicated that the SnO₂ layers are well formed and saturated when the molar ratios of Sn/Zn are larger than 0.005. These results suggest that the changes in the CL emissions can be attributed to a lowering of the junction barrier.     

The stereoselective synthesis of α-substituted β-amino secondary alcohols based on the proline-mediated, asymmetric, three-component Mannich reaction and its application to the formal total synthesis of nikkomycins B and Bx

A general method for the asymmetric synthesis of α-substituted β-amino secondary alcohols is described, which comprises the four-reaction sequence (1) the proline-mediated, asymmetric, three-component Mannich reaction of two different aldehydes, (2) nucleophilic carbon addition to aldehyde, (3) oxidation of the resulting alcohol to the corresponding ketone, and (4) diastereoselective reduction with LiAlH(O-t-Bu)₃ or catecholborane. The former reductant afforded the 1,2-syn isomer, while the latter gave the 1,2-anti isomer stereoselectively. The present method was successfully applied to the efficient asymmetric synthesis of the N-terminal amino acid moiety of nikkomycin B and B_X.     

Polyethylene-Montmorillonite Nanocomposites: Preparation,Characterization and Properties

Polyethylene(PE)/clay nanocomposites have been successfully prepared by in situ polymerization with an intercalation catalyst titanium-montmorillonite (Ti-MMT) and analyzed by X-ray diffraction analysis (XRD), Fourier transform infrared analysis (FT-IR), Transmission electron microscopy (TEM), differentail scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and tensile testing. XRD and TEM indicate that the clay is exfoliated into nanometer size and disorderedly dispersed in the PE matrix, and the PE crystallinity of PE/clay nanocomposite declines to 15∼30%. Compared with pure PE, PE/clay nanocomposites behave higher thermal, physical and mechanical properties; the layer structure of the clay decreases the polymerization activity and produce polymer with a high molecular weight. For PE/clay nanocomposites, the highest tensile strength of 33.4 MPa and Young's modulus of 477.4 MPa has been achieved when clay content is 7.7 wt %. The maximum thermal decomposition temperature is up to 110 °C higher, but the thermal decomposition temperature of the PE/clay nanocomposites decreases with the increases of the clay contents in the PE matrix.     

Indirect enantioseparation of fluoxetine in mouse serum by derivatization with 1R‐(–)‐menthyl chloroformate followed by ultra high performance liquid chromatography and quadrupole time‐of‐flight mass spectrometry

Here we describe a simple and sensitive analytical method for the enantioselective quantification of fluoxetine in mouse serum using ultra high performance liquid chromatography with quadrupole time‐of‐flight mass spectrometry. The sample preparation method included a simple deproteinization with acetonitrile in 50 μL of serum, followed by derivatization of the extracts in 50 μL of 2 mM 1R‐(–)‐menthyl chloroformate at 45ºC for 55 min. These conditions were statistically optimized through response surface methodology using a central composite design. Under the optimized conditions, neither racemization nor kinetic resolution occurred. The derivatized diastereomers were readily resolved on a conventional sub‐2 μm C₁₈ column under a simple gradient elution of aqueous methanol containing 0.1% formic acid. The established method was validated and found to be linear, precise, and accurate over the concentration range of 5.0–1000.0 ng/mL for both R and S enantiomers (r² > 0.993). Stability tests of the prepared samples at three different concentration levels showed that the R‐ and S‐fluoxetine derivatives were relatively stable for 48 h. No significant matrix effects were observed. Last, the developed method was successfully used for enantiomeric analysis of real serum samples collected at a number of time points from mice administered with racemic fluoxetine.     

Co-synthesis of nano-sized LSM–YSZ composites with enhanced electrochemical property

Nano-sized LSM–YSZ composite was co-synthesized by a glycine–nitrate process (GNP). Transmission electron microscopy revealed that the as-prepared LSM–YSZ particles consist of nano-sized powders with a dominant YSZ phase. Backscatter electron image shows that LSM and YSZ phases were regularly dispersed within the composite. Alternating current impedance measurement revealed that the co-synthesized LSM–YSZ electrode shows lower polarization resistance and activation energy than the physically mixed LSM–YSZ electrode. This electrochemical improvement would be attributed to the increase in three-phase boundary and good dispersion of LSM and YSZ phases within the composite. This paper is dedicated to Professor Su-Il Pyun on the occasion of his 65th birthday.