Thermal immobilization of ferrocene derivatives on (111) surface of n-type silicon: parallel between vinylferrocene and ferrocenecarboxaldehyde

Monolayers attached to a Si(111) surface through Si-C-C or Si-O-C covalent bonds were prepared by the thermally activated reaction (150 degrees C) of vinylferrocene (VFC) or ferrocenecarboxaldehyde (FCA) molecules with hydrogen-terminated Si(111) substrate in order to compare their reactivities. The resulting monolayers gave a couple of redox waves on voltammograms due to ferrocenyl moieties tethered at the surface. The voltammetric quantification revealed that the growth of electrochemically active layers was terminated within 5 h and the final surface coverages of the active ferrocenyl moieties were 58% and 16% for VFC- and FCA-based monolayers, respectively, indicating that the aldehyde molecule is less reactive. X-ray photoelectron spectroscopy and ellipsometry, however, gave an indication that the growth of the VFC layer did not self-terminate and proceeded beyond a monolayer, while this overgrown part of the layer was not electrochemically active.     

Synthesis of a well-defined cyclic polystyrene via α-carboxyl, ω-amino heterodifunctional polystyrene

Living anionic polymerization of styrene was carried out in benzene at room temperature using 1-(3-lithiopropyl)-4-methyl-2,6,7-trioxabicyclo[2.2.2]octane and 2,2,5,5-tetramethyl-1-(3-bromopropyl)-1-aza-2,5-disilacyclopentane as an initiator and terminator, respectively, to obtain α-2,2-bis(hydroxymethyl)propoxycarbonyl, ω-amino heterodifunctional polystyrene. It was hydrolyzed to α-carboxyl, ω-amino heterodifunctional polystyrene which gave a well-defined cyclic polystyrene by the intramolecular cyclization under high dilution conditions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2027–2033, 1999     

Chemoselective synthesis of polyamides containing hydroxyl and amino substituents by direct polycondensation

A convenient method for the synthesis of polyamides containing hydroxyl and amino substituents on the aromatic rings of the backbones was developed. These polymers were prepared readily by the chemoselective polycondensation of dicarboxylic acids with diamines with hydroxyl and amino functional groups via the activating agent diphenyl(2,3‐dihydro‐2‐thioxo‐3‐bezoxazolyl)phosphonate. The model reactions were studied in detail to demonstrate the feasibility of chemoselective polycondensation. The direct polycondensation of 5‐hydroxy or 5‐aminoisophthalic acid with 4,4′‐diamino‐4″‐hydroxytriphenylmethane proceeded smoothly under mild conditions and produced the desired polyamides with inherent viscosities up to 0.73 dL · g⁻¹. The polymers obtained were characterized by IR, ¹H NMR, and ¹³C NMR spectroscopies. The polymers were readily soluble in aprotic polar solvents such as N‐methyl‐2‐pyrrolidinone, N,N‐dimethyl formamide, and dimethyl sulfoxide. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3875–3882, 2000     

A Catalytic and Stereoselective Glycosylation with β‐Glycosyl Fluorides

A catalytic and stereoselective glycosylation of several glycosyl acceptors with β‐D ‐glycosyl fluoride was successfully performed in the presence of a catalytic amount of trityl tetrakis(pentafluorophenyl)borate (TrB(C₆F₅)₄) or trifluoromethanesulfonic acid (TfOH). When TrB(C₆F₅)₄ was used as a catalyst in the solvent pivalonitrile/(trifluoromethyl)benzene 1 : 5, the glycosylation proceeded smoothly to afford the glycosides in high yields with high β‐D ‐stereoselectivities (see Table 3). Further, the glycosylation by the armed‐disarmed strategy in the presence of this catalyst was established (see Table 4). Similarly, glycosylation catalyzed by the strong protic acid TfOH afforded the corresponding β‐D ‐glycosides in good‐to‐excellent yields on treating β‐D ‐ glycosyl fluorides having a 2‐O‐benzoyl group with various glycosyl acceptors including thioglycosides (see Tables 6 and 7).     

Modulation of the NOTCH1 Pathway by LUNATIC FRINGE Is Dominant over That of MANIC or RADICAL FRINGE

Fringes are glycosyltransferases that transfer a GlcNAc to O-fucose residues on Epidermal Growth Factor-like (EGF) repeats. Three Fringes exist in mammals: LUNATIC FRINGE (LFNG), MANIC FRINGE (MFNG), and RADICAL FRINGE (RFNG). Fringe modification of O-fucose on EGF repeats in the NOTCH1 (N1) extracellular domain modulates the activation of N1 signaling. Not all O-fucose residues of N1 are modified by all Fringes; some are modified by one or two Fringes and others not modified at all. The distinct effects on N1 activity depend on which Fringe is expressed in a cell. However, little data is available on the effect that more than one Fringe has on the modification of O-fucose residues and the resulting downstream consequence on Notch activation. Using mass spectral glycoproteomic site mapping and cell-based N1 signaling assays, we compared the effect of co-expression of N1 with one or more Fringes on modification of O-fucose and activation of N1 in three cell lines. Individual expression of each Fringe with N1 in the three cell lines revealed differences in modulation of the Notch pathway dependent on the presence of endogenous Fringes. Despite these cell-based differences, co-expression of several Fringes with N1 demonstrated a dominant effect of LFNG over MFNG or RFNG. MFNG and RFNG appeared to be co-dominant but strongly dependent on the ligands used to activate N1 and on the endogenous expression of Fringes. These results show a hierarchy of Fringe activity and indicate that the effect of MFNG and/or RFNG could be small in the presence of LFNG.     

Miniaturized Molecularly Imprinted Continuous Polymer Rods

Molecularly imprinted continuous polymer rods are prepared inside PEEK tubes of 1 mm i. d. by an in situ preparation technique; and chiral separations on such media have been demonstrated. The miniaturized column filled with (–)‐cinchonidine‐imprinted or (+)‐cinchonine‐imprinted polymer rods based on a copolymer of 2‐(trifluoromethyl)acrylic acid and ethylene glycol dimethacrylate permitted diastereoseparation of (–)‐cinchonidine and (+)‐cinchonine; the template molecule is retained to a greater extent than the corresponding antipode. Increasing the amount of cyclohexanol in the polymerization mixture decreased the backpressure of the resultant rod and the addition of latex beads suspended in water to the prepolymerization mixture affected the selectivity and affinity of the imprinted polymer rods. The column length is adjusted easily by cutting, thus allowing easy control of retention behavior and analysis time.     

Effect of eluent composition on retention behavior of anions in ion chromatography on anion-exchangers modified with heparin

Effects of eluent composition on retention behavior of inorganic anions have been investigated in ion chromatography using anion-exchangers modified with heparin. Both cation and anion of the eluent affected the retention of analyte anions and unusual retention behavior was observed on the modified stationary phase. The retention time of anions decreased with decreasing eluent concentration when sodium sulfate, magnesium sulfate and chlorides of alkali metals were used as the eluent, whereas it increased with decreasing eluent concentration when aluminum sulfate, copper sulfate and sulfuric acid were used as the eluent. The retention of nitrate increased in the order of Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ when their chlorides were used as the eluent. When sodium perchlorate and chlorides of alkaline-earth metals were used as the eluent, the eluent should include heparin. Otherwise, the modifier was partially bled from the column.     

In situ Mössbauer and magnetization studies of Fe–Si nanocrystallization in Fe73.5Si13.5B9Cu1Nb1 X2, with X = Nb, Zr, Mo, amorphous alloys

The Fe–Si nanosized particles were obtained by controlled partial crystallization of Fe_73.5Si_13.5B₉Cu₁Nb₁X₂ (X = Nb, Zr, Mo) amorphous alloys. In situ Mössbauer spectroscopy and magnetization measurements have been used to follow the temperature-dependent magnetization of the amorphous as well as of the nanosized Fe–Si particles. Our results, for the residual amorphous and of nanoparticles phases, show that the temperature dependence of the hyperfine field and magnetization of both residual amorphous and nanocrystalline Fe(Si) phases are different from that of the as-quenched bulk amorphous or crystalline Fe₃Si alloys. Likewise, from the temperature dependence studies it was possible to determine that the onset temperature of the nanocrystallization process increases in the sequence Mo < Nb < Zr, for the same annealing conditions.