Recyclable self-assembly-supported catalytic system for orthoalkylation

[reaction: see text] A new recyclable supported catalyst system for orthoalkylation was devised using a self-assembly consisting of the barbiturate and 2,4,6-triaminopyrimidine H-bonding motifs. At high temperature, the system is completely homogeneous so as to give an efficient catalytic activity, while it is heterogenized at room temperature to form an insoluble solid phase for the easy recovery of the catalyst after the reaction.     

Identification of flavonoids using liquid chromatography with electrospray ionization and ion trap tandem mass spectrometry with an MS/MS library

Searchable MS/MS spectra libraries, constructed using the results of liquid chromatography coupled with electrospray ionization (ESI) tandem mass spectrometry (LC/MS/MS) with data-dependent acquisition on an ion trap mass spectrometer, are presented with regard to the identification and confirmation of a variety of closely related flavonoids in a set of biological samples. Flavonoids were found to exhibit a maximum amount of structurally specific MS/MS spectra at 45% of normalized collision energy on the instrument used, without wideband activation. These MS/MS spectra were then searched automatically against a 297-substance MS/MS library that contains many previously acquired spectra of standard flavonoids. The possible applications of this powerful technique to biological samples are also discussed. Daidzein and genistein were identified through the MS/MS spectra library while searching through LC/MS/MS data for plant and microbial extracts. Moreover, these compounds proved completely distinguishable from other flavonoids of closely related structures in the MS/MS spectra library, using the NIST MS search program. The applicability of the library-searchable spectra at low concentrations was demonstrated by successful identification of daidzein and genistein at 0.05 and 0.5 microg/mL, respectively.     

Synthesis and characterization of polystyrene‐b‐poly (1,2‐isoprene‐ran‐3,4‐isoprene) block copolymers with azobenzene side groups

Polystyrene‐b‐poly(1,2‐isoprene‐ran‐3,4‐isoprene) block copolymers with azobenzene side groups were synthesized by the esterification of azobenzene acid chloride with polystyrene‐b‐hydroxylated poly(1,2‐isoprene‐ran‐3,4‐isopenre) block copolymers for creating new photochromic materials. The resulting block copolymers with azobenzene side groups were characterized for structural, thermal, and morphological properties. IR and NMR spectroscopies confirmed that the polymers obtained had the expected structures. Differential scanning calorimetric measurements by heating runs clearly showed the glass transitions of polystyrene and polyisoprene main chains and two distinct first‐order transitions at temperatures of azobenzene side groups around 48 and 83 °C. The microstructure of these block copolymer films was investigated using both transmission electron microscopy (TEM) and near‐field optical microscopy (NOM). TEM images revealed typical microphase‐separated morphologies such as sphere, cylinder, and lamellar structures. The domain spacing of microphase‐separated cylindrical morphology in the NOM image agreed with that of the TEM results. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2406–2414, 2002     

Sequential injection analysis system for on-line monitoring of l-cysteine concentration in biological processes

A sequential injection analysis (SIA) system was developed to monitor the concentration of l-cysteine in biological processes on-line. It is based on the redox reaction of l-cysteine with iron(III) in the presence of 1,10-phenanthroline (phen) and the detection of the red-iron(II)-phen complex with a spectrophotometry. The system was fully automated using software written in the LabVIEW™ development environment. A number of system variables such as the flow rate of the carrier buffer solution, the volume ratio of the sample to the reagents, and the reaction coil length, etc., were evaluated to increase the sensitivity and performance of the SIA system. Under partially optimized operating conditions the performance of the SIA system was linear up to a concentration of l-cysteine of 1 mM (R² = 0.998) with a detection limit of 0.005 mM and a sample frequency of 15 hr⁻¹. The SIA system was employed to monitor the concentration of l-cysteine on-line in a continuously stirred reactor and a fermentation process of Saccharomyces cerevisiae. The on-line monitored data were in good agreement with the off-line data measured by a HPLC with a fluorescence detector (n = 15, R² = 09899).     

On-line coupling of liquid chromatography,capillary gas chromatography and mass spectrometry for the determination and identification of polycyclic aromatic hydrocarbons in vegetable oils

Summary An on-line combination of liquid chromatography, gas chromatography and mass spectrometry has been realized by coupling a quadrupole mass spectrometer to an LC-GC apparatus. Liquid chromatography was used for sample pretreatment of oil samples of different origin. The appropriate LC fraction, containing polycyclic aromatic hydrocarbons, was transferred to the gas chromatograph using a loop-type interface. After solvent evaporation through the solvent vapour exit and subsequent GC separation, the compounds were introduced into the mass spectrometer for detection and identification. The GC column was connected to a short piece of deactivated fused silica that protruded into the ion source. The total analytical set-up allowed the direct analysis of oil samples after dilution in n-pentane without any sample clean-up. Detection limits are about 40 pg in the full scan mode and about 1 pg with selective ion monitoring, i.e. 20 ppb and 0.5 ppb respectively.     

Self-assembly of rectangles and prisms via a molecular "clip"

Aromatic molecular "clips" bearing two symmetrically bound platinum moieties have been prepared. The molecular "clip" 4 readily self-assembled with linear linkers such as 4,4'-bipyridyl, 1,4-bis[2-(4-isocyano-3,5-diisopropylphenyl)ethynyl]benzene, and nicotinic acid to form molecular rectangles. The overall dimensions of the rectangle 7 were 7.3 Angstroms x 15.3 Angstroms. The molecular "clip" also self-assembled with tritopic pyridyl and isocyanide ligands to form trigonal prismatic frameworks. The characterization of the supramolecules by multinuclear NMR, electrospray mass spectrometry, and X-ray crystal structures is also reported.     

Factors affecting the catalytic epoxidation of olefins by iron porphyrin complexes and H2O2 in protic solvents

The catalytic epoxidation of cyclohexene by iron(III) porphyrin complexes and H2O2 has been investigated in alcohol solvents to understand factors affecting the catalyst activity in protic solvents. The yields of cyclohexene oxide and the Fe(III/II) reduction potentials of iron porphyrin complexes were significantly affected by the protic solvents, and there was a close correlation between the product yields and the reduction potentials of the iron porphyrin catalysts. The role of alcohol solvents was proposed to control the electronic nature of iron porphyrin complexes that determines the catalyst activity in the epoxidation of olefins by H2O2. We have also demonstrated that an electron-deficient iron porphyrin complex can catalyze the epoxidation of olefins by H2O2 under conditions of limiting substrate with high conversion efficiency in a solvent mixture of CH3OH and CH2Cl2.     

bPAK-interacting exchange factor may regulate actin cytoskeleton through interaction with actin

p21-activated kinase (PAK)-interacting exchange factor (PIX) is known to be involved in regulation of Cdc42/Rac GTPases and PAK activity. PIX binds to the proline-rich region of PAK, and regulates biological events through activation of Cdc42/Rac GTPase. To further investigate the role of PIX we produced monoclonal antibodies (Mab) against bPIX. Three clones; N-C6 against N-terminal half and C-A3 and C-B7 against C- terminal half of bPIX were generated and characterized. N-C6 Mab detected bPIX as a major band in most cell lines. C-A3 Mab recognizes GIT-binding domain (GBD), but it does not interfere with GIT binding to bPIX. Using C-A3 Mab possible bPIX interaction with actin in PC12 cells was examined. bPIX Mab (C-A3) specifically precipitated actin of the PC12 cell lysates whereas actin Mab failed to immunoprecipitate bPIX. Co-sedimentation of PC12 cell lysates with the polymerized F-actin resulted in the recovery of most of bPIX in the cell lysates. These results suggest that bPIX may not interact with soluble actin but with polymerized F-actin and revealed that bPIX constitutes a functional complex with actin. These data indicate real usefulness of the bPIX Mab in the study of bPIX role(s) in regulation of actin cyoskeleton.