Approaches to dioxin analysis by HRGC-HRMS and hybrid HRGC-MS-MS

A hybrid mass spectrometer with an EBQQ configuration was used to investigate two approaches to trace dioxin analysis: high resolution gas chromatography – high resolution mass spectrometry (HRGC-HRMS) and high resolution gas chromatography – mass spectrometry – mass spectrometry (HRGC-MS-MS). It is shown that selected ion monitoring (SIM) HRGC-HRMS exhibits better selectivity for dioxins separated on a cyanopropyl column than is otherwise obtained under medium resolution mass spectrometry (3,000 resolution), while optimization of conditions for HRGC-MS-MS allowed the observation of 350 femtograms of the highly toxic 2,3,7,8-TCDF at a S/N ratio of 5:1. Both methods were applied to environmental samples with good results.     

Gas permeability and permselectivity of fluorinated polybenzoxazoles

Gas permeability and permselectivity are investigated for polybenzoxazoles from bis(3-amino-4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane (BAHHP) and aromatic diacid chlorides. Effects of thermal cyclization on the permeation properties are also investigated. The polybenzoxazole from BAHHP and 4,4′-(1,1,1,3,3,3-hexafluoroisopropylidene)dibenzoyl chloride (HFDB) displays high performance for CO₂/CH₄ separation ( $ {\rm P}_{{\rm CO}_2 } $ = 6.1 × 10^?9 cm³ (STP) cm^?1 s^?1 cm-Hg^?1, and $ {{{\rm P}_{{\rm CO}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm CO}_2 } } {{\rm P}_{{\rm CH}_4 } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_4 } }} $ = 38 at 35°C). The polybenzoxazole from BAHHP and 2,6-naphthalene dicarbonyl chloride displays high performance for H₂/CO or H₂/CH₄ separation ( $ {\rm P}_{{\rm H}_2 } $ = 2.4 × 10^?9 cm³ (STP) cm^?1 s^?1 cm-Hg^?1, $ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CO}} }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CO}} }} $ = 71, and $ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CH}_{\rm 4} } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_{\rm 4} } }} $ = 250). Permeation properties for the polybenzoxazole from BAHHP and HFDB are close to those for a polyimide of similar chemical structure. The permeation properties are discussed in connection with packing density and local segmental mobility. © 1992 John Wiley & Sons, Inc.     

REDUCTION OF BIS(BROMO(MESITYL)-{2,4,6-TRIS[BIS(TRIMETHYLSILYL)METHYL]- PHENYL}SILYL)BUTADIYNE WITH POTASSIUM GRAPHITE: UNEXPECTED FORMATION OF 2-ALLENYL-1-BENZOSILOLE

The reductive debromination of an very crowded bis(bromodiaryl- silyl)butadiyne 2 was performed with potassium graphite to give the corresponding 2-allenyl-1-benzosilole 3 was isolated as a main product.     

Mechanism of Macroscopic Motion of Oleate Helical Assemblies: Cooperative Deprotonation of Carboxyl Groups Triggered by Photoisomerization of Azobenzene Derivatives

Macroscopic and spatially ordered motions of self‐assemblies composed of oleic acid and a small amount of an azobenzene derivative, induced by azobenzene photoisomerization, was previously reported. However, the mechanism of the generation of submillimeter‐scale motions by the nanosized structural transition of azobenzene was not clarified. Herein, an underlying mechanism of the motions is proposed in which deprotonation of carboxyl groups in cooperation with azobenzene photoisomerization causes a morphological transition of the self‐assembly, which in turn results in macroscopic forceful dynamics. The photoinduced deprotonation was investigated by potentiometric pH titration and FTIR spectroscopy. The concept of hierarchical molecular interaction generating macroscale function is expected to promote the next stage of supramolecular chemistry.     

Titanocene(II)-Promoted Reactions of 2-(Alk-1-yn-1-yl)-2-(Trialkylsilyl)-1,3-dithianes with Olefins and Carbonyls

Abstract

Trialkylsilyl group-directed regioselective transformations of alkynyl thioacetals to alkynylcyclopropanes and enynes are described.     

The First Rotational Isomers of Stable Selenobenzaldehydes and their η1-Tungsten Complexes

The first rotational isomers of stable selenoaldehydes are synthesized by deselenation of cyclic polyselenides having an efficient steric protection group, 2, 4, 6-tris[bis(trimetylsilyl)methyl]phenyl (Tbt). Reactions of these selenoaldehydes with W(CO)₅.THF gives the corresponding η¹-selenoaldehyde tungsten complexes, the structures of which are established by X-ray crystallography.     

Synthesis and Polymerization of (S)-4-Methyl-2-N,N-dimethylaminopentyl Methacrylate

(S)-4-Methyl-2-N,N-dimethylaminopentyl methacrylate (DMAPM) was synthesized from the reaction of N,N-dimethyl-L-leucinol with methacryl chloride, and its radical polymerization was investigated. It was found that DMAPM readily polymerized by α,α¹-azobisisobutyronitrile (AIBN) as an initiator to give poly-DMAPM. The copolymerization of DMAPM(M₁) with styrene(Mz) was also studied in various solvents with AIBN as an initiator at 60°C. From the result obtained in benzene, Q and e values of DMAPM were determined to be 0.64 and -0.04, respectively. Specific rotations of the copolymers of DMAPM with styrene were not proportional to the weight percent of the DMAPM unit incorporated, but the observed relation gave a downward curve. The copolymerizations DMAPM with α, β-disubstituted monomers such as maleic acid, maleimide, and N-phenylmaleimide were carried out in order to induce asymmetric center in the polymer chain. After hydrolysis of the copolymers obtained, the hydrolyzed polymers were found to be optically active, suggesting an induction of asymmetric center into the polymer chain.