Spectroscopy and photophysics of methylphenylsiloxaneand diphenylsiloxane-based molecules and polymers

Spectroscopy and photophysics of various types of methylphenylsiloxane- and diphenylsiloxane-based oligomers and polymers are reviewed. The molecules treated here include homopolymers such as poly(methylphenylsiloxane) and copolymers such as poly(dimethylsiloxane-codiphenylsiloxane) as well as related oligomers or molecules such as diphenyltetramethyldisiloxane. These polymers and oligomers normally exhibit monomer fluorescence in fluid solution at temperatures near room temperature, and the monomer fluorescence and phosphorescence in rigid matrices at 77 K. In addition to these emissions, the excimer fluorescence is often observed depending on the molecular structure of the siloxanes. These emission properties are rationalized based on the molecular structure and kinetics of the excimer formation processes as well as on the flexibility of the Si-O-Si bonds.     

Glycosides of benzyl and salicyl alcohols from Alangium chinense

From the water-soluble fraction of the dried leaves of Alangium chinense, three new glycosides, benzyl alcohol beta-D-glucopyranosyl-(1 --> 2)-[beta-D-xylopyranosyl-(1 --> 6)]-beta-D-glucopyranoside, 2'-O-beta-D-glucopyranosylsalicin, and 2'-O-beta-D-glucopyranosyl-6'-O-beta-D-xylopyranosylsalicin were isolated along with seven known glycosides. The structures of the new compounds were determined by spectroscopic and chemical means.     

Diethylhydrogensilyl cyclic diethylsilylene derivatives in gas chromatography/mass spectrometry of hydroxylated steroids. III-Fragmentations of 5β-pregnane-17,20,21-triol derivatives

A reaction of N,O-bis-(diethylhydrogensilyl) trifluoroacetamide with 5β-pregnane-17,20,21-triols afforded diethylhydrogensilyl (DEHS) cyclic diethylsilylene (DES) derivatives. 5β-Pregnane-3α,17α,20β,21-tetraol yielded the 3α,21-bis-DEHS-17α,20β-DES compound, whereas the structure of the major product from its 20α isomer was assigned as the 3α,17α-bis-DEHS-20α,21-DES derivative, which would undergo facile isomerization to the unstable 3α,21-bis-DEHS-17α,20α-DES structure under electron ionization. Fragmentations of these DEHS-DES compounds are discussed on the basis of isotope labelling experiments, linked scanning data, and accurate mass measurements.     

Efficient biocatalysis for the production of enantiopure (S)-epoxides using a styrene monooxygenase (SMO) and Leifsonia alcohol dehydrogenase (LSADH) system

Herein we report the production of enantiopure epoxides through biocatalysis using recombinant Escherichia coli cells expressing Rhodococcus sp. ST-10 styrene monooxygenase (SMO) and Leifsonia sp. S749 alcohol dehydrogenase (LSADH) genes are described. Rhodococcus sp. ST-10 SMO catalyzed the epoxidation of various alkenes, including styrene derivatives, vinyl pyridines, and linear alkenes, to give (S)-epoxides. NADH was regenerated by the reduction of NAD⁺ by LSADH with 2-propanol. The E. coli biocatalyst was used in an aqueous/organic biphasic reaction system and the reaction conditions were optimized. Under the optimized conditions, 170 mM of (S)-styrene oxide was obtained from styrene in the organic phase with excellent enantiomeric excess (99.8%). This biocatalytic process was used to synthesize various (S)-epoxides.     

A Novel Synthesis of 4‐Pyridazineacetic Acids via Ring Expansion of N‐Cyanomethylated 3‐Pyrazoline‐4‐acetic Acids

A novel synthetic route to 4‐pyridazineacetic acids 10 – 12 has been achieved by the ring‐expansion reaction of N‐cyanomethylated 3‐pyrazoline‐4‐acetic acids 7 – 9 . 1H‐Pyrazole‐4‐acetic acids 1 – 3 were reacted with iodoacetonitrile in the presence of triethylamine in refluxing acetonitrile to give the corresponding C‐cyanomethylated 1H‐pyrazole‐4‐acetic acids 4 – 6 as major products together with N‐cyanomethylated 3‐pyrazoline‐4‐acetic acids 7 and 8 as minor products. On the other hand, reactions of 1 and 3 with chloroacetonitrile in the presence of triethylamine in refluxing chloroform afforded the corresponding N‐cyanomethylated 3‐pyrazoline‐4‐acetic acids 7 and 9 as major products. Thermal treatment of 7 – 9 with sodium hydride in N,N‐dimethylformamide caused ring expansion to yield the corresponding 4‐pyridazineacetic acids 10 – 12 .     

N-linked oligosaccharide analysis of rat brain Thy-1 by liquid chromatography with graphitized carbon column/ion trap-Fourier transform ion cyclotron resonance mass spectrometry in positive and negative ion modes

We have previously described the site-specific glycosylation analysis of rat brain Thy-1 by LC/multistage tandem mass spectrometry (MS(n)) using proteinase-digested Thy-1. In the present study, detailed structures of oligosaccharides released from Thy-1 were elucidated by mass spectrometric oligosaccharide profiling using LC/MS with a graphitized carbon column (GCC-LC/MS). First, using model oligosaccharides, we improved the oligosaccharide profiling by ion trap mass spectrometry (IT-MS) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Sequential scanning of a full MS(1) scan with FT-ICR-MS followed by data-dependent MS(n) with IT-MS in positive ion mode, and a subsequent full MS(1) scan with FT-ICR-MS followed by data-dependent MS(n) with IT-MS in negative ion mode enabled the monosaccharide composition analysis as well as profiling and sequencing of both neutral and acidic oligosaccharides in a single analysis. The improved oligosaccharide profiling was applied to elucidation of N-linked oligosaccharides from Thy-1 isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was demonstrated that Thy-1 possesses a significant variety of N-linked oligosaccharides, including Lewis a/x, Lewis b/y, and disialylated structure as a partial structure. Our method could be applicable to analysis of a small abundance of glycoproteins, and could become a powerful tool for glycoproteomics.