Oxoaminium salts as initiators for cationic polymerization of vinyl monomers

Oxoaminium salt ( 1 ), derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 2 ) by one-electron oxidation, could be an initiator for cationic polymerization of vinyl monomers such as isobutyl vinyl ether (IBVE), 2,3-dihydrofuran, p-methoxystyrene, N-vinyl pyrrolidone, etc., to give the corresponding polymers, when 1 had a low nucleophilic counter anion. Formation of the adducts of 1 and IBVE as well as ¹H-NMR and IR data suggested the formation of polymers containing N? O? C structure as the polymer head group. In the polymerization of IBVE, the effects of solvent and concentration of 1 were little observed, however the polymerization rate was dependent on temperature. Furthermore, the thermal reaction of the polymers obtained, which were regarded as prepolymers for block copolymerization and polymeric initiators for radical polymerization, was studied. For example, poly(2-benzylidene-1,3-dioxane) obtained by the polymerization of 2-benzylidene-1,3-dioxane with oxoaminium hexafluoroantimonate ( 1, X = SbF₆) was employed as an initiator for radical polymerization of MMA to give its block copolymer with PMMA. © 1993 John Wiley & Sons, Inc.     

Carbapenem and penem antibiotics. VI. Synthesis and antibacterial activity of 2-heteroaromatic-thiomethyl and 2-carbamoyloxymethyl 1-methylcarbapenems

The synthesis and antibacterial activity of the 1-methylcarbapenems, 2-heteroaromatic-thiomethyl and 2-carbamoyloxymethyl derivatives having a 6-[(R)-1-hydroxyethyl] side chain, are described. The introduction of a methyl substituent at the C-1 position was accomplished by a newly developed procedure using crotyl halides and zinc dust. The 2-hydroxymethyl carbapenems as key intermediates allowed an easy entry into the preparation of title carbapenems.     

High-performance liquid chromatographic identification of disaccharides generated from heparan sulphate isomers using heparitinases

Specific heparan sulphate-lyases, heparitinases I and II, were used to identify unsaturated disaccharide constituents generated from heterogeneous heparan sulphate isomers. All determinations were made using high-performance liquid chromatography with a column containing a sulphonized styrene-divinylbenzene copolymer. Unsaturated disaccharides generated from variously sulphated heparan sulphate isomers after simultaneous digestion with heparitinases I and II facilitated separation of the individual disaccharides, based on sulphate groups at the specific position of the uronic acid and glucosamine residues. The simultaneous digestion with heparitinases I and II produces unsaturated disaccharides from heparan sulphate isomers with the structure of 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-amino-deoxy-D-glucose, 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-deoxy-2-sulphamido-D-glucose, 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-aminodeoxy-6-O-sulpho-D-glucose, 4-deoxy-2-O-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-deoxy-2-sulphamido-6-O-sulpho-D-glucose, 4-deoxy-2-O-sulpho-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-amino-2-deoxy-6-O-sulpho-D-glucose and 4-deoxy-2-O-sulpho-alpha-L-threo-hex-4-enepyranosyluronic acid (1----4)-2-deoxy-2-sulphamido-6-O-sulpho-D-glucose.     

3,4-dihydro-6,7-dimethoxy-4-methyl-3-oxo-qinoxaline-2-carbonyl azide as a highly sensitive fluorescence derivatization reagent for primary,secondary and tertiary alcohols in high-performance liquid chromatography

3,4-Dhydro-6,7-dimethoxy-4-methyl-3-oxo-quinoxaline-2-carbonyl azide is a highly senstive fluorescence derivatization reagent for primary, secondary and tertiary alcohols for high-performance liquid chromatography. Reaction conditions are optimized with benzyl alcohol, n-hexanol, cyclohexanol and 2-methyl-2-butanol. The reagent reacts with the alcohols in benzene to produce the corresponding fluorescent carbamic acid esters, which can be separated on a reversed-phase column YMC Pack C₈ with aqueous methanol as eluent. the detection limits for the alchols are 2–5 fmol per 10-μl njection. The reagent also reacts with hydroxysteroids with primary, secondary and/or tertiary alcoholic group(s) to form fluorescent derivatives. Hydroxycarboxylic acids and phenols do not give any chromatographic peaks.     

The temperature dependence of the zero-field splitting of trimethylenemethane

Trimethylenemethane was generated by γ-irradiating polycrystalline methylenecyclopropane, and studied by EPR at various temperatures. The zero-field splitting constant, D, was observed to change from 0.0260 cm^?1 at 4 K to 0.0212 cm^?1 at 126 K, though the hyperfine coupling showed little temperature dependence.     

Cover Picture

The cover picture shows a section of the electron charge density of the first metal carbide endohedral metallofullerene (Sc(2)C(2))@C(84) obtained from a synchrotron X-ray powder diffraction study by the maximum entropy method (MEM). The several density maxima, which correspond to scandium and carbon atoms, are clearly seen inside the C(84) carbon cage. The MEM charge density distribution also reveals that the C(84) cage has D(2d) symmetry (no. 23) and that the C(2) axis is parallel to the <100> face-centered cubic (fcc) direction of the unit cell. As a consequence of the site symmetry being 4mm, the C(2) axis of (Sc(2)C(2))@C(84) is oriented to six equivalent <100> directions and shows a merohedral disorder. The resultant Sc small middle dot small middle dot small middle dotSc distances and C-C bond lengths of the Sc(2)C(2) cluster are 0.429(2) and 0.142(6) nm, respectively. The observed C-C bond length is between that of a typical single and a double bond, and is very close to that of the C-C bond (0.143 nm) combining two pentagons in a C(60) molecule. More about this fascinating structure can be found in the contribution by Shinohara and co-workers on p. 397 ff.     

Photoelectron spectroscopy of (CO2)n(H2O) m − clusters

Photoelectron spectra of (CO₂)_nH₂O^? (2≤n≤8) and (CO₂)_n(H₂O) ₂ ^? (1≤n≤2) were measured at the photon energy of 3.49 eV. The spectra show unresolved broad features, which are approximated by Gaussians. The vertical detachment energies (VDEs) were determined as a function of the cluster size. For (CO₂)_nH₂O^?, the VDE-n plots exhibit a sharp discontinuity between n=3 and 4; the VDE value is ≈3.5 eV at n=3, while it drops down abruptly to 2.59 eV at n=4. This discontinuity in VDE is ascribed to "core switching" at n=4; a C₂O ₄ ^? dimer anion forms the core of (CO₂)_nH₂O^? for n≤3, while a monomer CO ₂ ^? is the core for n≥4. The (CO₂)₂(H₂O) ₂ ^? ion has a VDE of 2.33 eV, indicating the presence of a CO ₂ ^? monomer core in the binary clusters containing two H₂O molecules.     

Collective dynamics of sub- and supercritical methanol by inelastic X-ray scattering

Inelastic X-ray scattering experiments have been performed on methanol as a function of density from ambient to the supercritical state. Positive dispersion of the sound velocity, as compared to the hydrodynamic values, is 50% in the ambient condition and decreases to zero at 0.50 g cm⁻³ over the momentum transfer Q = 1–10 nm⁻¹ with lowering density; however, it increases again with a further decrease in density down to 0.20 g cm⁻³in the supercritical state only in the Q-range above 5 nm⁻¹. These results have been interpreted as the formation of small oligomers in the low-density supercritical methanol.     

Rh(I)-catalyzed Pauson-Khand reaction and cycloisomerization of allenynes: selective preparation of monocyclic, bicyclo[m.3.0], and bicyclo[5.2.0] ring systems

[reaction: see text] Rhodium(I)-catalyzed PKR of allenynes was found to be applicable for constructing azabicyclo[5.3.0]decadienone as well as oxabicyclo[5.3.0]decadienone frameworks. In addition, a reliable procedure for constructing a 10-monosubstituted bicyclo[5.3.0]deca-1,7-dien-9-one ring system by the rhodium(I)-catalyzed PKR of allenynes was developed under the condition of 10 atm of CO. Investigation of the rhodium(I)-catalyzed cycloisomerization of 4-phenylsulfonylnona-2,3-dien-8-ynes under nitrogen atmosphere gave the corresponding cyclohexene derivatives, whereas the C1-homologated allenynes produced cycloheptene derivatives and/or bicyclo[5.2.0]nonene skeletons depending on the substitution pattern at the allenic terminus. Thus, proper choice of the starting allenynes and reaction conditions led to the selective formation of 2-phenylsulfonylbicyclo[5.3.0]deca-1,7-dien-9-ones (Pauson-Khand-type product), 3-alkylidene-1-phenylsulfonyl-2-vinylcycloheptene derivatives, and bicyclo[5.2.0]nonene frameworks.     

Degradation of crosslinked unsaturated polyesters in sub-critical water

The degradation of unsaturated polyesters crosslinked with styrene was performed in sub-critical water (SCW) in the absence and presence of organic additives. The unsaturated polyesters were de-crosslinked by hydrolysis of ester chains to form polystyrene derivatives on SCW treatment at 300 °C. With an increase in treating time, carboxylic acid groups in the polystyrene derivatives were turned into carboxylic anhydride groups in SCW. The de-crosslinking rate was much enhanced on SCW treatment in the presence of hydroxy compounds with a long alkyl chain and alkylamines, while carboxylic acids, benzenesulfonate salts, and quaternary ammonium salts were ineffective even though they had a long alkyl chain. The degree of de-crosslinking was reduced in the presence of diamines and amino acids because re-crosslinking at both ends of the additive molecules proceeded.