Constituents of Catha edulis: Isolation and structure of cathidine D

Work which has recently appeared on the structures of Celastraceae alkaloids in addition to physical and chemical evidence adduced with respect to cathidine D permits formulation of structure 7a or 7b for this component of Catha edulis.     

NMR Determination of the Microstructure of Polyvinyl Chloride Sulfone). II. 13C-(1H) Spectra

The ¹³C-(¹H) NMR spectra of poly(vinyl chloride sulfone)s with macroscopic compositions corresponding to the ratio vinyl chloride (V):SO₂(S) = n from ca. 1 to 4 have been analyzed in terms of comonomer sequences and configurational placements. In the copolymer with n ? 1, methylene and methine carbons in SVS sequences were resolved and were sensitive to “across SO₂” tacticity. No SVS sequences were observed in the copolymer with n = 2.0, confirming that it had a regular SVVS structure, which also showed a high “internal” stereosequence regularity. It was not possible to discriminate the methylene or methine carbon atoms in S(V)_n S sequences with n ≥ 2.     

Copolymerization of Vinyl Chloride and Sulfur Dioxide. II. Copolymerization Rates and Copolymer Compositions

The rate of copolymerization of vinyl chloride (VC) with sulfur dioxide and the composition of the poly (vinyl chloride sulfone) formed have been measured for comonomer liquid mixtures with X_VC = 0.1 to 1.0 and over the temperature range -95 to +46°C.

Polymerization was initiated by γ-irradiation (-95 to +46°C) and with the t-butyl hydroperoxide/SO₂/methanol redox system (-95 to -18°C). The copolymerization rates and copolymer compositions indicated two distinct temperature regions, with a change in mechanism around 0°C. For radiation initiation below 0°C, the rate versus comonomer composition relationship showed a maximum at an x_VC value which increased with increasing temperature. Above 0°C, the rate decreased with increasing temperature and was greatly retarded by SO₂. No high molecular weight copolymer or VC homopolymer was formed on irradiation of comonomer mixtures above ～55°C.     

Three-dimensional blow-up solutions of the Navier-Stokes equations

In this paper we extend the plane blow-up results of Grundy& McLaughlin (1997) to the three-dimensional Navier-Stokes equations.Using a solution structure originally due to Lin we first providenumerical evidence for the existence of blow-up solutions on- < x, z < , 0 y 1 with boundary conditions on y = 0and y = 1 involving derivatives of the velocity components.The formulation enables us to consider plane and radial flowas special cases. Various features of the computations are isolatedand are used to construct a formal asymptotic solution closeto blow-up. We show that the numerical and asymptotic analysesprovide a mutually consistent global picture which supportsthe conclusion that, for the family of problems we considerhere, blow-up in fact can take place in three dimensions butat an inverse linear rate rather than the faster inverse squareof the plane case.     

Long-term retention of ice-nucleating active Pseudomonas fluorescens by overwintering colorado potato beetles

Ice nucleating-active Pseudomonas fluorescens F264C was fed to Colorado potato beetles to determine bacterial retentioin in the beetle gut and its effect on the cold hardiness of this insect pest. The bacrterium was present in beetles recovered after overwintering in the field, seven months after their exposure to P. fluorescens. Retention was evident not only in the detection of the P. fluorescens ice nucleating gene, inaW, in bacterial cultures from beetle guts but also in the elevated supercooling points of some treated beetles.     

The dechlorination of poly(vinyl chloride) by zinc and tributyl tin hydride.: Characterization of the product microstructures by carbon-13 NMR

Poly(vinyl chloride) has been reacted with zinc in refluxing dioxane for times in the range 18–113 h. The structure of the polymeric product has been examined by ¹H and ¹³C NMR spectroscopy. Contrary to earlier predictions, the reaction does not proceed only by 1,3-chlorine elimination to form cyclopropyl rings. Double bonds and methylene units are formed also, to give a polymer of considerable structural complexity. This complexity can be reduced by replacement of remaining chlorine with hydrogen after treatment with tributyl tin hydride. Analysis of the fully dechlorinated polymer shows that cyclopropyl rings are distributed randomly with a trans/cis ratio of about 2.6. A small number of cyclopentyl rings is observed also. A maximum of 9% of the original vinyl chloride units are dehydrochlorinated to give unconjugated vinylene units with a predominantly trans structure.     

Electron-transfer reactions of amines with α-ferrocenylcarbonium ions

The production observed in the reactions of α-ferrocenylcarbonium ions with tertiary amines do not originate from ferrocenylcarbene intermediates. Evidence is presented in support of an electron-transfer mechanism leading to α-ferrocenylcarbinyl radicals as reaction intermediates.     

Low-lying (K π = 0+) states of gadolinium isotopes

The sd-interacting boson approximation (sd-IBA) and the df-interacting boson approximation (df-IBA) can be related to each other and the states of the interacting boson approximation model can be identified with the fully symmetric states in the sdf interacting boson approximation model. A systematic study of the sdf-IBA model showed that the constructed Hamiltonian can successfully describe the strong octupole correlations in the deformed nuclei. We showed that the interacting boson approximation may account for many of these K ^π ?=?0⁺ states. It was found that the calculated energy spectra of the gadolinium isotopes agree quite well with the experimental data. The observed B(E2) values were also calculated and compared with the experimental data.