Crystal and molecular structure of 1-epi-delphisine and nmr assignments for delphisine, 1-epi-delphisine and delphinine

The crystal and molecular structure of the norditerpenoid alkaloid 1-epi-delphisine (5), C₂₈H₄₃NO₈, M _r 521.66, has been confirmed by as X-ray diffraction study using the SIR 88 analysis program. The alkaloid crystallizes in the space groupP2₁ with cell parameters:a=11.853(1)Å,b=10.511(1)Å,c=11.854(1)Å,=112.58(1),V=1363.61(0)ų,Z=2,D _calc=1.27 g/cm³, (CuK)=1.54184 Å, (CuK=7.2 cm^–1,F(000)=564, temperature 23°C,R=0.052, for 2907 reflections. Ring A of 1-epi-delphisine exists in a chair conformation. By comparison, delphisine which bears a C-1 hydroxyl group, has ring A in a boat conformation stabilized by an intramolecular N----H-O hydrogen bond. Ring D of both of these alkaloids exists in a boat form. Unambiguous proton and carbon-13 nmr assignments for delphisine, 1-epi-delphisine and delphinine have been made by a detailed analysis of the DEPT, COSY, HETCOR, COLOC, DIFNOE, and selective INEPT nmr techniques.Dedicated to the memory of Dr. K. Krishna Bhandary (1946–1992).     

Relaxation experiments of polymeric systems confined in very narrow gaps

A new way of investigating the relaxation processes of polymeric systems confined between solid surfaces is presented here. The test is based on draining experiments by means of a surface force apparatus and consists in monitoring the hydrodynamic force release following a drainage motion. Experiments carried out with solutions of high polymers exhibit two distinct relaxation processes. The longest one is connected to the relaxation of the chains adsorbed onto the solid surfaces and which are pinned in the area of closest distance between the solid surfaces. Its variations as a function of spacing are consistent with the bridging of some macromolecules. The fastest process is connected to the flow of the solvent molecules through the pseudonetwork formed by the adsorbed layers carried by the solid surfaces. These results have been compared favorably with those obtained by oscillatory measurements as far as relaxation time and viscosity are concerned. The accuracy of the experimental relaxation function is not sufficient for describing reasonably the viscoelastic behavior of the confined fluid. © 1996 John Wiley & Sons, Inc.     

A biaxial nematic gel phase in aqueous vanadium pentoxide suspensions

Aqueous suspensions of V₂O₅ ribbons are one of the very few examples of mineral liquid crystals. In the concentrated regime, we show that these ribbons organize in a biaxial nematic gel phase. A Couette shear cell was used to produce a well oriented sample for in situ synchrotron X-ray scattering studies. We observed two perpendicular anisotropic sections of reciprocal space, which proves the biaxial symmetry of the nematic order. The thermodynamic and flow properties of the biaxial nematic are well described by hard-core theories. We suggest the use of a shear geometry to produce and investigate single domains of other biaxial nematics, reported but still questioned in the literature. Received 26 May 1999     

Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.     

Hydrophobically Associating Alginate Derivatives: Surface Tension Properties of Their Mixed Aqueous Solutions with Oppositely Charged Surfactants

The comparative study of the interfacial properties of an anionic polysaccharide, sodium alginate (Alg), and its hydrophobically modified derivative (Alg-C(12)), covalently substituted by dodecyl chains (12% mol/mol saccharide unit), was carried out in the absence or in the presence of an oppositely charged surfactant, dodecyltrimethylammonium bromide (DTAB). The drastically different behaviors which were observed are interpreted in terms of the arrangement and mobility of the hydrophobic long alkyl chains, depending on the nature of their fixation, covalent or ionic, on the polysaccharide backbone. Copyright 2000 Academic Press.     

Evaluation of 4-amino-2-hydroxybenzoic acid as an eluent for indirect photometric determination of uncommon anions

Summary The efficacity of 4-amino-2-hydroxybenzoic acids as an eluent for the separation and determination of uncommon anions has been evaluated. The intensely absorbing eluent (λ_max 320 nm) offers a convenient indirect photometric approach to quantitate the species of interest in ppm and sub-ppm range. In the singlecolumn ion chromatography mode at 2 mM/2 mL/min and pH=6.0, clean separations of common and uncommon anions can be realized.     

Determining micrometer-zero settings when making residual-strain measurements using the hole-drilling strain-gage method

Experimental Techniques -