Thermodynamic properties of alkali halides. V. Temperature and pressure dependence of excess free energies in water

A simple equation has been derived relating the temperature dependence of activity functions with excess enthalpies and excess heat capacities. Using experimentally determined parameters at 298.15°K, it is possible to predict osmotic coefficients and mean activity coefficients of alkali halides in water up to 1 m from 273°K to about 350°K. In general, the predicted functions agree with the measured values within the uncertainty of the activity data. An equation is also given for the pressure dependence of the excess free energies, but it was not possible to check the limitation of this equation due to lack of activity data at various pressures.To whom correspondence should be addressed.     

Synthesis of a New Bivalent Hirudin Analog (hirufos), which includes a stable 4′-phosphono-L-phenylalanine mimic of (L-tyrosine O4-sulfate)-63

The synthesis on solid phase of a new derivative of the anticoagulant protein hirudin is described (see Scheme and Fig.1, I ). The henicosapeptide is a bivalent conjugate of the C-terminus of hirudin and of the active-site-binding tetrapeptide D -Phe-Pro-Arg-Pro linked via a tetraglycine spacer. The peptide, for which the name hirufos was coined, incorporates a stable phosphono derivative of L -phenylalanine which, combined with the other structural modifications, leads to a potent anticoagulant agent. Synthesis was readily achieved by the (9H-fluoren-9-yl)-methoxycarbonyl (Fmoc) strategy followed by acidolytic cleavage from the resin and deprotection, including the liberation of the crucial phosphonic group on L -phenylalanine.     

Photochemistry of polymeric systems. I. Photocrosslinking of polymers and copolymers containing pyridine N-oxide groups

Vinylpyridine-N-oxide units were introduced in polymeric chains in order to study their photocrosslinking. Copolymers of styrene and 4-vinylpyridine-N-oxide were especially synthesized and studied. The methods used for characterization of photocrosslinked films were a “photoresist test” or the measurement of the insolubility and of the swelling ratio. The Cleavage of the N-oxide bond was responsible for the photocrosslinking. The competitive formation of carbonyl compounds took place and decreased the rate of photocrosslinking. This last reaction is favored by triplet-state quenchers. The photosensitivity of the copolymers was determined as a function of the wavelength of the radiation used. When the photocrosslinking proceeded, a film of the copolymeric material became transparent in the 280–320-nm range. Thick films could therefore be completely photocrosslinked when irradiated in this range of wavelength.     

Capillary electrophoresis-diode array detection--electrospray mass spectrometry for the analysis of selected tropane alkaloids in plant extracts

Capillary zone electrophoresis, coupled to UV and interfaced with electrospray ionization mass spectrometry (ESI-MS), is described for the simultaneous analysis of hyoscyamine and scopolamine. On-line UV detection occurred at 22 cm from the inlet of the capillary and ESI-MS monitoring was performed along the entire length of the capillary (85 cm). An alkaline solution of 40 mM ammonium acetate at pH 8.5 was suitable for the analysis of the alkaloids under consideration. Under the optimized conditions, including CE and ESI-MS parameters, the two alkaloids were resolved within a short time and with very high sensitivity. The differentiation of hyoscyamine and its positional isomer littorine, commonly encountered in plant material, is also presented using up-front collision-induced dissociation. Finally, the developed method was applied to the analysis of these alkaloids in Belladonna leaf extract and in Datura candida x D. aurea hairy root extract.     

Delocalization in platinum-alkynyl systems: a metal-bridged organic mixed-valence compound

A complex featuring two triarylamine redox centers bridged by Pt, trans-bis(triethylphosphine)-bis{4-[bis(4-methoxyphenyl)amino]phenylethynyl} platinum(II), has been synthesized as a model system for pi-conjugated Pt-containing polymers. Analysis of the intervalence charge-transfer band displayed by its mixed-valence monocation affords a quantitative assessment of electronic delocalization through the Pt bridge; this is found to be only slightly smaller than that determined for a benzene-bridged analogue. These results are supported by density functional theory calculations, which show that the active orbitals involved in the electron-transfer process in both cases have similar delocalization through the bridging unit.     

Analysis of basic compounds at high pH values by reversed-phase liquid chromatography

Reversed phase high performance liquid chromatography (RPLC) is currently the method of choice for the analysis of basic compounds. However, with traditional silica materials, secondary interactions between the analyte and residual silanols produce peak tailing which can negatively affect resolution, sensitivity, and reproducibility. In order to reduce these secondary interactions, which comprise ion exchange, hydrogen bonding, and London forces interactions, chromatographic analyses can be carried out at low or high pH values where silanol groups and basic compounds are mostly uncharged. The chromatographic behaviour of a particular bidentate stationary phase, Zorbax Extend C18, was studied with a set of basic and neutral compounds. Thanks to a higher chemical stability than traditional silica based supports, analyses were carried out with a high pH mobile phase, which represents a good alternative to the acidic mobile phases generally used to reduce ion exchange interactions. The performance of this bidentate stationary phase was also compared with that of other supports and it was proved that it is advantageous to work with high pH mobile phases when analyzing basic compounds.     

Differential operators on homogeneous spaces. I

Summary In this paper, we extend recent work of one of us [Br] to investigate an old problem of the other one [B2]. Given a connected semisimple complex Lie-groupG with Lie-algebrag, we study the representation of the enveloping algebra of by global differential operators on a complete homogeneous spaceX=G/P. It turns out that the kernelI _x of _X is the annihilator of a generalizedVerma-module. On the other hand, we study the associated graded ideal grI _x , and relate it to the geometry of a generalizedSpringer-resolution, that is a map of the cotangent-bundle ofX onto a nilpotent variety in , as studied e.g. in [BM1]. We prove, for instance, that grI _x is prime if and only if _X is birational with normal image. In general, we show that is prime. Equivalently, the associated variety ofI _x in is irreducible: In fact, it is the closure of theRichardson-orbit determined byP. For the homogeneous spaceY=G/(P, P), we prove that the analogous idealI _y has for associated variety the closure of theDixmier-sheet determined byP. From this main result, we derive as a corollary, that for any module induced from a finitedimensional LieP-module the associated variety of the annihilator is irreducible, proving an old conjecture [B2], 2.5. Finally, we give some applications to the study of associated varieties of primitive ideals.     

Simultaneous stereoselective analysis of tramadol and its main phase I metabolites by on-line capillary zone electrophoresis-electrospray ionization mass spectrometry

On-line combination of partial filling capillary electrophoresis and electrospray ionization mass spectrometry was demonstrated for the simultaneous enantioseparation of tramadol and its main phase I metabolites. The partial filling technique was efficient at avoiding MS contamination by the chiral selector. Different experimental factors were investigated, including the chiral selector nature and concentration, plug length as well as the separation temperature. The best enantioseparation of the investigated compounds was achieved with a coated polyvinyl alcohol capillary and a 40 mM ammonium acetate buffer, pH 4.0, adding sulfobutyl ether beta-cyclodextrin (2.5 mg/ml) as the chiral selector. The charged cyclodextrin not only allowed enantioseparation of tramadol and its metabolites, but also improved the selectivity of compounds with the same molecular mass. Finally, CE-electrospray ionisation-MS was successfully applied to the stereoselective analysis of tramadol and its main metabolites in plasma after a simple liquid-liquid extraction.     

New stereoselective preparation of (Z)-3-perfluoroalkyl-3-magnesiated enoates by an iodine-magnesium exchange reaction

(Z)-Ethyl-3-perfluoroalkyl-3-magnesiated crotonates were prepared from (Z)-ethyl-3-perfluoroalkyl-3-iodo enoates by iodine-magnesium exchange reaction with isopropylmagnesium bromide in THF at -78 degrees C. These new reagents reacted with a range of electrophiles, leading to polyfunctional products bearing a perfluoroalkyl group.     

Préparation d'aryloxyméthyl-1 triazoles-1,2,3

The preparation of 1-aryloxymethyl-1,2,3-triazoles, potential biologically active compounds particularly in the pesticide field, is described. The action of sodium azide on aryloxymethyl halides gave aryloxymethyl azides. The cycloaddition reactions of azides with acetylenic compounds provided the expected triazoles in good yields.