A Class of Conformally flat Contact Metric 3-Manifolds

It is shown that a conformally flat contact metric 3-manifold with Ricci curvature vanishing along the characteristic vector field, has non-positive scalar curvature. Such a manifold is flat if (i) it is compact, or (ii) the scalar curvature is constant, or (iii) the norm of the Ricci tensor is constant.     

New 1-alk(en)yl-1,3,5-trihydroxycyclohexanes from the Dufour gland of the African ant Crematogaster nigriceps

The Dufour gland of the African ant Crematogaster nigriceps contains a mixture of at least eight 1-heptadec(en)yl- and 1-nonadec(en)yl-1,3,5-trihydroxycyclohexane derivatives, the mono-unsaturated components being the major ones (about 65%). They are accompanied by small amounts of (Z,Z)-dienic derivatives (<10%). The structures, the relative and absolute configurations, and the preferred conformation of these new compounds have been established by spectroscopic and chemical methods, whereas the positions of the double bond in the alkenyl chains were determined by DMDS derivatisation followed by linked scan EIMS.     

A new synthetic approach to 2,3-dideoxy-2-fluoro-β-d-threo-pentofuranose, the fluorofuranose unit of the anti-HIV-active nucleoside, β-FddA

The fluorinated furanose unit of the anti-HIV-active nucleoside (2,3-dideoxy-2-fluoro-β-d-threo-pentofuranosyl)adenine, β-FddA, has been synthesized as its 5-trityl derivative with high stereocontrol from (S)-trityl glycidol and phenylthioacetic acid.     

Advanced polymers for electrooptics

Polymers have been in use for a long time as passive materials for components in electronics and electrooptics. They combine the possibility of easy processing with an infinite potential of functionalization. They can be conductors or semiconductors, ferroelectrics and can exhibit interesting properties such as photoconductivity, piezo, pyroelectricity or nonlinear optical properties. As a consequence they are now used for merging active components in the field of electrooptics such as displays, sensors or modulators for optical signal treatment. This paper describes the properties and applications of some recent polymers in the field of electroptics. In the first part of this paper the properties of amorphous copolymers with a pending group with large hyperpolarizability are described. These amorphous copolymers show high optical nonlinear coefficients after poling under an electric field. We have used these copolymers for the manufacture of an electrooptic modulator working at 1.3 μm at a frequency of 1 GHz. The second part deals with ferroelectric polymers and their pyroelectric properties. The realization and performance of an IR pyroelectric sensor using copolymers of polyvinylidene fluoride–ethylene trifluride are described. Some new results concerning polymersdispersed liquid crystals are also described.     

Synthesis of permethylated α-d-mannosylacetic acid, a new type of bioconjugate

A concise stereoselective 3-step conversion of methyl α-d-mannopyranoside to α-d-2,3,4,6-tetra-O-methyl-mannosylacetic acid is described. After methylation of the alcohol functions, an allylation is performed. The resulting alkene undergoes oxidative cleavage to the acid, an alkylated C-sugar, appropriate for attachment to peptides or other drug candidates for solubility enhancement.     

Asymptotics for the Tukey Median

The asymptotic distribution of the Tukey median has recently been obtained by Nolan in a bivariate setting and by Bai and He in the general multivariate case. To establish their theorem, these authors made a strong symmetry hypothesis on the distribution and, in the case of Bai and He, assumed the existence of a density function with a gradient satisfying a finite-moment condition. This paper extends the above result by deriving the asymptotic distribution of the above location estimate without making any symmetry or differentiability assumption on the distribution.     

On genericity for holomorphic curves in four-dimensional almost-complex manifolds

We consider spaces of immersed (pseudo-)holomorphic curves in an almost complex manifold of dimension four. We assume that they are either closed or compact with boundary in a fixed totally real surface, so that the equation for these curves is elliptic and has a Fredholm index. We prove that this equation is regular if the Chern class is ≥ 1 (in the case with boundary, if the ambient Maslov number is ≥ 1). Then the spaces of holomorphic curves considered will be manifolds of dimension equal to the index.     

Topoisomer Differentiation of Molecular Knots by FTICR MS: Lessons from Class II Lasso Peptides

Lasso peptides constitute a class of bioactive peptides sharing a knotted structure where the C-terminal tail of the peptide is threaded through and trapped within an N-terminal macrolactam ring. The structural characterization of lasso structures and differentiation from their unthreaded topoisomers is not trivial and generally requires the use of complementary biochemical and spectroscopic methods. Here we investigated two antimicrobial peptides belonging to the class II lasso peptide family and their corresponding unthreaded topoisomers: microcin J25 (MccJ25), which is known to yield two-peptide product ions specific of the lasso structure under collision-induced dissociation (CID), and capistruin, for which CID does not permit to unambiguously assign the lasso structure. The two pairs of topoisomers were analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR MS) upon CID, infrared multiple photon dissociation (IRMPD), and electron capture dissociation (ECD). CID and ECD spectra clearly permitted to differentiate MccJ25 from its non-lasso topoisomer MccJ25-Icm, while for capistruin, only ECD was informative and showed different extent of hydrogen migration (formation of c•/z from c/z•) for the threaded and unthreaded topoisomers. The ECD spectra of the triply-charged MccJ25 and MccJ25-lcm showed a series of radical b-type product ions ( b￠_n ^· ) \left( {b{\prime}_n^{ \bullet }} \right) . We proposed that these ions are specific of cyclic-branched peptides and result from a dual c/z• and y/b dissociation, in the ring and in the tail, respectively. This work shows the potentiality of ECD for structural characterization of peptide topoisomers, as well as the effect of conformation on hydrogen migration subsequent to electron capture.     

Heparin-like glycosaminoglycan/amine salt-bridge interactions: a new potential tool for HLGAGs analysis using mass spectrometry

Characterization of glycosaminoglycans poses a challenge for current analytical techniques, as they are highly acidic, polydisperse and heterogeneous compounds. The purpose of this study is the separation and analysis of a partially depolymerized heparin-like glycosaminoglycan by on-line ion-pairing reversed-phase high-performance liquid chromatography/electrospray mass spectrometry. The gas-phase behavior of two synthesized glycosaminoglycans has been investigated. Dibutylamine was found to be the best suited ion-pairing reagents for mass spectrometry analysis. The optimized ion-pairing conditions provide reproducible and easily interpretable electrospray mass spectra in both negative and positive ESI modes. The glycosaminoglycans are detected as a non-covalent complex with amines. In fact, the observed ionic species and their gas-phase dissociation under CID conditions revealed the presence of salt bridge interactions in the gas phase.