First synthesis of the beta-D-rhamnosylated trisaccharide repeating unit of the O-antigen from Xanthomonas campestris pv. campestris 8004

The trisaccharide repeating unit of the O-antigen of the lipopolysaccharide from Xanthomonas campestris pv. campestris 8004, a pathogen of cruciferous crops, presents some structural features that renders it a challenging synthetic target: the presence of a beta-D-rhamnosidic linkage, the steric crowd on a 1,2-cis-diglycosylated D-rhamnose, and finally the noncommercial availability of its monosaccharide constituents. The synthesis of this trisaccharide as methyl glycoside has been accomplished by exploiting a strategy whose key steps were the sequential beta-D-rhamnosylation with a 2-O-benzylsulfonyl-N-phenyltrifluoroacetimidate donor, debenzylsulfonylation, and coupling with a D-Fucp3NAc thioglycoside donor.     

Rheoreversible polymeric organogels: the art of science for art conservation

A new category of gels where gelification and breaking of the gels are chemically induced is presented. In particular, the latent gellant polyallylamine produced stable gels with some organic solvents after reaction with CO2 at room temperature, giving the gellant polyallylammonium carbamate. The rheological behavior switches from solution-type to gel-type. After weak acid-catalyzed displacement of CO2, the gel character disappears in a few seconds, making these polymeric organogels rheoreversible by a simple chemical action. This "intelligent" chemical switch between solution-type and gel-type rheological behavior has been exploited to clean pictorial surfaces in art conservation. In fact, during the cleaning procedure, there is a need for the gel supporting the cleaning solvent to have a very high viscosity. After cleaning has been successful, there is a strong necessity to reduce the viscosity, to better eliminate traces of the gellant that must be completely removed from the work of art. In the present study, we show that the art of science, in the sense of designing new physicochemical systems exploiting the "science palette", can lead to an improvement in the techniques used to protect and conserve the results of the "artists' palette".     

Analytic bounds and approximations for annuities and Asian options

Even in case of the Brownian motion as most natural rate of return model it appears too difficult to obtain analytic expressions for most risk measures of constant continuous annuities. In literature the so-called comonotonic approximations have been proposed but these still require the evaluation of integrals. In this paper we show that these integrals can sometimes be computed, and we obtain explicit approximations for some popular risk measures for annuities.Next, we show how these results can be used to obtain fully analytic expressions for lower and upper bounds for the price of a continuously sampled European-style Asian option with fixed exercise price. These analytic lower bound prices are as sharp as those from [Rogers, L.C.G., Shi, Z., 1995. The value of an Asian option. J. Appl. Probab. 32, 1077–1088], if not sharper, but in contrast do not require any longer the evaluation of a two-dimensional or a one-dimensional integral.     

Structure and absolute stereochemistry of novel C15-halogenated acetogenins from the anaspidean mollusc Aplysia dactylomela

Three novel halogenated C₁₅-acetogenins, compounds 1-3, have been isolated, together with known metabolites, from a South China Sea collection of the anaspidean mollusc Aplysia dactylomela. The structures have been suggested by both NMR analysis and comparison with literature data. The structure of 1 was confirmed by a single crystal X-ray study, which also allowed the establishment of its absolute stereochemistry.     

New γ-pyrone propionates from the Indian Ocean sacoglossan Placobranchus ocellatus

A new γ-pyrone propionate, compound 9, and its peroxy derivative 10 have been isolated from the sacoglossan Placobranchus ocellatus. The structure and the relative stereochemistry of the new molecules, which displayed an unprecedented carbon skeleton characterised by a bicyclo [4.2.0] octane, have been determined by both spectroscopic methods and comparison with model compounds. By analogy with photodeoxytridachione (2), a sunscreen protective role could be also suggested for compound 9 in living P. ocellatus.     

Occipital-parietal interactions during shifts of exogenous visuospatial attention: trial-dependent changes of effective connectivity

We studied neural interactions between brain areas involved in exogenous (stimulus-driven) control of visuospatial attention. With event-related functional magnetic resonance imaging (fMRI), we investigated changes of connectivity during shifts of spatial attention from an attended location to a previously unattended target location. Using a 3-T scanner, fMRI data were acquired from three healthy volunteers. According to a central visual cue, participants directed endogenous spatial attention to the left or the right visual hemifield for blocks of 56 s. Peripheral visual targets were presented unpredictably in either the attended hemifield (valid trials, 80%) or in the unattended hemifield (invalid trials, 20%) and participants performed a two-alternative forced-choice discrimination task with the target, irrespective of cue validity. In accordance with previous results, we found that the temporal–parietal junction (TPJ) mediates the shift of spatial attention toward stimuli presented at the unattended side (i.e., invalid trials). We critically studied the interaction between occipital areas responding to the visual stimuli and other brain regions in order to find regions functionally coupled with the occipital cortex during invalid trials. We found that the coupling between occipital areas processing visual stimuli and the TPJ selectively increased during invalid trials. Our results highlight how changes of connectivity between brain areas can describe attentional processes such as stimulus-driven shifts of spatial attention.     

High-order stimulated Raman scattering in a highly transient regime driven by a pair of ultrashort pulses

We demonstrate efficient generation of high-order anti-Stokes Raman sidebands in a highly transient regime, using a pair of approximately 100-fs laser pulses tuned to Raman resonance with vibrational transitions in methane or hydrogen. The use of this technique looks promising for efficient subfemtosecond pulse generation.     

Structure-dependent modulation of a pathogen response in plants by synthetic O-antigen polysaccharides

Many phytopathogenic bacteria display lipopolysaccharides (LPS) with the O-chain repeating unit [alpha-l-Rha-(1-->3)-alpha-l-Rha-(1-->3)-alpha-l-Rha-(1-->2)](n)(). This trisaccharide unit was synthesized and oligomerized to obtain hexa- and nonasaccharides. The deprotected rhamnans were effective in suppressing the hypersensitive response (HR) and in inducing PR-1 gene expression in Arabidopsis thaliana. Conformational analysis of the oligorhamnans by NMR spectroscopy and molecular dynamics calculations revealed that a coiled structure develops with increasing chain length of the oligosaccharide. This is associated with increasing efficacy in HR suppression and PR-1 gene expression. We therefore infer that the coiled structure of phytopathogenic bacteria is a plant-recognizable pathogen-associated molecular pattern (PAMP).     

Cladonia verticillaris (lichen) can exhibit defense mechanisms against Rn-222 under controlled conditions

Journal of Radioanalytical and Nuclear Chemistry - This study aimed to evaluate the effects of the Rn-222 progeny on the lichen Cladonia verticillaris under controlled conditions. The results...