An ab initio study of ion induced charge transfer dynamics in collision of carbon ions with thymine

Charge transfer in collisions of carbon ions on a thymine target has been studied theoretically in a wide collision range by means of ab initio quantum chemistry molecular methods. The process appears markedly anisotropic in the whole energy domain, significantly favoured in the perpendicular orientation. A specific decrease of the charge transfer cross sections at low collision energies may be pointed out and could induce an enhancement of the complementary fragmentation processes for collision energies down to about 10 eV, as observed for the low-electron fragmentation process. Such feature may be of important interest in ion-induced biomolecular radiation damage.     

A New Sphingolipid and Furanocoumarins with Antimicrobial Activity from <i>Ficus exasperata</i>

From the methanol extract of the stem bark of Ficus exasperata, a new sphingolipid named Ficusamide, (2S,3S,4R,11E)-2-[(2',3'-dihydroxyhexacosanoylamino)]-11-octadecene-1,3,4-triol (1), along with three known furanocoumarins, (S)-(－) oxypeucedanin hydrate (2), (R)-(+) oxypeucedanin hydrate (3), bergapten (5-methoxypsoralen) and six other known compounds, were isolated. Their structures were characterized basing on spectroscopic methods and chemical evidence. Compounds (1-3) were analyzed for their antimicrobial activity. Ficusamide (1) showed wick activity (minimal inhibitory concentration (MIC)=312.5?μg/mL) against Escherichia coli, while the furanocoumarins (2) and (3) showed significant activity (MIC=9.76?μg/mL) against Bacillus cereus, Candida albicans and Microsporum audouinii.     

Adenine and RNA in mineral samples. Surface-enhanced Raman spectroscopy (SERS) for picomole detections

Studies on the interactions of biological macromolecules with mineral surfaces are crucial for the detecting biomarkers. But before this can be done for real samples like rocks or sediments, rational methods based on mineral models plus known amounts of nucleic acids must be developed. The methods must be very sensitive, as the amount of bound macromolecule may be very small. Surface-enhanced Raman spectroscopy (SERS) is perfect for detecting picomolar amounts of nucleic acid materials. In this study, the models used were adenine and GAAA hairpin for nucleic acids materials and a clay (montmorillonite) plus colloidal silver (used for SERS detection) for mineral supports. We have shown that OH(-) anions compete with adenine and the adenyl residues in the GAAA loop for adsorption onto nano-sized silver particles in basic medium. The GAAA adenyl moieties are less well adsorbed onto either clay or silver than is adenine. Also, the transfer of either adenine or the RNA hairpin from the clay to the silver aggregates is pH-dependent. Contact between adenine and the montmorillonite also seems to disperse adenine aggregates. The clay could also increase the flexibility of the RNA hairpin so that it is released from the clay at pH 10, and the affinity of its adenyl moieties for the metallic substrate is enhanced.     

Bipolarity in argumentation graphs: Towards a better understanding

Different abstract argumentation frameworks have been used for various applications within multi-agents systems. Among them, bipolar frameworks make use of both attack and support relations between arguments. However, there is no single interpretation of the support, and the handling of bipolarity cannot avoid a deeper analysis of the notion of support.In this paper we consider three recent proposals for specializing the support relation in abstract argumentation: the deductive support, the necessary support and the evidential support. These proposals have been developed independently within different frameworks. We restate these proposals in a common setting, which enables us to undertake a comparative study of the modellings obtained for the three variants of the support. We highlight relationships and differences between these variants, namely a kind of duality between the deductive and the necessary interpretations of the support.     

Investigation of the aqueous transmetalation of pi-allylpalladium with indium salt: the use of the Pd(OAc)2-TPPTS catalyst

pi-Allylpalladium complexes could be generated in water by the palladium(0) water soluble catalyst prepared in situ from palladium acetate and TPPTS. These complexes were transmetalated with indium to react with benzaldehyde. The aqueous solution of Pd(0)(TPPTS)(n) could be reused without deterioration of the catalyst in the first and second recycling. The system proved to be efficient with primary and secondary allylic substrates. The stereochemical outcome of the allylation through umpolung of allylpalladium, was also studied using models with a restraint conformation.     

Nanoscopic assemblies between supramolecular redox active metallodendrons and gold nanoparticles: synthesis,characterization, and selective recognition of H2PO4-, HSO4-, and adenosine-5'-triphosphate (ATP2-) anions

Tri- and nonaferrocenyl thiol dendrons have been synthesized and used to assemble dendronized gold nanoparticles either by the ligand-substitution method from dodecanethiolate-gold nanoparticles (AB(3) units) or Brust-type direct synthesis from a 1:1 mixture of dodecanethiol and dendronized thiol (AB(9) units). The dendronized colloids are a new type of dendrimers with a gold colloidal core. Two colloids containing a nonasilylferrocenyl dendron have been made; they bear respectively 180 and 360 ferrocenyl units at the periphery. These colloids selectively recognize the anions H(2)PO(4)(-) and adenosine-5'-triphosphate (ATP(2)(-)) with a positive dendritic effect and can be used to titrate these anions because of the shift of the CV wave even in the presence of other anions such as Cl(-) and HSO(4)(-). Recognition is monitored by the appearance of a new wave at a less positive potential in cyclic voltammetry (CV). The anion HSO(4)(-) is also recognized and titrated by the dendronized colloid containing the tris-amidoferrocenyl units, because of the progressive shift of the CV wave until the equivalence point. These dendronized colloids can form robust modified electrodes by dipping the naked Pt electrode into a CH(2)Cl(2) solution containing the colloids. The robustness is all the better as the dendron is larger. These modified electrodes can recognize H(2)PO(4)(-), ATP(2)(-) and HSO(4)(-), be washed with minimal loss of adsorbed colloid, and be reused.     

Iodomethylzinc phosphates: powerful reagents for the cyclopropanation of alkenes

A new family of zinc carbenoids derived from phosphoric acids was developed and used in the cyclopropanation of allylic alcohols and ethers and also of unfunctionalized olefins. The use of the chiral phosphoric acid of a 3,3'-disubstituted BINOL leads to efficient stereocontrol, affording the cyclopropanes of allylic and homoallylic ethers with complete conversions and up to 93% ee. A catalytic version of this reaction using 10 mol % of the chiral phosphate reagent is also disclosed.     

Assemblies of redox-active metallodendrimers using hydrogen bonding for the electrochemical recognition of the H2PO4- and adenosine-triphosphate (ATP2-) anions

Two families of five metallodendrimers have been assembled by hydrogen bonding between the primary amino groups of DSM dendrimers G(n)-DAB-dendr-(NH(2))x (n = 1-5; x = 4, 8, 16, 32, 64) and the OH group of phenol dendrons containing a triallyl or a triferrocenylalkyl tripod in para position. These H-bonded dendrimers noted G(1)-DAB-12Fc, G(2)-DAB-24Fc, G(3)-DAB-48Fc, G(4)-DAB-96Fc, and G(5)-DAB-192Fc have been characterized as resulting from fast, reversible hydrogen bonding by the single broad signal observed in (1)H NMR for the three NH(2) + OH protons whose location depends on the concentration. The cyclic voltammograms (CVs) show a single reversible ferrocenyl wave due to the equivalence of these groups and the fast rotation of the supramolecular ensemble compared to the CV time scale. A new CV wave appears at less anodic potential upon addition of H(2)PO(4)(-) or adenosine-triphosphate (ATP(2)(-)) anion as a tetrabutylammonium salt as with previously studied ferrocenyl dendrimers. In addition, other specific and remarkable features are the fact that the new CV wave is much less intense than the initial one and the dramatically sudden disappearance of the initial CV wave at the equivalent point indicating the formation of a large supramolecular assembly with the hydrogenophosphate groups. Finally, the variation of the number of equivalent anions with the generation number to reach the equivalent point also suggests that the competition between the amino- and amido group for the interaction with hydrogenophosphate depends on the generation number. Recognition by these supramolecular dendrimers of H(2)PO(4)(-) and ATP(2)(-) follows the model of the relatively strong-interaction type in the Kaifer-Echegoyen model, which allows access to the ratio of association constants K(+)/K(0). A positive dendritic effect is found for the recognition of H(2)PO(4)(-) (i.e., the difference of potentials DeltaE(1/2) between the initial CV wave and the new one and the K(+)/K(0) value increase as the generation number increases) whereas the dendritic effect is slightly negative for the recognition of ATP(2)(-).