First enantiospecific synthesis of marine sesquiterpene quinol akaol A

The first enantiospecific synthesis of akaol A, a marine sesquiterpene quinol, has been achieved. Key steps of the synthetic sequence are the oxidative degradation of (-)-sclareol to a dinorlabdane ketoester, mediated by the ozone-lead(IV) acetate system, the diastereoselective α-methylation of a ketoaldehyde, followed by an intramolecular aldol condensation and the further Diels-Alder cycloaddition of a dienol ether.     

High performance poly(styrene-b-diene-b-styrene) triblock copolymers from a hydrocarbon-soluble and additive-free dicarbanionic initiator

A new hydrocarbon-soluble (additive-free) dicarbanionic organolithium initiator, obtained by a simple halogen-lithium exchange reaction (Gilman's reaction) from a diarylhalide containing a side C15 alkyl chain, has been designed and used to initiate the anionic polymerization of butadiene and styrene. The dilithiated species formed afford well-defined poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymers with a high percentage of 1,4-microstructure polybutadiene (91%) and excellent mechanical properties, such as ultimate tensile strength higher than 30 MPa and elongation at a break of 1000%. This represents a breakthrough in the synthesis of SBS polymers, one of the most used thermoplastic elastomers.     

Vasorelaxant Mechanism of Herbal Extracts from Mentha suaveolens,Conyza canadensis,Teucrium polium and Salvia verbenaca in the Aorta of Wistar Rats

Mentha suaveolens (MS), Conyza canadensis (CC), Teucrium polium (TP) and Salvia verbenaca (SV) are used in Morocco to treat hypertension. Our aim was to characterize the composition and vasoreactivity of extracts of MS, CC, TP and SV. The chemical compositions of aqueous extracts of MS, SV and TP, and of a hydromethanolic extract of CC, were identified by HPLC-DAD. The vasoreactive effect was tested in rings of the thoracic aorta of female Wistar rats (8–14 weeks-old) pre-contracted with 10 µM noradrenaline, in the absence or presence of L-NAME 100 µM, indomethacin 10 µM or atropine 6 µM, to inhibit nitric oxide synthase, cyclooxygenase or muscarinic receptors, respectively. L-NAME and atropine decreased the vasorelaxant effect caused by low concentrations of MS. Atropine and indomethacin decreased the vasorelaxant effect of low concentrations of SV. High concentrations of MS or SV and the effect of SV and TP were not altered by any antagonist. The activation of muscarinic receptors and NO or the cyclooxygenase pathway underlie the vasorelaxant effect of MS and SV, respectively. Neither of those mechanisms underlines the vasorelaxant effect of CC and TP. These vasorelaxant effect might support the use of herbal teas from these plants as anti-hypertensives in folk medicine.     

Transmission in Graphene through Tilted Barrier in Laser Field

The transmission of Dirac fermions in graphene through a tilted barrier potential in the presence of a laser field of frequency ω is studied. By using Floquet theory, the Dirac equation is solved and then the energy spectrum is obtained. The boundary conditions together with the transfer matrix method allow to determine the transmission probabilities corresponding to all energy bands $E+l\hslash \omega$ $(l=0,\pm 1,\text{…})$. By limiting to the central band $l=0$ and the two first side bands $l=\pm 1$, it is shown that the transmissions are strongly affected by the laser field and barrier. Indeed, it is found that the Klein effect is still present, a variety of oscillations are inside the barrier, and there is essentially no transmission across all bands.