First evaluation of the thermodynamic properties for spheres to elongated micelles transition of some propanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants in aqueous solution

The apparent and partial molar enthalpies, apparent molar volumes, and adiabatic compressibilities at 298 K of the aqueous solutions of the cationic gemini surfactants propanediyl-alpha,omega-bis(octyldimethylammonium bromide) (8-3-8) and propanediyl-alpha,omega-bis(dodecyldimethylammonium bromide) (12-3-12) have been measured as a function of concentration. The trends of the partial molar enthalpies versus concentration are the first well documented thermodynamic evidence of sphere to rod transition in the micellar phase, involving a detectable quantity of heat, and allow the determination of the change in enthalpy associated with this transition. The changes in enthalpies upon micellization and for the sphere to elongated micelles transition, DeltaH(s)(-->)(r), have been obtained from the experimental data by using a pseudo-phase transition approach: -1.5 kJ mol(-1) for 8-3-8 and -3.9 kJ mol(-1) for 12-3-12. No evidence of the above transition is found in the trends of volumetric properties versus m. The apparent adiabatic molar compressibilities for the compounds under investigation are also reported here for the first time: a negative group contribution for the methylene group is evaluated, when the surfactants are present in solution as a single molecule, reflecting its solvation structure. In the micellar phase, the -CH(2)- group contribution becomes positive. A value of 1.17 x 10(-3) cm(3) bar(-1) mol(-1) for the change in adiabatic molar compressibility upon micellization is obtained. The lower values of the methylene group contributions to the volumetric properties for the monomers support the hypothesis of partial association of the chains before the cmc.     

Cladding mode reorganization in high-refractive-index-coated long-period gratings: effects on the refractive-index sensitivity

We theoretically and experimentally investigated the reorganization of cladding modes in high-refractive-index- (HRI-) coated long-period gratings (LPGs), focusing on the influence of refractive-index sensitivity. When azimuthally symmetric nanoscale HRI coatings are deposited along LPG devices, a significant modification of the distribution of cladding modes occurs, depending on the layers' features (refractive index and thickness) and on the external refractive index. In particular, if these parameters are properly chosen, a transition between cladding modes and overlay modes occurs. Numerical and experimental effects of the mode transition on the sensitivity of the surrounding refractive index are described.     

Recycling asymmetric hydrogenation catalysts by their immobilisation onto ion-exchange resins

New systems based on cationic chiral phosphine-rhodium complexes anchored to a commercial cation-exchange gel-type resin showed high efficiency and easy recycling in the asymmetric hydrogenation of prochiral olefins.     

The Ghirlanda-Guerra Identities

If the variance of a Gaussian spin-glass Hamiltonian grows like the volume the model fulfills the Ghirlanda-Guerra identities in terms of the normalized Hamiltonian covariance.     

Palladium-catalyzed oxidative heterocyclodehydration-alkoxycarbonylation of 3-yne-1,2-diols: a novel and expedient approach to furan-3-carboxylic esters

A novel and convenient approach to furan-3-carboxylic esters 2 is presented, based on palladium-catalyzed direct oxidative carbonylation of readily available 3-yne-1,2-diols 1. The process, corresponding to a sequential combination between a 5-endo-dig heterocyclodehydration step and an oxidative alkoxycarbonylation stage, is catalyzed by PdI₂ in conjunction with an excess of KI under relatively mild conditions (100 °C in ROH under 40 atm of a 4:1 mixture of CO-air).     

Finite-Volume Excitations of the¶111 Interface in the Quantum XXZ Model

We show that the ground states of the three-dimensional XXZ Heisenberg ferromagnet with a 111 interface have excitations localized in a subvolume of linear size R with energies bounded by O(1/R²). As part of the proof we show the equivalence of ensembles for the 111 interface states in the following sense: In the thermodynamic limit the states with fixed magnetization yield the same expectation values for gauge invariant local observables as a suitable grand canonical state with fluctuating magnetization. Here, gauge invariant means commuting with the total third component of the spin, which is a conserved quantity of the Hamiltonian. As a corollary of equivalence of ensembles we also prove the convergence of the thermodynamic limit of sequences of canonical states (i.e., with fixed magnetization).