Raman spectroscopy and thermal analysis of gum and silica-filled NR/SBR blends prepared from latex system

Natural rubber/styrene-butadiene rubber (NR/SBR) blends, with and without silica, were prepared by co-coagulating the mixture of rubber latices and various amounts of well-dispersed silica suspension. An attempt to predict blend compositions was made using Raman spectroscopy in association with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It was found that the intensity of each Raman characteristic peak was strongly dependent on the blend composition, but there was no significant evolution with the presence of silica. Also, TGA results revealed an improvement in thermal stability of NR/SBR blends with increasing both SBR and silica contents due to the dilution effect. Two distinct glass transition temperatures (T_g) were observed in DSC thermograms of all blends, and their T_g values were independent on both blend composition and silica content. This indicated a physical blend formation, which agreed well with no shifts in Raman peaks of the blends in comparison with those of the individual rubbers. Linear regression with R² quality factor close to 0.99 was achieved when plotting intensity ratio at 1371/1302 cm^?1 versus blend ratios. On the other hand, the peak height ratio and heat capacity ratio from TGA and DSC analysis, respectively, yielded quadratic equations as a function of blend ratios.     

Natural bond orbital analysis in the ONETEP code: Applications to large protein systems

First principles electronic structure calculations are typically performed in terms of molecular orbitals (or bands), providing a straightforward theoretical avenue for approximations of increasing sophistication, but do not usually provide any qualitative chemical information about the system. We can derive such information via post‐processing using natural bond orbital (NBO) analysis, which produces a chemical picture of bonding in terms of localized Lewis‐type bond and lone pair orbitals that we can use to understand molecular structure and interactions. We present NBO analysis of large‐scale calculations with the ONETEP linear‐scaling density functional theory package, which we have interfaced with the NBO 5 analysis program. In ONETEP calculations involving thousands of atoms, one is typically interested in particular regions of a nanosystem whilst accounting for long‐range electronic effects from the entire system. We show that by transforming the Non‐orthogonal Generalized Wannier Functions of ONETEP to natural atomic orbitals, NBO analysis can be performed within a localized region in such a way that ensures the results are identical to an analysis on the full system. We demonstrate the capabilities of this approach by performing illustrative studies of large proteins—namely, investigating changes in charge transfer between the heme group of myoglobin and its ligands with increasing system size and between a protein and its explicit solvent, estimating the contribution of electronic delocalization to the stabilization of hydrogen bonds in the binding pocket of a drug‐receptor complex, and observing, in situ, the n → π* hyperconjugative interactions between carbonyl groups that stabilize protein backbones. © 2012 Wiley Periodicals, Inc.     

Influence of β‐Cyclodextrin on the Mixed Micellization Process of Sodium Dodecyl Sulfate and Sodium Lauroyl Sarcosine and Formation of Inclusion Complexes

In this work, we have studied the influence of different concentrations of β‐Cyclodextrin (β‐CD) on the mixed micellization of anionic surfactants sodium dodecyl sulfate (SDS) and sodium lauroyl sarcosine (SLAS) at different SDS mole fractions (α_SDS). From conductivity data, the critical micellar concentration (cmc), the equivalent ionic conductivities of the monomeric species (Λ_m), the associated species (Λ_assc) and the micelle (Λ_mic), the degree of counterion dissociation (α) in the presence of β‐CD were evaluated from the slope of the conductivity versus concentration plots for the pure and binary mixtures. The apparent cmc of the surfactants vary linearly with the β‐CD concentrations. From the dependence of cmc of the surfactants on β‐CD concentration, we have deduced the association constant (K) of surfactant‐β‐CD inclusion complexes assuming 1∶1 stoichiometry. Theories of Clint, Regular solution, and Motomura's have been used for the evaluation of ideality or nonideality of the mixed system. Mixed micelles were found to be rich in SDS content at the cmc in the presence and the absence of β‐CD. The cmc values have been used to evaluate the transfer of standard free energy of micelles (ΔG⁰ _M,tr) from the aqueous medium to additive medium.     

Interactions of γ-Cyclodextrin with the Mixed Micelles of Anionic Surfactants and Their Inclusion Complexes Formation

Interactions of γ-cyclodextrin (γ-CD) with the single and mixed micelles of sodium dodecyl sulfate (SDS) and sodium lauroyl sarcosine (SLAS) have been studied at different concentrations of γ-CD by using conductivity measurements. From conductivity data, the pure and mixed critical micellar concentration (cmc), the equivalent ionic conductivities of the monomeric species (Λ _m), the associated species (Λ _assc) and the micelle (Λ _mic), the degree of counterion dissociation (χ) in the presence of γ-CD have been evaluated from the slope of the conductivity versus concentration plots for the pure and binary mixture of surfactants. From the dependence of cmc of the surfactantson γ-CD concentration, we have deduced the association constant (K) of surfactant-γ-CD inclusion complexes assuming 2:1 stoichiometry. Theories of Clint, regular solution, and Motomura's have been used for the evaluation of ideality or nonideality of the mixed system. Mixed micelles were found to be rich in SDS content in the presence and the absence of γ-CD. The cmc values have been used to evaluate the transfer of standard free energy of micelles (ΔG⁰ _M,tr) from the aqueous medium to additive medium.     

Selenides and diselenides containing oxadiazoles: a new class of functionalised materials

A simple and efficient procedure for the synthesis of a new class of organoselenium liquid crystal compounds was developed. The coupling of aryl bromides with elemental selenium was catalysed using copper oxide nanopowder in the presence of potassium hydroxide employing dimethyl sulfoxide as the solvent. This is the first report of the synthesis and characterisation of liquid crystal-based diselenides. Their mesophases were characterised by polarising optical microscopy and differential scanning calorimetry. Compounds 1, 2 and 4b exhibited the smectic A phase. In addition, these compounds showed weak blue fluorescence in solution (λ_{max. em.} 350–405 nm) and a Stokes shift of around 90 nm.     

Surface Modification of Smectite Clay Induced by Non-thermal Gliding Arc Plasma at Atmospheric Pressure

Smectite clay from Sabga (west-Cameroon) was treated in aqueous suspension by gliding arc plasma to modify its surface properties. The evolution of the modifications was followed with the exposure time and post-discharge duration using Fourier transformed infra red spectroscopy and scanning electron microscopy. X-ray diffraction and nitrogen physisorption analyses were also performed to evaluate if both crystalline and textural properties of the material are affected by the treatment. The results obtained show that the plasma treatment causes the breakdown of structural bounds at the clay surface and induces the formation of new hydroxyl groups (Si–OH and Al–OH) on the clay edges. Crystallinity, sheet structure and textural properties are not significantly affected by the plasma treatment. However, it should be noted that an intensive treatment of the clay lowers the pH of the suspension, which subsequently induces an acid attack of the clay. In such case, the specific surface area of the clay increases. This study demonstrates that gliding arc plasma treatments can be used to activate clay minerals for environmental application.     

Magnetic hollow poly(N-isopropylacrylamide-co-N,N′-methylenebisacrylamide-co-glycidyl acrylate) particles prepared by inverse emulsion polymerization

To prepare functionalized magnetic polymer particles that are thermally responsive, inverse emulsion copolymerization of N-isopropylacrylamide, N,N′-methylenebisacrylamide and glycidyl acrylate (GA) was investigated in paraffin oil in the presence of γ-Fe₂O₃ nanoparticles dispersed in a water/glycerol mixture. The resulting polymer particles were characterized regarding the morphology, size, polydispersity, iron content, and the temperature-dependent phase transition using optical microscopy, transmission electron microscopy, scanning electron microscopy, atomic absorption spectroscopy, and differential scanning calorimetry. Magnetic properties were examined using hysteresis loop measurements and by analyzing the magnetic susceptibility with respect to temperature. We have also investigated the influence of the concentration of γ-Fe₂O₃ and GA in monomers on properties of the particles (morphology, size, and presence of oxirane groups). The particles possessed a hollow structure as a result of phase separation between water/glycerol hydrophilic solvents in the polymerization feed and the forming polymer. Depending on the concentration of γ-Fe₂O₃ in the monomer phase, the magnetic hollow particles contained 5–24 wt% iron. In water, the particles gradually collapsed when the temperature was raised to 40 °C because the elevated temperature weakened hydration and the PNIPAAm chains gradually became more hydrophobic.     

Synthesis and characterization of ferromagnetic Fe3C/C composite nanoparticles as a catalyst for carbon nanotube growth

Polystyrene template microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. These template particles dispersed in aqueous solution have been used for the entrapment of ferrocene by a swelling process of methylene chloride emulsion droplets containing ferrocene within these particles, followed by evaporation of methylene chloride. The effects of CH₂Cl₂ volume and the [CH₂Cl₂]/[FeC₁₀H₁₀] (w/w) ratio on the size and size distribution of the swollen template particles were elucidated. Air-stable Fe₃C nanoparticles embedded in amorphous carbon matrix (Fe₃C/C) have been prepared by thermal decomposition of the ferrocene-swollen template polystyrene particles at 500 °C for 2 h in a sealed cell. Decomposition of these swollen template particles for 2 h at higher temperatures led to the formation of carbon nanotubes (CNTs) in addition to the Fe₃C/C composite nanoparticles. The yield of the CNTs increased as the annealing temperature was raised. An opposite behavior was observed for the diameter of the formed CNTs. The size and size distribution, crystallinity, and magnetic properties of the different Fe₃C/C composite nanoparticles have also been controlled by the annealing temperature.     

“Surface water” and “strong-bonded water” in cyclodextrins: a Karl Fischer titration approach

Cyclodextrins are some of the most used carriers for bioactive compounds (as host–guest complex) and many factors influence the association–dissociation of this complex, some of them being related to hydrophobicity. In the solid state, cyclodextrins contain two types of water molecules: “surface” water molecules (especially close to the crystal surface) and “strong-bonded” water molecules (especially from the cyclodextrin cavity), but the classification is hard to do, and the concentration of these water molecules are relatively difficult to estimate by simple methods. In the present study we used the volumetric Karl Fischer titration to estimate these types of water molecules in cyclodextrins by means of the rate of water reaction (related to diffusion from cyclodextrin crystals). “Surface” water molecules are titrated with rates between 1.8–2.8 mM/s for α-cyclodextrin, while for β-cyclodextrin these rates are little bit higher (2.9–3.4 mM/s). The rates corresponding to “strong-bonded” water molecules are approximately tens fold lower (0.05–0.3 mM/s for α-cyclodextrin and 0.15–0.33 mM/s for β-cyclodextrin). The approximate ratio between “surface” and “strong-bonded” water molecules could also be estimated by this simple and rapid method.     

Nouvelle Classe de Sucres a Liaison Osidique Stabilisee : 1-Desoxy-1,1,1-trifluoro-pent(hex)-2-uloses; Obtention de Quelques Derives

Abstract

L'hydrolyse acide des acétals et en particulier des osides fait intervenir un carbocation intermédiaire stabilisé par l'oxygène voisin; un substituant électroattracteur en α de l'atome d'oxygène ou de carbone d'un tel cation déstabilise cedernier et rend l'hydrolyse des acétals plus difficile. C'est ainsi que pour un 2-méthoxy-tétrahydropyrane, le remplacement en C-6 d'un groupement CH₂OH par CO₂Et¹ provoque une diminution de la vitesse d'hydrolyse d'un facteur de 200. Il est également bien connu que les 2-désoxy glycosides sont hydrolysés bien plus rapidement que leurs analogues 2-hydroxylés. Le même résultat est obtenu avec un atome d'halogène; c'est ainsi que Horton et coll.² en introduisant un atome d'iode en position 2′ d'analogues de la daunorubicine et de l'adriamycine ont pu augmenter leur efficacité in vivo. Compte tenu de la taille réduite de l'atome de fluor qui modifie peu l'encombrement de la molécule, plusieurs travaux ont été consacrés à l'introduction d'un fluor en position 2 d'osides pour ralentir leur vitesse d'hydrolyse in vivo. ^3-5 Cette même démarche a conduit d'autres auteurs à synthétiser des 2,2-difluorosucres.⁶ On pouvait donc envisager de remplacer l'hydrogène en C-1 de certains sucres par un groupement trifluorométhyle pour obtenir ainsi une nouvelle classe d'osides, dont la liaison osidique serait très stabilisée, ce qui devrait accroître leur durée de vie in vivo; on sait en effet ⁷ que les acétals de trifluorométhylcétones sont très difficiles à hydrolyser. Nous avons récemment décrit⁸ l'obtention des composés 1 et 9 et, on pouvait envisager de substituer l'hydroxyle anomérique de tels 2-uloses par divers nucléophiles. Les substitution nucléophiles en α d'un groupe CF₃ sont difficiles^9,10 et font en général intervenir un carbocation du type CF₃-C⁺R¹-XR² stabilisé par un hétéroatome X(O, S)^11-15 ou par un phényle.⁹ Ce carbocation est formé dans quelques cas par voie électrochimique,^14-15 mais, dans la plupart des travaux, il résulte soit de la rupture d'une liaison CR¹-Y assistée par un acide de Lewis soit de la solvolyse de cette liaison.⁹ Pour éviter l'emploi d'un acide de Lewis incompatible avec des groupes protecteurs acido-sensibles, nous avons mésylé l'hydroxyle anomérique pour obtenir un meilleur groupe partant. Nous décrivons dans cette note les résultats préliminaires obtenus principalement par action de divers nucléophiles sur ces mésylates.