PMMA/organomodified montmorillonite nanocomposites prepared by in situ bulk polymerization

Kinetics of the in situ bulk polymerization of methyl methacrylate in the presence of organomodified montmorillonite (MMT) was investigated using differential scanning calorimetry (DSC) and gravimetrically. Different amount and types of MMT under the trade names Cloisite were employed. Using DSC, the amount of heat released versus time, under isothermal conditions, was recorded, and eventually, the time evolution of polymerization rate and monomer conversion was calculated. Results on the variation of monomer conversion with reaction time were in good agreement to corresponding from the gravimetric measurements. The nanocomposites prepared were characterized with WAXD, TEM and FTIR, and their glass transition temperature, T _g, was measured with DSC. Depending on the added amount of nano-MMT, either exfoliated or intercalated structures were obtained. An enhancement of the polymerization rate with the presence of the nanoparticles was observed especially in the gel effect region. This was accompanied by a higher T _g and average molecular weight, as measured by GPC, of all nanocomposites compared to neat PMMA.     

Adsorption of block copolymers in nanoporous alumina

We have studied the adsorption of end-attaching block copolymer chains inside the cylindrical pores of nanoporous alumina. Highly asymmetric PS-PEO block copolymers, with a small PEO anchoring block and a long PS dangling block, were allowed to adsorb onto porous alumina substrates with an average pore diameter of ∼200 nm from toluene solution. The adsorption process was monitored using FTIR spectroscopy, whereas depth profile analysis was performed by means of XPS and Ar⁺ ion sputtering. It is found that the PS-PEO adsorption kinetics in porous alumina are ∼4 orders of magnitude slower than the corresponding case of a flat alumina substrate. It appears that chains adsorbed near the pore entrance early on tend to form a barrier for chains entering the pore at later times, thereby slowing down the adsorption process significantly. This effect is much more pronounced for large chains whose dimensions are comparable with the pore diameter. The equilibrium adsorbance value is also affected by chain size due to the additional entropic penalty associated with chain confinement, the adsorbance falling substantially when the chain dimensions become comparable with the pore diameter. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1676–1682, 2010     

Diastereocontrol in the intramolecular cycloadditions of 2-substituted-erythro-3,4-isopropylidenedioxyhex-5-enenitrile oxides

The influence of the 2-substituent on the diastereoselectivity of the intramolecular cycloadditions in a series of 2-substituted-erythro-3,4-isopropylidene-dioxyhex-5-enenitrile oxides, generated in situ from selected sugar derivatives, was examined.     

Estimate of the truncation error of finite volume discretization of the Navier–Stokes equations on colocated grids

A methodology is proposed for the calculation of the truncation error of finite volume discretizations of the incompressible Navier–Stokes equations on colocated grids. The truncation error is estimated by restricting the solution obtained on a given grid to a coarser grid and calculating the image of the discrete Navier–Stokes operator of the coarse grid on the restricted velocity and pressure field. The proposed methodology is not a new concept but its application to colocated finite volume discretizations of the incompressible Navier–Stokes equations is made possible by the introduction of a variant of the momentum interpolation technique for mass fluxes where the pressure part of the mass fluxes is not dependent on the coefficients of the linearized momentum equations. The theory presented is supported by a number of numerical experiments. The methodology is developed for two‐dimensional flows, but extension to three‐dimensional cases should not pose problems. Copyright © 2005 John Wiley & Sons, Ltd.     

How complex is the dynamics of Peptide folding?

Classical molecular dynamics simulations of the folding of alanine peptides in aqueous solution are analyzed by constructing a deterministic model of the dynamics, using methods from nonlinear time series analysis. While the dimension of the free energy landscape increases with system size, a Lyapunov analysis shows that the effective dimension of the dynamic system is rather small and even decreases with chain length. The observed reduction of phase space is a nonlinear cooperative effect that is caused by intramolecular hydrogen bonds that stabilize the secondary structure of the peptides.     

Investigation of confined ionic liquid in nanostructured materials by a combination of SANS, contrast-matching SANS, and nitrogen adsorption

Small-angle neutron scattering (SANS), contrast-matching SANS, and nitrogen adsorption have been utilized to investigate the confined ionic liquid (IL) [bmim][PF(6)] phase in ordered mesoporous silica MCM-41 and SBA-15. The results suggest that the pores of SBA-15 are completely filled with IL whereas a small fraction of the pore volume, the pore "core", of MCM-41 is empty. The contrast-matching SANS measurements confirm the enhanced solubility of water in IL. In addition, they provide strong evidence that water does not enter the empty pore core of MCM-41, possibly because of the preferred orientation of the IL molecules in the adsorbed layer.     

Simple method for detection of extremely diluted anti beta-casein antibodies from glass bead based receptors

The current work describes the elaboration of a simple, sensitive and reliable β-casein modified glass beads, for the detection and quantification of its specific antibody anti β-casein. This is an elementary receptor without electronic part, developed by grafting glass bead surface with the antigenic β-casein via 3-aminopropyltriethoxy silane and then glutaraldehyde as cross-linker. The whole is realized by a classical process, called in two steps and in mild conditions where chemical protocol is optimized for β-casein use. The detection and quantification of the specific reaction antibody-receptor is carried out by the technique of the second antibody labeled with horse radish peroxidase (HRP). Our receptor can detect the β-casein antibody present in the serum at dilutions up to a factor 10⁷ in strong ionic strength medium. The same antibody of the same serum and in the same conditions can be detected by ELISA test at dilutions up to a factor 10⁵. The whole test, after our receptor realization, takes about 5 h.     

Accessing the structural diversity of pyridone alkaloids: concise total synthesis of rac-citridone A

A unique route to the structural diversity of pyridone alkaloids is described based on the concept of a common synthetic strategy. Three different core structure analogues corresponding to akanthomycin, septoriamycin A, and citridone A have been prepared by using a highly selective and novel carbocyclization reaction.     

Synthesis of 2H-labeled alkoxyethyl phosphodiester (AZT) derivatives for solid-state 2H-NMR studies

Two specifically ²H-labeled alkoxyethyl phosphodiester AZT derivatives 9 and 14 were synthesized. Pilot [²H]-solid-state nmr experiments on conjugate 14 demonstrated their usefulness in studying interactions with model or biological membranes.