Evolution of glassy gratings with variable aspect ratios under surface diffusion

The structural evolution of surface gratings on a glassy material is investigated by means of molecular simulations. The gratings provide a means to probe surface diffusion in the vicinity of the glass transition temperature. A theory by Mullins [J. Appl. Phys. 30, 77 (1959)] is used to extract qu-antitative measures of surface diffusivity that rely on calculation of grating amplitude as a function of time. The simulations are implemented in the context of a model binary glass mixture [S. S. Ashwin and S. Sastry, J. Phys.: Condens. Matter 15, S1253 (2003)]. We find that surface diffusion is faster than bulk diffusion by several orders of magnitude, consistent with recent experimental data for an organic glass former. The diffusivities extracted by the grating-decay approach are consistent with those estimated on the basis of mean-squared particle displacements. The grating-decay approach, however, is more efficient than traditional techniques based on Einstein's diffusion equation. Grating decay is also more versatile and is shown to be applicable in a variety of sample geometries.     

Making unilamellar liposomes using focused ultrasound

Several techniques are available for making large unilamellar vesicles (LUV) with an average diameter of approximately 100 nm, widely employed as model biomembranes as well as vehicles for drug delivery. Here we describe the use of adaptive focused ultrasound (AFU) for the preparation of LUV from multilamellar vesicles (MLV) and studied the effects of ultrasound intensity and number of cycles per burst (CPB) on the average size of vesicles produced. CPB determines the duration of the intermittent pressure wavetrains emitted by the transducer, and the corresponding relaxation periods. Preliminary experiments indicated that CPB controls the size of vesicles assembling after the disruption of MLV by ultrasound and optimum values for obtaining LUV could be iterated. The sizes and lamellarity of LUV were assessed by dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and fluorescence quenching. AFU provides a simple and easy to use approach for making liposomes with several advantages: it is minimally invasive and involves no loss of material. Precisely controlled wavelengths are employed with a significant reduction in the presence of hot spots, which could destroy some biological materials of interest.     

Effect of ionic liquid treatment on the structures of lignins in solutions: molecular subunits released from lignin

The solution structures of three types of isolated lignin-organosolv (OS), Kraft (K), and low sulfonate (LS)-before and after treatment with 1-ethyl-3-methylimidazolium acetate were studied using small-angle neutron scattering (SANS) and dynamic light scattering (DLS) over a concentration range of 0.3-2.4 wt %. The results indicate that each of these lignins is comprised of aggregates of well-defined basal subunits, the shapes and sizes of which, in D(2)O and DMSO-d(6), are revealed using these techniques. LS lignin contains a substantial amount of nanometer-scale individual subunits. In aqueous solution these subunits have a well-defined elongated shape described well by ellipsoidal and cylindrical models. At low concentration the subunits are highly expanded in alkaline solution, and the effect is screened with increasing concentration. OS lignin dissolved in DMSO was found to consist of a narrow distribution of aggregates with average radius 200 ± 30 nm. K lignin in DMSO consists of aggregates with a very broad size distribution. After ionic liquid (IL) treatment, LS lignin subunits in alkaline solution maintained the elongated shape but were reduced in size. IL treatment of OS and K lignins led to the release of nanometer-scale subunits with well-defined size and shape.     

Diffusion of methane and carbon dioxide in carbon molecular sieve membranes by multinuclear pulsed field gradient NMR

Carbon molecular sieve (CMS) membranes are promising materials for energy efficient separations of light gases. In this work, we report a detailed microscopic study of carbon dioxide and methane self-diffusion in three CMS membrane derived from 6FDA/BPDA(1:1)-DAM and Matrimid polymers. In addition to diffusion of one-component sorbates, diffusion of a carbon dioxide/methane mixture was investigated. Self-diffusion studies were performed by the multinuclear (i.e., (1)H and (13)C) pulsed field gradient (PFG) NMR technique which combines the advantages of high field (17.6 T) NMR and high magnetic field gradients (up to 30 T/m). Diffusion measurements were carried out at different temperatures and for a broad range of the root-mean-square displacements of gas molecules inside the membranes. The diffusion data obtained from PFG NMR are compared with the corresponding results of membrane permeation measurements reported previously for the same membrane types. The observed differences between the transport diffusivities and self-diffusion coefficients of carbon dioxide and methane are discussed.     

Crystal lattice properties fully determine short-range interaction parameters for alkali and halide ions

Accurate models of alkali and halide ions in aqueous solution are necessary for computer simulations of a broad variety of systems. Previous efforts to develop ion force fields have generally focused on reproducing experimental measurements of aqueous solution properties such as hydration free energies and ion-water distribution functions. This dependency limits transferability of the resulting parameters because of the variety and known limitations of water models. We present a solvent-independent approach to calibrating ion parameters based exclusively on crystal lattice properties. Our procedure relies on minimization of lattice sums to calculate lattice energies and interionic distances instead of equilibrium ensemble simulations of dense fluids. The gain in computational efficiency enables simultaneous optimization of all parameters for Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I- subject to constraints that enforce consistency with periodic table trends. We demonstrate the method by presenting lattice-derived parameters for the primitive model and the Lennard-Jones model with Lorentz-Berthelot mixing rules. The resulting parameters successfully reproduce the lattice properties used to derive them and are free from the influence of any water model. To assess the transferability of the Lennard-Jones parameters to aqueous systems, we used them to estimate hydration free energies and found that the results were in quantitative agreement with experimentally measured values. These lattice-derived parameters are applicable in simulations where coupling of ion parameters to a particular solvent model is undesirable. The simplicity and low computational demands of the calibration procedure make it suitable for parametrization of crystallizable ions in a variety of force fields.     

A chimeric antibody to L1 cell adhesion molecule shows therapeutic effect in an intrahepatic cholangiocarcinoma model

Intrahepatic cholangiocarcinoma (ICC), a malignant tumor derived from the intrahepatic bile duct epithelium, has a poor prognosis and is refractory to conventional chemotherapy and radiation therapy. Thus, there is an urgent need to develop new effective therapeutic strategies for this disease. We previously found that L1 cell adhesion molecule (L1CAM) plays an important role in tumor progression of ICC, and we generated a murine mAb, A10-A3 (IgG1), that binds to the Ig1 domain of L1CAM. In the present study, we further characterized A10-A3, constructed a chimeric A10-A3 antibody (cA10-A3) containing the constant regions of human IgG1, and evaluated the therapeutic potential in a human ICC xenograft nude mice model. The affinities (KD) of A10-A3 and cA10-A3 for soluble L1CAM were 1.8 nM and 1.9 nM, respectively, as determined by competition ELISA. A10-A3 inhibited L1CAM homophilic binding and was slowly internalized into the tumor cells, but it did not significantly inhibit proliferation of ICC cells in vitro. cA10-A3 mediated antibody- dependent cell-mediated cytotoxicity in vitro and displayed anti-tumor activity in the ICC animal model. These results suggest that the humanized A10-A3 antibody may have potential as an anticancer agent for the treatment of ICC.     

Bio-inspired motifs via tandem assembly of polypeptides for mineralization of stable CaCO3 structures

A macromolecular-assembly of polypeptides constructs a network of anionic and cationic charges vital for recognizing and coassembling Ca(2+) and CO(3)(2-) ions to mineralize and stabilize different mineral forms of CaCO(3) with core-shell or solid morphologies in an aqueous solution.     

Synthesis, biological evaluation, and radioiodination of halogenated closo-carboranylthymidine analogues

The synthesis and initial biological evaluation of 3-carboranylthymidine analogues (3CTAs) that are (radio)halogenated at the closo-carborane cluster are described. Radiohalogenated 3CTAs have the potential to be used in the radiotherapy and imaging of cancer because they may be selectively entrapped in tumor cells through monophosphorylation by human thymidine kinase 1 (hTK1). Two strategies for the synthesis of a (127)I-labeled form of a specific 3CTA, previously designated as N5, are described: (1) direct iodination of N5 with iodine monochloride and aluminum chloride to obtain N5-(127)I and (2) initial monoiodination of o-carborane to 9-iodo-o-carborane followed by its functionalization to N5-(127)I. The former strategy produced N5-(127)I in low yields along with di-, tri-, and tetraiodinated N5 as well as decomposition products, whereas the latter method produced only N5-(127)I in high yields. N5-(127)I was subjected to nucleophilic halogen- and isotope-exchange reactions using Na(79/81)Br and Na(125)I, respectively, in the presence of Herrmann's catalyst to obtain N5-(79/81)Br and N5-(125)I, respectively. Two intermediate products formed using the second strategy, 1-(tert-butyldimethylsilyl)-9-iodo-o-carborane and 1-(tert-butyldimethylsilyl)-12-iodo-o-carborane, were subjected to X-ray diffraction studies to confirm that substitution at a single carbon atom of 9-iodo-o-carborane resulted in the formation of two structural isomers. To the best of our knowledge, this is the first report of halogen- and isotope-exchange reactions of B-halocarboranes that have been conjugated to a complex biomolecule. Human TK1 phosphorylation rates of N5, N5-(127)I, and N5-(79/81)Br ranged from 38.0% to 29.6% relative to that of thymidine, the endogenous hTK1 substrate. The in vitro uptake of N5, N5-(127)I, and N5-(79/81)Br in L929 TK1(+) cells was 2.0, 1.8, and 1.4 times greater than that in L929 TK1(-) cells.     

Synthesis,characterization and hydrogen sorption studies of mixed sodium‐potassium alanate

The aim of the present investigation is to synthesize mixed sodium potassium alanate (K₂NaAlH₆) and to explore its hydrogen sorption characteristics. K₂NaAlH₆ is synthesized through ball milling of KH and NaAlH₄ in the molar ratio 2:1 under hydrogen pressure of 10 bar. The temperature programmed desorption experiment shows that the synthesized K₂NaAlH₆ has peak desorption temperature of ∼352°C and reveals appreciable rehydrogenation kinetics under 6 bar hydrogen pressure at 300°C. The investigations are also focused on the catalytic effect of carbon nanostructures (CNS) namely, the graphene sheet (GS) and single wall carbon nanotube (SWCNT) and titanium halides (TiCl₃ and TiF₃) on K₂NaAlH₆. In the case of graphene and SWCNT catalyzed K₂NaAlH₆, the peak desorption temperature gets reduced to ∼347°C and ∼341°C respectively. The catalytic effects of CNS and titanium halide on K₂NaAlH₆ are also compared in the investigation. Between the two types of catalysts, halides are found to be better than CNS and out of the two halides, TiF₃ is found to be the best catalyst for hydrogen sorption in K₂NaAlH₆. The peak desorption temperature decreases significantly from 352°C to ∼324°C for TiF₃ catalyzed K₂NaAlH₆. Thus, the desorption activation energy reduces drastically from 124.43 kJ/mol (synthesized K₂NaAlH₆) to 88.05 kJ/mol for TiF₃ catalyzed K₂NaAlH₆.