Tacticity, molecular weight, and molecular-weight-distribution relationships in stereoregular polyacrylonitrile prepared by electron beam irradiation canal polymerization

The preparation and characterization of stereoregular isotactic polyacrylonitrile (PAN) by electron beam (EB) irradiation on a urea canal complex are described. The EB method has several advantages over the ordinary γ-ray irradiation method: a very short polymerization time is needed (within a few seconds) and EB irradiation is carried out intermittently, and so all the polymer properties can be studied as a function of the EB irradiation dose. The structure–properties relationships of PAN, such as intrinsic viscosity versus the number-average molecular weight and the viscosity versus the isotacticity range were clarified. Significant information for the optimization of the tacticity of PAN was extracted. Received: 23 August 1999 Accepted : 10 January 2000     

The Formation of Organogels and Helical Nanofibers from Simple Organic Salts

Simple organic salts based on aniline‐derived cations and D ‐tartrate anions formed organogels and helical nanofibers. The organic salt (p‐fluoroanilinium)(D ‐tartrate) was found to generate an organogel despite the absence of a hydrophobic alkyl chain, whereas (p‐iodoanilinium)(D ‐tartrate) formed helical nanofibers in braided ropelike structures through a rolling‐up process. The helicity of these nanofibers could be reversed by changing the growth solvent. The driving forces responsible for the formation of the nanofibers were determined to be 1D O?H???O^? hydrogen‐bonding interactions between D ‐tartrate anions and π stacking of anilinium cations, as well as steric hindrance between the hydrogen‐bonded chains.     

Bionanodot monolayer array fabrication for nonvolatile memory application

A polyelectrolyte thin film which was simply spin-coated on a substrate showed the high-density adsorption of bionanodot-accommodated ferritins through electrostatic interaction. Solution pH adjustment facilitated the control of adsorption density to a value grater than 80% of the theoretical maximum density. The formed polyelectrolyte film was very thin and vulnerable like protein, therefore, only the array with densely adsorbed bionanodot was left on the substrate after organic component removal. The floating nanodot gate type MOS capacitor fabricated with this bionanodot array showed a memory effect, and no negative influences of polymer such as carrier trapping on the capacitance-voltage characteristics was observed.     

Controlled cationic ring‐opening polymerization of cyclic thiocarbonates with ester groups

This work deals with the cationic ring‐opening polymerization of the cyclic thiocarbonates 5‐benzoyloxymethyl‐5‐methyl‐1,3‐dioxane‐2‐thione ( 1 ), 5,5‐dimethyl‐1,3‐dioxane‐2‐thione ( 2 ), and 4‐benzoyloxymethyl‐1,3‐dioxane‐2‐thione ( 3 ). The polymerization was carried out with 2 mol % trifluoromethanesulfonic acid, methyl trifluoromethanesulfonate, boron trifluoride etherate, or triethyloxonium tetrafluoroborate as the initiator to afford the polythiocarbonate with a narrow molecular weight distribution accompanying isomerization of the thiocarbonate group. The molecular weight of the obtained polymer could be controlled by the feed ratio of the monomer to the initiator and increased when the second monomer was added to the polymerization mixture after the quantitative consumption of the monomer in the first stage. The block copolymerization of 2 and 3 was also achieved, and this supported the idea that the cationic ring‐opening polymerization of these monomers proceeded via a living process. The order of the polymerization rate was 3 > 2 > 1 . The cationic ring‐opening polymerization of 1 and 3 involved the neighboring group participation of ester groups according to the polymerization rate and molecular orbital calculations with the ab initio method. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 185–195, 2003     

Montmorillonite-supramolecular hydrogel hybrid for fluorocolorimetric sensing of polyamines

Fluorescent sensor materials for rapidly and conveniently detecting polyamines in biological fluids are highly desirable for cancer diagnosis. We herein describe the hybridization of a supramolecular hydrogel with a layered inorganic host adsorbing a fluorescent dye which produces a fluorocolorimetric sensor for spermine and spermidine, important biomarkers for cancers, in artificial urine.     

Physicochemical mechanism for the enhanced ability of lipid membrane penetration of polyarginine

Arginine-rich, cell-penetrating peptides (e.g., Tat-peptide, penetratin, and polyarginine) are used to carry therapeutic molecules such as oligonucleotides, DNA, peptides, and proteins across cell membranes. Two types of processes are being considered to cross the cell membranes: one is an endocytic pathway, and another is an energy-independent, nonendocytic pathway. However, the latter is still not known in detail. Here, we studied the effects of the chain length of polyarginine on its interaction with an anionic phospholipid large unilamellar vesicle (LUV) or a giant vesicle using poly-l-arginine composed of 69 (PLA69), 293 (PLA293), or 554 (PLA554) arginine residues, together with octaarginine (R8). ζ-potential measurements confirmed that polyarginine binds to LUV via electrostatic interactions. Circular dichroism analysis demonstrated that the transition from the random coil to the α-helix structure upon binding to LUV occurred for PLA293 and PLA554, whereas no structural change was observed for PLA69 and R8. Fluorescence studies using membrane probes revealed that the binding of polyarginine to LUV affects the hydration and packing of the membrane interface region, in which the degree of membrane insertion is greater for the longer polyarginine. Isothermal titration calorimetry measurements demonstrated that although the binding affinity (i.e., the Gibbs free energy of binding) per arginine residue is similar among all polyarginines the contribution of enthalpy to the energetics of binding of polyarginine increases with increasing polymer chain length. In addition, confocal laser scanning microscopy showed that all polyarginines penetrate across giant vesicle membranes, and the order of the amount of membrane penetration is R8 ≈ PLA69 < PLA293 ≈ PLA554. These results suggest that the formation of α-helical structure upon lipid binding drives the insertion of polyarginine into the membrane interior, which appears to enhance the membrane penetration of polyarginine.     

Energetic protons from a few-micron metallic foil evaporated by an intense laser pulse

With detailed experimental studies and hydrodynamics and particle-in-cell simulations we investigate the role of the prepulse in laser proton acceleration. The prepulse or pedestal (amplified spontaneous emission) can completely evaporate the irradiated region of a sufficiently thin foil; therefore, the main part of the laser pulse interacts with an underdense plasma. The multiparametric particle-in-cell simulations demonstrate that the main pulse generates the quasistatic magnetic field, which in its turn produces the long-lived charge separation electrostatic field, accelerating the ions.     

X ray crystallography of (+)-(R)p methyl phenyl phosphoramidate of ethyl L-phenylalaninate

The absolute configuration of (+)-(R)_p methyl phenyl phosphoramidate of ethyl L-phenylalaninate $\text{1}$ was determined by X ray crystallography.