Aromatic poly(1,3,4‐oxadiazole)s and poly(amide‐1,3,4‐oxadiazole)s containing ether sulfone linkages

Polyhydrazides and poly(amide‐hydrazide)s were prepared from two ether‐sulfone‐dicarboxylic acids, 4,4′‐[sulfonylbis(1,4‐phenylene)dioxy]dibenzoic acid and 4,4′‐[sulfonylbis(2,6‐dimethyl‐1,4‐phenylene)dioxy]dibenzoic acid, or their diacyl chlorides with terephthalic dihydrazide, isophthalic dihydrazide, and p‐aminobenzhydrazide via a phosphorylation reaction or a low‐temperature solution polycondensation. All the hydrazide polymers were found to be amorphous according to X‐ray diffraction analysis. They were readily soluble in polar organic solvents such as N‐methyl‐2‐pyrrolidone and N,N‐dimethylacetamide and could afford colorless, flexible, and tough films with good mechanical strengths via solvent casting. These hydrazide polymers exhibited glass‐transition temperatures of 149–207 °C and could be thermally cyclodehydrated into the corresponding oxadiazole polymers in the solid state at elevated temperatures. Although the oxadiazole polymers showed a significantly decreased solubility with respect to their hydrazide prepolymers, some oxadiazole polymers were still organosoluble. The thermally converted oxadiazole polymers had glass‐transition temperatures of 217–255 °C and softening temperatures of 215–268 °C and did not show significant weight loss before 400 °C in nitrogen or air. For a comparative study, related sulfonyl polymers without the ether groups were also synthesized from 4,4′‐sulfonyldibenzoic acid and the hydrazide monomers by the same synthetic routes. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2271–2286, 2001     

4-Fluorinated L-lysine analogs as selective i-NOS inhibitors: methodology for introducing fluorine into the lysine side chain

In the literature, the introduction of fluorine into bioactive molecules has been known to enhance the biological activity relative to the parent molecule. Described in this article is the synthesis of 4R-fluoro-L-NIL (12) and 4,4-difluoro-L-NIL (23) as part of our iNOS program. Both 12 and 23 were found to be selective iNOS inhibitors as shown in Table 2 below. Secondarily, methodology to synthesize orthogonally protected 4-fluoro-L-lysine and 4,4-difluoro-L-lysine has been developed.     

Insights into the molecular mechanism of membrane fusion from simulation: evidence for the association of splayed tails

We present coarse-grained simulations of fusion between two liposomes from which a detailed picture of lipid movements emerges. In these simulations the bilayers dilate at the contact edge, and the resulting increase in the area per lipid produces a tilting of the individual molecules as predicted. Fusion is initiated when some of these tilted lipids splay their aliphatic tails, such that the molecules are shared between the opposing leaflets. Multiple splayed lipids subsequently associate with their aliphatic tails in contact, which produces a new hydrophobic core. As the tails extend into a more parallel conformation the two outer leaflets become contiguous to produce a hemifused structure. The results have interesting implications for biological membrane fusion and suggest new possibilities for designing molecules that control fusion.     

A semiempirical free energy force field with charge-based desolvation

The authors describe the development and testing of a semiempirical free energy force field for use in AutoDock4 and similar grid-based docking methods. The force field is based on a comprehensive thermodynamic model that allows incorporation of intramolecular energies into the predicted free energy of binding. It also incorporates a charge-based method for evaluation of desolvation designed to use a typical set of atom types. The method has been calibrated on a set of 188 diverse protein-ligand complexes of known structure and binding energy, and tested on a set of 100 complexes of ligands with retroviral proteases. The force field shows improvement in redocking simulations over the previous AutoDock3 force field.     

Effect of Thermal Annealing on the Surface Properties of Electrospun Polymer Fibers

Electrospun polymer fibers are gaining importance because of their unique properties and applications in areas such as drug delivery, catalysis, or tissue engineering. Most studies to control the morphology and properties of electrospun polymer fibers focus on changing the electrospinning conditions. The effects of post‐treatment processes on the morphology and properties of electrospun polymer fibers, however, are little studied. Here, the effect of thermal annealing on the surface properties of electrospun polymer fibers is investigated. Poly(methyl methacrylate) and polystyrene fibers are fist prepared by electrospinning, followed by thermal annealing processes. Upon thermal annealing, the surface roughness of the electrospun polymer fibers decreases. The driving force of the smoothing process is the minimization of the interfacial energy between polymer fibers and air. The water contact angles of the annealed polymer fibers also decrease with the annealing time.

     

Template free electrochemical deposition of ZnSb nanotubes for Li ion battery anodes

ZnSb nanotubes were grown through a template free electrodeposition method under over-potential conditions. The growth of the nanotubes was attributed to the template effect from H(2) bubbles. Due to their hollow structure, the ZnSb nanotubes depicted better Li ion storage performance compared to that of ZnSb nanoparticles deposited under different conditions.     

A new approach to control crystallinity of resulting polymers: Self‐condensing ring opening polymerization

The cationic polymerization of 3‐methyl‐3‐oxetanemethanol was initiated using BF₃·OEt₂. The low ratio of catalyst to monomer results in a mainly linear or slightly branched polymer, and the high catalyst to monomer ratio leads to a hyperbranched polymer. The hyperbranched polyether yielded is amorphous, and the essentially linear version obtained is partially crystalline. In other words, the degree of branching and the crystallinity of resulting polymers are dependent on the catalyst to monomer ratio. Therefore a new approach to control the crystallinity of resulting polymers in self‐condensing ring opening polymerization was developed.