Stochastic Bullvalene Architecture Modulates Structural Rigidity in π-Rich Macromolecules

The synthesis and processing of π-rich polymers found in novel electronics and textiles is difficult because chain stiffness leads to low solubility and high thermal transitions. The incorporation of “shape-shifting” molecular cages into π-rich backbone provides an ensemble of structural kinks to modulate chain architecture via a self-contained library of valence isomers. In this work, we report the synthesis and characterization of (bullvalene-co-phenylene)s that feature smaller persistence lengths than a prototypical rigid rod polymer, poly(p-phenylene). By varying the amount of bullvalene incorporation within a poly(p-phenylene) chain (0–50 %), we can tune thermal properties and solution-state conformation. These features are caused by stochastic bullvalene isomers within the polymer backbone that result in kinked architectures. Synthetically, bullvalene incorporation offers a facile method to decrease structural rigidity within π-rich materials without concomitant crystallization. VT NMR experiments confirm that these materials remain dynamic in solution, offering the opportunity for future stimuli-responsive applications.     

Efficient synthesis of a beta-peptide combinatorial library with microwave irradiation

The predictable relationship between beta-amino acid sequence and folding has inspired several biological applications of beta-peptides. For many such applications, it would be desirable to prepare and screen beta-peptide libraries. However, standard peptide synthesis protocols are not efficient enough to support a library approach for many types of beta-peptides. We recently optimized the solid-phase synthesis of beta-peptides using microwave irradiation, and we have now adapted this approach to synthesis on polystyrene macrobeads. We rapidly prepared a high-quality beta-peptide combinatorial library via a split-and-mix strategy. This library was screened in search of beta-peptide antagonists of the p53-MDM2 protein-protein interaction.     

Anion-excluding polypyrrole films

A new method for modifying polypyrrole films is described. It involves complete oxidation of the film. The film produced is electronically non-conductive but ionically conductive, and has ion-selective properties based on the exclusion of anionic species. The effective pH within the film can be controlled by the choice of supporting electrolyte used during the oxidative treatment, without loss of selectivity. Cyclic voltammetry is used to demonstrate the effect of film pH on the rate of dopamine oxidation in a neutral supporting electrolyte.