Modeling the Interplay of Conformational and Electronic Structure in Conjugated Polyelectrolytes

Conjugated polyelectrolytes (CPEs) combine ionic, electronic, and optical functionality with the mechanical and thermodynamic properties of semiflexible, amphiphilic polyelectrolytes. Critical to CPE design is the coupling between macromolecular conformations, ionic interactions, and electronic transport, the combination of which spans electronic to mesoscopic length scales, rendering coherent theoretical analysis challenging. Here, we utilize a recently developed anisotropic CG model in combination with a phenomenological tight-binding Hamiltonian to explore the interplay of single-chain conformational and electronic structure in CPEs. Accessible single chain conformations are explored as a function of solvent conditions and chain stiffness, reproducing a rich landscape of rod-like, racquet, pearl necklace, and helical conformations observed in previous works. The electronic structure of each conformational archtype is further analyzed, incorporating through-bond coupling, through-space coupling, and electrostatic contributions to the Hamiltonian. Electrostatics is observed to influence electronic structure primarily by modifying the accessible conformational space, and only minimally by direct modulation of on-site energies. Electron transport in CPEs is most efficient in helical and racquet conformations, which is attributed to the flattening of dihedrals and through-space coupling within collapsed conformations. Relatedly, kink formation within racquets does not significantly deteriorate electronic conjugation within CPEs - an insight critical to understanding transport within locally ordered aggregates. These conclusions provide unprecedented computational insight into structure function relationships defining emerging classes of CPEs.

Biobased Terpene Derivatives: Stiff and Biocompatible Compounds to Tune Biodegradability and Properties of Poly(butylene succinate)

Different copolymers incorporating terpene oxide units (e.g., limonene oxide) have been evaluated considering thermal properties, degradability, and biocompatibility. Thus, polycarbonates and polyesters derived from aromatic, monocyclic and bicyclic anhydrides have been considered. Furthermore, ring substitution with myrcene terpene has been evaluated. All polymers were amorphous when evaluated directly from synthesis. However, spherulites could be observed after the slow evaporation of diluted chloroform solutions of polylimonene carbonate, with all isopropene units possessing an R configuration. This feature was surprising considering the reported information that suggested only the racemic polymer was able to crystallize. All polymers were thermally stable and showed a dependence of the maximum degradation rate temperature (from 242 °C to 342 °C) with the type of terpene oxide. The graduation of glass transition temperatures (from 44 °C to 172 °C) was also observed, being higher than those corresponding to the unsubstituted polymers. The chain stiffness of the studied polymers hindered both hydrolytic and enzymatic degradation while a higher rate was detected when an oxidative medium was assayed (e.g., weight losses around 12% after 21 days of exposure). All samples were biocompatible according to the adhesion and proliferation tests performed with fibroblast cells. Hydrophobic and mechanically consistent films (i.e., contact angles between 90° and 110°) were obtained after the evaporation of chloroform from the solutions, having different ratios of the studied biobased polyterpenes and poly(butylene succinate) (PBS). The blend films were comparable in tensile modulus and tensile strength with the pure PBS (e.g., values of 330 MPa and 7 MPa were determined for samples incorporating 30 wt.% of poly(PA-LO), the copolyester derived from limonene oxide and phthalic anhydride. Blends were degradable, biocompatible and appropriate to produce oriented-pore and random-pore scaffolds via a thermally-induced phase separation (TIPS) method and using 1,4-dioxane as solvent. The best results were attained with the blend composed of 70 wt.% PBS and 30 wt.% poly(PA-LO). In summary, the studied biobased terpene derivatives showed promising properties to be used in a blended form for biomedical applications such as scaffolds for tissue engineering.

Some aspects of a two-pore translocation problem

We report Brownian dynamics (BD) simulation results for a coarse-grained (CG) model semi-flexible polymer threading through two nanopores. Particularly we study a “tug-of-war” situation where equal and opposite forces are applied on each pore to avoid folds for the polymer segment in between the pores. We calculate mean first passage times (MFPT) through the left and the right pores and show how the MFPT decays as a function of the off-set voltage between the pores. We present results for several bias voltages and chain stiffness. Our BD simulation results validate recent experimental results and offer avenues to further explore various aspects of multi-pore translocation problem using BD simulation strategies which we believe will provide insights to design new experiments.