Poly(n-methylene 2,5-furanoates) is a family of biobased polymers with outstanding gas barrier and mechanical properties and with the potential to frame the future in certain applications (e.g., food packaging, fibers, and engineering thermoplastics). Herein, we used combined efforts by density functional theory calculations and experiments to explore in detail the conformational properties, the thermodynamics, and the molecular dynamics in the poly(n-methylene 2,5-furanoate) series as a function of n in the range from 2 poly(ethylene furanoate) (PEF) to 12 poly(dodecylene furanoate). The computational study employed the conformers suggested earlier [Macromolecules 2018, 51, 3515−3526] but used additional functionals and investigated, in addition to the monomer and trimer, the PEF nonamer with respect to conformations pertinent to the amorphous state. Depending on the conformer, variable dipole moments were obtained in the range from 2.1 to 6.1, 3.0 to 8.2, and 1.8 to 7.1 debye, respectively, for the monomer, the trimer, and the nonamer. Strikingly, both the trimer and more importantly, the nonamer exhibited very compact helical structures stabilized by π−π interactions of the furan rings. We suggest that the helical motifs within the amorphous state contribute to the barrier improvement for carbon dioxide in PEF as compared to PET. The distinct structural motifs of poly(n-methylene 2,5-furanoate)s exerted an influence on the sub-T g and the segmental dynamics (average relaxation times and distribution of relaxation times, fragility, and dielectric strength). The segmental process shows Vogel−Fulcher−Tammann temperature dependence with distinctly different behaviors in the amorphous and crystalline states with T g dependencies following an approximate linear dependence with n −1 as T g cr = 249 ± 5 + (231 ± 18/n) and T g am = 240 ± 5 + (232 ± 17/n). The large T g reduction is compared with another homologous series, namely, poly(n-alkyl methacrylates), where the internal plasticization takes place at the side group. Internal plasticization is more efficient in the latter because of the mobile free end. Apart from T g reduction, they show (i) subglass dynamics with activation energies that decrease with increasing alkyl length [from 57.8 kJ/mol in PEF (n = 2) to 47 kJ/mol in PNF (n = 9)], revealing the unlocking of local dipolar motions by the flexible spaces, (ii) a narrow distribution within the segmental process, α am , (corresponding Kohlrausch−Williams−Watts stretching exponent of 0.48, i.e., among the narrower for amorphous polymers), (iii) segments with locally nearly antiparallel dipolar orientation correlations, and (iv) a constant fragility in the amorphous state independent of alkyl chain length. We suggest that pertinent to these dynamic features is the local packing of chains composed of compact helical segments.

Hexasubstituted benzenes have been synthesized with the highest known dipole moments, as determined by dielectric spectroscopy and DFT methods. Based on the preparation of 4,5-diamino-3,6-dibromophthalonitrile, combined with a novel method to synthesize dihydrobenzimidazoles, these benzene derivatives have dipole moments in excess of 10 debye. Such dipole moments are desirable in ferroelectrics, nonlinear optics, and in organic photovoltaics. Structure determination was achieved through single-crystal X-ray crystallography, and the optical properties were determined by UV/Vis absorption and fluorescence spectroscopy.

We report the results of a combined work based on density functional theory (DFT) calculations and experiments of the factors that influence the glass temperature, T g , and the associated ion conductivity in polymerized ionic liquids bearing imidazolium salts in the side group. This study consists of four different N-alkyl side-chain lengths [with n = 4 (butyl), 6 (hexyl), 8 (octyl), and 10 (decyl)] and seven different counteranionsDFT calculations of the anion−cation complexation energies were combined with thermodynamics (differential scanning calorimetry), structural (X-ray scattering), as well as temperature-and pressure-dependent dielectric spectroscopy measurements of ion conduction. Our results show that ion conduction is facilitated by local anion jumps with a length scale on the order of the charge alteration distance. Ion complexation strongly influences the backbone dynamics and the associated T g . A simple "stick and jump" model can account for the increased backbone mobility (reduced T g ) and the concomitant enhanced ion conductivity for anions with intermediate size. Among the different anions, [TFSI] − with its comparably large size and broad charge delocalization is only weakly coordinated with the cation. This best facilitates anion motion within the "ion paths" of the hexagonally packed cylinders and smectic morphologies.

The current understanding of epigenetic signaling assigns a central role to post-translational modifications that occur in the histone tails. In this context, it has been proposed that methylation of K9 and phosphorylation of S10 in the tail of histone H3 represent a binary switch that controls its reversible association to heterochromatin protein 1 (HP1). To test this hypothesis, we performed a comprehensive molecular dynamics study in which we analyzed a crystallographically defined complex that involves the HP1 chromodomain and an H3 tail peptide. Microsecond-long simulations show that the binding of the trimethylated K9 H3 peptide in the aromatic cage of HP1 is only slightly affected by S10 phosphorylation, because the modified K9 and S10 do not interact directly with one another. Instead, the phosphate group of S10 seems to form a persistent intramolecular salt bridge with R8, an interaction that can provoke a major structural change and alter the hydrogen-bonding regime in the H3-HP1 complex. These observations suggest that interactions between adjacent methyl-lysine and phosphoserine side chains do not by themselves provide a binary switch in the H3-HP1 system, but arginine-phosphoserine interactions, which occur in both histones and nonhistone proteins in the context of a conserved RKS motif, are likely to serve a key regulatory function.