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.

Polymethacrylates with polyhedral oligomeric silsesquioxane (POSS) moieties (poly­(POSS-MA)­s) with flexible spacers between the POSS cages and the methacrylate group have distinctly different properties from their linear counterpart, i.e., PMMA. POSS cages modify interchain correlations and result in multiple dynamic processes that reflect the cooperative relaxations of both the pendant POSS units and ester dipoles and the polymer backbone. As a result, the freezing of the backbone dynamics is shifted to lower temperatures, and the nanocomposites appear softer than linear PMMA chains of similar degrees of polymerization. POSS cages can be employed as nanometer size blocks that, depending on the polymer backbone and the spacer, can impart mobility and control over the mechanical properties of nanocomposites.

PW91 XC functional has recently been assessed for the interaction energies of selected dimers in which the nonbonded interactions play a critical role. In this study, we assess the PW91 XC functional with the 6-31+G* basis set for the vibrational spectra of amide and amide dimers. The set of molecules chosen consists of (a) the monomeric amides: formamide, acetamide, cis-NMF, trans-NMF, N,N-DMF, cis-NMA, trans-NMA, (b) the covalent dipeptides N-acetyl-glycine-N′-methylamide in C 7 eq and C 5 conformations and the C 7 ax , C 7 eq , C 5 ext , β 2 , R p conformers of N-acetyl-L-alanine-N′-methylamide, (c) the dimers cis-NMA cyclic dimer, two conformations of trans-NMA dimer and four conformations of formamide dimer. This set has been also used for the assessment of the EDF1 functional for the prediction of vibrational spectra. Comparison of PW91 XC / 6-31+G* results with EDF1, B3LYP, and MP2 values with the same basis set accentuate PW91 XC as the best performing functional for amide I and II modes while for amide III mode EDF1 performs better. Overall, PW91 XC has the better performance with EDF1 following close. We propose that PW91 may be used for the study of proteins and polypeptidic chains.

Circular dichroism (CD) spectroscopy in the visible region (vis‐CD) is a powerful technique to study metal–protein interactions. It can resolve individual d–d electronic transitions as separate bands and is particularly sensitive to the chiral environment of the transition metals. Modern quantum chemical methods enable CD spectra calculations from which, along with direct comparison with the experimental CD data, the conformations and the stereochemistry of the metal–protein complexes can be assigned. However, a clear understanding of the observed spectra and the molecular configuration is largely lacking. In this study, we compare the experimental and computed vis‐CD spectra of Cu2+‐loaded model peptides in square‐planar complexes. We find that the spectra can readily discriminate the coordination pattern of Cu2+ bound exclusively to main‐chain amides from that involving both main‐chain amides and a side‐chain (i.e. histidine side‐chain). Based on the results, we develop a set of empirical rules that relates the appearance of particular vis‐CD spectral features to the conformation of the complex. These rules can be used to gain insight into coordination geometries of other Cu2+–or Ni2+–protein complexes.

The effect of oxygen substitution is studied in two homologous compounds of n-cyanobiphenyls with n = 8 in the bulk and under confinement within self-ordered nanoporous alumina (AAO). Oxygen substitution in 8OCB increases the dipole moment and stabilizes the crystalline, smectic, and nematic phases to higher temperatures relative to 8CB. Within their smectic- A (SmA) phase both 8CB and 8OCB behave as weak viscoelastic solids with low shear moduli reflecting the underlying supramolecular defect structure. Dielectric spectroscopy assisted by DFT calculations identified strong dipolar associations within the isotropic phases characterized by a Kirkwood-Fröhlich interaction parameter, g ∼ 0.36. Dielectric spectroscopy further identified a slow process (∼ kHz) of low dielectric strength. The proximity of this process to the rheology time scale suggests as common origin a cooperative relaxation of the defect structure. Confinement alters the phase diagram by stabilizing certain crystalline phases and by reducing the N-I transition temperature in agreement with surface tension effects. However, the N-I transition seems to retain its first order character. Surface treatment with n-decyltrichlorosilane results in destabilization of the SmA phase at the expense of the N phase. This is consistent with a picture of surface anchored LC molecules at the pore walls that stabilize the nematic phase.