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Molecular Design and Property Prediction of Sterically Confined Polyimides for Thermally Stable and Transparent Materials.

ABSTRACT: To meet the demand for next-generation flexible optoelectronic devices, it is crucial to accurately establish the chemical structure-property relationships of new optical polymer films from a theoretical point of view, prior to production. In the current study, computer-aided simulations of newly designed poly(ester imide)s (PEsIs) with various side groups (?H, ?CH?, and ?CF?) and substituted positions were employed to study substituent-derived steric effects on their optical and thermal properties. From calculations of the dihedral angle distribution of the model compounds, it was found that the torsion angle of the C?N imide bonds was effectively constrained by the judicious introduction of di-, tetra-, and hexa-substituted aromatic diamines with ?CF? groups. A high degree of fluorination of the PEsI repeating units resulted in weaker intra- and intermolecular conjugations. Their behavior was consistent with the molecular orbital energies obtained using density functional theory (DFT). In addition, various potential energy components of the PEsIs were investigated, and their role in glass-transition behavior was studied. The van der Waals energy (E_vdW) played a crucial role in the segmental chain motion, which had an abrupt change near glass-transition temperature (T_g). The more effective steric effect caused by ?CF? substituents at the 3-position of the 4-aminophenyl group significantly improved the chain rigidity, and showed high thermal stability (T_g > 731 K) when compared with the ?CH? substituent at the same position, by highly distorting (89.7°) the conformation of the main chain.

SUBMITTER: Nam KH

PROVIDER: S-EPMC6403577 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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Molecular Design and Property Prediction of Sterically Confined Polyimides for Thermally Stable and Transparent Materials.

Nam Ki-Ho KH Choi Hoi Kil HK Yeo Hyeonuk H You Nam-Ho NH Ku Bon-Cheol BC Yu Jaesang J

Polymers 20180607 6

To meet the demand for next-generation flexible optoelectronic devices, it is crucial to accurately establish the chemical structure-property relationships of new optical polymer films from a theoretical point of view, prior to production. In the current study, computer-aided simulations of newly designed poly(ester imide)s (PEsIs) with various side groups (⁻H, ⁻CH₃, and ⁻CF₃) and substituted positions were employed to study substituent-derived steric effects on their optical and thermal propert ...[more]

PMID: 30966664

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Project description:Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is highly contagious, and transmission involves a series of processes that may be targeted by vaccines and therapeutics. During transmission, host cell invasion is controlled by a large-scale (200-300 Å) conformational change of the Spike protein. This conformational rearrangement leads to membrane fusion, which creates transmembrane pores through which the viral genome is passed to the host. During Spike-protein-mediated fusion, the fusion peptides must be released from the core of the protein and associate with the host membrane. While infection relies on this transition between the prefusion and postfusion conformations, there has yet to be a biophysical characterization reported for this rearrangement. That is, structures are available for the endpoints, though the intermediate conformational processes have not been described. Interestingly, the Spike protein possesses many post-translational modifications, in the form of branched glycans that flank the surface of the assembly. With the current lack of data on the pre-to-post transition, the precise role of glycans during cell invasion has also remained unclear. To provide an initial mechanistic description of the pre-to-post rearrangement, an all-atom model with simplified energetics was used to perform thousands of simulations in which the protein transitions between the prefusion and postfusion conformations. These simulations indicate that the steric composition of the glycans can induce a pause during the Spike protein conformational change. We additionally show that this glycan-induced delay provides a critical opportunity for the fusion peptides to capture the host cell. In contrast, in the absence of glycans, the viral particle would likely fail to enter the host. This analysis reveals how the glycosylation state can regulate infectivity, while providing a much-needed structural framework for studying the dynamics of this pervasive pathogen.

Dataset Information

Molecular Design and Property Prediction of Sterically Confined Polyimides for Thermally Stable and Transparent Materials.

Publications

Molecular Design and Property Prediction of Sterically Confined Polyimides for Thermally Stable and Transparent Materials.

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