Dataset Information

Glassy and Polymer Dynamics of Elastomers by ¹H Field-Cycling NMR Relaxometry: Effects of Cross-Linking.

ABSTRACT: ¹H spin lattice relaxation rate (R ₁) dispersions were acquired by field-cycling (FC) NMR relaxometry between 0.01 and 35 MHz over a wide temperature range on polyisoprene (IR), polybutadiene (BR), and poly(styrene-co-butadiene) (SBR) rubbers, obtained by vulcanization under different conditions, and on the corresponding uncured elastomers. By exploiting the frequency-temperature superposition principle, ??(??_s) master curves were constructed by shifting the total FC NMR susceptibility, ??(?) = ?R ₁(?), curves along the frequency axis by the correlation times for glassy dynamics, ?_s. Longer ?_s values and, correspondingly, higher glass transition temperatures were determined for the sulfur-cured elastomers with respect to the uncured ones, which increased by increasing the cross-link density, whereas no significant changes were found for fragility. The contribution of polymer dynamics, ? _pol ^?(?), to ??(?) was singled out by subtracting the contribution of glassy dynamics, ? _glass ^?(?), well represented using a Cole-Davidson spectral density. For all elastomers, ? _pol ^?(?) was found to represent a small fraction, on the order of 0.05-0.14, of the total ??(?), which did not show a significant dependence on cross-link density. In the investigated temperature and frequency ranges, polymer dynamics was found to encompass regimes I (Rouse dynamics) and II (constrained Rouse dynamics) of the tube reptation model for the uncured elastomers and only regime I for the vulcanized ones. This is clear evidence that chemical cross-links impose constraints on chain dynamics on a larger space and time scale than free Rouse modes.

SUBMITTER: Martini F

PROVIDER: S-EPMC7690040 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Glassy and Polymer Dynamics of Elastomers by 1H Field-Cycling NMR Relaxometry: Effects of Cross-Linking.

Martini Francesca F Carignani Elisa E Nardelli Francesca F Rossi Elena E Borsacchi Silvia S Cettolin Mattia M Susanna Antonio A Geppi Marco M Calucci Lucia L

Macromolecules 20201105 22

1H spin lattice relaxation rate (R 1) dispersions were acquired by field-cycling (FC) NMR relaxometry between 0.01 and 35 MHz over a wide temperature range on polyisoprene (IR), polybutadiene (BR), and poly(styrene-co-butadiene) (SBR) rubbers, obtained by vulcanization under different conditions, and on the corresponding uncured elastomers. By exploiting the frequency-temperature superposition principle, χ″(ωτs) master curves were constructed by shi ...[more]

PMID: 33250523

Similar Datasets

Project description:The remarkable power and specificity of enzyme catalysis rely on the dynamic alignment of the enzyme, substrates, and cofactors, yet the role of dynamics has usually been approached from the perspective of the protein. We have been using an underappreciated NMR technique, subtesla high-resolution field cycling 31P NMR relaxometry, to investigate the dynamics of the enzyme-bound substrates and cofactor on guanosine-5'-monophosphate reductase (GMPR). GMPR forms two dead end, yet catalytically competent, complexes that mimic distinct steps in the catalytic cycle: E·IMP·NADP+ undergoes a partial hydride transfer reaction, while E·GMP·NADP+ undergoes a partial deamination reaction. A different cofactor conformation is required for each partial reaction. Here we report the effects of mutations designed to perturb cofactor conformation and ammonia binding with the goal of identifying the structural features that contribute to the distinct dynamic signatures of the hydride transfer and deamination complexes. These experiments suggest that Asp129 is a central cog in a dynamic network required for both hydride transfer and deamination. In contrast, Lys77 modulates the conformation and mobility of substrates and cofactors in a reaction-specific manner. Thr105 and Tyr318 are part of a deamination-specific dynamic network that includes the 2'-OH of GMP. These residues have comparatively little effect on the dynamic properties of the hydride transfer complex. These results further illustrate the potential of high-resolution field cycling NMR relaxometry for the investigation of ligand dynamics. In addition, exchange experiments indicate that NH3/NH4+ has a high affinity for the deamination complex but a low affinity for the hydride transfer complex, suggesting that the movement of ammonia may gate the cofactor conformational change. Collectively, these experiments reinforce the view that the enzyme, substrates, and cofactor are linked in intricate, reaction-specific, dynamic networks and demonstrate that distal portions of the substrates and cofactors are critical features in these networks.

Dataset Information

Glassy and Polymer Dynamics of Elastomers by ¹H Field-Cycling NMR Relaxometry: Effects of Cross-Linking.

Publications

Glassy and Polymer Dynamics of Elastomers by <sup>1</sup>H Field-Cycling NMR Relaxometry: Effects of Cross-Linking.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets