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Single-Site Binding of Pyrene to Poly(ester-Imide)s Incorporating Long Spacer Units: Prediction of NMR Resonance-Patterns from a Fractal Model

preprint
revised on 09.07.2020 and posted on 10.07.2020 by Marcus Knappert, Tianqi Jin, Scott D. Midgley, Guanglu Wu, Oren Scherman, Ricardo Grau-crespo, Howard Colquhoun
Co-polycondensation of the diimide-based diols N,N'-bis(2-hydroxyethyl)hexafluoro-isopropylidene-diphthalimide, (HFDI), and N,N'-bis(2-hydroxy-ethyl)naphthalene-1,4,5,8-tetracarboxylic-diimide, (NDI), with aliphatic diacyl chlorides ClOC(CH2)xCOCl (x = 5 to 8) affords linear copoly(ester-imide)s. Such copolymers interact with pyrene via supramolecular binding of the polycyclic aromatic molecule at NDI residues. This results in upfield complexation shifts and sequence-related splittings of the NDI 1H NMR resonances, but gives a very different resonance-pattern from the corresponding copolymer where x = 2. Computational modelling of the polymer with x = 5 suggests that, in this system, each pyrene molecule binds to just a single NDI residue rather than to an adjacent pair of NDI's in a tight chain-fold ("dual-site" binding) as found for x = 2. The new single-site binding model enables the pattern of 1H NMR resonances for copolymers with longer spacers (x = 5 to 8) to be reproduced and assigned by simulation from sequence-specific shielding factors based on the fractal known as the fourth-quarter Cantor set. As this set also enables an understanding of dual-site binding systems, it evidently provides a general numerical framework for supramolecular sequence-analysis in binary copolymers.

Funding

EU Marie Sklodowska-Curie ITN, Euro-Sequences, grant number 642083

Leverhulme Trust, Emeritus Fellowship, grant number EM-2018-0161/4

ERC Consolidator Grant, CAM-RIG, 726470

EPSRC programme grant, number EP/L027151/1

History

Email Address of Submitting Author

h.m.colquhoun@rdg.ac.uk

Institution

University of Reading

Country

UK

ORCID For Submitting Author

0000-0002-3725-4085

Declaration of Conflict of Interest

There are no conflicts of interest to declare.

Version Notes

Email address added to MS and ESI

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