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Hierarchy of π-Stacking Determines the Conformational Preference of Bis-Squaraines

preprint
submitted on 02.10.2020 and posted on 05.10.2020 by Abhishek Singh, Reman K. Singh, G Naresh Patwari
The rational design of conformationally controlled foldable modules can lead to a deeper insight into the conformational space of complex biological molecules where non-covalent interactions such as hydrogen bonding and π-stacking are known to play a pivotal role. Squaramides are known to have excellent hydrogen bonding capabilities and hence, are ideal molecules for designing foldable modules that can mimic the secondary structures of bio-molecules. The π-stacking induced folding of bis-squaraines tethered using aliphatic primary and secondary-diamine linkers of varying length is explored with a simple strategy of invoking small perturbations involving the length linkers and degree of substitution. Solution phase NMR investigations in combination with molecular dynamics simulations suggest that bis-squaraines predominantly exist as extended conformations. Structures elucidated by X-ray crystallography confirmed a variety of folded and extended secondary conformations including hairpin turns and 𝛽-sheets which are determined by the hierarchy of π-stacking relative to N–H···O hydrogen bonds.

History

Email Address of Submitting Author

naresh@chem.iitb.ac.in

Institution

Indian Institute of Technology Bombay

Country

India

ORCID For Submitting Author

0000-0003-0811-7249

Declaration of Conflict of Interest

No conflict of interest

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