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. 2023 Jan 11;14:155. doi: 10.1038/s41467-023-35850-4

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© The Author(s) 2023

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Fig. 3 — The cross peaks marked with black and encircled numbers are assigned to the protons of free [2a]⁺ and entrapped [2a]⁺, respectively. The upfield (<0) and downfield shifts (>0) in the ¹H NMR spectrum caused by the host–guest formation are shown as Δδ in parentheses.