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Unraveling the Structure-Affinity Relationship Between Cucurbit[n]urils (n = 7, 8) and Cationic Diamondoids

Sigwalt, David; Šekutor, Marina; Cao, Liping; Zavalij, Peter Y.; Hostaš, Jirí; Ajani, Haresh; Hobza, Pavel; Mlinarić-Majerski, Kata; Glaser, Robrt; Isaacs, Lyle (2017) Unraveling the Structure-Affinity Relationship Between Cucurbit[n]urils (n = 7, 8) and Cationic Diamondoids. Journal of the American Chemical Society, 139 (8). pp. 3249-3258. ISSN 0002-7863

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We report measurement of the binding constants (Ka) for cucurbit[n]uril (n = 7, 8) toward four series of guests based on 2, 6-disubstituted adamantanes, 4, 9-disubstituted diamantanes, 1, 6-disubstituted diamantanes, and 1-substituted adamantane ammonium ions by direct and competitive 1H NMR spectroscopy. Compared to B[7]•Diam(NMe3)2, the adamantane diammonium ion complexes (e.g. CB[7]•2, 6-Ad(NH3)2 and CB[7]•2, 6-Ad(NMe3)2 are less effective at realizing the potential 1000-fold enhancement in affinity due to ion dipole interactions at the second ureidyl C=O portal. Comparative crystallographic investigation of CB[7]•Diam(NMe3)2, B[7]•DiamNMe3, and CB[7]•1-AdNMe3 reveals that the preferred geometry positions the +NMe3-groups ≈ 0.32 Å above the C=O portal ; the observed 0.80Å spacing observed for CB[7]•Diam(NMe3)2 reflects the simultaneous geometrical constraints of CH2•••O=C close contacts at both portals. Remarkably, the CB[8]•IsoDiam(NHMe2)2 complex displays femtomolar binding affinity placing it firmly alongside the CB[7]•Diam(NMe3)2 complex. Primary or quaternary ammonium ion looping strategies lead to larger increases in binding affinity for CB[8] than for CB[7] which we attribute to the larger size of the carbonyl portals of CB[8] which suggests routes to develop CB[8] as the tightest binding host in the CB[n] family. We report that alkyl group fluorination (e.g. CB[7]•1-AdNH2Et versus CB[7]•1-AdNH2CH2CF3) does not result in the expected increase in Ka value. Finally, we have discussed the role of solvation in non-empirical quantum mechanical computational methodology which is used to estimate the relative changes in Gibbs binding free energies.

Item Type: Article
Additional Information: We thank the National Science Foundation (CHE-1404911 to L.I.), the Croatian Ministry of Science, Education, and Sports (grant 098-0982933-2911 to K.M.-M.), the Croatian Academy of Sciences and Arts (K.M.-M. and M.S.), and the Ben-Gurion Univ. Scientific Relations Research Fund (R.G.) for financial support. This work was also supported by research project RVO 61388963 awarded to the Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, the Czech Science Foundation (grant number P208/12/G016) and by project L01305 of the Ministry of Education, Youth and Sports of the Czech Republic.
Uncontrolled Keywords: diamondoids ; ammonium salts ; cucurbit[n]urils ; high affinity host-guest pairs ; X-ray diffraction
Subjects: NATURAL SCIENCES > Chemistry
NATURAL SCIENCES > Chemistry > Organic Chemistry
Divisions: Division of Organic Chemistry and Biochemistry
Project titleProject leaderProject codeProject type
Kavezasti spojevi: ugradbene jedinice u molekularnim sustavima-Kata Majerski098-0982933-2911MZOS
Depositing User: Marina Šekutor
Date Deposited: 27 Nov 2018 14:58
DOI: 10.1021/jacs.7b00056

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