Abstract
We report the molecular recognition of the Au(CN)2- anion, a crucial intermediate in today's gold mining industry, by α-cyclodextrin. Three X-ray single-crystal superstructures - KAu(CN)2α-cyclodextrin, KAu(CN)2(α-cyclodextrin)2, and KAg(CN)2(α-cyclodextrin)2 - demonstrate that the binding cavity of α-cyclodextrin is a good fit for metal-coordination complexes, such as Au(CN)2- and Ag(CN)2- with linear geometries, while the K+ ions fulfill the role of linking α-cyclodextrin tori together as a result of [K+···O] ion-dipole interactions. A 1:1 binding stoichiometry between Au(CN)2- and α-cyclodextrin in aqueous solution, revealed by 1H NMR titrations, has produced binding constants in the order of 104 M-1. Isothermal calorimetry titrations indicate that this molecular recognition is driven by a favorable enthalpy change overcoming a small entropic penalty. The adduct formation of KAu(CN)2α-cyclodextrin in aqueous solution is sustained by multiple [C-H···π] and [C-H···anion] interactions in addition to hydrophobic effects. The molecular recognition has also been investigated by DFT calculations, which suggest that the 2:1 binding stoichiometry between α-cyclodextrin and Au(CN)2- is favored in the presence of ethanol. We have demonstrated that this molecular recognition process between α-cyclodextrin and KAu(CN)2 can be applied to the stripping of gold from the surface of activated carbon at room temperature. Moreover, this stripping process is selective for Au(CN)2- in the presence of Ag(CN)2-, which has a lower binding affinity toward α-cyclodextrin. This molecular recognition process could, in principle, be integrated into commercial gold-mining protocols and lead to significantly reduced costs, energy consumption, and environmental impact.
Original language | English (US) |
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Pages (from-to) | 1984-1992 |
Number of pages | 9 |
Journal | Journal of the American Chemical Society |
Volume | 143 |
Issue number | 4 |
DOIs | |
State | Published - Feb 3 2021 |
ASJC Scopus subject areas
- Chemistry(all)
- Biochemistry
- Catalysis
- Colloid and Surface Chemistry
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CCDC 2040418: Experimental Crystal Structure Determination
Liu, W. (Contributor), Jones, L. O. (Contributor), Wu, H. (Contributor), Stern, C. L. (Contributor), Sponenburg, R. A. (Contributor), Schatz, G. C. (Contributor) & Stoddart, J. F. (Contributor), Cambridge Crystallographic Data Centre, 2021
DOI: 10.5517/ccdc.csd.cc26h6yw, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/ccdc.csd.cc26h6yw&sid=DataCite
Dataset
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CCDC 2040417: Experimental Crystal Structure Determination
Liu, W. (Contributor), Jones, L. O. (Contributor), Wu, H. (Contributor), Stern, C. L. (Contributor), Sponenburg, R. A. (Contributor), Schatz, G. C. (Contributor) & Stoddart, J. F. (Contributor), Cambridge Crystallographic Data Centre, 2021
DOI: 10.5517/ccdc.csd.cc26h6xv, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/ccdc.csd.cc26h6xv&sid=DataCite
Dataset
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CCDC 2040419: Experimental Crystal Structure Determination
Liu, W. (Contributor), Jones, L. O. (Contributor), Wu, H. (Contributor), Stern, C. L. (Contributor), Sponenburg, R. A. (Contributor), Schatz, G. C. (Contributor) & Stoddart, J. F. (Contributor), Cambridge Crystallographic Data Centre, 2021
DOI: 10.5517/ccdc.csd.cc26h6zx, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/ccdc.csd.cc26h6zx&sid=DataCite
Dataset