TY - JOUR
T1 - Supramolecular Gold Stripping from Activated Carbon Using α-Cyclodextrin
AU - Liu, Wenqi
AU - Jones, Leighton O.
AU - Wu, Huang
AU - Stern, Charlotte L.
AU - Sponenburg, Rebecca A.
AU - Schatz, George C.
AU - Stoddart, J. Fraser
N1 - Funding Information:
We thank Professor Brad Smith at the University of Notre Dame for discussions on receptors for dicyanoaurate, which was the source of the inspiration for this work. We thank Professor Martín Mosquera at Montana State University for help with DFT calculations. We thank Northwestern University (NU) for their support of this research. This research work was also funded by the Center for Sustainable Separations of Metals (CSSM), a National Science Foundation (NSF) Center for Chemical Innovation (CCI), Grant CHE-1925708. This research was supported in part by the computational resources and staff contributions provided for the Quest High Performance Computing Facility at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. This work made use of the Integrated Molecular Structure Education and Research Center (IMSERC) NMR facility at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633) and Northwestern University. Metal analysis was performed at the Northwestern University Quantitative Bio-Element Imaging Center, generously supported by NASA Ames Research Center Grants NNA04CC36G and NNA06CB93G.
Publisher Copyright:
© 2020 American Chemical Society.
PY - 2021/2/3
Y1 - 2021/2/3
N2 - 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.
AB - 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.
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U2 - 10.1021/jacs.0c11769
DO - 10.1021/jacs.0c11769
M3 - Article
C2 - 33378203
AN - SCOPUS:85100082007
VL - 143
SP - 1984
EP - 1992
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 4
ER -