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Selective isolation of Gold facilitated by second sphere coordination with a cyclodextrin

Selective isolation of Gold facilitated by second sphere coordination with a cyclodextrin the interaction of human beings with Gold is an activity that has been ongoing since ancient times as a result of this precious metal’s unique physical and chemical properties. As the price of Gold has skyrocketed during the past decade, a significant economic incentive exists for its recovery1, not only from ores, but also from the waste products of consumer electronics. | nature v COMMUNICATIONS ARTICLE Received 9 Jan 2013 Accepted 18 Apr 2013 Published 14 May 2013 DOI 10.1038 ncomms2891 OPEN Selective isolation of gold facilitated by second-sphere coordination with a-cyclodextrin 7 1 I I 1 ft 4 I- 1 I I 1 -7 1 I 1 -7 1 -71 1 l f- 111 I I 1 Zhichang Liu1 Marco Frasconi Juying Lei1 Zachary J. Brown1 Zhixue Zhu1 Dennis Cao1 Julien Iehl1 Guoliang Liu1 Albert C. Fahrenbach1 Youssry Y. Botros2 3 4 Omar K. Farha1 Joseph T. Hupp1 Chad A. Mirkin1 J. Fraser Stoddart1 Gold recovery using environmentally benign chemistry is imperative from an environmental perspective. Here we report the spontaneous assembly of a one-dimensional supramolecular complex with an extended K OH2 6 AuBr4 C a-cyclodextrin 2 n chain superstructure formed during the rapid co-precipitation of a-cyclodextrin and KAuBr4 in water. This phase change is selective for this gold salt even in the presence of other square-planar palladium and platinum complexes. From single-crystal X-ray analyses of six inclusion complexes between a- P- and g-cyclodextrins with KAuBr4 and KAuCl4 we hypothesize that a perfect match in molecular recognition between a-cyclodextrin and AuBr4 leads to a near-axial orientation of the ion with respect to the a-cyclodextrin channel which facilitates a highly specific second-sphere coordination involving AuBr4 and K OH2 6 and drives the co-precipitation of the 1 2 adduct. This discovery heralds a green host-guest procedure for gold recovery from gold-bearing raw materials making use of a-cyclodextrin an inexpensive and environmentally benign carbohydrate. 1 Department of Chemistry Northwestern University 2145 Sheridan Road Evanston Illinois 60208-3113 USA. 2 Department of Materials Science and Engineering Northwestern University 2145 Sheridan Road Evanston Illinois 60208-3113 USA. 3 Intel Labs Building RNB-6-61 2200 Mission College Boulevard Santa Clara California 95054-1549 USA. 4 National Center for Nanotechnology Research King Abdulaziz City for .