{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,19]],"date-time":"2026-08-19T15:26:30Z","timestamp":1787153190537,"version":"build-2736575974"},"reference-count":82,"publisher":"American Chemical Society (ACS)","issue":"32","license":[{"start":{"date-parts":[[2026,8,5]],"date-time":"2026-08-05T00:00:00Z","timestamp":1785888000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001691","name":"KAKENHI","doi-asserted-by":"crossref","award":["JP21H04674"],"award-info":[{"award-number":["JP21H04674"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100001691","name":"KAKENHI","doi-asserted-by":"crossref","award":["JP25K01726"],"award-info":[{"award-number":["JP25K01726"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"crossref"}]},{"name":"Cooperative Research Program of the ?Network Joint Research Center for Materials and Devices?, MEXT, Japan"},{"name":"Research Center for Computational Science, Okazaki, Japan"},{"name":"Core-to-Core program, Japan Society for the Promotion of Science","award":["JPJSCCA20240002"],"award-info":[{"award-number":["JPJSCCA20240002"]}]},{"name":"World Research Hub Initiative (WRHI), Tokyo Institute of Technology"},{"name":"Kurita Water and Environmental Foundation"},{"name":"Precise Measurement Technology Promotion Foundation (PMTP-F)"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026,8,19]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>Crown ethers exhibit pronounced ion selectivity and have long provided an excellent platform in supramolecular chemistry. This selectivity has been rationalized by a match between the ionic radius and the nominal cavity size of the crown ether, largely driven by the success of the K+18-crown-6 system. However, this concept omits the role of conformational flexibility of the crown ethers and fails to directly connect binding structures with ion selectivity. To gain molecular-level insight into the intrinsic binding structures of crown ethers with alkali metal ions, we present a systematic study of crown ethers with varying ring sizes using cryogenic gas-phase infrared spectroscopy in conjunction with anharmonic analysis of the CH stretch region. The CH stretch region serves as a sensitive probe of ion-binding structures and interactions, enabling definitive structural assignments of Li+\u2013Cs+ complexes across different crown ethers. Our results reveal that the intrinsic binding structures vary systematically with both ionic radius and crown ring size. It appears that successful selectivity for a specific ion-crown ether system depends on two factors: the ability of the crown ether to encapsulate the ion, and having a configuration where the ion is equidistant from the oxygen atoms within a plane formed by the etheric oxygens. While encapsulation of Li+, Na+ and K+ is achieved by 18-crown-6, only K+18-crown-6 has the oxygen distances uniformly positioned about this plane, resulting in truly selective encapsulation. For 12-crown-4 and 15-crown-5, the most favorable structures, involving Li+ and Na+, respectively, are unable to achieve selective encapsulation, as the ions are positioned at varying distances with respect to the plane of the etheric oxygens. These distinctions can be traced to the differing conformational flexibility of the crown ethers.<\/jats:p>","DOI":"10.1021\/jacs.6c05693","type":"journal-article","created":{"date-parts":[[2026,8,5]],"date-time":"2026-08-05T12:02:33Z","timestamp":1785931353000},"page":"34209-34218","source":"Crossref","is-referenced-by-count":0,"title":["Spectroscopic Tracking\nof Size Selectivity in Crown\nEthers: A Unified Molecular Picture of Encapsulation"],"prefix":"10.1021","volume":"148","author":[{"given":"Ryu","family":"Sakuma","sequence":"first","affiliation":[{"name":"Institute of Science Tokyo , , 2-12-1 Ookayama , , ,","place":["Meguro-Ku, Tokyo, Japan, 152-8550"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Keisuke","family":"Hirata","sequence":"additional","affiliation":[{"name":"Institute of Science Tokyo , , 2-12-1 Ookayama , , ,","place":["Meguro-Ku, Tokyo, Japan, 152-8550"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9894-9163","authenticated-orcid":true,"given":"James M.","family":"Lisy","sequence":"additional","affiliation":[{"name":"Institute of Science Tokyo , , Nagatsuta-cho , Midori-Ku, ,","place":["Yokohama, Japan, 226-8503"]},{"name":"University of Illinois at Urbana\u2212Champaign , , , ,","place":["Urbana, Illinois, United States, 61801"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4858-4618","authenticated-orcid":true,"given":"Masaaki","family":"Fujii","sequence":"additional","affiliation":[{"name":"Institute of Science Tokyo , , 4259 Nagatsuta-cho , Midori-Ku, ,","place":["Yokohama, Japan, 226-8503"]},{"name":"Chuo University , , 1-13-27 Kasuga , , ,","place":["Bunkyo-ku, Tokyo, Japan, 112-8551"]},{"name":"Institute of Science Tokyo , , Nagatsuta-cho , Midori-Ku, ,","place":["Yokohama, Japan, 226-8503"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shun-Ichi","family":"Ishiuchi","sequence":"additional","affiliation":[{"name":"Institute of Science Tokyo , , 2-12-1 Ookayama , , ,","place":["Meguro-Ku, Tokyo, Japan, 152-8550"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"316","published-online":{"date-parts":[[2026,8,5]]},"reference":[{"key":"2026081910205680100_cit1","doi-asserted-by":"publisher","first-page":"2781","DOI":"10.1021\/ar4000136","article-title":"Ion Transport through Lipid Bilayers by Synthetic Ionophores:\nModulation of Activity and Selectivity","volume":"46","author":"De Riccardis","year":"2013","journal-title":"Acc.\nChem. 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Chem."},{"key":"2026081910205680100_cit32","doi-asserted-by":"publisher","first-page":"5080","DOI":"10.1021\/jacs.4c15074","article-title":"Conformationally\nAdaptable Extractant\nFlexes Strong Lanthanide Reverse-Size Selectivity","volume":"147","author":"Islam","year":"2025","journal-title":"J. Am. Chem. Soc."},{"key":"2026081910205680100_cit33","doi-asserted-by":"publisher","first-page":"5736","DOI":"10.1021\/ja00066a045","article-title":"Macrocyclic Chemistry in the Gas\nPhase: Intrinsic Cation Affinities and Complexation Rates for Alkali\nMetal Cation Complexes of Crown Ethers and Glymes","volume":"115","author":"Chu","year":"1993","journal-title":"J. Am. Chem. 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Solution Chem."},{"key":"2026081910205680100_cit38","doi-asserted-by":"publisher","first-page":"475","DOI":"10.1021\/ja00522a005","article-title":"A Systematic\nStudy of the Effect of Macrocycle Ring Size and Donor Atom Type on\nthe Log K, \u0394H, and T\u0394S of Reactions at 25 \u00b0C in Methanol\nof Mono- and Divalent Cations with Crown Ethers","volume":"102","author":"Lamb","year":"1980","journal-title":"J. Am. Chem. Soc."},{"key":"2026081910205680100_cit39","doi-asserted-by":"publisher","first-page":"627","DOI":"10.1246\/bcsj.61.627","article-title":"A Conductance Study\nof 1: 1 Complexes of 15-Crown-5, 16-Crown-5, and Benzo-15-crown-5\nwith Alkali Metal Ions in Nonaqueous Solvents","volume":"61","author":"Takeda","year":"1988","journal-title":"Bull. Chem. Soc. Jpn."},{"key":"2026081910205680100_cit40","doi-asserted-by":"publisher","first-page":"277","DOI":"10.1007\/BF00646180","article-title":"The Influence\nof Acetonitrile on Complex Formation of Crown Ethers Containing Different\nDonor Atoms","volume":"17","author":"Buschmann","year":"1988","journal-title":"J. Solution Chem."},{"key":"2026081910205680100_cit41","doi-asserted-by":"publisher","first-page":"4375","DOI":"10.1039\/ft9959104375","article-title":"Thermodynamics of Complexation of\nSodium, Potassium, Rubidium, Caesium and Ammonium Ions with 18-Crown-6\nin Acetonitrile and Propylene Carbonate","volume":"91","author":"Ohtsu","year":"1995","journal-title":"J.\nChem. Soc., Faraday Trans."},{"key":"2026081910205680100_cit42","doi-asserted-by":"publisher","first-page":"4858","DOI":"10.1021\/acs.jpcb.3c01875","article-title":"Alkali Metal Ion Recognition\nby 18-Crown-6 in Aqueous Solutions: Evidence from Local Structures","volume":"127","author":"Jing","year":"2023","journal-title":"J. Phys. Chem. B"},{"key":"2026081910205680100_cit43","doi-asserted-by":"publisher","first-page":"6954","DOI":"10.1021\/ja00131a018","article-title":"Mechanism\nand Thermodynamics of Ion Selectivity in Aqueous Solutions of 18-Crown-6\nEther: A Molecular Dynamics Study","volume":"117","author":"Dang","year":"1995","journal-title":"J. Am. Chem.\nSoc."},{"issue":"18","key":"2026081910205680100_cit44","doi-asserted-by":"publisher","first-page":"5076","DOI":"10.1021\/j100329a004","article-title":"Molecular Dynamics\nof 18-Crown-6 Complexes with Alkali-Metal Cations: Calculation of\nRelative Free Energies of Complexation","volume":"92","author":"Van Eerden","year":"1988","journal-title":"J. Phys.\nChem."},{"issue":"1","key":"2026081910205680100_cit45","doi-asserted-by":"publisher","first-page":"84","DOI":"10.1186\/1752-153X-6-84","article-title":"Binding Selectivity of Dibenzo-18-crown-6 for Alkali\nMetal Cations in Aqueous Solution: A Density Functional Theory Study\nUsing a Continuum Solvation Model","volume":"6","author":"Choi","year":"2012","journal-title":"Chem. Cent.\nJ."},{"key":"2026081910205680100_cit46","doi-asserted-by":"publisher","first-page":"12797","DOI":"10.1021\/acs.jpcb.1c07902","article-title":"Cationic Effects on\nthe Structural Dynamics of the\nMetal Ion\u2013Crown Ether Complexes Investigated by Ultrafast Infrared\nSpectroscopy","volume":"125","author":"Zhou","year":"2021","journal-title":"J. Phys. Chem. B"},{"key":"2026081910205680100_cit47","doi-asserted-by":"publisher","first-page":"9154","DOI":"10.1021\/acs.jpcb.0c07032","article-title":"Specific Host\u2013Guest\nInteractions in the Crown Ether Complexes with K+ and NH4+ Revealed from the Vibrational Relaxation Dynamics\nof the Counteranion","volume":"124","author":"Zhou","year":"2020","journal-title":"J. Phys. Chem. B"},{"key":"2026081910205680100_cit48","doi-asserted-by":"publisher","first-page":"10159","DOI":"10.1021\/ja00145a046","article-title":"Gas Phase Conformations\nof Li+, Na+, K+, and Cs+ Complexed with 18-Crown-6","volume":"117","author":"Lee","year":"1995","journal-title":"J. Am. Chem. Soc."},{"key":"2026081910205680100_cit49","doi-asserted-by":"publisher","first-page":"227","DOI":"10.1016\/S1387-3806(99)00165-7","article-title":"Cation-ether\ncomplexes in the gas phase: Thermodynamic insight into molecular recognition","volume":"193","author":"Armentrout","year":"1999","journal-title":"Int. J. Mass Spectrom."},{"key":"2026081910205680100_cit50","doi-asserted-by":"publisher","first-page":"417","DOI":"10.1021\/ja9823159","article-title":"Intrinsic\naffinities of alkali cations\nfor 15-crown-5 and 18-crown-6: Bond dissociation energies of gas-phase\nM+-crown ether complexes","volume":"121","author":"More","year":"1999","journal-title":"J. Am.\nChem. Soc."},{"key":"2026081910205680100_cit51","doi-asserted-by":"publisher","first-page":"10657","DOI":"10.1021\/ja00102a035","article-title":"An ab Initio Investigation of the\nStructure and Alkali Metal Cation Selectivity of 18-Crown-6","volume":"116","author":"Glendening","year":"1994","journal-title":"J. Am. Chem. Soc."},{"key":"2026081910205680100_cit52","doi-asserted-by":"publisher","first-page":"2723","DOI":"10.1021\/jp9700185","article-title":"Ab initio\nstudy of M+: 18-crown-6 microsolvation","volume":"101","author":"Feller","year":"1997","journal-title":"J. Phys. Chem. 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