Ethylene oxide-bridged bipyridine oligomers that function as selective host molecules for the encapsulation of small alkali cation guests |
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Authors: | Marc Harris Kenneth Houser Johanna Scarino Scott Wallace Brandon Arndt Amy Smith Gary Romberger Allix Sanders |
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Institution: | (1) Department of Chemistry, Lebanon Valley College, 101 N. College Ave., Annville, PA 17003, USA |
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Abstract: | Two novel ethylene oxide-bridged bipyridine oligomers were synthesized that contain host pockets with four (1) or six (2) oxygen donor atoms and a pyridyl nitrogen donor. The alkali picrate extracting ability and selectivity of these free ligands
was investigated using a liquid–liquid dichloromethane–water extraction study. Both open-chain oligomer frameworks display
unexpectedly high extraction efficiency (EE) values for specific guest ions (EE = 57% Na+ extracted by 1, and EE = 39% Cs+ extracted by 2). These extraction values are comparable to macrocyclic analogues and their ion selectivities follow the ‘same-fit’ concept
that has been extensively reported for fixed pocket systems. The shorter chain oligomer (1) binds ions in the series (Na+ > K+ > Cs+), while the larger oligomer (2) binds ions in the reverse order (Cs+ > K+ > Na+). Formation of the host–guest ligand–ion complexes were verified by 1H NMR spectroscopy and MALDI-TOF mass spectrometry experiments. A Job’s plot analysis based on UV spectral data also supported
the 1:1 (oligomer to ion) complexation observed in the MALDI mass spectra. |
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Keywords: | Alkali picrate Binding selectivity Bipyridine oligomers Ethylene oxide pocket Extraction efficiency (EE) Host– guest Inclusion complex Open-chain ‘ same-fit’ concept |
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