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Mass spectrometric study of oligourea macrocycles and their anion binding behavior
Authors:Tobias Becherer  Denys Meshcheryakov  Andreas Springer  Volker Böhmer  Christoph A Schalley
Institution:1. Institut für Chemie und Biochemie der Freien Universit?t, 14195 Berlin, Germany;2. Fachbereich Chemie, Pharmazie und Geowissenschaften, Abteilung Lehramt Chemie, Johannes Gutenberg Universit?t, Duesbergweg 10‐14, 55099 Mainz, Germany
Abstract:Two series, one of tris‐urea macrocycles and another of hexakis‐urea macrocycles, are examined by (tandem) Fourier‐transform ion cyclotron resonance (FTICR) mass spectrometry with respect to their fragmentation patterns and anion binding properties. All macrocycles are based on two different building blocks, one of which is a very rigid xanthene unit and the other one is a more flexible diphenyl ether. The composition and the sequence of these units thus determine their flexibility. During the fragmentation of deprotonated oligourea macrocycles in the gas phase, one urea N? CO bond is cleaved followed by a scrambling reaction within the macrocycle structure. Consequently, fragments are observed that deviate from those that would be expected from the sequence of the subunits. Interesting anion binding properties involve the simultaneous recognition of two chloride anions by one of the hexakis‐urea macrocycles, whose flexibility allows this host to form a double‐helical structure. Flexibility also determines which of the hexameric receptors bears a high sulfate affinity. The interaction energy between some of the macrocycles and sulfate is high enough to even stabilize the intrinsically unstable sulfate dianion. Copyright © 2009 John Wiley & Sons, Ltd.
Keywords:supramolecular chemistry  hydrogen bonding  anion recognition  urea compounds  macrocycles  gas‐phase chemistry  H/D exchange
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