Synthesis and Characterization of Polyamine Bicycles for Anion Binding
Morehouse, Paula Kay
University of Kansas
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Abstract This thesis details the interaction between anions, such as Br-, Cl-, and F- and a group of familiar Schiff base derived azacryptands. Often these systems are synthesized by tosylating i.e., protecting, the bridging amine sites to prevent them from undesirable interactions. Only after detosylation to retrieve the secondary amines are the anion binding properties investigated. Through our research, we have discovered that when protected (tosylated), the m-xylyl azacryptand [1,4,12,15,18,26,31,39-octaazapentacyclo [184.108.40.206.6,101.20,241.33,37] tetratetraconta-6, 7,9,20(43), 21,23,33(42),34,36-nonaene], N(CH2CH2NHCH2-m-xylyl-CH2NHCH2CH2)3N), 12, is readily capable of being protonated at the bridgehead amines. As a result it is also capable of binding anions. Results from these studies are presented, including the binding of the Brˉ ion, and the crystallographic findings for both the bromide and neutral tosylated azacryptand receptor. Two species were isolated: the neutral cryptand and the dibromide salt. Binding studies and crystal structures are discussed within. Structural aspects of the binding of halides in the p-xylyl octaaza cryptand [1,4,11,14,17,24,29,36-octa-azapentacyclo [220.127.116.11,9.219,22.231,34]-tetratetraconta-6 (43), 7,9(44), 19(41), 20,22(42), 31(39), 32,34(40)-nonaene], N(CH2CH2NHCH2-p-xylyl-CH2NHCH2CH23N), 13, were examined. Crystallographic results for two different Fˉ ion complexes indicated cascade-like coordination, with two F- ions inside the tren-based cavity, bridged by a H2O molecule. In two different Cl- structures, a single Cl- ion and a H2O molecule occupied the cavity. Association constants for the anions, determined by NMR titrations in aqueous solution at pH 5, revealed Log K = 3.15(5) and 3.37(3) for F- and Cl-, respectively. Aspects of the binding of halides, the HSO4- ion, and the SO42- ion in the pyridine-based octaaza cryptand [1,4,12,15,18,26,31,39,42,23,44-undecaaza-pentacyclo- [18.104.22.168,10.120,24.233,37]-tetratetraconta-6,7,9,20(43),21,23,33(42),3436-nonaene], N(CH2CH2NHCH2-pyridine-CH2NHCH2CH2)3N), 14, were examined. Crystallographic results for the Br- ion complex indicated cleft binding, with three internal bromides and three external Br- ions. Association constants for the anions determined by NMR titrations in aqueous solution at pH 3.0 (pH 4.0 for F-), revealed Log K = 3.6 (F-), 1.7 (Cl-), 1.0 (Br-), and less than 1.0 (I-). A 1:2 ligand-to-anion binding mode was observed for the SO42- ion, with respective binding constants of log 4.6 and 2.6. Titrations performed in DMSO-d6 determined the binding constant with HSO4- to be log 3.2. Various methods were used to analyze the ligands and to measure ligand-anion interactions, including mass spectroscopy, 1H NMR, 13C NMR, X-ray crystallography, and elemental analysis.
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