Browsing by Subject "Calix[4]arene"
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Item Calix[4]pyrrole-based ion pair receptors(2011-08) Kim, Sung Kuk; Sessler, Jonathan L.; Bielawski, Christopher W.; Siegel, Dionicio R.; Humphrey, Simon M.; Kerwin, Sean M.; Anslyn, Eric V.Compared with simple ion receptors, ion pair receptors display significantly enhanced affinity to ions through allosteric effects and additional electrostatic interactions between the bound ions, as well as host-guest interactions. Taken in concert, these necessarily permit a higher level of control over ion recognition and transport than that obtainable from simple ion binding. However, in spite of their potential applications in various fields, such as salt solublization, extraction, and membrane transport, ion pair receptors, which are able to form simultaneous complexation with an anion and a cation, still remains in a relatively unexplored area in supramolecular chemistry. This dissertation describes efforts to develop such systems on the basis of calix[4]arenes and calix[4]pyrroles. Calix[4]pyrroles and calix[4]arene derivatives bearing crown ethers or ester groups are known to act as efficient receptors for anions and cations, respectively. Therefore, the synthetic combination or modification of these two macrocyclic subunits provides an entry into novel ion pair receptors. The focus of this dissertation is on matched systems that form strong and specific complexes with cesium or potassium salts, depending on the exact structure in question. The selectivity demonstrated by these receptors is ascribed to a tuning of the cation recognition sites and control of the calix[4]arene conformation. Solid state structural and 1H NMR spectroscopic analyses reveal that potassium and cesium cations are bound to different sites within these ion pair receptors. A strong dependence on the counter anion (e.g., fluoride, chloride and nitrate) is also seen. In some cases this dependence is near-absolute, thus mimicking AND logic gates. Noticeably, the ion pair receptor consisting of a 1,3-alterate calix[4]arene crown-5 and a calix[4]pyrrole is able to extract various cesium and potassium salts from a water phase into an organic phase in various binding modes, depending on the counter anions. Furthermore, the extraction behavior of this ion pair receptor towards such ion pairs can be controlled by cation switching and the use of different solvents.Item Synthesis of new proton-ionizable lariat ethers and calix[4]arene ligands for separation of metal cations(Texas Tech University, 2006-05) Liu, Xiaodong; Bartsch, Richard A.; Birney, David M.; Li, GuigenA series of novel proton-ionizable dibenzo-22-crown-7 lariat ethers, i.e. sym-(alkyl)dibenzo-22-crown-7-oxyacetic acids, 3-[sym-(alkyl) dibenzo-22-crown-7-oxy]-propanesulfonates, N-trifluoromethanesulfonyl sym-(alkyl)dibenzo-22-crown-7-oxyacetamides and monoethyl sym-[(alkyl)dibenzo-22-crown-7-oxy]-methylphosphonic acids, have been synthesized as part of the systematic investigation of the effect of structural features on the metal cation complexation and selectivity. Also, several series of novel di-ionizable calix[4]arene, i.e. di-ionizable p-tetraallylcalix[4]arene ligands, di-ionizable p-diallylcalix[4]arene ligands, cone di-ionizable p-tert-butylcalix[4]arene-crown-4 ligands, 1,3-alternate di-ionizable p-tert-butyl-calix[4]arene-crown-4 ligands, cone di-ionizable p-tert-butylcalix[4]arene-benzocrown-4 ligands and 1,3-alternate di-ionizable p-tert-butyl-calix[4]arene-benzocrown-4 ligands, have been prepared in an effort to investigate the effect of subtituents, crown size and conformations on metal cation complexation and selectivity.Item Synthesis of Novel Calix[4]arene-Based Ligands for Selective Metal Cation Extraction(Texas Tech University, 2009-08) Yang, Yanfei; Bartsch, Richard A.; Birney, David M.; Li, GuigenThe synthesis of ligands with superior binding efficiency and selectivity toward targeted metal cations is an important area of scientific endeavor. Calix[4]arene-based ligands with interesting properties in binding with various metal cation species have been prepared during the past 20 years. This dissertation research presents the design and synthesis of a variety of novel calix[4]arene-based ligands. To evaluate the metal cation binding behavior of these ligands, solvent extraction was employed for proton-ionizable ligands and an ion-selective electrode (ISE) method for non-ionizable analogues. Proton di-ionizable calix[4]arene-crown-4 ligands in three conformations were synthesized. This is part of continuing research for construction of a comprehensive library of calix[4]arene-crown ethers for various metal cations. The N-(X)sulfonyl carboxamide groups with tunable acidity are employed as novel proton-ionizable groups. By varying X from methyl to trifluoromethyl, a wide pH window was created for the ligands. Spatial arrangement of donor atoms in the macrocyclic ligands was shown to be an important factor that influences metal cation binding properties and selectivities of ligands. To further explore the impact of this factor on calix[4]arene-crown ether ligands, a series of calix[4]arene-crown-4 compounds in the cone conformation with an expanded crown ether ring was synthesized. In solvent extraction, the calix[4]arene-crown-4 ligands with an expanded crown ether ring were found to be better extractants for some heavy metal cations compared to the conventional calix[4]arene-crown-4 analogues. Design and evaluation of ionophores that can selectively bind with heavy metal cations, such as Pb2+ and Hg2+, have important potential applications. According to the soft nature of these metal cations, they are rather thiophilic than oxophilic. A relatively simple approach for enhancing ligand/metal cation interaction is the incorporation of soft donor atoms in the ligand. Compared to thiacalixarene and mercaptocalixarene, less effort has been paid to the design and synthesis of calix[4]arene-crown ethers with thiacrown fragments. A series of di-ionizable p-tert- butylcalix[4]arene-monothiacrown-5 ligands is synthesized and examined by solvent extraction. The ligands were good extractants for Hg2+ and Pb2+. Binding with these soft metal cations is accomplished in a very acidic environment. Some miscellaneous di-ionizable calix[4]arene-based ligands also are prepared. These ligands include di-ionizable calix[4]arene-1,2-crown-5 with elongated proton-ionizable groups and the upper-rim functionalized calix[4]arene-crown-5 ligands. Calix[4]arene-1,2-crowns are less studied compared to 1,3-crown analogues due to their relatively poor metal cation binding behavior. However, some 1,2-crown analogues synthesized recently in the Bartsch Research Group exhibited very good metal cation binding properties and selectivities. The study of 1,2-crowns that incorporated elongated proton-ionizable groups allows us to enhance our understanding of calix[4]arene-1,2-crowns. Some di-ionizable calix[4]arene-crown-5 compounds with proton-ionizable groups on the upper rim are also prepared. The aromatic region of calix[4]arenes could behave as a potential binding site for some soft cations. The modified upper rim has proton-ionizable groups closely located to this potential binding site and possibly an enhanced binding with these soft metal cations could be observed. Finally, some di-benzyl calix[4]arene-dithiacrowns with various crown ether ring sizes, conformations, and para-substituents were synthesized. The increment number of sulfur donor atoms in the crown ether fragment was proposed to improve the ligand binding behavior with heavy metal cations. The binding behaviors of these ligands were evaluated by ion selective electrodes (ISEs). This is the first systematic study of the metal cation binding properties of the calix[4]arene-dithiacrown ligands by this method.