Calixarene chemistry en route to nano-fabrication of phosphonated analogues

Thomas Clark

Research output: ThesisDoctoral Thesis

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Abstract

[Truncated abstract] An efficient synthesis of the p-phosphonic acid calix[n]arenes, (n = 4, 5, 6 and 8) in five steps and excellent yield has been developed. This includes the key use of an acetyl protecting group, which is straightforward to introduce and remove using acetic anhydride and potassium hydroxide respectively. The synthesized p-phosphonic acid calixarenes are water-soluble and the hydrogen bonding prowess of the acidic groups dominates its selfassembly processes. For p-phosphonic acid calix[4]arene these include the formation of nano-rafts in the gas phase (≤ 20 molecules) and nano-particles (3.0(3) and 20.0(2) nm) of the calixarene in water using spinning disc processing stabilized by acetonitrile. The larger p-phosphonic acid calix[5,6,8]arenes also show nano-raft formation in both solution and the gas phase. An extensive study of the supramolecular chemistry of calix[5]arene has also been undertaken to better understand its rich structural diversity. This includes the formation of chloromethane inclusion complexes of p-tert-butyl-calix[5]arene and p-H-calix[5]arene with dichloromethane, p-phenyl-calix[5]arene with chloroform and their potential application as gas storage materials. Along with these three investigated inclusion complexes are two sublimates of p-H-calix[5]arene (α and β) with only the β-polymorph active for sorption of carbon dioxide at room temperature and 1 atm. The α-polymorph adopts an inverted cone conformation and forms helical stacks in the extended structure whereas the β-polymorph adopts the usual cone conformation and packs in both 'self included' and 'back-to-back' helical arrangements. ... Complementary to this study involved the p-H-calix[5]arene inclusion complexes with fluoro-, chloro-, bromo- and iodobenzene. All but the iodobenzene complexes are isostructural forming columnar arrays in the extended packing comprised of 'tri-calix[5]arene' segments. Iodobenzene is too large to form the respective 'tri-calix[5]arene' segments and instead forms sheets in the extended packing. To better understand the type and nature of the intermolecular interactions present within the supermolecules and extended structures a detailed Hirshfeld surface analysis was performed. A detailed Hirshfeld surface analysis was also performed on O-octadecyl-calix[6]arene, which crystallizes in the inverted double cone conformation. Three alkyl chains on either side interplay to form one side of hexagon in an hexagonal close packed array of interdigitated alkyl chains. This was the first Hirshfeld surface analysis performed at variable temperatures and enhanced the description of such a large supramolecular system. The related compound O-octadecyl-calix[4]arene was found to crystallize from toluene or benzene as supramolecular bilayers, 32.2(4) and 32.7(2) Å thick respectively. The calixarenes adopt the cone conformation and the alkyl chains interplay to form a continuous hexagonal motif similar to that seen for O-octadecyl-calix[6]arene. The formation of stable bilayers using octadecyl chains leads to the possibility of inserting long chain calixarenes with suitable functionalization into biological membranes. Such functionalization could include upper rim phosphorylation as seen for the p-phosphonic acid calixarenes to produce phospholipid mimics.
Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2007

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