Jack M. Harrowfield

Calixarenes in the nanoworld

Introductory chapter.- Calixdendrimers.- Molecular tubes derived of calixarenes.- Catenated calixarenes.- Capsules and catenands.- Calixarenes as Cluster Keepers.- Calixarenes and C60.- Calixarene-Based Nanoporous Supramolecular Architectures.- Calixarenes on molecular printboards: multivalent binding, surface patterning, and capsule formation.- Calixarene-based Supramolecular Materials for Sensing and Fixation of Gases.- Enzyme models.- Supramolecular and Biomimetic Properties of Peptido- and Glycocalixarenes.- Fluorescent calixarene-based sensors.- Nanoprotein sensing.- Pharmaceutical applications of calixarenes.

Calixarenes as Polyhapto-aromatic Ligands: Alkali Metal Ions and Sulfonated Calixarenes

Crystal structure determinations for the hexarubidium and octacesium derivatives of calix[6]arene hexasulfonic acid, as well as of a new solvate of the pentasodium derivative of calix[4]arene tetrasulfonic acid, and comparison with structural data from the literature for alkali metal complexes of sulfonated calixarenes, have provided further evidence for the importance of interactions with aromatic ~ -electrons for the heavier alkali metal cations. There is evidence as well that this interaction can be enhanced by extended ionization of the sulfonated calixarene.

Supramolecular Influences on Metal Ion Coordination: Lead(II) under Eight-coordination

Crystal structure determinations on the “acid salt” of Pb(II) and dipicolinic acid (pyridine-2,6-dicarboxylic acid, dipicH2), regarded as composed of dimer entities, [Pb2(dipic)2(dipicH2)2(OH2)6], 1, infinitely cross-linked, and on the complex of 2,4-dinitrophenol (2,4-DNPH), a simpler coordination polymer, [Pb(2,4-DNP)2]n, 2, show both solid state structures to be influenced by π-stacking of the ligands. Although the Pb(II) coordination environment in 1 can be regarded as “hemidirected” and that in 2 as “holodirected”, it is argued that inter-dimer stacking interactions, rather than lone pair effects, are responsible for the distorted 9-coordination of Pb in 1. In 2, Pb adopts close-to-cubic 8-coordination.

Synthesis and complexing properties of methylated calix[4](aza)crown derivatives

Abstract The synthesis of methylated calix[4](aza)crowns and their complexing properties towards Co2+, Ni2+ and Cu2+ are described. The crystal structure of one of those ligands, hydrogen bonded to a picric acid molecule via a water molecule, is given.

Complexation of the p-t-butyl-calix[4]arene anion with alkali metal cations in polar, non-aqueous solvents: experimental and theoretical studies

Abstract Complexation of the p -t-butyl-calix[4]arene monoanion (L − ) with alkali metal cations (M + ) in acetonitrile has been studied experimentally using NMR spectroscopy and UV spectrophotometry, and computationally using molecular dynamics and free energy perturbation simulations. Experiment indicates that in polar solvents such as acetone and acetonitrile, all the cations form 1:1 complexes which have an exo (non-inclusive) structure, with stability constant values falling in the order Li + > Na + > K + > (Rb + ) > Cs + . This is in full accord with the calculations, which indicate that an endo structure, as found for CsL in the solid state and chloroform solution should only result when cation solvation energies are small. For Li + , there is experimental evidence for the formation of a 2:1 (metal/ligand) species but its exact nature is obscure. The cone conformation adopted by the monoanion both when free and complexed (as indicated by room temperature NMR spectroscopy) has been characterised by a single crystal X-ray structure determination of a salt containing a large, ‘non-coordinating’ cation, [N((CH 2 ) 3 CH 3 ) 4 ][ p -t-butyl-calix[4]arene] CH 3 CN.

Linear, Divergent Molecular Receptors – Subtle Effects of Transition Metal Coordination Geometry

Reaction between deprotonated p-tert-butyltetrathiacalix[4]arene and CoII or ZnII under strictly defined conditions leads to the formation of sandwich species in which a trimetallic unit is held between two opposed, divergently oriented, staggered O- and S-bound calixarene ligands in the cone conformation. Despite the isomorphous nature of the crystalline compounds, there is a subtle difference in the coordination of CoII and ZnII, presumably related to the differences in metal radius and electron configuration combined with structural restrictions imposed by the calixarene framework, in that whereas all three Co atoms may be considered six-coordinate (and approximately octahedral), only two of the Zn atoms appear so, the third being five-coordinate and more nearly trigonal bipyramidal in its coordination geometry.

Calixarene complexes of anion-bridged oligouranyl species

The syntheses and structures of uranyl complexes of p-t-Bu-calix[6]arene (calix[6]H6) and p-t-Bu-calix[9]arene (calix[9]H9) are reported, further developing the role of calixarenes as cluster keepers. The calix[6]arene complex, formulated as [(HO){UO2(calix[6]H4)(dmso)}3H], is trinuclear and linked symmetrically by the hydroxyl O atom. The calix[9]arene complex is binuclear, with a carbonate atom bridging between the two uranyl cations to give the complex, (HNEt3)3[(OCO2)(UO2)3(calix[9]H4)].

Functionalization of Cage Amines with Pendant Aromatic and Heteroaromatic Substituents

Structural studies have confirmed that it is possible to exploit the relatively low nucleophilicity of the “external” amino substituents on the CoIII complex of 1,8-diaminosarcophagine (“sarcophagine” = sar = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) in acylation and alkylation reactions leading to a variety of functionalized cage amine complexes. With the appropriate choice of solvent, all these reactions can be conducted with high efficiency, and the new complexes display properties foreshadowing the application of cage systems in, for example, electroactive polymers.

Cation- and solvent-induced conformational changes of 25,27-dimethoxy-26,28-dimethylester-p-tert-butylcalix[4]arene

The synthesis of 25,27-dimethoxy-26,28-dimethylacetate-p-tert-butylcalix[4]arene is presented. Complexation studies towards alkali metal cations showed selectivities for Na + and Li + . Different conformations for the 1:1 complexes are detected depending on the solvent used. X-ray structures of the ligand and some complexes are given.

Solubility of p-t-butylcalixarenes in supercritical carbon dioxide: a comparison of static and dynamic measurement techniques

Abstract The solubilities of p - t -butylcalix[ n ]arenes ( n =4,6,8) and calix[4]arene have been measured in supercritical carbon dioxide. Solubility measurements were conducted in a high pressure cell with in situ spectrophotometric detection. Measurements were taken over the ranges of 10 to 20 MPa and 40 to 60°C. The p - t -butylcalix[4]arene showed solubility approximately 10 fold higher than both p - t -butylcalix[6]arene and p - t -butylcalix[8]arene with a maximum measured solubility over the studied pressure and temperature ranges of 1.84×10 −5 mol/l. A comparison of these results with measurements made with a commercially available analytical SFE unit for p - t -butylcalix[4]arene showed less than 10% deviation between the two sets of data over a common range of conditions. The SFE unit allows measurements to be made over significantly wider ranges of pressure and temperature than are currently available using the solubility cell.