Thomas E. Clark

Engineering nanorafts of calixarene polyphosphonates

The water-soluble calix[4]arene bearing p-substituted phosphonic acid groups is accessible in five steps in overall 62 % yield, with the hydrogen-bonding prowess of the acidic groups dominating its self-assembly processes. These include the formation of 3.0(3) nm and 20(2) nm nanorafts of the calixarene in water using spinning disc processing, stabilized by acetonitrile, and nanorafts in the gas phase (<or=20 molecules). The 20(2) nm particles transform into 3.0(3) nm particles prior to crystallization into a compact bilayer, whereas crystallization in the presence of large organic molecules gives an expanded bilayer interposed by layers of water molecules.

Self-organised nano-arrays of p-phosphonic acid functionalised higher order calixarenes

Water-soluble p-phosphonic acid calix[n]arenes (n = 5, 6 or 8) have been synthesized in five steps in overall 68, 66, 67% yield, respectively, by the recently developed procedure for p-phosphonic acid calix[4]arene. The hydrogen bonding prowess of the phosphonic acids dominates their self assembly into nano-arrays in both solution and the gas phase. In DMSO, nano-arrays of p-phosphonic acid calix[6]arene are stable for over 24 h, with the solvent molecules slowly disrupting the hydrogen bonded network affording solvated monomeric units. In the gas phase, nano-arrays of around 20 calixarene units were observed for the p-phosphonic acid calix[n]arenes using MALDI-TOF-MS, and ESI-MS revealed the presence of heteroleptic nano-arrays for a 1 : 1 mixture of p-phosphonic acid calix[4,5]arenes.

Selective diameter uptake of single-walled carbon nanotubes in water using phosphonated calixarenes and ‘extended arm’ sulfonated calixarenes

Single-walled carbon nanotubes (SWCNTs) have been successfully solubilized using water-soluble p-phosphonated calix[n]arenes (n = 4, 6, 8) and ‘extended arm’ upper rim functionalized (benzyl, phenyl) p-sulfonated calix[8]arenes. Selective SWCNT diameter solubilization has been demonstrated and subsequent preferential enrichment of SWCNTs with semiconducting or metallic electronic properties has been achieved. These water-soluble supramolecular systems can be incorporated into post-growth purification protocols with direct implications in areas such as nano-electronics and device fabrication.

Supersized bilayers based on an O-alkyl substituted calix[4]arene

Attaching C18 alkyl chains to the O-rim of calix[4]arene in the cone conformation affords crystalline solids, as toluene or benzene inclusion complexes, where the four alkyl chains from each calixarene form a continuous hexagonal motif through interplay with alkyl chains from other calixarenes orientated in the same and opposite directions in a bilayer arrangement, despite the absence of polar head groups.

Carborane inclusion chemistry for the uncommon calix[7,9]arenes

The inclusion of o-carborane by p-Bu(t)-calix[7,9]arenes has been investigated by solid state and solution studies, with both resulting complexes in the solid state being rich in carborane with the ratio of calixarene to carborane at 1 : 7 and 2 : 7 respectively. The carboranes reside in clefts within the calixarenes which arise from specific local conformations of adjacent phenolic groups, or are included in the extended structure through other interplay of the calixarenes and carboranes in such clefts.

Variable temperature Hirshfeld surface analysis of interdigitated calix[6]arene bearing O-alkyl C18 linear chains

Calix[6]arene bearing linear C18 alkyl chains crystallises in the inverted double cone conformation with three chains on either side forming a side of a hexagon in an hexagonal close packed array of interdigitated alkyl chains. The nature of the interactions has been probed over different temperatures using Hirshfeld surfaces.