Gibb and co-workers have extensively investigated so-called "deep-cavity" cavitands, 180 such as 87 and 88, the latter of which consists of a hydrophilic surface functionalised with carboxylic acid groups, and a hydrophobic cavity, the entrance to which is surrounded by a hydrophobic rim (Fig. ). By itself, the cavitand was shown to exist in monomeric form in basic aqueous solution; addition of a suitable hydrophobic template (e.g. estradiol), however, led to formation of a dimeric capsule. Depending on the size of the guest, one (e.g. estradiol) or two (e.g. butane, naphthalene) 182 molecules might be encapsulated within the host dimer. Whilst remarkably stable in water at various concentrations (suggesting a minimum association constant of 10 8 M -1 ), 181 addition of other solvents (acetonitrile, THF, acetone, DMSO) led to capsule degradation to varying extents. Successful deposition of capsule host-guest complexes on silica surfaces has been demonstrated, with retention of the capsular structure. 184 Cationic analogues of these have been reported by replacing the carboxylic acid moieties with amine/ammonium functionalities, enabling capsule formation in acidic media. Through small structural modifications and choice of guest template, higher-order assemblies including tetramers and hexamers have been reported, 186 as have heteromeric assemblies 187 and externally functionalised systems. Hiraoka, Shionoya and co-workers reported the selfassembly of a remarkable hexameric cube from the gearshaped monomer, 89, in a water/methanol solvent mixture. The solid-state SCXRD structure showed the hexamer to apparently be held together by van der Waals, π-π and CH-π interactions; the delicate balance of these interactions was demonstrated by comparison with an analogous monomer in which the tolyl substituents were replaced with phenyl units, which did not form an analogous assembly. Whilst this hexameric structure was able to encapsulate appropriately sized substituted benzenes, adamantane induced a rearrangement of the host to give a tetrameric architecture (Fig. ). Methylation of two of the pyridine rings to cationic pyridinium moieties gave a fully water-soluble monomer that, in the absence of a template, assembled into a hexameric cube, 191 the thermal stability of which could be modified by tailoring the electronics and sterics of the non-pyridinium arm of the monomer. Detailed reviews on well-defined capsules assembled using the hydrophobic effect are available for perusal. For these systems, the precise number of component building blocks incorporated into the self-assembled structures can be determined. For others, there can be a distribution of compositions. Yoshizawa and co-workers have extensively studied micelle-like structures assembled from small-molecule amphiphiles incorporating hydrophobic aromatic shells (Fig. ). Amphiphiles with the general structure of 90 incorporating anthracene, 195 naphthalene, phenanthrene, 196 phenothazine 197 and even aliphatic adamantane 198 have been investigated. NMR spectroscopy was used to confirm the formation of aggregates, whilst dynamic light scattering (DLS) and atomic force microscopy (AFM) reveal the approximate size and narrow size distribution of the assemblies. A U-shaped amphiphile was shown to assemble into a dimeric capsule, 199 whilst an anthracene-based amphiphile formed capsules composed of and an adamantlyfunctionalised monomer formed a larger assembly with approximately demonstrating that, through structural design, some control over the aggregate size is possible, although formation of different sized aggregates through encapsulation of smaller or larger guests has been observed. Given the inherently low directionality of relatively weak forces that contribute to self-assembly under hydrophobic conditions, the rational design of hydrophobically-driven assemblies is somewhat challenging. Structural factors common to the different systems discussed herein include hydrophilic solubilising groups and accessible hydrophobic surfaces that can aggregate together in aqueous media. 1 H NMR, NOESY, DOSY and MS have all been used to demonstrate the persistence of structures self-assembled by the hydrophobic effect in solution, with some structures able to be confirmed in the solid-state by SCXRD. Other analytical techniques that have been used include dynamic light scattering (DLS) and atomic force microscopy (AFM), which can also reveal size-distribution of non-uniform assemblies. Although often limited to the binding of guests that are themselves hydrophobic, this class of capsules has demonstrated utility in a number of areas, including as molecular reaction flasks, 200 in molecular separations, 182a modulation of photophysical/photochemical properties, 201 and solubilisation of hydrophobic species.