Hollow self-assembly

Self-Assembled Molecular Containers/Capsules Discrete, hollow self-assembled structures that are capable of holding one or more guests. 

Maity, S., Jana, P., Maity, S.K., Haidar, D., 2011. Eabrication of hollow self-assembled peptide microvesicles and transition from sphere-to-rod structure. Langmuir 27, 3835-3841. 

There are a variety of routes currently utilized to fabricate a wide range of hollow capsules of various compositions. Among the more traditional methods are nozzle reactor processes, emnlsion/phase-separation procednres (often combined with sol-gel processing), and sacrificial core techniques [78], Self-assembly is an elegant and attractive approach for the preparation of hollow capsules. Vesicles [79,80], dendrimers [81,82], and block hollow copolymer spheres [83,84] are all examples of self-assembled hollow containers that are promising for the encapsnlation of various materials. 

The foregoing results demonstrate that the thickness of the capsule wall can be controlled at the nanometer level by varying the number of deposition cycles, while the shell size and shape are predetermined by the dimensions of the templating colloid employed. This approach has recently been used to produce hollow iron oxide, magnetic, and heterocomposite capsules [108], The fabrication of these and related capsules is expected to open up new areas of applications, particularly since the technology of self-assembly and colloidal templating allows unprecedented control over the geometry, size, diameter, wall thickness, and composition of the hollow capsules. This provides a means to tailor then-properties to meet the criteria of certain applications. 

Lu W, Gao W, Wang S (2008) One-pot synthesis of Ag/ZnO self-assembled 3d hollow microspheres with enhanced photocatalytic performance. J Phys Chem C 112 16792-16800... 

Sithambaram, S., Garces, H.F. and Suib, S.L. (2009) Controlled synthesis of self-assembled metal oxide hollow spheres via tuning redox potentials versatile nanostructured cobalt and cobalt manganese oxides. Advanced Materials, 20, 1205-1209. 

Lanthanide-doped inverse photonic crystals have been reported.282 The lattices were prepared by infilling self-assembled polystyrene sphere templates with a mixture of zirconium alkoxide and europium at 450 °C, the polystyrene spheres were burnt out leaving hollow spheres of air, and the infilled material was converted to Zr02 Eu3+. The PL properties of the resulting photonic lattice were reported.282 The possibility of including phosphors into photonic lattices could lead to many... 

Organoclay materials with higher-order organization can also be prepared by template-directed methods involving self-assembled supramolecular structures. In this approach, preformed organic architectures in the form of tubes, fibers, hollow shells, gyroids, helicoids, and so on are transferred into hybrid materials exhibiting structural hierarchy, complex form and ordered mesoporosity [47-55]. For example,... 

The chiral l,3,5-triazepane-2,6-dione 149 and its ring fused analogue 150 have been shown to form H-bonded helical molecular tapes with P chirality on self assembly in the solid state. With 149, this self assembly proceeds through aromatic-aromatic ring interactions resulting in hollow tubular structures <06CC4069>. 

Dou H, Jiang M, Peng H et al (2003) pH-dependent self-assembly micellization and micelle-hollow-sphere transition of cellulose-based copolymers. Angew Chem Int Ed 42 1516-1519... 

The most versatile method to prepare such hollow capsules is self-assembly [203-205, 214, 215]. Owing to their amphiphilic nature and molecular geometry, lipid-based amphiphiles can aggregate into spherical closed bilayer structures in water so-called liposomes. It is quite reasonable that the hollow sphere structure of liposomes makes them suitable as precursors for the preparation of more functional capsules via modification of the surfaces with polymers and ligand molecules [205, 216, 217]. Indeed, numerous studies based on liposomes in this context have been performed [205, 209, 213]. 

Zhang L, Bartels C, Yu Y, Shen H, Eisenberg A. Mesosized crystal-like structure of hexagon-ally packed hollow hoops by solution self-assembly of diblock copolymers. Phys Rev Lett 1997 79 5034-5037. 

We can think of the previous methods for generating capsules as liquid templating, where self-assembly occurs around a hquid. An alternative is to use a solid template, usually called colloidal templating. The shell is generated around a solid particle that is later digested, leaving a hollow sphere (Caruso 2000). Deposition of... 

Caruso E. Hollow capsule processing through colloidal templating and self-assembly. Chem EurJ 2000 6 413-419. 

In addition to chemical composition, as discussed in Sect. 3, the route of self-assembly also significantly affects the resulting structure because different kineti-cally folded structures may be formed. For example, subtilisin-triggered formation of Fmoc-Ls via ester hydrolysis gives rise to hollow nanotubular structures [22], whereas Fmoc-Ls gel formed by the thermolysin-catalysed reversed hydrolysis of the Fmoc-L/L2 system gives rise to nanofibrillar morphology [21]. 

Lehn and coworkers also discussed the principles of design of self-assembling helical structures on the basis of conformational control. Depending on the solvent used, they were able to obtain helicate fibers and bundles possessing extended molecular channels characterized by hollow cores of limited diameter ofca. 8 A. This finding could form the basis of functional materials for multichannel ion active transport [28]. 

FIGURE 7.30. Different morphologies found upon self-assembly of PS-fr-PAA copolymers, (a) micellar spheres (b) micellar rods (c) lamellae (d) vesicles (e) hexagonally packed hollow hoop (HHH) structures (f) LCMs and (g) the internal structure of a LCM. Reproduced with permission from the Canadian Chemical Society. 

---