Confined self-assembled space

Self-assembled capsules are of significant interest as molecular reaction vessels and in the control of confined inner space . 

Entrapment of guests within self-assembled capsules provides a fourth method for the construction of chiral supramolecular aggregates. In fact, confinement of guests into cavities with a proper shape and size limits their available space and allows the control over their reciprocal positioning. This reflects directly into their mutual electronic and steric interaction and, as a consequence, in their stereorecognition (Fig. 4D). 

Mineralization is a biological process as cells are intimately involved in almost all aspects. The basic question that arises from the fact that the mineralization process itself occurs in a confined space is how remote the cellular control is from the active sites of mineralization. It can be assumed that the more remote the control is, the more know-how is built into the macromolecules that need to self-assemble and function, and the greater dependence there is on exerting control through the microenvironment of mineralization. 

The supramolecular (host) system is viewed as a confined space in which the probes and/or quenchers are located. Assumptions have to be made regarding the availability of complexation sites in each system. For host-guest complexes, such as cyclodextrins, stoichiometries of complexation are assumed or determined experimentally [50,51]. In the case of self-assembled systems, such as micelles or vesicles, the most common assumption is that at low probe/mi-celle ratios the distribution of probes follows a Poisson distribution [30]. This means that the probability of encountering a molecule in a particular micelle is independent of how many molecules are already in that micelle. 

Hosts and guests are part of the same supramolecular assembly and affect each other in ways that can be detected by NMR. The confined space in the interior of supramolecular hosts provides a peculiar environment for the guest, which reflects in unusual chemical shifts that can be used to detect the formation of self-assembled capsules by NMR. However, the symmetry of the guest can also affect the NMR spectra of the host. 

Molecular arrangements where one or more molecules accommodate other molecules or ions within a confined space have received the name of molecular containers. To date molecular cOTitainers of various sizes and shapes have been reported, as have those containing interior recognition sites [73]. The nature of the molecular container can be permanent, in which the architecture of the container is constituted by covalent bonds, [74] or temporary with the structures being spontaneously self-assembled via weaker interactions, such as metal-ligand interactions [75], hydrogen bonds [76], or hydrophobic forces [77]. Containers that self-assemble through supramolecular interactions are typically referred to as capsules. 

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