Shape host-guest molecular assemblies

With reference to hosts and a guest, molecular assemblies have to conform to certain circumstances, generally called complementary relationships. They involve both steric and electronic terms. The objects may be achieved by the use of properly chosen sensor groups and by a suitably tailored basic skeleton as exemplified by the present scissor- or roof-shaped host molecules. From the point of view of the introductory thoughts of this chapter (cf. Sect. 3.1), it is a matter of consideration to see how consistent the scissor or the roof simile is in the light of crystal structures. 

Noncovalent interactions play a special role in synthetic procedures used to assemble various types of supramolecular species. These syntheses rely on the stabilization provided by non-covalent interactions between recognition sites incorporated within precursors. Various types of non-covalent interactions can be used as a recognition motif utilized to guide the synthesis.Targeted synthesis of macro- and supramolecular structures of various sizes, shapes, and functionality has now become possible. Supramolecular chemistry offers incredible applications in various fields such as medicinal chemistry (drug delivery systems),host-guest chemistry,catalysis,and molecular electronics. ... 

A major impetus for the design and construction of a finite molecular assembly is to create function not realized by the individual components.3 The size, shape, and functionality of each component, which are achieved via methods of organic syntheses, are thus amplified within a final functional structure. The components may be synthesized, e.g., to give an assembly with cavities that host ions and/or molecules as guests.3 The components may also react to form covalent bonds.1 That a molecular assembly is, de facto, larger than a component molecule means that the components may be designed to assemble to form functional assemblies that reach nanometer-scale dimensions, and beyond.4... 

In fact, an emerging field of nanoscale science is envisaged in molecular capsules which can host guest molecules through noncovalent interactions. These synthetic molecular receptors exert their peculiar activity upon the conjugation of parameters such as size, shape, and chemical complementarity and are proposed for applications in catalysis of chemical reactions and for the stabihzation of reactive species [38]. For example, hollow hydrophilic metal functionahzed nanostructures can be produced from an amphiphilic metallic diblock copolymer which supramolecularly self-assemble into monodisperse noncovalently connected micelle and can be used as nanocages [39]. 

Self-assembled molecular capsules come in different shapes and cavity sizes and hold together through a variety of non-covalent forces they are capable of reversible encapsulation. Small molecule guests are entirely surrounded by larger molecular assemblies and the steric barriers imposed by a host retain the encapsulated molecules. 

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