Overview-What is Supramolecular Chemistry

In 1967, Pedersen observed that crown ether showed molecular recognition - the first artificial molecule found to do so. Cram developed this concept to cover a wide range of molecular systems and established a new field of chemistry, host-guest chemistry, where the host molecule can accommodate another molecule, called the guest molecule. In 1978, Lehn attempted to organize these novel chemistries, and first proposed the term supramolecular chemistry . This represented the moment that supramolecular chemistry was clearly estabhshed. Together, Pedersen, Cram and Lehn received the Nobel Prize for Chemistry in 1987. 

Another type of self-assembly mode is based on looser molecular interactions, where one of the main binding forces comes from hydrophobic interactions in aqueous media. Amphiphihc molecules (amphiphiles) that have a hydrophihc part and a hydrophobic part form various assembhes in water and on water. The simplest example of this kind of assembly is a micelle, where amphiphiles seh-assemble in order to expose their hydrophilic part to water and shield the other part from water due to hydrophobic interactions. A similar mechanism also leads to the formation of other assembhes, such as hpid bilayers. These molecules form spherical assembhes and/or two-dimensional membranes that are composed of countless numbers of molecules. These assembhes are usually very flexible. When external signals are applied to them, they respond flexibly while maintaining their fundamental organization and shape. This research held was initiated by the work of Bangham in 1964. It was found that dispersions of hpid molecules extracted from cells in water spontaneously form cell-like assembhes (liposomes). In 1977, Kunitake and Okahata demonstrated the formation of similar assembhes from various arti-flcial amphiphiles. The latter finding showed that natural lipids and artificial amphiphiles are not fundamentally different. 

In Chap. 6, biological supermolecules are explained and classified by function. Artificial supramolecular systems that mimic biological ones are also described. Biomimetic chemistry, which mimics the essence of a biosystem and then develops an artificial system that is better than the biological one, is widely used in this field. Fimctional developments, such as molecular transport, information transmission and conversion, energy conversion and molecular conversion (enzymatic functionaUty) based on biomimetic chemistry are described. New methodologies such as combinatorial chemistry and in vitro selection mimic evolutionary processes in nature. We leave this topic until the end of the book because we want to show that there is still lots to do in supramolecular chemistry, and that supramolecular chemistry has huge future potential. 

Therefore, to summarize. Chaps. 2,3, and 4 explain the basics of supramolecular chemistry in a hierarchical way, while the appHcations of this field are described in Chaps. 5 and 6. New findings in supramolecular chemistry appear each day it is a highly exciting area of research. 

Lichtenthaler, 100 Years Schliissels-Schloss-Prinzip - What Made Fischer Emil Use This Analogy , Angew. Chem. Int. Ed., 33, 2364 (1994) 

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The synthesis of interlocked molecules has become commonplace over the past 25 years with the gradual development of a number of highly facile template methods for their construction. What were once laboratory curiosities have now taken a prominent place in the broad field of supramolecular chemistry, especially regarding their uses and further potential as molecular switches and machines [1], We present here an overview of the main synthetic approaches to these molecules, with a focus on methods in which macrocyclization reactions result in interlocked products. The analysis is by no means meant to be comprehensive or exhaustive in detail, but rather to convey the variety and utility of the selected synthetic strategies in generating abiotic rotaxane and catenane superstructures. 

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