Language of Supramolecular Chemistry

The intrinsic language of chemistry is formed by the vocabulary of chemical formulae and structural representations connected by the syntax of their interconversions. It describes a tangible reality it is a reification of the word and the text its signs are engraved into matter [1.18,1.19]. 

As a novel field of science emerges, grows and matures, it evolves basic concepts and generates novel terminology to name the concepts that define it and to describe the objects that constitute it. 

Definitions have a clear, precise core but often fuzzy borders, where interpenetration between areas takes place. These fuzzy regions in fact play a positive role since it is often there that mutual fertilization between areas may occur. This is certainly also true for the case at hand, the case of supramolecular chemistry and its language [1.20]. 

The field, as we now know it, started with the selective binding of alkali metal cations by natural [1.21-1.23] as well as by synthetic macrocyclic and macropoly-cyclic ligands, the crown ethers [1.24,1.25] and the cryptands [1.26,1.27]. The out- 

The concept and the term of supramolecular chemistry were introduced in 1978 [1.29] (see also [2.17]) as a development and generalization of earlier work in which the seed had been planted [1.27, 1.30]. It was defined in words, Just as there is a field of molecular chemistry based on the covalent bond, there is a field of supramolecular chemistry, the chemistry of molecular assemblies and of the intermolecu-lar bond , as well as in diagrammatic fashion (Fig. 1) [1.29]. 

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Clearly one of the most important goals of the Encyclopedia < Supramolecular Chemistry then is to provide a broad-based overview of the discipline and to capture the significance of research in this area, with special emphasis on a synthesis of the concepts and language of supramolecular chemistry across a wide range of related disciplines. Furthermore, this Encyclopedia is not written by, nor written exclusively for "supramolecular chemists" it is for students and practitioners of the chemistry (indeed science) of the noncovalent bond wherever it occurs. We have made specific efforts to direct the reader to the defining literature in the field and specifically included cross-references to help the researcher locate other entries of interest. 

In this chapter, we briefly describe the main principles and provide examples from the fleld of supramolecular chemistry devoted to potential analytical application. While in analytical science a chemical sensor is defined as a device that responds to a particular analyte, that is, ion or molecule of interest, in a selective way through a physical or chemical interaction, and can be used for qualitative or quantitative determination of the analyte , from the supramolecular chemistry perspective, the sensor is usually called the molecule or the material, for example, a polymer, used to test and apply the tools and lessons learned in the supramolecular chemistry studies. While from the purist s perspective the responsive molecules or materials should, perhaps, be more accurately called probes, chemical sensors, and so on to reserve the term sensor for the final devices, vide supra, the truth is that a large portion of the supramolecular studies refers to the actual molecules and calls these simply sensors. Thus, there is a potential for discrepancy between the analytical and supramolecular chemistry community language, of which the reader should be aware. We use the term sensor and chemical sensor interchangeably to refer to a molecule or material. 

Abstract Chemistry is a central science because all the processes that sustain life are based on chemical reactions, and all things that we use in everyday life are natural or artificial chemical compounds. Chemistry is also a fantastic world populated by an unbelievable number of nanometric objects called molecules, the smallest entities that have distinct shapes, sizes, and properties. Molecules are the words of matter. Indeed, most of the other sciences have been permeated by the concepts of chemistry and the language of molecules. Like words, molecules contain specific pieces of information that are revealed when they interact with one another or when they are stimulated by photons or electrons. In the hands of chemists, molecules, particularly when they are suitably combined or assembled to create supramolecular systems, can play a variety of functions, even more complex and more clever than those invented by nature. The wonderful world of chemistry has inspired scientists not only to prepare new molecules or investigate new chemical processes, but also to create masterpieces. Some nice stories based on chemical concepts (1) show that there cannot be borders on the Earth, (2) underline that there is a tight connection among all forms of matter, and (3) emphasize the irreplaceable role of sunlight. 

In chemistry, like in other areas, the language of information is extending that of constitution and structure as the field develops towards more and more complex architectures and behaviors. Supramolecular chemistry has paved the way towards apprehending chemistry as an information science. This change in paradigm will profoundly influence our perception of chemistry, how we think about it, how we perform it. Instructed chemistry extends from the selective synthesis and reactivity of molecular structures to the organisation and function of complex supramolecular entities. It will consider sets of instructed constituents rather than pure substances, performing reactions in complex environments that will lead to the desired substances and properties by the action of built-in self-processes. 

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