Specific hydrogen-bonding patterns chemistry

Since this book provides a wide selection of relevant topics presented by some of the major actors in the domain, we shall emphasize here the conceptual and prospective aspects, illustrated by a brief retrospective of our own work. It started with the exploration of the concept of supramolecular polymers, introduced in 1990 [3a], through the implementation of the principles of supramolecular chemistry to generate polymers and liquid crystals of supramolecular nature from molecular components interacting through specific hydrogen-bonding patterns. The chemistry of supramolecular polymeric entities based on these as well as on other types of noncovalent interactions has since then actively developed [3-17]. 

In this account we have attempted to provide a brief overview of the concepts of first-principles methods tailored for the calculation of structures, energetics, and properties of supramolecular assemblies. The presentation of the theory focussed on the most essential building blocks in order to provide a general frame to interrelate the various methods available. Thereafter, we discussed the relation of these methods to experiment and to well-known concepts for the description of typical interaction patterns. Also, new methods tailored for tackling problems specific to supramolecular chemistry have been discussed (like the calculation of local dipole moments in CPMD simulations, the Mode-Tracking protocol for the selective calculation of vibrational frequencies and intensities, or the SEN method for the calculation of hydrogen bond energies). 

The next era of supramolecular chemistry will undoubtedly be one of adaptability and evolution. As the complexity and the sophistication of these systems increases the need for viable alternatives to covalent synthesis is essential. One such is offered by the exploitation of weak intermolecular forces for the construction of arrays and aggregates with defined composition, shape and functionahty. Hydrogen bonding provides and ideal motif for such systems, and together with the well-established reactivity patterns and shape adaptability of porphyrins, the way is clear to the development of new systems with increasing chemical diversity and controlled dynamics. It is clear that the most rapid advances will be made through the use of dynamic combinatorial libraries, which allows for the chemical evolution of mixtures and amplification of specific components, with built-in error checking and control. 

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