Practical Systems Involving Hydrogen Bonding

With the descriptive matter in the preceding chapters as a background, the perceptive reader will not be surprised to find that much of the chemistry in his everyday life depends on H bonding. After all, our bodies themselves, as well as plant cellulose and animal protein which form a major part of our food, clothing, fuel, and shelters, are H bonded in nontrivial ways. Huggins remarks (990) have been prophetic, and entire industries have been founded on the connecting and disconnecting of H bonds. 

In this chapter we present, in most cursory fashion, discussions of some of these important examples of H bonding. In some cases we can augment remarks which were initially made as asides in previous chapters however, we have made no attempt to be exhaustive in this survey. In general, we discuss those regions of technology in which the theories and properties of H bonds have found explicit use. The order is more or less random, but some attempt has been made to present first those uses in which the effects of H bonds are most clearly established. 

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Vm being the molar voliune. As expressed in terms of the solubility parameter, the interaction parameter X12 is necessarily a positive quantity. In practice, negative X12 can be obtained when, because of specific interaction, [1, 2] contacts are favored compared to contacts between like molecules. Thus the solubihty parameter concept is only applicable to systems involving dispersive interactions and fails for those involving hydrogen bonds, donor-acceptor interactions, etc. 

One of the corner-stones of life is recognition. This phenomenon occurs on a macroscopic level as well as on a microscopic one. For example, the ability to recognize a familiar face is practical in our everyday life and the recognition of a transmitter substance by its receptor is essential for the function of the nervous system. Molecular recognition is the creation of a complex between a host molecule and a guest molecule and often involves non-covalent interactions such as hydrogen bonds, hydrophobic interactions, metal coordination, van der Waals interactions and ionic interactions. 

After direct high-resolution structural measurements on proteins became practicable, interest in crystalline amino acids decreased, but became renewed in attempts to simulate the distribution of electronic charge density in biopolymers using amino acids and simple peptides as model systems, to derive some transferable parameters and potentials [2-15]. Another research direction involved these systems and their packing patterns to mimic selected folds and interaction patterns of biopolymers. Typical molecular conformations and patterns of hydrogen bonds and packing in the structures of crystalline amino acids have been reviewed [16-19]. Similar analyses were performed for small peptides [18, 20-22]. 

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