Ionic and Molecular Recognition

Ionic or molecular recognition by a host molecule will depend upon the degree of structural and electronic complementarity between host and guest. Structural 

Maitland, M. Rigby, E.B. Smith and W.A. Wakeham, Intermolecular Forces Their Origin and Determination, Oxford University Press, Oxford, 1981. 

Of course, for many host-guest systems the distinetion between structural and electronic effects is not necessarily clear cut. It is the subtle interplay between both the nature and shape of the respective potential energy surfaces of the two (or more) molecules in a host-guest system that will control both molecular recognition and binding strength. 

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Application of Boron-Containing Hosts in Ionic and Molecular Recognition... 

Modified electrodes for electrocatalytic processes have been prepared from PT/metal hybrid materials [192, 193] and 3-methylPT [194]. Ionic and molecular recognition has been found with some functionalized PTs in selectively modified electrodes for electrocatalytic or electroanalytic applications [195, 196]. Organic electrochemical transistors have been realized with a 3-methylPT film deposited between the source and the drain the drain current is driven by the electrochemi-cally controlled conductivity of the 3-methylPT film [197]. This device has been shown to be sensitive to oxidants and reductants and to amplify signals up to kilohertz frequencies [198]. 

Sheng Dai, leader of Nanomaterials Chemistry Group and senior research scientist at Chemical Sciences Division of Oak Ridge National Laboratory (ORNL) and adjunct professor at the University of Tennessee at Knoxville (UTK), received his PhD in chemistry from UTK in 1990. He has authored or coauthored more than 180 peer-reviewed journal or book publications. He currently holds five U.S. patents. His research interest includes chemical synthesis of novel materials, separation, catalysis, sensor development, and molecular recognition. Many of these publications are in the area of ionic liquids. 

A large number of application fields can be overlaid by this type of electroactive structure endowed with recognition properties namely, (i) ionic and molecular detection (biological and chemical sensors, microsensors) (ii) extraction for recuperation and depollution (water and radioactive wastes, environmental protection) (iii) ionic and molecular transport for separation (artificial membranes) (iv) chemical and electrochemical syntheses, e.g., asymmetric synthesis (Fig. 1). 

The principal applications of ionosilicas take benefit from the mixed ionic mineral nature of these materials and are situated in the fields of catalysis, separation, and molecular recognition. 

The applications talce benefit of the mixed ionic mineral nature of silica iono-gel and ionosilica materials and are particularly used in electrochemical devices, catalysis, separation, and molecular recognition. However, the investigations in these fields are at their very beginning and further studies are necessary in order to obtain detailed knowledge of physicochemical and chemical properties of this original femily of materials, situated at the interfece of salt and silica. 

Different classifications for the chiral CSPs have been described. They are based on the chemical structure of the chiral selectors and on the chiral recognition mechanism involved. In this chapter we will use a classification based mainly on the chemical structure of the selectors. The selectors are classified in three groups (i) CSPs with low-molecular-weight selectors, such as Pirkle type CSPs, ionic and ligand exchange CSPs, (ii) CSPs with macrocyclic selectors, such as CDs, crown-ethers and macrocyclic antibiotics, and (iii) CSPs with macromolecular selectors, such as polysaccharides, synthetic polymers, molecular imprinted polymers and proteins. These different types of CSPs, frequently used for the analysis of chiral pharmaceuticals, are discussed in more detail later. 

Nucleic acids, proteins, some carbohydrates, and hormones are informational molecules. They carry directions for the control of biological processes. With the exception of hormones, these are macromolecules. In all these interactions, secondary forces such as hydrogen bonding and van der Waals forces, ionic bonds, and hydrophobic or hydrophilic characteristics play critical roles. Molecular recognition is the term used to describe the ability of molecules to recognize and interact bond—specifically with other molecules. This molecular recognition is based on a combination of the interactions just cited and on structure. 

As the electrostatic potential is of importance in the study of intermolecular interactions, it has received considerable attention during the past two decades (see, e.g., articles on the molecular potential of biomolecules in Politzer and Truhlar 1981). It plays a key role in the process of molecular recognition, including drug-receptor interactions, and is an important function in the evaluation of the lattice energy, not only of ionic crystals. 

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