Small molecules theoretical background

In a previous section of this chapter a general discussion of the theoretical background of the molecular orbital method was presented. There are correlations of orbitals between large and small internuclear distances and also between different geometrical conformations of the final molecule. 

Piezoelectric sensors have become a versatile tool in biosensorics to study protein-protein and protein-small molecule interactions. Here we present theoretical background on piezoelectric sensors and instructions, how to modify their surface with various recognition elements for cholinesterases. These recognition elements comprise an organophosphate (paraoxon), a cocaine derivative (BZE-DADOO), and a tricyclic, aromatic compound (propidium). Additionally, a guide to the kinetic evaluation of the obtained binding curves is given in this chapter. 

The relativistic calculations on the electronic structure of actinide compounds were reviewed by Pyykko (1987). He also reviewed relativistic quantum chemistry in 1988, whereas the relativistic calculations were limited to small molecules containing one heavy atom only (Pyykko 1988). Calculations on the uranyl and neptunyl ions were introduced in the review article. The general information on the computational chemistry of heavy elements and relativistic calculation techniques appear in the book written by Balasubramanian (1997). There are several first-principle approaches to the electronic structure of actinide compounds. The relativistic effective core potential (ECP) and relativistic density functional methods are widely used for complex systems containing actinide elements. Pepper and Bursten (1991) reviewed relativistic quantum chemistry, while Schreckenbach et al. (1999) reviewed density functional calculations on actinide compounds in which theoretical background and application to actinide compounds were described in detail. The Encyclopedia of computational chemistry also contains examples including lanthanide and actinide elements (Schleyer et al. 1998). The various methods for the computational approach to the chemistry of transuranium elements are briefly described and summarized below. 

It is mentioned above that in the usual procedure the theoretical background cannot be used for small s values (see Figure 5). The reason is mainly the difference in the electron distribution in the molecule from the distribution assumed in the independent atom approximation. If the first Born approximation is valid the total intensity scattered by a molecule may be expressed by distribution functions similar to those in equation (53) - ... 

Electron Spin Echo Envelope Modulation, or ESEEM, is widely used to investigate structure of the immediate surroundings of paramagnetic species. In combination with site-specific spin labeling and selective deuterium substitution, it becomes a helpful tool to study location of proteins and small peptides within membranes, interaction of small molecules with proteins, supramolecular assemblies, water accessibility to specific regions of proteins and water penetration into membranes, protein folding and secondary structures. In this review, experimental approaches and limitations, theoretical background of the method, and recent applications are discussed. 

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