Structure-defining interaction

In molecular crystals, the relative importance of the electrostatic, repulsive, and van de Waals interactions is strongly dependent on the nature of the molecule. Nevertheless, in many studies the lattice energy of molecular crystals is simply evaluated with the exp-6 model of Eq. (9.45), which in principle accounts for the van der Waals and repulsive interaction only. As underlined by Desiraju (1989), this formalism may give an approximate description, but it ignores many structure-defining interactions which are electrostatic in nature. The electrostatic interactions have a much more complex angular dependence than the pairwise atom-atom potential functions, and are thus important in defining the structure that actually occurs. 

Many proteins consist of two or more interacting polypeptide chains of characteristic tertiary structure, each of which is commonly referred to as a subunit of the protein. Subunit organization constitutes another level in the hierarchy of protein structure, defined as the protein s quaternary (4°) structure (Figure 5.10). Questions of quaternary structure address the various kinds of subunits within a protein molecule, the number of each, and the ways in which they interact with one another. 

E. Umbach, Electronic structure and interactions in well-defined coadsorbed layers, Appl. Phys. 47, 25-36 (1988). 

The goal of component implementation is to define an internal structure and interactions that satisfy the behavioral, technological, nonfunctional, and software engineering requirements for a component. In Catalysis the component specification (type) mentioned earlier identifies the behavioral requirements. 

A structurally defined component able to comply with the requirements quoted in 1 and 2 and to establish interactions with specific receptor sites of the organ taken as the target for the drug treatment. 

The characteristics of particulate filled polymers are determined by the properties of their components, composition, structure and interactions [2]. These four factors are equally important and their effects are interconnected. The specific surface area of the filler, for example, determines the size of the contact surface between the filler and the polymer, thus the amount of the interphase formed. Surface energetics influence structure, and also the effect of composition on properties, as well as the mode of deformation. A relevant discussion of adhesion and interaction in particulate filled polymers cannot be carried out without defining the role of all factors which influence the properties of the composite and the interrelation among them. 

In this approach, well-dehned subunits (small molecules similar to, e.g., nucleotides) tire first formed through covalent synthesis, Second, these subunits aggregate with themselves or with other subunits through covalent or noncovalent (or both) interactions to form large, stable, structurally defined assemblies. For the final supramolecular structure to be stable and to have a well-defined shape, the noncovalent connections must be collectively stable. Therefore, molecules must be stabilized by many noncovalent interactions. 

In biological recognition phenomena, protein-protein interactions are of primary importance. In an attempt to mimic these processes, LaBrenz and Kelly [51] synthesized the peptidic host 64. In this receptor, the dibenzofuran template separates the two peptide units by roughly 10 A and allows for the complexation of a guest peptide (65), as depicted in Fig. 21. The complex first forms a three-stranded, antiparallel /J-sheet that is stabilized by hydrogen bonds, electrostatic interactions, and aromatic-aromatic interactions between the dibenzofuran and the benzamide moieties. This complex can further self associate to form more complex structures. This example shows that structurally defined peptide nanostructures can interfere with biological recognition processes and potentially have therapeutic applications. 

Quality of a food product is related to its sensorial (shape, size, color) and mechanical (texture) characteristics. These features are strongly affected by the food structural organization (Stanley, 1987) that, according to Fardet et al. (1998), can be studied at molecular, microscopic, and macroscopic levels. In particular, micro structure and interactions of components, such as protein, starch, and fat, determine the texture of a food that could be defined as the external manifestation of this structure (Allan-Wojtas et al., 2001). 

It should be mentioned that the defined interaction of dextran sulfate with amino functions is not only applied for the design of structures on the su-permolecular level but also on the molecular level. Thus, a preferred handed helical structure was induced into the polyaniline main chains by chemical polymerisation of achiral aniline in the presence of dextran sulfate as a molecular template. This affords a novel chemical route for the synthesis of chiral conducting polymers [158]. 

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