Organized Supramolecular Structures of Macromolecules

We have seen above that the conjugation of structural and thermodynamic properties of weak H-bonds, namely their directionality combined with their enthalpies of about 5-lOkr at room temperature, allows building well-defined molecular structures that combine stability with flexibility and adaptability or evolution. Snch structures are most important in the organization of macromolecules, especially biomacromolecules for which the appearance or disappearance of such supramolecular organization may completely change their properties, making for instance a living protein irreversibly becomes a bio-inert polypeptide. 

Similar l - 4 condensations of glucopyranoses are possible once these dimers are formed. We thus obtain trisaccharides and higher polymers named polysaccharides that are widespread forms of biological carbohydrates. Those obtained from the a and p forms of D-glucopyranose are most common but have, however, completely different macroscopic 

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Polystyrene (PS) is the simplest carbon-chain polymer, which contains a phenyl ring. This polymer contains no heteroatoms and is readily soluble in most organic solvents this makes it possible to use its solutions to assess the effect of the spatial organization of macromolecules (conformation) on the micro structure of the carbon obtained, for it is known that the change in fumed carbon structure may be caused by a difference in the supramolecular structure of carbonization precursors [12]. According to Ref.[13], the mean size of aggregates for solutions of PS in ethyl acetate with a concentration of 0.25 g/100 mL is 1000 A at 1.5g/100 mL concentration, it is 4000 A, and for 5.0 g/100 mL it is 890 A, their number (N10"9/sm"3) being 0.017, 0.27 and 6.88 respectively. 

The molecular structure (chemical structure) of any polymeric substance, that is, its chemical composition and way the atoms are connected in the molecule, does not unambiguously determine the behaviour and properties of biopolymer materials constructed of these macromolecules. The properties of such substances depend also on their supramolecular (physical) structure. This refers to the three-dimensional organization of the macromolecules. The supramolecular structures of the polymeric compounds have various forms that determine the structural and functional properties of biopolymers. It is impossible to observe the structure of biological molecules and their dynamics at the atomic level in vivo, though several different physical research methods could be used including hydrodynamic, optical, low-angle X-rays and neutrons diffraction. X-ray structural and neutron-structural analyses, NMR, electron microscopy and scan micro-calorimetry. 

From the atomic to the macroscopic level chirality is a characteristic feature of biological systems and plays an important role in the interplay of structure and function. Originating from small chiral precursors complex macromolecules such as proteins or DNA have developed during evolution. On a supramolecular level chirality is expressed in molecular organization, e.g. in the secondary and tertiary structure of proteins, in membranes, cells or tissues. On a macroscopic level, it appears in the chirality of our hands or in the asymmetric arrangement of our organs, or in the helicity of snail shells. Nature usually displays a preference for one sense of chirality over the other. This leads to specific interactions called chiral recognition. 

Because of the focus on new materials, macromolecular chemists are concerned with the relation between molecular structure and the material properties, which results from intermolecular interactions and the organization within supramolecular architectures. However, the structures of synthetic macromolecules are polydisperse and not well defined, and the dominant intermolecular interactions, such as entanglements, are mostly not directed and localized [5]. So far, it must be stated that our ability to prepare high molar mass molecules lacks the perfection which is necessary for the reproducible assembly of well-defined supramolecular units [4,6]. 

Since 1987, supramolecular chemistry has developed into a major field [1], New structures with novel properties have been created from existing molecules via non-covalent interactions, including hydrophobic interactions, electrostatic forces, H-bonding, van der Waals forces, etc. At the very beginning, supramolecular chemistry dealt with small molecules such as crown ethers and cryptands. Later, non-covalent interactions were applied to the field of macromolecules, yielding an important concept of a supramolecular polymer [2], Connected by non-covalent interactions, the dynamic supramolecular polymer fused the two fields of small organic molecules and macromolecules. The principle of supramolecular chemistry is central not only to chemical sciences but also to life and material sciences [3-7]. 

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