Structures molecular-level construction

Other than the above structural features there are two important and exclusive properties that make DNA suitable for molecular level constructions. These are molecular recognition and self-assembly. The nucleotide bases A and T on two different ss-DNA have affinity towards each other, so do G and C. Effective and stable cis-DNA structures are only formed if the base orders of the individual strands are complementary. Hence, if two complementary single strands of DNA are in a solution, they will eventually recognize each other and hybridize or zip-up forming a cis-DNA. This property of molecular recognition and self-assembly has been exploited in a number of ways to build complex molecular structures [ 114-121]. In the mechanical perspective, if the free energy released by hybridization of two complementary DNA strands is used to lift a hypothetical load, a force capacity of 15 pN can be achieved [122], comparable to that of other molecular machines like kinesin (5 pN) [123],... 

In parallel, the challenge continues for the chemist to prepare compounds whose properties are similar to objects belonging to other fields of human science or culture. Platonic solids have been a target in synthetic chemistry for decades. Among them, the dodecahedron [7] is certainly one of the most beautiful examples. Molecular-level construction of a tetrahedron [36] or a cube [37] also represent remarkable accomplishements. Buckminsterfullerene Cgq and all its derived structures represent an explosive field of research in which aesthetics and applications are intricately Iinked.[38]... 

FIGURE 3.4 Molecular level alignment diagrams constructed using the HOMO and vacuum levels measured using UPS. The lowest unoccupied molecular orbital LUMO positions are inferred assuming a HOMO/LUMO gap equal to the onset of optical absorption. The chemical structure of CuPc is shown. (From Hill, I.G. and Kahn, A., J. Appl. Phys., 86, 2116, 1991. With permission.)... 

The structure of an alphavirus particle is simpler than that of all known cellular organelles, but it is built according to the same principles. This is because the viral genome is small and the virus must use for its construction those cellular components normally engaged in the biogenesis of host cell membranes. This means that studies of viral replication can be exploited to study cellular functions at the molecular level. Naturally viral infections also perturb cellular physiology, but there is usually enough time early in infection for studies to be carried out before cellular malfunction becomes a source of error. 

The partition of molecular distance correlations into intra- and intermolecular contributions allows us to interpret these correlations in terms of a simple geometrical model. By this means, we are able to elicit structural units as for example segment-clusters that include intermolecular interference phenomena. These clusters are the primary structure units which we call monodomains . These natural units characterize the basic symmetry of the whole structure. If we keep in mind this basic symmetry, we can construct our structure model from a molecular level up to the level of the monodomain treating intra- and intermolecular correlations independently. If we do so, every X-ray pattern can be represented by accounting for the orientation distribution of these monodomains. 

The LB technique enables us to obtain ultrathin films with the structures and thicknesses controlled at the molecular level, which promises applications to various fields. One of the challenges is to construct a new type of switching device based on conductive LB films. For this purpose, a supramolecular system is used since the geometrical alignment of the functional units are defined by the molecular design of the supermolecules to be used. 

---