Crystalline structures supramolecular investigations

We should also mention an early work by Slonimsky and Askadsky 74 who were apparently the first to observe structural changes taking place in extension under condition s of constant force. Three characteristic sections (see Fig. 20) were identified on the curves of strain versus tension time at F = const. These sections correspond to polymer flow in the amorphous state, the process of molecular ordering and crystallization, and, finally, to polymer flow in the crystalline state. The presence of crystalline formations on the latter section was detected with the help of X-ray-structural and electron-microscopic investigation of extended samples. As the tensile stress was lifted, the sample amorphised again and contracted. The occurrence of a drastic increase in strain on the second section was accounted for 74) by exhaustion of the longevity of supramolecular structures. 

Up until 1977, the non-covalent polymeric assemblies found in biological membranes rarely attracted any interest in supramolecular organic chemistry. Pure phospholipids and glycolipids were only synthesized for biophysical chemists who required pure preparations of uniform vesicles, in order to investigate phase transitions, membrane stability and leakiness, and some other physical properties. Only very few attempts were made to deviate from natural membrane lipids and to develop defined artificial membrane systems. In 1977, T. Kunitake published a paper on A Totally Synthetic Bilayer Membrane in which didodecyl dimethylammonium bromide was shown to form stable vesicles. This opened the way to simple and modifiable membrane structures. Since then, organic chemists have prepared numerous monolayer and bilayer membrane structures with hitherto unknown properties and coupled them with redox-active dyes, porous domains and chiral surfaces. Recently, fluid bilayers found in spherical vesicles have also been complemented by crystalline mono-... 

Of course, the use of AFM is not restricted to the investigation of supramolecular structures in the material sciences. Xrtificial" biomaterials were also recently probed by AFM. For instance, two-dimensional crystalline forms of DNA that self-assemble from synthetic DNA double-crossover molecules were assembled, and their patterned crystals were visualized by AFM. Intermolecular interactions between the structural units are programmed by the design of sticky ends that associate according to Watson-Crick complementarity.Recently, biohybrids, formed by the association of two biotinylated polystyrene... 

The supramolecular assemblies that form the structural units of liquid crystalline phases lead to length scales of order in the nanometer range. Mesophases thus represent nanostructured materials already in the bulk state. Under certain circumstances, these materials can be dispersed into liquid crystalline nanoparticles (LCNP) which will be the focus of this chapter. Due to their specific properties, liquid crystalline phases offer interesting drug carrier properties which may be even more advantageous when used in the nanoparticulate dispersions. Hitherto, most investigations into this direction have been performed with lyotropic mesophases and this topic will be discussed in the first part of this chapter. In the second part, nanoparticulate carriers based on thermotropic mesophases will be introduced. 

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