Synthetic silks molecular structure

Naturally occurring polymers—those derived from plants and animals—have been used for many centuries these materials include wood, rubber, cotton, wool, leather, and silk. Other natural polymers, such as proteins, enzymes, starches, and cellulose, are important in biological and physiological processes in plants and animals. Modern scientific research tools have made possible the determination of the molecular structures of this group of materials and the development of numerous polymers that are synthesized from small organic molecules. Many of our useful plastics, rubbers, and fiber materials are synthetic polymers. In fact, since the conclusion of World War II, the field of materials has been virtually revolutionized by the advent of synthetic polymers. The synthetics can be produced inexpensively, and their properties may be managed to the degree that many are superior to their natural counterparts. In some applications, metal and wood parts have been replaced by plastics, which have satisfactory properties and can be produced at a lower cost. 

Orientational constraints have been collected for a wide variety of molecular systems from synthetic polymers [32, 33] to structural proteins, such as silk [34, 35]. Orientational constraints have also been collected for retinal bound to bacteriorhodopsin [36], suggesting a host of ligand receptor systems that might be studied. Orientational constraints have been collected on other synthetic and biosynthetic polypeptides in bilayer environments, such as Magainin-2, a toxin from frog skin [37], the M2 8 from the acetylcholine receptor [38] and M2-TMP from Influenza A virus [39]. Such studies have led to a description of the orientation of a-helices relative to the bilayer. Proteins such as the fd and Pfl bacteriophage coat proteins have also been... 

Class II includes flexible macromolecules. They stay only in the states of liquid and solid, in order to reserve the integrity of chemical bonds. Evaporation of such macromolecules requires so high level of thermal energy that the chemical bonds are actually broken before reaching that level. The molecular flexibility in the liquid mainly comes from the internal rotation of the main-chain C-C bonds. This class includes structural materials of synthetic polymers such as Nylon, PVC, PET, and PC, adhesives such as PVA, epoxy resins and Glue 502, elastomers such as natural rubber, polyurethane, SBS and EPDM (mbber could be regarded as the cross-linked liquid polymers.), biomaterials such as celluloses, starch, silks and wools, and even bio-macromolecules such as DNA, RNA and proteins. The class of flexible macromolecules corresponds to the soft matter defined above. 

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