Coil molecules shape

The lowermost curve in Fig. 45 represents P(0) plotted against according to Eq. (31) for random coil molecules. The results of similar calculations for spherical and for rod-shaped particles of uniform density are shown also. The curve for the former of these is not very different from that for randomly coiled polymers at corresponding values of the abscissas the factor P(0) for rods differs appreciably, however. 

The rubber band is made of coiled molecules. When you stretch the rubber band the coiled molecules are straightened. When you release the rubber band the molecules return to their coiled shapes. 

For spheres and random coil molecules, the shape factor tu in Eq. (3-33) is 2.5 and this equation becomes... 

The HA polymer can adopt a vast number of shapes, sizes, and configurations, whereas in the ECM under normal physiological conditions it is believed to exist as a random coiled molecule. It can... 

The shape of coiled molecules is often incorrectly taken to be spherical. In fact, the innumerable macroconformations of a coiled molecule never adopt a simple geometrical form, not even instantaneously. A mean shape may be... 

Calculations have shown, however, that the squares of the principal components are not equal in magnitude, but have about the relationship 11.8 2.7 1 to each other. The instanteous shape of a coil molecule is not spherical it is more in the form of a kidney. However, increased branching of the main chain will cause the molecule to become more symmetrical. 

Coil-like macromolecules, however, may form a great many contacts with a substrate, and the shape of the adsorbed coil molecule may be very different according to polymer-substrate, polymer-solvent, polymer-polymer, and substrate-solvent interactions (Figure 12-5). The number and order of adsorbed segments leads to a definite macroconformation, and a definite macroconformation, in turn, determines the thickness of and polymer concentration in the adsorbed layer. 

The helix has a high degree of internal order in comparison with the coil molecule. The chain structure of the helix is unambiguously defined in one direction The molecule assumes the overall shape of a rod. 

From this point of view, it is clear that rigid-chain macromolecules, i.e., macromolecules in which the length of the Kuhn segment of the chain / is much greats than the charactmstic thickness of the chain d, should easily form a liquid-crystalline phase. This is actually so coiled molecules (a-helical polypeptides, macromolecules of DNA, etc.), aromatic polyamides, a number of cellulose ethers, and some polyisocyanates are examples of macromolecules capable of forming liquid-crystalline phases of different types [3-5]. The asymmetric shape parameter of such macromolecules (i.e., ratio l/d) can be very large (it can attain several hundred for the first two polymers mentioned above). 

As far as the criterion for sectioiung this review article is concerned, it is not straightforward. For conveiuence, we will review 1-D assemblies of molecular rods in terms of molecular architecture. We classify rod assemblers into six molecular categories (1) rod-coil molecifles, (2) macrocyclic molecules, (3) dendron-rod-coil molecules, (4) dumbbell-shaped molecules, (5) wedge-typed molecules, and (6) conjugate rods with lateral chains. We will describe biomimetic or bioconjugate amphiphiUc rods in the last section. 

As an alternative approach, flexible coil parts in rod-coil molecules can be structurally modihed into dendritic shapes. In comparison to linear-type coils, dendritic coils would cause a larger steric repulsion at the rod/coil interface, which influences rod-packing structures. Lee et al. devised a dumbbellshaped molecule (12) based on an elongated dodeca-para-phenylene rod block and aliphatic polyether dendritic coils with chiral carbon centers, and investigated the self-assembly behavior in aqueous solution [54]. In remarkable contrast to ordinary one-dimensional fibers, the aggregate structures... 

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