Coil molecular structure

Figure 9.9 A segment of a protein showing areas of a-helical, P-pleated sheet, and coil molecular structure.

It is not the purpose of this book to discuss in detail the contributions of NMR spectroscopy to the determination of molecular structure. This is a specialized field in itself and a great deal has been written on the subject. In this section we shall consider only the application of NMR to the elucidation of stereoregularity in polymers. Numerous other applications of this powerful technique have also been made in polymer chemistry, including the study of positional and geometrical isomerism (Sec. 1.6), copolymers (Sec. 7.7), and helix-coil transitions (Sec. 1.11). We shall also make no attempt to compare the NMR spectra of various different polymers instead, we shall examine only the NMR spectra of different poly (methyl methacrylate) preparations to illustrate the capabilities of the method, using the first system that was investigated by this technique as the example. 

The structure of any molecule is a unique and specific aspect of its identity. Molecular structure reaches its pinnacle in the intricate complexity of biological macromolecules, particularly the proteins. Although proteins are linear sequences of covalently linked amino acids, the course of the protein chain can turn, fold, and coil in the three dimensions of space to establish a specific, highly ordered architecture that is an identifying characteristic of the given protein molecule (Figure 1.11). 

Milk proteins are subdivided into random coiled caseins, which can be precipitated by acidification of raw skim milk to pH 4.6 at 20°C, and into more globular whey proteins, which remain in the serum after precipitation of the caseins (42). In Table 8, an overview is given of the molecular structure and basic properties of the major protein fractions present in milk. Some specific properties that might be of importance for their determination in foods and food products are also listed. For the young of mammals, including humans, milk is the first and, for most, the only food ingested for a considerable period of time. With the domestication of animals, it became possible to include milk in the diet of adult humans as well. For much of the world, particularly in the West, milk from cattle (Bos taurus) accounts for nearly all the milk processed for human consumption (43). 

Theoretical approaches to structural biophysics, like the theories of transport and reaction kinetics explored in other chapters of this book, are grounded in physical chemistry concepts. Here we explore a few problems in molecular structural dynamics using those concepts. The first two systems presented, helix-coil transitions and actin polymerization, introduce classic theories. The material in the remainder of the chapter arises from the study of macromolecular interactions and is motivated by current research aimed at uncovering and understanding how large numbers of proteins (hundreds to thousands) interact in cells [7],... 

In theory, it is not difficult to associate this elastic behavior with the molecular structure of polymers. The coiled conformation of polymers is responsible for the anomalous macroscopic deformation observed in... 

Lee et al. showed that control of the supramolecular structure in rod—coil molecular systems containing either polyethylene oxide) (8) or polypropylene oxide) (17) coils and induction of ordered structures... 

Rod—coil molecular architecture containing poly-(ethylene oxide) endows an amphiphilic character as discussed earlier, and thus hydrophilic solvents such as acryl amide would be selectively dissolved in the microphase-separated coil domains, which gives rise to a variety of supramolecular structures. Polymerization of acryl amide solution in ordered state can give rise to ordered nanocomposite materials. Similar... 

Fig. 3. (left) Molecular structure of TmDOTP. (right) Section of the in vivo H spectrum of TmDOTP at 25.7, 27.0 and 29.1 °C acquired using a surface coil placed over the abdomen of a rat. The chemical shift scale was established by assigning the water proton shift as 0 ppm. The spectra were acquired with 1024 averages using a TR of 30 ms and total acquisition time of 30 s. (Reprinted from ref. 37 by permission of John Wiley Sons, Inc. Copyright 1996 John Wiley.)... 

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