Fiber diffraction analysis

Fiber diffraction methods are outlined in the next section. In the following section, exsunples of the application of these techniques to some polysaccharide structures are described. The examples have been chosen to illustrate a range of situations that can arise in a fiber diffraction analysis. 

In conclusion, we have demonstrated that high resolution TEM is a valuable complement to x-ray fiber diffraction analysis and chemical structural elucidation. Its application provided information about the organization of pectin in cell walls and in calcium-free gels. Using freeze-dried samples that were Pt/C replicated, we demonstrated tobacco pectin filaments in a gel to be of the same diameter as the filaments on the noncutinized lower epidermal surface of senescing Coker 319 tobacco leaves. These filaments were 7.1 3A and 4.6 4.8A, respectively, and roughly the same diameter, 7A, as fiber-diffraction modeled citrus pectin (32). Replicated... 

Oda, T., Namba, K., and Maeda, Y. (2005). Position and orientation of phalloidin in F-actin determined by X-ray fiber diffraction analysis. Biophys. J. 88, 2727-2736. 

There are two ways for including the contribution from bulk water. One was first introduced in fiber diffraction analysis of polynucleotides. It subtracts the X-ray scattering contribution of bulk water from the individual atomic scattering factors used in the structure analysis [700,836], The other incorporates the continuous electron density of liquid water, 0.34 e/A3, in the electron density calculations. As a result the more localized solvent atoms are I more clearly defined in difference electron density maps [837]. 

Molecular conformations [71,72] and associations can be determined by CP-MAS- C-NMR and two-dimensional NMR methods [73], but the primary means of determining molecular conformations has been X-ray fiber diffraction analysis coupled with molecular modeling as practiced by Chandraskeran and co-workers. Examples are found in references [74,75,76,77,78,79,80,81,82,83,84]. The technique has also been used to study polysaccharide-polysaccharide interactions [85]. Recently, powder diffraction data has been used to determine a molecular conformation [86]. Modeling alone has been used to predict possible conformations [87]. 

Langan P., Nishiyama Y., and Chanzy H. 1999. A revised structure and hydrogen bonding system in cellulose II from a neutron fiber diffraction analysis. J Am Chem Soc 121 9940-9946. 

Computerized modeling studies of carbohydrates date from 1960 when Jones published a fiber diffraction analysis of cellulose carried out using software written in Atlas Autocode. Rao, Sundararajan, Ramakrishnan, and Ramachandran predicted polysaccharide structures in their pioneering work in 1963, along with studies on proteins. Other landmark works... 

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