Cellulose spectral study

In summary then, the Raman and infrared spectral studies undertaken after the discovery of the composite nature of native celluloses point to the conclusion that the only difference between the two forms is in the pattern of hydrogen bonding between chains that possess identical conformations. Yet electron diffractometric studies have been interpreted to indicate that the two forms represent two crystalline phases with different crystal habits." More recently, diffractometric studies by Nishiyama have also been interpreted along... 

Two classes of spectral studies have been applied for the first time during the past decade as the basis of structural studies of cellulose. These are Raman spectroscopy, and solid state NMR using the CP/MAS technique. Both have raised questions concerning the assumptions about symmetry incorporated in the diffractometric studies. And while they cannot provide direct information concerning the structures, they establish criteria that any structure must meet to be regarded as an adequate model. The information from spectroscopic studies represents one of the major portions of the phenomenology that any acceptable structural model must rationalize. 

Takahashi, S.-L, Fujimoto, T., Bama, B.M., Miyamoto, T., Inogaki, H., 1986, 13C-NMR spectral studies on the distribution of substituents in some cellulose derivative. J. Polym. Sci.. Part A Polym. Chem. 24 2981-2993. 

The impurity peak at RRT 3.4 was observed in all samples exposed to accelerated conditions. Structural identification of this peak could not be established since this component did not show any response in the mass spectral analysis. The presence of this peak in large amounts in both active and placebo tablets lead to the conclusion that the late eluting impurity observed at RRT 3.4 was indeed a degradation product of one or more of the excipient components present in the tablets. Because of the large amounts of this impurity in the samples, a study using the individual excipients was conducted to identify the source of this degradant. The study lead to the conclusion that the excipients exposed to accelerated conditions in powder form did not produce the degradation product. However, when the same excipients were compressed into pellets and exposed to the same conditions, lactose, microcrystaUine cellulose and croscarmellose sodium compacts showed the presence of the peak at RRT 3.4. 

These studies indicate that electrostatic forces contribute greatly to the binding process. The interaction between tilorone and DNA may, however, involve other kinds of forces. Tilorone forms a reversible complex with DNA, since the drug could be completely dissociated from a DNA-cellulose column. Interaction of apurinic and apyrimidinic DNA s with tilorone hydrochloride also gave spectral changes. However, only with the apyrimidinic DNA, the spectrum of the bound drug was similar to that found with native DNA. 

In addition to the disallowed reflections in the electron diffraction patterns that placed the crystallographic models in question, new spectral evidence was developed pointing to the need for further refinement of structural models, particularly for native celluloses. The models derived from the crystallographic studies could not rationalize many features of the spectral data known to be quite sensitive to structural variations. 

In an effort to further validate the proposal that the Iq, and forms were the primary constituents of native celluloses, VanderHart and Atalla undertook another extensive study to exclude the possibility that experimental artifacts contributed to the key spectral features assigned to the two forms. A number of possible sources of distinctive spectral features were explored. The first was the question whether the surface layers associated with crystalline domains within particular morphological features in the native celluloses could give rise to features other than those of the core crystalline domains. The second was whether variations in the anisotropic... 

Figure 7 where it is clear that even in the spectrum representative of the Iq form the upfield wings of the C4 and C6 resonances are reduced to a minimum. With the completion of this study hy VanderHart and Atalla, most of the questions about the possibility that the spectral features were the results of artifacts were put to rest, and the hypothesis that all native celluloses belong to one or to a combination of these forms was generally accepted. 

The studies undertaken on the basis of further examination of the solid-state NMR spectra of celluloses are in a number of categories. The first group is focused on further examination of the spectra of different native celluloses, in part aided by mathematical procedures for deconvolution of the spectra or for resolution enhancement. Another group relies on exploring the spectral manifestations of native celluloses that have been modified in different ways. Yet a third approach is based on investigation of celluloses subjected to different but well-known procedures for inducing structural transformations in the solid-aggregated state of cellulose. 

With respect to the con arison between celluloses I and II, the spectral data leave little question that the molecular conformations are indeed different. The chapter by Wiley and Atalla sets forth some of the evidence based on Raman spectroscopy. The validity of the theoretical arguments developed in support of the hypothesis that two distinct conformations do indeed occur has been demonstrated through its application in studies of model compounds. The most con rehensive is a study of the vibrational spectra of the inositols (47), wherein spectra of seven of the isomers were investigated and the effects of conformational differences accounted for. 

R 126 M. A. Kabel, H. A. Schols and A.G.J. Voragen, Identification of Structural Features of Various (O-Acetylated) Xylo-Oligosaccharides from Xylan-Rich Agricultural By-Products A Review , p. 108 R 127 P.T. Larsson, Interaction between Cellulose I and Hemicelluloses Studied by Spectral Fitting of CP/MAS C-NMR Spectra , p. 254 Vol. 867, 2004... 

This study shows that 2-D NMR analysis of intact EC can provide structural information, such as confirming the presence of cellulose ethoxylated at the C3 position, but does not readily yield quantitative information such as positional DS. 2-D NMR analysis of TFA-hydrolyzed EC confirms formation of a complex mixture of ethoxylated a and p- glucose anomers. A combination of HMQC and HMBC analyses was used to confirm the assignments used for quantitative 1-D C NMR analysis without reference to external standards. Because of improved spectral resolution, HOHAHA analysis of hydrolyzed EC afforded relative positional DS that agreed well with values determined by GC-... 

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