Calculation of conformations and vibrational spectra of a monomeric fragment of the 2,6-carboxymethyl cellulose molecule |
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Authors: | V M Andrianov |
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Institution: | (1) B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 68 prosp. Nezavisimosti, Minsk, 220072 |
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Abstract: | A theoretical conformational analysis has been carried out for the side substituents of a fragment of the molecule for 2,6-carboxymethyl
cellulose (a water-soluble cellulose ether), and the frequencies and the potential energy distribution of the normal vibrations
have been calculated for the most stable conformers of the ether groups of this fragment in the approximation of the molecular
mechanics method. It has been shown that the most stable conformers are those that have the conformations gg, t, g−, g−, g−-for the groups of atoms on the bonds C5-C6, C6-O6, C13-O6, C10-C13, C10-O9 and the conformations g+g−, g+, g−, g−; g+g−, g−, g−, g−; g+g−, g−, g+, t for the groups of atoms on the bonds C2-O2, C11-O2, C7-C11, C7-O8. Comparative analysis of the calculated frequencies
and the potential energy distribution of the normal vibrations for 13 of the most stable conformers showed, as in the case
of the 2,6-hydroxyethyl cellulose molecule, that the frequencies and modes of the normal vibrations are highly sensitive to
conformational transitions in the analyzed spectral region (800–1500 cm−1). The characteristic patterns for the change in the frequencies and modes of the normal vibrations have been established
in connection with conformational transitions within both side substituents. The observed conformational lability of the bulky
substituents in the cellulose ether molecules and its manifestations in the vibrational spectrum provide a basis for hypothesizing
that one of the major mechanisms for the process of their thermal gelation in aqueous solutions is conformational transitions
within these substituents.
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 5–15, January–February, 2007. |
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Keywords: | cellulose ether conformation vibrational spectrum normal vibration molecular mechanics |
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