| Popis: |
A study was made of spectra of repeated disrupted complete internal reflection (RDCIR) in the region of 700–1000 cm−1 and the Raman effect (RE) in the range of 200–1600 cm−1 of crystalline and amorphous dextran. From spectra of RDCIR and spectra of RE of various structural modifications of dextran a conclusion was reached concerning possible conformations of anhydro-D-glucopyranose units in dextran macromolecules. In amorphous dextran elementary units are in Cl conformation. During crystallization of dextran by heating the polymer above the glass temperature, followed by slow cooling, the conformation of elementary units of dextran macromolecules remains unchanged. In macromolecules of dextran crystallized during the treatment of amorphous dextran with a plasticizing liquid (water, DMSO, formamide), followed by slow evaporation, anhydro-D-glucopyranose units are in Cl conformation and in a Cl conformation distorted in directions B1 and 3B, which is, apparently, due to a change in the mutual steric arrangement of elementary units during crystallization. An assumption was put forward about the causes of various reactivities of crystalline modifications of dextran during exterification in a heterogeneous medium, which is based on the analysis of spectroscopic results obtained. |
