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It may be noted that the exponent in the plot (0.41) is well below the random
coil limit (0.5). This is in fact ascribed to the presence of branches, which are
present at about 1 of 25 backbone residues23. Most of these branches are
only one to three glucose units long, but there are also a few very long
branches. The number of these long branches probably never exceeds 1% of
the total number of glucose units. However, they have a great influence on the
solution properties of dextran, as can be seen by comparison with the
corresponding pullulan properties
1
.
The compact nature of dextrans may cause considerable errors when they
are used as calibration substances in methods like gel filtration (SEC or GPC).
23 Residue = sugar