Molecular structure of carboxymethyl starch in dilute aqueous sodium chloride solutions

Abstract

The dilute solution behavior of six carboxymethyl starch (CMS) samples was investigated in aqueous NaCl solutions of different concentration (0.01, 0.05, 0.1, and 0.5 M) by dynamic light scattering (DLS) at 258C. The values of weight average molar mass, M w , of the investigated CMS samples were in the range from 9 Â 10 5 to 2.1 Â 10 7 g/mol. Three of the CMS samples were obtained from corn starch and the other three from potato starch. They had different degrees of substitution, DS, ranging from 0.4 to 1.1. The translational diffusion coefficient, D z , and hydrodynamic radius, R h , were determined for all CMS samples in aqueous NaCl solutions of different concentrations by the DLS method. The obtained results were treated together with previous results obtained by static light scattering and viscometry, which enabled the calculation of the structure-sensitive parameter, r, and the dependence of R h , radius of gyration, R g , and viscosity radius, R h , on molar mass. The calculated values of the r parameter were independent of molar mass. The parameter r did not change significantly with the variation of the salt concentration in water, its values being in the range from 1.10 to 1.19. The values of exponent n i in the log-log dependence of R g , R h , and R h on M w were in the range between 0.42 and 0.47; 0.36 and 0.49; 0.42 and 0.44, respectively. These values are characteristic of branched structures of macromolecules.

The Effects of NaCl on Starch Molecular Conformation

“…It has been confirmed that NaCl treatment had no significant effect on the average molecular weight of starch. [ 17 ] Namely, NaCl could not break the covalent bond (glycosidic bond) of starch molecules. Thus, as two important secondary interactions, the changes of VDW and electrostatic interactions may play an important role in the change of structures and properties of starch during the NaCl treatment.…”

“…Curiously, it was found that after NaCl treatment, starch molecular structure (average molecular weight and chain length distribution) was not obviously affected, but the properties of starch were significantly changed. [ 17 ] Therefore, it can be speculated that the changes in starch properties caused by NaCl treatment may be caused by the change in the stacking mode of molecules and starch molecular conformation.…”

Comparative study on molecular size, multi‐branched structure, and chain conformation of amylopectins from three rice cultivars

“…One of the sensitive parameters to describe the branching topology is the interpenetration function, ψ : which expresses the penetration of hydrodynamic volume from two connected polymer segments and also increases with increasing branches. The formula of [ η ] versus chain dimension is described as the Flory coefficient, Φ : which reflects the penetration of the hydrodynamic volume of the polymer by solvent molecules and is expected to increase with an increase in branches.…”

“…One of the sensitive parameters to describe the branching topology is the interpenetration function, c [33]:…”