Hydrodynamic and equilibrium properties of sodium chitin/chitosan carboxymethyl ether macromolecules in dilute aqueous solution of different ionic strength

The behavior of Na-carboxymethyl ether of chitin/chitosan (weak polyampholyte)—poly-N-acetyl-D-glucose-2-amine derivative—was studied in dilute solutions using a set of hydrodynamic methods (sedimentation velocity, translational diffusion, viscous flow of dilute solutions) in a wide range of ionic strengths from approximately 10⁻⁶ to 4.5 M NaCl. The molar masses and scaling relationships (Kuhn–Mark–Houwink–Sakurada equations) were determined in 0.2 M NaCl, where polyelectrolyte effects are virtually suppressed. The Kuhn segment length (persistent length) of chitin/chitosan Na-carboxymethyl ether chains in 0.2 M NaCl was estimated using the Multi-HYDFIT suite (A. Ortega et. al., 2011 Methods 54, 115–123. https://doi.org/10.1016/j.ymeth.2010.12.004), which is a method for computer processing of an array of experimental data obtained in a series of independent experiments. As a result, the following estimates were obtained: Kuhn segment length A = 24 ± 4 nm, hydrodynamic chain diameter d = 1.7 ± 0.7 nm. For the first time, using a method proposed earlier (G. M. Pavlov et al., 2006 Rus. J. Appl. Chem., 79(9), 1407–1412. https://doi.org/10.1134/s1070427206090035), intrinsic viscosity of Na-carboxymethyl ether of chitin/chitosan in salt-free solutions, where most strong polyelectrolyte effects were demonstrated, was estimated. Viscometric data were interpreted using the persistent cylinder theory (Yamakawa-Fujii), which led to an estimate of the equilibrium rigidity A ≥ 500 nm. This estimate is discussed within the framework of modern theories of polyelectrolyte linear chains.

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