Hydrodynamic characteristics and equilibrium rigidity of pullulan molecules

Area of Science:

• Polymer Science
• Biophysical Chemistry
• Materials Science

Background:

• Pullulan (polymaltotriose) is a polysaccharide with significant applications.
• Understanding its hydrodynamic and molecular characteristics is crucial for its effective use.
• Previous studies have not fully elucidated the influence of excluded volume effects on pullulan's chain dynamics.

Purpose of the Study:

• To investigate the hydrodynamic characteristics of pullulan in water.
• To determine the molecular characteristics of pullulan, including molecular weight and chain dimensions.
• To evaluate the influence of excluded volume effects on pullulan's chain conformation and properties.

Main Methods:

• Sedimentation velocity experiments to determine the sedimentation coefficient (S).
• Translational diffusion measurements to determine the diffusion coefficient (D).
• Viscometry to determine intrinsic viscosity ([eta]).
• Application of the wormlike necklace model incorporating excluded volume effects.

Main Results:

• Experimental ranges: 0.9 < S < 11.2, 1.1 < D < 14.7 (x 10^-7 cm^2 s^-1), 6.7 < [eta] < 164 cm^3 g^-1.
• Corresponding molecular weight range: 3.9 < M_SD < 644 (x 10^3).
• Excluded volume effects were found to predominantly influence pullulan's chain length.
• Equilibrium rigidity and hydrodynamic chain diameter were evaluated using the wormlike necklace model.
• At low molecular weights (M < 30 x 10^3), translational friction data deviated from linear molecule theories.

Conclusions:

• Excluded volume effects are a primary determinant of pullulan's chain length in solution.
• The wormlike necklace model, accounting for excluded volume, effectively describes pullulan's hydrodynamic properties.
• Deviations in translational friction at low molecular weights suggest limitations of linear polymer theories for certain pullulan fractions.