Length scale dependence of the dynamic properties of hyaluronic acid solutions in the presence of salt

Abstract

In solutions of the charged semirigid biopolymer hyaluronic acid in salt-free conditions, the diffusion coefficient D(NSE) measured at high transfer momentum q by neutron spin echo is more than an order of magnitude smaller than that determined by dynamic light scattering, D(DLS). This behavior contrasts with neutral polymer solutions. With increasing salt content, D(DLS) approaches D(NSE), which is independent of ionic strength. Contrary to theoretical expectation, the ion-polymer coupling, which dominates the low q dynamics of polyelectrolyte solutions, already breaks down at distance scales greater than the Debye-Hückel length.

Figure 1

Variation of the hydrodynamic correlation length ξ = k_BT/(6πηD) with ionic strength J in 2% w/w solutions of HA. The slope of the power law fit is 0.64±0.04.

Figure 2

SAXS spectrum of a 2% w/w HA solution in 0.1M NaCl (filled symbols). SLS response of the same solution (open symbols). The size of each symbol reflects the range of the experimental error.

Figure 3

Dependence on q of the NSE scattering intensity from 2% w/w HA solutions at different ionic strengths.

Figure 4

Intensity correlation function g₂(t) -1 from HA solution containing 0.1 M NaCl + 0.05 M CaCl₂, measured at θ=90°. Continuous line: fit to eq 8, dashed line : slow component of eq 8.

Figure 5

DLS relaxation rate Γ vs q² of fast decay for 2% w/w HA solutions in 0.1 M NaCl, 0.1 M NaCl + 0.05 M CaCl₂, and 0.1 M NaCl + 0.2 M CaCl₂.

Figure 6

Dependence on q³ of the slow relaxation rate Γ_s for 2% w/w HA solutions in 100 mM NaCl (open symbols) and in 0.1 mM NaCl + 0.1 mM CaCl₂ (filled symbols)

Figure 7

NSE echo decay at q=0.087 Å⁻¹ for same sample as in Figure 3.

Figure 8

NSE relaxation rate Γ vs q², for 2% HA solutions in zero added salt (●), 0.1 M NaCl + 0.05 M CaCl₂ (○), and 0.1 M NaCl + 0.1 M CaCl₂ (×).

Figure 9

Left axis: dependence of diffusion coefficient D on J in 2% w/w HA solutions; O: D_DLS, ●: D_NSE; continuous line : mode coupling model (eq 7) with D₁=3×10⁻⁷ cm²s⁻¹, D₂=D₃=2×10⁻⁵ cm²s⁻¹, Z₁=−4.5. Right axis : dependence of osmotic modulus c∂Π/∂c on J (♦).