Polyelectrolyte chain dimensions and concentration fluctuations near phase boundaries

Prabhu, V. M.; Muthukumar, M.; Wignall, G. D.; Melnichenko, Y. B.

doi:doi:10.1063/1.1592496

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The polymerization of actin: Thermodynamics near the polymerization line

Studies of the dependence of actin polymerization on thermodynamic parameters are important for understanding processes in living systems, where actin polymerization and depolymerization are crucial to cell structure and movement. We report measurements of the extent of polymerization, Φ, of rabbit muscle actin as a function of temperature [T = (0–35) °C], initial G-actin concentration [[G0] = (1–3) mg/ml], and initiating salt concentration [[KCl]=(5–15) mmol/l with bound Ca2+], in H2O and D2O b...

We have measured the temperature (T) dependence of the correlation length (ξ) for concentration fluctuations in aqueous solutions of sodium–poly(styrene sulfonate) with a fixed level of added barium chloride salt. Apparent critical behavior is observed upon lowering the temperature to precipitation phase boundaries that complements our earlier work on salt-dependent behavior. We interpret experimental deviations from ξ⁻² versus T⁻¹ as crossover from the mean field to the Ising universality class. We also measured the radius of gyration (R_g) of labeled chains and ξ for semidilute polyelectrolyte solutions at low ionic strengths. We recovered the familiar result of ξ scaling with polymer concentration (C_p) and degree of polymerization (N), such that ξ = (73±9) N⁰Cp−0.48±0.03 [Å], and using SANS high concentration labeling R_g = (400±28)Cp−0.24±0.01 [Å] (for N = 577) and R_g = (2.8±2.1)N^0.6±0.1 [Å] (for C_p = 206 gL⁻¹), respectively. The indices recovered are in agreement with theoretical predictions for low ionic strength semidilute solutions. Such experiments offer insight into relatively unexplored phase behavior in charged macromolecular solutions. © 2003 American Institute of Physics.