The field of applications of polyelectrolyte complexes ranges from large-scale industrial products up to special uses in biotechnology and medicine. An important problem is their stability against environmental conditions, particularly the presence of different salts, that is, the colloidal stability as well as the stability of ionic bindings. Most of the previous work has been focused on the effect of sodium chloride. This paper deals with the effect of salts of different cations, stressing both the influences of the ion radius of monovalent cations and the valency of the cations. Polyelectrolyte complexes were prepared between sodium poly-(styrene sulfonate) and poly(methacrylate) as polyanions and poly(diallyldimethylammonium chloride) and a copolymer of this polycation with 53 mol % of acrylamide in pure water. The changes in the structural parameters of these complexes during addition of LiCl, NaCl, KCl, CaCl2, MgCl2, AlCl3, and FeCl3, respectively, were followed by light scattering measurements. The ion radius of monovalent cations has practically no effects on the response of the complex particles. In the case of polyanions being in excess in the complexes, higher valency of the cation led to rapid flocculation in agreement with theoretical expectations. The polyelectrolyte complexes with polycation excess were strongly stabilized by addition of salts with multivalent cations, against both coagulation and dissolution. Especially for the complexes with sodium poly(methacrylate), the multivalent cations take part in complex formation and partly displace the polycations.

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The structure and dynamics of two synthetic elastin-like polypentapeptides, poly(G(1)V(1)G(2)V(2)P) and poly(AV(1)GV(2)P), were studied in D(2)O and H(2)O at various temperatures by using (1)H, (2)H,(13)C, and (15)N NMR spectra, relaxations, and PGSE self-diffusivity measurement. Signal assignments were made using COSY, NOESY, HXCORR, HSQC, HMBC, and SSLR INEPT techniques. Temperature-induced conformation changes were studied using (3)J(NHCH) couplings, NOESY connectivity, chemical shifts, and signal intensities. Hydrodynamic radii were derived from self-diffusion coefficients measured by the pulsed-gradient spin-echo (PGSE) method. Selective hydration (hydrophilic or hydrophobic) was explored using NOESY and ROESY spectral methods and longitudinal and transverse (1)H relaxation of HOD and quadrupolar (2)H relaxation of D(2)O. Four different physical states were discerned in different temperature regions for both polymers: state I of a rather extended, statistically shaped and fully hydrated polymer below the critical temperature (approximately 299-300 K); state II, a relatively coiled and globular but disordered preaggregation state, developing in a rather narrow region, 300-303 K, in the case of poly(AV(1)GV(2)P) and in a broader region, overlapping with the next one, in poly(G(1)V(1)G(2)V(2)P); state III, a tightly coiled, more compact state in the region 303-313 K; and, finally, state IV, an aggregated (and eventually flocculating and sedimenting) state beyond 313 K. States II-IV coexist in varying proportions in the whole temperature range above 299 K. A structure characterized by a beta-turn stabilized by H-bonding between the Ala carbonyl and Val(2) NH groups of poly(AV(1)GV(2)P) was detected by NOESY just above the transition temperature. States II and III are progressively more stripped of their hydration sheath but retain some molecules of water confined and relatively immobilized in their coils.