Transition Highly Aggregated ComplexesSoluble Complexes via Polyelectrolyte Exchange Reactions:  Kinetics, Structural Changes, and Mechanism

Abstract

The dissolution of highly aggregated polyelectrolyte complex particles formed in water after addition of salt was studied. The dissolution of aggregates proceeded to soluble complexes on the molecular level of the long-chain component. The driving force of the process is the polyelectrolyte exchange reaction between the aggregates and the free long chains in excess. The kinetics of the process was studied by different light scattering techniques. The rate of dissolution showed a strong dependence on the salt concentration in the solution and on the concentration of the species. The dependence on concentration of the species in solution weakened with increasing salt concentration. Investigations of the structural changes during the dissolution process revealed the presence of only two generations of particles in solution: aggregates and soluble complexes. While the scattering intensity decreased strongly, the dimensions of the aggregates changed only slightly during dissolution, indicating a spontaneous disaggregation of the particles. A mechanism of the dissolution process was proposed, which is in agreement with the experimental findings and previous results in the literature. The process represents a two-step reaction: The first step consists of the release of the short-chain component from the aggregates by an exchange reaction via the free long-chain component in solution (second-order reaction). The second step is the destruction of the aggregates by increasing osmotic pressure in the particle (first-order reaction). The dissolution process may be understood as a model process for the release of DNA from polyelectrolyte complexes in gene therapy.

Formation of Native-like Mammalian Sperm Cell Chromatin with Folded Bull Protamine

“…4, the average light-scattering intensity of a BP-DNA condensate solution in 1 M NaCl increases exponentially with condensation time. Given the 90°d etection angle used to detect scattered light, the increase in average light scattering can be attributed to the increase in concentration of densely packed DNA condensates as well as a decrease in the extent of aggregation of condensate particles (35)(36)(37). These light-scattering results are perfectly consistent with the BP-DNA condensates shown by the TEM images in Fig.…”

“…However, the average light-scattering intensity of BP-DNA condensate solutions decreased exponentially with time after the addition of the denaturing solution containing the reducing agent (Fig. 5A), which correlates directly with the decondensation of the BP-DNA particles (37). Decondensation of BP-DNA condensates by the denaturing solutions containing the reducing agent was also supported by dynamic light-scattering experiments where the observed changes in the intensity correlation function demonstrated an initial decrease in diffusion coefficient and an eventual conversion to a two-step intensity correlation function as 2-mercaptoethanol concentration was increased above 200 mM (Fig.…”

Modeling competitive substitution in a polyelectrolyte complex

“…The presence of added salt significantly reduces the substitution time, in agreement with experimental observations. 13,14 Our simulation results for the monovalent salt concentration of 0.15M are shown in Fig. 8(b), where τ is plotted against N C /N A for N A = 30, N B = 30, Γ = 2.8, and L = 50l 0 .…”

“…The literature on this subject is extensive [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and there are also several excellent reviews describing the phenomenology of solutions of oppositely charged polyelectrolytes. [1][2][3] There are also many simulation and theoretical investigations related to adsorption of polyelectrolytes to oppositely charged solid surfaces and inter-chain interactions.…”

“…Regarding the substitution reaction (second step) in Fig. 1, extensive kinetic studies were conducted some time ago by the Kabanov and Dautzenberg schools, [5][6][7][8][9][10][12][13][14] with many unexpected findings. For example, smaller polycations would complex first with a longer polyanion before these get displaced ultimately by longer polycations, demonstrating an interplay between kinetics and thermodynamics.…”