Sodium dodecyl sulfate—polyethyleneimine—water system. Self-organization and catalytic activity

Abstract

Concentration boundaries within which polymer-colloid structures exist in a sodium dodecyl sulfate-polyethyleneimine-water system were determined. The catalytic effect of this composition was found for the hydrolysis of phosphonic acid esters. The found accelera tion of hydrolysis up to 25 fold is caused by reagent concentrating in a catalytic complex.Mixed systems surfactant-polymer are objects of a promising interdisciplinary scientific area that attract great researchers´ interest. 1-6 The development of this avenue of investigation is stimulated by a wide scope of practi cally useful properties of mixed solutions and a possibility of their purposeful control by the variation of the compo nent ratio in the system. In addition, the study of regulari ties of the formation of polymolecular ensembles extends potentialities of self assembly modelling in biological sys tems. The main goal of fundamental studies of aqueous surfactant-polymer solutions is to prove the combined aggregation, find concentration boundaries for the exist ence of mixed structures, estimate their stability, and char acterize the nature of intermolecular interactions. The reactivity of compounds in mixed polymer-colloid sys tems is poorly studied and, therefore, is one of the main tasks of the present work.We have previously 7,8 studied the physical and cata lytic properties of polymer-colloid systems based on the cationic surfactant cetyltrimethylammonium bromide (CTAB) and polyethyleneimine (PEI). Different points of view about the possible cooperative binding of cationic surfactants with nonionic and likely charged polymers can be found in the literature. 9 The published results 7,8 favor the hypothesis on the self organization and forma tion of supramolecular structures in the CTAB-PEI sys tem. These structures efficiently catalyze the hydrolysis of phosphorus esters. Taking into account that the electro static interaction contributes unfavorably to the free en ergy of formation of complexes of the likely charged sur factant and polymeric species, it should be assumed that combined aggregates are formed in these systems mainly due to hydrophobic interactions. To gain more compre hensive information on the contribution from differ ent types of intermolecular interactions in the surfac tant-polymer systems, we continued to study the cata lytic properties of PEI based compositions, using an un likely charged surfactant, sodium dodecyl sulfate (SDS). The hydrolysis of phosphonates 1-3 was studied as a model process (Scheme 1). Scheme 1 1 2 3 X NO 2 NO 2 Br R Et n С 6 Н 13 Et ExperimentalCompounds 1-3 were synthesized by a known procedure. 10 Sodium dodecyl sulfate (Sigma) and branched PEI (Aldrich, molecular weight 30000) containing the primary, secondary, and tertiary nitrogen atoms in a ratio of 1 : 2 : 1 were used. Molar concentrations of PEI presented in the work are based on the

Interaction of Sodium Dodecyl Sulfate with Poly(ethyleneimine) in Bulk Solution and at the Air-Solution Interface

“…Above this concentration micelles unbound to the polymer formed in solution with the surfactant=polymer complexes. [20] Results of the current work also showed that PEI concentration is greatly influence the precipitate formation because at very high PEI concentrations rod like precipitate formation initiated. Therefore, it is possible to conclude that the system can be described as thermodynamically stable solution of the solvated SDS=PEI complex molecules at low surfactant concentrations.…”

“…Zakharova et al reported that the polymer-surfactant complexes in solutions exhibits surfactant properties so that even at low surfactant concentrations the surface tension at the liquid-air interface decreases sharply. [20] Therefore, surface tension values of solutions containing SDS=PEI mixtures become lower compared to SDS solution without PEI. Above the CMC of the surfactant the surface tension of SDS=PEI mixtures increases but remains lower than that for a miceller surfactant solution.…”

“…This may be attributed to the desorption of some SDS ions unbound to PEI from interface to the bulk solution. [20] The strength of interactions between two surfactants in mixed systems can be determined by calculating the interaction parameter using the CMC's obtained from the surface tension to log concentration plots of aqueous solutions of individual surfactants and their mixtures. [36] The molecular interaction parameter for the mixed surfactant-polyelectrolyte system can be calculated using the following equation based on the regular solution theory derived by Rubingh: [10,36] M is a parameter measures the nature and extent of interaction between the surfactant and polymer molecules in the mixed micelle solution.…”

“…They found that hydrophobic interactions contribute substantially to the formation of SDS=PEI complexes. [20] Dedinaite et al reported the effect of SDS on the properties of adsorbed layers of PEI. According to their study interfacial association between PEI and SDS is different from that observed for other cationic polyelectrolyte-surfactant complexes.…”

Design of High-Relaxivity Polyelectrolyte Nanocapsules Based on Citrate Complexes of Gadolinium(III) of Unusual Composition

“…At first glance, since the tris complexes and PEI have opposite charges, their association should have led to a decrease in the ZP, as is the case for the citrate-PEI system at pH 6. Elsewhere was reported [60][61][62] that the degree of PEI protonation at pH 4-6 ranges from 0.3 to 0.89. Thus, it can be assumed that the association with metal complexes (not disturbed by a large excess of chloride ions, Figure 6a) stimulates additional protonation of PEI in the pH range 3-6, which provides both the strength of ternary associates and leads to an increase in the ZP of such nanoparticles at the same pH values (Table 4).…”