No abstract

No abstract

Effective nanoreactors based on polyethyleneimines (PEIs) for the hydrolytic cleavage of O-alkyl O-p-nitrophenyl chloromethylphosphonates (alkyl = ethyl, hexyl) and di(p-nitrophenyl)phosphate were developed in conformity with the idea of modeling the polyfunctional catalytic mechanism of enzymes. A step-by-step modification of the single PEI solution by additives with their own catalytic activities (sodium dodecyl sulfate and lanthanum salt) gave rise to a marked improvement in the reaction efficiency. A 104-106-fold acceleration of the reaction compared to the aqueous basic hydrolysis of the substrates was achieved in the sodium dodecyl sulfate-polyethyleneimine-La(III) ternary system. This system can be considered to be metallomicelles immobilized on a hydrophilic polymer matrix. When the PEI immobilized on silica gel was used as a catalyst, the full completion of the reaction was achieved for 100 min under mild conditions, while the half-life of the reaction in a comparable homogeneous regime exceeds 100 h.

New amphiphilic pyrimidinic macrocycles (APMs) with two (APM-1) and three (APM-2) decyl tails have been synthesized by quaternization of the bridged N. Complex examination of the APM-based systems with the help of tensiometry, conductometry, dynamic light scattering, and UV and NMR spectroscopy provides evidence for their aggregation. Calculations based on surface tension isotherms and on packing parameter considerations make it possible to assume a lamellar packing of macrocycles when aggregating. Marked differences in the aggregation behavior of APM-1 and APM-2 have been found. The additives of polyethylenimine (PEI) exert little influence on the critical micelle concentration (cmc) of APM-1, while in the APM-2/PEI systems there occurs a pronounced decrease in the cmc and also a ca. 2-fold decrease in the surface area per molecule. The APM-based assemblies are explored as nanoreactors for the hydrolysis of O-alkyl O-p-nitrophenyl (chloromethyl)phosphonates (alkyl = ethyl, hexyl). The kinetic study reveals a minor rate effect of the APM-1-based systems. In the APM-2-based systems an acceleration of the hydrolysis of both phosphonates occurs as compared to the uncatalyzed process. Within the APM-2 --> APM-2/PEI --> APM-2/PEI/La(III) series, due to the cooperative contributions of the supramolecular, polymer, and homogeneous catalysis, an increase in the catalytic effect is observed from 30 times to 3 orders of magnitude as compared to that of the basic hydrolysis of the substrates.

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

No abstract

No abstract

A new macrocyclic bolaamphiphile with thiocytosine fragments in the molecule (B1) has been synthesized and advanced as perspective platform for the design of soft supramolecular systems. Strong concentration-dependent structural behavior is observed in the water-DMF (20% vol) solution of B1 as revealed by methods of tensiometry, conductometry, dynamic light scattering, and atomic force microscopy. Two breakpoints are observed in the surface tension isotherms. The first one, around 0.002 M, is identified as a critical micelle concentration (cmc), whereas the second critical concentration of 0.01 M is a turning point between the two models of the association involved. Large aggregates of ca. 200 nm are mostly formed beyond the cmc, whereas small micelle-like aggregates exist above 0.01 M. The growth of aggregates between these critical points occurs, resulting in a gel-like behavior. An unusual decrease in the solution pH with concentration takes place, which is assumed to originate from the steric hindrance around the B1 head groups. Because of controllable structural behavior, B1 is assumed to be a candidate for the development of biomimetic catalysts, nanocontainers, drug and gene carriers, etc.