Nanoreactors Based on Amphiphilic Uracilophanes:  Self-Organization and Reactivity Study

Abstract

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.

Supramolecular systems based on cationic surfactants and amphiphilic macrocycles

“…A number of new dicationic surfactants containing a biofragment, in particular, nucleotide base, uracyl (Scheme 3), was studied in [34][35][36][37][38][39][40][41]. The acyclic and macrocyclic (pyrimidinophanes, PP) analogs were compared, while the macrocycle sizes, positions and lengths of alkyl radicals, and counterion natures were varied.…”

“…The acyclic and macrocyclic (pyrimidinophanes, PP) analogs were compared, while the macrocycle sizes, positions and lengths of alkyl radicals, and counterion natures were varied. Macrocycle incorporation markedly increases the packing parameter (almost to 1) [34]. Therefore, the association within the framework of the so called closed model, which causes micellization in solutions of typical colloid surfactants, becomes energetically unfavorable.…”

“…The realization of different packing models is con firmed by calculations based on surface tension iso therms [34]. It is probable that, in some cases, the aggregation of pyrimidine containing surfactants in a bent (over the pyrimidine spacer) conformation takes place, which is evident from comparing the areas occupied by head groups A min ; these values differ by almost two times for the nearest homologs PP 5 2 and PP 5 3 [34].…”

“…In this case, the nature of the head groups is widely varied, in particular, via the functionalization of trimethylammonium (TMA) group with hydroxyalkyl substituents [24][25][26]; incor poration of cyclic and bicyclic fragments [27][28][29]; and variations in the nature of the charged atom, for exam ple, by passing from surfactants of the TMA series to triphenylphosphonium (TPP) derivatives [30]. Among the above listed surfactants, mono and dicationic (gemini) analogs are being investigated [31][32][33] A separate field of research is devoted to mono and dicationic surfactants, which contain "natural" fragments in their molecules, e.g., nucleotide bases, steroid residues, etc., and have various structures, including acyclic and macrocyclic analogs with spac ers of different length and different numbers of hydro phobic fragments [34][35][36][37][38][39][40][41].…”

Synthesis and antimicrobial activity of pyrimidinophanes with two uracil units and bridging nitrogen atoms

“…Moreover, introducing an n-decyl substituent into both uracil moieties caused a sharp decrease of bacteriostatic and fungistatic activity of the macrocycles (pyrimidinophanes IVa -b and VIa -b). Such differences in activity was probably explained by the different aggregation properties of the pyrimidinophanes (I, IIa, IIb and IIIa -b -VIa -b) in aqueous solutions [8]. This could affect passage of the macrocycles through cell membranes.…”