Imidazole derivatives as absorption probes for pluronics core-shell aggregates micropolarity investigation

Abstract

Their specific absorption parameters, sensitive to changes in micropolarity, were calibrated using the reference curves carried out in homogeneous tetraethyleneglycol/water mixtures. The probes were able to detect changes in the micelle micropolarity induced by hydration. Thus, with the help of calibration solutions, the effective local hydration of the polymeric chain sensed by the molecular probe solubilized in the guest aggregate was quantified and hypothetical relative locations of the probes in micelles have been proposed. The probes evidence differences in the micropolarity function of the structure (nature) and concentration of the Pluronic block copolymers.Introduction. The investigation of the self-organization of polymers in solutions is of fundamental and applicative interest. The triblock copolymers, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO), Pluronics, are the focus of many researchers for their important industrial applications (detergency, cosmetics, emulsification, solubilization) and interesting aggregation properties in different solutions [1][2][3][4][5][6][7][8]. When mixed with water or oil, they form aggregates of various shapes and sizes [9][10][11]. Their preparation and properties have been reviewed in a series of publications and books [12][13][14][15]. In ternary (Pluoronic/oil/water) systems they present a rich structural polymorphism [16,17]. Many phase diagrams have been reported, and it has been established that the type of self-assembled microstructure depends on the block copolymer molecular weight, the PEO/PPO block ratio, the solvent type, and the polymer concentration and temperature [18][19][20][21].It is known that above a specific temperature (critical micellization temperature (CMT)) or concentration (critical micellization concentration (CMC)), PEO-PPO-PEO copolymers self-assemble in water as micelles where a hydrophobic core of PPO is surrounded by a hydrophilic shell (or corona) of hydrated PEO units. As described by a micellar model proposed by Pedersen and Gerstenberg [22], the dense spherical core is surrounded by non-interacting polymer chains. The size, shape, and kinetics of the aggregate formation are concentration-and temperature-dependent [9,10,23,24]. As the PPO core may contain some PEO and water, the interface between core and shell regions is not as distinct as in the case of the surfactant micelles in aqueous solution [9,10,22,23].Molecular probes (especially fluorescence probes) have been used by us to characterize nonionic poly(oxyethylenic) surfactant micelles [25][26][27][28][29] and polymeric micelles [30] and to study interactions of poly(oxyethylenic) surfactants with PEO [31], poly(acrylic acid) [32], and globular proteins [33]. The micropolarity variation in reverse micelles (RM) of nonionic PEO surfactants of the alkyl ether type (Brij 30), alkyl-aryl ethers (Triton X-100), and of Pluronics L62, L64, P123, and F127 copolymers has been studied using a UV-vis absorption probe, 4-nitropyridine-Noxide (NP) [29,34,35...

Molecular interactions between Pluronic F127 and the peptide tritrpticin in aqueous solution

“…Fluorescence spectroscopy studies have shown that the CMC of F127 depends on the temperature. For example, at 30 and 35°C, CMC equals 2.23 × 10 −5 and 1.03 × 10 −5 mol kg −1 , respectively [34]. Overall, the temperature, above which F127 micelles are formed, displays an inverse dependence on the F127 (logarithmic) composition, as demonstrated by Lin and Alexandridis [35].…”

“…Accordingly, if the increase of an F127 concentration is beyond ca 250 μmol L −1 , there is a pronounced increase in fluorescence until a plateau was attained past ca 500 μmol L −1 , which can be ascribed to the critical micellar concentration (CMC) for the F127, at the experiment temperature 25°C. There are, however, conflicting CMC values for F127 reported in the literature obtained through different methods, solvent and temperature conditions, as well as different manufacturers and batch [34]. This may be probably due to the degree of purity of the product supplied by different manufacturers.…”