Preparation of micelles with azobenzene at their coronas or cores from ‘nonamphiphilic’ diblock copolymers

Micelles with azobenzene at the coronas or the cores were prepared by the micellization of nonamphiphilic diblock copolymers through hydrogen bond cross-linking. We used 4-(phenylazophenoxymethyl)styrene (AS) as the azobenzene. A poly(vinylphenol)-block-poly(AS-co-styrene) diblock copolymer (PVPh-b-P(AS-co-St)) was prepared by combination of the nitroxide-mediated living radical polymerization and the hydrolysis. The copolymer contained ca. 1 mol% of the azobenzene units in the P(AS-co-St) blocks on the basis of ¹H NMR analysis. The PVPh-b-P(AS-co-St) copolymer showed no micellization in 1,4-dioxane, the nonselective solvent. Dynamic light scattering demonstrated that the copolymer formed micelles in the presence of 1,4-butanediamine (BDA) in this solvent. ¹H NMR analysis revealed that the azobenzene moieties were located at the coronas of the micelles, because the signals of the aromatic protons originating from the azobenzene had no changes in the shape and the intensity by the micellization. UV analysis supported the presence of the azobenzene at the micellar coronas. The size of the PVPh-b-P(AS-co-St) micelles was independent of the copolymer concentration. On the other hand, the aggregation number of the micelles was dependent not only on the copolymer concentration but also on the kind of the diamine. A poly(AS-co-vinylphenol)-block-polystyrene diblock copolymer (P(AS-co-VPh)-b-PSt) formed the micelles with the azobenzene at the cores of the micelles by BDA. UV analysis demonstrated that the azobenzene at the micellar cores still had the potential to function as photorefractive switching.     

Process of destruction of large unilamellar vesicles by a nonionic detergent,octylglucoside, and size growth factor in vesicle formation from phospholipid–detergent mixed micelles

The process of vesicle solubilization and size growth by detergents, especially by octylglucoside, was examined in detail in order to elucidate the phenomena observed in the vesicle-to-micelle transition and to clarify the size-determining factor of vesicles prepared by removing detergent from phospholipid–detergent mixed micelles. In the vesicle solubilization process, when the detergent concentration in the vesicle membrane reached a critical value, the collapse of large unilamellar vesicles (LUV) into small unilamellar vesicles (SUV) was observed. This newly appeared SUV were named SUV*. The SUV* could be produced by adding an appropriate amount of detergent to the SUV prepared by an ultrasonication method so as to increase the concentration to a little over the critical value, such as, in the case of adding octylglucoside, a molar ratio of 1.0–1.1 to phospholipid in the membrane phase. The SUV* containing octylglucoside were fusible and grow time-dependently, but those containing sodium cholate were not fusible. On the basis of the SUV* data, the following problems were solved: the variety of the size of the vesicles prepared by detergent removal from mixed micelles composed of a phospholipid and different detergents, or by different removal methods; the complex appearance of turbidity or vesicle size observed in vesicle destruction and formation; the conflict between LUV and SUV in the partition behavior of detergent and the size change with addition of detergent.     

Surface activity and micellar properties of anionic gemini surfactants and their analogues

The properties of didodecyldiphenylether disulfonate gemini-type surfactants have been studied and compared to mono-alkylated and monosulfonated analogous surfactants. Dynamic and equilibrium surface tension measurements indicate that the gemini surfactants have a higher surface activity compared to that of the monoalkyl analogues. The gemini-type surfactants have much larger surface area per molecule, opposite effect of carbon number on CMC and considerable swelling of the micelles upon increasing surfactant concentration. Determination of aggregation numbers by fluorescence measurements reveals that the longer chain gemini surfactants form micelles having less than 10 molecules per micelle.     

Phasenumwandlung in mizellaren Lösungen von ionogenen Tensiden und Metallionen

Summary The time course of the phase transition in the system Th⁴⁺/dodecylsulfate/HClO₄ has been measured by kinetic photometry. In micellar solutions initially formed solid particles are slowly dissolved by solubilisation.

     

Thermal transitions in associating aqueous block copolymers: light scattering,rheology and spectroscopy

Solutions containing a polyoxy-ethylene/polyoxy-propylene/polyoxy-ethylene (PEO–PPO–PEO) block copolymer, indicated as F68, in water were investigated as a function of composition and temperature. Hydrogen nuclear magnetic resonance (¹H NMR) line width, chemical shift, self-diffusion, spin-lattice relaxation times, laser light scattering and rheological methods were used. The monomer–micelle equilibrium and the micelle–liquid crystalline phase transitions depend on the F68 content in the mixture and temperature. Significant changes in light scattering intensity and apparent hydrodynamic radius are associated to micelle formation above the critical micellar temperature (CMT). According to a Contin analysis, this behaviour is reflected in the presence of two populations in the intensity–intensity autocorrelation functions. The contributions due to molecules and micelles can be evaluated separately. No such effects are observed below the CMT. Micelle onset is also associated to variations in ¹H NMR spectra, affecting the chemical shift, line width and spin-lattice relaxation time of the PPO methyl protons and self-diffusion, as well. Spin-lattice relaxation times of PEO chains, conversely, change significantly at temperatures close to the micelle–liquid crystalline thermal transition. Similar results were obtained from the line width of ²H NMR spectra as a function of T. Significant changes in both viscous and elastic modulus were also observed and ascribed to PPO dehydration, at the CMT, as well as to squeezing and dehydration of PEO units in liquid crystal formation, respectively.     

Photophysical and Photochemical Processes in Micellar Systems

A fascinating feature inherent to aqueous surfactant solutions is the phenomenon of self-organization: above a certain critical concentration (the critical micelle concentration, CMC) detergent molecules associate spontaneously to build up structural entities of colloidal dimensions called micelles. The architecture of these agglomerates is such that the interior contains the hydrophobic alkyl chain of the amphiphile while the hydrophilic head groups are located at the surface and are in contact with bulk water. In the case of ionic micelles the interface is charged giving rise to an electrical double layer and a potential difference of up to several hundred millivolts between the micellar pseudophase and water. Thus micellar systems are microheterogeneous in character: the electrostatic potential and polarity prevailing in the interior of the aggregate differ from those of the bulk aqueous phase. A particularly attractive aspect of photochemical studies in micellar systems is the possibility of organizing the reactants at a molecular level: by comparison of the data in micelles with similar data in homogeneous solution one can learn about the molecular details of a given reaction and establish which conditions favor one pathway or another. In simple surfactant systems differences in rate and efficiency of a reaction will often be controlled by local electrostatic potentials and the compartmentalization of the reagents within the surfactant aggregates. Through the latter effect the statistics of probe distribution over the micelles becomes important in controlling fast photochemical events. Functional micelles are distinguished by the fact that the surfactant molecule contains a group which itself participates in the photoprocess. These units are unique in that self-assembly often introduces striking cooperative effects.     

Effect of inorganic salts on the micellar behaviour of ethylene oxide-propylene oxide block copolymers in aqueous solution

The aggregation behaviour of two ethylene oxide-propylene oxide block copolymers (PEO-PPO-PEO) in aqueous solution has been investigated in the presence of added salts (KCNS, KI, KBr, KCl and KF) by viscosity, cloud point, light scattering, pulse gradient spin echo NMR, and solubilization measurements. The salts have a strong effect on the cloud points of the pluronics. Both P-85 and L-64 form micelles which increase in size and change into elongated shapes when the cloud point is approached. The changes of size and shape of the micelles, revealed by the intrinsic viscosity and rheological properties, seem to occur at the same temperature relative to the cloud point, independent of the nature of the salt. The onset of micelle formation is also shifted in the same direction as the cloud point by the salts, but by a much smaller amount.     

Spectral studies of N-nonyl acridine orange in anionic, cationic and neutral surfactants

The spectroscopic and photophysical properties of N-nonyl acridine orange – a metachromatic dye useful as a mitochondrial probe in living cells – are reported in water and microheterogeneous media: anionic sodium dodecylsulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and neutral octylophenylpolyoxyethylene ether (TX-100). The spectral changes of N-nonyl acridine orange were observed in the presence of varying amount of SDS, CTAB and TX-100 and indicated formation of a dye–surfactant complex. The spectral changes were also regarded to be caused by the incorporation of dye molecules to micelles. It was proved by calculated values K_b and f in the following order: K_b TX-100 > K_b CTAB > K_b SDS and f_TX-100 > f_CTAB > f_SDS. NAO binds to the micelle regardless the micellar charge. There are two types of interactions between NAO and micelles: hydrophobic and electrostatic. The hydrophobic interactions play a dominant role in binding of the dye to neutral TX-100. The unexpected fact of the binding NAO to cationic CTAB can be explained by a dominant role of hydrophobic interactions over electrostatic repulsion. Therefore, the affinity of NAO to CTAB is smaller than TX-100. Electrostatic interactions play an important role in binding of NAO to anionic micelles SDS. We observed a prolonged fluorescence lifetime after formation of the dye–surfactant complex τ_SDS > τ_TX-100 > τ_CTAB > τ_water, the dye being protected against water in this environment. TX-100 is found to stabilize the excited state of NAO which is more polar than the ground state. Spectroscopic and photophysical properties of NAO will be helpful for a better understanding of the nature of binding and distribution inside mammalian cells.     

Chemometrics-assisted spectrophotometric methods for simultaneous determination and complexation study of Fe(III), Al(III) and V(V) with morin in micellar media

Evolutionary factor analysis (EFA) and rank annihilation factor analysis (RAFA) were applied to resolve the two-way equilibrium spectrophotometric data belonging to the complexes of Fe(III), Al(III) and V(V) with morin (3,5,7,20,40-penta hydroxy flavone) as chelating agent in triton X-100 micellar media. Then, partial least square regression combined with genetic algorithm for wavelength selection (GA-PLS) was used for simultaneous determination of the metal ions. The parameters controlling behavior of the system were investigated and optimum conditions were selected. The predictive abilities of partial least squares regression (PLS) and genetic algorithm-partial least squares regression (GA-PLS) were examined in simultaneous determination of ternary mixtures of metal ions over the concentration range of 17.0-170.0ngml(-1), 25.0-180.0ngml(-1) and 40.0-325.0ngml(-1) for Fe(III), Al(III) and V(V), respectively. The relative standard errors for prediction of the ions in synthetic mixtures were lower than 5% and the mean recoveries in the tap water spiked samples were 104.2 and 101.7% for PLS and GA-PLS, respectively.     

The synthesis of biodegradable graft copolymer cellulose-graft-poly(L-lactide) and the study of its controlled drug release

According to the concept of green chemistry and sustainable development, a new biodegradable copolymer comprised of hydrophobic poly(l-lactide) (PLLA) segments and hydrophilic cellulose segment (cellulose-g-PLLA) was designed and synthesized. The structure of the copolymer was characterized by (1)H NMR, FT-IR, (13)C NMR, DSC and WAXD. The cytotoxicity study shows that cellulose-g-PLLA exhibits good biocompatibility. The copolymer can self-assemble into micelles in water with the hydrophobic PLLA segments at the cores of micelles and the hydrophilic cellulose segments as the outer shells. Transmission electron microscopy (TEM) shows that the micelles exhibit nanospheric morphology within a size range of 30-80nm. The drug loaded micelles formed by the copolymer in aqueous media show sustained drug release which indicates their potential applicability in drug carrier.