Conductometric and fluorometric investigations on the mixed micellar systems of cationic surfactants in aqueous media

ROS-responsive celastrol-nanomedicine alleviates inflammation for dry eye disease

Dry eye disease (DED) is a major global eye disease leading to severe eye discomfort and even vision impairment. The incidence of DED has been gradually increasing with the high frequency of use of electronic devices. It has been demonstrated that celastrol (Cel) has excellent therapeutic efficacy in ocular disorders. However, the poor water solubility and short half-life of Cel limit its further therapeutic applications. In this work, a reactive oxygen species (ROS) sensitive polymeric micelle was fabricated for Cel delivery. The micelles improve the solubility of Cel, and the resulting Cel loaded micelles exhibit an enhanced intervention effect for DED. Thein vitroresults demonstrated that Cel-nanomedicine had a marked ROS responsive release behavior. The results ofin vitroandin vivoexperiments demonstrated that Cel has excellent biological activities to alleviate inflammation in DED by inhibiting TLR4 signaling activation and reducing pro-inflammatory cytokine expression. Therefore, the Cel nanomedicine can effectively eliminate ocular inflammation, promote corneal epithelial repair, and restore the number of goblet cells and tear secretion, providing a new option for the treatment of DED.

Hydration of ions in confined spaces and ion recognition selectivity

The hydration of ions in confined spaces, such as the interior of ion-exchange resins, micelles, and surface monolayers, is discussed on the basis of results obtained with X-ray absorption fine structure studies, electrophoresis, and ion-transfer voltammetry. The general trends are that anions are partly dehydrated therein, whereas cations are likely to keep their first hydration shells. For bromide ions, the hydration numbers under various circumstances have been determined. The extents of dehydration depend not only on the structure of the cationic sites electrostatically attracting bromide ions but also on whether the cationic sites are exposed to a solution or are effectively shielded from it. These findings will be useful for designing the systems for ionic recognition and separation.

Unusual behavior of CMC for binary mixtures of alkyltrimethylammonium bromides: Dependence on chain length difference

The critical micelle concentrations (CMC) of binary mixtures of alkyltrimethylammonium bromides (CnTAB) were measured by a conductivity method. The CMCs of C12TAB-C14TAB and C14TAB-C16TAB systems exhibit the usual behavior, namely a monotonic decrease of the CMC with the mole fraction of the longer chain surfactant. However, the CMC behaviors of C10TAB-C16TAB, C11TAB-C16TAB, C12TAB-C16TAB, and C11TAB-C14TAB are unusual. The behaviors of the CMCs with mole fraction for these systems consist of three regions, of which the first is characterized by a very small decrease of the CMC in the range of low mole fraction, followed by a second where there is an abrupt decrease of the CMC, and a third where the CMCs exhibit their usual behavior. The molecular interaction parameter omega is almost equal to zero for mixtures that have the usual CMC behavior, but is small and positive for those systems with unusual CMCs. We infer that for very low mole fractions of C16TAB, the C16TA ion in the C12TAB-C16TAB system penetrates imperfectly into the micelle and its two methylene groups exist outside the micelle.

Hydration Structures of Bromides on Cationic Micelles

The peripheral structures of bromides on dodecyltrimethylammonium bromide (DTAB) and hexadecyltrimethylammonium bromide (HTAB) micelles have been studied by X-ray absorption fine structure (XAFS) at the Br-K edge. The XAFS spectra indicate that water is a dominant scattering group for Br- even in these micellar solutions. However, the oscillation intensity decreases with increasing micellar concentration, suggesting that the bromides are dehydrated to some extent when they are bound to the micelles. A XAFS analysis routine gives unusually short Br-O (water) distances and is inapplicable to the present systems. This comes from the structure of the first coordination shell, in which two or more scattering paths are involved. The second scattering group is obviously the head group of the surfactants forming the micelles. The detailed analysis has allowed us to estimate the hydration number of the bromides bound on the DTAB and HTAB micelles (N = ca. 4.2). The assumption that all of the bromides form direct ion-associates with the head groups causes the contradiction to the results of the XAFS analyses. This strongly implies that some of the bromides partitioned into the micelle are completely hydrated as far as their first coordination shell is concerned. Assuming that the maximum hydration number of the bromides bound to the head groups of the micelle is three, 40% of the bromides partitioned into the micelle are completely hydrated.

Thermodynamics of micelle formation of alkyltrimethylammonium chlorides from high performance electric conductivity measurements

Understanding micelle formation requires its complete thermodynamic characterization. In this work micellization of the model ionic surfactants decyltrimethylammonium chloride (DETAC), dodecyltrimethylammonium chloride (DTAC) and tetradecyltrimethylammonium chloride (TTAC) was investigated by high performance conductivity measurements, using instrumentation developed in our laboratory. The temperature dependence of the critical micelle concentration exhibits a minimum characterized by Delta(mic)H(0)=0 (endothermic to exothermic process) and the degree of micelle ionization increases slightly with increasing temperature. The temperature change of Delta(mic)S(0) indicates that the process of micellization is entropically driven. Delta(mic)G(0) is always negative and slightly temperature dependent. The temperature dependence of the thermodynamic parameters is discussed in terms of the alkyl chain length and nature of the counterion. The micellization process is more favourable for surfactants with longer alkyl chain length and larger (less hydrated) counterions.