Giant vesicles of a single-tailed chiral cationic surfactant, (1R,2S)-(–)-N-dodecyl-N-methylephedrinium bromide, in water

Engineering hollow mesoporous silica nanoparticles to increase cytotoxicity

Hollow mesoporous silica nanoparticles (HMSNs) consist of a network of cavities confined by mesoporous shells that have emerged as promising tools for drug delivery or diagnostic. The physicochemical properties of HMSNs are dictated by the synthesis conditions but which conditions affect which property and how it impacts on biological interactions is unclear. Here by changing the concentration of the structure-directing agent (SDA), the pH and the ratio between SDA and added salt (NaCl) we determine the effects in size, morphology, surface charge and density or degree of compaction (physicochemical properties) of HMSNs and define their impact on their biological interactions with human colon cancer or healthy cells at the level of cellular uptake and viability. Increased size or density/degree of compaction of HMSNs increases their cytotoxicity. Strikingly, high salt concentrations in the synthesis medium leads to a spiky-shell morphology that provokes nuclear fragmentation and irreversible cell damage turning HMSNs lethal and unveiling intrinsic therapeutic potential. This strategy may open new avenues to design HMSNs nanoarchitectures with intrinsic therapeutic properties without incorporation of external pharmaceutical ingredients.

Thermodynamically stable vesicle formation of biodegradable double mPEG-tailed amphiphiles with sulfonate head group

The development of efficient, biodegradable and biocompatible surfactants has become a pressing need because of adverse effects of surface-active compounds on the aquatic environment and human health. Cleavable surfactants containing a labile functional group have the ability to eliminate some of these problems. Consequently, PEGylated amphiphiles have found widespread applications in pharmaceutics, household purposes, and drug delivery. Herein we report synthesis and characterization of two novel amphiphiles which to our knowledge are the first examples of double PEG-tailed amphiphiles with an anionic head group. Considering their chemical structure, they are expected to be biodegradable, biocompatible, milder and less irritant than conventional surfactants. The solution behavior of these newly developed amphiphiles was thoroughly investigated in aqueous buffer (pH 7.0) at 25 °C. The surface activity of the compounds in aqueous buffer was studied by surface tension measurements. The self-assembly properties were investigated by various techniques such as fluorescence and NMR spectroscopy, dynamic light scattering, transmission electron microscopy, atomic force microscopy, and isothermal titration calorimetry. Both molecules were found to be surface active in water and exhibit spontaneous vesicle formation in the absence of any additives at room temperature. As in the cases of conventional surfactants, the self-assembly is driven by the hydrophobic effect. The vesicles produced in aqueous media were shown to encapsulate hydrophobic dyes and exhibit structural transitions upon addition of salts. The sensitivity of the vesicles to change in environments qualifies them for potential use in drug delivery.

Spontaneous vesicle formation by biodegradable novel double mPEG-tailed amphiphiles.

Micelles of the chiral biocompatible surfactant (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB): molecular dynamics and fragmentation patterns in the gas phase

RATIONALE

The study of self-assembly processes of surfactant molecules in the gas phase is of great interest for several theoretical and technological reasons related to their possible exploitation as drug carriers, protein shields and cleaning agents in the gas phase.

METHODS

The stability and fragmentation patterns of singly and multiply charged (either positively or negatively) aggregates of the surfactant (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethyl ammonium bromide (DMEB) in the gas phase have been studied by ion mobility mass spectrometry and tandem mass spectrometry. Molecular dynamics (MD) simulations of positively and negatively singly and multiply charged DMEB aggregates have been performed to obtain structural and energetics information. Finally, in order to ascertain some clues on the DMEB growth mechanism, quantum mechanics calculations were carried out.

RESULTS

It has been evidenced that positively and negatively singly charged aggregates at low collision energy decompose preferentially by loss of only one DMEB molecule. Increasing the collision energy, the loss of neutrals becomes increasingly abundant. Multiply charged DMEB aggregates are unstable and decompose forming singly charged monomers or dimers. MD simulations show reverse micelle-like structures with polar heads somewhat segregated into the aggregate interior. Finally, a good correlation between experimental and calculated collisional cross sections (CCS) was found.

CONCLUSIONS

The fragmentation pathways of DMEB charged species evidenced for singly charged aggregates exhibit features similar to that of other detergent aggregates, but multiply charged aggregates showed a system-specific behavior. QM calculations on the optimized structures (2¹⁺ , 3¹⁺ , 1^1- and 2^1- ) indicate that the most determinant interactions are due to an OH---Br hydrogen bonding that is also involved in the link between monomeric DMEB units. The MD models gave CCS values in good agreement with experimental ones, evidenced by a less strict reverse micelle-like structure and a reasonably spread bromine anion distribution Copyright © 2017 John Wiley & Sons, Ltd.

Electrospray ion mobility mass spectrometry of positively and negatively charged (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide aggregates

RATIONALE

Self-assembling processes of surfactants in the gas phase constitute a developing research field of interest since they allow information to be gained on the peculiar structural organization of these aggregates, on their ability to incorporate from small molecules up to proteins and on their possible use as carriers of drugs in the gas phase or as cleaning agents and exotic reaction media.

METHODS

The mass spectra of charged aggregates of the chiral surfactant (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB) in the gas phase have been recorded using a Synapt G2-Si mass spectrometer in the positive and negative ion mode. For comparison purposes, the mass spectra of sodium bis(2-ethylhexyl)sulfosuccinate and sodium octane sulfonate aggregates have also been recorded under the same experimental conditions. The collisional cross sections of positively and negatively charged DMEB aggregates were obtained through an appropriate calibration of the measured drift times.

RESULTS

For all the surfactants investigated, it has been found that there is a lowest and a highest limit of the aggregation number at each charge state: no aggregates are found outside this range. Moreover, the occurrence at each aggregation number and extra charge of a unique value of drift time points toward aggregates whose conformations do not show discernible shape change in the experiment time scale. The analysis of the collisional cross sections emphasizes that the DMEB aggregates are nearly spherical clusters somewhat affected by the charge state and constituted by interlaced polar and apolar domains.

CONCLUSIONS

The analysis of all the experimental findings indicates that in the gas phase DMEB forms supramolecular aggregates characterized by an internal organization whose stability is triggered by the charge state. The comparison of the behavior of DMEB aggregates with that of sodium bis(2-ethylhexyl)sulfosuccinate and sodium octane sulfonate aggregates allows us to highlight the effects on the aggregate organization in gas phase due to nature of the head group and alkyl chain steric hindrance.

The UV Spectroscopic Determination of Two Critical Micelle Concentrations of Domiphen Bromide in Solutions with KBr and Calculations of the Packing Parameter

Three different forms of the surface-active domiphen cations were detected by the UV spectroscopy in aqueous solutions of domiphen bromide, eventually with KBr additive. In sufficiently dilute solutions there are free domiphen cations, which aggregate into two types of micelles at two distinct concentrations, interpreted as the first and second critical micelle concentration, cmc and cmc2. From the logarithmic dependences of cmc and cmc2 on the bromide concentrations the corresponding degrees of counterion binding were estimated. Conformation analysis of the domiphen cation was performed and the packing parameters of the lowest energy conformers were calculated. The observed spectral shifts and the calculated packing parameters suggest that two conformers of domiphen cation with different arrangement of the phenoxyethyl group are responsible for the respective formation of two types of micelles.

Self-assembly and morphology control of new L-glutamic acid-based amphiphilic random copolymers: giant vesicles, vesicles, spheres, and honeycomb film

New amphiphilic random copolymers containing hydrophobic dodecyl (C12) chain and hydrophilic L-glutamic acid were synthesized, and their self-assembly in solution as well as on the solid surfaces was investigated. The self-assembly behavior of these polymers are largely dependent on their hydrophilic and hydrophobic balances. The copolymer with a more hydrophobic alkyl chain (∼90%) self-assembled into giant vesicles with a diameter of several micrometers in a mixed solvent of ethanol and water. When the hydrophobic ratio decreased to ca. 76%, the polymer self-assembled into conventional vesicles with several hundred nanometers. The giant vesicles could be fused in certain conditions, while the conventional vesicles were stable. When the content of the hydrophilic part was further increased, no organized structures were formed. On the other hand, when the copolymer solutions were directly cast on solid substrates such as silicon plates, films with organized nanostructures could also be obtained, the morphology of which depended on solvent selection. When ethanol or methanol was used, spheres were obtained. When dichloromethane was used as the solvent, honeycomb-like morphologies were obtained. These results showed that through appropriate molecular design, random copolymer could self-assemble into various organized structures, which could be regulated through the hydrophobic/hydrophilic balance and the solvents.

Effect of hydrogen bonding on the physicochemical properties and bilayer self-assembly formation of N-(2-hydroxydodecyl)-L-alanine in aqueous solution

The aggregation behavior of N-(2-hydroxydodecyl)-L-alanine (C12HAla) and N-(n-dodecyl)-L-alanine (C12Ala) was studied in aqueous buffer (pH 12) over a concentration range above their critical aggregation concentration (cac). The C12HAla amphiphile has two cacs in contrast to only one cac value for C12Ala. The micropolarity and microviscosity of the aggregates were studied by use of pyrene and 1,6-diphenyl-1,3,5-hexatriene, respectively, as fluorescent probes. Dynamic light scattering was used to measure the average hydrodynamic diameter and size distribution of the aggregates. Large size, high microviscosity, and low micropolarity values of the aggregates suggested the formation of bilayer structures in dilute solutions of C12HAla. In contrast, C12Ala was observed to form micelles. Transmission electron micrographs of dilute and moderately concentrated solutions of C12HAla revealed the existence of spherical vesicles and branching tubular structures, respectively. Comparison of the aggregation behavior of these amphiphiles to that of C12Ala and the FT-IR spectrum suggested that intermolecular hydrogen-bonding interactions between adjacent hydrocarbon chains through the -OH and -NH- groups of C12HAla are responsible for bilayer formation. The mechanism of nanotube formation was discussed. The temperature dependence of aggregate formation of the amphiphile also was investigated.

Tunable sustained release properties of “onion-like” phospholipids multilamellar vesicles

"Onion-type" multilamellar micro-vesicles of phospholipids (spherulites) were doped with different amounts of a cationic cosurfactant ((-)N-dodecyl-N-methylephedrinium bromide) for the purpose of controlling the sustained release of anionic drugs. Three weak acid probes (methyl red, chlorophenol red, and ibuprofen) were encapsulated in the vesicles as drug models. The kinetics and rate of release were studied by absorption spectroscopy and HPLC. The effect of probe charge (pH above and below pKa of the probes), of cosurfactant concentration and of added salt was investigated. It was found that, above pKa (i.e., when the probes are anionic), the release can be almost totally inhibited by doping the vesicles with 2.4 wt% of cationic cosurfactant. The release properties can even be finely tuned by controlling the amounts of the cosurfactant. Salt and pH effects demonstrate the role of electrostatic interactions in sustaining the release.

Characterization of micelle formation of dodecyldimethyl-N-2-phenoxyethylammonium bromide in aqueous solution

Aggregation behavior of dodecyldimethyl-N-2-phenoxyethylammonium bromide commonly called domiphen bromide (DB) was studied in aqueous solution. The Krafft temperature of the surfactant was measured. The surfactant has been shown to form micellar structures in a wide concentration range. The critical micelle concentration was determined by surface tension, conductivity, and fluorescence methods. The conductivity data were also employed to determine the degree of surfactant counterion dissociation. The changes in Gibb's free energy, enthalpy, and entropy of the micellization process were determined at different temperature. The steady-state fluorescence quenching measurements with pyrene and N-phenyl-1-naphthylamine as fluorescence probes were performed to obtain micellar aggregation number. The results were compared with those of dodecyltrimethylammonium bromide (DTAB) surfactant. The micelle formation is energetically more favored in DB compared to that in DTAB. The 1H-NMR spectra were used to show that the 2-phenoxyethyl group, which folds back onto the micellar surface facilitates aggregate formation in DB.