Shuli Dong

Tunable Amphiphilicity and Multifunctional Applications of Ionic-Liquid-Modified Carbon Quantum Dots

During the past decade, increasing attention has been paid to photoluminescent nanocarbon materials, namely, carbon quantum dots (CQDs). It is gradually accepted that surface engineering plays a key role in regulating the properties and hence the applications of the CQDs. In this paper, we prepared highly charged CQDs through a one-pot pyrolysis with citric acid as carbon source and a room-temperature imidazolium-based ionic liquid as capping agent. The as-prepared CQDs exhibit high quantum yields up to 25.1% and are stable under various environments. In addition, the amphiphilicity of the CQDs can be facilely tuned by anion exchange, which leads to a spontaneous phase transfer between water and oil phase. The promising applications of the CQDs as ion sensors and fluorescent inks have been demonstrated. In both cases, these ionic-liquid-modified CQDs were found to possess novel characteristics and/or superior functions compared to existing ones.

Transfection efficiency of DNA enhanced by association with salt-free catanionic vesicles.

The interaction of DNA with salt-free tetradecyltrimethylammonium hydroxide and lauric acid lamellar vesicles with positive charges was investigated to probe potential applications of vesicles in DNA transfection. The aggregation morphology of the vesicles changes greatly with the addition of DNA due to the dissociation of anionic surfactants, as indicated by (1)H nuclear magnetic resonance, and the expelled surfactant molecules self-assemble into micelles at high concentrations of DNA. Salt-free cationic and anionic (catanionic) vesicles have a much higher binding saturation point with DNA at R = 2.3 (the ratio of DNA to the excess positive charge in vesicles) than formerly reported salt-containing systems, implying high transfection efficiency. DNA retains its native stretched state during the interaction process. This very interesting result shows that catanionic vesicles could help transport undisturbed and extended DNA molecules into the target cells, which is of great importance in gene delivery, nanomedicine field, and controlling the formation of certain morphological aggregates.

Transition from Vesicle Phase to Lamellar Phase in Salt-Free Catanionic Surfactant Solution

A salt-free cationic and anionic (catanionic) surfactant system was formed by mixing a double-tailed di-(2-ethylhexyl) phosphoric acid (DEHPA, commercial name P204), which is an excellent extractant of rare earth metal ions, with a single-tailed cationic trimethyltetradecylammonium hydroxide (TTAOH) in water. With the mole ratio (r) of DEHPA to TTAOH varying from 0.9 to 1, the phase transition occurred from a densely stacked vesicle phase (Lalphav) to a lamellar phase (Lalphal). Macroscopic properties, such as polarization and rheology, were measured and changed greatly during the course of the phase transition. When r was 0.96 or 0.98, the steady state shear curves exhibited two yield stress values, indicating the coexistence of the Lalphav phase and the Lalphal phase. The Lalphal phase formed in the salt-free and zero-charged system (r=1.0) is defective and undulating, which was confirmed by cryogenic transmission electron microscopy (cryo-TEM). The deuterium nuclear magnetic resonance spectra (2H NMR) showed that a single peak (singlet) split into two symmetric peaks (doublet) gradually, indicating the phase transition from the Lalphav phase to the Lalphal phase. Correspondingly, phosphorus nuclear magnetic resonance spectra (31P NMR) presented changes in both the chemical shift and the peak width, indicating that these two types of bilayer structures are of different anisotropy degrees and different viscosities. When the Lalphal phase is subjected to a certain shear force, it can be reversed to a Lalphav phase again, which was proved by rheological, 2H NMR, and 31P NMR measurements. Furthermore, a theoretical consideration about the formation of the defective and undulating Lalphal phase was taken into account from a viewpoint of energy.

Aggregation Behavior of Fluorocarbon and Hydrocarbon Cationic Surfactant Mixtures : A Study of 1H NMR and 19F NMR

The aggregation behavior and the interaction of four mixed systems for a cationic fluorocarbon surfactant, diethanolheptadecafluoro-2-undecanolmethylammonium chloride (DEFUMACl), mixing with cationic hydrocarbon surfactants, alkyltrimethylammonium chloride, CnTACl (n=12, 14, 16, and 18; where n=12 is DTACl, n=14 is TTACl, n=16 is CTACl, and n=18 is OTACl), were studied by 1H and 19F NMR in more detail. The results of 19F NMR measurements strongly indicate that in the three mixed systems of DEFUMACl/DTACl, DEFUMACl/TTACl, and DEFUMACl/CTACl at different molar fractions of fluorocarbon surfactant (alphaF=(cDEFUMACl/cDEFUMACl+cCnTACl)), with an increase of the total concentration of fluorocarbon and hydrocarbon surfactants (cT=cF+cH), the mixed micelles at the first break point and the individual DEFUMACl micelles at the second break point form. However, three different types of micelles were determined in DEFUMACl/OTACl mixtures by 19F NMR measurements, OTACl-rich and DEFUMACl-rich mixed micelles and individual DEFUMACl micelles, respectively. The chemical shifts of proton Deltadelta (1H) for -CH3 in the mixed systems of DEFUMACl/CnTACl (n=12, 14, 16, and 18) have different variation trends from the 19F NMR measurements. For the two systems of DEFUACl/DTACl and DEFUMACl/TTACl, the mixed micelles form at the first break point. At the second break point, for lower alpha F values the DTACl-rich and TTACl-rich mixed micelles form with a strong downfield shift and for higher alpha F values DEFUMACl-rich mixed micelles form with a strong upfield. For the other two systems of DEFUMACl/CTACl and DEFUMAC/OTACl, the chemical shifts of proton Deltadelta (1H) of -CH3 increase with an increase of the total concentration of DEFUMACl/CTACl or OTACl, and mixed CH- and CF-surfactant micelles form. At higher total concentration, the greater effect of fluorinated chains of DEFUMACl on CH-chains was obvious, resulting in the strong upfield chemical shifts. In cationic fluorocarbon and hydrocarbon surfactant mixtures, the different kinds of micelles observed by 19F and 1H NMR measurements could be caused by the increase in alkyl chain length of hydrocarbon surfactants with different critical micelle concentrations. Combining two theoretical models for mixing, for the four different chain-length hydrocarbon surfactants studied, one can conclude that the two components of mixtures interact with each other and form mixed micelles in two completely different ways according to their molecular properties and cmc values in a certain range of total concentrations. One is close to an ideal mixing case with the formation of one type of mixed micelles, such as the DEFUMACl/DTACl and DEFUMACl/TTACl systems. The other is a demixing case with the formation of two types of micelles, i.e., fluorocarbon-rich and hydrocarbon-rich mixed micelles, such as DEFUMACl/CTACl and DEFUMACl/OTACl systems. However, as the total concentrations of the mixed systems are high enough, the four systems tend to demix and to form individual micelles of corresponding components due to the initial respective interaction between fluorocarbon and hydrocarbon chains. That is to say, at high total concentration, the individual DEFUMACl micelles in all four systems could form. These results may be primarily directed toward acquiring an understanding of the mechanism of CF-CH mixtures in aqueous solution and secondarily directed toward providing more detailed information on nonideal mixing.

Functional materials from the covalent modification of reduced graphene oxide and β-cyclodextrin as a drug delivery carrier

We report a drug delivery system based on the covalently reduced graphene oxide (rGO) with p-aminobenzoic acid (rGO-C6H4-COOH) for the loading and targeted delivery of the anticancer drug, doxorubicin (DOX). The colloidal solution of rGO-C6H4-COOH conjugated by polyethyleneimine (PEI) and Biotin was prepared. This endows the colloidal solution of rGO-C6H4-CO-NH-PEI-NH-CO-Biotin, which presents excellent water-solubility and targeting as a drug delivery system. β-Cyclodextrin (β-CD) molecules, which are host molecules for accommodating guest molecules, such as water insoluble anticancer drugs, were introduced to reduce the cytotoxicity of the drug delivery system and to improve the biocompatibility. The drug delivery of rGO-C6H4-CO-NH-PEI-NH-CO-CD-Biotin has a ∼24.64% drug (DOX) loading ratio. The drug release behavior was pH dependent at higher DOX concentrations, but salt dependent at lower DOX concentrations, which could be exploited for controlled drug release in cancer cells. The DOX loaded on rGO-C6H4-CO-NH-PEI-NH-CO-CD-Biotin could effectively induce HepG2 cancer cell apoptosis. This can be explained by the conjugation of DOX and rGO-C6H4-CO-NH-PEI-NH-CO-CD-Biotin being able to arrest the cancer cells in the G2 phase, which is the most sensitive to the anticancer drug.

Compaction and decompaction of DNA dominated by the competition between counterions and DNA associating with cationic aggregates.

A systematic work concerning the DNA compaction and decompaction controlled by cationic surfactants, cetyltrimethylammonium with [FeCl3Br](-) (CTAFe), Br(-) (CTABr) and Cl(-) (CTACl) as counterions, respectively, was performed. We discovered that cationic surfactants with complex counterions, [FeCl3Br](-), cannot promote the decompaction of DNA like those with Br(-) and Cl(-) as counterions. The rod-like CTAFe micelles were found to remain free in supernatants and cannot directly promote any redissolution or decompaction of DNA. These interesting findings could provide a better understanding of the interaction behavior of DNA and cationic surfactants. We conclude that the fundamental reason of the DNA decompaction lies upon the electrostatic competition between the counterions and DNA for associating with the cationic aggregates. At a high concentration, the binding of counterions to cationic CTA(+) aggregates is promoted, which weakens and screens the electrostatic attraction between DNA and cationic aggregates. This could cause the decompaction of DNA as the cases of CTABr/DNA and CTACl/DNA mixtures. Our data revealed the fundamental reason of the compaction and decompaction behavior of DNA induced by cationic surfactants independently, a reasonable three-step model of the conformational changes of DNA controlled by different amounts of cationic surfactants was presented. The current work could provide a clear guidance in gene delivery, gene therapy and biomedicine fields.

Self-Assembled Switching Gels with Multiresponsivity and Chirality

A multiresponsive hydrogel material consisting of a commercial cationic surfactant and an azobenzene derivative functionalized with four carboxylic acid groups was constructed. The achiral azobenzene molecule as a gelator produces chirality at the supramolecular level in the presence of H(+). The acid-induced gelation and morphology change of supramolecular gels were investigated in detail by cryogenic transmission electron microscopy (cryo-TEM), rheological measurements, circular dichroism (CD), and (1)H NMR spectra. Based on the results, a mechanism of the intermolecular H-bond-directed gelation and supramolecular chirality was proposed. Other than the pH sensitivity, the microstructure and the chirality of the hydrogel demonstrate reversible switching behavior in response to photoirradiation, on account of the photoisomerization of the azobenzene derivative. Accordingly, a chiroptical switch comprising four different states in response to pH and light stimuli is strategically constructed. Not only does the present system provide a good opportunity for investigating the gelation-induced supramolecular chirality by symmetry breaking totally based on achiral molecules, but it also proposes a new strategy to build multiresponsive supramolecular switches as particularly attractive for the future development of functional materials.

First Fluorinated Zwitterionic Micelle with Unusually Slow Exchange in an Ionic Liquid

The micellization of a fluorinated zwitterionic surfactant in ethylammonium nitrate (EAN) was investigated. The freeze-fracture transmission electron microscope (FF-TEM) observations confirm the formation of spherical micelles with the average diameter 25.45 ± 3.74 nm. The micellization is an entropy-driven process at low temperature but an enthalpy-driven process at high temperature. Two sets of (19)F NMR signals above the critical micelle concentration (cmc) indicate that the unusually slow exchange between micelles and monomers exists in ionic liquid; meanwhile, surfactant molecules are more inclined to stay in micelle states instead of monomer states at higher concentration. Through the analysis of the half line width (Δν1/2), we can obtain the kinetic information of fluorinated zwitterionic micellization in an ionic liquid.

Colloidal Wormlike Micelles with Highly Ferromagnetic Properties.

For the first time, a new fabrication method for manipulating the ferromagnetic property of molecular magnets by forming wormlike micelles in magnetic-ionic-liquid (mag-IL) complexes is reported. The ferromagnetism of the mag-IL complexes was enhanced 4-fold because of the formation of wormlike micelles, presenting new evidence for the essence of magnetism generation at a molecular level. Characteristics such as morphology and magnetic properties of the wormlike micelle gel were investigated in detail by cryogenic transmission electron microscopy (Cryo-TEM), rheological measurements, circular dichroism (CD), FT-IR spectra, and the superconducting quantum interference device method (SQUID). An explanation of ferromagnetism elevation from the view of the molecular (ionic) distribution is also given. For the changes of magnetic properties (ferromagnetism elevation) in the wormlike micelle systems, the ability of CTAFe in magnetizing AzoNa4 (or AzoH4) can be ascribed to an interplay of the magnetic [FeCl3Br](-) ions both in the Stern layer and in the cores of the wormlike micelles. Formation of colloidal aggregates, i.e., wormlike micelles, provides a new strategy to tune the magnetic properties of novel molecular magnets.

Phase behavior, rheological properties, and vesicles of alkyldimethylamine oxide and fluorinated acidic surfactant mixtures

Weakly basic alkyldimethylamine oxide (CnDMAO, n = 12, 14, and 16) molecules can be protonated to form a cationic surfactant, CnDMAOH+, by an acidic fluorocarbon surfactant, 8-2-fluorotelomer unsaturated acid (C7F15CFCHCOOH), to produce the salt-free cationic and anionic (catanionic) surfactant mixtures in aqueous solution. These comparative studies on phase behavior and rheological properties of these salt-free catanionic hydrocarbon–fluorocarbon surfactant mixtures in detail clearly indicate the existence of a birefringent Lα-phase for C12DMAO/C7F15CFCHCOOH and C14DMAO/C7F15CFCHCOOH systems at 25.0 ± 0.1 °C. However, the birefringent Lα-phase of C16DMAO/C7F15CFCHCOOH system exist at 60.0 ± 0.1 °C. The birefringent Lα-phase which consists of uni- and multilamellar vesicles, and oligovesicular vesicles is independent of the hydrocarbon chain of CnDMAO at controlled temperatures. The vesicles were demonstrated by cryo-transmission electron microscopy (cryo-TEM) and negative-staining TEM images, in which pliability of the bilayer membranes decreases with the increasing length of hydrogenated chains of hydrocarbon surfactants. The formation of the salt-free catanionic Lα-phase consisting of vesicles could be induced by the strong electrostatic interaction between the cationic hydrocarbon C14DMAOH+ and the anionic fluorocarbon C7F15CFCHCOO−, C14DMAOH+ is produced through acid–base reaction of C14DMAO and C7F15CFCHCOOH. The rheological properties of micelles and vesicles in the three mixture systems were measured, which provided much more information about the hydro- and fluorocarbon surfactant mixtures. The size distribution and structural transition of these similar systems but having different length chains of hydrocarbon surfactants were studied by dynamic light scattering (DLS) and 1H and 19F NMR spectroscopy.