Fuyou Ke

Active control of surface properties and aggregation behavior in amino acid-based Gemini surfactant systems

Two types of Gemini surfactants containing a disulfide bond in the spacer, sodium dilauroyl cystine (SDLC) and sodium didecamino cystine (SDDC), were synthesized, and their surface properties and aggregation behavior in aqueous solution were studied by means of surface tension measurements, dynamic light scattering (DLS), transmission electron microscopy (TEM), and fluorescence. During the transition of the Gemini surfactants to their corresponding monomers through the reduction of disulfide bonds, the surface tensions of their aqueous solutions, as well as their aggregation behavior, changed greatly. The reduction of SDLC and SDDC led to disruption of the vesicle, and the oxidation of corresponding monomers to Gemini surfactants led to vesicle re-formation. These results demonstrated the control of surface properties and aggregation behavior by the reversible transition between the Gemini surfactant and its monomer via reduction/oxidation reactions.

Endowing catanionic surfactant vesicles with dual responsive abilities via a noncovalent strategy: introduction of a responser, sodium cholate†

A noncovalent strategy is proposed for endowing responseless catanionic surfactant (a mixture of cationic and anionic surfactants) aggregates with responsive abilities by addition of a responser. In this strategy, the composition of catanionic surfactant can be carefully selected to render aggregates sensitive to added responsers, and the responsers can be chosen from plenty of commercialized candidates, which bear responsive groups and will be noncovalently incorporated into the aggregates. In this paper, we report an illustrative example for the strategy: dual-responsive vesicles are realized by simply adding a responser, SC (sodium cholate), to a stimuli-inert DEAB/SDS (dodecyl triethyl ammonium bromide/sodium dodecyl sulfate) vesicular aqueous solution at a low responser/surfactant molar ratio of 0.045. The resultant DEAB/SDS/SC aggregates undergo reversible transitions between vesicles and micelles in response to temperature or pH variations. Possible mechanisms for these responsive behaviors are speculated, where the temperature-responsive hydroxyl groups and pH-responsive carboxylate group of SC are thought to be crucial. This responsive ability-endowing noncovalent strategy shows potential as a general, versatile, and economical method for fabricating stimuli-responsive self-assemblies.

Characterizing DNA Condensation and Conformational Changes in Organic Solvents

Organic solvents offer a new approach to formulate DNA into novel structures suitable for gene delivery. In this study, we examined the in situ behavior of DNA in N, N-dimethylformamide (DMF) at low concentration via laser light scattering (LLS), TEM, UV absorbance and Zeta potential analysis. Results revealed that, in DMF, a 21bp oligonucleotide remained intact, while calf thymus DNA and supercoiled plasmid DNA were condensed and denatured. During condensation and denaturation, the size was decreased by a factor of 8–10, with calf thymus DNA forming spherical globules while plasmid DNA exhibited a toroid-like conformation. In the condensed state, DNA molecules were still able to release the counterions to be negatively charged, indicating that the condensation was mainly driven by the excluded volume interactions. The condensation induced by DMF was reversible for plasmid DNA but not for calf thymus DNA. When plasmid DNA was removed from DMF and resuspended in an aqueous solution, the DNA was quickly regained a double stranded configuration. These findings provide further insight into the behavior and condensation mechanism of DNA in an organic solvent and may aid in developing more efficient non-viral gene delivery systems.

Improving the mechanical properties of cellulose diacetate fibers via using an ionic liquid as processing solvent

The solutions of cellulose diacetates (CDA) in ionic liquids, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) and 1-butyl-3-methylimidazolium formate ([BMIM]COOH), have been investigated to identify the solvent for optimal CDA fiber performance. The CDA/[BMIM]Cl and CDA/[BMIM]BF4 solutions both behave as typical shear-thinning fluids that are beneficial for fiber spinning. The CDA/[BMIM]Cl solution exhibits higher flowability and spinnability than the CDA/[BMIM]BF4 solution. CDA fibers with compact morphology and smooth surface have been fabricated from the [BMIM]Cl solution. The tensile strength of the resulting CDA fibers (3.00 cN per dtex) is significantly improved over that of commercial CDA fibers (1.44 cN per dtex), even when the commercial fibers (3.83 dtex) are thinner than the new CDA fibers (5.20 dtex). The present method to fabricate CDA fibers with improved mechanical properties can be directly used for the production of fabric yarns and garments.

The self-aggregation behaviour of amphotericin B-loaded polyrotaxane-based triblock copolymers and their hemolytic evaluation

As part of our continuing research work, studies toward the self-aggregation behaviour of amphiphilic triblock copolymers containing β-CD-Pluronic F127 polyrotaxane as a central block and hydrophilic brush-like PPEGMA as flanking blocks in aqueous solution were conducted by using dynamic and static light scattering (DLS and SLS) analyses and transmission electron microscopy (TEM). These self-aggregates are characterized by a unique random coil structure. Their hydrodynamic radius (Rh) and radius of gyration (Rg) decrease as the number of the entrapped β-CD molecules increases, while the core of the random coils becomes looser due to the increase of the rigidity and steric hindrance of the brush-like polymer chains. Interestingly, it was observed that the morphology of the aggregates changes greatly after loading amphotericin B (AmB). According to the DLS/SLS and TEM results, it was speculated that a solid sphere is formed, and that the density of spheres increases as the number of entrapped β-CDs increases. For these self-aggregates, as the number of entrapped β-CDs increases, their drug-loading content (DLC) and drug-loading efficiency (DLE) for AmB increases, while their hemolytic activity against rabbit erythrocytes decreases. It appears that the multiple hydrogen-bonding interactions between AmB and the entrapped β-CDs make a significant contribution to the morphology change of the self-aggregates and their high loading capability for AmB.

Ion Competition in Condensed DNA Arrays in the Attractive Regime

Physical origin of DNA condensation by multivalent cations remains unsettled. Here, we report quantitative studies of how one DNA-condensing ion (Cobalt(3+) Hexammine, or Co(3+)Hex) and one nonDNA-condensing ion (Mg(2+)) compete within the interstitial space in spontaneously condensed DNA arrays. As the ion concentrations in the bath solution are systematically varied, the ion contents and DNA-DNA spacings of the DNA arrays are determined by atomic emission spectroscopy and x-ray diffraction, respectively. To gain quantitative insights, we first compare the experimentally determined ion contents with predictions from exact numerical calculations based on nonlinear Poisson-Boltzmann equations. Such calculations are shown to significantly underestimate the number of Co(3+)Hex ions, consistent with the deficiencies of nonlinear Poisson-Boltzmann approaches in describing multivalent cations. Upon increasing the concentration of Mg(2+), the Co(3+)Hex-condensed DNA array expands and eventually redissolves as a result of ion competition weakening DNA-DNA attraction. Although the DNA-DNA spacing depends on both Mg(2+) and Co(3+)Hex concentrations in the bath solution, it is observed that the spacing is largely determined by a single parameter of the DNA array, the fraction of DNA charges neutralized by Co(3+)Hex. It is also observed that only ∼20% DNA charge neutralization by Co(3+)Hex is necessary for spontaneous DNA condensation. We then show that the bath ion conditions can be reduced to one variable with a simplistic ion binding model, which is able to describe the variations of both ion contents and DNA-DNA spacings reasonably well. Finally, we discuss the implications on the nature of interstitial ions and cation-mediated DNA-DNA interactions.

Solution behavior of copolymers with poly(ethylene oxide) as the “hydrophobic” block

Block copolymers containg poly(ethylene oxide) (PEO) have been widely used in biomedical applications. The PEO block is generally treated as the hydrophilic moiety. In this work, we demonstrated that PEO could serve as the “hydrophobic” block under certain conditions by using PEO-b-poly(vinyl alcohol) (PEO-b-PVA) as the example. Water is a non-selective solvent for both of the blocks, however, the addition of NaCl decreases the solubility of PEO in aqueous solution while it shows no effect on the PVA block. With the solubility of PEO being deteriorated by adding NaCl, PEO-b-PVA exhibited amphiphilic feature in aqueous solution with PEO being the “hydrophobic” block. Therefore, by just adding salts, uniform gel-like particles were formed by PEO-b-PVA of proper block ratio. These solid particles formed by dual hydrophilic copolymers with excellent biocompability may have great potential in biomedical applications.

Phase Separation in Mixtures of Ionic Liquids and Water

The phase separation of ionic liquids (ILs) in water is studied by laser light scattering (LLS). For the ILs with longer alkyl chains, such as [C(8)mim]BF(4) and [C(6)mim]BF(4) (mim = methylimidazolium), macroscopic phase separation occurs in the mixture with water. LLS also reveals the coexistence of the mesoscopic phase, the size of which is in the order of 100-800 nm. In aqueous mixtures of ILs with shorter alkyl chains, such as [C(4)mim]BF(4), only the mesoscopic phase exists. The mesoscopic phase can be effectively removed by filtration through a 0.22 μm filter. However, it reforms with time and can be enhanced by lowering the temperature, thus indicating that it is controlled by thermodynamics. The degree of mesoscopic phase separation can be used to evaluate the miscibility of ILs with water. This study helps to optimize the applications of ILs in related fields, as well as the recycling of ILs in the presence of water.

Controlling the morphology and property of carbon fiber/polyaniline composites for supercapacitor electrode materials by surface functionalization

The effect of surface functionalization of carbon materials on the morphology and performance of carbon/polymer composite materials for supercapacitor electrodes was investigated here. Three kinds of functionalized carbon fibers were prepared by the simple chemical modification of carbon fiber, named oxidated carbon fiber (OCF), amino-functionalized carbon fiber (AFCF) and aminated triazine functionalized carbon fiber (ATFCF). Then functionalized carbon fibers were used to fabricate nanostructural polyaniline/CFs composites (PANI/OCF, PANI/AFCF, PANI/ATFCF) by electrochemical in situ polymerization under pulse current. The chemical compositions and morphologies of these PANI/CFs composites were studied by FTIR, Raman spectra and SEM. It was found that PANI on OCF composites displayed a disordered nanofiber structure owing to the non-covalent connection between PANI with OCF. Conversely, PANI grew on the surface of AFCF and ATFCF in an ordered fashion due to chemically covalent connection, exhibiting nanowire arrays and petal-like nanosheets, respectively. It hints that the morphology of PANI/CFs composites can be effectively adjusted by molecular structural design of functional groups on the functionalized CF. The electrochemical properties of these PANI/CF composites were evaluated by an electrochemical workstation. In comparison with noncovalent PANI/OCF composites, the strong covalent interactions together with the ordered nanostructures of PANI/AFCF and PANI/ATFCF facilitated faster charge transfer, smaller internal resistance and better mechanical properties, resulting in improved electrochemical performance.

Controllable preparation and properties of active functional hybrid materials with different chromophores

A convenient and efficient strategy for preparing active functional hybrid materials was proposed based on an investigation of the controllable preparation of a series of anthracene-containing organic–inorganic functional hybrid materials with active ethylene groups. These functional hybrid materials with different active vinyls were controllably prepared through a Heck reaction with octavinyl-polyhedral oligomeric silsesquioxane (OV-POSS) as the raw material by adjusting the feed ratio. Their structures and properties were characterized and evaluated by various measurements. The influence of molecular structure on the optical properties of the resulting hybrids was investigated in detail. It was found that the incorporation of nano-sized inorganic polyhedral oligomeric silsesquioxane (POSS) can efficiently prevent aggregation of hybrid molecules owing to the prohibition of π–π stacking between chromophore groups, which was also confirmed by theoretical simulation. Simultaneously, thermogravimetric analysis (TGA) results also show that the inorganic POSS causes the good thermal stabilities of the hybrids.