Yazhuo Shang

Structure of the complex monolayer of gemini surfactant and DNA at the air/water interface.

The properties of the complex monolayers composed of cationic gemini surfactants, [C(18)H(37)(CH(3))(2)N(+)-(CH(2))(s)-N(+)(CH(3))(2)C(18)H(37)],2Br(-) (18-s-18 with s = 3, 4, 6, 8, 10 and 12), and ds-DNA or ss-DNA at the air/water interface were in situ studied by the surface pressure-area per molecule (π-A) isotherm measurement and the infrared reflection absorption spectroscopy (IRRAS). The corresponding Langmuir-Blodgett (LB) films were also investigated by the atomic force microscopy (AFM), the Fourier transform infrared spectroscopy (FT-IR), and the circular dichroism spectroscopy (CD). The π-A isotherms and AFM images reveal that the spacer of gemini surfactant has a significant effect on the surface properties of the complex monolayers. As s ≤ 6, the gemini/ds-DNA complex monolayers can both laterally and normally aggregate to form fibril structures with heights of 2.0-7.0 nm and widths of from several tens to ~300 nm. As s > 6, they can laterally condense to form the platform structure with about 1.4 nm height. Nevertheless, FT-IR, IRRAS, and CD spectra, as well as AFM images, suggest that DNA retains its double-stranded character when complexed. This is very important and meaningful for gene therapy because it is crucial to maintain the extracellular genes undamaged to obtain a high transfection efficiency. In addition, when s ≤ 6, the gemini/ds-DNA complex monolayers can experience a transition of DNA molecule from the double-stranded helical structure to a typical ψ-phase with a supramolecular chiral order.

Biophysical characterization of complexation of DNA with oppositely charged Gemini surfactant 12-3-12

The interaction between DNA and cationic gemini surfactant trimethylene-1, 3-bis (dodecyldimethylammonium bromide) (12-3-12) has been investigated by the measurements of fluorescence, surface tension, UV spectrum and circular dichroism (CD). Micelle-like structure of 12-3-12 induced by DNA appears at critical aggregation concentration (CAC), which is much lower than critical micelle concentration (CMC) of 12-3-12 in DNA-free solution. CAC is independent of DNA concentration, but the CMC of the mixed solutions of DNA and 12-3-12(CMC(mix)) increases with the increasing of DNA concentration. The surface tensions of the mixed system are higher than that of the pure surfactant solution, much different from the so-called synergistic lowering of the surface tension for other polymer-surfactant systems. Phase separation occurs after the neutralization point and the precipitate redissolves with superfluous 12-3-12. Cationic surfactant 12-3-12 can exclude ethidium bromide (EB) from the DNA/EB complex, and this process does not depend on the DNA concentration but on the charge ratio of 12-3-12 to DNA. The binding constant of EB to DNA decreases sharply at the charge ratio from 0.5 to 1.0. Circular dichroism (CD) spectra show that DNA undergoes a conformational transition from native B-form to chiral psi-phase with increasing of 12-3-12.

Interactions between ionic liquid surfactant [C12mim]Br and DNA in dilute brine

Interactions between ionic liquid surfactant [C(12)mim]Br and DNA in dilute brine were investigated in terms of various experimental methods and molecular dynamics (MD) simulation. It was shown that the aggregation of [C(12)mim]Br on DNA chains is motivated not only by electrostatic attractions between DNA phosphate groups and [C(12)mim]Br headgroups but also by hydrophobic interactions among [C(12)mim]Br alkyl chains. Isothermal titration calorimetry analysis indicated that the [C(12)mim]Br aggregation in the presence and absence of DNA are both thermodynamically favored driven by enthalpy and entropy. DNA undergoes size transition and conformational change induced by [C(12)mim]Br, and the charges of DNA are neutralized by the added [C(12)mim]Br. Various microstructures were observed such as DNA with loose coil conformation in nature state, necklace-like structures, and compact spherical aggregates. MD simulation showed that the polyelectrolyte collapses upon the addition of oppositely charged surfactants and the aggregation of surfactants around the polyelectrolyte was reaffirmed. The simulation predicted the gradual neutralization of the negatively charged polyelectrolyte by the surfactant, consistent with the experimental results.

Micellization of cationic gemini surfactant and its interaction with DNA in dilute brine.

The micellization of cationic gemini surfactant trimethylene-1,3-bis (dodecyldimethylammonium bromide) (12-3-12·2Br) was investigated and critical micelle concentrations (CMC) and thermodynamic parameters were evaluated as functions of ionic strength and temperature. The micellization of 12-3-12·2Br is entropically driven and thermodynamically favored. Raising the temperature slightly increases the CMC, while increasing the ionic strength lowers the CMC. A multi-technique study of the 12-3-12·2Br/DNA interaction and its dependence on ionic strength, temperature and DNA concentration were presented. DNA with loose coil conformation, necklace-like structure, highly ordered toroidal aggregates and coexisting of large aggregates and small structures in DNA/12-3-12·2Br system were observed. Critical aggregation concentrations (CAC), interaction saturation concentrations (C(2)), and associated thermodynamic parameters were determined. The screening effect of salt decreases the DNA/12-3-12·2Br electrostatic attraction, but favors the formation of free 12-3-12·2Br micelles or aggregates on the DNA chain. DNA acts as a separate phase contacting with the surfactant molecules and therefore CAC is independent of DNA concentration. Increasing DNA concentration postpones the appearance of free micelle in bulk phase, consequently increases the C(2). Finally an interaction mechanism between 12-3-12·2Br and DNA was proposed.

Synthesis and Characterization of Needle‐Like ZnO by Gemini Surfactant‐Assisted Hydrothermal Process

Needle‐like ZnO was synthesized by gemini surfactant‐assisted hydrothermal oxidization of zinc metal at 170°C. X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDX), and scaning electron microscopy (SEM) were used to characterize the structure features and chemical compositions of the as‐made products. The results indicated that the as‐prepared needle‐like products are hexagonal and composed of ZnO. The needle‐like ZnO at the tip was found to be 50–100 nm and its lengths ranged from 10 to 15 um. The needle grains connect with each other to form a continuous network. The unique morphology of ZnO may make it attractive to be used in many fields.

Interaction of DNA with Cationic Gemini Surfactant Trimethylene-1, 3-bis(dodecyldimethyl-ammonium bromide)and Anionic Surfactant SDS Mixed System

Abstract The interaction of DNA with cationic gemini surfactant trimethylene-1,3-bis (dodecyl dimethyl-ammonium bromide) (12-3-12) and anionic surfactant sodium dodecyl sulfate (SDS) mixed system has been investigated by measuring the fluorescence, zeta potential, UV-Vis spectrum, and circular dichroism. In the absence of SDS, owing to the electrostatic and hydrophobic interactions, 12-3-12 forms micelle-like structure on the DNA chain before the micellization in bulk phase. For the mixed system of 12-3-12 and SDS, the negative charges on SDS can compete against DNA to bind with cationic 12-3-12 because of the stronger interaction between oppositely charged surfactants, and thus, the catanionic mixed micelles are formed before the formation of DNA/12-3-12 complexes. Thereafter, the positive charges on the mixed micelles bind with DNA, and thus, the change of the zeta potential from negative to positive is distinctly different from the system without SDS. Meanwhile, the existence of SDS postpones the exclusion of ethidium bromide (EB) from DNA/EB complexes. The conformation of DNA undergoes a change from native B-form to chiral ψ-phase as binding with 12-3-12 process. Upon adding SDS to the DNA/12-3-12 complex solution, however, DNA is released to the bulk and the ψ-phase returns to B-form again.

Characterization and release kinetics of liposomes inserted by pH-responsive bola-polymer

One important thing in tumor chemotherapy is to develop the targeting, precise timing, and quantitative drug delivery/release system. According to the weak acid of tumor extracellular environment, a pH-sensitive bola-type triblock copolymer (PEGm-PDPAn-PEGm) was synthesized and mixed with phospholipid to form functional hybrid liposomes (liposome@Bola). When compared to pure liposome, the stability of the liposome@Bola was enhanced greatly and the drug leakage was inhibited at pH 7.4. However, under pH 6.0, the drug released quickly through the nanopores on the lipid bilayer created by the escape of copolymers. Under a strongly acidic environment, the drug release of liposome@Bola could be blocked again due to the coverage of free copolymers. The kinetic curves of drug release had been modeled by using some frequently used models. It was found that the release of liposome@Bola under pH 6.0 was biphasic with a slow release by means of membrane permeation and a rapid second phase which was released through nanopores on liposome membrane. The results indicated that the pH-responsive liposome@Bola could be expected to be a good potential in controllable drug delivery system.

Aqueous Two‐Phase System (ATPS) Containing Gemini (12‐3‐12,2Br−) and SDS I: Phase Diagram and Properties of ATPS

Two phases coexist in an aqueous system that contains the two surfactants cationic gemini 12‐3‐12,2Br− and anionic SDS. An aqueous two‐phase system (ATPS) is formed in a narrow region of the ternary phase diagram different from that of traditional aqueous cationic‐anionic surfactant systems. In that region, the molar ratio of gemini to SDS varies with the total concentration of surfactants. ATPS not only has higher stability but also has longer phase separation time for the new systems than that of the traditional system. Furthermore, the optical properties of ATPS are different at different total concentrations. All of these experimental observations can be attributed to the unique properties of gemini surfactant and the synergy between the cationic gemini surfactant and the anionic surfactant SDS.

Phase Behavior of n‐Butanol/n‐Octane/Water/Cationic Gemini Surfactant System

Phase diagrams of the n‐butanol/n‐octane/water/(12‐3‐12,2Br−1) system were determined, where n‐octane usually represents oil (O), 12‐3‐12,2Br−1 is a gemini cationic surfactant trimethylene‐1,3‐bis(dodecyldimethyl ammonium bromide) abbreviated as S, and n‐butanol is a co‐surfactant written as A. Effects of the weight ratio of gemini surfactant to cosurfactant, S/A, and of temperature on the phase behavior were studied. The microemulsion structures including O/W, bi‐continuous (B.C.), W/O, and liquid crystal were determined by the conductivity method and polarization measurement. Experimental results show that the gemini surfactant, used facilitates the formation of microemulsions compared with its corresponding monomeric surfactant, n‐dodecyl trimethylammonium bromide (DTAB). When S/A=1/1, and the total concentration of gemini surfactant and alcohol is 20–40%, microemulsions with higher water content can form in a wider region. When the temperature increases, the size and position of each type of microemulsion region changes notably.

Insertion of pH-sensitive bola-type copolymer into liposome as a "stability anchor" for control of drug release.

How to design intelligent carriers for delivering drugs to the target accurately and releasing drug timely with the help of a certain environmental stimulus is still a challenge in tumor treatment. In this work, pH-sensitive bola-type triblock copolymers, composed of poly(2-(diisopropylamino) ethylmethacrylate) (PDPA) and methoxy-poly(ethyleneglycol) (mPEG), were synthesized. Liposomes containing these copolymers (Liposome@Bola) have been prepared by simply mixing the copolymer with phospholipids and cholesterol. From the fluorescence polarization measurement, the stability of Liposome@Bola was found to be increased a lot comparing to the pure liposome. As a result, the doxorubicin (DOX) leakage of the former was restrained in neutral environment. However, when pH decreased from 7.4 to 6.0, DOX released percentage had been increased 30-60 points, which was heavily depend on the phospholipid composition. Furthermore, the size effects of PEG and PDPA segments were also investigated. These results indicated the synthesized bola-type copolymers improved the pH-controllability of drug release of liposome, i.e., increased the difference between the release amount under pH 7.4 and pH 6.0. The bola-type copolymer exhibited a good potential application in smartly controlling drug delivery system.