Magnetizing DNA and proteins using responsive surfactants

A dual-responsive microemulsion with macroscale superlubricity and largely switchable friction

Although stimuli-responsive microemulsions (MEMs) consisting of water, oil and surfactants have found extensive potential applications in industrial fields, a responsive MEM exhibiting either macroscale superlubricity or two friction states where its coefficient of friction (CoF) can be switched by more than one order of magnitude has not yet been reported. Moreover, although traditional liquid superlubricants can provide ultralow friction and wear, effective control over the friction between two contacting surfaces is crucial for both achieving accurate control of the operation of an instrument and fabricating smart devices. Here we create a thermo- and magneto-responsive MEM capable of providing superlubrication for metallic materials in a broad temperature range from -30 to 20 °C using n-hexane, water, surfactant DDACe ((C12H25)2N+(CH3)2[CeCl4]-) and ethylene glycol. The MEM can abruptly and dramatically switch its CoF by approximately 25 fold based on a thermally reversible MEM-emulsion (EM) transition. Its anti-freezing performance allows it to provide effective lubrication even when the surrounding temperature attains as low as -60 °C. Together with its facile preparation, ultrahigh colloidal stability and magnetically controlled migration, such a novel smart MEM is envisioned to find widespread applications in materials science.

Self-Assembly of a C16M[Mn] Magnetic Surfactant in Water

A magnetic surfactant, which combines the properties of a surfactant with magnetic responsiveness, shows great potential in biotechnology, separation, adsorption, and catalysis, especially in non-invasive manipulation through a magnetic field. However, a molecularly magnetic surfactant is usually paramagnetic for the amorphous and less ordered structures. In this work, magnetic surfactant 1-methyl-3-hexadecane-imidazolium [MnCl₂Br] (C₁₆M[Mn]) is reported to self-assemble in water. The C₁₆M[Mn] magnetic surfactant self-assembles in water to form a lamellar hydrogel from 10 to 50 wt % at and below room temperature. The hydrogel changes from a gel to a sol at 30 °C, and the hexadecane chains in the hydrogel change from noncrystalline to crystalline at 0 °C. In the hydrogel state, the lamellar domain spacing is varied from 36 to 45 nm depending on the concentration and self-assembly temperature. After self-assembly, the magnetic susceptibility of the freeze-dried magnetic surfactant is increased. Most important is the fact that the freeze-dried sample at a high concentration (40-50 wt %) shows the highest magnetic susceptibility, which is related to the closer molecular packing and the more ordered structures. The self-assembly-induced increase in magnetic susceptibility provides a method for improving the magnetic properties of a magnetic surfactant.

A Dual pH‐ and Light‐Responsive Spiropyran‐Based Surfactant: Investigations on Its Switching Behavior and Remote Control over Emulsion Stability

A cationic surfactant containing a spiropyran unit is prepared exhibiting a dual‐responsive adjustability of its surface‐active characteristics. The switching mechanism of the system relies on the reversible conversion of the non‐ionic spiropyran (SP) to a zwitterionic merocyanine (MC) and can be controlled by adjusting the pH value and via light, resulting in a pH‐dependent photoactivity: While the compound possesses a pronounced difference in surface activity between both forms under acidic conditions, this behavior is suppressed at a neutral pH level. The underlying switching processes are investigated in detail, and a thermodynamic explanation based on a combination of theoretical and experimental results is provided. This complex stimuli‐responsive behavior enables remote‐control of colloidal systems. To demonstrate its applicability, the surfactant is utilized for the pH‐dependent manipulation of oil‐in‐water emulsions.

Magnetic surfactants: A review of recent progress in synthesis and applications

Magnetic surfactants are a special class of surfactants with magneto-responsive properties. These surfactants possess lower critical micelle concentrations and are more effective in reducing surface tension as compared to conventional surfactants. Such surfactants' ability to manipulate self-assembly in a controlled way by tuning the magnetic field makes them an attractive choice for several applications, including drug delivery, catalysis, separation, oilfield, and water treatment. In this work, we reviewed the properties of magnetic surfactants and possible explanations of magnetic behavior. This article also covers the synthesis methods that can be used to synthesize different types of cationic, anionic, nonionic, and zwitterionic magnetic surfactants. The applications of magnetic surfactants in different fields such as biotechnology, water treatment, catalysis, and oilfield have been discussed in detail.

Void-free 3D Bioprinting for In-situ Endothelialization and Microfluidic Perfusion

Two major challenges of 3D bioprinting are the retention of structural fidelity and efficient endothelialization for tissue vascularization. We address both of these issues by introducing a versatile 3D bioprinting strategy, in which a templating bioink is deposited layer-by-layer alongside a matrix bioink to establish void-free multimaterial structures. After crosslinking the matrix phase, the templating phase is sacrificed to create a well-defined 3D network of interconnected tubular channels. This void-free 3D printing (VF-3DP) approach circumvents the traditional concerns of structural collapse, deformation and oxygen inhibition, moreover, it can be readily used to print materials that are widely considered "unprintable". By pre-loading endothelial cells into the templating bioink, the inner surface of the channels can be efficiently cellularized with a confluent endothelial layer. This in-situ endothelialization method can be used to produce endothelium with a far greater uniformity than can be achieved using the conventional post-seeding approach. This VF-3DP approach can also be extended beyond tissue fabrication and towards customized hydrogel-based microfluidics and self-supported perfusable hydrogel constructs.

Using Remote Fields for Complex Tissue Engineering

Great strides have been taken towards the in vitro engineering of clinically relevant tissue constructs using the classic triad of cells, materials, and biochemical factors. In this perspective, we highlight ways in which these elements can be manipulated or stimulated using a fourth component: the application of remote fields. This arena has gained great momentum over the last few years, with a recent surge of interest in using magnetic, optical, and acoustic fields to guide the organization of cells, materials, and biochemical factors. We summarize recent developments and trends in this arena and then lay out a series of challenges that we believe, if met, could enable the widespread adoption of remote fields in mainstream tissue engineering.

From Paramagnetic to Superparamagnetic Ionic Liquid/Poly(ionic liquid): The Effect of π-π Stacking Interaction

Magnetic ionic liquids (MILs) and poly(magnetic ionic liquids) (PMILs) with FeCl₄^- as anions usually show weak magnetism, such as paramagnetism or antiferromagnetism, at room temperature. Inspired by the natural inorganic ferromagnet with ordered crystal structures, a soft superparamagnetic ionic liquid (TMBBDI[FeCl₄]) and corresponding poly(ionic liquid) (PTMBBDI[FeCl₄]) were prepared by introducing π-π stacking biphenyl groups into the organic cations. Both of the compounds exhibited superparamagnetism from 100 to 300 K, while a ferromagnetic hysteresis loop was found at 300 K. Ferromagnetic interactions were observed from zero field cooling and field cooling studies for both TMBBDI[FeCl₄] and PTMBBDI[FeCl₄]. However, the MIL and PMIL without π-π stacking interaction were paramagnetic without ferromagnetic interaction. The superparamagnetism of the TMBBDI[FeCl₄] and PTMBBDI[FeCl₄] was ascribed to the π-π stacking interactions between biphenyl groups, which not only shortened the Fe-Fe distance to the ferromagnetic interaction range but also increased the order degree of the molecules.

Stability of Ionic Magnetic Surfactants in Aqueous Solutions: Measurement Techniques and Impact on Magnetic Processes

Predicting the behavior of magnetic surfactants in magnetic fields is critical for designing magnetically driven processes such as chemical separations or the tuning of surface tensions. The ability of magnetic fields to alter the interfacial properties of magnetic surfactant solutions may be dependent upon the strength of association between the magnetic and surfactant moieties of the surfactant molecules. This research shows that the stability of a magnetic surfactant in an aqueous environment is dependent upon the type of complex that contains the paramagnetic ion, and these findings provide valuable insight for the design of magnetic surfactants for applications in aqueous media. The surfactants investigated were ionic surfactants, which contained paramagnetic counterions. This investigation looked at both anionic and cationic surfactants; it utilized solution conductivity, cyclic voltammetry (CV), sampled current voltammetry (SCV), and solution pH measurements to qualitatively evaluate the stability of the magnetic counterions in aqueous solution. In addition, solution conductivity was used to quantify the degree of binding between the paramagnetic ions and surfactant micelles in solution. These results indicate metal halide-based cationic surfactants are unstable in aqueous solutions. We hypothesize that this instability results in the difference in the magnetic response of the anionic vs cationic surfactants examined in this study.

Magnetic Gemini Surfactants

A homologous series of Gemini surfactants, dimethylene-1,2-bis(alkyldimethyl-ammonium bromide) (referred to as n-2-n·2Br, n = 14, 16, and 18) and Fe- or lanthanide metal-based magnetic Gemini surfactants (abbreviated as n-2-n·2X, X = Fe, Ce, and Gd), were first synthesized. Measurements of surface tension and electrical conductivity determine the physical quantities related to the surface activities of n-2-n·2Br and n-2-n·2X, and the magnetic behaviors of n-2-n·2X are elucidated by superconducting quantum interference device magnetometry. Thermogravimetric analysis and differential scanning calorimetry have been used to investigate thermotropic liquid crystalline properties of all aforementioned surfactants, and the liquid crystal textures were further observed via polarizing optical microscopy. These results reveal that for magneto-responsive Gemini surfactants, both magnetic counterions and alkyl chain lengths have certain effect on surface activities, magnetism, and thermotropic phase behavior. We summed up these changes and discussed the causes, which could provide a new insight into controlling the properties of magnetic surfactants.

Co-assemblies of polyoxometalate {Mo72Fe30}/double-tailed magnetic-surfactant for magnetic-driven anchorage and enrichment of protein

Covalent grafting and electrostatic-driven assembly have been two strategies in constructing well-defined polyoxometalate (POM) assemblies to produce specific morphologies and desirable properties. The modification of anionic counter-ions of amphiphilic compounds in POM-surfactant hybrid systems is still unexploited. Herein, we report the co-assembly of a synthetic double-tailed magnetic surfactant (MagSurf), (C₁₈)₂C₂N⁺[FeCl₄]^-, and POM, {Mo₇₂Fe₃₀}. The magnetic aggregate (POM/MagSurf) results from the building up hierarchical structures at a time-dependent interface. In this construct, both the MagSurfs and {Mo₇₂Fe₃₀} POMs contribute to and mutually strengthen the magnetization of the designed magnetic assembles. Interestingly, the POM/MagSurf aggregates are compatible with aqueous mixtures and successfully employed to serve as magnetic transporting vehicles to anchor and deliver a protein molecule, myoglobin (Mb). Upon applying a magnetic field (0.3 T), the magnetic aggregates induced a directional migration and enrichment of the Mb protein (71-90%). During this process, the protein/POM/MagSurf complexes exhibited strong interactions facilitating stable anchoring and efficient enrichment of the Mb.

Block copolymer-assisted synthesis of monodisperse colloidal patchy nanoparticles

Amphiphilic block copolymers are able to assemble into spherical micelles in an aqueous solution. Spherical micelles are expected to adsorb on the surface of colloidal nanoparticles (NPs) through hydrogen-bonding interaction. Hence, it should be possible to guide the area-selective deposition of precursors onto the exposed surface of colloidal seeds, where no micelles are adsorbed. Using colloidal silica and polydopamine nanospheres as seeds, block copolymer F127 and P123 are used as surface modifiers to guide the controlled solution-phase deposition of precursors on a selectively exposed surface of seed NPs, leading to the formation of patchy NPs. Effects of the addition amount of tetraethoxysilane (TEOS), types of block copolymers, and the volume fraction of miscible organic solvents on the size and morphology of patchy silica NPs are investigated systematically through electron microscopic imaging. Block copolymer micelles adsorption model for the formation of colloidal patchy NPs is first proposed. Our study suggests that the shape and size of patchy silica NPs are determined by the amount of TEOS and dielectric constant of solution.

Self-Assembled Magnetic Viruslike Particles for Encapsulation and Delivery of Deoxyribonucleic Acid

Developing nontoxic artificial carriers for stimuli-responsive capture, transport, and delivery of biomolecules is of immense scientific interest. Herein, for the first time, we synthesize a double-tailed cationic surfactant, (C₁₆H₃₃)₂(CH₃)₂N⁺[FeCl₃Br]^-, which possesses magnetic properties [magnetic surfactants (Mag-Surfs)]. The time-dependent formation of virus-shaped hybrid mixed assemblies of polyoxometalates (POMs) {Mo₇₂Fe₃₀}/Mag-Surf with hollow-shell structures is followed. These structures serve well as robust high-surface-area shuttles, which can be manipulated with applied magnetic fields. By using cationic Mag-Surfs, the anionic POMs and DNA can be complexed in these ternary mixtures. These virus-shaped complexes act as nanoanchors and nanomotors, which can be utilized for binding, anchoring, and delivery of biomolecules, such as DNA. It is found that they have a good absorption capacity for DNA and myoglobin over 24 h, after application of a magnetic field. The realization of magnetic virus-shaped {Mo₇₂Fe₃₀}/Mag-Surf spheres may open possibilities for designing other functional nanoparticles, allowing effective control over the delivery/separation of biomolecules.

Effect of Cationic Surfactants with Different Counterions on the Growth of Au Nanoclusters

The influence of a series of cationic surfactants composed of cetyltrimethylammonium cations with different counterions (Br^-, Cl^-, OH^-, C₇H₈O₃S^-, [CeCl₃Br]^-, and NO₃^-) on the aging process of gold nanoclusters (Au NCs) was studied. The finely different points of Au NCs treated by different surfactants were demonstrated by UV-vis and fluorescence spectra, transmission electron microscopy images, etc. Because of the difference of counterions, these surfactants have diverse physicochemical properties in surface activity, specific conductivity, pH, and viscosity, which may account for the difference of Au NCs in the aging process. In addition, the affinity of the counterions in surfactants to the surface of Au has also been demonstrated completely. This affinity may further guide the difference of the synthesized Au nanomaterials.

A new surfactant–copper(ii) complex based on 1,4-diazabicyclo[2.2.2]octane amphiphile. Crystal structure determination, self-assembly and functional activity

A new complex [Cu(L)Br₃] (where LBr is 1-cetyl-4-aza-1-azoniabicyclo[2.2.2]octane bromide) has been synthesized and characterized.

CO2-Reactive Ionic Liquid Surfactants for the Control of Colloidal Morphology

This article reports on a new class of stimuli-responsive surfactant generated from commercially available amphiphiles such as dodecyltrimethylammmonium bromide (DTAB) by substitution of the halide counterion with counterions such as 2-cyanopyrrolide, 1,2,3-triazolide, and L-proline that complex reversibly with CO₂. Through a combination of small-angle neutron scattering (SANS), electrical conductivity measurements, thermal gravimetric analysis, and molecular dynamics simulations, we show how small changes in charge reorganization and counterion shape and size induced by complexation with CO₂ allow for fine-tunability of surfactant properties. We then use these findings to demonstrate a range of potential practical uses, from manipulating microemulsion droplet morphology to controlling micellar and vesicular aggregation. In particular, we focus on the binding of these surfactants to DNA and the reversible compaction of surfactant-DNA complexes upon alternate bubbling of the solution with CO₂ and N₂.

Electrically-responsive core-shell hybrid microfibers for controlled drug release and cell culture

It is an active research field to develop fiber-shaped smart materials for biomedical applications. Here we report the development of the multifunctional core-shell hybrid microfibers with excellent mechanical and electrical performance as a new smart biomaterial. The microfibers were synthesized using a combination of co-axial spinning with a microfluidic device and subsequent dip-coating, containing a hydrogel core of bacterial cellulose (BC) and a conductive polymer shell layer of poly(3,4-ethylenedioxythiophene) (PEDOT). The hybrid microfibers were featured with a well-controlled microscopic morphology, exhibiting enhanced mechanic properties. A model drug, diclofenac sodium, can be loaded in the core layer of the microfibers in situ during the process of synthesis. Our experiments suggested that the releasing behaviors of the drug molecules from the microfibers were enhanced by external electrical stimulation. Interestingly, we demonstrated an excellent biocompatibility and electroactivity of the hybrid microfibers for PC12 cell culture, thus promising a flexible template for the reconstruction of electrically-responsive tissues mimicking muscle fibers or nerve networks.

STATEMENT OF SIGNIFICANCE

Fiber-shaped biomaterials are useful in creating various functional objects from one dimensional to three-dimensional. The fabrication of microfibers with integrated physicochemical properties and bio-performance has drawn an increasing attention on researchers from chemical to biomedical. This study combined biocompatible bacterial cellulose with electroconductive poly(3,4-ethylenedioxythiophene) and further reduced them to a highly electroactive BC/PEDOT core-shell microfiber electrode for electrochemical actuator design. The result showed that the microfibers were well fabricated and the release of drugs from the microfibers was enhanced and could be controlled under electrical stimulation externally. Considering the excellent biocompatibility and electroactive toward PC12 cells, these microfibers may find use as templates for the reconstruction of fiber-shaped functional tissues that mimic muscle fibers, blood vessels or nerve networks in vivo.

Surfactant-Modified Ultrafine Gold Nanoparticles with Magnetic Responsiveness for Reversible Convergence and Release of Biomacromolecules

It is difficult to synthesize magnetic gold nanoparticles (AuNPs) with ultrafine sizes (<2 nm) based on a conventional method via coating AuNPs using magnetic particles, compounds, or ions. Here, magnetic cationic surfactants C₁₆H₃₃N⁺(CH₃)₃[CeCl₃Br]^- (CTACe) and C₁₆H₃₃N⁺(CH₃)₃[GdCl₃Br]^- (CTAGd) are prepared by a one-step coordination reaction, i.e., C₁₆H₃₃N⁺(CH₃)₃Br^- (CTABr) + CeCl₃ or GdCl₃ → CTACe or CTAGd. A simple strategy for fabricate ultrafine (<2 nm) magnetic gold nanoparticles (AuNPs) via surface modification with weak oxidizing paramagnetic cationic surfactants, CTACe or CTAGd, is developed. The resulting AuNPs can highly concentrate the charges of cationic surfactants on their surfaces, thereby presenting strong electrostatic interaction with negatively charged biomacromolecules, DNA, and proteins. As a consequence, they can converge DNA and proteins over 90% at a lower dosage than magnetic surfactants or existing magnetic AuNPs. The surface modification with these cationic surfactants endows AuNPs with strong magnetism, which allows them to magnetize and migrate the attached biomacromolecules with a much higher efficiency. The native conformation of DNA and proteins can be protected during the migration. Besides, the captured DNA and proteins could be released after adding sufficient inorganic salts such as at c_NaBr = 50 mmol·L^-1. Our results could offer new guidance for a diverse range of systems including gene delivery, DNA transfection, and protein delivery and separation.

Self-Assembly of Magnetic Bacillus-Shaped Bilayer Vesicles in Catanionic Surfactant Solutions

Bacillus-shaped bilayer vesicles of nanoscale size are very rare structures of stable surfactant self-assembly, because they are both thermodynamically and electrostatically unfavorable in solution. It is evidently demonstrated that appropriately aqueous mixtures of single-tailed cationic and anionic (catanionic) surfactants can produce rigidly bacillus-shaped bilayer vesicles with both flat parts and bent edges. The crucial requirement for forming bacillus-shaped bilayer vesicles is the use of cationic surfactants with relatively hydrophobic [FeCl₃Br]^- as counterions. [FeCl₃Br]^- can strongly associate with cationic surfactants to partition into the hydrophobic bilayer of bacillus-shaped bilayer vesicles, significantly increasing the edge energy of cationic surfactants to make them distribute in the low curvature part of bilayers. This causes the formation of bacillus-shaped bilayer vesicles, but not completely bent spherical vesicles, in the case of cationic surfactant excess. The specificity of hydrophobic counterions, [FeCl₃Br]^-, could also make the catanionic mixtures do not precipitate at the stoichiometric point. This new self-assembly on catanionic systems is culminated in the discovery of beautifully structured colloidal objects which are of practical use for molecular templating and controlled drug or DNA release.

Thermo-reversible capture and release of DNA by zwitterionic surfactants

The thermo-reversible capture and release of DNA were studied by the protonation and deprotonation of alkyldimethylamine oxide (CnDMAO, n = 10, 12 and 14) in Tris-HCl buffer solution. DNA/C14DMAO in Tris-HCl buffer solution with pH = 7.2 is transparent at 25 °C, indicating that DNA molecules exist mainly in individuals and the binding of C14DMAO is weak. With the increase of temperature, the pH of the buffer solution continuously decreases, which leads to protonation of C14DMAO (C14DMAO + H(+)→ C14DMAOH(+)) and an obvious increase of the turbidity of the samples. This indicates a stronger binding of the protonated C14DMAOH(+) to DNA. Further investigations demonstrated the formation of DNA/C14DMAOH(+) complexes, in which the stretched DNA molecules are effectively compacted as evidenced from UV-vis absorptions, circular dichroism (CD) measurements, atomic force microscopy (AFM) observations, dynamic light scattering (DLS) measurements and agarose gel electrophoresis (AGE). Interestingly, when the temperature is turned back to 25 °C, the compacted DNA molecules can fully recover to the stretched conformation. This cycle can be repeated several times without obvious loss of efficiency. The effect of the chain length of CnDMAO has also been investigated. When C14DMAO was replaced by C12DMAO, similar phenomena can be observed with a slightly higher critical surfactant concentration for DNA compaction and a slightly lower pH of Tris-HCl buffer solution with pH = 6.8. For the DNA/C10DMAO system, however, no DNA compaction was observed even in Tris-HCl buffer solution with a much lower pH and a much higher C10DMAO concentration. The negative charges of DNA molecules can easily be neutralized by positive charges of cationic CnDMAOH(+) (n = 12 and 14) micelles. DNA was compacted and then insoluble DNA/CnDMAOH(+) complexes were formed. Because of the much higher critical micelle concentration (cmc) of the shorter chain length C10DMAOH(+), cationic C10DMAOH(+) micelles cannot form under the studied condition to compact DNA. The strategy may provide an efficient and alternative approach for stimuli-responsive gene therapy and drug release.

Magnetic surfactants as molecular based-magnets with spin glass-like properties

This paper reports the use of muon spin relaxation spectroscopy to study how the aggregation behavior of magnetic surfactants containing lanthanide counterions may be exploited to create spin glass-like materials. Surfactants provide a unique approach to building in randomness, frustration and competing interactions into magnetic materials without requiring a lattice of ordered magnetic species or intervening ligands and elements. We demonstrate that this magnetic behavior may also be manipulated via formation of micelles rather than simple dilution, as well as via design of surfactant molecular architecture. This somewhat unexpected result indicates the potential of using novel magnetic surfactants for the generation and tuning of molecular magnets.

Kinetics of Photocontrollable Micelles: Light-Induced Self-Assembly and Disassembly of Azobenzene-Based Surfactants Revealed by TR-SAXS

The kinetics of micelles involving photosensitive surfactants is still not well understood. In this work, we unravel the mechanistic pathways involved in the micelle formation and dissolution of photocontrollable micelles. We focus on the fast self-assembly processes of photosensitive cationic azobenzene-containing surfactants (AzoTMA) that display a change in hydrophobicity induced by a reversible cis-trans conformational transition upon exposure to light. By combining both in situ time-resolved small-angle X-ray scattering (SAXS) and light scattering, we characterized the detailed structure and phase behavior of AzoTMA in mixtures of water and dimethylformamide (DMF). Time-resolved synchrotron SAXS with monochromatic light as a trigger enabled us to observe the nonequilibrium formation and dissolution process of micelles (demicellization) directly on the nanoscale with a time resolution starting from milliseconds. The structural results show that in pure water UV-light illumination leads to a 12% reduction of the aggregation number of the micelles and more than a 50% increase in the critical micelle concentration (CMC). Close to the CMC, adjusted by the addition of DMF, UV light illumination leads to a complete dissolution of the micelles, while shining blue light reverses the process and leads to the reformation of micelles. The UV-triggered dissolution follows a two-step mechanism; the first and rapid (second time scale) release of unimers is followed by a slower decomposition of the micelles (over tens of seconds) as a result of an increase in temperature due to optical absorption. Similarly, the reverse process, i.e., micelle formation, occurs rapidly upon photoconversion to trans conformers under blue light, and micelles are disrupted at long exposure time due to the optical absorption and corresponding increase in temperature. Interestingly, the coexistence of unimers with regular micelles is found at all times, and no other transient assemblies could be detected by SAXS.

Magnetic Surfactants and Polymers with Gadolinium Counterions for Protein Separations

New magnetic surfactants, (cationic hexadecyltrimethlyammonium bromotrichlorogadolinate (CTAG), decyltrimethylammonium bromotrichlorogadolinate (DTAG), and a magnetic polymer (poly(3-acrylamidopropyl)trimethylammonium tetrachlorogadolinate (APTAG)) have been synthesized by the simple mixing of the corresponding surfactants and polymer with gadolinium metal ions. A magnetic anionic surfactant, gadolinium tri(1,4-bis(2-ethylhexoxy)-1,4-dioxobutane-2-sulfonate) (Gd(AOT)3), was synthesized via metathesis. Both routes enable facile preparation of magnetically responsive magnetic polymers and surfactants without the need to rely on nanocomposites or organic frameworks with polyradicals. Electrical conductivity, surface tensiometry, SQUID magnetometry, and small-angle neutron scattering (SANS) demonstrate surface activity and self-aggregation behavior of the magnetic surfactants similar to their magnetically inert parent analogues but with added magnetic properties. The binding of the magnetic surfactants to proteins enables efficient separations under low-strength (0.33 T) magnetic fields in a new, nanoparticle-free approach to magnetophoretic protein separations and extractions. Importantly, the toxicity of the magnetic surfactants and polymers is, in some cases, lower than that of their halide analogues.

Structural Transition of Cinnamate-Based Light-Responsive Ionic Liquids in Aqueous Solutions and Their Light-Tunable Rheological Properties

Light-responsive wormlike micelles have important applications in fields such as microfluids, photoswichable fluids, and rheology control. However, single-component light-responsive wormlike micelles formed only from a single tail surfactant have not been reported in literature. In this work, self-assembly behavior of 1-alkyl-3-methylimidazolium trans-ortho-methoxycinnamate [Cnmim][OMCA] (n = 8, 10, 12, 14, 16) ionic liquids in aqueous solutions is studied by UV-vis spectroscopy, viscosity, rheology, conductivity, and cryo-TEM measurements. It is found for the first time that, among the single tail ionic liquid surfactants studied, [C16mim][OMCA] can form wormlike micelles in aqueous solutions without any additives and light irradiation. Then these wormlike micelles are able to transform into cylindrical micelles under UV light irradiation, resulting in significantly tunable rheological properties of the solutions. The photoisomerization of anion of [C16mim][OMCA] from trans- to cis-isomer as well as the relative hydrophilicity and structural feature of the cis-isomer are suggested to be responsible for such transition.

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.

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.

Noncovalent magnetic control and reversible recovery of graphene oxide using iron oxide and magnetic surfactants

The unique charging properties of graphene oxide (GO) are exploited in the preparation of a range of noncovalent magnetic GO materials, using microparticles, nanoparticles, and magnetic surfactants. Adsorption and desorption are controlled by modification of pH within a narrow window of <2 pH units. The benefit conferred by using charge-based adsorption is that the process is reversible, and the GO can be captured and separated from the magnetic nanomaterial, such that both components can be recycled. Iron oxide (Fe2O3) microparticles form a loosely flocculated gel network with GO, which is demonstrated to undergo magnetic compressional dewatering in the presence of an external magnetic field. For composites formed from GO and Fe2O3 nanoparticles, it is found that low Fe2O3:GO mass ratios (<5:1) favor flocculation of GO, whereas higher ratios (>5:1) cause overcharging of the surfaces resulting in restabilization. The effectiveness of the GO adsorption and magnetic capture process is demonstrated by separating traditionally difficult-to-recover gold nanoparticles (d ≈ 10 nm) from water. The fully recyclable nature of the assembly and capture process, combined with the vast adsorption capacity of GO, presents obvious and appealing advantages for applications in decontamination and water treatment.