Ferrofluids of Thermotropic Liquid Crystals by DNAâLipid Hybrids

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Ferrofluids of Thermotropic Liquid Crystals by DNA-Lipid Hybrids Lu Xu, Mengjun Chen, and Jingcheng Hao J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.6b09595 • Publication Date (Web): 21 Dec 2016 Downloaded from http://pubs.acs.org on January 9, 2017

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The Journal of Physical Chemistry

Ferrofluids

of

Thermotropic

Liquid

Crystals

by

DNA-Lipid Hybrids Lu Xu, Mengjun Chen, and Jingcheng Hao* Key Laboratory of Colloid and Interface Chemistry & Key Laboratory of Special Aggregated Materials (Ministry of Education), Shandong University, Jinan 250100, P. R. China.

* To whom correspondence should be addressed. E-mail: [email protected]

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ABSTRACT Here is first report the creation of ferrofluids of thermotropic liquid crystals in the absence of any solvent or nanoparticle. These ferrofluids were prepared by the electrostatic coupling of single-strand (ss) DNA with paramagnetic lipids. DNA molecules, as rigid parts, offer the orientational anisotropy and lipids (surfactants) due to the flexible hydrocarbon chains suppress crystallization, hybrids with DNA significantly increase the Cure temperature (Tc) of the lipids. The ferrofluids possess good fluidity and low viscosity. They serve as excellent solvents for both hydrophilic and lipophilic compounds. Their strong magnetism further allows the solutes to be controlled by external magnetic force. The DNA-lipid hybrid ferrofluids show liquid crystal (LC) behavior at low temperatures, and the LC phase is made of ordered multilamellar structures. Compared with conventional magnetic nanoparticle dispersions, the solvent-free lipoplex ferrofluids provide potential applications for nanotechnology, material science, and biotechnology.

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INTRODUCTION Magnetic fluids, i.e., ferrofluids, defined by both fluidity and magnetism, are most often produced from amphiphilic magnetic nanoparticles dispersed in a carrier fluid. This kind of colloidal suspension has fueled the development of nanotechnology, material science, and biomedicine by creating new strategies for catalysis,1,2 targeted cargo delivery,3-6 preparation of optical devices,7,8 and the separation and purification of biomolecules or cells.9-11 In all the paradigms, proper carrier fluids for preparing or dispersing magnetic particles are necessary.1-13 Here for the first time ferrofluids are produced without using solvents and magnetic nanoparticles. These ferrofluids were prepared from the electrostatic coupling of single-strand DNA (ssDNA) and a paramagnetic cationic lipid. Negatively charged DNA acts as rigid parts, introducing orientational anisotropy;14 the flexible alkyl chains of surfactants suppress crystallization.14 The complexation with DNA highly increases the Cure temperature (Tc, the critical temperature for the transition of a magnetic substance from ferromagnetic to paramagnetic, above Tc, a magnetic substance turns paramagnetic, below Tc, it becomes ferromagnetic) of the paramagnetic lipids.15 The interplay contributes to the production of thermotropic solvent-free ferrofluids using lipoplexes. Compared to conventional nanoparticle solutions-based ferrofluids, these lipoplexes-based solvent-free ferrofluids are worth investigation, as they are supra-molecular liquids. They provide potential opportunities for use in sciences and technologies: i) The ferrofluids are non-volatile and avoid the use of evaporable, flammable, and/or toxic organic solvents. ii) They are able to inhibit the interference of solvents on structures and properties, such as the electrical conductivity, self-assembly behavior, and magneto-responsiveness of DNA and lipids, leading to new possibilities for magnetic, optical, or electronic devices. iii) These ferroliquids 3



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are soft matters possessing viscoelasticity, which may be much easier to process into films or other functional forms than hard inorganic materials. iv) The ferrofluids consist of both the strong polar DNA and the non-polar alkyl chains, which can act as solvents or reaction media for both hydrophilic and hydrophobic compounds or nanoparticles. v) The strong magnetism of the ferrofluids allows the solutes to be effectively controlled by external magnetic force. vi) The ferrofluids can spontaneously form ordered multilamellar microstructures within a certain range of temperatures without the use of solvents. In fact, most of the studies on DNA self-assembly materials are limited to aqueous solutions or hydrogels.16-23 This kind of solvent-free magnetic DNA architecture may offer guidance for constructing novel DNA nano-machines in biocatalysis, biosensing, and bioelectronic devices.

EXPERIMENTAL SECTION Materials and Methods. Single-strand (ss) DNA stock solutions were prepared by thermal degradation method. Briefly, double-strand (ds) DNA was denatured at 90 ºC for 45 min and then immediately dipping into ice bath for fast cooling to prevent renaturation. Salmon testes double-strand DNA (dsDNA) sodium salt was purchased from ACROS (Fairlawn, NJ). Its molar weight was about 100 bp, as determined by agarose gel electrophoresis (AGE), and its concentration was examined by considering DNA bases molar extinction coefficient to be 6600 mol-1·cm-1 at 260 nm. The absorbance ratio of DNA stock solution was 1.8 to 1.9 at 260 and 280 nm, suggesting no existence of protein. Paramagnetic lipid, DDACe ((C12H25)2N+(CH3)2[CeCl3Br]-), was prepared by mixing equal molar amount of DDABr ((C12H25)2N+(CH3)2Br-) and CeCl3 in methanol and stirring overnight at room temperature.20,21 The solvent was then removed and the product dried at reduced pressure at 80 ºC overnight yielding white solids. The critical 4


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micelle concentration (cmc) and the dissociation constant (β) of DDACe were determined by electrical conductivity method (Figure S1 in the Supporting Information (SI)) to be 3.8 mmol·L-1 and 0.13, respectively. SQUID magnetometry (Figure S2 in the SI) shows that DDACe is a paramagnetic compound. DDABr (> 98%) and CeCl3·7H2O (> 99.9%) were purchased from Aladdin Industrial Corporation, China. All the chemicals were used without further purification. Thrice-distilled water (18.25 MΩ·cm) was used to prepare all the sample solutions. ssDNA (~6 mmol·L-1) and DDACe (~30 mmol·L-1) stock solutions was respectively prepared. Both the DNA and surfactant solutions (~5 mol equivalents of lipid relative to DNA) were mixed together and as a result the insoluble complexes precipitated from the aqueous solution. After centrifugation at 8000 rpm for 30 min, the water and unreacted surfactants were removed. The lipoplexes were lyophilized at -65 °C and 0.05 mbar for 12 h before further characterization. The prepared progress was shown in Scheme S1 in the SI. Electrical Conductivity. A DDSJ-308A analyzer was used to perform electrical conductivity experiments. The Pyrex glass measuring cell was placed in a water bath at 25 ± 0.3 ºC. The cmc was determined from the breakpoint between the higher [dκ/d(conc)] and lower [dκ/d(conc)] linear curves. The ionic dissociation constant (β) was estimated by the ratio of the slopes and the cmc can be determined, as shown in Figure S1 in the SI. Each sample was measured three times for the average value. SQUID Magnetometry.

Dried samples of lipid DDACe and DDACe/DNA

lipoplexes were placed in sealed polypropylene tubes and mounted inside a plastic straw for measuring in a magnetometer with a superconducting quantum interference device (MPMSXL, Quantum Design, USA) and a reciprocating sample option (RSO). The data were collected at 300 K. 5



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Thermogravimetric analysis (TGA) was

Thermal Gravity Analysis (TGA).

carried out using a Rheometric Scientific TGA1500 (Piscataway, NJ) to investigate the thermal properties of the lipoplexes. Measurements were conducted under inert atmosphere of nitrogen using 8-10 mg samples with a heating rate at 10 ºC min-1 from ambient temperature to 600 ºC. Polarizing Light Microscopy (PLM).

Birefringent lamellar textures of the

DNA-DDACe complexes were characterized by a polarizing light microscopy, Axioskop 40/40 FL (Zeiss, Germany). Differential Scanning Calorimetry (DSC).

The phase transition temperatures

from solids to liquid crystals or from liquid crystals to isotropic fluids were obtained from DSC8500 (PerkinElmer, Waltham, MA, USA). The heating rate was set as 2 ºC/min. Small-Angle X-ray Scattering (SAXS).

SAXS measurements were carried out

using a SAXSess MC2 high flux SAXS instrument (Anton Paar, Austria, Cu-Kα, λ = 0.154 nm), equipped with a Kratky block-collimation system and using an image plate (IP) as the detector. The X-ray generator was operated at 40 kV and 50 mA. A standard temperature control unit (Anton-Paar TCS 120) connected to the SAXSess instrument was used to regulate the temperature and maintain it at the desired level. Samples were transferred into 1 mm standard quartz capillaries. An exposure time of 2 h was long enough to provide a good signal-to-noise ratio. The scattering curve of solvent water in the same capillaries was recorded as background. The data were normalized to the same incident primary beam intensity and corrected for background scattering from the capillaries and water. Rheological Measurements.

Rheological measurements were performed on a

Haake RS6000 rheometer with a vertebral plate sensor system (Z41 Ti) at 25.0 ± 0.1 6


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ºC. The viscoelastic properties were determined by oscillatory measurements from 0.01 to 10 Hz. In steady shear experiments, the shear rate was typically increased from 0.1 to 10 s-1 in a step wise mode within approximately 10-35 min. To achieve equilibrium as far as possible, the rheometer was set to ensure the gradient was less than 0.5 (∆τ/τ)/∆t % at each shear rate step, and the maximum waiting time was 60 s.

RESULTS AND DISCUSSION The paramagnetic double-chain cationic DDACe was synthesized by coordinating the commercially available compounds DDABr and CeCl3 to contain high-spin Ce3+-based counterion.24,25 The pathway for which is displayed in Scheme 1. The paramagnetism of DDACe was evidenced by SQUID magnetometry (Figure S1 in the SI), as its magnetic moment linearly increases relative to the strength of the magnetic field.15 In an aqueous solution, DDACe can self-assemble into vesicles of varied sizes and multiple curvatures, as shown in Figure S3 in the SI, which was determined by observations of cryogenic transmission electron microscopy (cryo-TEM).

C12H 25

N + Br- + CeCl 3

Methanol, 12 h

C12H25

C12H 25

N + [CeCl3Br]C12H 25

Scheme 1. Synthesis of the paramagnetic double-chain DDACe.

When ssDNA was added to the vesicle solution, it is of note that water-insoluble solids (Figure 1A and Scheme S1 in the SI) were produced. The solids were able to maintain a high thermo-stability up to 200 oC, as verified by thermo-gravimetric analysis (TGA, Figure S4 in the SI). No evident weight loss was discovered at around 100 oC, suggesting that the solids of the complexes are nearly anhydrous.

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Heating the DNA-DDACe solids to 35 oC, the solids converted to flowing complexes with low viscosity in macroscopy (Figure 1B). The complexes remained constant as macroscopic fluids with negligible volatilization until the temperature reached 200 oC, after which the lipoplexes underwent thermal degradation. Using PLM, further characterization of the optical properties of the solvent-free liquids when exposed to temperature changes showed that the solvent-free hybrid fluids presented liquid crystal (LC) behavior at below 65 oC, with a multitude of typical Maltese-cross textures being traced in Figure 1C and Figure S5 in the SI. It indicated a spontaneous formation of ordered lamellar microstructures of the lipoplex melts.26 To the best of our knowledge, this is the first example of a solvent-free magnetic LC. A further increase in temperature caused the disruption of DNA-DDACe microstructures and led to the formation of isotropic fluids (IF). The birefringent property disappeared completely (Figure 1D). Two discrete endothermic peaks at 35 o

C and 65 oC respectively were found in differential scanning calorimetry (DSC) data

(Figure S6 in the SI), corresponding to both phase transition temperatures. According to this evidence, a phase diagram exhibiting the solid-LC-IF transition of the solvent-free hybrid ferrofluids upon increasing the temperature can be concluded (Figure 1E).

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35°C

Solids Cr -20

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LC 20

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Temperature / ºC

Figure 1. Solvent-free DNA-DDACe ferrofluids below (A) and above (B) 35 oC. Polarizing light microscopy (PLM) images of the solvent-free ferrofluids below (C) and above (D) 65 oC. The scale bars for A and B are equal to 5 mm, the bars for C and D are 5 µm. (E) Phase behavior of the DNA-DDACe lipoplexes at different temperatures, LC = liquid crystal and IF = isotropic fluids.

SQUID magnetometry (Figure 2a) offered direct evidence of the successful preparation of solvent-free ferrofluids of ssDNA and cationic DDACe above 35 oC, as a typical “hysteresis loop” can be observed.15 The producing possibility of the solvent-free ferrofluids of lipoplexes was enabled by the complexation with DNA that strongly increases the Tc of the paramagnetic lipid,5,15 inducing the formation of ferromagnetic complexes. The effective magnetic moment of the solvent-free fluids is approximately 0.08 emu·g-1 at 35 oC, and linearly decreased relative to temperature (Figure 2b). The ferro-magnetism of the solvent-free liquids can be maintained at least within the measuring limit of the employed instrument until 100 oC. The strong magnetism of the fluids made them able to respond to and be controlled by an external magnetic force.

The formation of ferrofluids by DNA-DDACe hybrids is usual since the combination of DNA and lipids can cause the elimination of the counterions of lipids from the complexes.20-23 The mechanism of DDACe assembling with DNA into magnetic complexes can be explained by referring to our previous work.15 It is an

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interplay between the magnetic [CeCl3Br]- ions in the Stern layer and those in the bilayers. According to classical models describing colloid particles,27,28 electric double layer of colloid particles are divided into two regions, the so-called Stern and diffuse layers. In the Stern layer, counterions are strongly bound and move with the particles as a whole dynamic entity. In the second, counterions move freely in the bulk and maintain dynamic equilibrium with those in the Stern layer. The surface that separates the two layers is a slipping plane. The location of the slipping plane is quite sensitive to the presence of polyelectrolytes, and the interaction with oppositely charged polyelectrolytes normally causes a displacement in the two layers and leads to the release of counterions in the diffuse layer.15,26,27 Although the complexation of DNA with cationic surfactants will cause the release of counterions in the diffuse layer, the [CeCl3Br]- in the Stern layer will still move with DNA/surfactant aggregates as a whole dynamic entity and should contribute to the formation of magnetic complexes. Both Eastoe24,25 and Hao15,27 have confirmed that magnetic coordination counterions such as [CeCl3Br]-, [FeCl3Br]- and [GdCl3Br]- are strong hydrophobic, they exhibit strong hydrophobic interaction with the alkyl chains of surfactants and can partition into the core of cationic micelles or the bilayer of vesicles. In this system, the partition of [CeCl3Br]- into the bilayer of DDACe vesicles resulting from the hydrophobic interaction between the magnetic ions and the hydrocarbon chains should also contribute to the formation of ferromagnetic complexes. SQUID magnetometry (Figure S7 in the SI) of DDABr-DNA liquids, which was prepared by Herrmann

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et al.14 showed that the complexes are diamagnetic as the magnetic moment decreases linearly as a function of the strength of magnetic fields.21 The result better confirmed that the [CeCl3Br]- plays an essential role in the formation of ferrofluids. The solvent-free ferrofluids were demonstrated to have the ability to dissolve hydrophilic dyes such as rhodamine B (Figure 2c and Figure S8 in the SI), affording transparent, colored solutions. Compared with common polar solvents, the strong magnetism of the lipoplexes made the dye solutes able to be effectively controlled by a weak external magnetic force. As evidenced in Figure 2c, vertically applying a 1.0 T NdFeB magnet overcame the gravity of the dye solution, lifting the magnetic solution and drawing a sample of it to the surface of the magnet. Lipophilic dyes, e.g. dimethyl yellow, can also be dissolved in the magnetic fluids (Figure S9 in the SI). The affinity to both hydrophilic and lipophilic compounds may benefit from the ferrofluids being

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Figure 2. (a) SQUID magnetometry of the solvent-free DNA-DDACe ferrofluids at 35 oC. (b) Variation of the magnetic moment of the solvent-free ferrofluids vs. the temperature. (c) Effect of a 1 T NdFeB magnet on the rhodamine B solution prepared with the DNA-DDACe ferrofluids. The magnet was smoothly moved up and down by 11



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hand; the entire sequence, left to right, was rapid, occurring within a few seconds. Tips: the dyes were dissolved in pre-heated DNA-DDACe complexes at 60 oC. The experiment shown in (c) was operated during a hot summer with a room temperature > 30 oC and should be finished quickly before the mixtures cool down and recrystallize.

A small-angle X-ray scattering (SAXS) analysis (Figure 3a) of the magnetic LC at 35 oC expressed two sharp Bragg reflection peaks at q1 = 0.145 Å-1 and q2 = 0.288 Å-1, respectively, indicating that the ferrofluids consist of long-range ordered multilamellar microstructures with a periodicity of 43.5 Å (d = 2π/q1). The dimension of a ssDNA sublayer is ~10 Å thick,30 while the thickness of lipid bilayers with fully extended hydrocarbon chains is ~33.5 Å, as calculated according to the equation l = 0.127 nc + 0.15.31 Here l refers to the length of the fully extended hydrophobic chain of a surfactant and nc the number of the carbon atoms in a hydrocarbon chain. The layer spacing suggests that the lamellar structures were made of ssDNA sublayers and fully extended DDACe bilayers. In the SAXS results (Figure 3a), no typical DNA intralayer packing peaks are discovered, meaning that the DNA chains were randomly packed in the sublayer without any orientational or positional order.32 A further increase in temperature caused a slight increase in the q1 value, as well as a decrease in the layer spacing of the lamellar structure (Figure 3a). This revealed that heating the LC favors the interdigitation of the surfactant hydrocarbon chains. SAXS results of the IF phase did not exhibit evident diffraction peaks (Figure S10 in the SI), only a very weak broad halo at 0.23 Å-1 in association with randomly arrayed lipoplex scattering (27.3 Å) was observed, confirming that no ordered microstructures of the DNA-DDACe complexes formed.

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Freeze-fracture transmission electron microscopy (FF-TEM) observations verified that the LC phase was composed of multilamellar DNA-DDACe architectures (Figure 3b). Closely packed and stretched multi-layers of long-range self-assembled microstructures of lipoplexes with an average repeat distance of 4.27 ± 0.70 nm were discovered. The value of the periodicity was in accordance with that measured by SAXS. The size of the multilamella is approximate 73 nm. One can find that the DNA-DDACe layers were not completely flat and smooth, indicating that the nucleic acids attached on the lipid bilayers are randomly orientated, the result was also consistent with the SAXS data. According to FF-TEM images and SAXS data, a schematic diagram showing the micro-structures of the magnetic LC was concluded in Figure 3c. 1000

Intensity / a.u.

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308 K 318 K 328 K

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Figure 3. (a) SAXS profiles of the solvent-free DNA-DDACe ferrofluids in the LC phase at different temperatures. (b) FF-TEM image of the ferrofluids in the LC phase

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at 35oC. The bar is 50 nm. (c) The proposed model of the microstructures of the solvent-free ferrofluids between 35-65 oC.

The viscoelasticity of the ferrofluids was determined by shear rheometry. Both the storage modulus (G’) revealing the elastic portion and the loss modulus (G”) representing the viscous part were measured at a stress (τ) of 1 Pa. A characteristic liquid behavior of the lipoplexes above 35 oC was evidenced by the phenomenon that the value of G” kept higher than that of G’ over the frequency ( f ) range (Figure 4a). Both G’ and G’’ evidently decreased with the increase in temperature. The viscosity (η) of the magnetic fluids possessed low values within the measuring range and did not show clear changes relative to the increase in the shear rate but rather expressed slight shear thickening behavior at high shear rate (Figure 4b). This revealed a low viscosity in the solvent-free ferrofluids. Heating the ferrofluids also resulted in a decrease in η, and the value reduced notably as the phase transitioned from LC to IF. This is a result of the disruption of DNA-DDACe self-assembled structures, as well as a much higher mobility of nucleic acid and lipid molecules at high temperatures.

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0 0.1

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Figure 4. Rheological diagrams displaying the variations of G’ and G” vs. the frequency (a) and the changes of η as a function of shear rate (b) at different temperatures.

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CONCLUSIONS In conclusion, thermotropic liquid crystal ferrofluids without solvent, based on the self-assembly of ssDNA and paramagnetic cationic lipids, were achieved. The high fluidity as well as the low viscosity enabled them to act as solvents for both hydrophilic and lipophilic compounds. Their affinity to both hydrophilic and hydrophobic substances may allow them to act as new reaction media. The strong magnetism further allows the resulting solutions to be manipulated by weak external magnetic fields. The responsiveness, as well as the solvent-free conditions, offer strategies for preparing magnetic dispersions that are important to creating catalysis, targeted delivery, sensing, or device systems. These magnetic liquids consist of ordered multilamellar architectures within a certain range of temperatures, thus, displaying LC behavior. The LC properties may also lead to the creation of new optical devices. The obtained anhydrous magnetic DNA self-assembly liquid materials, differing from conventional DNA aqueous solutions or hydrogels, also may offer potential applications for biocatalysis, biosensing, and bioelectronic devices.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Tel: +86-531-883666074.

ACKNOWLEDGEMENTS This work was financially supported by the NSFC (Grant Nos. 21420102006 & 21273134). Supporting Information Available Chemicals and materials, experimental details, electrical conductivity, and SQUID magnetometry results, cryo-TEM images of the cationic lipid DDACe, TGA, DSC, 15



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additional PLM and SAXS data of the ferrofluids, additional photographs of the dye solutions prepared with the solvent-free ferrofluids. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org.

REFERENCES (1) Hu, A.; Yee, G. T.; Lin, W. Magnetically recoverable chiral catalysts immobilized on magnetite nanoparticels for asymmetric hydrogenation of aromatic ketones. J. Am. Chem. Soc. 2005, 127, 12486-12487. (2) Gijs, M. A. M.; Lacharme, F.; Lehamann, U. Microfluidic applications of magnetic particles for biological analysis and catalysis. Chem. Rev. 2010, 110, 1518-1563. (3) Namiki, Y.; Namiki, T.; Yoshida, H.; Ishii, Y.; Tsubota, A.; Koido, S.; Nariai, K.; Mitsunaga, M.; Yanagisawa, S.; Kashiwagi, H. et al. A novel magnetic crystal-lipid nanostructure for magnetically guided in vivo gene delivery. Nature Nanotech. 2009, 4, 598-606. (4) Dobson, J. Gene therapy progress and prospects: magnetic nanoparticel-based gene delivery. Gene Ther. 2006, 13, 283-287. (5) Xu, L.; Wang, Y.; Wei, G.; Feng, L.; Dong, S.; Hao, J. Ordered DNA-surfactant hybrid nanospheres triggered by magnetic cationic surfactants for photon- and magneto-manipulated drug delivery and release. Biomacromolecules 2015, 16, 4004-4012. (6) He, Q.; Tian, Y.; Gui, Y.; Mohwald, H.; Li, J. Layer-by-layer assembly of magnetic polypeptide nanotubes as a DNA carrier. J. Mater. Chem. 2008, 18, 748-754. (7) Hu, Y.; He, L.; Yin, Y. Magnetically responsive photonic nanochains. Angew. Chem. Int. Ed. 2011, 50, 3747-3750.

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(8) Yan, X.; Su, Y.; Li, J.; Fruh, J.; Mohwald, H. Uniaxially oriented peptide crystals for active optical waveguiding. Angew. Chem. Int. Ed. 2011, 50, 11186-11191. (9) Lee, I. S.; Lee, M.; Park, J.; Kim, B. H.; Yi, Y. W.; Kim, T.; Kim, T. K.; Lee, I. H.; Paik, S. R.; Hyeon, T. Ni/NiO core/shell nanoparticles for selective binding and magnetic separation of histidine-tagged proteins. J. Am. Chem. Soc. 2006, 128, 10658-10659. (10) McCloskey, K. E.; Chalmers, J. J.; Zborowski, M. Magnetic cell separation: Characterization of magnetophoretic mobility. Anal. Chem. 2003, 75, 6868-6874. (11) VanDelinder, V.; Groisman, A. Perfusion in microfluidic cross-flow: separation of white blood cells from whole blood and exchange of medium in a continuous flow. Anal. Chem. 2007, 79, 2023-2030. (12) Fu, M.; Wang, A.; Zhang, X.; Dai, L.; Li, J. Direct observation of the distribution of gelatin in calcium carbonate crystals by super-resolution fluorescence microscopy. Angew. Chem. Int. Ed. 2016, 55, 908-911. (13) Zhu, P.; Yan, X.; Su, Y.; Yang, Y.; Li, J. Solvent-induced structural transition of self-assembled dipeptide: from organogels to microcrystals. Chem. Eur. J. 2010, 16, 3176-3183. (14) Liu, K.; Chen, D.; Macrozzi, A.; Zheng, L.; Su, J.; Pesce, D.; Zajaczkowski, W.; Kolbe, A.; Pisula, W.; Mullen, K. et al. Thermotropic liquid crystals from biomacromolecules. Proc. Natl. Acad. Sci. 2014, 111, 18596-18600. (15) Xu, L.; Feng, L.; Hao, J.; Dong, S. Controlling the capture and release of DNA with a dual-responsive cationic surfactant. ACS Appl. Mater. Interfaces 2015, 7, 8876-8885.

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(16) Rothemund, P. W. K. Folding DNA to create nanoscale shapes and patterns. Nature 2006, 440, 297-302. (17) Nakata, M.; Zanchetta, G.; Chapman, B. D.; Jones, C. D.; Cross, J. O.; Pindak, R.; Bellini, T.; Clark, N. A. End-to-end stacking and liquid crtstal condensation of 6-to 20-base pair DNA duplexes. Science 2007, 318, 1276-1279. (18) Guo, W.; Lu, C.; Qi, X.; Orbach, R.; Fadeev, M.; Yang, H.; Willner, I. Switchable bifunctional stimuli-triggered poly-N-isopropylacrylamide/DNA hydrogels. Angew. Chem. Int. Ed. 2014, 53, 10134-10138. (19) Kwak, M.; Herrmann, A. Nucleic acid/organic polymer hybrid materials: synthesis, superstructures, and applications. Angew. Chem. Int. Ed. 2010, 49, 8574-8587. (20) Kwon, Y. W.; Choi, D. H.; Jin, J. I. Optical, electro-optic and optoelectronic properties of natural and chemically modified DNAs. Polym. J. 2012, 44, 1191-1208. (21) Kwon, Y. W.; Choi, D. H.; Jin, J. I.; Lee, C. H.; Koh, E. K.; Grote, J. G. Comparison of magnetic properties of DNA-cetyltrimethyl ammonium complex with those of natural DNA. Sci. China Chem. 2012, 55, 814-821. (22) Okahata, Y.; Kobayashi, T.; Tanaka, K.; Shimomura, M. Anisotropic electric conductivity in an aligned DNA cast film. J. Am. Chem. Soc. 1998, 120, 6165-6166. (23) Tanaka, K.; Okahata, Y. A DNA-lipid complex in organic media and formation of an aligned cast film. J. Am. Chem. Soc. 1996, 118, 10679-10683. (24) Brown, P.; Bushmelev, A.; Butts, C. P.; Cheng, J.; Eastoe, J.; Grillo, I.; Heenan, R. K.; Schmidt, A. N. Magnetic control over liquid surface properties with responsive surfactants. Angew. Chem. Int. Ed. 2012, 51, 2414-2466. 18


Page 18 of 21

Page 19 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25) Brown, P.; Bushmelev, A.; Butts, C. P.; Eloi, J.-C.; Grillo, I.; Baker, P. J.; Schmidt, A. M.; Eastoe, J. Properties of new magnetic surfactants. Langmuir 2013, 29, 3246-3251. (26) Shen, Y.; Hao, J.; Hoffmann, H. Reversible phase transition between salt-free catanionic vesicles and highsalinity catanionic vesicles. Soft Matter 2007, 3, 1407-1412. (27) Wiersma, P. H.; Loeb, A. L.; Overbeek, J. T. G. Calculation of the electrophoretic mobility of a spherical colloid particle. J. Colloid Interface Sci. 1966, 22, 78-99. (28) O’Brien, R. W.; White, L. R. Electrophoretic mobility of a spherical collodial particle. J. Chem. Soc., Faraday Trans. 2 1978, 74, 1607-1626. (29) Xu, L.; Feng, L.; Hao, J.; Dong, S. Compaction and decompactionof DNA dominated by thecompetition between counterions and DNA associating with cationic aggregates. Colloids and Surfaces B 2015, 134, 105-112. (30) Zhou, J.; Gregurick, S. K.; Krueger, S.; Schwarz, F. P. Conformational changes in single-strand DNA as a function of temperature by SANS. Biophys. J. 2006, 90, 544-551. (31) Dias, R. S.; Lindman, B.; Miguel, M. G. DNA interaction with catanionic vesicles. J. Phys. Chem. B 2002, 106, 12600-12607. (32) Bouxsein, N. F.; Leal, C.; McAllister, C. S.; Ewert, K. K.; Li, Y.; Samuel, C. E.; Safinya, C. R. J. Am. Chem. Soc. Two-dimensional packing of short DNA with nonpairing overhangs in cationic liposome-DNA complexes: from onsager nematics to columnar nematics with finite-length columns. 2011, 133, 7585-7595.

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Ferrofluids of Thermotropic Liquid Crystals by DNAâLipid Hybrids

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