24 research outputs found
Magnetic-Field-Induced Orientational Phase Structure Transition
Magnetic
field effect on the phase transition at high temperature
(from 50 Ā°C) inside the magnetic field has been found in C<sub>14</sub>G<sub>2</sub> (<i>N</i>-tetradecyllactobionamide)/C<sub>12</sub>EO<sub>4</sub> (tetraethylene glycol monododecyl ether)/D<sub>2</sub>O system. The phase was transited quickly from lamellar phase
to isotropic phases [bottom, micellar phase (L<sub>1</sub> phase)
and top, sponge phase (L<sub>3</sub> phase)] induced by a magnetic
field, which was demonstrated by <sup>2</sup>H NMR and FF-TEM measurements.
The isotropic phases induced by magnetic field were not stable, and
the upper L<sub>3</sub> phase can recover to lamellar phase after
being restored in a 55 Ā°C thermostat outside the magnetic field
for about one month. During the mechanism study, the C<sub>12</sub>EO<sub>4</sub> molecule was proved to be the dominant component for
the phase transition induced by the magnetic field, while the C<sub>14</sub>G<sub>2</sub> molecule was the auxiliary and just affected
the transition speed. The breaking and rebuilding of hydrogen bonds
could play an important role in the phase transition and recovering.
Moreover, the surfactant concentration had an effect on the speed
of phase transiting and phase recovering. These observations could
provide an understanding of the phase transition and also the applications
for the controlled drug delivery system of bilayer membranes driving,
induced by the magnetic field
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
AzoNa<sub>4</sub> (or AzoH<sub>4</sub>) can be ascribed to an interplay
of the magnetic [FeCl<sub>3</sub>Br]<sup>ā</sup> 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
Controlling the Capture and Release of DNA with a Dual-Responsive Cationic Surfactant
A dual-responsive cationic surfactant,
4-ethoxy-4ā²-(trimethyl- aminoethoxy) azobenzene trichloromonobromoferrate
(azoTAFe), which contains both a light-responsive moiety azobenzene
and a paramagnetic counterion, [FeCl<sub>3</sub>Br]<sup>ā</sup>, was designed and synthesized. Not only does this cationic surfactant
abundantly utilize inexhaustible and clean sources, i.e., light and
magnetic field, but it also serves as a powerful dual-switch molecule
for effectively controlling the capture and release of DNA. Our results
could provide potential applications in gene therapy for creating
smart and versatile machines to control the transport and delivery
of DNA more intelligently and robustly. It was proved that the light
switch can independently realize a reversible DNA compaction. The
introduction of a magnetic switch can significantly enhance the compaction
efficiency, help compact DNA with a lower dosage and achieve a magnetic
field-based targeted transport of DNA. In addition, the light switch
can make up the irreversibility of magnetic switch. This kind of self-complementation
makes the cationic azoTAFe be useful as a potential tool that can
be applied to the field of gene therapy and nanomedicine
First Fluorinated Zwitterionic Micelle with Unusually Slow Exchange in an Ionic Liquid
The micellization of a fluorinated
zwitterionic surfactant in ethylammonium
nitrate (EAN) was investigated. The freeze-fracture transmission electron
microscope (FF-TEM) observations confirm the formation of spherical
micelles with the average diameter 25.45 Ā± 3.74 nm. The micellization
is an entropy-driven process at low temperature but an enthalpy-driven
process at high temperature. Two sets of <sup>19</sup>F NMR signals
above the critical micelle concentration (cmc) indicate that the unusually
slow exchange between micelles and monomers exists in ionic liquid;
meanwhile, surfactant molecules are more inclined to stay in micelle
states instead of monomer states at higher concentration. Through
the analysis of the half line width (ĪĪ½<sub>1/2</sub>),
we can obtain the kinetic information of fluorinated zwitterionic
micellization in an ionic liquid
Magnetic Fullerene-DNA/Hyaluronic Acid Nanovehicles with Magnetism/Reduction Dual-Responsive Triggered Release
We created the dual-responsive
nanovehicle that can effectively
combine and abundantly utilize magnetic and glutathione (GSH)-reductive
triggers to control the drug delivery and achieve more intelligent
and powerful targeting. In the nanovehicles, paramagnetic fullerene
(C<sub>60</sub>@CTAF) was prepared via one-step modification of fullerene
with magnetic surfactant CTAF by hydrophobic interaction for the first
time. The perfect conjugation of C<sub>60</sub> and CTAF increased
the solubility or dispersity of fullerenes and qualified CTAF with
more powerful assembly capability with DNA. DNA molecule in the nanovehicles
acted as an electrostatic scaffold to load anticancer drug Dox as
well as the important building block for assembly with C<sub>60</sub>@CTAF into C<sub>60</sub>@CTAF/DNA. The further combination of deshielding
and targeting functions in reduction-responsive disulfide modified
HA-SS-COOH coating on C<sub>60</sub>@CTAF/DNA complexes could reduce
the agglomeration and regulate the morphology of C<sub>60</sub>@CTAF/DNA
complexes from irregular microstructures to more uniform ones. More
importantly, the introduction of HA-SS-COOH provided a response to
a simulating reductive extra-tumoral environment by efficient cleavage
of disulfide linkages by GSH and site-specific drug delivery to HepG2
cells. Amazingly, the final nanovehicles presented an increased magnetic
susceptibility compared with paramagnetic CTAF, and they āwalkedā
under an applied magnetic field. Because of their facile fabrication,
rapid responsiveness to extra tumoral environment, and external automatic
controllability by external magnet, the drug delivery nanovehicles
constructed by magnetic fullerene-DNA/hyaluronic acid might be of
great interest for making new functional nucleic-acid-based drug carriers
Spontaneous Transformation of Lamellar Structures from Simple to More Complex States
Spontaneous
transformation of lamellar structures, such as multilamellar
vesicles from micelles or unilamellar vesicles, is an important challenge
in the field of amphiphile molecules, which may serve as models to
understand biologically relevant bilayer membranes. Herein, we report
a progressive self-assembly progress of <i>N</i>-tetradecyllactobionamide
(C<sub>14</sub>G<sub>2</sub>) and tetraethylene glycol monododecyl
ether (C<sub>12</sub>EO<sub>4</sub>) mixtures in aqueous solution.
Increasing temperature or surfactant compositions causes spontaneous
transformation from simple to high-level aggregates, i.e., from unilamellar
vesicles, to coexisting multilamellar vesicles, terraced planar bilayers,
and finally terraced planar bilayers. Deuterium nuclear magnetic resonance
(<sup>2</sup>H NMR), freeze-fracture transmission electron microscopy
(FF-TEM), and small-angle X-ray scattering (SAXS) measurements clearly
demonstrate the spontaneously progressive self-assembly process. The
interlamellar spacing (<i>d</i>) of the bilayers decreases
from unilamellar vesicles to the terraced planar bilayers with an
increase of the temperature or surfactant compositions. Lamellar samples
consisting of terraced planar bilayers at higher temperature still
show viscoelastic properties, being Bingham fluids, and both the viscoelasticity
and yield stress increase with the composition and decrease with the
temperature. The spontaneous transformation of the progressive self-assembly
progress of C<sub>14</sub>G<sub>2</sub> and C<sub>12</sub>EO<sub>4</sub> aqueous mixtures is due to a balance of three driving forces, hydrophobic
interactions, hydrogen bonding, and steric effects
Nanocapsules of Magnetic Au Self-Assembly for DNA Migration and Secondary Self-Assembly
To endow valuable
responsiveness to self-assemblies of Au nanoparticles
(Au NPs), the magnetic Au nanoparticles (Au NPs)/C<sub>16</sub>H<sub>33</sub>(CH<sub>3</sub>)<sub>3</sub>N<sup>+</sup>[CeCl<sub>3</sub>Br]<sup>ā</sup> (CTACe) mixtures were first prepared by using
an emulsion self-assembly of a magnetic surfactant, C<sub>16</sub>H<sub>33</sub>(CH<sub>3</sub>)<sub>3</sub>N<sup>+</sup>[CeCl<sub>3</sub>Br]<sup>ā</sup>. A versatile morphology of self-assemblies
of Au NPs could be controlled by the counterions in surfactants including
[CeCl<sub>3</sub>Br]<sup>ā</sup>, [FeCl<sub>3</sub>Br]<sup>ā</sup>, and Br<sup>ā</sup> as well as solvent. In
particular, the magnetic counterion, [CeCl<sub>3</sub>Br]<sup>ā</sup>, can induce self-growth of Au NPs in an emulsion self-assembly process
due to the oxidability of [CeCl<sub>3</sub>Br]<sup>ā</sup>.
It enhances the rigidity of Au NPs/CTACe scaffolds template compared
with Au NPs/hexadecyltrimethylammonium bromide. [CeCl<sub>3</sub>Br]<sup>ā</sup> engaged Au NPs/CTACe with fascinating capability of
conglutination and targeted migration of DNA (150 Ī¼mol/L) under
a magnet field. The conglutination capability of the DNA molecules
can increase to 39.8% by adopting the magnetic strategy when using
Au NPs/CTACe as a magnetic booster. Au NPs/CTACe mixtures can ideally
self-assemble to be scaffolds, providing abundant conjugation sites
of surface charges. Magnetic Au NPs/CTACe can serve as a template
scaffold to secondary self-assemble with DNA (40 mmol/L) outside,
producing smooth-faced and hollow DNA nanocapsules. We believe that
the creative Au NPs/CTACe/DNA nanocapsules will extend the biological
application field of Au NPs assemblies
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 C<sub>16</sub>H<sub>33</sub>N<sup>+</sup>(CH<sub>3</sub>)<sub>3</sub>[CeCl<sub>3</sub>Br]<sup>ā</sup> (CTACe) and C<sub>16</sub>H<sub>33</sub>N<sup>+</sup>(CH<sub>3</sub>)<sub>3</sub>[GdCl<sub>3</sub>Br]<sup>ā</sup> (CTAGd) are
prepared by a one-step coordination reaction, i.e., C<sub>16</sub>H<sub>33</sub>N<sup>+</sup>(CH<sub>3</sub>)<sub>3</sub>Br<sup>ā</sup> (CTABr) + CeCl<sub>3</sub> or GdCl<sub>3</sub> ā 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 <i>c</i><sub>NaBr</sub> = 50
mmolĀ·L<sup>ā1</sup>. Our results could offer new guidance
for a diverse range of systems including gene delivery, DNA transfection,
and protein delivery and separation
A Systematic Investigation and Insight into the Formation Mechanism of Bilayers of Fatty Acid/Soap Mixtures in Aqueous Solutions
Vesicles are the most common form
of bilayer structures in fatty
acid/soap mixtures in aqueous solutions; however, a peculiar bilayer
structure called a āplanar sheetā was found for the
first time in the mixtures. In the past few decades, considerable
research has focused on the formation theory of bilayers in fatty
acid/soap mixtures. The hydrogen bond theory has been widely accepted
by scientists to explain the formation of bilayers. However, except
for the hydrogen bond, no other driving forces were proposed systematically.
In this work, three kinds of weak interactions were investigated in
detail, which could perfectly demonstrate the formation mechanism
of bilayer structures in the fatty acid/soap mixtures in aqueous solutions.
(i) The influence of hydrophobic interaction was detected by changing
the chain length of fatty acid (C<sub><i>n</i></sub>H<sub>2<i>n</i>+1</sub>COOH), in which <i>n</i> = 10
to 18, the phase behavior was investigated, and the phase region was
presented. With the help of cryogenic transmission electron microscopy
(cryo-TEM) observations, deuterium nuclear magnetic resonance (<sup>2</sup>H NMR), and X-ray diffraction (XRD) measurements, the vesicles
and planar sheets were determined. The chain length of C<sub><i>n</i></sub>H<sub>2<i>n</i>+1</sub>COOH has an important
effect on the physical state of the hydrophobic chain, resulting in
an obvious difference in the viscoelasticity of the solution samples.
(ii) The existence of hydrogen bonds between fatty acids and their
soaps in aqueous solutions was demonstrated by Fourier transform infrared
(FT-IR) spectroscopy and molecule dynamical simulation. From the pH
measurements, the pH ranges of the bilayer formation were at the p<i>K</i><sub>a</sub> values of fatty acids, respectively. (iii)
Counterions can be embedded in the stern layer of the bilayers and
screen the electrostatic repulsion between the COO<sup>ā</sup> anionic headgroups. FT-IR characterization demonstrated a bidentate
bridging coordination mode between counterions and carboxylates. The
conductivity measurements provided the degree of counterion binding
(Ī² = 0.854), indicating the importance of the counterions
Near-Infrared-Light-Responsive Magnetic DNA Microgels for Photon- and Magneto-Manipulated Cancer Therapy
Functional
DNA molecules have been introduced into polymer-based nanocarrier
systems to incorporate chemotherapy drugs for cancer therapy. Here
is the first report of dual-responsive microgels composed of a core
of Au nanorods and a shell of magnetic ionic liquid and DNA moieties
in the cross-linking network simultaneously, as effective drug delivery
vectors. TEM images indicated a magnetic polymer shell has an analogous
ādoughnutā shape which loosely surround the AuNRs core.
When irradiated with a near-infrared-light (near-IR) laser, Au nanorods
are the motors which convert the light to heat, leading to the release
of the encapsulated payloads with high controllability. DNA acts not
only as a cross-linker agent, but also as a gatekeeper to regulate
the release of drugs. The internalization study and MTT assay confirm
that these coreāshell DNA microgels are excellent candidates
which can enhance the cytotoxicity of cancer cells controlled by near-IR
laser and shield the high toxicity of chemotherapeutic agents to improve
the killing efficacy of chemotherapeutic agents efficiently in due
course