5 research outputs found
Enzyme Kinetics in Liquid Crystalline Mesophases: Size Matters, But Also Topology
Lyotropic liquid crystalline systems
(LLCs) are excellent immobilizing
carriers for enzymes, due to their biocompatibility and well-defined
pore nanostructure. Here we show that the liquid crystalline mesophase
topology can greatly influence the enzymatic activity in a typical
peroxidase (Horseradish peroxidase, HRP) enzymatic reaction. Enzyme
kinetics was investigated in different LLC mesophases based on monolinolein,
with varying symmetries and dimensions such as the 1D cylindrical
inverse hexagonal phase (H<sub>II</sub>), the 2D planar lamellar phase
(L<sub>α</sub>), and two 3D bicontinuous cubic phases of double
diamond (Pn3m) and gyroid (Ia3d) space groups. As expected, the mesophase
with largest water channel size shows highest activity, regardless
of the topology. Interestingly, however, when mesophases with different
topologies have the same water channel size, then the topology plays
the dominant role, and the enzyme showed the highest activity in the
3D tetra-fold connected Pn3m, followed by the Ia3d with trifold connectivity,
and finally the 1D H<sub>II</sub> phase. This study demonstrates that
the enzymatic activity in LLC mesophases depends on both the water
channel size and the topology of the mesophase
Controlling Anisotropic Drug Diffusion in Lipid-Fe<sub>3</sub>O<sub>4</sub> Nanoparticle Hybrid Mesophases by Magnetic Alignment
We present a new strategy to control the anisotropic
diffusion
of hydrophilic drugs in lyotropic liquid crystals via the dispersion
of magnetic nanoparticles in the mesophase, followed by reorientation
of the mesophase domains via an external magnetic field. We select
a lipid reverse hexagonal phase doped with magnetic iron oxide nanoparticles
and glucose and caffeine as model hybrid mesophase and hydrophilic
drugs, respectively. Upon cooling through the disorder–order
phase transition of the hexagonal phase and under exposure to an external
moderate magnetic field (1.1 T), both the nanoparticles and the hexagonal
domains align with their columnar axes along the field direction.
As a result, the water nanochannels of the inverted hexagonal domains
also align parallel to the field direction, leading to a drug diffusion
coefficient parallel to the field direction much larger than what
was measured perpendicularly: in the case of glucose, for example,
this difference in diffusion coefficients approaches 1 order of magnitude.
Drug diffusion of the unaligned reverse hexagonal phase, which consists
of randomly distributed domains, shows values in between the parallel
and transversal diffusion values. This study shows that modifying
the overall alignment of anisotropic mesophases via moderate external
fields is a valuable means to control the corresponding transport
tensor of the mesophase and demonstrates that the orientation of the
domains plays an important role in the diffusion process of foreign
hydrophilic molecules
Magnetic-Responsive Hybrids of Fe<sub>3</sub>O<sub>4</sub> Nanoparticles with β‑Lactoglobulin Amyloid Fibrils and Nanoclusters
We report on the synthesis and magnetic-responsive behavior of hybrids formed by dispersing negatively charged iron oxide (Fe<sub>3</sub>O<sub>4</sub>) magnetic nanoparticles in positively charged β-lactoglobulin protein solutions at acidic pH, followed by heating at high temperatures. Depending on the pH used, different hybrid aggregates can be obtained, such as nanoparticle-modified amyloid fibrils (pH 3) and spherical nanoclusters (pH 4.5). We investigate the effect of magnetic fields of varying strengths (0–5 T) on the alignment of these Fe<sub>3</sub>O<sub>4</sub>-modified amyloid fibrils and spherical nanoclusters using a combination of scattering, birefringence and microscopic techniques and we find a strong alignment of the hybrids upon increasing the intensity of the magnetic field, which we quantify <i>via</i> 2D and 3D order parameters. We also demonstrate the possibility of controlling magnetically the sol–gel behavior of these hybrids: addition of salt (NaCl, 150 mM) to a solution containing nanoparticles modified with β-lactoglobulin amyloid fibrils (2 wt % fibrils modified with 0.6 wt % Fe<sub>3</sub>O<sub>4</sub> nanoparticles) induces first the formation of a reversible gel, which can then be converted back to solution upon application of a moderate magnetic field of 1.1 T. These hybrids offer a new appealing functional colloidal system in which the aggregation, orientational order and rheological behavior can be efficiently controlled in a purely noninvasive way by external magnetic fields of weak intensity
Twofold Light and Magnetic Responsive Behavior in Nanoparticle–Lyotropic Liquid Crystal Systems
We demonstrate the dual magnetic and light responsive
nature of
hybrid mesophases constituted by Fe<sub>3</sub>O<sub>4</sub> nanoparticles
dispersed in lipid-based lyotropic liquid crystals (LC). When subjected
to an external magnetic field in the mesophase isotropic state, the
nanoparticles aggregate and orient along the magnetic field direction,
and upon cooling the system through the disorder–order transition
the aggregates drive the orientation of the mesophase via heterogeneous
nucleation; furthermore, order–disorder transitions in the
lipidic mesophase can be triggered by Fe<sub>3</sub>O<sub>4</sub>-induced
photothermal effect under visible light exposure. Both the orientational
order and the photothermal effect of the hybrid mesophase can be tuned
by the nanoparticle content, offering a general route for controlled
assembly of complex fluids with combined magnetic and light responsiveness
Lyotropic Liquid Crystalline Cubic Phases as Versatile Host Matrices for Membrane-Bound Enzymes
Lyotropic
liquid crystalline cubic mesophases can function as host
matrices for enzymes because of their biomimetic structural characteristics,
optical transparency, and capability to coexist with water. This study
demonstrates that the in meso immobilized membrane-bound enzyme d-fructose dehydrogenase (FDH) preserves its full activity,
follows ideal Michaelis–Menten kinetics, and shows improved
stability compared to its behavior in solution. Even after 5 days,
the immobilized FDH retained its full activity in meso, whereas a
model hydrophilic enzyme, horseradish peroxidase, maintained only
21% of its original activity. We reason that the lipidic bilayers
in the three-dimensional structures of cubic mesophases provide an
ideal environment for the reconstitution of a membrane-bound enzyme.
The preserved activity, long-term stability, and reusability demonstrate
that these hybrid nanomaterials are ideal matrices for biosensing
and biocatalytic fuel cell applications