14 research outputs found
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A highly oriented cubic phase formed by lipids under shear
We demonstrate the formation of a macroscopically
oriented inverse bicontinuous cubic (QII) lipid
phase from a sponge (L3) phase by controlled hydration
during shear flow. The L3 phase was the monoolein/
butanediol/water system; the addition of water reduces
the butanediol concentration, inducing the formation of a
diamond (QIID) cubic phase, which is oriented by the shear
flow. The phenomenon was reproduced in both capillary
and Couette geometries, indicating that this represents a
robust general route for the production of highly aligned
bulkQII samples, with applications in nanomaterial templating and protein research
High-resolution strain-mapping during in-situ nanoindentation of CVD thin films
The NanoMAX beamline is a hard X-ray nanoprobe beamline at MAX IV Laboratory, Lund, Sweden. This beamline was designed to take full advantage of the exceptionally low emittance and the resulting coherence properties of the X-ray beam. A nano-focus beam of 50×50 nm2 of high X-ray photon intensity is available for experiments. This small focus is ideal to investigate heterogeneous samples in materials science with high spatial resolution, utilizing techniques such as scanning X-ray diffraction, 2D X-ray fluorescence mapping, and coherent imaging in the Bragg geometry.
Chalmers University of Technology and MAX IV Laboratory have acquired a nanoindenter to be installed at the NanoMAX beamline. The combination of in-situ micro-mechanical testing and nano-focused scanning X-ray diffraction permits time-resolved high-resolution in-situ strain mapping. The experimental configuration is based on an Alemnis nanoindenter which is transferrable between the beamline and a scanning electron microscope (SEM). This allows for a sample characterization in a SEM prior to the X-ray beamline experiment. A potential science case is the investigation of local residual stress fields and their changes under increasing load.
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Elongation rate and average length of amyloid fibrils in solution using isotope-labelled small-angle neutron scattering.
Funder: Boehringer Ingelheim FondsFunder: University of BathWe demonstrate a solution method that allows both elongation rate and average fibril length of assembling amyloid fibrils to be estimated. The approach involves acquisition of real-time neutron scattering data during the initial stages of seeded growth, using contrast matched buffer to make the seeds effectively invisible to neutrons. As deuterated monomers add on to the seeds, the labelled growing ends give rise to scattering patterns that we model as cylinders whose increase in length with time gives an elongation rate. In addition, the absolute intensity of the signal can be used to determine the number of growing ends per unit volume, which in turn provides an estimate of seed length. The number of ends did not change significantly during elongation, demonstrating that any spontaneous or secondary nucleation was not significant compared with growth on the ends of pre-existing fibrils, and in addition providing a method of internal validation for the technique. Our experiments on initial growth of alpha synuclein fibrils using 1.2 mg ml-1 seeds in 2.5 mg ml-1 deuterated monomer at room temperature gave an elongation rate of 6.3 ± 0.5 Å min-1, and an average seed length estimate of 4.2 ± 1.3 μm
Thermoresponsive Segments Retard the Formation of Equilibrium Micellar Interpolyelectrolyte Complexes by Detouring to Various Intermediate Structures
The kinetics of interpolyelectrolyte
complexation involving architecturally complex (star-like) polymeric
components is addressed. Specifically, the spontaneous coupling of
branched cationic star-shaped miktoarm polymers, i.e., quaternized
polyÂ(ethylene oxide)<sub>114</sub>-(polyÂ(2-(dimethylamino)Âethyl
methacrylate)<sub>17</sub>)<sub>4</sub> (PEO<sub>114</sub>-(<i>q</i>PDMAEMA<sub>17</sub>)<sub>4</sub>), and temperature-sensitive
linear anionic diblock copolymers polyÂ(vinyl sulfonate)<sub>31</sub>-<i>b</i>-polyÂ(<i>N</i>-isopropylÂacrylamide)<sub>27</sub> (PVS<sub>31</sub>-<i>b</i>-PNIPAM<sub>27</sub>) and further rearrangements of the formed complexes were investigated
by means of stopped-flow small-angle X-ray scattering (SAXS). Colloidally
stable micelles were obtained upon mixing both polymers at a 1:1 charge
molar ratio in saline solutions. The description of the time-resolved
SAXS data with appropriate form factor models yielded dimensions for
each micellar domain and detailed the picture of the time-dependent
size changes and restructuring processes. A fast interpolyelectrolyte
coupling and structural equilibration were observed when mixing occurs
below the lower critical solution temperature (LCST) of PNIPAM, resulting
in small spherical-like assemblies with hydrated PNIPAM coronal blocks.
Above the LCST, the collapsed PNIPAM decelerates equilibration, though
temperature as such is expected to boost the kinetics of complex formation:
after a fast initial interpolyelectrolyte coupling, different nonequilibrium
structures of spherical and worm-like shape are observed on different
time scales. This study illustrates how a thermoresponsive component
can modulate the influence of temperature on kinetics, particularly
for rearrangement processes toward equilibrium structures during interpolyelectrolyte
complexation
Temperature-induced structure switch in thermo-responsive micellar interpolyelectrolyte complexes: toward core–shell–corona and worm-like morphologies
Tuning phase transitions of aqueous protein solutions by multivalent cations
In the presence of trivalent cations, negatively charged globular proteins show a rich phase behaviour including reentrant condensation, crystallisation, clustering and lower critical solution temperature metastable liquid–liquid phase separation (LCST–LLPS). Here, we present a systematic study on how different multivalent cations can be employed to tune the interactions and the associated phase behaviour of proteins. We focus our investigations on the protein bovine serum albumin (BSA) in the presence of HoCl3, LaCl3 and YCl3. Using UV-Vis spectroscopy and small-angle X-ray scattering (SAXS), we find that the interprotein attraction induced by Ho3+ is very strong, while the one induced by La3+ is comparatively weak when comparing the data to BSA–Y3+ systems based on our previous work. Using zeta potential and isothermal titration calorimetry (ITC) measurements, we establish different binding affinities of cations to BSA with Ho3+ having the highest one. We propose that a combination of different cation features such as radius, polarisability and in particular hydration effects determine the protein–protein interaction induced by these cations. Our findings imply that subtle differences in cation properties can be a sensitive tool to fine-tune protein–protein interactions and phase behaviour in solution
Salt-induced hydrogelation of functionalised-dipeptides at high pH
Addition of divalent cations to a solution of a naphthalene-diphenylalanine that forms worm-like micelles at high pH results in the formation of a rigid, self-supporting hydroge
On the question of two-step nucleation in protein crystallization
We report a real-time study on protein crystallization in the presence of multivalent salts using small angle X-ray scattering (SAXS) and optical microscopy, focusing particularly on the nucleation mechanism as well as on the role of the metastable intermediate phase (MIP). Using bovine beta-lactoglobulin as a model system in the presence of the divalent salt CdCl2, we have monitored the early stage of crystallization kinetics which demonstrates a two-step nucleation mechanism: protein aggregates form a MIP, which is followed by the nucleation of crystals within the MIP. Here we focus on characterizing and tuning the structure of the MIP using salt and the related effects on the two-step nucleation kinetics. The results suggest that increasing the salt concentration near the transition zone pseudo-c∗∗ enhances the energy barrier for both MIPs and crystal nucleation, leading to slow growth. The structural evolution of the MIP and its effect on subsequent nucleation is discussed based on the growth kinetics. The observed kinetics can be well described, using a rate-equation model based on a clear physical two-step picture. This real-time study not only provides evidence for a two-step nucleation process for protein crystallization, but also elucidates the role and the structural signature of the MIPs in the nonclassical process of protein crystallization
Intramicrogel Complexation of Oppositely Charged Compartments As a Route to Quasi-Hollow Structures
Real-Time Observation of Nonclassical Protein Crystallization Kinetics
We
present a real-time study of protein crystallization of bovine
β-lactoglobulin in the presence of CdCl<sub>2</sub> using small-angle
X-ray scattering and optical microscopy. From observing the crystallization
kinetics, we propose the following multistep crystallization mechanism
that is consistent with our data. In the first step, an intermediate
phase is formed, followed by the nucleation of crystals within the
intermediate phase. During this period, the number of crystals increases
with time, but the crystal growth is slowed down by the surrounding
dense intermediate phase due to the low mobility. In the next step,
the intermediate phase is consumed by nucleation and slow growth,
and the crystals are exposed to the dilute phase. In this stage, the
number of crystals becomes nearly constant, whereas the crystals grow
rapidly due to access to the free protein molecules in the dilute
phase. This real-time study not only provides evidence for a two-step
nucleation process for protein crystallization but also elucidates
the role and the structural signature of the metastable intermediate
phase in this process