26 research outputs found
Monitoring of Pore Orientation by <i>in Operando</i> Grazing Incidence Small-Angle Xāray Scattering during Templated Electrodeposition of Mesoporous Pt Films
We have used in operando grazing incidence
small-angle
X-ray scattering (GISAXS) to monitor structural changes during templated
electrodeposition of mesoporous platinum films on gold electrodes
from a ternary lyotropic liquid crystalline mixture of aqueous hexachloroplatinic
acid and the diblock copolymer surfactant Brij56. While the cylindrical
micelles of the lyotropic liquid crystal (LLC) in the hexagonal phase
have a center-to-center distance of 7.5 nm with a preferential alignment
parallel to the electrode surface, the electrodeposited platinum films
contain highly ordered mesopores arranged in a 2D hexagonal structure,
with a center-to-center distance of about 8.5 nm and a preferential
orientation perpendicular to the electrode surface. The progression
of structural changes of the LLC template and the deposited mesoporous
Pt could be monitored for the first time in operando by GISAXS: within the first 14 s of deposition, a nucleation burst
of Pt coincides with a loss of preferential alignment of the LLC.
Initially, the morphology of the 2-dimensionally nucleated Pt replicates
the Au substrate. During the following 5 to 7 min, the growth morphology
of the Pt film changes, and vertically aligned mesopores form. Our
results indicate mutual interaction between the species involved in
the electrodeposition and the LLC template, leading to a partial loss
of horizontal orientation of the LLC during Pt nucleation before vertical
rearrangement of the micelles to the electrode surface. The vertically
aligned mesopores in the Pt and the possibility to produce freestanding
films make these materials interesting in fields such as electrocatalysis,
energy harvesting, and nanofluidics
Monitoring of Pore Orientation by <i>in Operando</i> Grazing Incidence Small-Angle Xāray Scattering during Templated Electrodeposition of Mesoporous Pt Films
We have used in operando grazing incidence
small-angle
X-ray scattering (GISAXS) to monitor structural changes during templated
electrodeposition of mesoporous platinum films on gold electrodes
from a ternary lyotropic liquid crystalline mixture of aqueous hexachloroplatinic
acid and the diblock copolymer surfactant Brij56. While the cylindrical
micelles of the lyotropic liquid crystal (LLC) in the hexagonal phase
have a center-to-center distance of 7.5 nm with a preferential alignment
parallel to the electrode surface, the electrodeposited platinum films
contain highly ordered mesopores arranged in a 2D hexagonal structure,
with a center-to-center distance of about 8.5 nm and a preferential
orientation perpendicular to the electrode surface. The progression
of structural changes of the LLC template and the deposited mesoporous
Pt could be monitored for the first time in operando by GISAXS: within the first 14 s of deposition, a nucleation burst
of Pt coincides with a loss of preferential alignment of the LLC.
Initially, the morphology of the 2-dimensionally nucleated Pt replicates
the Au substrate. During the following 5 to 7 min, the growth morphology
of the Pt film changes, and vertically aligned mesopores form. Our
results indicate mutual interaction between the species involved in
the electrodeposition and the LLC template, leading to a partial loss
of horizontal orientation of the LLC during Pt nucleation before vertical
rearrangement of the micelles to the electrode surface. The vertically
aligned mesopores in the Pt and the possibility to produce freestanding
films make these materials interesting in fields such as electrocatalysis,
energy harvesting, and nanofluidics
Resveratrol Interaction with Lipid Bilayers: A Synchrotron Xāray Scattering Study
Resveratrol
belongs to the large group of biologically active polyphenol
compounds, with several beneficial health effects including antioxidant
activity, anti-inflammatory action, cardiovascular protection, neuroprotection,
and cancer chemoprevention. In the present study,
the possibility that the effects of resveratrol described above are
caused by resveratrol membrane interactions and structural modifications
of lipid bilayers is evaluated. In this context, it is possible that
resveratrol interacts selectively with lipid domains present in biological
membranes, thereby modulating the localization of the anchored proteins
and controlling their intracellular cascades. This study was conducted
in a synchrotron particle accelerator, where the influence of resveratrol
in the structural organization of lipid domains in bilayers was investigated
using small- and wide-angle X-ray scattering (SAXS and WAXS) techniques.
Membrane mimetic systems composed of egg l-Ī±-phosphatidylcholine
(EPC), cholesterol (CHOL), and sphingomyelin (SM), with different
molar ratios, were used to access the effects of resveratrol on the
order and structure of the membrane. The results revealed that resveratrol
induces phase separation, promoting the formation of lipid domains
in EPC, EPC:CHOL [4:1], and EPC:CHOL:SM [1:1:1] bilayers, which brings
some structural organization to membranes. Therefore, resveratrol
controls lipid packing of bilayers by inducing the organization of
lipid rafts. Moreover, the formation of lipid domains is important
for modulating the activity of many receptors, transmembrane proteins,
and enzymes whose activity depends on the structural organization
of the membrane and on the presence or absence of these organized
domains. This evidence can thereby explain the therapeutic effects
of resveratrol
Synchrotron Small-Angle Xāray Scattering Studies of Hemoglobin Nonaggregation Confined inside Polymer Capsules
The effect of confinement on the structure of hemoglobin
(Hb) within polymer capsules was investigated here. Hemoglobin transformed
from an aggregated state in solution to a nonaggregated state when
confined inside the polymer capsules. This was directly confirmed
using synchrotron small-angle X-ray scattering (SAXS) studies. The
radius of gyration (<i>R</i><sub>g</sub>) and polydispersity
(<i>p</i>) of the proteins in the confined state were smaller
compared to those in solution. In fact, the <i>R</i><sub>g</sub> value is very similar to theoretical values obtained using
protein structures generated from the Protein Databank. In the temperature
range (25ā85 Ā°C, Tm 59 Ā°C), the <i>R</i><sub>g</sub> values for the confined Hb remained constant. This observation
is in contrary to the increasing <i>R</i><sub>g</sub> values
obtained for the bare Hb in solution. This suggested higher thermal
stability of Hb when confined inside the polymer capsule than when
in solution. Changes in protein configuration were also reflected
in the protein function. Confinement resulted in a beneficial enhancement
of the electroactivity of Hb. While Hb in solution showed dominance
of the cathodic process (Fe<sup>3+</sup> ā Fe<sup>2+</sup>),
efficient reversible Fe<sup>3+</sup>/Fe<sup>2+</sup> redox response
is observed in the case of the confined Hb. This has important protein
functional implications. Confinement allows the electroactive heme
to take up positions favorable for various biochemical activities
such as sensing of analytes of various sizes from small to macromolecules
and controlled delivery of drugs
Detailed Study of the Nanocasting Process by in Situ Xāray Scattering and Diffraction
The nanocasting method is a valuable
tool for producing metal oxides
with a well-defined nanostructure. However, the precise details on
how the metal oxide is developed inside the mesoporous silica template
remain unclear. In this study, we clarify how nickel nitrate species
are evolving to nickel oxide and how they are redistributed inside
mesoporous SBA-15 particles as a function of heating temperature and
surrounding gas atmosphere by a combination of in situ small-angle
X-ray scattering, X-ray diffraction and thermogravimetric techniques
as well as ex situ transmission electron microscopy and nitrogen physisorption
measurements. The SBA-15 template was initially impregnated with NiĀ(NO<sub>3</sub>)<sub>2</sub>Ā·6H<sub>2</sub>O using the wet infiltration
method. The results indicate an initial redistribution of the nickel
nitrate salt located outside the pore system into the mesopores due
to dissolution, while at temperatures of 110ā150 Ā°C (depending
on which type of gas flow is used) the mobility of the salt is lost
due to drying of the salt. Above 220 Ā°C, the nickel nitrate decomposes,
possibly via nickel hydroxynitrate, to NiO, forming nanoparticles
inside the pore channels. The results shed light on the events occurring
during the nanocasting process and can be used for further optimization
of the fidelity of replication
Position Accuracy of Gold Nanoparticles on DNA Origami Structures Studied with Small-Angle Xāray Scattering
DNA origami objects allow for accurate
positioning of guest molecules
in three dimensions. Validation and understanding of design strategies
for particle attachment as well as analysis of specific particle arrangements
are desirable. Small-angle X-ray scattering (SAXS) is suited to probe
distances of nano-objects with subnanometer resolution at physiologically
relevant conditions including pH and salt and at varying temperatures.
Here, we show that the pair density distribution function (PDDF) obtained
from an indirect Fourier transform of SAXS intensities in a model-free
way allows to investigate prototypical DNA origami-mediated gold nanoparticle
(AuNP) assemblies. We analyze the structure of three AuNP-dimers on
a DNA origami block, an AuNP trimer constituted by those dimers, and
a helical arrangement of nine AuNPs on a DNA origami cylinder. For
the dimers, we compare the model-free PDDF and explicit modeling of
the SAXS intensity data by superposition of scattering intensities
of the scattering objects. The PDDF of the trimer is verified to be
a superposition of its dimeric contributions, that is, here AuNP-DNA
origami assemblies were used as test boards underlining the validity
of the PDDF analysis beyond pairs of AuNPs. We obtain information
about AuNP distances with an uncertainty margin of 1.2 nm. This readout
accuracy in turn can be used for high precision placement of AuNP
by careful design of the AuNP attachment sites on the DNA-structure
and by fine-tuning of the connector types
<i>In Situ</i> SAXS Study on a New Mechanism for Mesostructure Formation of Ordered Mesoporous Carbons: Thermally Induced Self-Assembly
A new mechanism for mesostructure formation of ordered
mesoporous
carbons (OMCs) was investigated with in situ small-angle X-ray scattering
(SAXS) measurements: thermally induced self-assembly. Unlike the well-established
evaporation-induced self-assembly (EISA), the structure formation
for organicāorganic self-assembly of an oligomeric resol precursor
and the block-copolymer templates Pluronic P123 and F127 does not
occur during evaporation but only by following a thermopolymerization
step at temperatures above 100 Ā°C. The systems investigated here
were cubic (<i>Im</i>3Ģ
<i>m</i>), orthorhombic <i>Fmmm</i>) and 2D-hexagonal (plane group <i>p</i>6<i>mm</i>) mesoporous carbon phases in confined environments, as
thin films and within the pores of anodic alumina membranes (AAMs),
respectively. The thin films were prepared by spin-coating mixtures
of the resol precursor and the surfactants in ethanol followed by
thermopolymerization of the precursor oligomers. The carbon phases
within the pores of AAMs were made by imbibition of the latter solutions
followed by solvent evaporation and thermopolymerization within the
solid template. This thermopolymerization step was investigated in
detail with in situ grazing incidence small-angle X-ray scattering
(GISAXS, for films) and in situ SAXS (for AAMs). It was found that
the structural evolution strongly depends on the chosen temperature,
which controls both the rate of the mesostructure formation and the
spatial dimensions of the resulting mesophase. Therefore the process
of structure formation differs significantly from the known EISA process
and may rather be viewed as thermally induced self-assembly. The complete
process of structure formation, template removal, and shrinkage during
carbonization up to 1100 Ā°C was monitored in this in situ SAXS
study
Hierarchical Formation Mechanism of CoFe<sub>2</sub>O<sub>4</sub> Mesoporous Assemblies
The development of synthetic hybrid organicāinorganic approaches and the understanding of the chemico-physical mechanisms leading to hierarchical assembly of nanocrystals into superstructures pave the way to the design and fabrication of multifunction microdevices able to simultaneously control processes at the nanoscale. This work deals with the design of spherical mesoporous magnetic assemblies through a surfactant assisted water-based strategy and the study of the formation mechanism by a combined use of transmission electron microscopy, X-ray diffraction, and time-resolved small angle X-ray scattering techniques. We visualize the hierarchical mechanism formation of the magnetic assemblies in the selected sodium dodecylsulfate (SDS)-assisted water-based strategy. At the first stage, an intermediate lamellar phase (L) represented by Ī²-Co(OH)<sub>2</sub> and FeOOH hexagonal plates is formed. Then, the nucleation of primary CoFe<sub>2</sub>O<sub>4</sub> (N<sub>1</sub>) nanocrystals of about 6ā7 nm occurs by the dissolution of FeOOH and the reaction of Fe<sup>III</sup> ions coordinated to the SDS micelles, at the reactive sites provided by vertices and edges of the Ī²-Co(OH)<sub>2</sub> plates. The intermediate phase consumes as the primary crystalline nanoparticles form, confined by the surfactant molecules around them, and assembly in spherical mesoporous assemblies. The key role of the surfactant in the formation of porous assemblies has been evidenced by an experiment carried out in the absence of SDS and confirmed by the pore size diameter of the assemblies (about 2ā3 nm), that can be correlated with the length of the surfactant dodecylsulfate molecule
Peptides at the Interface: Self-Assembly of Amphiphilic Designer Peptides and Their Membrane Interaction Propensity
Self-assembling
amphiphilic designer peptides have been successfully
applied as nanomaterials in biomedical applications. Understanding
molecular interactions at the peptideāmembrane interface is
crucial, since interactions at this site often determine (in)Ācompatibility.
The present study aims to elucidate how model membrane systems of
different complexity (in particular single-component phospholipid
bilayers and lipoproteins) respond to the presence of amphiphilic
designer peptides. We focused on two short anionic peptides, V<sub>4</sub>WD<sub>2</sub> and A<sub>6</sub>YD, which are structurally
similar but showed a different self-assembly behavior. A<sub>6</sub>YD self-assembled into high aspect ratio nanofibers at low peptide
concentrations, as evidenced by synchrotron small-angle X-ray scattering
and electron microscopy. These supramolecular assemblies coexisted
with membranes without remarkable interference. In contrast, V<sub>4</sub>WD<sub>2</sub> formed only loosely associated assemblies over
a large concentration regime, and the peptide promoted concentration-dependent
disorder on the membrane arrangement. Perturbation effects were observed
on both membrane systems although most likely induced by different
modes of action. These results suggest that membrane activity critically
depends on the peptideās inherent ability to form highly cohesive
supramolecular structures
Surface Passivation Improves the Synthesis of Highly Stable and Specific DNA-Functionalized Gold Nanoparticles with Variable DNA Density
We report a novel and multifaceted
approach for the quick synthesis of highly stable single-stranded
DNA (ssDNA) functionalized gold nanoparticles (AuNPs). The method
is based on the combined effect of surface passivation by (1-mercaptoundec-11-yl)ĀhexaĀ(ethylene
glycol) and low pH conditions, does not require any salt pretreatment
or high excess of ssDNA, and can be generalized for oligonucleotides
of any length or base sequence. The synthesized ssDNA-coated AuNPs
conjugates are stable at salt concentrations as high as 3.0 M, and
also functional and specific toward DNAāDNA hybridization,
as shown from UVāvis spectrophotometry, scanning electron microscopy,
gel electrophoresis, fluorescence, and small angle X-ray scattering
based analyses. The method is highly flexible and shows an additional
advantage of creating ssDNA-AuNP conjugates with a predefined number
of ssDNA strands per particle. Its simplicity and tenability make
it widely applicable to diverse biosensing applications involving
ssDNA functionalized AuNPs