35 research outputs found
Synthesis of Neutral, Water-Soluble Oligo–Ethylene Glycol-Containing Dendronized Homo- and Copolymers of Generations 1, 1.5, 2, and 3
Oligo-ethylene glycol-containing
dendronized monomers <b>MG1</b>, <b>MG1.5</b>, <b>MG2</b>, and <b>MG3</b> were
synthesized in a particularly easy fashion on the gram scale involving
only few steps. Their corresponding homopolymers (<b>PG1</b>, <b>PG1.5</b>, <b>PG2</b>, and <b>PG3</b>) and
copolymers (<b>PG1</b><i><b>co</b></i><b>2, PG1</b><i><b>co</b></i><b>3</b>, and <b>PG2</b><i><b>co</b></i><b>3</b>) were synthesized
via free radical polymerization. All the polymers are soluble in water
and also in organic solvents such as DCM, CHCl<sub>3</sub>, 1,4-dioxolane,
DMF, and DMSO. Their glass transition temperatures (<i>T</i><sub>g</sub>) are in the range −68 °C < <i>T</i><sub>g</sub> < −48 °C and thus rather low. All polymers
show thermoresponsive behavior which was investigated by turbidity
measurements. Interestingly, a 1:1 mixture of homopolymers <b>PG1</b> and <b>PG2</b> behaves identical with <b>PG1</b> alone,
while the collapse curve of copolymer <b>PG1</b><i><b>co</b></i><b>2</b> is almost superimposable with that
of <b>PG2</b> alone. Thus, in the former case <b>PG1</b> dominates the thermoresponsive behavior while in the latter this
is done by the G2-dendrons in the copolymer. Finally, the polymer
chains were visualized by AFM, confirming the rod-like behavior of
these rigidified polymers
Probing the Effect of Salt on Asphaltene Aggregation in Aqueous Solutions Using Molecular Dynamics Simulations
The
presence of salts in different processes of oil production
has attracted wide attention because of its effects on asphaltene
aggregation, stability, interactions of emulsions, etc. In this work,
molecular dynamics simulations were employed to study the effect of
salts on aggregation of model asphaltenes. Four types of polyaromatic
compounds possessing key structural features of continental-type asphaltenes
were dispersed into NaCl solutions of different concentrations. These
models have the same polyaromatic core but different lengths for the
side chains. In the two models with relatively long side chains, the
hydrophobic association among side chains is the main driving force
for aggregation. The effect of salt on aggregation is therefore closely
tied to its influence on the hydrophobic interaction: the salt ions
promote the hydrophobic interaction at a low salt concentration while
suppressing it at a high salt concentration. For the model with an
intermediate side chain length, the hydrophobic interaction between
side chains becomes less dominant and the salt has mutual influences
on the core–core, chain–chain, and core–chain
interactions. For the model with the shortest side chains, although
the core–core and core–chain interactions are more important,
the side chains still play a role in aggregation when the salt is
present. Our results provide new insights into the fundamental understanding
of the influence of salts on the aggregation and interaction behaviors
of polyaromatic compounds in an aqueous environment
Cellular Contact Guidance through Dynamic Sensing of Nanotopography
We investigate the effects of surface nanotopography on the migration and cell shape dynamics of the amoeba <i>Dictyostelium discoideum</i>. Multiple prior studies have implicated the patterning of focal adhesions in contact guidance. However, we observe significant contact guidance of <i>Dictyostelium</i> along surfaces with nanoscale ridges or grooves, even though this organism lacks integrin-based adhesions. Cells that move parallel to nanoridges are faster, more protrusive at their fronts, and more elongated than are cells that move perpendicular to nanoridges. Quantitative studies show that nanoridges spaced 1.5 μm apart exhibit the greatest contact guidance efficiency. Because <i>Dictyostelium</i> cells exhibit oscillatory shape dynamics, we model contact guidance as a process in which stochastic cellular harmonic oscillators couple to the periodicity of the nanoridges. In support of this connection, we find that nanoridges nucleate actin polymerization waves of nanoscale width that propagate parallel to the nanoridges
Unraveling Partial Coalescence Between Droplet and Oil–Water Interface in Water-in-Oil Emulsions under a Direct-Current Electric Field via Molecular Dynamics Simulation
When the electric field strength (E)
surpasses
a certain threshold, secondary droplets are generated during the coalescence
between water droplets in oil and the oil–water interface (so-called
the droplet-interface partial coalescence phenomenon), resulting in
a lower efficiency of droplet electrocoalescence. This study employs
molecular dynamics (MD) simulations to investigate the droplet-interface
partial coalescence phenomenon under direct current (DC) electric
fields. The results demonstrate that intermolecular interactions,
particularly the formation of hydrogen bonds, play a crucial role
in dipole–dipole coalescence. Droplet-interface partial coalescence
is categorized into five regimes based on droplet morphology. During
the contact and fusion of the droplet with the water layer, the dipole
moment of the droplet exhibits alternating increases and decreases
along the electric field direction. Electric field forces acting on
sodium ions and the internal interactions within droplets promote
the process of droplet-interface partial coalescence. High field strengths
cause significant elongation of the droplet, leading to its fragmentation
into multiple segments. The migration of hydrated ions has a dual
impact on the droplet-interface partial coalescence, with both facilitative
and suppressive effects. The time required for droplet-interface partial
coalescence initially decreases and subsequently increases as the
field strength increases, depending on the competitive relationship
between the extent of droplet stretching and the electric field force.
This work provides molecular insights into the droplet-interface coalescence
mechanisms in water-in-oil emulsions under DC electric fields
Unraveling Partial Coalescence Between Droplet and Oil–Water Interface in Water-in-Oil Emulsions under a Direct-Current Electric Field via Molecular Dynamics Simulation
When the electric field strength (E)
surpasses
a certain threshold, secondary droplets are generated during the coalescence
between water droplets in oil and the oil–water interface (so-called
the droplet-interface partial coalescence phenomenon), resulting in
a lower efficiency of droplet electrocoalescence. This study employs
molecular dynamics (MD) simulations to investigate the droplet-interface
partial coalescence phenomenon under direct current (DC) electric
fields. The results demonstrate that intermolecular interactions,
particularly the formation of hydrogen bonds, play a crucial role
in dipole–dipole coalescence. Droplet-interface partial coalescence
is categorized into five regimes based on droplet morphology. During
the contact and fusion of the droplet with the water layer, the dipole
moment of the droplet exhibits alternating increases and decreases
along the electric field direction. Electric field forces acting on
sodium ions and the internal interactions within droplets promote
the process of droplet-interface partial coalescence. High field strengths
cause significant elongation of the droplet, leading to its fragmentation
into multiple segments. The migration of hydrated ions has a dual
impact on the droplet-interface partial coalescence, with both facilitative
and suppressive effects. The time required for droplet-interface partial
coalescence initially decreases and subsequently increases as the
field strength increases, depending on the competitive relationship
between the extent of droplet stretching and the electric field force.
This work provides molecular insights into the droplet-interface coalescence
mechanisms in water-in-oil emulsions under DC electric fields
Protease-Activated Ratiometric Fluorescent Probe for pH Mapping of Malignant Tumors
A protease-activated ratiometric fluorescent probe based on fluorescence resonance energy transfer between a pH-sensitive fluorescent dye and biocompatible Fe<sub>3</sub>O<sub>4</sub> nanocrystals was constructed. A peptide substrate of MMP-9 served as a linker between the particle quencher and the chromophore that was covalently attached to the antitumor antibody. The optical response of the probe to activated MMP-9 and gastric cell line SGC7901 tumor cells was investigated, followed by <i>in vivo</i> tumor imaging. Based on the ratiometric pH response to the tumor microenvironment, the resulting probe was successfully used to image the pH of subcutaneous tumor xenografts
Cross-cohort comparisons of VMHC.
<p><b>A</b>: The AD subjects showed significantly decreased VMHC in the OFC, ACC, POC, NAcc, putamen, caudate and insula compared to CN. <b>B</b>: The AD subjects showed significantly decreased VMHC in the OFC, putamen, caudate, insula, SMC, and OcG compared to MCI. <b>C</b>: The MCI subjects showed significantly increased VMHC in the SMC compared to CN. <b>D-H</b> show the locations of the five anatomical structures where the VMHC was significantly different across the three cohorts. The values in the bar graphs are z-scores transformed from the VMHC values. * represents statistical differences between groups (*, <i>p</i> ≤ 0.05; ***, <i>p</i> ≤ 0.001).</p
Normative VMHC map of the CN group (one-sample t-test, family-wise error corrected, p < 0.001, extent threshold = 10).
<p>Normative VMHC map of the CN group (one-sample t-test, family-wise error corrected, p < 0.001, extent threshold = 10).</p
Correlation between diffusion parameters, volume of the genu of corpus callosum, VMHC, and MMSE scores of all the subjects.
<p>The values in the table are the correlation coefficients and corresponding p-values (partial correlation with age effect corrected).</p><p>*, p ≤ 0.05;</p><p>**, p ≤ 0.01;</p><p>***, p ≤ 0.001.</p><p>Abbreviations: FA, fractional anisotropy; MD, mean diffusivity (×10–3 mm2/s); λ‖, axial diffusivity (×10–3 mm2/s); λ┴, radial diffusion (×10–3 mm2/s); VMHC, voxel mirror homotopic connectivity; OFC, orbitofrontal cortex; ACC, anterior cingulate cortex; NAcc, nucleus accumbens; SMC, sensorimotor cortex; OcG, occipital gyrus.</p><p>Correlation between diffusion parameters, volume of the genu of corpus callosum, VMHC, and MMSE scores of all the subjects.</p
DTI and volumetric differences among AD, MCI and CN.
<p><b>A:</b> Voxel-based analysis showed significant difference of FA between AD and CN in the genu of the corpus callosum (family-wise error corrected, <i>p</i> < 0.05, extent threshold = 10). <b>B-F:</b> Group comparisons revealed the patterns of diffusion parameters and volume changes in the genu of the corpus callosum (FA: AD < MCI < CN; MD: AD > CN / MCI; λ<sub>┴</sub>: AD > CN / MCI; λ<sub>‖</sub>: no difference; Volume: AD < CN/MCI). * represents statistical differences between groups (*, <i>p</i> ≤ 0.05; ***, <i>p</i> ≤ 0.001)</p