5 research outputs found
Densification of Ionic Liquid Molecules within a Hierarchical Nanoporous Carbon Structure Revealed by Small-Angle Scattering and Molecular Dynamics Simulation
The
molecular-scale properties of the room temperature ionic liquid
(RTIL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide,
[C<sub>4</sub>mim<sup>+</sup>][Tf<sub>2</sub>N<sup>–</sup>],
confined in nanometer-scale carbon pores have been investigated using
small-angle X-ray and neutron scattering and fully atomistic molecular
dynamics simulations. [C<sub>4</sub>mim<sup>+</sup>][Tf<sub>2</sub>N<sup>–</sup>] densities significantly higher than that of
the bulk fluid at the same temperature and pressure result from the
strong affinity of the RTIL cation with the carbon surface during
the initial filling of slitlike, subnanometer micropores along the
mesopore surfaces. Subsequent filling of cylindrical ∼8 nm
mesopores in the mesoporous carbon matrix is accompanied by weak RTIL
densification. The relative size of the micropores compared to the
ion dimension, and the strong interaction between the RTIL and the
slit-like micropore, disrupt the bulk RTIL structure. This results
in a low-excluded volume, high-RTIL ion density configuration. The
observed interfacial phenomena are simulated using a molecular dynamics
model consisting of a linear combination of mesopore and micropore
effects. These observations highlight the importance of including
the effects of a porous substrate’s internal surface morphology,
especially roughness and microporosity, on the resulting electrolyte
structural properties and performance in electrical energy storage
applications
Alkyl Chain Length and Temperature Effects on Structural Properties of Pyrrolidinium-Based Ionic Liquids: A Combined Atomistic Simulation and Small-Angle X-ray Scattering Study
Molecular dynamics (MD) simulations of 1-alkyl-1-methylpyrrolidinium
bis(trifluoromethanesulfonyl)imide ([C<sub><i>n</i></sub>MPy][Tf<sub>2</sub>N], <i>n</i> = 3, 4, 6, 8, 10) were
conducted using an all-atom model. Radial distribution functions (RDF)
were computed and structure functions were generated to compare with
new X-ray scattering experimental results, reported herein. The scattering
peaks in the structure functions generally shift to lower <i>Q</i> values with increased temperature for all the liquids
in this series. However, the first sharp diffraction peak (FSDP) in
the longer alkyl chain liquids displays a marked shift to higher <i>Q</i> values with increasing temperature. Alkyl chain-dependent
ordering of the polar groups and increased tail aggregation with increasing
alkyl chain length were observed in the partial pair correlation functions
and the structure functions. The reasons for the observed alkyl chain-dependent
phenomena and temperature effects were explored
Structure of Spontaneously Formed Solid-Electrolyte Interphase on Lithiated Graphite Determined Using Small-Angle Neutron Scattering
We address the reactivity of lithiated
graphite–anode material
for Li-ion batteries with standard organic solvents used in batteries
(ethylene carbonate and dimethyl carbonate) by following changes in
neutron scattering signals. The reaction produces a nanosized layer,
the solid-electrolyte interphase (SEI), on the graphite particles.
We probe the structure and chemistry of the SEI using small-angle
neutron scattering (SANS) and inelastic neutron scattering. The SANS
results show that the SEI fills 20–30 nm sized pores, and inelastic
scattering experiments with H/D substitution show that this “chemical”
SEI is primarily organic in nature; that is, it contains a large amount
of hydrogen. The graphite–SEI particles show surface fractal
scattering characteristic of a rough particle–void interface
and are interconnected. The observed changes in the SEI structure
and composition provide new insight into SEI formation. The chemically
formed SEI is complementary and simpler in composition to the electrochemically
formed SEI, which involves a number of different reactions and products
that are difficult to deconvolute
Fate of Liposomes in the Presence of Phospholipase C and D: From Atomic to Supramolecular Lipid Arrangement
Understanding the
origins of lipid membrane bilayer rearrangement
in response to external stimuli is an essential component of cell
biology and the bottom-up design of liposomes for biomedical applications.
The enzymes phospholipase C and D (PLC and PLD) both cleave the phosphorus–oxygen
bonds of phosphate esters in phosphatidylcholine (PC) lipids. The
atomic position of this hydrolysis reaction has huge implications
for the stability of PC-containing self-assembled structures, such
as the cell wall and lipid-based vesicle drug delivery vectors. While
PLC converts PC to diacylglycerol (DAG), the interaction of PC with
PLD produces phosphatidic acid (PA). Here we present a combination
of small-angle scattering data and all-atom molecular dynamics simulations,
providing insights into the effects of atomic-scale reorganization
on the supramolecular assembly of PC membrane bilayers upon enzyme-mediated
incorporation of DAG or PA. We observed that PC liposomes completely
disintegrate in the presence of PLC, as conversion of PC to DAG progresses.
At lower concentrations, DAG molecules within fluid PC bilayers form
hydrogen bonds with backbone carbonyl oxygens in neighboring PC molecules
and burrow into the hydrophobic region. This leads initially to membrane
thinning followed by a swelling of the lamellar phase with increased
DAG. At higher DAG concentrations, localized membrane tension causes
a change in lipid phase from lamellar to the hexagonal and micellar
cubic phases. Molecular dynamics simulations show that this destabilization
is also caused in part by the decreased ability of DAG-containing
PC membranes to coordinate sodium ions. Conversely, PLD-treated PC
liposomes remain stable up to extremely high conversions to PA. Here,
the negatively charged PA headgroup attracts significant amounts of
sodium ions from the bulk solution to the membrane surface, leading
to a swelling of the coordinated water layer. These findings are a
vital step toward a fundamental understanding of the degradation behavior
of PC lipid membranes in the presence of these clinically relevant
enzymes, and toward the rational design of diagnostic and drug delivery
technologies for phospholipase-dysregulation-based diseases
Fate of Liposomes in the Presence of Phospholipase C and D: From Atomic to Supramolecular Lipid Arrangement
Understanding the
origins of lipid membrane bilayer rearrangement
in response to external stimuli is an essential component of cell
biology and the bottom-up design of liposomes for biomedical applications.
The enzymes phospholipase C and D (PLC and PLD) both cleave the phosphorus–oxygen
bonds of phosphate esters in phosphatidylcholine (PC) lipids. The
atomic position of this hydrolysis reaction has huge implications
for the stability of PC-containing self-assembled structures, such
as the cell wall and lipid-based vesicle drug delivery vectors. While
PLC converts PC to diacylglycerol (DAG), the interaction of PC with
PLD produces phosphatidic acid (PA). Here we present a combination
of small-angle scattering data and all-atom molecular dynamics simulations,
providing insights into the effects of atomic-scale reorganization
on the supramolecular assembly of PC membrane bilayers upon enzyme-mediated
incorporation of DAG or PA. We observed that PC liposomes completely
disintegrate in the presence of PLC, as conversion of PC to DAG progresses.
At lower concentrations, DAG molecules within fluid PC bilayers form
hydrogen bonds with backbone carbonyl oxygens in neighboring PC molecules
and burrow into the hydrophobic region. This leads initially to membrane
thinning followed by a swelling of the lamellar phase with increased
DAG. At higher DAG concentrations, localized membrane tension causes
a change in lipid phase from lamellar to the hexagonal and micellar
cubic phases. Molecular dynamics simulations show that this destabilization
is also caused in part by the decreased ability of DAG-containing
PC membranes to coordinate sodium ions. Conversely, PLD-treated PC
liposomes remain stable up to extremely high conversions to PA. Here,
the negatively charged PA headgroup attracts significant amounts of
sodium ions from the bulk solution to the membrane surface, leading
to a swelling of the coordinated water layer. These findings are a
vital step toward a fundamental understanding of the degradation behavior
of PC lipid membranes in the presence of these clinically relevant
enzymes, and toward the rational design of diagnostic and drug delivery
technologies for phospholipase-dysregulation-based diseases