6 research outputs found
Dynamics and Structure of a Bitumen Emulsion as Studied by <sup>1</sup>H NMR Diffusometry
Self-diffusion in
a bitumen emulsion was studied by 1H NMR. The emulsion
forms two phases: continuous and dispersed. The
continuous aqueous phase contains mainly water, with the energy of
activation of the diffusion process equal to that of bulk water, while
its diffusivity is smaller than that of bulk water by a factor of
2. The dispersed phase consists of bitumen droplets containing confined
water, whose dynamics is characterized by a fully restricted diffusion
regime in cavities with sizes of ā¼0.11 Ī¼m. Therefore,
the studied bitumen emulsion can be described by a model of a complex
multiple emulsion of the water/oil/water (WOW) type. The suggested
model does agree well with data from 1H NMR spectroscopy
and diffusometry of the bitumen emulsion doped with paramagnetic MnSO4(aq) as well as with an additional 1H NMR study
of the emulsion structure, in which emulsion stability was compromised
by freezing at 253 K
Effect of Curcumin on Lateral Diffusion of Phosphatidylcholines in Saturated and Unsaturated Bilayers
Curcumin,
a dietary polyphenol, is a natural spice with preventive
and therapeutic potential for neurodegenerative diseases such as Alzheimerās
and Parkinsonās diseases. Curcumin possesses a spectrum of
antioxidant, anti-inflammatory, anticarcinogenic, and antimutagenic
properties. Because of this broad spectrum of pharmacological activity,
it has been suggested that, like cholesterol, curcumin exerts its
effect on a rather basic biological level, such as on lipid bilayers
of biomembranes. The effect of curcumin on translational mobility
of lipids in biomembranes has not yet been studied. In this work,
we used <sup>1</sup>H NMR diffusometry to explore lateral diffusion
in planar-oriented bilayers of dimyristoylphosphatidylcholine (DMPC)
and dioleoylphosphatidylcholine (DOPC) at curcumin concentrations
of up to 40 mol % and in the temperature range of 298ā333 K.
The presence of curcumin at much lower concentrations (ā¼7 mol
%) leads to a decrease in the lateral diffusion coefficient of DOPC
by a factor of 1.3 at lower temperatures and by a factor of 1.14 at
higher temperatures. For DMPC, the diffusion coefficient decreases
by a factor of 1.5 at lower temperatures and by a factor of 1.2 at
higher temperatures. Further increasing the curcumin concentration
has no effect. Comparison with cholesterol showed that curcumin and
cholesterol influence lateral diffusion of lipids differently. The
effect of curcumin is determined by its solubility in lipid bilayers,
which is as low as 10 mol % that is much less than that of cholesterolĢs
66 mol %
Atomistic Insight into Orthoborate-Based Ionic Liquids: Force Field Development and Evaluation
We have developed an all-atomistic
force field for a new class
of halogen-free chelated orthoborate-phosphonium ionic liquids. The
force field is based on an AMBER framework with determination of force
field parameters for phosphorus and boron atoms, as well as refinement
of several available parameters. The bond and angle force constants
were adjusted to fit vibration frequency data derived from both experimental
measurements and <i>ab initio</i> calculations. The force
field parameters for several dihedral angles were obtained by fitting
torsion energy profiles deduced from <i>ab initio</i> calculations.
To validate the proposed force field parameters, atomistic simulations
were performed for 12 ionic liquids consisting of tetraalkylphosphonium
cations and chelated orthoborate anions. The predicted densities for
neat ionic liquids and the [P<sub>6,6,6,14</sub>]Ā[BOB] sample, with
a water content of approximately 2.3ā2.5 wt %, are in excellent
agreement with available experimental data. The potential energy components
of 12 ionic liquids were discussed in detail. The radial distribution
functions and spatial distribution functions were analyzed and visualized
to probe the microscopic ionic structures of these ionic liquids.
There are mainly four high-probability regions of chelated orthoborate
anions distributed around tetraalkylphosphonium cations in the first
solvation shell, and such probability distribution functions are strongly
influenced by the size of anions
Experimental and First-Principles NMR Analysis of Pt(II) Complexes With <i>O</i>,<i>O</i>ā²āDialkyldithiophosphate Ligands
Polycrystalline
bisĀ(dialkyldithiophosphato)ĀPtĀ(II) complexes of
the form [PtĀ{S<sub>2</sub>PĀ(OR)<sub>2</sub>}<sub>2</sub>] (R = ethyl, <i>iso</i>-propyl, <i>iso</i>-butyl, <i>sec</i>-butyl or <i>cyclo</i>-hexyl group) were studied using
solid-state <sup>31</sup>P and <sup>195</sup>Pt NMR spectroscopy,
to determine the influence of R to the structure of the central chromophore.
The measured anisotropic chemical shift (CS) parameters for <sup>31</sup>P and <sup>195</sup>Pt afford more detailed chemical and structural
information, as compared to isotropic CS and <i>J</i> couplings
alone. Advanced theoretical modeling at the hybrid DFT level, including
both crystal lattice and the important relativistic spināorbit
effects qualitatively reproduced the measured CS tensors, supported
the experimental analysis, and provided extensive orientational information.
A particular correction model for the non-negligible lattice effects
was adopted, allowing one to avoid a severe deterioration of the <sup>195</sup>Pt anisotropic parameters due to the high requirements posed
on the pseudopotential quality in such calculations. Though negligible
differences were found between the <sup>195</sup>Pt CS tensors with
different substituents R, the <sup>31</sup>P CS parameters differed
significantly between the complexes, implying the potential to distinguish
between them. The presented approach enables good resolution and a
detailed analysis of heavy-element compounds by solid-state NMR, thus
widening the understanding of such systems
Exploiting the Synergy of Powder Xāray Diffraction and Solid-State NMR Spectroscopy in Structure Determination of Organic Molecular Solids
We report a strategy for structure
determination of organic materials in which complete solid-state nuclear
magnetic resonance (NMR) spectral data is utilized within the context
of structure determination from powder X-ray diffraction (XRD) data.
Following determination of the crystal structure from powder XRD data,
first-principles density functional theory-based techniques within
the GIPAW approach are exploited to calculate the solid-state NMR
data for the structure, followed by careful scrutiny of the agreement
with experimental solid-state NMR data. The successful application
of this approach is demonstrated by structure determination of the
1:1 cocrystal of indomethacin and nicotinamide. The <sup>1</sup>H
and <sup>13</sup>C chemical shifts calculated for the crystal structure
determined from the powder XRD data are in excellent agreement with
those measured experimentally, notably including the two-dimensional
correlation of <sup>1</sup>H and <sup>13</sup>C chemical shifts for
directly bonded <sup>13</sup>Cā<sup>1</sup>H moieties. The
key feature of this combined approach is that the quality of the structure
determined is assessed <i>both</i> against experimental
powder XRD data <i>and</i> against experimental solid-state
NMR data, thus providing a very robust validation of the veracity
of the structure
Amyloid Hydrogen Bonding Polymorphism Evaluated by <sup>15</sup>N{<sup>17</sup>O}REAPDOR Solid-State NMR and Ultra-High Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
A combined
approach, using Fourier transform ion cyclotron resonance
mass spectrometry (FTICR-MS) and solid-state NMR (Nuclear Magnetic
Resonance), shows a high degree of polymorphism exhibited by AĪ²
species in forming hydrogen-bonded networks. Two Alzheimerās
AĪ² peptides, Ac-AĪ²<sub>16ā22</sub>-NH<sub>2</sub> and AĪ²<sub>11ā25</sub>, selectively labeled with <sup>17</sup>O and <sup>15</sup>N at specific amino acid residues were
investigated. The total amount of peptides labeled with <sup>17</sup>O as measured by FTICR-MS enabled the interpretation of dephasing
observed in <sup>15</sup>NĀ{<sup>17</sup>O}ĀREAPDOR solid-state
NMR experiments. Specifically, about one-third of the AĪ² peptides
were found to be involved in the formation of a specific >Cī»<sup>17</sup>OĀ·Ā·Ā·Hā<sup>15</sup>N hydrogen bond
with their neighbor peptide molecules, and we hypothesize that the
rest of the molecules undergo Ā± <i>n</i> off-registry
shifts in their hydrogen bonding networks