Dynamics and Structure of a Bitumen Emulsion as Studied by ¹H 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 ∼0.11 μm. 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 Alzheimer’s and Parkinson’s 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 ¹H 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 298–333 K. The presence of curcumin at much lower concentrations (∼7 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 cholesteroĺs 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_6,6,6,14]­[BOB] sample, with a water content of approximately 2.3–2.5 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>′‑Dialkyldithiophosphate Ligands

Polycrystalline bis­(dialkyldithiophosphato)­Pt­(II) complexes of the form [Pt­{S₂P­(OR)₂}₂] (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 ³¹P and ¹⁹⁵Pt NMR spectroscopy, to determine the influence of R to the structure of the central chromophore. The measured anisotropic chemical shift (CS) parameters for ³¹P and ¹⁹⁵Pt 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 spin–orbit 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 ¹⁹⁵Pt anisotropic parameters due to the high requirements posed on the pseudopotential quality in such calculations. Though negligible differences were found between the ¹⁹⁵Pt CS tensors with different substituents R, the ³¹P 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 X‑ray 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 ¹H and ¹³C 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 ¹H and ¹³C chemical shifts for directly bonded ¹³C–¹H 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 ¹⁵N{¹⁷O}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 Aβ species in forming hydrogen-bonded networks. Two Alzheimer’s Aβ peptides, Ac-Aβ_16–22-NH₂ and Aβ_11–25, selectively labeled with ¹⁷O and ¹⁵N at specific amino acid residues were investigated. The total amount of peptides labeled with ¹⁷O as measured by FTICR-MS enabled the interpretation of dephasing observed in ¹⁵N­{¹⁷O}­REAPDOR solid-state NMR experiments. Specifically, about one-third of the Aβ peptides were found to be involved in the formation of a specific >C¹⁷O···H–¹⁵N hydrogen bond with their neighbor peptide molecules, and we hypothesize that the rest of the molecules undergo ± <i>n</i> off-registry shifts in their hydrogen bonding networks