The Uptake and Assembly of Alkanes within a Porous Nanocapsule in Water: New Information about Hydrophobic Confinement

Kopilevich S, Gottlieb H, Keinan-Adamsky K, Müller A, Weinstock IA. The Uptake and Assembly of Alkanes within a Porous Nanocapsule in Water: New Information about Hydrophobic Confinement. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION. 2016;55(14):4476-4481.In Nature, enzymes provide hydrophobic cavities and channels for sequestering small alkanes or long-chain alkyl groups from water. Similarly, the porous metal oxide capsule [{(Mo6O21)-O-VI(H2O)(6)}(12){((Mo2O4)-O-V)(30)(L)(29)(H2O)(2)}](41-) (L=propionate ligand) features distinct domains for sequestering differently sized alkanes (as in Nature) as well as internal dimensions suitable for multi-alkane clustering. The ethyl tails of the 29 endohedrally coordinated ligands, L, form a spherical, hydrophobic shell, while their methyl end groups generate a hydrophobic cavity with a diameter of 11 angstrom at the center of the capsule. As such, C-7 to C-3 straight-chain alkanes are tightly intercalated between the ethyl tails, giving assemblies containing 90 to 110 methyl and methylene units, whereas two or three ethane molecules reside in the central cavity of the capsule, where they are free to rotate rapidly, a phenomenon never before observed for the uptake of alkanes from water by molecular cages or containers

Preparation of Ge@Organosilicon Core–Shell Structures and Characterization by Solid State NMR and Other Techniques

Many core–shell materials having a protecting outer layer have lately been proposed. In such materials it is not uncommon that chemical or thermal stability issues of the core material are resolved by a proper choice of the shell material. We report here the formation of core–shell structures by pyrolysis of a mixture of tetraethyl germanium and tetramethyl silicon at 750 °C in a simple one-step reaction without the use of catalysts under “RAPET” conditions. The composite product, germanium–core/organosilicon–shell (Ge@Organosilicon), is formed in two morphologies, rods and spheroids. The rods radial distribution is rather narrow while the spheroids exhibit a broader distribution due to their tendency to agglomerate. The germanium core phase is crystalline covered by a disordered organosilicon layer. The contribution of each of the precursors to the final product is shown by selected-area EDS and solid state NMR spectroscopy and further corroborated by RAMAN, EPR, and powder X-ray diffraction analysis

Changes to the Disordered Phase and Apatite Crystallite Morphology during Mineralization by an Acidic Mineral Binding Peptide from Osteonectin

Noncollagenous proteins regulate the formation of the mineral constituent in hard tissue. The mineral formed contains apatite crystals coated by a functional disordered calcium phosphate phase. Although the crystalline phase of bone mineral was extensively investigated, little is known about the disordered layer’s composition and structure, and less is known regarding the function of noncollagenous proteins in the context of this layer. In the current study, apatite was prepared with an acidic peptide (ON29) derived from the bone/dentin protein osteonectin. The mineral formed comprises needle-shaped hydroxyapatite crystals like in dentin and a stable disordered phase coating the apatitic crystals as shown using X-ray diffraction, transmission electron microscopy, and solid-state NMR techniques. The peptide, embedded between the mineral particles, reduces the overall phosphate content in the mineral formed as inferred from inductively coupled plasma and elemental analysis results. Magnetization transfers between disordered phase species and apatitic phase species are observed for the first time using 2D ¹H–³¹P heteronuclear correlation NMR measurements. The dynamics of phosphate magnetization transfers reveal that ON29 decreases significantly the amount of water molecules in the disordered phase and increases slightly their content at the ordered-disordered interface. The peptide decreases hydroxyl to disordered phosphate transfers within the surface layer but does not influence transfer within the bulk crystalline mineral. Overall, these results indicate that control of crystallite morphology and properties of the inorganic component in hard tissue by biomolecules is more involved than just direct interaction between protein functional groups and mineral crystal faces. Subtler mechanisms such as modulation of the disordered phase composition and structural changes at the ordered–disordered interface may be involved

Multinuclear Magnetic Resonance Spectroscopy and Density Function Theory Calculations for the Identification of the Equilibrium Species in THF Solutions of Organometallic Complexes Suitable As Electrolyte Solutions for Rechargeable Mg Batteries

We present a multinuclear nuclear magnetic resonance (NMR) and density functional theory (DFT) study of electrolyte solutions based on organometallic complexes with aromatic ligands. These solutions constitute a unique electrolyte family possessing a wide electrochemical window, making them suitable for rechargeable magnesium batteries. In our previous study we identified equilibrium species in the solutions based on a combination of Raman spectroscopy and single-crystal XRD analyses, and herein we extend our studies to include multinuclear NMR analyses. These solutions are comprised of the metathesis reaction products of MgCl_2–<i>x</i>Ph_<i>x</i> and AlCl_3–<i>y</i>Ph_<i>y</i> in various proportions, in THF. In principle, these reactions involve the exchange of ligands between the magnesium and the aluminum based compounds, forming ionic species and neutral molecules, such as Mg₂Cl₃⁺·6THF, MgCl₂·4THF and AlCl_4–<i>y</i>Ph_<i>y</i>^– (<i>y</i> = 0–4). The identification of the solution phase species from the spectroscopic results is supported by spectral analyses of specially synthesized reference compounds and DFT quantum-mechanical calculations. The current approach reveals new aspects about the NMR shift of the organometallic complexes and, in particular, facilitates differentiation between ionic and neutral species

Neotendon formation induced by manipulation of the Smad8 signalling pathway in mesenchymal stem cells

Tissue regeneration requires the recruitment of adult stem cells and their differentiation into mature committed cells. In this study we describe what we believe to be a novel approach for tendon regeneration based on a specific signalling molecule, Smad8, which mediates the differentiation of mesenchymal stem cells (MSCs) into tendon-like cells. A biologically active Smad8 variant was transfected into an MSC line that coexpressed the osteogenic gene bone morphogenetic protein 2 (BMP2). The engineered cells demonstrated the morphological characteristics and gene expression profile of tendon cells both in vitro and in vivo. In addition, following implantation in an Achilles tendon partial defect, the engineered cells were capable of inducing tendon regeneration demonstrated by double quantum filtered MRI. The results indicate what we believe to be a novel mechanism in which Smad8 inhibits the osteogenic pathway in MSCs known to be induced by BMP2 while promoting tendon differentiation. These findings may have considerable importance for the therapeutic replacement of tendons or ligaments and for engineering other tissues in which BMP plays a pivotal developmental role

Structural Analysis of Magnesium Chloride Complexes in Dimethoxyethane Solutions in the Context of Mg Batteries Research

Recently, MgTFSI₂/MgCl₂ electrolyte solutions in dimethoxyethane (DME) have been shown to function as viable electrolyte solutions for secondary Mg batteries that can facilitate reversible magnesium deposition/dissolution. MgCl₂ is a crucial component in these solutions. On its own, however, it is practically insoluble in DME. Therefore, the fact that it is readily dissolved in MgTFSI₂/DME solution is remarkable. Addition of MgCl₂ greatly improves the electrochemical performance of MgTFSI₂/DME electrolyte solutions. Thus, identifying the species formed in MgTFSI₂/MgCl₂ solutions is intriguing. In this study, we implemented a wide variety of analytical tools, including single crystal X-ray diffraction, multinuclear NMR, and Raman spectroscopy, to elucidate the structure of these solutions. Various solution species were determined, and a suitable reaction scheme is suggested

Interfacial Mineral–Peptide Properties of a Mineral Binding Peptide from Osteonectin and Bone-like Apatite

Osteonectin is a regulator of bone mineralization. It interacts specifically with collagen and apatite through its N-terminal domain, inhibiting crystal growth. In this work, we investigated the interface formed between the mineral and an acidic peptide, ON29, derived from the protein’s apatite binding domain. The structural properties of the peptide bound to the mineral and the mineral–peptide interface are characterized using NMR and computational methods. A biomaterial complex is formed by precipitation of the mineral in the presence of the acidic peptide. The peptide gets embedded between mineral particles, which comprise a disordered hydrated coat covering apatite-like crystals. ³¹P SEDRA measurements show that the peptide does not affect the overall proximity between phosphate ions in the mineral. {¹⁵N}¹³C REDOR measurements reveal an α-turn in the center of the free peptide, which is unchanged when it is bound to the mineral. {³¹P}¹³C REDOR and ¹H–¹³C HETCOR measurements show that Glu/Asp carboxylates and Thr/Ala/Val side chains from ON29 are proximate to phosphate and hydroxyl groups in the mineral phases. Predictions of ON29’s fold on and off hydroxyapatite crystal faces using ROSETTA-surface are used to model the molecular conformation of the peptide and its apatite-binding interface. The models constructed without bias from experimental results are consistent with NMR measurements and map out extensively the residues forming an interface with apatitic crystals