Preparation and reactivity with azo-species of hydride and dihydrogen complexes of osmium stabilised by tris(pyrazolyl)borate and phosphite ligands

Mixed-ligand OsCl(Tp)L(PPh₃) complexes 1 [Tp = hydridotris(pyrazolyl)borate; L = P(OMe)₃, P(OEt)₃ and PPh(OEt)₂] were prepared by allowing OsCl(Tp)(PPh₃)₂ to react with an excess of phosphite. Treatment of chlorocomplexes 1 with NaBH₄ in ethanol afforded hydride OsH(Tp)L(PPh₃) derivatives 2. Stable dihydrogen [Os(η²-H₂)(Tp)L(PPh₃)]BPh₄ derivatives 3 were prepared by protonation of hydrides 2 with HBF₄ · Et₂O at −80 °C. The presence of the η²-H₂ ligand is supported by short T_1 min values and J_HD measurements on the partially deuterated derivatives. Treatment of the hydride OsH(Tp)[P(OEt)₃](PPh₃) complex with the aryldiazonium salt [4-CH₃C₆H₄N₂]BF₄ afforded aryldiazene [Os(4-CH₃C₆H₄NNH)(Tp){P(OEt)₃}(PPh₃)]BPh₄ derivative 4. Instead, aryldiazenido [Os(4-CH₃C₆H₄N₂)(Tp)[P(OEt)₃](PPh₃)](BF₄)₂ derivative 5 was obtained by reacting the hydride OsH(Tp)[P(OEt)₃](PPh₃) first with methyltriflate and then with aryldiazonium [4-CH₃C₆H₄N₂]BF₄ salt. Spectroscopic characterisation (IR, ¹⁵N NMR) by the ¹⁵N-labelled derivative strongly supports the presence of a near-linear Os-NN-Ar aryldiazenido group. Imine [Os{η¹-NHC(H)Ar}(Tp){P(OEt)₃}(PPh₃)]BPh₄ complexes 6 and 7 (Ar = C₆H₅, 4-CH₃C₆H₄) were also prepared by allowing the hydride OsH(Tp)[P(OEt)₃](PPh₃) to react first with methyltriflate and then with alkylazides.     

Grape Canes from Typical Cultivars of Campania (Southern Italy) as a Source of High-Value Bioactive Compounds: Phenolic Profile,Antioxidant and Antimicrobial Activities

The purpose of the current study was to determine the phenolic composition, antioxidant, and antimicrobial activities in grape cane extracts from typical cultivars of Southern Italy. Aqueous extracts at different pHs (1–13) were prepared from “Aglianico”, “Fiano”, and “Greco” grape canes. The results demonstrated that an alkaline pH (13.00) produced the best polyphenol-rich extracts, as the total phenolic content was more than double when compared to the respective extracts prepared at pH 1.00. “Greco” grape canes gave the highest quantity of phenolic compounds at each pH, ranging from 42.7 ± 0.4 to 104.3 ± 3.0 mg Gallic Acid Equivalents (GAE)/g Dry Extract (DE) from pH 1.00 to 13.00. The Radical Scavenging Activity (RSA) and the Ferric Reducing Antioxidant Power (FRAP) were measured. The highest antioxidant activity was showed by “Greco” extract at pH 7.00. Seventy-five compounds were identified in the extracts by HPLC-MS with six of them described for the first time in grape canes. Procyanidins were highly abundant in extracts at pH 7.00, whereas stilbenoids were the most represented compounds at pH 13.00. Very strong antiviral activity against herpes simplex viruses was recorded for the extracts at pH 7.00 and 13.00 that were active in the early stages of infection by acting directly against the viral particles. The overall results suggest that grape canes, currently underutilized, can be usefully valorised by providing active extracts to use as antioxidant and antiviral agents.     

Unraveling the Guest-Induced Switchability in the Metal-Organic Framework DUT-13(Zn)**

The switching mechanism of the flexible framework Zn₄O(benztb)_1.5 (benztb=N,N,N’,N’-benzidine tetrabenzoate), also known as DUT-13, was studied by advanced powder X-ray diffraction (PXRD) and gas physisorption techniques. In situ synchrotron PXRD experiments upon physisorption of nitrogen (77 K) and n-butane (273 K) shed light on the hitherto unnoticed guest-induced breathing in the MOF. The mechanism of contraction is based on the conformationally labile benztb ligand and accompanied by a reduction in specific pore volume from 2.03 cm³ g⁻¹ in the open-pore phase to 0.91 cm³ g⁻¹ in the contracted-pore phase. The high temperature limit for adsorption-induced contraction of 170 K, determined by systematic temperature variation of methane adsorption isotherms, indicates that the DUT-13 framework is softer than other mesoporous MOFs like DUT-49 and does not support the formation of overloaded metastable states required for negative gas-adsorption transitions.     

Using low-E resonators to reduce RF heating in biological samples for static solid-state NMR up to 900 MHz

RF heating of solid-state biological samples is known to be a destabilizing factor in high-field NMR experiments that shortens the sample lifetime by continuous dehydration during the high-power cross-polarization and decoupling pulses. In this work, we describe specially designed, large volume, low-E 15N-1H solid-state NMR probes developed for 600 and 900 MHz PISEMA studies of dilute membrane proteins oriented in hydrated and dielectrically lossy lipid bilayers. The probes use an orthogonal coil design in which separate resonators pursue their own aims at the respective frequencies, resulting in a simplified and more efficient matching network. Sample heating at the 1H frequency is minimized by a loop-gap resonator which produces a homogeneous magnetic field B1 with low electric field E. Within the loop-gap resonator, a multi-turn solenoid closely matching the shape of the sample serves as an efficient observe coil. We compare power dissipation in a typical lossy bilayer sample in the new low-E probe and in a previously reported 15N-1H probe which uses a double-tuned 4-turn solenoid. RF loss in the sample is measured in each probe by observing changes in the 1H 360 degrees pulse lengths. For the same values of 1H B1 field, sample heating in the new probe was found to be smaller by an order of magnitude. Applications of the low-E design to the PISEMA study of membrane proteins in their native hydrated bilayer environment are demonstrated at 600 and 900 MHz.     

A new di-C-prenylated coumarin from Sophora interrupta

A new di-C-prenylated coumarin, 7-methoxy-6,8-bis-(2,3-dihydroxy-3-methylbutyl)-coumarin (1), together with seven known compounds, isopimpinellin (2), an arylbenzofuran (3), three flavonoids (4–6), (+)-maackianin (7) and echinoisoflavanone (8), were isolated from the leaves of Sophora interrupta Bedd. The structure of the new compound 1 as well as known compounds was elucidated by extensive 1D and 2D NMR spectral studies.     

Size-Mediated Recurring Spinel Sub-nanodomains in Li- and Mn-Rich Layered Cathode Materials

Li- and Mn-rich layered oxides are among the most promising cathode materials for Li-ion batteries with high theoretical energy density. Its practical application is, however, hampered by the capacity and voltage fade after long cycling. Herein, a finite difference method for near-edge structure (FDMNES) code was combined with in situ X-ray absorption spectroscopy (XAS) and transmission electron microscopy/electron energy loss spectroscopy (TEM/EELS) to investigate the evolution of transition metals (TMs) in fresh and heavily cycled electrodes. Theoretical modeling reveals a recurring partially reversible LiMn₂O₄-like sub-nanodomain formation/dissolution process during each charge/discharge, which accumulates gradually and accounts for the Mn phase transition. From the modeling of spectra and maps of the valence state over large regions of the cathodes, it was found that the phase change is size-dependent. After prolonged cycling, the TMs displayed different levels of inactivity.     

Tetracycline prevents Aβ oligomer toxicity through an atypical supramolecular interaction

The antibiotic tetracycline was reported to possess an anti-amyloidogenic activity on a variety of amyloidogenic proteins both in in vitro and in vivo models. To unveil the mechanism of action of tetracycline on Aβ1-40 and Aβ1-42 at both molecular and supramolecular levels, we carried out a series of experiments using NMR spectroscopy, FTIR spectroscopy, dynamic laser light-scattering (DLS) and atomic force microscopy (AFM). Firstly we showed that the co-incubation of Aβ1-42 oligomers with tetracycline hinders the toxicity towards N2a cell lines in a dose-dependent manner. Therefore, the nature of the interaction between the drug and Aβ oligomers was investigated. To carry out NMR and FTIR studies we have prepared Aβ peptide solutions containing assemblies ranging from monomers to large oligomers. Saturation transfer difference (STD) NMR experiments have shown that tetracycline did not interact with monomers at variance with oligomers. Noteworthy, in this latter case we observed that this interaction was very peculiar since the transfer of magnetization from Aβ oligomers to tetracycline involved all drug protons. In addition, intermolecular cross-peaks between tetracycline and Aβ were not observed in NOESY spectra, indicating the absence of a specific binding site and suggesting the occurrence of a supramolecular interaction. DLS and AFM studies supported this hypothesis since the co-dissolution of Aβ peptides and tetracycline triggered the immediate formation of new aggregates that improved the solubility of Aβ peptides, preventing in this way the progression of the amyloid cascade. Moreover, competitive NMR binding experiments showed for the first time that tetracycline competes with thioflavin T (ThT) in the binding to Aβ peptides. Our data shed light on a novel mechanism of anti-amyloidogenic activity displayed by tetracycline, governed by hydrophobic and charge multiparticle interactions.     

The challenge to quantify proteins with charge trains due to isoforms or conformers

Single proteins separated by 2-DE often show multiple spots spreading along the first dimension. In many cases, such charge trains are explained by isoform differences or by putative post-translational modifications including phosphorylation, glycosylation and others. We now report that individual spots of such charge trains on 2-D gels in fact often represent the same protein, but, apparently due to conformational changes, segregate to different isoelectric points. If MS analysis reveals protein identity, we therefore suggest integrating all individual spots within a charge train for quantification. Especially in quality control of pharmaceutical proteins, the integration of the spot groups of all active contents is preferable in order to obtain reproducible and reasonable quantitative results. However, most commercial software packages for gel analysis integrate the signals spot-wise. We provide an improved quantification tool for proteins with charge train groups. This calculation can be implemented using the MATLAB software and the self-developed "Correct Integration Software System" or the commercial software package Delta2D.     

Singular sets of planar hyperbolic billiards are regular

Many planar hyperbolic billiards are conjectured to be ergodic. This paper represents a first step towards the proof of this conjecture. The Hopf argument is a standard technique for proving the ergodicity of a smooth hyperbolic system. Under additional hypotheses, this technique also applies to certain hyperbolic systems with singularities, including hyperbolic billiards. The supplementary hypotheses concern the subset of the phase space where the system fails to be C ² differentiable. In this work, we give a detailed proof of one of these hypotheses for a large collection of planar hyperbolic billiards. Namely, we prove that the singular set and each of its iterations consist of a finite number of compact curves of class C ² with finitely many intersection points.