The aim of this study is to investigate the effects of chemically modified hexagonal boron nitride (hBN) particles on the tribological properties of polyethylene glycol (PEG) based lubricant and sedimentation in PEG. Thermally purified and chemically modified hBN particles were compared with commercially available hBN particles of various sizes. Tribological tests were performed on a ball-on-disk optical tribometer under rolling–sliding conditions using a 100Cr6 steel ball and BK7 glass disk. The effects of hBN particle size and surface modification on the frictional behavior across boundary, mixed, and elastohydrodynamic (EHL) lubrication regimes were examined. The most pronounced reduction in the friction was achieved with the largest hBN particles (≈6.6 μm), which unfortunately tend to agglomerate in liquid PEG though. It was observed that agglomeration was strongly suppressed by chemical modification of hBN´s surface. The work also includes a post-experimental analysis which demonstrated good durability of hBN particles in PEG lubricant after tests.
The growing demand for enantioselective pharmaceutical analysis has prompted the development of novel chiral stationary phases (CSPs) tailored for high-performance liquid chromatography (HPLC). More recently, particular attention has been paid to multimodal (mixed-mode) stationary phases, which combine several interaction principles and broaden the applicability of the CSP. In this study, multimodal CSPs based on N-(3,5-dinitrobenzoyl)-tyrosine derivatives, featuring both donor-acceptor and ion-exchange/ion-pairing functionalities, were applied for the enantioseparation of omeprazole, pantoprazole, and lansoprazole, widely used proton pump inhibitors. Two in-house-developed CSPs were evaluated under multiple chromatographic modes, using polar-organic (PO), polar-organic-water (POW), and normal-phase (NP) mobile-phase conditions. PO and POW modes were selected as optimal due to their MS compatibility and sustainable solvent composition. The effect of mobile-phase composition, including MeCN/MeOH ratio and acidic/basic additives, on retention and enantioselectivity was systematically studied. The optimized method enabled the direct analysis of omeprazole enantiomers in a commercial tablet formulation using LC-MS. In parallel, molecular dynamics (MD) simulations were employed to investigate the mechanistic basis of chiral recognition at the molecular level. Key interaction energies and conformational behaviors were analyzed, supporting the experimentally observed enantioselectivity trends and providing insight into the spatial arrangement of the chiral selector-analyte associates. These findings highlight the potential of tyrosine-based multimodal CSPs for robust enantioselective analysis of PPI-type drugs under UV and MS-compatible conditions.
Montmorillonite, a widely available clay mineral known for its high cation-exchange capacity and versatile surface chemistry, was strategically functionalized to serve as a heterogeneous catalyst for the cycloaddition of carbon dioxide to styrene oxide. Two preparation strategies for heterogeneous catalysts were explored: ion-exchange of interlayer cations incorporating pyridinium and imidazolium salts, and surface grafting via halogenated silanes followed by quaternization with pyridine and 1-methylimidazole. The result in both cases was an immobilized quaternary salt, representing a catalytically active species. The grafted materials exhibited superior performance, achieving up to 98
van der Waals magnets are attracting a great deal of attention for their potential integration into spintronic and magnonic technologies. CrSBr is an A-type antiferromagnet that shows a coupling between its electronic band structure and magnetic properties. This property is appealing for applications, and it also offers the possibility to investigate magnetic ground states and gigahertz magnons using visible optics techniques. Using Raman scattering and (magneto)-optical experiments, we describe the magnetic and optical properties of alloys of CrSBr1-xClx with x ⩽ 0.46. Similar to CrSBr, these alloys are direct band gap semiconductors with a coupling of their electronic and magnetic properties. Exciton energies evolve weakly with composition, and we describe the large changes in the saturation magnetic fields and their implications for the magnetic properties. We show that both the interlayer magnetic exchange and electronic interactions are modified by halogen mixing, offering the possibility to tune magnon energies with alloy composition.
Excitons in recently discovered two-dimensional magnetic semiconductors have emerged as a promising vehicle for optoelectronic and spin-photonic applications. To exploit novel possibilities magnetic degrees of freedom offer, insight into the interplay of magnetism, lattice and optical excitations becomes essential. We consider Chromium Sulphur Bromide, which has two kinds of excitons, XB at 1.8 eV and XA at 1.38 eV. Here we show, through a combination of many body perturbation theory and experiment, that XB is an order of magnitude more sensitive to magnetic and lattice perturbations than XA. We trace the difference to the latter being localised (Frenkel-like), while the former is delocalised (Wannier-Mott-like) – a coexistence rarely seen in two-dimensional materials. This finding is supported by the strong temperature and magnetic field (up to 85 Tesla) dependent shifts in optical response for XB (much smaller for XA), and we show it is related to XB’s tendency for delocalisation (in-plane and out-of-plane) and enhanced coupling with Ag phonon modes. This study shows that CrSBr hosts Frenkel-like and Wannier-Mott-like excitons whose distinct spatial character explains their contrasting sensitivity to magnetic order and lattice vibrations, challenging the standard dichotomy in describing excitons.
