Metal-organic frameworks (MOFs) draw increasing attention as nanoenvironments for chemical reactions, especially in the field of catalysis. Knowing the specifics of MOF cavities is decisive in many of these cases; yet, obtaining them in situ remains very challenging. We report the first direct assessment of the apparent polarity and solvent organization inside MOF cavities using a dedicated structurally flexible spin probe. A stable ß-phosphorylated nitroxide radical was incorporated into the cavities of a prospective MOF ZIF-8 in trace amounts. The spectroscopic properties of this probe depend on local polarity, structuredness, stiffness and cohesive pressure and can be precisely monitored by Electron Paramagnetic Resonance (EPR) spectroscopy. Using this approach, we have demonstrated experimentally that the cavities of bare ZIF-8 are sensed by guest molecules as highly non-polar inside. When various alcohols fill the cavities, remarkable self-organization of solvent molecules is observed leading to a higher apparent polarity in MOFs compared to the corresponding bulk alcohols. Accounting for such nanoorganization phenomena can be crucial for optimization of chemical reactions in MOFs, and the proposed methodology provides unique routes to study MOF cavities inside in situ, thus aiding in their various applications.
A novel synthetic approach has been employed to synthesize a series of new nitronyl nitroxides: 2-(1-propyl-1H-imidazol-5-yl)- (Ln-Pr ), 2-(1-isopropyl-1H-imidazol-5-yl)- (Li-Pr ) and 2-(1-butyl-1H-imidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (Ln-Bu ). The reaction of Cu(hfac)2 with LR in a 1 : 2 ratio yields mononuclear heterospin complexes [Cu(hfac)2 (LR )2 ] (LR =Ln-Pr , Li-Pr , Ln-Bu ), which have a similar crystal structure to the "jumping" crystals [Cu(hfac)2 (LMe )2 ] that exhibit chemomechanical activity. It was shown that an increase in the alkyl substituent R leads to changes in the crystal packing of the molecules and the absence of chemomechanical activity. Furthermore, it was found that two polymorph modifications of the heterospin complex [Cu(hfac)2 (Ln-Pr )2 ] can be obtained, and magnetic properties of [Cu(hfac)2 (Ln-Pr )2 ] strongly depend on the angle between the planes of the paramagnetic fragment Oâ¢-N-C=NâO and the imidazole ring in Ln-Pr .
This study explores the antiarrhythmic and hypotensive potential of pyridyl-substituted nitronyl nitroxides derivatives, uncovering the crucial role of a single carbon moiety of the pyridine cycle alongside radical and charged oxygen centers of the imidazoline fragment. Notably, the introduction of fluorine atoms diminished the antiarrhythmic effect, while the most potent derivatives featured the nitronyl nitroxide pattern positioned at the third site of the pyridine cycle. Gender-dependent responses were observed in lead compounds LCF3 and LMe, with LMe inducing temporary bradycardia and hypotension specifically in female rats, and LCF3 causing significant blood pressure reduction followed by rebound in females compared to milder effects in males. Mechanistic insights point towards ß1 adrenoceptor blockade as an underlying mechanism, supported by experiments on isolated rat atria. This research underscores the interplay between structure, cardiovascular effects and gender-specific responses, offering insights for therapeutic strategies for treating free radical-associated cardiovascular disorders.
Antihypertensive Agents , Nitrogen Oxides , Male , Rats , Female , Animals , Nitrogen Oxides/chemistry , Free Radicals , Pyridines
Functionalized perfluoroalkyl lithium ß-diketonates (LiL) react with lanthanide(III) salts (Ln = Eu, Gd, Tb, Dy) in methanol to give heterobimetallic Ln-Li complexes of general formula [(LnL3)(LiL)(MeOH)]. The length of fluoroalkyl substituent in ligand was found to affect the crystal packing of complexes. Photoluminescent and magnetic properties of heterobimetallic ß-diketonates in the solid state are reported. The effect of the geometry of the [LnO8] coordination environment of heterometallic ß-diketonates on the luminescent properties (quantum yields, phosphorescence lifetimes for Eu, Tb, Dy complexes) and single-ion magnet behavior (Ueff for Dy complexes) is revealed.
Fluorocarbons , Lanthanoid Series Elements , Lanthanoid Series Elements/chemistry , Lithium , Magnets , Luminescence
Probes sensitive to mechanical stress are in demand for the analysis of pressure distribution in materials, and the design of pressure sensors based on metal-organic frameworks (MOFs) is highly promising due to their structural tunability. We report a new pressure-sensing material, which is based on the UiO-66 framework with trace amounts of a spin probe (0.03 wt%) encapsulated in cavities. To obtain this material, we developed an approach for encapsulation of stable nitroxide radical TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl) into the micropores of UiO-66 during its solvothermal synthesis. Pressure read-out using electron paramagnetic resonance (EPR) spectroscopy allows monitoring the degradation of the defected MOF structure upon pressurization, where full collapse of pores occurs at as low a pressure as 0.13 GPa. The developed methodology can be used in and ex situ and provides sensitive tools for non-destructive mapping of pressure effects in various materials.
