ABSTRACT
We describe a [2]rotaxane whose recognition sites for the ring are a dibenzylammonium moiety, endowed with acidic and H-bonding donor properties, and an imidazolium center bearing a photoactive phenylazo substituent. Light irradiation of this compound triggers a network of E/Z isomerization and proton transfer reactions that enable autonomous and reversible ring shuttling away from equilibrium.
Subject(s)
Protons , Rotaxanes , Catalysis , IsomerismABSTRACT
Invited for the cover of this issue is Alberto Credi and co-workers at the University of Bologna and National Research Council, Bologna, Italy. The image represents the photostationary non-equilibrium operation of supramolecular pumps as a hydraulic circuit in which water flows between reservoirs. Read the full text of the article at 10.1002/chem.202101163.
Subject(s)
Water , HumansABSTRACT
The development of artificial nanoscale motors that can use energy from a source to perform tasks requires systems capable of performing directionally controlled molecular movements and operating away from chemical equilibrium. Here, the design, synthesis and properties of pseudorotaxanes are described, in which a photon input triggers the unidirectional motion of a macrocyclic ring with respect to a non-symmetric molecular axle. The photoinduced energy ratcheting at the basis of the pumping mechanism is validated by measuring the relevant thermodynamic and kinetic parameters. Owing to the photochemical behavior of the azobenzene moiety embedded in the axle, the pump can repeat its operation cycle autonomously under continuous illumination. NMR spectroscopy was used to observe the dissipative non-equilibrium state generated inâ situ by light irradiation. We also show that fine changes in the axle structure lead to an improvement in the performance of the motor. Such results highlight the modularity and versatility of this minimalist pump design, which provides facile access to dynamic systems that operate under photoinduced non-equilibrium regimes.
Subject(s)
Rotaxanes , Kinetics , Motion , ThermodynamicsABSTRACT
Calix[6]arenes disubstituted at the methylene bridges, which are stable in the cone or 1,2,3-alternate conformation, form pseudorotaxanes with dialkylammonium axles. The cone wheel-based pseudorotaxanes are 10-100 times more stable than those obtained with the native conformationally mobile calix[6]arene wheel, as a consequence of their higher degree of preorganization. The threading of conformationally stable 1,2,3-alternate calix[6]arenes is unprecedented in the literature. Therefore, very peculiar NMR features are here evidenced for this threading process involving the less symmetrical 1,2,3-alternate calix[6]arene conformation, which implies a peculiar rototranslation motion of the axle.
ABSTRACT
This study describes the application of microwave-assisted extraction (MAE) as an innovative technique for isolation of polyphenols from tomato peel waste. Effects of solvents, temperatures (25, 55 and 90 °C) and times (5 and 10 min) were evaluated with regard to total phenols (TP), total flavonoids (TF) and phenolic compound contents. Tomato peel extracts contain high amounts of kaemferol-3-O-rutinoside (8.5 to 142.5 mg kg-1), p-coumaric acid (3 to 111.5 mg kg-1) and chlorogenic acid derivative (10.5 to 109 mg kg-1). Results revealed that extraction time has no significant (p > 0.05) influence on TP, TF and phenolic compounds recovery (exception is cis-p-coumaric acid hexoside). On the other hand, the influence of temperature and chosen solvent on polyphenols yield is significant. Considering interest of consumers to intake natural compounds exhibiting antioxidant properties, this work suggests that tomato peel waste can be used as one of sustainable resources for polyphenols production by MAE.
