The influence of the presence of synthetic structurally related N-oxide and corresponding cationic surfactants with different chain lengths on the properties of 1,2-dimyristoyl-sn-glycero-3-phosphocholine liposomes was investigated. Their potentiality as delivery systems of (+)-usnic acid was also evaluated by studying its entrapment efficiency and its antioxidant activity. In fact, (+)-usnic acid has many pharmacological properties that, as many natural substances, are often strictly linked to their antioxidant power. N-oxide surfactants can enhance this property and improve the efficacy of the system. Based on this premise, we verified how and to what extent the molecular structure of liposomes components affects this effect: the best antioxidant effectiveness was observed when (+)-usnic acid was included in liposomes containing the N-oxide surfactant with C14 alkyl chain. Our results underline the importance of the hydrophilic/hydrophobic balance of the monomer in determining the properties of the aggregates in which it is included.
Aiming at extending the tagged zinc bipyrazolate metal–organic frameworks (MOFs) family, the ligand 3,3’‐diamino‐4,4’‐bipyrazole (3,3’‐H2L) has been synthesized in good yield. The reaction with zinc(II) acetate hydrate led to the related MOF Zn(3,3’‐L). The compound is isostructural with its mono(amino) analogue Zn(BPZNH2) and with Zn(3,5‐L), its isomeric parent built with 3,5‐diamino‐4,4’‐bipyrazole. The textural analysis has unveiled its micro‐/mesoporous nature, with a BET area of 463 m2 g−1. Its CO2 adsorption capacity (17.4 wt. % CO2 at pCO2 = 1 bar and T = 298 K) and isosteric heat of adsorption (Qst = 24.8 kJ mol−1) are comparable to that of Zn(3,5‐L). Both Zn(3,3’‐L) and Zn(3,5‐L) have been tested as heterogeneous catalysts in the reaction of CO2 with the epoxides epichlorohydrin and epibromohydrin to give the corresponding cyclic carbonates at T = 393 K and pCO2 = 5 bar under solvent‐ and co‐catalyst‐free conditions. In general, the conversions recorded are higher than those found for Zn(BPZNH2), proving that the insertion of an extra amino tag in the pores is beneficial for the epoxidation catalysis. The best catalytic match has been observed for the Zn(3,5‐L)/epichlorohydrin couple, with 64 % conversion and a TOF of 5.3 mmol(carbonate) (mmolZn)−1 h−1. To gain better insights on the MOF‐epoxide interaction, the crystal structure of the [epibromohydrin@Zn(3,3’‐L)] adduct has been solved, confirming the existence of Br⋅⋅⋅(H)−N non‐bonding interactions. To our knowledge, this study represents the first structural determination of a [epibromohydrin@MOF] adduct.
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