Carbon Dioxide Capture and Utilization with Isomeric Forms of Bis(amino)-Tagged Zinc Bipyrazolate Metal-Organic Frameworks.

Aiming at extending the tagged zinc bipyrazolate metal-organic frameworks (MOFs) family, the ligand 3,3'-diamino-4,4'-bipyrazole (3,3'-H2 L) 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.

On the Capability of Oxidovanadium(IV) Derivatives to Act as All-Around Catalytic Promoters Since the Prebiotic World.

For a long time the biological role of vanadium was not known, while now the possibility of using its derivatives as potential therapeutic agents has given rise to investigations on their probable side effects. Vanadium compounds may inhibit different biochemical processes and lead to a variety of toxic effects and serious diseases. But, on the other hand, vanadium is an essential element for life. In recent years, increasing evidence has been acquired on the possible roles of vanadium in the higher forms of life. Despite several biochemical and physiological functions that have been suggested for vanadium and notwithstanding the amount of the knowledge so far accumulated, it still does not have a clearly defined role in the higher forms of life. What functions could vanadium or its very stable oxidovanadium(IV) derivatives have had in the prebiotic world and in the origins of life? In this review, we have briefly tried to highlight the most useful aspects that can be taken into consideration to give an answer to this still unresolved question and to show the high versatility of the oxidovanadium(IV) group to act as promoter of several oxidation reactions when coordinated with a variety of ligands, including diketones like acylpyrazolones.

Influence of structurally related micelle forming surfactants on the antioxidant activity of natural substances.

Physicochemical properties of micelles, like other lipid aggregates, mostly depend on the composition and on the structure of the surfactants used as monomers. The preparation and the characterization of three cationic L-prolinol derivative surfactants with different chain lengths and their corresponding N-oxide are described. UV measurements were carried out to investigate the effect of the inclusion in micelles on the degradation of L-ascorbic acid and (+)-usnic acid. An influence on antioxidant activity was exerted to an extent strictly dependent on i) surfactant chain length, ii) charge, iii) pH (in the case of (+)-usnic acid) and iv) on the hydrophilicity of the solute, determinant parameter for their location in the aggregates. In general the extent of the antioxidant activity of the system in the case of N-oxides micelles depends on surfactant chain length. On the other hand, cationic micelles formed by the surfactant with the shortest chain behave more like N-oxides ones rather than those formed by its relative structural homologues featuring longer alkyl chains, probably as a consequence of a concentration effect.