Antonio J. Mota

Metal-free intermolecular formal cycloadditions enable an orthogonal access to nitrogen heterocycles.

Nitrogen-containing heteroaromatic cores are ubiquitous building blocks in organic chemistry. Herein, we present a family of metal-free intermolecular formal cycloaddition reactions that enable highly selective and orthogonal access to isoquinolines and pyrimidines at will. Applications of the products are complemented by a density functional theory mechanistic analysis that pinpoints the crucial factors responsible for the selectivity observed, including stoichiometry and the nature of the heteroalkyne.

Novel ortho-OPE metallofoldamers: binding-induced folding promoted by nucleating Ag(I)–alkyne interactions

We have developed a new family of ortho-oligophenylene ethynylene (o-OPE) metallofoldamers. The folding of these helicates is induced by nucleating carbon–metal interactions between Ag(I) cations and the alkynes of the inner core of the o-OPEs. These o-OPEs form metal–organic assemblies where at least three alkyne moieties are held in close proximity to form novel Ag(I)-complexes with the metal ion lodged into the helical cavity. NMR titration experiments and photokinetic studies have provided quantitative data about the thermodynamic and kinetic features of such binding/folding phenomena. X-ray diffraction and DFT studies have been performed to extract structural information on how the Ag(I) cation is accommodated into the cavity. The great simplicity and versatility of these new metallofoldamers open up the possibility to develop novel structures with applications in material science and/or in asymmetric catalysis.

Zinc-mediated diastereoselective assembly of a trinuclear circular helicate

Coordination of a triptycene-based ditopic Schiff base ligand (H2L) with Zn2+ leads to the formation of a novel trinuclear circular species. A combination of 1H NMR spectroscopy, infrared spectroscopy, mass spectrometry and elemental analysis allow the unambiguous characterization of H2L and Zn3L3·8H2O. DFT molecular modelling has been used to study the possible isomers of the cyclic trinuclear Zn(II) complex that results from the combination of conformational and optical isomers of the ligand. A NOESY experiment demonstrated that in the trinuclear circular zinc(II) helicate the three isomers of the ligand have an anti configuration of N,O-donor domains and an s-cis configuration of their imine bonds. Besides, a UV-VIS absorption and fluorescence emission study of H2L and Zn3L3·8H2O has been performed.

Photocatalytic oxidation of diuron using nickel organic xerogel under simulated solar irradiation

In this study, a nickel organic xerogel (X-Ni) was used as semiconductor photocatalyst for the degradation of the herbicide diuron (DRN) in aqueous solution. The main objective of this work was to analyze and compare the effectiveness of solar irradiation to remove DRN from water both by direct photolysis and photocatalytic degradation. We examined the influence of the initial concentration of the herbicide, the solution pH, the presence of different ions in the medium, the chemical composition of the water, and the presence of a photocatalyst, after 240u202fmin of irradiation. Direct photolysis achieved a low percentage of DRN degradation but was favored: i) by a reduction in the initial concentration of the herbicide (from 35.6% to 79.0% for 0.150u202f×u202f10-3u202fmol/L and 0.021u202f×u202f10-3u202fmol/L of DRN, respectively) and ii) at solution pHs at which diuron is positively charged (78.6% for pHu202f2 and 50.4% for pHu202f7), as suggested by DFT calculations carried out for DRN and its protonated form (DRN-H+). The corresponding mono-demethylated DRN derivative, 1-(3,4-dichlorophenyl)-3-methylurea (DCPU), was identified as a DRN degradation byproduct. In addition, the presence of certain anions in the medium significantly affected the overall degradation process by direct photolysis, due to the additional generation of HO radicals. We highlight that the presence of X-Ni considerably improved the photodegradation process under solar irradiation. The photocatalytic degradation rate constant was directly proportional to the xerogel concentration, because an increase in catalyst dose produced an increase in surface active sites for the photodegradation of DRN, enhancing the overall efficiency of the process. Thus, when 4167u202fmg/g of X-Ni was added, the DRN removal rate was 3-fold higher and both percentage of degradation and mineralization increased 88.5% with respect to the results obtained by direct photolysis.