The interaction of AMP, ADP, ATP and related phosphate, diphosphate and triphosphate anions with the positively charged forms of the HL ligand, constituted by a tren molecule functionalized with a pyrimidine residue, was studied by potentiometric titrations, affording the stability constants of the formed anion complexes, ³¹P and ¹H NMR spectroscopy in aqueous solutions and modelling calculations. The equilibrium data show that electrostatic forces make an important, but not decisive contribution, to the stability of the anion complexes. For nucleotides, ¹H NMR spectra showed that the formation of π-stacking interactions between nucleotide adenine and ligand pyrimidine moieties contribute to the stability of these complexes, being very important for those complexes of higher stability. The synergistic action of the different binding groups of the polyfunctional HL receptor leads to a marked recognition of ADP over ATP with a selectivity coefficient as high as 116 at pH 3.3, which is unprecedented in the context of synthetic receptor in water. According to modelling calculations, such exceptional binding selectivity has a strong relation with the increase of stability experienced by ADP complexes upon ADP protonation. A similar phenomenon is observed for HAMP⁻ whose interaction with H₃L²⁺ is at least as strong as that of the more charged HATP^{3 −} anion, which is another rare occurrence.

The binding properties of HL1, HL2, and HL3 ligands toward Cu(II) and Zn(II) ions, constituted by tetraaza-macrocyclic rings decorated with pyrimidine pendants, were investigated by means of potentiometric and UV spectrophotometric measurements in aqueous solution, with the objective of using the related HL-M(II) (HL = HL1–HL3; M = Cu, Zn) complexes for the preparation of hybrid MWCNT-HL-M(II) materials based on multiwalled carbon nanotubes (MWCNTs), through an environmentally friendly noncovalent procedure. As shown by the crystal structure of [Cu(HL1)](ClO₄)₂, metal coordination takes place in the macrocyclic ring, whereas the pyrimidine residue remains available for attachment onto the surface of the MWCNTs via π–π stacking interactions. On the basis of equilibrium data showing the formation of highly stable Cu(II) complexes, the MWCNT-HL1-Cu(II) material was prepared and characterized. This compound proved very stable toward lixiviation processes (release of HL1 and/or Cu(II)); thus, it was used for the preparation of its reduced MWCNT-HL1-Cu(0) derivatives. X-ray photoelectron spectroscopy and transmission electron microscopy images showed that MWCNT-HL1-Cu(0) contains Cu(0) nanoparticles, of very small (less than 5 nm) and regular size, uniformly distributed over the surface of the MWCNTs. Also, the MWCNT-HL1-Cu(0) material proved very resistant to detachment of its components. Accordingly, both MWCNT-HL1-Cu(II) and MWCNT-HL1-Cu(0) are promising candidates for applications in heterogeneous catalysis.

Binding of S₂O₃ ²⁻, SeO₄ ²⁻, Pt(CN)₄ ²⁻, Co(CN)₆ ³⁻, Au(S₂O₃)₂ ³⁻ and Fe(CN)₆ ⁴⁻ anions by the protonated (positively charged) forms of tren (tris(2-aminoethyl)amine) and of the tren-derivative (HL) containing a pyrimidine residue was studied by means of potentiometric measurements in 0.1 M NMe₄Cl solutions at 298.1 ± 0.1 K. Both ligands form stable complexes with these anions which appear to be mostly stabilized by electrostatic forces. In the case of HL, an anion–π interaction with the pyrimidine residue of the ligand also affords a significant contribution to complex stability. Some shape preference for tetrahedral and octahedral anions over square planar ones is observed. A hybrid AC/HL material obtained by adsorption of HL on commercial activated carbon (AC) was used to study the extraction of these anions from water. AC/HL shows enhanced adsorption capacity toward all the anions studied with respect to AC. This behavior is ascribed to the stronger interaction of anions with the HL function of AC/HL than with the Cπ-H₃O⁺ sites of unfunctionalized AC. Of special interest is the enhancement of the adsorption capacities found for Au(S₂O₃)₂ ³⁻ and Pt(CN)₄ ²⁻, two anions of great relevance for the extraction of platinum and gold from ores and from metallic wastes.

A new G-(H₂L)-Pd heterogeneous catalyst has been prepared via a self-assembly process consisting in the spontaneous adsorption, in water at room temperature, of a macrocyclic H₂L ligand on graphene (G) (G + H₂L = G-(H₂L)), followed by decoration of the macrocycle with Pd²⁺ ions (G-(H₂L) + Pd²⁺ = G-(H₂L)-Pd) under the same mild conditions. This supramolecular approach is a sustainable (green) procedure that preserves the special characteristics of graphene and furnishes an efficient catalyst for the Cu-free Sonogashira cross coupling reaction between iodobenzene and phenylacetylene. Indeed, G-(H₂L)-Pd shows an excellent conversion (90%) of reactants into diphenylacetylene under mild conditions (50 °C, water, aerobic atmosphere, 14 h). The catalyst proved to be reusable for at least four cycles, although decreasing yields down to 50% were observed.