Carlo Mangano

The extraction of technetium, present in nitric acid medium as pertechnetate anion, is an issue in solvent extraction processes used to recover uranium and plutonium. In the present study, a complexing agent is added in the aqueous nitric acid solution to bind selectively the pertechnetate anion and prevent its extraction into the organic phase or to back extract it in the aqueous phase. Several azacryptands with the addition of hydrophilic groups were synthesized to improve the solubility of the previously studied cage molecule in nitric acid medium. Solvent extraction tests reveal that all the synthesized ligands have a similar complexation strength towards pertechnetate and are able to maintain this anion in the aqueous phase (0.5 M HNO₃). These ligands are able to overcome the Hofmeister bias and selectively bind technetium in nitric acid solution. The azacryptand concentration can be increased by a factor of three in the liquid–liquid extraction conditions compared to our previous work. Coordination studies using microcalorimetry, Single Crystal X-Ray Diffraction (SC-XRD), infrared and Raman spectroscopies show the formation of an inclusion complex with hydrogen bonds stabilizing the oxo-anion within the cavity. This solubility improvement is promising for the introduction of this kind of macrocyclic azacryptands in a solvent extraction process.

A monolayer of the neutral Cu ²⁺ complex of a silane-bearing diamino–diamido ligand is formed on glass, exhibiting (decreased) antibacterial properties.

In this work, we have investigated the properties of novel fluorescent semi(thio)carbazone systems with anions by UV-vis, spectrofluorimetric and NMR studies, in acetonitrile and DMSO solutions. Conformational preferences were determined by theoretical calculations within the DFT approach. For the free receptors, these studies pointed out a marked prevalence of anti conformations, which are stabilized by intramolecular H-bonds between the (thio)urea NH group and the imino nitrogen atom. For the julolidine-based thiosemicarbazone system, intermolecular interactions involving the thiourea NH groups and the S atoms of two receptor molecules were also found in the crystals, leading to the formation of supramolecular dimers. Theoretical studies showed that anion binding involved a change of the conformation of the receptors from anti to syn. In the syn isomers, two NH groups actually point in the same direction, thus favouring the binding of anions, e.g. the Y-shaped acetate ion. This thorough study on the novel semi(thio)carbazones provides useful information for the application of this type of molecule in all the fields of chemistry, in which urea-based systems are employed (e.g. anion recognition and transport, catalysis, soft materials, etc.).

In this work, we investigated the dicopper(II) complex of Mozobil^TM as a potential receptor for anions in MeOH and MeOH/water mixture. The results were compared with those obtained for the mononuclear complex, copper(II) benzyl-cyclam as a model system. Experimental investigations were also supported by computational studies on both the dinuclear and the mononuclear species. Among the investigated anionic guests, the dicopper complex showed an outstanding affinity for the pyrophosphate anion, leading to the formation of a stable adduct in MeOH solution. Our computational studies strongly suggested a 2:2 stoichiometry for the adduct. At least in MeOH, this dimeric structure, with two pyrophosphate anions sandwiched between two dicopper Mozobil^TM units, is stabilized by H-bonding interactions between the receptor and pyrophosphate. In MeOH:water mixture, beside the strong competition of solvent, the affinity toward the anion was preserved. We exploited this property to develop a novel indicator displacement assay (IDA) for pyrophosphate in aqueous solution, using Pyrocatechol Violet (PV) as the indicator.

Mozobil^™ (1,1′-[1,4-phenylenebis(methylene)]bis[1,4,8,11-tetraazacyclotetradecane], 1, also known as JM3100 and AMD 3100) is a specific antagonist of the chemokine coreceptor CXCR4 and favours the mobilisation from the bone marrow of stem cells, which can be used for autologous transplantation. It is believed that the interaction, of both hydrogen bonding and electrostatic nature, involves a partly protonated form of Mozobil^™, LH_n ⁿ⁺ and the COO⁻ groups of Asp¹⁷¹ and Asp²⁶² residues protruding from the walls of the pocket of the membrane protein CXCR4. We have investigated, through potentiometric titrations in 0.1 M NaNO₃ at 25 °C, the interaction equilibria between 1 (L) and linear dicarboxylates A²⁻. These studies have demonstrated that the main equilibrium takes place: LH₅ ⁵⁺ + A²⁻ ⇄ [LH₅⋯A]³⁺, and that the most stable [LH₅⋯A]³⁺ complex forms for A²⁻ = diphenyl-4,4′-dicarboxylate, whose length matches that of LH₅ ⁵⁺. ¹H NMR titration experiments have shown that in the 7–10 pH interval, LH₃ ³⁺, LH₂ ²⁺ and LH⁺ forms establish π–π interactions with diphenyl-4,4′-dicarboxylate, according to a topological arrangement which excludes the formation of H-bonds. It is finally suggested that, in the pocket of the CXCR4 membrane protein, Mozobil^™ operates as a pentammonium cation, which establishes with carboxylate groups of Asp¹⁷¹ and Asp²⁶² strong interactions of hydrogen bonding and electrostatic nature.

The three nitrophenyl-cyclam derivatives (nitrocyclams): 1-(4-nitrophenyl)-1,4,8,11-tetraazacyclotetradecane (2), 1-(2-nitrophenyl)-1,4,8,11-tetraazacyclotetradecane (3), and 1-(2,4-dinitrophenyl)-1,4,8,11-tetraazacyclotetradecane (4), in an MeCN solution, specifically incorporate the Cu(II) ion according to an irreversible process signaled by disappearance of the yellow color for a concentration c < 1 × 10(-4) M and by a yellow-to-red color change for c ≥ 1 × 10(-3), and must be considered efficient and specific dosimeters of copper(II) salts. When present in the ortho position of the nitrophenyl substituent, the -NO2 group coordinates the Cu(II) according to a scorpionate mode, while the metallocyclam system exhibits a trans-I configuration. In an MeCN solution the red trans-I-[Cu(II)(3)](2+) and trans-I-[Cu(II)(4)](2+) scorpionate complexes slowly convert into the violet trans-III scorpionate complexes. Kinetic aspects of the trans-I-to-trans-III configurational rearrangement were investigated in detail for the [Cu(II)(4)](2+) system. In particular, the conversion is spectacularly accelerated by catalytic amounts of Cl(-), NCO(-), and F(-). While for Cl(-) and NCO(-) the effect can be associated with the capability of the anion to stabilize through coordination a possible dissociative intermediate, the amazingly powerful effect of F(-) must be related to the preliminary deprotonation of one N-H fragment of the macrocycle, driven by the formation of the HF2(-) ion. Most of the metal complex species studied in solution were isolated in a crystalline form, and their molecular structures were elucidated through X-ray diffraction studies. This study documents the first examples of effective metal coordination by the nitro group.

The two coordinatively unsaturated complexes [Cu(cyclam)]²⁺ (cyclam: 1,4,8,11-tetraazacyclotetradecane, 1) and [Cu(Bn₄cyclam)]²⁺ (Bn4cyclam: 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclotetradecane, 2) in an MeCN solution uptake an anion X⁻ (halide, pseudohalide) to give square pyramidal ternary complexes, whose stability has been determined through spectrophotometric titration experiments. The formation of a five-cordinate complex is favored by the trans-I configuration of the [Cu(Bn₄cyclam)]²⁺ receptor, but it is contrasted by the severe steric repulsions exerted by the benzyl substituents on the macrocyclic framework. No significant repulsive effects have been observed in anion binding to the [Cu(cyclam)]²⁺ receptor, exhibiting a trans-III configuration. The existence of a linear relationship between the magnitude of the red shift experienced by the d−d absorption band on anion binding and log K values is discussed.

A propyltrimethoxysilane-modified 2,2′-bipyridine ligand is synthesized and its acetonitrile solutions are used to prepare monolayers of the molecule on glass surfaces. Absorption and X-ray photoelectron spectroscopy demonstrate that the modified glass surfaces bind Cu²⁺ with a 1 : 1 ratio with respect to the 2,2′-bipyridine moieties under the chosen preparative conditions, producing materials bearing 0.016 μg cm⁻² of copper. Although in trace amounts, the bound Cu²⁺ cations exert a significant microbicidal effect against Escherichia coli and Staphylococcus aureus.

Three new ligands made of two iminoquinoline halves separated by an (R,R)-trans-1,2-cyclohexenediyl spacer have been synthesized. These ligands feature –OR functions appended in the 8-positions of the quinoline rings (R = n-alkyl). The ligands display a behaviour similar to that of their analogues that contain unsubstituted quinolines, forming a bistable system with copper. [Cu₂L₂]²⁺ helicates are obtained with Cu⁺ and [CuL]²⁺ monomers with Cu²⁺, as shown by UV/Vis titrations, determination of complex formation constants, mass and NMR measurements, and X-ray crystallographic analysis. The OR groups are found to be non-coordinating, but the presence of such substituents on the quinoline rings slows the electrochemical interconversion of [Cu₂L₂]²⁺ into [CuL]²⁺. In particular, oxidation of [Cu₂L₂]²⁺ gives a reversible two-step profile in cyclic voltammetry experiments, due to the formation of the Cu²⁺ helicate [Cu₂L₂]⁴⁺, that does not evolve into [CuL]²⁺in the CV experiment time scale.