Showing papers by "Vieri Fusi published in 2020"

N2S2 pyridinophane-based fluorescent chemosensors for selective optical detection of Cd2+ in soils

Abstract: Herein we describe the synthesis and coordination properties in solution towards Zn2+ and Cd2+ of the ligands L1 and L2 containing the 2,8-dithia-5-aza-2,6-pyridinophane (L) macrocyclic receptor unit and the 2-(2′-hydroxy-3′-naphthyl)-4-methylbenzoxazole (HNBO) or 7-(2-ethylamino)-4-methylcoumarin chromophores. Spectrophotometric and spectrofluorimetric measurements in the UV-visible region (MeCN/H2O solution 4 : 1 v/v) and 1H NMR measurements provided insight into the nature of complex species and transduction mechanisms responsible for the optical responses. The ligands showed an OFF–ON response upon addition of Zn2+ and Cd2+, for L1, and only Cd2+, for L2, in both cases attributable to the formation of 1 : 1 metal-to-ligand complexes. The crystal structure of [CdL2(NO3)2] is reported, Cd2+ being heptacoordinated by L and NO3− anions in a N2S2O3 environment. Exploiting the fluorescence properties of L1 and L2, an optical sensor array was developed featuring PVC membranes containing the dispersed sensing material and based on the Photoassisted Technique (PT) for signal acquisition, which allowed a quantitative determination of Cd2+ in real samples (soils). All phases from the design of the chemosensors to the development of the sensing device are discussed.

Zn(ii) detection and biological activity of a macrocycle containing a bis(oxadiazole)pyridine derivative as fluorophore.

Abstract: The synthesis, photochemical properties, biological effects and the X-ray crystal structure of a fluorescent polyamine macrocycle L are reported. L is a polyamine cyclophane macrocycle in which 2,6-bis(5-(2-methylphenyl)-1,3,4-oxadiazol-2-yl)pyridine (POXAPy) acts as a fluorescent sensor and the polyamine as a metal ion binding unit. L performs as a PET-mediated chemosensor, with a maximum emission wavelength close to 360 nm. This gives rise to a signal that is visible to the naked eye in the blue visible range. L is able to detect the Zn(ii) and Cd(ii) metal ions in an aqueous solution at pH = 7, with the coordination of the ions switching the emission ON through a CHEF effect. In contrast, paramagnetic metal ions like Cu(ii) and Ni(ii) completely quench the already low emission of L at this pH value. L affects the cell survival of a leukemic cellular model (U937) at micromolar concentrations with cell death starting after only 24 h of exposure; starting from a final concentration of 5 μM, L almost completely abrogates the survival of the leukemic cells over 72 h, with a mechanism that is compatible with a genomic DNA interaction.

Zn2+ and Cu2+ complexes of a fluorescent scorpiand-type oxadiazole azamacrocyclic ligand: crystal structures, solution studies and optical properties.

Abstract: A ligand comprised of a macrocyclic pyridinophane core having a pendant arm containing a secondary amine group linked through a methylene spacer to a pyridyl–oxadiazole–phenyl (PyPD) fluorescent system has been prepared (L). The crystal structures of [ZnL](ClO4)2 and [CuL](ClO4)2 show that M2+ is coordinated to all the nitrogen atoms of the macrocyclic core, the secondary amine of the pendant arm and the nitrogen atom of the pyridine group of the fluorescent moiety, the latter bond being clearly weaker than the one with the pyridine of the macrocycle. Solution studies showed the formation of a highly stable Cu2+ complex with 1 : 1 stoichiometry, whereas with Zn2+ least stable complexes were formed and, given the right conditions, a [Zn3L2]6+ species was also detected, but it was not possible to isolate this species in the solid state. Following Zn2+ coordination, a strong chelation-induced enhancement of fluorescence was observed, a behaviour that was not observed with any of the other metal cations tested.

Playing with Structural Parameters: Synthesis and Characterization of Two New Maltol-Based Ligands with Binding and Antineoplastic Properties.

Abstract: Two maltol-based ligands, N,N′-bis((3-hydroxy-4-pyron-2-yl)methyl)-1,4-piperazine (L1) and N,N′,N′-tris((3-hydroxy-4-pyron-2-yl)methyl)-N-methylethylendiamine (L2), were synthesized and characterized. L1 and L2, containing, respectively, two and three maltol units spaced by a diamine fragment, were designed to evaluate how biological and binding features are affected by structural modifications of the parent compound malten. The acid-base behavior and the binding properties towards transition, alkaline-earth (AE) and rare-earth (RE) cations in aqueous solution, studied by potentiometric, UV-Vis and NMR analysis, are reported along with biological studies on DNA and leukemia cells. Both ligands form stable complexes with Cu(II), Zn(II) and Co(II) that were studied as metallo-receptors for AE and RE at neutral pH. L1 complexes are more affected than L2 ones by hard cations, the L1-Cu(II) system being deeply affected by RE. The structural modifications altered the mechanism of action: L1 partially maintains the ability to induce structural alterations of DNA, while L2 provokes single strand (nicks) and to a lesser extent double strand breaks of DNA.

Fluorescent macrocyclic chemosensor for Zn(II) detection at alkaline pH values

Abstract: The new macrocyclic ligand L (28,29-dimethoxy-27-oxa-8,11,14,17,25,26-hexaazatetracyclo[22.2.1.1(2,6).1(19,23)]nonacosa-2,4,6(28),19,21,23(29),24,26(1)-octaene) has been synthesised. It contains a ...

Hetero-Tetranuclear Cu2+ /Ca2+ /Ca2+ /Cu2+ Architectures Based On Malten Ligand: Scaffold for Anion Binding.

Abstract: The hetero-tetranuclear Cu2+ /Ca2+ /Ca2+ /Cu2+ complex obtained with the N,N'-bis((3-hydroxy-4-pyron-2-yl)methyl)-N,N'-dimethylethylendiamine (Malten) ligand has been studied in solid and solution states as scaffold to bind anions. Three crystal structures showing the same metal ions sequence have been examined; they display a tetracharged complex cation neutralized by four monocharged anions. The anions play two different roles: as coordinated (two ClO4 - , Cl- or NO3 - ) or ancillary (two ClO4 - ) guests. The tetranuclear scaffold hosts two anions also in aqueous and ethanol solutions. Spectrophotometric studies in ethanol allowed to determine the addition constant values for Cl- and Br- (Log K1-2 =4.43(4), 4.39(3) for Cl- , 3.80(3), 3.54(2) for Br- ) while the others, although bound, showed lower affinity for the scaffold. Both the crystals and the solutions change their color depending on the added anion, namely pink, dark green or blue in the presence of ClO4 - , Cl- or NO3 - , respectively, thus the presence of the different anions is visible to the naked eye. The hetero-tetranuclear Cu2+ /Ca2+ /Ca2+ /Cu2+ complex is a versatile architecture to be used as scaffold for anion binding.