Alessandra Garau

Copper(II)-selective membrane electrodes based on some recently synthesized mixed aza-thioether crowns containing a 1,10-phenanthroline sub-unit

Three different mixed aza-thioether crowns containing a 1,10-phenanthroline sub-unit were investigated to characterize their abilities as copper(II) ion carriers in PVC-membrane electrodes. The electrode based on L1 exhibited a Nernstian response for Cu(2+) ions over a wide concentration range (2x10(-1) to 1x10(-5) M) with a limit of detection of 8.0x10(-6) M (0.5 p.p.m.). The response time of sensor is 15 s, and the membrane can be used for more than 3 months without observing any deviation. The electrode revealed comparatively good selectivities with respect to many alkali, alkaline earth, transition and heavy metal ions, and could be used in a pH range of 2.5-5.5. It was applied to the direct determination and potentiometric titration of the copper(II) ion.

CHARGE-TRANSFER ADDUCTS BETWEEN DONORS CONTAINING CHALCOGENS (S AND SE) AND DI-IODINE : SOLUTION STUDIES

Abstract The solution equilibria related to the 1:1 charge-transfer adduct formation between molecular iodine and several substrates containing sulfur and selenium donor atoms have been reviewed and the corresponding thermodynamic parameters ( K and Δ H °) reported for a series of thiones, selones, sulfides and selenides. A survey of the several calculation methods, based on UV–vis and in some cases 13 C-NMR spectroscopies, is also reported. Although the methods and techniques employed are very different, some correlations between the thermodynamic parameters and other experimental data, such as ν (II) Raman frequencies or UPS-binding energies, are reviewed and general conclusions drawn.

Multimodal use of new coumarin-based fluorescent chemosensors: Towards highly selective optical sensors for Hg2+ probing

Despite several types of fluorescent sensing molecules have been proposed and examined to signal Hg(2+) ion binding, the development of fluorescence-based devices for in-field Hg(2+) detection and screening in environmental and industrial samples is still a challenging task. Herein, we report the synthesis and characterization of three new coumarin-based fluorescent chemosensors featuring mixed thia/aza macrocyclic framework as receptors units, that is, ligands L1-L3. These probes revealed an OFF-ON selective response to the presence of Hg(2+) ions in MeCN/H2 O 4:1 (v/v), which allowed imaging of this metal ion in Cos-7 cells in vitro. Once included in silica core-polyethylene glycol (PEG) shell nanoparticles or supported on polyvinyl chloride (PVC)-based polymeric membranes, ligands L1-L3 can also selectively sense Hg(2+) ions in pure water. In particular we have developed an optical sensing array tacking advantage of the fluorescent properties of ligand L3 and based on the computer screen photo assisted technique (CSPT). In the device ligand L3 is dispersed into PVC membranes and it quantitatively responds to Hg(2+) ions in natural water samples.

Separation, preconcentration and determination of trace amounts of silver ion in aqueous samples using octadecyl silica membrane disks modified with some recently synthesized mixed aza-thioether crowns containing 1,10-phenanthroline sub-unit and atomic absorption spectrometry

Abstract A new simple and reliable method for rapid and selective extraction and determination of trace levels of Ag+ ion is developed. Silver ions are adsorbed quantitatively during passage of aqueous samples through octadecyl silica membrane disks modified with some recently synthesized mixed aza-thioether crowns containing 1,10-phenanthroline sub-unit. Almost all matrix elements were found to pass through the disk to drain. The retained Ag+ ions are then stripped from the disk with a minimal amount of thiosulfate solution as eluent and subsequently measured by atomic absorption spectrometry. The proposed method permitted large enrichment factors of about 200 and higher. The limit of detection of the proposed method is 100 ng Ag+ per 1000 ml. The method was applied to the recovery of Ag+ ions from different synthetic and water samples.

Redox chemosensors: coordination chemistry towards CuII, ZnII, CdII, HgII, and PbII of 1-aza-4,10-dithia-7-oxacyclododecane ([12]aneNS2O) and its N-ferrocenylmethyl derivativeElectronic supplementary information (ESI) available: synthetic details including analytical and spectroscopic data for the isolated complexes. Ortep views of the coordination sphere around the metal centres in 1, 2 and 5. See http://www.rsc.org/suppdata/dt/b2/b210806m/

The coordination chemistry of the mixed donor 12-membered macrocyclic ligand 1-aza-4,10-dithia-7-oxacyclododecane ([12]aneNS2O) with CuII, ZnII, CdII, HgII, and PbII has been investigated both in water solution and in the solid state. The protonation constant for [12]aneNS2O and stability constants with the aforementioned metal ions have been determined potentiometrically and compared with those reported for other mixed N/S/O-donor tetradentate 12-membered macrocycles. The measured values are consistent with trends observed previously for aza macrocycles as secondary N-donors are replaced by O- and S-donors. In particular our results show that HgII in water has the highest affinity for [12]aneNS2O followed by CuII, CdII, PbII, and ZnII. For each considered metal ion, 1 ∶ 1 complexes of [12]aneNS2O have been isolated in the solid state; those of CuII, HgII, and CdII have also been characterised by X-ray crystallography. In the cases of copper(II) and cadmium(II) complexes the ligand adopts a folded [2424] conformation, whereas a more planar [3333] conformation is observed in the case of the mercury(II) complex. The macrocycle [12]aneNS2O and its structural analogue [12]aneNS3 have then been used as receptor units in the design and synthesis of the new ferrocene-containing redox-active ionophores N-ferrocenylmethyl 1-aza-4,10-dithia-7-oxacyclododecane (L1) and N-ferrocenylmethyl 1-aza-4,10,7-trithiacyclododecane (L2). Electrochemical studies carried out in MeCN in the presence of increasing amounts of CuII, ZnII, CdII, HgII, and PbII showed that the wave corresponding to the Fc/Fc+ couple of the uncomplexed ionophores L1 and L2 is gradually replaced by a new reversible wave at more positive potentials and corresponding to the Fc/Fc+ couple of the complexed ionophores. The maximum shift of the ferrocene oxidation wave was found for L1 in the presence of ZnII (230 mV) and PbII (220 mV), whereas for L2 a selective sensing response for CuII over the other guest metal cations was observed with an oxidation peak shift of 230 mV.

An efficient and selective flourescent chemical sensor based on 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane as a new fluoroionophore for determination of iron(III) ions. A novel probe for iron speciation.

A novel fluorescent chemical sensor for the highly sensitive and selective determination of Fe(3+) ions in aqueous solutions is prepared. The iron sensing system was prepared by incorporating 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a neutral Fe(3+)-selective fluoroionophore in the plasticized PVC membrane containing sodium tetraphenylborate as a liphophilic anionic additive. The response of the sensor is based on the strong fluorescence quenching of L by Fe(3+) ions. At pH 5.5, the proposed sensor displays a calibration curve over a wide concentration range from 6.0 × 10(-4) to 1.0 × 10(-7) M, with a relatively fast response time of less than 2 min. In addition to a high stability and reproducibility, the sensor shows a unique selectivity toward Fe(3+) ion with respect to common coexisting cations. The proposed fluorescence optode was applied to the determination of iron(III) content of straw of rice, spinach and different water samples. The fluorescent sensor was also used as a novel probe for Fe(3+)/Fe(2+) speciation in aqueous solution.

Colorimetric response to anions by a "robust" copper(II) complex of a [9]aneN3 pendant arm derivative: CN- and I- selective sensing.

The 1 : 1 complex [Cu(L)](BF(4))(2)·MeCN (1) of the tetradentate ligand 1-(2-quinolinylmethyl)-1,4,7-triazacyclononane (L) selectively changes its colour in the presence of CN(-) in H(2)O and MeCN (without undergoing decomplexation from the macrocyclic ligand). The same complex in MeCN assumes different colours in the presence of CN(-) or I(-).

Interaction of Methimazole with I2: X-ray Crystal Structure of the Charge Transfer Complex Methimazole−I2. Implications for the Mechanism of Action of Methimazole-Based Antithyroid Drugs

The antithyroid drug methimazole (MMI) reacts with molecular iodine to form, in a multistep process, 1-methylimidazole as final product. In this process, the charge transfer complex MMI-I 2 and the ionic disulfide [(C 4H 6N 2S-) 2] (2+) ( 1, dication MMI disulfide) have been isolated and their X-ray crystal structures solved. Dication MMI disulfide perchlorate acts effectively both in reducing I 2 to I (-) ions and in showing antioxidant properties in inactivating the enzyme lactoperoxidase compound I.

Silver ion imprinted polymer nanobeads based on a aza-thioether crown containing a 1,10-phenanthroline subunit for solid phase extraction and for voltammetric and potentiometric silver sensors

A new nano-sized silver(I) ion-imprinted polymer (IIP) was prepared via precipitation copolymerization using ethyleneglycol dimethacrylate, as a cross-linking agent in the presence of Ag(+) and an aza-thioether crown containing a 1,10-phenanthroline subunit as a highly selective complexing agent. The imprint silver(I) ion was removed from the polymeric matrix using a 1.0M HNO3 solution. The resulting powder material was characterized using IR spectroscopy and scanning electron microscopy. The SEM micrographs showed colloidal nanoparticles of about 52 nm and 75 nm in diameter and slightly irregular in shape for leached and unleached IIPs, respectively. The optimal pH for quantitative enrichment was 6.0 and maximum sorbent capacity of the prepared IIP for Ag(+) was 18.08 μmol g(-1). The relative standard deviation and limit of detection (LOD=3Sb/m) for flame atomic absorption spectrometric determination of silver(I) ion, after its selective extraction by the prepared IIP nanobeads, were evaluated as 2.42% and 2.2×10(-8) M, respectively. The new Ag(+)-IIP was also applied as a suitable sensing element to the preparation of highly selective and sensitive voltammetric and potentiometric sensors for ultra trace detection of silver(I) ion in water samples, with limits of detection of 9.0×10(-10) and 1.2×10(-9) M, respectively.

A new pyridine-based 12-membered macrocycle functionalised with different fluorescent subunits; coordination chemistry towards CuII, ZnII, CdII, HgII, and PbII

The coordination chemistry of the new pyridine-based, N2S2-donating 12-membered macrocycle 2,8-dithia-5-aza-2,6-pyridinophane (L1) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) has been investigated both in aqueous solution and in the solid state. The protonation constants for L1 and stability constants with the aforementioned metal ions have been determined potentiometrically and compared with those of ligand L2, which contains a N-aminopropyl side arm. The measured values show that Hg(II) in water has the highest affinity for both ligands followed by Cu(II), Cd(II), Pb(II), and Zn(II). For each metal ion considered, 1:1 complexes with L1 have also been isolated in the solid state, those of Cu(II) and Zn(II) having also been characterised by X-ray crystallography. In both complexes L1 adopts a folded conformation and the coordination environments around the two metal centres are very similar: four positions of a distorted octahedral coordination sphere are occupied by the donor atoms of the macrocyclic ligand, and the two mutually cis-positions unoccupied by L1 accommodate monodentate NO3- ligands. The macrocycle L1 has then been functionalised with different fluorogenic subunits. In particular, the N-dansylamidopropyl (L3), N-(9-anthracenyl)methyl (L4), and N-(8-hydroxy-2-quinolinyl)methyl (L5) pendant arm derivatives of L1 have been synthesised and their optical response to the above mentioned metal ions investigated in MeCN/H2O (4:1 v/v) solutions.