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Macrocyclic ligand L, in which a 2,6-bis(2-benzoxazolyl)phenol (bis-HBO) group is incorporated in triethylenetetramine, was designed and synthesized with the aim of creating a chemosensor with high selectivity and specificity for metal cations in an aqueous environment. The availability of several proton acceptors and donors, and amine and phenol hydroxy groups, respectively, affects the keto-enol equilibrium in both the ground and excited states, and the ligand properties show dependence on the pH of the solution. L is fluorescent in the visible range, through an excited-state intramolecular proton transfer (ESIPT) mechanism. The results of an exhaustive characterization of L by spectroscopic techniques and DFT calculations, as well as of its Zn(II), Cd(II) and Pb(II) complexes, show promising properties of L as a ratiometric metal cation chemosensor, since metal coordination prevents the ESIPT and gives rise to a peculiar displacement of the fluorescence emission from green to blue with Zn(II) and Cd(II), while with Pb(II) the fluorescence is quenched.

Bis-squaramide receptors L1–L4 bearing a dansyl moiety were considered as fluorescent probes for non steroidal antinflamatory drugs naproxene and ketoprofen.

The synthesis, solution studies, photochemical properties and the X-ray structure of a chromone based fluorescent PdII complex are reported. The ligand contains two chromone units linked as side arms to an ethylenediamine moiety; in the PdII complex the metal ion preorganizes the two hydroxychromone units forming a rigid structure with a negatively charged pocket formed by four oxygen atoms that is able to interact with hard metal cations, such as ions, giving rise to stable bimetallic complexes. Upon interaction with LaIII and GdIII, in particular, the emission intensity at 423 nm increases by a factor of 2 and 8, respectively, while the other rare earth ions quench the fluorescence. Spectrofluorimetric studies on real matrices showed the possibility to use this system as a selective fluorescence probe to detect and trace the presence of Gadolinium in environmental water acting as an OFF–ON chemosensor, with a LOD of 0.4 ppm and a LOQ of 1.2 ppm.

A new series of ligands containing the 2-(2-hydroxy-3- naphthyl)-4-methylbenzoxazole (HNBO) fluorophore showed selectivity for Mg

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.

The synthesis, solution studies, photochemical properties and the X-ray structure of a chromone based fluorescent Pd

The fluorescent probes represent an important tool in the biological study, in fact characterization of cellular structures and organelles are an important tool-target for understanding the mechanisms regulating most biological processes. Recently, a series of polyamino-macrocycles based on 1,4,7,10-tetraazacyclododecane was synthesized, bearing one or two NBD units (AJ2NBD·4HCl) useful as sensors for metal cations and halides able to target and to detect apolar environment, as lipid membranes. In this paper, we firstly illustrate the chemical synthesis of the AJ2NBD probe, its electronic absorption spectra and its behavior regarding pH of the environment. Lack of any cellular toxicity and an efficient labelling on fresh, living cells was demonstrated, allowing the use of AJ2NBD in biological studies. In particular, this green fluorescent probe may represent a potential dye for the compartments involved in the endosomal/autophagic pathway. This research’s field should benefit from the use of AJ2NBD as a vesicular tracer, however, to ensure the precise nature of vesicles/vacuoles traced by this new probe, other more specific tests are needed.

A scorpionate Zn2+ complex, constituted by a macrocyclic pyridinophane core attached to a pendant arm containing a fluorescent pyridyl-oxadiazole-phenyl unit (PyPD), has been shown to selectively recognize chloride anions, giving rise to changes in fluorescence emission that are clearly visible under a 365 nm UV lamp. This recognition event has been studied by means of absorption, fluorescence, and NMR spectroscopy, and it involves the intramolecular displacement of the PyPD unit by chloride anions. Moreover, since the chromophore is not removed from the system after the recognition event, the fluorescence can readily be restored by elimination of the bound chloride anion.

Two new maltol-based ligands are presented, L1 (N,N′-bis((3-hydroxy-6-methyl-4-pyron-2-yl)methyl)-N,N′-dimethylethylenediamine) and L2 (N,N′-bis((3-hydroxy-6-hydroxymethyl-4-pyron-2-yl)methyl)-N,N′-dimethylethylenediamine). They were strategically designed by inserting a methyl or hydroxymethyl function at C6, to study the previously hypothesized involvement of that ring position in the anticancer properties and the peculiar metal coordination ability in aqueous solution already shown by this family of ligands. Solid state and solution studies revealed differences neither in the molecular conformation or crystal packing nor in the acid–base behavior compared with the precursor Malten. The introduced substituent groups seem to affect instead both the degradation time (ca. 4–5 h for L1 and L2vs. 10 h for Malten) and the binding properties towards Cu(II), Zn(II) and Co(II), log K values being the highest for L1 within the series of the diamino-bis-maltol ligands. The introduction of –CH2OH at C6 is sufficient to impair the biological activity of the compound and is coherent with the hypothesized mechanism of action.

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.

The hetero-tetranuclear Cu

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](ClO

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 tetramine chain and the 2,5-bis(2-methoxy-3-metyl-phenyl)-1,3,4-oxadiazole (PPD-OMe) chromophore, acting as coordinating and sensing units, respectively. The fluorescent emission of L depends on the pH being highly fluorescent at pH = 2 and not emitting from pH >10. The studies highlighted that L is a PET mediated emitting chemosensor, being the PET effect regulated by the degree of the tetraamine protonation. L coordinates metal ions (Cu(II), Zn(II) and Cd(II)) in water giving rise to an OFF-ON fluorescent response for the presence of Zn(II) ion thus signalling its presence in the medium. This response is particularly notable at pH = 9 allowing to extend the Zn(II) sensing also in the alkaline pH field.

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.

The coordination and photochemical properties of three hydroxypyrazole-based ligands - tert-butyl 2-[1-[3-(4-cianophenyl)-5-hydroxy-1-phenyl-1H-pyrazol-4-yl]ethylidene]hydrazinecarboxylate (L1), tert-butyl 2-[1-[3-(3,5-bis(trifluoromethyl)phenyl)-5-hydroxy-1-phenyl-1H-pyrazol-4-yl]ethylidene]hydrazinecarboxylate (L2), and tert-Butyl 2-[1-[3-(phenantrene-9-yl)-5-hydroxy-1-phenyl-1H-pyrazol-4-yl]ethylidene]hydrazinecarboxylate (L3) - are reported. The ligands are fluorescent and able to coordinate a Zn(II) ion in a water/acetonitrile solvent with concomitant keto-enol tautomerism, giving rise to large Stokes shifts in the emission spectra. Ligand L1 has a peculiar double emission and can be exploited as a ratiometric fluorescent sensor.

The title compound is a new heterotrinuclear CoII–CaII–CoII dimer of L1. L1 undergoes a cobalt-driven preorganization, leading to the formation of an electron-rich area able to host a hard metal ion such as CaII. In the dimer, two neutral [Co(H–2 L1)] moieties, held together by the CaII ion, are rotated by 90°. The trinuclear complexes form layers perpendicular to the c axis; the perchlorate anions are located between the layers and inter­act with the complexes, as well as the lattice water mol­ecules., The title compound, [CaCo2(C22H30N4O6)2](ClO4)2·1.36H2O or {Ca[Co(H–2 L1)]2}·2ClO4·1.36H2O {where L1 is 4,10-bis­[(3-hy­droxy-4-pyron-2-yl)meth­yl]-1,7-dimethyl-1,4,7,10-tetra­aza­cyclo­dodecane}, is a trinuclear complex whose asymmetric unit comprises a quarter of the {Ca[Co(H–2 L1)]2}2+ trinuclear complex, half of a perchlorate ion and 0.34-water mol­ecules. In the neutral [Co(H–2 L1)] moiety, the cobalt ion is hexa­coordinated in a trigonal–prismatic fashion by the surrounding N4O2 donor set. A Ca2+ cation holds together two neutral [Co(H–2 L1)] moieties and is octa­coordinated in a distorted trigonal–dodeca­hedral fashion by the surrounding O atoms belonging to the deprotonated oxide and carbonyl groups of two [Co(H–2 L1)] units. The coordination of the CoII cation preorganizes L1 and an electron-rich area forms, which is able to host hard metal ions. The comparison between the present structure and the previously published ones suggests a high versatility of this ligand; indeed, hard metal ions with different nature and dimensions lead to complexes having different stoichiometry (mono- and dinuclear monomers and trinuclear dimers) or even a polymeric structure. The heterotrinuclear CoII–CaII–CoII complexes are connected in three dimensions via weak C—H⋯O hydrogen bonds, which are also responsible for the inter­actions with the perchlorate anions and the lattice water mol­ecules. The perchlorate anion is disordered about a twofold rotation axis and was refined giving the two positions a fixed occupancy factor of 0.5. The crystal studied was refined as a two-component inversion twin [BASF parameter = 0.14 (4)].

The title compound, {[Ba{Co(H-2L1)}(ClO4)(H2O)]ClO4}n,L1 =4,10-bis[(3-hydroxy-4-pyron-2-yl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane, is a one-dimensional coordination polymer. The asymmetric unit consists of a {Ba[Co(H–2L1)](ClO4)(H2O)}+cationic fragment and a non-coordinating ClO4−anion. In the neutral [Co(H–2L1)] moiety, the cobalt ion is hexacoordinated in a trigonal–prismatic fashion by the surrounding N4O2donor set. The Ba2+ion is nine-coordinated and exhibits a distorted [BaO9] monocapped square-antiprismatic geometry, the six oxygen atoms coming from three distinct [Co(H–2L1)] moieties, while the remaining three vertices are occupied by the oxygen atoms of a bidentate perchlorate anion and a water molecule. A barium–μ2-oxygen motif develops along theaaxis, connecting symmetry-related dinuclear BaII–CoIIcationic fragments in a wave-like chain, forming a one-dimensional metal coordination polymer. Non-coordinating ClO4−anions are located in the space between the chains. Weak C—H...O hydrogen bonds involving both coordinating and non-coordinating perchlorate anions build the whole crystal architecture. To our knowledge, this is the first example of a macrocyclic ligand forming a BaII-based one-dimensional coordination polymer, containing CoIIions surrounded by a N4O2donor set.

A series of five fluorescent ligands (L1–L5) for anions were designed and synthesized. Urea, thiourea, and cyanoguanidine moieties were chosen as the binding groups, while 3,5-bis(trifluoromethyl)phenyl, coumarin, and BODIPY were used as the chromophores. The cyanoguanidines L3–L5 were promptly synthesized from corresponding thioureas using EDCI followed by reaction with cyanamide in the presence of triethylamine. The absorption and emission properties of the ligands L1–L5 were studied in CH3CN; their coordination properties towards phosphate, pyrophosphate, and hydroxide anions, together with binding constants were evaluated.

Rare earth elements (REEs) are a group of fifteen elements ranging from lanthanum (Z = 57) to lutetium (Z = 71), also called lanthanides. Two further elements, namely scandium (Z = 21) and yttrium (Z = 39), are often referred to as REEs because they have chemical properties similar to lanthanides and are commonly found in the same mineral assemblages. The modern applications of these elements are countless. They constitute critical components of many technological devices and new functional materials, as well as they are extensively used in medical diagnostic applications and for these reasons, REEs are raising new interests of scientists worldwide. The search for chemical sensors suitable for selective sensing of trivalent REE ions represents an important and hard challenge because of their complicated coordination properties due to not well-defined stereo-chemical requirements and an uncertain coordination number, especially in aqueous solution. This review focuses on some of the main works published in the area of fluorescent and electrochemical probes for the detection of REE ions.

We synthesized and characterized the ligand N,N'-bis[(2,2'-dihydroxybiphen-3-yl)methyl]-N,N'-dimethylethylenediamine (L), which contains two biphenol moieties linked as side arms to an N,N'-dimethylethylenediamine scaffold. The ligand is highly soluble in a 50/50 (v/v) water/ethanol mixture and, in its deprotonated form H-2L(2-), is able to coordinate transition-metal ions such as Ni(II), Zn(II), Cu(II), Cd(II), and Pd(II). The crystal structures of [Ni(H-2L)·2n-BuOH], [Ni(H-2L)·2MeOH], [Cd(H-2L)·2DMF], [Cu(H-2L)(DMF)], and [Pd(H-2L)(DMF)] were also determined and described. Potentiometric titrations were carried out in a mixed solvent with Zn(II), Cu(II), and Ni(II) metal ions to determine the acid-base and stability constants. L was highly fluorescent in the visible range (400 nm). Moreover, its emission intensity increased upon the addition of Zn(II) or Cd(II) ions in an ethanol/water solution and behaved as a chemosensor for the presence of these ions in the solution.

The fluorescent ligand (L) based on the N2S2 pyridinophane macrocycle and the 7-nitrobenzo[1,2,5]oxadiazole (NBD) fluorogenic fragment has been synthesized to coordinate Pd(II) ions. Loaded on dye-doped silica nanoparticles, L can be used as a ratiometric fluorescent chemosensor for Pd(II) in water with high selectivity toward other metal ions including the platinum group ones.

The discovery of cisplatin (cis-Pt(NH3)2Cl2) as an antineoplastic agent has focussed attention on the rational design of metal complexes that can be potentially used in cancer chemotherapy. Today, the pharmaceutical industry invests more than $1 billion each year in the development of new metal-based drugs to improve biological activities, in terms of cellular selectivity, therapeutic efficiency and minimization of side effects. Chemotherapies based on transition metals play a key role in cancer treatment, and among them platinum and palladium are the most fruitful. This article reviews the main recent advances in the design and synthesis of platinum- and palladium-based drugs, their structural features and biological studies of them. The rationale for the choice of the ligand, related to leaving groups, the geometry of the complex and the oxidation state of the metal ion, is discussed. An overview of the main biological techniques and approaches for testing the interaction of these molecules with the biological environment, mainly DNA, to validate the effect is also provided.

Two maltol-based ligands, N,N&prime, bis((3-hydroxy-4-pyron-2-yl)methyl)-1,4-piperazine (L1) and N,N&prime, N&prime, 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.

The coordination properties and photochemical response of two fluorescent ligands 2,5-bis{2-[bis(2-pyridylmethyl)aminomethyl]phenyl}[1,3,4]oxadiazole (L1) and 2,5-bis{2-[(1,4,7-triazacyclononane-1-yl)methyl]phenyl}[1,3,4]oxadiazole (L2) towards ZnII and CdII are reported. The ligands contain the 2,5-diphenyl[1,3,4]oxadiazole (PPD) fluorescent probe linked to two coordinating units, namely dipicolylamine (DPA) for L1 and 1,4,7-triazacyclononane (TACN) for L2, through a methylene spacer. Both ligands form mononuclear and dinuclear complexes with these metal ions in aqueous or hydro-alcoholic media. With regard to L1, only the mononuclear CdII complex is highly fluorescent at 368 nm, while the mononuclear ZnII and dinuclear CdII and ZnII complexes are not emissive. Ligand L2 forms an excimer emitting at 474 nm only in the presence of one equivalent of CdII, and potentiometric, spectrophotometric, spectrofluorimetric, and NMR studies and DFT calculations were performed to explain this peculiarity. The discrimination between CdII and ZnII is mainly due to the different coordination environments of the metal ions in the mononuclear complexes; namely CdII is coordinated by both the side arms of each ligand, while ZnII is bound only to one coordinating unit.

The properties of two Cu(II) and Co(II) complexes with two maltol derivative ligands [ L1 = N,N′-bis[(3-hydroxy-4-pyron-2-yl)methyl]-N,N′-dimethylethylendiamine (Malten) and L2 = 4,10-bis[(3-hydroxy-4-pyron-2-yl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (Maltonis)] as binders for lanthanide cations [Eu(III) and Dy(III)], were investigated by means of single crystal X-ray diffraction and by UV–Vis experiments. [M(II)(H -2 L)] species [Cu(H -2 L1 )] and [Co(H -2 L2 )] are able to stabilize one hard metal ion such as Eu(III) and Dy(III), giving rise to the formation of hetero-trinuclear complexes of {Ln(III)[M(II)(H -2 L)] 2 } 3+ general formula. The crystal structures of all the studied hetero-trinuclear species highlight that such systems are formed thanks to the synergy between the different stereochemical requirement of the transition metal (Cu(II) or Co(II)) and the different donor atoms set of the ligands. The suitable transition metal ion preorganizes the maltol units in the [M(II)(H -2 L)] complexes for the binding of the hard Ln(III) metal, otherwise difficult to bind in water.

We report here the synthesis of a new thio-aza macrocyclic chemosensor based on the 2,5-diphenyl[1,3,4]oxadiazole in which two thioether groups were inserted in a macrocycle with the aim to make it suitable for the coordination of soft and heavy metal ions. In acetonitrile solution, the fluorescence of the chemosensor changes upon addition of different metal ions, such as Cu(II), Zn(II), Cd(II), Pb(II), Hg(II) and Ag(I), that form a not fluorescent ML species and a fluorescent M2L species characterized also via NMR experiments. The hosting of the chemosensor inside the PluS Nanoparticles leads to a high water solubility, allowing to perform the metal detection without the use of additional solvents and also induced an higher selectivity towards Ag(I) and Hg(II). Moreover, it was demonstrated for the first time the possibility to control the stoichiometry of the formed complex upon changing the number of ligands per nanoparticles. To our opinion, this possibility can give an additional tool for the tuning of the affinity and selectivity of the chemosensor that could be of great interest for the design of more and more efficient systems.

By means of X-ray diffraction analysis the solid state structure of the diprotonated species of the ligand L1_Me (9,12-Dimethyl-9,12,27,28-tetraaza-15,18-dithia-29-oxatetracyclo[24.2.1.02,7.020,25]-enneicosa-2,4,6,20,22,24,26,281-octaene), a macrocycle containing a mixed sulfur-nitrogen set of donor atoms decorated with the PPD signaling group, and of its dinuclear platinum complex was investigated . The information retrieved were used as starting point for a deep computational study. Then, with the aim to get hints for the design of possibly improved strictly related receptors, the molecular modeling study was extended to the all-nitrogen ligand L2_H which, at variance with L1_Me, has four nitrogen atoms as donors. Finally, to complete the modeling investigation we design the related ligands L1_H, L2_Me and L3_H on which computational studies were performed. The aim was to investigate and try to rationalise the parameters affecting the overall shape of the host-guest adducts.

Ligand L (2,6-bis{[7-(7-nitrobenzo[1,2,5]oxadiazole-4-yl)-3,10-dimethyl-1,4,7,10-tetraazacyclododeca-1-yl]methyl}phenol) is a fluorescent sensor that is useful for detecting Cu(II), Zn(II), and Cd(II). Some of the complexes formed are able to sense the presence of halides in solution. L passes through the cellular membrane, becoming fluorescent inside cells. The H(-1)L- species is able to form dinuclear complexes with [M(2)H(-1)L]3+ stoichiometry with Cu(II), Zn(II), and Cd(II) ions, experiencing a CHEF effect upon metal coordination in an acetonitrile/water 95:5 (v/v) solution. In all three of the complexes investigated, the metal cations are coordinatively unsaturated and can therefore bind secondary ligands as anionic species. The crystal structure of [Cd(2)(H(-1)L)Cl(2)](ClO(4))·4H(2)O is discussed. The Zn(II) complex behaves as an OFF-ON sensor for fluoride and chloride anions.

The ligational properties of the ligand 2-[bis-(2-aminoethyl)-aminomethyl]phenol (L) towards Co(II) ion were studied by means of potentiometric measurements in aqueous solution (298.1 ± 0.1 K, I = 0.15 mol dm−3). L forms a stable mononuclear [CoH−1L]+ (log K = 13.42), a hydroxylated mononuclear [CoH−1LOH] and a dinuclear [(CoH−1L)2]2+ species in which the ligand/metal ratio is 2:2. The Co(II) species is prone to bind dioxygen forming a μ-peroxo-μ-hydroxo [(CoH−1L)2(μOH)(μO2)]+ dinuclear species. The stability constants of μ-peroxo-μ-hydroxo dinuclear and μ-peroxo-mono-hydroxo species were analyzed in a series of open-chain polyamine and polyamino phenol ligands pointing out the role played by the ligand on the stability and the reversibility of the bound dioxygen. DFT calculations were carried out to predict the structure of the oxygenated Co(II)–dinuclear species for L and the related LI amino-phenol ligand. The crystal structure of the Co(III) species, derived from the oxydation of the Co(II)–oxygenated one, was also reported.

Two new Pt

Two new PtII and PdII complexes of formula [LMCl2] (M=Pt, Pd) were synthesized and characterized both in solution and solid state. They were obtained using the thio-aza macrocycle 9,18-dimethyl-12,17dithia-9,18,27,28-tetraaaza-29-oxatetracyclo[24.2.1.02,7.020,25]enneicosa-2,4,6,20,22,24,26,281-octaene (L) containing the 2,5-diphenyl [1, 3, 4]oxadiazole as intercalating fragment. MII is coordinated in cis-position by the two S atoms of L. The two crystal structures of [LPtCl2] and [LPdCl2] complexes showed that the MII ion is located outside the macrocyclic cavity. The square planar coordination sphere is fulfilled by two chloride anions in a cisplatin-like arrangement with the chloride leaving groups exposed to the environment. The biological activity of both [LPtCl2] and [LPdCl2], monitored towards a leukemic cellular model (U937), is coherent with their ability to interfere, at different levels, with the DNA structure.

After a brief introduction on the main transduction mechanisms for metal ion detection by fluorescence, this paper reviews ligand molecules containing fluorophores synthesized and employed in metal ions sensing in solution in the last few years. With the aim of making more readable the paper we have organized it by dividing the subject first for type of fluorophore, then type of metal ion. Because of many acronyms a glossary has been inserted.

The synthesis and anion binding studies of the new neutral receptor 1,1′-(2,2′-(4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-diyl)bis(2-oxoethane-2,1-diyl))bis(3-(3,5-bis(trifluoromethyl)phenyl)urea) (L1) are reported. L1 is a macrocyclic ligand containing the 3,5-trifluoromethylphenylureido-binding fragment attached as a side arm on the tetraazacyclododecane. L1 is soluble in numerous organic solvents; the binding properties of L1 towards several simple anions (G) were investigated by NMR, UV–vis and fluorescence techniques in DMSO and CH3CN solutions. L1 is able to bind F− , Cl− and AcO− in both solvents; in addition, it binds Br− in CH3CN. Fluoride shows the highest constant values in the halide series (F− > Cl− > Br− ) and AcO− is the most strongly bound among all the anions investigated. L1 is able to signal the presence of the anions in solution by fluorescence change; in the case of acetate, this occurs in the visible range.

The syntheses of three new compartmental ligands are reported. Each ligand shows two 1,4,7-triazaheptane (dien) moieties separated by different rigid aromatic groups. The dien unit is linked to the spacer through its central N-atom, while each aromatic moiety contains two hydroxyl-phenolic functions. The synthetic aspects involved in attaching two dien subunits to an aromatic group containing two hydroxyl functions were explored. Each ligand synthesized can coordinate two metal ions positioned far from each other; the single dinuclear units will be useful as building blocks in new supramolecular aggregates. The basicity and binding properties of one of the synthesized ligands (3,3′-bis[N,N-bis(2-aminoethyl)aminomethyl]-4,4′-dihydroxybiphenyl (L2)) were potentiometrically studied in aqueous solution. L2 was found to behave as a diprotic acid and as a pentaprotic base under the experimental conditions used. L2 forms stable mononuclear and dinuclear complexes with Cu(II) and Zn(II) ions; the mononuclear species show a tendency to dimerize, while the dinuclear ones are predominant in the presence of two equivalents of M(II) ions in solution. Both protonation and the presence of Zn(II) strongly affect the fluorescence emission properties of L2, which can be used as a new chemosensor for H+ and Zn(II) ions. L2 exhibits pH-dependent fluorescence and the emission due to the different protonation of L2 and can be ascribed, above all, to the degree of protonation of the 4,4′-biphenol unit; thus, L2 is more emitting at acidic pH values where the aromatic unit is fully protonated. On the contrary, the Zn-dinuclear species are more emitting from neutral to alkaline pH values exhibiting a CHEF effect which reaches its maximum values (seven times those of the free ligand) at pH 9 with the [Zn2H−2L2]2+ species, thus highlighting the sensing properties of this new chemosensor towards Zn(II).

A new and efficient synthetic protocol for the preparation of unsymmetrical difunctionalized cyclen and its close derivatives using a modified Ugi reaction (N-split Ugi) is described. The scope of this methodology is further extended by the successful use of various isocyanides, highly functionalized carboxylic acids, and aldehydes.

The synthesis and characterization of the new ligand 2,9-bis[N,N-bis(2-aminoethyl)aminomethyl]-1,10-phenanthroline (L) are reported. L contains two diethylenetriamine units connected on the central nitrogen atom by a 1,10-phenanthroline group forming a symmetrical branched ligand. The basicity and binding properties of L toward Cu(II) and Zn(II) in aqueous solution were determined by means of potentiometric, UV-vis, fluorescence, and 1H and 13C NMR techniques. L behaves as pentaprotic base under the experimental conditions used; from HL+ to H4L4+ species it is the secondary amine functions that are protonated while in the H5L5+ species also the phenanthroline is involved in protonation. L does not show fluorescence properties in the range of pH (0-14) investigated. It forms both mono- and dinuclear stable species where the phenanthroline is directly involved with both nitrogens in the coordination of the first metal which is coordinated in a pentacoordination environment also by one dien unit. The other dien unit undergoes easy protonation in the mononuclear complex while it binds the second metal in the dinuclear species. For this reason, L, in providing two different binding areas for metal coordination, behaves as an unsymmetrical compartmental ligand; one area is formed by one dien unit and by the phenanthroline, and the other by the remaining dien unit. This produces unsymmetrical metal complexes both for the mono- and dinuclear species; however, the role of the binding areas is fast exchanging in aqueous solution, at least on the NMR time scale. Solution studies and the three crystal structures of the [Zn(H2L)]4+, [[Cu(H2L)](ClO4)]3+, and [[Cu2LCl2](ClO4)]+ species highlight the unsymmetrical compartmental behavior of L as well as the host properties of the complexes in adding exogenous ligands such as hydroxide, pherchlorate, and chloride anions.

The synthesis and characterization of the new polyamino-phenolic ligand 3,3'-bis[N,N-bis(2-aminoethyl)aminomethyl]-2,2'-dihydroxybiphenyl (L) are reported. L contains two diethylenetriamine units linked by a 1,1'-bis(2-phenol) group (BPH) on the central nitrogen atom which allows two separate binding amino subunits in a noncyclic ligand. The basicity and binding properties of L toward Cu(II) and Zn(II) were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm-3). L behaves as a pentaprotic base and as a monoprotic acid under the experimental conditions used, yielding the H5L5+ or H-1L- species, respectively. L forms both mono- and dinuclear species with both metal ions investigated; the dinuclear species are largely prevalent in aqueous solution with a L/M(II) molar ratio of 1:2 at pH higher than 7. L shows different behavior in Cu(II) and Zn(II) binding, affecting the dinuclear species formed and the distance between the two coordinated metal ions, which is greater in the Zn(II) than in the Cu(II) dinuclear species. This difference can be attributed to the different degree of protonation of BPH which influences the angle between the phenyl rings in the two systems. In this way, it is possible to modulate the M(II)-M(II) distance by the choice M(II) and to space the two M(II) farther away than was possible with the previously synthesized ligands. L does not saturate the coordination sphere of the coordinated M(II) ions in the dinuclear species, and thus, these latter species are prone to add guests. 1H and 13C NMR experiments carried out in aqueous solution, as well as the crystal structures of the dinuclear Cu(II) and Zn(II) species formed in aqueous solution, aided in elucidating the involvement of L and BPH in Zn(II) and Cu(II) stabilization.

We have analyzed the interactions of a series of nitroxide radicals with ligands containing a phenol moiety coupled with different polyamine fragments, and their CuII and ZnII complexes, by EPR experiments. Nitroxide radicals are good mimics of the properties of pollutant molecules, e.g., organic compounds having different polarities and charges, surfactants, and polyaromatics. Charged, polar, and low-polarity sites in the ligands and complexes are all available for interactions; in particular, the ability to entrap the radicals in a vice-like structure, by the formation of phenyl sandwich complexes, determines the type of selective interaction that occurs when a chain or planar aromatic structure is present. For closely packed complexes, ZnII has a cooperative effect in the interaction with the radical; it allows both the entrance of low-polarity radicals at the low-polarity sites of the complex and the interactions of polar or charged radicals at the polar sites of the complexes. Conversely, CuII coordinates to the amino groups of the ligands and blocks the entry of radicals, which, thus, impedes their insertion into the structure of the complexes. The opposite behavior, with respect to that of CuII and ZnII, was found for the complexes that have more open structures. The complexes that have cyclic ligands exhibit a poor ability to interact with radicals, but, for the ligands in the absence of the coordinating metals, the interactions are significantly enhanced as a result of the entrance of the radicals into the cyclic structures. In all cases, stronger interactions occur when both hydrophilic and hydrophobic sites are involved. The neutral-surfactant probe forms aggregates mainly with the cooperative effect of the copper complexes. UV/Vis measurements confirmed the results obtained by EPR and indicate that weak interactions occur between the radicals and the complexes or ligands; they also confirmed the formation of 1:1 adducts. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The coordination properties of the ligand 2-[bis-(aminoethyl)-aminomethyl]-phenol (L) toward Cd(II) and Pb(II) are reported. The studies were carried out using potentiometric measurements (298.1 K, I=0.15 mol dm−3), UV–Vis absorption and 1H, 13C, 113Cd NMR spectra both in aqueous and non-aqueous solution. By potentiometric measurements performed in aqueous solution, L was found to form only mononuclear species with both the ions investigated; [MH−1L]+ is the main species formed. A dinuclear species with stoichiometry [M2(H−1L)2](ClO4)2 was almost quantitatively isolated in solid state from an aqueous solution in the pH range in which the [MH−1L]+ mononuclear species are present. This behavior is ascribed mainly to the low solubility of the dinuclear complex formed. L does not fulfill the coordination requirement of the ion in the mononuclear species and to saturate it, each metal ion binds the phenolate oxygen of another mononuclear species. The dinuclear species were characterized in organic solution by NMR and ESI mass spectroscopy. The results are confirmed by the crystal structure of [Cd2(H−1L)2](ClO4)2, which displays the two Cd(II) ions close to each other and bridged by two phenolic oxygens each belonging to a H−1L− species.