Synthesis, photophysical characterisation and metal ion binding properties of new ligands containing anthracene chromophores

Two new fluorescent chemosensors for heavy metal ions have been synthesised and their photophysical properties have been investigated. They present a pyridyl-thioether-based binding site and the anthracene moiety as a chromophore. In the experimental conditions used, no evidence is found for the formation of complexes with Pb²⁺, Zn²⁺, Cd²⁺, and Ag⁺ ions. On the contrary, in acetonitrile solutions both ligands strongly bind Cu²⁺ and Hg²⁺ cations according to a 1:1 and a 1:2 (metal:ligand) stoichiometry. In these complexes, the intense luminescence typical of anthracene derivatives is almost completely quenched and this phenomenon can be mainly attributed to an intraligand electron transfer process from the anthracene chromophore to the complexed pyridine. These results are of interest for the development of new chemosensors for the design of efficient electronic tongues for the detection of transition metal ions.     

Selective binding of Ni2+ and Cu2+ metal ions with naphthazarin esters isolated from Arnebia euchroma

Naphthazarin esters (C1–C4) isolated from the roots of Arnebia euchroma are found as skilled dual chemosensors for Ni²⁺ and Cu²⁺ among Pb²⁺, Na²⁺, K²⁺, Hg²⁺, Mg²⁺, and Ca²⁺ metal ions. C1–C4 esters exhibited a red shift of 54 nm with Ni²⁺ and 30 nm with Cu²⁺ metal ions in absorption. There is a formation of red-shifted bands between 517 and 613 nm in the absorption spectrum of C1–C4 sensors on binding with Ni²⁺ and Cu²⁺ ions. The addition of Ni²⁺ and Cu²⁺ ions to sensors C1–C4 stimulates a remarkable color change from reddish pink to purple and light blue, respectively. These color changes can be identified with the naked eye. The significant downfield shifts of CO and OH peaks in nuclear magnetic resonance (NMR) spectrum confirm the chelation as binding mechanism. With ultraviolet–visble and NMR studies, it is found that C1–C4 esters possessed notable selectivity and sensitivity toward Ni²⁺ and Cu²⁺ over other metal ions.     

Optical chemosensors for Cu(II) ion based on BODIPY derivatives: an experimental and theoretical study

Two BODIPY derivatives for Cu²⁺ ion chemosensors containing 4-[2-(diethylamino)-2-oxoethoxy]phenyl (BDP1) and 3,4-bis[2-(diethylamino)-2-oxoethoxy]phenyl (BDP2) were synthesized by coupling appropriate N,N-diethyl-2-(4-formylphenoxy)acetamide and 2,4-dimethylpyrrole moieties in the presence of trifluoroacetic acid and anhydrous dichloromethane at room temperature. The binding abilities between these chemosensors and 50 equivalents of Na⁺, K⁺, Ag⁺, Ca²⁺, Fe²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ ions were studied using UV-vis and fluorescence spectrophotometry. The results show that, compared to other ions, both the UV-vis absorption and fluorescence emission intensity of BDP2 decreased dramatically when Cu²⁺ ion was added. To explain this behavior, ab initio quantum chemical calculations were performed using correlated second-order Møller-Plesset perturbation theory (MP2/LanL2DZ). The calculated orbital energies indicated that the decrease in UV-vis absorption intensity and the quenching of fluorescene emission were due to the single-electron reduction of Cu²⁺ to Cu⁺ ion.

Synthesis, characterization, fluorescence and computational studies of new Cu, Ni and Hg complexes with emissive thienylbenzoxazolyl-alanine ligands

The interaction of four fluorescent compounds containing thiophene and benzoxazole moieties combined with an alanine residue with alkaline, alkaline-earth, transition and post-transition metal ions was explored. The highly fluorescent heterocyclic alanine derivatives are strongly quenched in the solid state after complexation with the paramagnetic metal ions Cu²⁺ and Ni²⁺, and with the diamagnetic Hg²⁺. Absorption and steady-state fluorescence titrations reveal a selective interaction with Cu²⁺, Ni²⁺ and Hg²⁺. In all cases the formation of mononuclear or dinuclear metal complexes in solid state and in solution are postulated. DFT calculations on the mercury(II) complexes confirm the formation of dinuclear species. Our results suggest that one metal ion is coordinated by the chelate group formed by the amine and the protonated carboxylic groups present in the amino acid residue while a second metal ion is directly linked to the chromophore. As parent compound, L4 shows no interaction with Cu²⁺ and Ni²⁺ salts. However, the interaction with Hg²⁺ induces a strong quenching and a red shift of the fluorescence emission.     

Optimization of manganese peroxidase and laccase production in the South American fungus<Emphasis Type="Italic"> Fomes sclerodermeus</Emphasis> (Lév.) Cke

Fomes sclerodermeus produces manganese peroxidase (MnP) and laccase as part of its ligninolytic system. A Doehlert experimental design was applied in order to find the optimum conditions for MnP and laccase production. The factors studied were Cu²⁺, Mn²⁺ and asparagine. The present model and data analysis allowed us not only to define optimal media for production of both laccase and MnP, but also to show the combined effects between the factors. MnP was strongly influenced by Mn²⁺, which acts as an inducer. Under these conditions Cu²⁺ negatively affected MnP activity. At 13 days of growth 0.75 U ml^–1 were produced in the optimized culture medium supplemented with 1 mM MnSO₄ and 4 g l^–1 asparagine. The laccase titer under optimized conditions reached maximum values at 16 days of growth: 13.5 U ml^–1 in the presence of 0.2 mM CuSO₄, 0.4 mM MnSO₄ and 6 g l^–1 asparagine. Mn²⁺ promoted production of both enzymes. There were important interactions among the nutrients evaluated, the most significant being those between Cu²⁺ and asparagine.     

Electron injection from the side of an M-DNA duplex

M-DNA is a complex formed between duplex DNA and divalent metal ions (Zn²⁺, Cu²⁺ or Ni²⁺) at pHs above 8. Previous results showed that the fluorescence of an electron donor fluorophore was quenched when an acceptor flourophore was placed in the opposite end of an M-DNA duplex suggesting electron transfer through the duplex and indicating M-DNA may operate as a better conductor than B-DNA. To further investigate the properties of M-DNA, oligodeoxynucleotides were prepared with fluorescein (Fl) as an electron donor placed at different positions along the helix. An internal position of the chromophore was made possible by attaching it to the extra hydroxyl arm in the branched monomer 4′-C-hydroxymethylthymidine. Upon excitation of the donor fluorophore, it was demonstrated that electrons could be injected into the side of an M-DNA helix thereby extending the range of nanoelectronic structures that can be prepared from DNA. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Facile synthesis,cytotoxicity and bioimaging of Fe3+ selective fluorescent chemosensor

The designing and development of fluorescent chemosensors have recently been intensively explored for sensitive and specific detection of environmentally and biologically relevant metal ions in aqueous solution and living cells. Herein, we report the photophysical results of alanine substituted rhodamine B derivative 3 having specific binding affinity toward Fe³⁺ with micro molar concentration level. Through fluorescence titration at 599 nm, we were confirmed that ligand 3 exhibited ratiometric fluorescence response with remarkable enhancement in emission intensity by complexation between 3 and Fe³⁺ while it appeared no emission in case of the competitive ions (Sc³⁺, Yb³⁺, In³⁺, Ce³⁺, Sm³⁺, Cr³⁺, Sn²⁺, Pb²⁺, Ni²⁺, Co²⁺, Cu²⁺, Ba²⁺, Ca²⁺, Mg²⁺, Ag⁺, Cs⁺, Cu⁺, K⁺) in aqueous/methanol (60:40, v/v) at neutral pH. However, the fluorescence as well as colorimetric response of ligand–iron complex solution was quenched by addition of KCN which snatches the Fe³⁺ from complex and turn off the sensor confirming the recognition process was reversible. Furthermore, bioimaging studies against L-929 cells (mouse fibroblast cells) and BHK-21 (hamster kidney fibroblast), through confocal fluorescence microscopic experiment indicated that ligand showed good permeability and minimum toxicity against the tested cell lines.     

Identification of Ion-Selectivity Determinants in Heavy-Metal Transport P<Subscript>1B</Subscript>-type ATPases

P_1B-type ATPases transport a variety of metals (Cd²⁺, Zn²⁺, Pb²⁺, Co²⁺, Cu²⁺, Ag⁺, Cu⁺) across biomembranes. Characteristic sequences CP[C/H/S] in transmembrane fragment H6 were observed in the putative transporting metal site of the founding members of this subfamily (initially named CPx-ATPases). In spite of their importance for metal homeostasis and biotolerance, their mechanisms of ion selectivity are not understood. Studies of better-characterized P_II-type ATPases (Ca-ATPase and Na,K-ATPase) have identified three transmembrane segments that participate in ion binding and transport. Testing the hypothesis that metal specificity is determined by conserved amino acids located in the equivalent transmembrane segments of P_1B-type ATPases (H6, H7, and H8), 234 P_1B-ATPase protein sequences were analyzed. This showed that although H6 contains characteristic CPX or XPC sequences, conserved amino acids in H7 and H8 provide signature sequences that predict the metal selectivity in each of five P_1B-ATPase subgroups identified. These invariant amino acids contain diverse side chains (thiol, hydroxyl, carbonyl, amide, imidazolium) that can participate in transient metal coordination during transport and consequently determine the particular metal selectivity of each enzyme. Each subgroup shares additional structural characteristics such as the presence (or absence) of particular amino-terminal metal-binding domains and the number of putative transmembrane segments. These differences suggest unique functional characteristics for each subgroup in addition to their particular metal specificity.     

Mn 2+ , and Zn 2+ 1:1 complexes with biochemically significant thioether carboxylic acids and some of the sulfoxide and sulfone derivatives

The 1:1 complexes of Mn²⁺, Cu²⁺, and Zn²⁺ with S-carboxymethyl alkyl and S-carboxymethyl aryl mercaptans were studied in water containing 50% dioxane (I = 0.1; t = 25 °). The determination of the stability constants and a comparison with simple carboxylate complexes reveals that the complexes of Cu²⁺ (and slightly also of Zn²⁺) with the S-carboxymethyl alkyl mercaptans are more stable than expected from only basicity of the carboxylate groups. This suggests that the thioether group participates in complex formation, i.e., chelates are formed. The Mn²⁺ complexes of both kinds of ligands, and the Cu²⁺ or Zn²⁺ complexes with S-carboxymethyl aryl mercaptans have the stability expected according to the basicity of the carboxylate groups. NMR experiments with S-carboxymethyl ethyl mercaptan confirm the formation of chelates with Cu²⁺ and suggest simple carboxylate complexes with Mn²⁺. Analogous experiments with (S-carboxymethyl phenyl mercaptan do not allow an unequivocal statement about the distribution between simple carboxylate complexes and chelates for both metal ions. Also, as the thioether acids are biologically oxidized, the complex stabilities of several of such oxidized derivatives were measured.     

A spectrophotometric method for the determination of zinc, copper, and cobalt ions in metalloproteins using Zincon

Zincon (2-carboxy-2′-hydroxy-5′-sulfoformazylbenzene) has long been known as an excellent colorimetric reagent for the detection of zinc and copper ions in aqueous solution. To extend the chelator’s versatility to the quantification of metal ions in metalloproteins, the spectral properties of Zincon and its complexes with Zn²⁺, Cu²⁺, and Co²⁺ were investigated in the presence of guanidine hydrochloride and urea, two common denaturants used to labilize metal ions in proteins. These studies revealed the detection of metals to be generally more sensitive with urea. In addition, pH profiles recorded for these metals indicated the optimal pH for complex formation and stability to be 9.0. As a consequence, an optimized method that allows the facile determination of Zn²⁺, Cu²⁺, and Co²⁺ with detection limits in the high nanomolar range is presented. Furthermore, a simple two-step procedure for the quantification of both Zn²⁺ and Cu²⁺ within the same sample is described. Using the prototypical Cu²⁺/Zn²⁺-protein superoxide dismutase as an example, the effectiveness of this method of dual metal quantification in metalloproteins is demonstrated. Thus, the spectrophotometric determination of metal ions with Zincon can be exploited as a rapid and inexpensive means of assessing the metal contents of zinc-, copper-, cobalt-, and zinc/copper-containing proteins.     

4,5-Bis(diphenylphosphinoyl)-1,2,3-triazole ligand: Studies on metal complex formations in liquid-liquid distribution systems

The formation reactions of hydrophobic metal complexes of divalent typical element and transition metal ions with a novel chelating ligand containing N and O donor atoms, 4,5-bis(diphenylphosphinoyl)-1,2,3-triazole (L^TH), were investigated by the liquid-liquid distribution method carried out on metal ions between chloroform and aqueous solutions. The liquid-liquid distribution reaction formulae of metal ions via the formation of hydrophobic metal complexes were revealed, along with their equilibrium constants. Three types of hydrophobic mononuclear and binuclear metal complexes distributed into chloroform solutions were found, namely, ML₂ (M = Mg²⁺, Zn²⁺, Pb²⁺; L = L^T−), ML₂(HL) (M = Cd²⁺, Mn²⁺), and M₂L₃(OH) (M = Co²⁺, Ni²⁺, Cu²⁺). Linear free energy relationships were found between the equilibrium constants of the liquid-liquid distribution reactions and the stability constants of 1:1 complexes consisting of a divalent metal ion and a glycinate. These relationships suggest the chelate formation of N,O-coordination with a heterocyclic five-membered ring in the metal complexes with L^TH.     

Induction of the β-form of poly(S-carboxyethyl-l-cysteine) by divalent metalchlorides

The effects of eight divalent metal ions on fully neutralized poly(S-carboxyethyl-l-cysteine) have been studied by means of circular dichroism. Four ionic species (Cd²⁺, Cu²⁺, Zn²⁺ and Ni²⁺) effectively induce the β-form, while the other four species (Co²⁺, Ba²⁺, Ca²⁺ and Mg²⁺) are not effective. Specifically, Mg(ClO₄)₂ is ineffective, even at 1.86 m. The effect of Cu²⁺ ions on the polypeptide conformation is significant at pH values other than in the neural range. Comparison of the present results with previous ones from the lower side chain homologue, poly(S-carboxymethyl-l-cysteine), shows that Cd²⁺ and Zn²⁺ ions are more effetive but Co²⁺ ions are much less effective in the polypeptide studied here. Random coils of poly(S-carboxyethyl-l-cysteine) are more soluble while the β-form is less soluble compared with the respective conformations of the lower side-chain homologue.     

Induction of the β-form of poly(S-carboxyethyl-l-cysteine) by divalent metalchlorides

The effects of eight divalent metal ions on fully neutralized poly(S-carboxyethyl-l-cysteine) have been studied by means of circular dichroism. Four ionic species (Cd²⁺, Cu²⁺, Zn²⁺ and Ni²⁺) effectively induce the β-form, while the other four species (Co²⁺, Ba²⁺, Ca²⁺ and Mg²⁺) are not effective. Specifically, Mg(ClO₄)₂ is ineffective, even at 1.86 m. The effect of Cu²⁺ ions on the polypeptide conformation is significant at pH values other than in the neural range. Comparison of the present results with previous ones from the lower side chain homologue, poly(S-carboxymethyl-l-cysteine), shows that Cd²⁺ and Zn²⁺ ions are more effetive but Co²⁺ ions are much less effective in the polypeptide studied here. Random coils of poly(S-carboxyethyl-l-cysteine) are more soluble while the β-form is less soluble compared with the respective conformations of the lower side-chain homologue.     

Probing the coordination properties of glutathione with transition metal ions (Cr2+,Mn2+,Fe2+,Co2+, Ni2+,Cu2+,Zn2+,Cd2+,Hg2+) by density functional theory

Complexes formed by reduced glutathione (GSH) with metal cations (Cr²⁺, Mn²⁺,Fe²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺,Cd²⁺,Hg²⁺) were systematically investigated by the density functional theory (DFT). The results showed that the interactions of the metal cations with GSH resulted in nine different stable complexes and many factors had an effect on the binding energy. Generally, for the same period of metal ions, the binding energies ranked in the order of Cu²⁺>Ni²⁺>Co²⁺>Fe²⁺>Cr²⁺>Zn²⁺>Mn²⁺; and for the same group of metal ions, the general trend of binding energies was Zn²⁺>Hg²⁺>Cd²⁺. Moreover, the amounts of charge transferred from S or N to transition metal cations are greater than that of O atoms. For Fe²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺,Cd²⁺ and Hg²⁺ complexes, the values of the Wiberg bond indices (WBIs) of M-S (M denotes metal cations) were larger than that of M-N and M-O; for Cr²⁺ complexes, most of the WBIs of M-O in complexes were higher than that of M-S and M-N. Furthermore, the changes in the electron configuration of the metal cations before and after chelate reaction revealed that Cu²⁺, Ni²⁺,Co²⁺ and Hg²⁺ had obvious tendencies to be reduced to Cu⁺,Ni⁺,Co⁺ and Hg⁺ during the coordination process.     

Theoretical insights into the metal chelating and antimicrobial properties of the chalcone based Schiff bases

The emergence of multi-drug resistant pathogens in infectious disease conditions accentuates the need for the design of new classes of antimicrobial agents that could defeat the multidrug resistance problems. As a new class of molecules, the Heterocyclic Schiff base is of considerable interest, owing to their preparative accessibility, structural flexibilities, versatile metal chelating properties, and inherent biological activities. In the present study, CAM-B3LYP/LANL2DZ and M062X/DEF2-TZVP level of density functional method is used to explore the complexation of chalcone based Schiff base derivatives by Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ metal ions. The HL(1-3)-Co²⁺, HL(1-3)-Ni²⁺ and HL(1-3)-Zn²⁺ complexes formed the distorted tetrahedral geometry. Whereas, the HL(1-3)-Cu²⁺ complexes prefers distorted square-planar geometry. The BSSE corrected interaction energies of the studied complexes reveals that Cu²⁺ ion forms the most stable complexes with all three chalcone based Schiff bases. Of the three Schiff bases studied, the HL2 Schiff base acts as a potent chelating agent and forms the active metal complexes than the HL1 and HL3 Schiff bases. Further, the strength of the interaction follows the order as Cu^2+?>?Ni^2+?>?Co^2+?>?Zn²⁺. The QTAIM analysis reveals that the interaction between the metal ions and coordinating ligand atoms are electrostatic dominant. The metal interaction increases the π-delocalisation of electrons over the entire chelate. Hence, the antimicrobial activity of the metal complexes is more effective than the free Schiff bases. Moreover, the HL(1-3)-Cu²⁺ complexes shows higher antimicrobial activities than the other complexes studied.     

Removal of copper using marine brown alga, Undaria Pinnatifida modified with oxime

Summary As oxime is selective for Cu²⁺, oxime groups were introduced to the cell wall of alga by glutaraldehyde. Such modified biomass showed high affinity for Cu²⁺, which resulted in the increase of copper sorption capacity about 4.5 times higher than that of natural alga. For pH range from 2.5 to 3.0, only Cu²⁺ were removed by alga biomass modified with oxime, while other heavy metal ions such as Ca²⁺,Cd²⁺,Pb²⁺ were not adsorbed. By changing pH, selective recovery of Cu²⁺ was achieved.     

Calix[4]arene based molecular sensors with pyrene as fluoregenic unit: Effect of solvent in ion selectivity and colorimetric detection of fluoride

Fluorescent molecular sensors having excimer emission property have been designed and synthesised incorporating calix[4]arene derivatives in cone and 1,3-alternate conformation as ionophore and two pyrene moieties at close proximity as fluorophore. They exhibit strong excimer emission around 515 nm, which is used to monitor interaction of metal ions with the ionophores. Ion-binding study of these fluoroionophore has been investigated in acetonitrile-chloroform and THF-H₂O with a wide range of cations and anions and the recognition process is monitored by luminescence, UV-Vis and ¹H NMR (for F⁻) spectral changes. The present study demonstrated profound influence of solvent in ion selectivity, in acetonitrile-chloroform they formed complexes with Hg²⁺, Pb²⁺, Cu²⁺ and Ni²⁺, whereas in THF-H₂O they exhibit selectivity only for Cu²⁺. In the case of anions, selectivity for only F⁻ with color change is observed. Composition of the complexes formed was determined from mass spectrometry and the binding constants were determined from fluorescence titration data. The reasons for formation of excimer emission, quenching of it in presence of certain metal ions, role of solvent in selectivity and energy/electron transfer process involved in the ion-recognition event have been discussed on the basis of experimental data.     

Compartments for the Management of Municipal Solid Waste

Despite technological developments and improved liner-material applications, heavy metals in landfill leachate still penetrate the soil profile, polluting the soil and ground-water. An alternative approach therefore must be explored to reduce heavy-metal migration in soil-bentonite landfill liners. By considering the interaction of different heavy metals and their synergetic and antagonistics behaviors, such an approach could be developed. Low mobility metals such as Cu²⁺, and Pb²⁺ inhibit the adsorption of Cd²⁺ which is a moderate-mobility metal and Cu²⁺ sorption is decreased by the presence of Zn²⁺ and Cd²⁺. Therefore, Zn²⁺, a low-mobility metal, cannot be grouped with Cu²⁺. This way, four compatible metal groups have been identified: (1) low mobility: Pb²⁺, Cu²⁺, and Ag, (2) low mobility: Zn²⁺ and Cr³⁺; (3) moderate mobility: As²⁺, Fe²⁺, and Ni²⁺; (4) high mobility: Cd²⁺ and Hg²⁺. Cd²⁺ with a moderate mobility pattern is synergetic to Fe²⁺ and is more mobile with Ni²⁺. Therefore, Cd²⁺ is separated from the moderate-mobility group and is consigned with Hg, a high-mobility metal. The liner materials suitable for Hg²⁺ are assumed to be suitable for Cd²⁺ as well. Based on this concept, and to reduce heavy metal mobility, wastes should be segregated on compatibility basis according to their heavy metal contents before being disposed in different individual compartments. For wastes containing several incompatible heavy metals, sorting should be based on the heavy-metal with the highest concentration. Another solution is the manufacturing of products using compatible heavy metal combinations and then labeling them accordingly. Such waste segregation and landfill compartmentalization lowers risks of groundwater contamination and liner cost.     

Naked eye sensing of toxic metal ions in aqueous medium using thiophene‐based ligands and its application in living cells

Thiophene‐based diimine (R1) and monoimine (R2) were synthesized in a single step, and their cation binding affinity was tested using colorimetric and UV–vis spectral studies. R1 selectively shows a colorimetric turn‐on response for Pb²⁺, Hg²⁺ ions and colorimetric turn‐off with Sn²⁺ ions, and R2 shows visual response for Cu²⁺ and Hg²⁺ over other examined metal ions in aqueous medium. R1 forms 1:1 complex with Pb²⁺, Hg²⁺, and Sn²⁺ and exhibits fluorescence quenching, whereas R2 shows 2:1 complex with Hg²⁺, Cu²⁺ and shows fluorescence enhancement. The structural and electronic properties of the sensors and their metal complexes were also investigated using Density Functional Theory calculations. R2 was also successfully demonstrated as a fluorescent probe for detecting Cu²⁺ ions in living cells. Copyright © 2014 John Wiley & Sons, Ltd.     

Spectroscopic Analysis of the Cu<Superscript>2+</Superscript>-Induced Fluorescence Quenching of Fluorescent Proteins AmCyan and mOrange2

Fluorescent proteins show fluorescence quenching by specific metal ions, which can be applied towards metal biosensing applications. In order to develop metal-biosensor, we performed spectroscopic analysis of the fluorescence quenching of fluorescent protein AmCyan and mOrange2 by various metal ions. The fluorescence intensity of AmCyan was reduced to 48.54% by Co²⁺ and 67.77% by Zn²⁺; Cu²⁺ reduced the fluorescence emission of AmCyan to 19.30% of its maximum. The fluorescence intensity of mOrange2 was quenched by only Cu²⁺, to 11.48% of its maximum. When analyzed by Langmuir equation, dissociation constants for AmCyan and mOrange2 were 56.10 and 21.46 µM, respectively. The Cu²⁺ quenching of AmCyan and mOrange2 were reversible upon treatment with the metal chelator EDTA, indicating that the metal ions were located on the protein surface. Their model structures suggest that AmCyan and mOrange2 have novel metal-binding sites.