Relevant Metal Ions Research Articles

A 2-(2'-hydroxyphenyl)benzothiazole (HBT)-quinoline conjugate: a highly specific fluorescent probe for Hg(2+) based on ESIPT and its application in bioimaging.

A benzothiazole derived chemosensor L has been designed based on the excited-state intramolecular proton transfer (ESIPT) mechanism to afford a fluorescence turn-on response specifically in the presence of Hg(2+) ions over a host of biologically relevant metal ions as well as toxic heavy metal ions. The chemosensor exhibits high sensitivity with the detection limit down to 0.11 μM. The metal binding is supported by (1)H NMR titrations, ESI-MS spectral analysis and substantiated by theoretical calculations using the density functional theory. The probe shows cell membrane permeability and efficiency for the detection of Hg(2+) in HeLa cells.

A highly selective dual-channel Cu2+ and Al3+ chemodosimeter in aqueous systems: Sensing in living cells and microfluidic flows

The design and development of fluorescent chemosensors have recently been the focus of considerable attention for the sensitive and specific detection of environmentally and biologically relevant metal ions in aqueous solutions and in living cells. Herein, we report photophysical results for a 1H-pyrrole-2-carboxaldehyde-substituted rhodamine 6G derivative (RCS) that possesses specific binding affinity toward Al3+ and Cu2+ at micromolar concentration levels. In an N,N-dimethylformamide (DMF) and water (v/v=2/8) medium, the RCS chemosensor exhibits a substantially enhanced absorbance intensity at 532nm and a color change from colorless to pink for Cu2+; it also exhibits significant “off–on” fluorescence at 557nm, accompanied by a color change from colorless to fluorescent-yellow upon binding to Al3+. The RCS sensor exhibits extremely high fluorescence enhancement upon complexation with Al3+, and it can be used as a “naked eye” sensor. Through fluorescence titration at 557nm, we confirmed that RCS exhibits a fluorescence response with a remarkable enhancement in emission intensity resulting from the complexation between RCS and Al3+, whereas no emission appeared in the case of competitive metal ions (Cu2+, Al3+, Li+, Na+, K+, Cs+, Mg2+, Ca2+, Fe2+, Co2+, Ag+, Zn2+, Cd2+, Hg2+ and Pb2+) in a DMF and water (v/v=2/8) solution. The reversible ring-opening mechanism of the rhodamine spirolactam induced by Al3+/Cu2+ binding and the 1:1 stoichiometric structure between RCS and Al3+ were adequately supported by Job-plot evaluation, optical titration and FT-IR analysis. The lowest detection limit for Al3+ is 3.20×106M−1 in a DMF and water (v/v=2/8) solution. Al3+-induced chelation-enhanced fluorescence (CHEF) is associated with spirolactam ring opening of the rhodamine unit. Finally, RCS was successfully applied for the bio-imaging of Al3+ in living HeLa cells and for fluorescence imaging of a microfluidic system.

A highly selective and sensitive fluorescent probe for quantitative detection of Hg2+ based on aggregation-induced emission features

A π-conjugated cyanostilbene derivative of (Z)-2-(4-nitrophenyl)-3-(4-(vinyloxy)phenyl)acrylonitrile (CN-vinyl) had been designed, synthesized and confirmed by the standard spectroscopic analyses. CN-vinyl possesses an unusual high emissive aggregation-induced emission (AIE) feature in a tetrahydrofuran/water mixture (2:8, v/v). The fluorescence intensity of CN-vinyl can be quenched linearly with the addition of Hg2+ in a range of 0–50μM with a correlation coefficient of R2=0.9957. The detection limit of Hg2+ is 37nM. The mechanism for Hg2+-mediated optical properties of CN-vinyl is due to the selective cleavage of vinyl group by Hg2+. Accuracy of the proposed methodology was evaluated by means of the recovery study in real samples and the analyzing certified reference material of the standard solution of Hg2+. By this novel strategy, CN-vinyl can be used for quantitative detection of Hg2+ as well as the presence of other physiological relevant metal ions.

An “off–on” optical sensor for mercury ion detection in aqueous solution and living cells

A rhodamine-based optical sensor Rh–3S has been developed for selective detection of Hg2+ in aqueous solution as well as in living cells. UV–vis and fluorescence spectroscopic studies reveal that Rh–3S shows marked sensitivity and selectivity to Hg2+ with a chelation-induced “off–on” response in acetonitrile (ACN)/MOPS buffer (10mM, pH7.3, v/v, 1:1). The Rh–3S sensor binds Hg2+ in a 1:1 stoichiometry with an apparent binding constant 3.71×106M−1 (log K=6.57) and displays a distinct change in color and fluorescence upon the alteration of free Hg2+ levels in solution with a reversible response and little interference with other biological relevant metal ions. Live cell confocal imaging studies demonstrate that the sensor is also capable of imaging the presence of Hg2+ ions as well as its dynamic changes in live cells.

Fluorescence signaling of Zn2+ levels in synthetic urine by dipicolylamine-armed hydroxynaphthalimide

A novel Zn2+-selective fluorescent sensor based on dipicolylamine-armed hydroxynaphthalimide (DPA-NPI) was developed. DPA-NPI showed selective and sensitive fluorescence turn-on type signaling behavior toward Zn2+ ions. The detection of Zn2+ ions was not affected by the presence of commonly encountered physiologically relevant metal ions. Interference from Hg2+, Cd2+, and Cu2+ ions was observed but not critical, because they are present in trace amounts under physiological conditions. The complex formation was confirmed by 1H NMR and mass measurements. The practical application of the sensor for determining Zn2+ levels in synthetic urine was possible with a detection limit of 2.7×10−8M. The signaling of Zn2+ ions in biological samples using fetal bovine serum was also tested.

A Schiff base derivative from cinnamaldehyde for colorimetric detection of Ni2+ in water

A novel Schiff base (L1) derivative from cinnamaldehyde with a simple structure was synthesized and evaluated as a sensitive colorimetric Ni2+ sensor in aqueous solution. Addition of nickel dissolved in water into a L1 solution produced a rapid color change from faded yellow to deep orange, corresponding to a large red shift in the absorption peak from 435 to 480nm. L1 exhibited a detection limit for Ni2+ in water of 1×10−7M measured by absorption spectroscopy, whereas by naked eye the detection limit was of the order of 5×10−6M. Interaction between L1 and other biologically and environmentally relevant metal ions such as Hg2+, Pb2+, Co2+, Cu2+ and Mn2+, induced minimal spectral changes. These results show that the Schiff base L1 could be an excellent Ni2+ chemosensor with high metal selectivity and with the capability to perform the detection in water over a pH range of 5.5–8.

A Highly Selective Rhodamine Based Colorimetric Sensor Toward Cu2+

A probe for recognition of Cu2+ was developed based on rhodamine B. The probe was synthesized by condensation between rhodamine B and quinoline-2-carbaldehyde. The probe exhibits highly selectivity toward Cu2+ detection. It binds Cu2+ in a 1:1 stoichiometry in acetonitrile solution. Distinct color change can be observed upon the addition of Cu2+ and little interference with other biologically relevant metal ions. Only Fe3+ addition shows a little disturbance in absorption enhancement. In addition, the limit of detection toward Cu2+ is about 235 times lower than the World Health Organization (WHO) recommended level in drinking water.

Permeation, regulation and control of expression of TRP channels by trace metal ions.

Transient receptor potential (TRP) channels form a diverse family of cation channels comprising 28 members in mammals. Although some TRP proteins can only be found on intracellular membranes, most of the TRP protein isoforms reach the plasma membrane where they form ion channels and control a wide number of biological processes. There, their involvement in the transport of cations such as calcium and sodium has been well documented. However, a growing number of studies have started to expand our understanding of these proteins by showing that they also transport other biologically relevant metal ions like zinc, magnesium, manganese and cobalt. In addition to this newly recognized property, the activity and expression of TRP channels can be regulated by metal ions like magnesium, gadolinium, lanthanum or cisplatin. The aim of this review is to highlight the complex relationship between metal ions and TRP channels.

Quantum dots modified with the Al(III)-pefloxacin complex as a novel bioprobe for the sensitive turn-on and dual-fluorescence detection of dsDNA

We describe a novel fluorescent bioprobe for the sensitive and selective detection of double-stranded DNA (dsDNA). It consists of quantum dots (Q-dots) whose fluorescence is quenched (through photoinduced electron transfer) on covering them with the Al(III)-pefloxacin complex. It is found, however, that dsDNA has an affinity for this complex that is so strong that it can break up the binding to the quantum dots, this leading to a complete recovery of the fluorescence of both the Q-dots and the Al(III)-pefloxacin complex. Dual fluorescence (peaking at 420 and 547 nm) is observed under a single excitation wavelength of 350 nm. Neither ribonucleic acid, bovine serum albumin, nor biologically relevant metal ions are capable of giving this effect. The detection limit (3σ/k) for herring sperm DNA is 15.3 μg L−1 if determined via the fluorescence of the Q-dots, and 48 μg L−1 via the Al(III)-pefloxacin complex. The method was applied to the determination of hsDNA in synthetic samples and gave excellent results.

A rhodamine-based fluorescent probe for Cu(II) determination in aqueous solution.

An 'off-on' rhodamine-based fluorescence probe for the selective detection of Cu(II) has been designed, exploiting the guest-induced structure transform mechanism. This system shows a sharp Cu(II)-selective fluorescence enhancement response in an aqueous system under physiological pH, and possesses high selectivity against a background of environmentally and biologically relevant metal ions. Under optimum conditions, the fluorescence intensity enhancement of this system is linearly proportional to the Cu(II) concentration from 50 nM to 6.0 μM with a detection limit of 29 nM.

Desferrioxamine as an appropriate chelator for 90Nb: Comparison of its complexation properties for M-Df-Octreotide (M = Nb, Fe, Ga, Zr)

The niobium-90 radioisotope (90Nb) holds considerable promise for use in immuno-PET, due to its decay parameters (t½=14.6h, positron yield=53%, Eß+mean=0.35MeV and Eß+max = 1.5MeV). In particular, 90Nb appears well suited to detect in vivo the pharmacokinetics of large targeting vectors (50–150kDa). In order to be useful for immuno-PET chelators are required to both stabilize the radionuclide in terms of coordination chemistry and to facilitate the covalent attachment to the targeting vector. Different chelators were evaluated for this purpose in terms of radiolabelling efficiency and stability of the radiolabelled Nb(V) complex and in order to determine the most suitable candidate for conjugation to a biologically relevant targeting vector. For the purpose of studying the complexation properties the niobium radioisotope 95Nb was used as an analogue of 90Nb, by virtue of its longer half-life (35days) and lower cost (reactor-based production). Acyclic and cyclic chelators were investigated, with desferroxamine [Df: (N'-{5-[acetyl(hydroxy)amino]pentyl}-N-[5-({4-[(5-aminopentyl) (hydroxy)amino]-4-oxobutanoyl} amino)pentyl]-N-hydroxysuccinamide)] emerging as the best candidate. Greater than 99% radiolabelling was achieved at room temperature over a wide pH range. The 95Nb-Df complex is sufficiently stable for immuno-PET (<7% degradation over 7days in vitro). As a proof-of-principle, a Df conjugate featuring a well-established targeting vector, (D)-Phe1-octreotide, was evaluated. The fast labelling kinetics of the unconjugated chelator (Df) were retained for Df-succinyl-(D)Phe1-octreotide (Df-OC), with>90% labelling after 1h at room temperature over the pH range 5–7. Stability studies, performed in vitro in serum at physiological temperature (37°C), revealed that 87±2% of the radiolabelled molecule remained intact after 7days. Competition studies with relevant metal ions (zirconium(IV), gallium(III) and iron(III)) have been performed with Df-OC to gain insight to the relative stability [Nb-Df]-OC complex to transmetallation. At equimolar metal ion concentrations the [Nb-Df]-OC complex showed the greatest overall stability. The favourable radiolabelling characteristics of Df-OC and its stability indicate that Df is a potentially very useful chelator for the development of radiopharmaceuticals for 90Nb-PET.

Synthesis, X-ray crystal structures, spectroscopic and electrochemical studies of Zn(II), Cd(II), Ni(II) and Mn(II) complexes of N1,N4-bis(pyridoxylidene)triethylenetetramine

Zn(II), Cd(II), Ni(II) and Mn(II) complexes of a new hexadentate ligand N1,N4-bis(pyridoxylidene)triethylenetetramine have been synthesized. X-ray crystal structures show that in all the complexes the metal: ligand stoichiometry is 1:1 and the ligand coordinates in a di-deprotonated hexadentate manner through two phenolate oxygens, two imine nitrogens and two secondary amine nitrogen atoms. Fluorescence spectroscopy shows that the ligand centered emission undergoes threefold enhancement of intensity on complexation with Zn(II) ion, whereas it is quenched or remains unaffected in presence of various biologically relevant divalent metal ions. The Zn(II) specific fluorescence enhancement indicates that the ligand may be used as a fluorogenic sensor for Zn(II) in biological systems, with a sensitivity of detection of 10−8M. The electronic structures of the ligand as well as the complexes and their UV–Vis absorption spectra are explained on the basis of DFT and TD-DFT calculations respectively. It is found that that covalence of the metal ligand bond follows the order Ni(II)⋙Mn(II)>Zn(II)≈Cd(II).

Silicate sol–gel stabilized silver nanoparticles for sensor applications toward mercuric ions, hydrogen peroxide and nitrobenzene

Here, we developed a silver nanoparticles (Ag NPs) based sensor for the detection of mercuric ions (Hg(II)), hydrogen peroxide (H2O2) and nitrobenzene. The silicate sol–gel (SSG) stabilized Ag NPs were synthesized via one-pot synthetic route using the mixture of hydrazine, ammonium chloride and nitric acid as reduction solution. The Ag NPs were further characterized by absorption spectra, XRD, SEM, TEM, EDX and SAED analyses. The spectral and colorimetric methods revealed the efficiency of Ag NPs to detect Hg(II) ions and the lowest detection limit was found to be 5μM. Also, Ag NPs exhibited selectivity toward Hg(II) ions in the presence of other environmentally relevant heavy metal ions. For the detection of H2O2, an enzymeless electrochemical sensor was prepared by modifying glassy carbon electrode with SSG stabilized Ag NPs. Using the linear sweep voltammetry (LSV) and differential pulse voltammetry (DPV) techniques, the lowest experimental detection limits for H2O2 sensing were found to be 0.5 and 0.1μM, respectively. Similarly, the electrochemical sensing of nitrobenzene using the modified electrode was identified to have the lowest experimental detection limit of 1μM by square wave voltammetry (SWV).

Advances in preconcentration/removal of environmentally relevant heavy metal ions from water and wastewater by sorbents based on polyurethane foam

Abstract An increased interest in the removal of heavy metal ions from aqueous media is encountered due to their toxicity and negative impacts on ecosystems, human health and economic activities. A variety of processes may be used for the removal of heavy metal ions from water and wastewater, such as chemical precipitation, ion exchange, adsorption, membrane processes, etc. However, the removal efficiencies of heavy metals by adsorption depend on several factors such as initial loads of heavy metals in the influent, purpose of treatment (drinking/industrial water production, wastewater treatment for disposal or recycling), costs of the overall process, and properties and conditions for regeneration of the sorbent materials. In this context, the use of polyurethane foams as heavy metal ion sorbents is of a special interest because they provide versatile applications in heavy metal effluent management. This study reviews relevant published researches that are concerned with new sorbents based on polyurethane foams applied in batch and dynamic systems for separation and/or preconcentration of heavy metal ions in environmental aqueous media. This review is divided into the following sections: synthesis of polyurethane foams; physical and chemical properties of polyurethane foams; preconcentration of pollutant metal ions from environmental aqueous media by different types of polyurethane foam (untreated, loaded, reacted and composite polyurethane foams); the applicability of sorbents based on polyurethane foams for water and wastewater treatment; comparison of sorbents based on polyurethane foam with other sorbents for heavy metal ion removal.

A highly selective rhodamine based color turn on and fluorescence turn off sensor toward late IB metal ions

A fluorescence “turn-off” and color “turn-on” probe for late IB metal ions (Fe3+/Co2+/Ni2+/Cu2+/Zn2+) was developed based on rhodamine B. The probe was synthesized by condensation between rhodamine B and 8-hydroxyjulolidine-9-carboxaldehyde, which provided excellent selectivity function for late IB metal ions detection. It binds Cu2+ in a 1:1 stoichiometry in acetonitrile solution. This probe displays distinct color and fluorescence change upon the addition of late IB metal ions and little interference with other biologically relevant metal ions. Limit of detection for Cu2+, Fe3+, and Co2+ is higher than that of Zn2+ and Ni2+. In addition, the limit of detection toward Cu2+ is about 312 times lower than the World Health Organization (WHO) recommended level in drinking water.

A ratiometric fluorescent chemosensor for Al3+ in aqueous solution based on aggregation-induced emission and its application in live-cell imaging

A ratiometric fluorescent chemosensor 1 was developed for the detection of Al3+ in aqueous solution based on aggregation-induced emmision (AIE). The chemosensor showed the fluorescence of its aggregated state and Al3+-chelated soluble state in the absence and in the presence of Al3+, respectively, and resulted in a fluorescence ratio (I461/I537) response to Al3+ in neutral aqueous solution at a detection limit as low as 0.29μmolL−1. The method was also highly selective to Al3+ over other physiological relevant metal ions investigated in this study. Taking advantage of its AIE characteristics, the chemosensor was successfully applied on test papers for simple and rapid detection of Al3+. Moreover, the application of 1 for the imaging of Al3+ in living cells by ratiometric fluorescence changes was also achieved.

Two new rhodamine‐based fluorescent chemosensors for Fe3+ in aqueous solution

Two new rhodamine-based fluorescent probes were synthesized and characterized by NMR, high resolution mass spectrometer (HR-MS) and IR. The probes displayed a high selectivity for Fe(3+) among environmentally and biologically relevant metal ions in aqueous solution (CH3OH-H2O = 3 : 2, v/v). The significant changes in the fluorescence color could be used for naked-eye detection. Job's plot, IR and (1)H NMR indicated the formation of 1: 1 complexes between sensor 1 and Fe(3+). The reversibility establishes the potential of both probes as chemosensors for Fe(3+) detection. The probe showed highly selectivity in aqueous solution and could be used over the pH range between 5 and 9. A simple paper test-strip system for the rapid monitoring of Fe(3+) was developed, indicating its convenient use in environmental samples.

Structural and kinetic bases for the metal preference of the M18 aminopeptidase from Pseudomonas aeruginosa

The peptidases in clan MH are known as cocatalytic zinc peptidases that have two zinc ions in the active site, but their metal preference has not been rigorously investigated. In this study, the molecular basis for metal preference is provided from the structural and biochemical analyses. Kinetic studies of Pseudomonas aeruginosa aspartyl aminopeptidase (PaAP) which belongs to peptidase family M18 in clan MH revealed that its peptidase activity is dependent on Co2+ rather than Zn2+: the kcat (s−1) values of PaAP were 0.006, 5.10 and 0.43 in no-metal, Co2+, and Zn2+conditions, respectively. Consistently, addition of low concentrations of Co2+ to PaAP previously saturated with Zn2+ greatly enhanced the enzymatic activity, suggesting that Co2+may be the physiologically relevant cocatalytic metal ion of PaAP. The crystal structures of PaAP complexes with Co2+ or Zn2+ commonly showed two metal ions in the active site coordinated with three conserved residues and a bicarbonate ion in a tetragonal geometry. However, Co2+- and Zn2+-bound structures showed no noticeable alterations relevant to differential effects of metal species, except the relative orientation of Glu-265, a general base in the active site. The characterization of mutant PaAP revealed that the first metal binding site is primarily responsible for metal preference. Similar to PaAP, Streptococcus pneumonia glutamyl aminopeptidase (SpGP), belonging to aminopeptidase family M42 in clan MH, also showed requirement for Co2+ for maximum activity. These results proposed that clan MH peptidases might be a cocatalytic cobalt peptidase rather than a zinc-dependent peptidase.

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 599nm, 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.

Facile colorimetric detection of Hg2+ based on anti-aggregation of silver nanoparticles

This paper describes an investigation of a facile colorimetric sensor for Hg2+ in aqueous solution based on the anti-aggregation of silver nanoparticles (AgNPs). In the absence of Hg2+, the addition of 6-Thioguanine to AgNPs solution led to the aggregation of AgNPs, resulting in a color change from yellow to brown with a red shift of absorption spectra. However, the presence of Hg2+ inhibited the 6-Thioguanine-induced aggregation of AgNPs accompanying with a color change from brown to yellow. Under the optimal conditions, the ratio between the absorbance at 530nm and 394nm (A530/A394) was linearly proportional to the Hg2+ concentration in a range from 0 to 333nM with a detection limit of 4nM. Other environmentally relevant metal ions did not interfere with the detection of Hg2+. The proposed method was simple, cost-effective and rapid without any complicated modifying step. It was successfully applied to detect Hg2+ in environmental water samples.