Relevant Metal Ions Research Articles

Ratiometric detection of Cu+ in aqueous buffered solutions and in live cells using fluorescent peptidyl probe to mimic the binding site of the metalloprotein for Cu+

Ratiometric detection of Cu+ in aqueous buffered solutions and live cells is highly recomended. We synthesized a fluorescent probe (1) based on the peptide receptor to mimic the binding site of the metalloprotein (CusF) for Cu+. 1 sensitively and selectively detected Cu+ among various biological relevant metal ions in aqueous solutions at physiological pH through a ratiometric response. Job’s plot analysis indicated that 1 formed a 2:1 complex with Cu+ and the binding affinity of 1 for Cu+ was measured to be 5.73×10−21 M2 from a competition experiment with bathocuproine disulfonate. The probe showed significant ratiometric responses to Cu+ over a wide range of pH (6.5∼10.5). The binding mode study showed that the imidazole and indole groups of the peptide receptor played a critical role in the tight binding to Cu+. 1 penetrated successfully in living A549 cells and detected intracellular Cu+ ions in Golgi apparatus through ratiometric response. Giving the recent growing interests in fluorescent imaging of Cu+, the development of a fluorescent ratiometric probe (1) based on the peptide receptor to mimic the binding site of the metalloprotein for Cu+ will provide a potential tool for detection of intracellular metal ions in live cells.

Rhodamine – Cyclohexane diamine based “turn-on” fluorescence chemosensor for Cr3+: Photophysical & confocal cell imaging studies

A new rhodamine based fluorescent turn on sensor L has been reported as a highly selective and sensitive chemosensor for the Cr3+ ion in a CH3CN-H2O solution. In presence of Cr3+ ion, the strong fluorescence enhancement is attributed due to the interaction of Cr3+ with L, leading to opening of the spirolactam ring of rhodamine B to the amide form. The Cr3+ sensing mechanism is also supported by the Job’s plot, ESI-MS, 1H NMR titration experiments. Importantly, this probe shows high selectivity over other biologically relevant metal ions. Also, anions do not show any effect. In addition, the detection limit is found to be up to 7.5 nM which is acceptable within the EPA (US) limit. The probe is also able to function within a broad biological pH range of 4–8. Furthermore, the probe L shows cellular penetrability for its potential use in confocal cell imaging studies.

Water-Soluble Colorimetric Amino[bis(ethanesulfonate)] Azobenzene pH Indicators: A UV-Vis Absorption, DFT, and 1H-15N NMR Spectroscopy Study.

Water-soluble azobenzene derivatives containing amino[bis(ethanesulfonate)] groups are demonstrated as colorful pH indicators in water and on filter paper. Vibrant color changes were observed from yellow/orange to pink between pH 1 and 4, which are attributed to an intramolecular charge-transfer mechanism. The pKas of the indicators range from 2.1 to 2.6. 1H/1H–15N NMR studies in deuterium oxide reveal that the protonation of the azobenzene pH indicators occurs predominantly at the β-azo nitrogen atom, in agreement with the density functional theory calculations. Excellent selectivity for protons was confirmed in water over common biologically relevant metal ions. Studies in methanol, however, indicate that the pH indicator with a methoxy group ortho to the amino[bis(ethanesulfonate)] group facilitates the selective coordination of Cu2+ with a binding constant pβCu2+ of 4.6 ± 0.1. The indicators complement the existing library of azobenzene indicator dyes and may be useful for measuring the environmental pH at higher proton concentrations.

A Rationally Designed Reversible 'Turn-Off' Sensor for Glutathione.

γ-Glutamyl-cysteinyl-glycine (GSH) plays a critical role in maintaining redox homeostasis in biological systems and a decrease in its cellular levels is associated with diseases. Existing fluorescence-based chemosensors for GSH acts as irreversible reaction-based probes that exhibit a maximum fluorescence (‘turn-on’) once the reaction is complete, regardless of the actual concentration of GSH. A reversible, reaction-based ‘turn-off’ probe (1) is reported here to sense the decreasing levels of GSH, a situation known to occur at the onset of various diseases. The more fluorescent merocyanine (MC) isomer of 1 exists in aqueous solution and this reacts with GSH to induce formation of the ring-closed spiropyran (SP) isomer, with a measurable decrease in absorbance and fluorescence (‘turn-off’). Sensor 1 has good aqueous solubility and shows an excellent selectivity for GSH over other biologically relevant metal ions and aminothiol analytes. The sensor permeates HEK 293 cells and an increase in fluorescence is observed on adding buthionine sulfoximine, an inhibitor of GSH synthesis.

Nanosecond Dynamics at Protein Metal Sites: An Application of Perturbed Angular Correlation (PAC) of γ-Rays Spectroscopy.

Metalloproteins are essential to numerous reactions in nature, and constitute approximately one-third of all known proteins. Molecular dynamics of proteins has been elucidated with great success both by experimental and theoretical methods, revealing atomic level details of function involving the organic constituents on a broad spectrum of time scales. However, the characterization of dynamics at biomolecular metal sites on nanosecond time scales is scarce in the literature. The aqua ions of many biologically relevant metal ions exhibit exchange of water molecules on the nanosecond time scale or faster, often defining their reactivity in aqueous solution, and this is presumably also a relevant time scale for the making and breaking of coordination bonds between metal ions and ligands at protein metal sites. Ligand exchange dynamics is critical for a variety of elementary steps of reactions in metallobiochemistry, for example, association and dissociation of metal bound water, association of substrate and dissociation of product in the catalytic cycle of metalloenzymes, at regulatory metal sites which require binding and dissociation of metal ions, as well as in the transport of metal ions across cell membranes or between proteins involved in metal ion homeostasis. In Perturbed Angular Correlation of γ-rays (PAC) spectroscopy, the correlation in time and space of two γ-rays emitted successively in a nuclear decay is recorded, reflecting the hyperfine interactions of the PAC probe nucleus with the surroundings. This allows for characterization of molecular and electronic structure as well as nanosecond dynamics at the PAC probe binding site. Herein, selected examples describing the application of PAC spectroscopy in probing the dynamics at protein metal sites are presented, including (1) exchange of Cd2+ bound water in de novo designed synthetic proteins, and the effect of remote mutations on metal site dynamics; (2) dynamics at the β-lactamase active site, where the metal ion appears to jump between the two adjacent sites; (3) structural relaxation in small blue copper proteins upon 111Ag+ to 111Cd2+ transformation in radioactive nuclear decay; (4) metal ion transfer between two HAH1 proteins with change in coordination number; and (5) metal ion sensor proteins with two coexisting metal site structures. With this Account, we hope to make our modest contribution to the field and perhaps spur additional interest in dynamics at protein metal sites, which we consider to be severely underexplored. Relatively little is known about detailed atomic motions at metal sites, for example, how ligand exchange processes affect protein function, and how the amino acid composition of the protein may control this facet of metal site characteristics. We also aim to provide the reader with a qualitative impression of the possibilities offered by PAC spectroscopy in bioinorganic chemistry, especially when elucidating dynamics at protein metal sites, and finally present data that may serve as benchmarks on a relevant time scale for development and tests of theoretical molecular dynamics methods applied to biomolecular metal sites.

Di- and Trivalent Metal-Ion Solution Studies with the Phosphinate-Containing Heterocycle DEDA-(PO).

A 7-membered triprotic heterocycle, DEDA-(PO), was synthesized, characterized, and tested for its solution properties with three trivalent lanthanides (La3+, Gd3+, and Lu3+) and three biologically relevant divalent metal ions (Ca2+, Zn2+, and Cu2+). The ligand synthesis has been reported once before; however, the characterization results were previously misinterpreted to correspond to a larger, 14-membered heterocycle, TETA-(PO)2. This manuscript serves to correct the original paper. Potentiometric titrations were carried out with each of the metal ions, and the thermodynamic stability values in terms of log β and log KML were calculated showing a 1:1 metal-to-ligand ratio preference for the divalent metal ions and a 1:2 ratio for the lanthanides. The stability of the 1:2 complexes decreased across the lanthanide series, presumed to be a steric effect. Further resolution to the potentiometry results was given via pH-dependent NMR spectrometry (with La3+) and pH-dependent UV-vis spectroscopy (with Cu2+), and the pM values were calculated for all metal ions. The solid-state structure of the 1:1 Cu2+-DEDA-(PO) complex was further characterized by X-ray crystallography.

A highly selective, sensitive and reusable BODIPY based ‘OFF/ON' fluorescence chemosensor for the detection of Hg2+ Ions

A BODIPY (borondipyrromethane) based fluorescence probe anchored with N,N-bis(2-(pyridin-2-ylmethoxy)ethyl)aniline receptor (BDPS) has been designed, synthesized and successfully characterized. It can selectively sense Hg2+ ion by giving significant emission enhancement at 514nm over other biologically and environmentally relevant metal ions in CH3CN/H2O (1:1) medium. The turn-on behaviour of the sensor is due to the metal chelation enhanced fluorescence (MCHEF) effect which has been confirmed by deriving the Job's plot from titration experiment and the high binding constant of 4.19±2.67×105M‐1 between Hg2+ and BDPS. Furthermore, the sensor can efficiently detect Hg2+ in a competitive environment upto submicromolar range revealing high selectivity towards Hg2+. The sensing probe is reversible on adding excess amount of S2− to the solution of BDPS pre-incubated with Hg2+. Reusability of the probe has been demonstrated successfully by multiple cycles of alternative addition of Hg2+ ions followed by S2− ions. Consequently, INHIBIT molecular logic gate can be constructed with the help of OFF-ON-OFF signal on successive addition of Hg2+ (input 1) and S2− (input 2) to the probe. Finally, the test paper experiment demonstrates the practical utility of BDPS for the easy and visual detection of Hg2+.

Development of a new chemosensor for Al3+ ion: Tuning of properties

We have synthesized and characterized three Schiff-base molecules, namely, 1-(((2-hydroxybenzylidene)hydrazono)methyl)naphthalen-2-ol (H2L), (1-(((2-hydroxy-5-nitrobenzylidene)hydrazono)methyl)naphthalen-2-ol (H2L-NO2) and 1-(((2-hydroxy-5-methylbenzylidene)hydrazono)methyl)naphthalen-2-ol) (H2L-Me). Out of these three compounds, H2L-NO2 has been found to be a selective fluorescent chemosensor for Al3+. Fluorescence intensity of H2L-NO2 at 517nm (λex = 390nm) is increased significantly in the presence of Al3+. Other relevant metal ions cannot induce considerable enhancement in its emission intensity. The enhancement has been explained using PET and CHEF mechanism. Quantum yield and life-time of H2L-NO2 have increased in the presence of one equivalent of Al3+. H2L-NO2 forms 1:1 complex with the metal ion which is confirmed from Job's plot and ESI mass spectral analysis. Its sensitivity has been determined by 3σ method and found to be moderate. Emission intensity of H2L and H2L-Me does not increase appreciably in the presence of Al3+. Presence of electron withdrawing group in H2L-NO2 may be responsible for its aluminum sensing properties.

Click synthesis of a quinoline-functionalized hexahomotrioxacalix[3]arene: A turn-on fluorescence chemosensor for Fe3+

A novel quinoline-functionalized hexahomotrioxacalix[3]arene L was synthesized via Click chemistry and its chemosensing properties with various metal ions were investigated. The chemosensor L exhibited a high selectivity for Fe3+ with little interference from other environmentally and biologically relevant metal ions, leading to a prominent ‘off-on’ type fluorescent signalling behaviour. Our studies demonstrated that the detection limit on fluorescence response of the sensor to Fe3+ is in the 10−7M range. The mechanism of the interaction between the L and Fe3+ has been investigated in detail by 1H NMR spectroscopic titration experiments.

Dual Functions of Selective Ferric Ion Detection and Removal by a Recyclable Fluorescence Active Multifunctional Silica Material and Toxic Dye Removal from Aqueous Solution

Excess iron and its toxic dye Naphthol Green B is a threat to aquatic environment and human health. Therefore, effective detection and remediation of ferric ion and Naphthol Green B in aqueous system is a necessity. In our paper, to bring out synergy in dual functions of ferric ion sensing and extraction/removal by same material, a new ionophore based functionalized silica material (SiO2@Nap) was synthesized by immobilization of bis (tetradentate) naphthalene ligand on silica surface. Physicochemical properties of the adsorbent were studied by scanning and transmission electron microscopy, atomic force microscopy, XRD, FT-IR, thermo-gravimetric analysis and elemental (CHN) analysis. The selective sensing studies by SiO2@Nap material towards ferric ion in presence of 17 other relevant metal ions were evaluated through the fluorescence quenching phenomenon which gives limit of detection value of 74 ppb (1.31 μM). The adsorption studies for ferric ion were assessed in view of effect of solution pH, extraction efficiency (99%), adsorption capacity (79 mg/g) and adsorption isotherms. This material can be recycled upon simple acid-base treatments for further usage after recovery of ferric ions which is supported by reversibility studies. The strong affinity towards ferric ion enabled this material to remove iron containing industrial toxic dye Naphthol Green B with 99.5% efficiency with recyclability. Adsorption, striping and regeneration studies reveals that SiO2@Nap is a recyclable extracting cum sensory probe material for ferric ions.

Colorimetric Determination of Pb2+ in Perfect Aqueous Solution Using Carminic Acid as a Selective Chemosensor.

The commercially available natural organic dye, carminic acid (CA), an anthraquinone derivative bearing hydroxyl and carboxyl groups as recognition sites was found to be a colorimetric probe for Pb2+ in perfect aqueous solution under neutral conditions with specific selectivity and high sensitivity. Upon addition of Pb2+, the absorption maximum of CA showed a large red shift, and the resulted color change from red to purple could be easily identified even by the naked eye. The chemical stoichiometric ratio between CA and Pb2+ was determined to be 1:2 through Job plot, Pb2+ titration, and kinetic experiments. Moreover, other environmental relevant metal ions induced no or minimal spectral and color changes. The reversibility of Pb2+ to CA with EDTA even through several cycles was established for practical applications. The results indicated that CA can be a good candidate for simple, convenient and reversible colorimetric detection of Pb2+ in aqueous solution even though it was hard to be applied to determine Pb2+ on the water testing by US EPA.

Rapid colorimetric detection of mercury using biosynthesized gold nanoparticles

There is an increasing focus on expanding the applicability of biologically synthesized nanomaterials. Herein, we show the use of Cinnamomum tamala (cinnamon) leaf extract for the synthesis of gold nanoparticles with controllable optical properties. This ability to synthesize optically tunable AuNPs was exploited for the detection of mercuric ions (Hg2+) by capitalizing upon the amalgamation tendency of mercury with gold. The changes in both the longitudinal and transverse plasmon absorption bands of gold nanoparticles (AuNPs) suggest the potential of using both of these SPR features either independently using traditional analyses or in combination using discriminant analysis for the detection of mercury in aqueous media. Minimal cross-reactivity with other environmentally relevant metal ions confirms that the change in the optical property is exclusively due to the strong amalgamation of mercury and gold. Natural plant-based esters were found to act as capping agents during biological synthesis of AuNPs, and the involvement of these esters during Hg2+ ions sensing revealed underlying mechanistic processes.

Triptycene scaffolds: Synthesis and properties of triptycene-derived Schiff base compounds for the selective and sensitive detection of CN− and Cu2+

A series of triptycene-derived Schiff bases were synthesized by condensation between amino triptycenes with an appropriate aldehyde and were isolated in good to excellent (85–90%) yields. Amongst these, a triptycene-hydroxybenzaldehyde Schiff base compound proved to be a selective sensor for cyanide. It exhibited a “turn-on” fluorescence response at 490 nm to CN− facilitated by the nucleophilic addition of CN− to the aldehyde group, accompanied by a visible color change from orange to yellow. Likewise, a triptycene salicylaldehyde adduct was shown to be highly sensitive towards the detection of the CN− ion with a detection limit of 0.9 μM. On the other hand a triptycene-BODIPY Schiff base compound could be used for the detection of Cu2+ ions over other competing, biologically relevant metal ions in acetonitrile. Photophysical studies revealed a 1:1 binding model for the triptycene-BODIPY compound.

A fluorescent probe based upon anthrancene-dopamine thioether for imaging Hg2+ ions in living cells

A novel anthrancene-dopamine thioether L compound was designed as fluorescent probe for detecting Hg2+ in living cells sample. L exhibits a good sensitive and selective recognition towards Hg2+ ions in the presence of other important relevant metal ions and amino acids in HEPES solution. The addition of Hg2+ causes a marked enhancement in the fluorescence emission intensity with the detection limit as low as 1.1×10−6M, combining with obvious colormetric change from colorless to pale brown. Mechanistic studies show that catechol group and sulfur atom in L all participate in the coordination with Hg2+, though catechol group contributes mainly to chelation-enhanced fluorescence enhancement and sulfur atom to selectivity. Furthermore, L demonstrates good cell permeability and compatibility for sensitive fluorescent detection of Hg2+ in HepG2 cells. This present probe will have broad applications in biological imaging.

Zn2+‐Ion Sensing by Fluorescent Schiff Base Calix[4]arene Macrocycles

A macrocyclic ligand (H2 L) containing two o,o'-bis(iminomethyl)phenol and two calix[4]arene head units has been synthesized and its coordination chemistry towards divalent Ni and Zn investigated. The new macrocycle forms complexes of composition [ML] (M=Zn, M=Ni) and [ZnL(py)2 ], which were characterized by elemental analysis; IR, UV/Vis, and NMR spectroscopy; electrospray ionization mass spectrometry (ESI-MS); and X-ray crystallography (for [ZnL(py)2 ] and [NiL]). H2 L allows the sensitive optical detection of Zn2+ among a series of biologically relevant metal ions by a dual fluorescence enhancement/quenching effect in solution. The fluorescence intensity of the macrocycle increases by a factor of ten in the presence of Zn2+ with a detection limit in the lower nanomolar region.

Preparation of a disperse Fe–Al–Mo system and production of bulk materials on its base

We show the feasibility to prepare a disperse Fe–Al–Mo polymetal system by contact exchange in chloride-containing aqueous solutions. Reaction schemes are suggested to describe the processes that proceed on aluminum microparticles in aqueous solutions where the relevant metal ions are contained. The system is shown to be a precursor for intermetallic compounds, which are generated by high-temperature processes, e.g., spark plasma sintering (SPS).

A schiff-base dual emission ratiometric fluorescent chemosensor for Hg2+ ions and its application in cellular imaging

A schiff-base dual emission ratiometric fluorescent chemosensor which includes coumarin dye and 5-aminoisophthalic acid methyl ester has been designed and synthesized. The chemosensor CA high selectively detects Hg2+ ions in the presence of other biologically important and environmentally relevant metal ions at physiological pH. The double bond of schiff-base was broken accompanied by fluorescence enhancement when the chemosensor interacts with Hg2+ ions, and the coumarin aldehyde and 5-aminoisophthalic acid methyl ester shows strong ratiometric fluorescent emission respectively. And the chemosensor could be applied in cellular imaging at nano molarity by dual fluorescent emission.

A macrocyclic 19F-MR based probe for Mn2 + sensing

We report a novel fluorinated aza-macrocycle that affords a linear increase in longitudinal and transverse 19F NMR relaxation rates between 100μM to 1mM Mn2+ concentrations. The linear response which is unaffected in the presence of other biologically relevant metal ions and 19F-MR phantom images of macrocycle solutions in presence of Mn2+ indicate the potential applicability of the probe as a 19F-MR based Mn2+ sensor.

Single cytosine-based electrochemical biosensor for low-cost detection of silver ions

The development of Ag+ detection system with high sensitivity, selectivity and quantitatively accurate analysis is crucial because of the potential risk of Ag ion increasingly applied in various fields. As synthetic oligodeoxyribonucleotides are available to use, there have been few studies reported in the literature regarding techniques for electrochemical biosensors based on cytosine-enriched DNA used as the capture material of Ag ion. The high price and complex process for connecting NH2-terminal to DNA make it expensive to fabricate the Ag detecting system. In this study, we investigated the Ag ion detection system with single-cytosine (SC) used in the place of DNA with a functional group. The proposed system can guarantee the effect of span increase, price reduction of detection system, and lower detection limit due to the increase of immobilization efficiency by using SC as a capture probe.Three-electrode system was microfabricated on a glass wafer. SC was immobilized on the working electrode surface, and then this electrode was exposed to a solution with Ag ions and other SC for mismatching cytosine-Ag+-cytosine. Before detecting Ag ion, cyclic voltammetry and energy-dispersive X-ray spectroscopy were used for the identification of stable immobilization of SC on the surface of the functionalized Au electrode. The electrochemical analysis for increasing Ag ion concentration and the Ag+ selectivity of the SC probe were performed by square wave voltammetry. The resulted current increase is linear with the logarithmic concentration of Ag ion from 0.5nM to 1mM with ∼20pM of detection limit. The slope of in a target concentration range mentioned above are 9.14×10−2 per concentration decade with R2 value of 0.9814. The reason why our system has a lower detection limit than the previous studies is because the bound each single Ag ion performs a path role for electron transfer. Moreover, the proposed electrochemical assay has good selectivity to other environmentally relevant metal ions.

Ratiometric fluorescent probe based on symmetric peptidyl receptor with picomolar affinity for Zn2+ in aqueous solution

It is still a significant challenge to synthesize ratiometric fluorescent probes based on the new receptor with potent and tunable binding affinities for Zn2+. A fluorescent probe (1) based on the symmetric peptide receptor bearing two imidazole and two sulfonamide groups was synthesized for the ratiometric detection of Zn2+ in aqueous solution. 1 selectively and sensitively detected Zn2+ among biological relevant metal ions by a ratiometric response. Upon addition of Zn2+, monomer emissions of the pyrenes at 379 and 399nm increased significantly and the excimer emission at 508nm decreased with a blue shift. About 1 equiv of Zn2+ ions completely induced the ratiometric response of 1. Job’s plot analysis indicated that 1 formed a 1:1 complex with Zn2+. The dissociation constant for Zn2+ was found to be 300 pM. The binding mode study revealed that two imidazole and two sulfonamide groups of the peptide receptor played an important role in the binding with Zn2+. The peptidyl probe successfully penetrated and detected intracellular Zn2+ in live cells.