Highly selective recognition of mercury ions through the “naked-eye”

A new sensor 2-((E)-(3-(1H-imidazol-1-yl)propylimino)methyl)-5-(diethylamino)phenol (1) based on the combination of diethylaminosalicylaldehyde and imidazole groups was designed and synthesized as a Hg^2 + selective colorimetric chemosensor. Upon treatment of 1 with mercury ions, sensor 1 showed a color-change from colorless to yellow in a mixture of H₂O/DMF (5:95), while many other ions such as Al^3 +, Zn^2 +, Cd^2 +, Cu^2 +, Fe^2 +, Mg^2 +, Cr^3 +, Ag⁺, Co^2 +, Ni^2 +, Na⁺, K⁺, Ca^2 +, Mn^2 + and Pb^2 + had no influence. Notably, this chemosensor could distinguish clearly Hg^2 + from Cu^2 +, Ag⁺, Fe^2 + and Pb^2 +. The underlying signaling mechanism is a ligand-to-metal charge-transfer (LMCT) process. Compound 1 showed the serial formation of the 1:1 and the 1:2 complexation between 1 and Hg^2 +. This two-step binding mode was proposed based on the UV titration, ¹H NMR titration and ESI-mass studies.     

A fluorescein derivative FLTC as a chemosensor for Hg2 + and Ag+ and its application in living-cell imaging

FLTC was synthesized and used as a fluorescent chemosensor to detect Hg^2 +. It showed high selectivity toward Hg^2 + over many heavy metal ions in an ethanol–H₂O (3:2, v/v, HEPES buffer, 0.5 mM, pH 7.15) solution with a detection limit of 0.21 μM. After complexation with Hg^2 +, FLTC showed extremely high selectivity toward Ag⁺ with a detection limit of 0.009 μM. Therefore, detection of Hg^2 + and Ag⁺ could be realized using FLTC and the FLTC–Hg^2 + complex, respectively. Cytotoxicity assays and fluorescence microscopy analysis showed that FLTC could be used as a fluorescent probe to detect Hg^2 + and Ag⁺ in L-02 human liver cells.     

Highly sensitive colorimetric phosphorescent chemodosimeter for Hg2 + based iridium(III) complex with (Ph2PS)2N auxiliary ligand

A colorimetric phosphorescent iridium(III) complex chemodosimeter (Ir1) for Hg^2 + has been prepared and confirmed by NMR, MS, and crystal data, which displays a high selectivity and antidisturbance for Hg^2 + detection among relevant metal ions. Phosphorescent studies show that the luminescence intensity at 598 nm decreased to ca. 12%, while the luminescence intensity in 441 nm increased to ca. 195%. The ratio of Ir1 responding to Hg^2 + was determined to be 1:1 by UV–vis absorption and phosphorescent emission measurements. Further study demonstrates that the detection limit on phosphorescent response of the sensor to Hg^2 + is down to 10^− 6 M range. The mechanism study shows that the interaction between the S atom of ancillary ligand and Hg^2 + is responsible for the highly selective and sensitive phosphorescent senor for Hg^2 +.     

Fluorescence of Kryptofix 5 metal complexes

Kryptofix 5 forms complexes with a variety of metal cations. The coordination with the crown ether moiety affects only slightly the emission wavelength of the free Kryptofix 5 ligand (λ_max = 425 nm) in a buffer (pH = 9) solution, but the emission intensity of this blue fluorescence can increase strongly upon complex formation, probably owing to the rigidity of the complex. This applies e.g. to Ba^2 +, Zn^2 +, Cd^2 +, Hg^2 +, Ag⁺ and La^3 +. A second group of metal ions such as Al^3 +, Pb^2 +, Sb^3 +, Bi^3 +, Te^4 +, Gd^3 + and Th^4 + causes a large red shift of the fluorescence of free Kryptofix 5 to approximately λ_max = 500 nm. This green fluorescence resembles that of Kryptofix 5 in acidic solution. It is suggested, that the second group of metal ions is also coordinated to the pyridine nitrogen atoms of the quinoline substituents.     

Optimized K+ pre-intercalation in layered manganese dioxide nanoflake arrays with high intercalation pseudocapacitance

Intercalation pseudocapacitance is emerging as a highly promising mechanism for high rate energy storage applications. However, it is still debatable how the alkali metal ion pre-intercalation in layered metal oxides affects the intercalation pseudocapacitance. Herein，the layered birnessite-MnO₂ nanoflakes with K⁺ pre-intercalation were in- situ fabricated on the graphene foam via a one-step facile hydrothermal method. The amount of pre-intercalated K⁺ can be controlled by adjusting the reaction parameter. The electrochemical tests indicate that the amount of pre-intercalated ions has the optimal value and intercalated slight or excessive amount of ions may lead to the pseudocapacitance decline. The K_0.19MnO₂/graphene foam electrode shows a high pseudocapaitance of 344 F g⁻¹ (based on the mass of the whole electrode) at a scan rate of 2 mV s⁻¹, which is the best among the as-prepared samples. Cycling tests demonstrate that the pre-intercalated K⁺ can greatly improve the cycling stability of layered birnessite-MnO₂ nanoflakes. This work provides new insights on understanding the role of pre-intercalation ions and brings new strategies to further improve the performance of layered metal oxide electrodes.     

Rhodamine-based fluorescent sensor for mercury in buffer solution and living cells

A novel fluorescent sensor based on thiooxorhodamine B has been prepared to detect Hg²⁺ in aqueous buffer solution. It demonstrates high selectivity for sensing Hg²⁺ with about 383-fold enhancement in fluorescence emission intensity and micromolar sensitivity (K_d = 7.5 × 10⁻⁶ mol L⁻¹) in comparison with alkali and alkaline earth metal ions (K⁺, Na⁺, Mg²⁺, Ca²⁺) and other transition metal ions (Mn²⁺, Ni²⁺, Co²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ag⁺, Pb²⁺, Cr³⁺, Fe³⁺). Meanwhile the distinct color changes and rapid switch-on fluorescence also provide ‘naked eyes’ detection for Hg²⁺ over a broad pH range. Moreover, such sensor is cell-permeable and can visualize the changes of intracellular mercury ions in living cells using fluorescence microscopy.     

The first substituted macrocyclic ligand Py2N4S2 containing four naphthylmethylene pendant-armed groups: Synthesis and photophysical properties

The synthesis of a pendant donor emissive macrocyclic ligand Py₂N₄S₂ with up to four naphthylmethylene arms (L) has been achieved. Their derivative solid metal complexes (Co^2 +, Ni^2 +, Cu^2 +, Zn^2 +, Cd^2 +, Hg^2 + and Ag⁺) have been isolated and characterized. The photophysical properties of the free ligand L and their complexation behaviour have been investigated in solution. In dichloromethane, the free ligand presents two emission bands which are related to the monomer naphthalene emission and a red-shifted band attributable to ground state dimers (interaction between two naphthalene chromophores), which was further validated from time-resolved data, with bi-exponential decay with absence of dynamic components. UV–Vis spectroscopy has revealed a 2:1 binding stoichiometry for Co^2 +, Cu^2 +, Zn^2 +, Hg^2 + and Ag⁺.     

Electrochromic performance and ion sensitivity of a terthienyl based fluorescent polymer

A novel terthienyl based fluorescent polymer bearing strong electron-withdrawing substituents directly attached to the 3,4-positions of the central thiophene ring was synthesized by electrochemical polymerization of diethyl 2,5-di(3,4-ethylenedioxythiophen-2-yl)thiophene-3,4-dicarboxylate. The corresponding polymer was characterized by cyclic voltammetry, FT-IR and UV–vis spectroscopy. The polymer has a well-defined redox process (E_p,1/2 = 0.74 V) and demonstrates a reversible electrochromic behavior; lilac in the neutral state and transparent sky blue in the oxidized state. Also, the polymer had low band gap (E_g = 1.82 eV) and high redox stability (retaining 94.0% of its electro-activity after 500th switch). Moreover, the sensitivity of both the monomer and its polymer towards metal cations was investigated by monitoring the change in the fluorescence intensity. Among various common ions both the monomer and its polymer were found to be selective towards Cu²⁺ and Cu⁺ ions by quenching the fluorescence efficiency with a Stern–Volmer constant (K_sv) of (1.4–1.6 × 10³ M^?1) and (1.5–1.8 × 10² M^?1) for monomer and polymer solutions, respectively.     

A new copper(II) selective fluorescence probe based on naphthalimide: Synthesis,mechanism and application in living cells

A new fluorescence probe L based on naphthalimide has been synthesized for selective and quantitative detection of Cu^2 + in CH₃CN:H₂O (4:1, v/v) solution. L exhibited a strong green fluorescence. Upon addition of 2 equiv. of Cu^2 +, the fluorescence emission shows a steady and smooth decrease until a plateau is reached with a 30-fold quenching of fluorescence intensity. In the presence of Cu^2 +, the absorbance peak of L maximum at 466 nm decreased, and a new absorption band at 600 nm appeared. Under the identical conditions, other physiological and environmental important metal ions induced negligible spectroscopic changes. The 1:2 stoichiometry binding mode of L with Cu^2 + was supported by the Benesi–Hildebrand analysis and ESI-MS spectra studies. The detection limit for Cu^2 + was estimated to be 64 ppb. Fluorescence microscopy experiments showed that L has practical application in living cells.     

Selective detection of mercury ions using benzothiazole based colorimetric chemosensor

Three new receptors L1, L2 and L3 were designed and synthesized in a single pot synthesis. The synthesized receptors were characterized by ¹H NMR, FT-IR and Mass spectrometry. The cation binding affinity was studied using colorimetric and UV–Vis spectral methods for the three receptors. Receptor L1 showed high selectivity with a significant color change from yellow to colorless (turn-off response) in the presence of Hg^2 + ions over the other cations such as, Ni^2 +, Cr^3 +, Pb^2 +, Cu^2 +, Cd^2 +, Co^2 +, Zn^2 + and Fe^2 + and the receptor L2, L3 did not show any color change or change in the absorption in UV–Vis spectral studies with Hg^2 + ions and other tested metal ions, this may be due to lack of –OH group in receptor L2 and L3. The B-H Plot shown 1:1 complex between L1and Hg^2 + ions.     

A rhodamine-B-based turn-on fluorescent sensor for biological iron(III)

Rhodenal, a turn-on fluorescent sensor for iron, derived from rhodamine-B, was synthesized and characterized. Its electronic absorption spectrum in ethanol has bands at 410 (ε = 500 cm^− 1 mol^− 1 L), 316 (ε = 14 × 10³ cm^− 1 mol^− 1 L), and 272 nm (ε = 32 × 10³ cm^− 1 mol^− 1 L), and it is pH sensitive with two pK_a values (1.2 and 2.8). It reacts promptly with Fe^3 +, with a pesudo-first order rate constant of 1 × 10³ s^− 1, with an equilibrium constant of 1.3 × 10⁶ mol^− 1 L, forming a violet complex (λ_max = 540 nm) with a fluorescent emission at 582 nm, with a higher sensitivity and selectivity compared to those of Fe^2 +, Ba^2 +, Al^3 +, K⁺, Ca^2 +, Ni^2 +, Co^2 +, Cd^2 +, Cr^3 +, Hg^2 +, Mg^2 +, Mn^2 +, Na⁺, or Cu^2 +. Biological assays with B16-F10 showed high permeability of plasma membrane to rhodenal and, according to confocal microscopy results, the fluorescent source originated from within the cell revealed iron pools within cytoplasmic and nuclear sub-compartments, making rhodenal a very good prospective Fe^3 + sensor, in aqueous solution and especially for biological iron pool detection.     

An unusual emissive and colorimetric copper (II) detection by a selective probe based on a pseudo-crown cysteine dye: Solution and gas phase studies

An off-on-off emissive and colorimetric probe L, based on a Pseudo-Crown cysteine dye was designed for Copper (II). Compound L was studied in solution and in gas-phase (MALDI-MS) over alkaline, alkaline, earth-alkaline and transition metal ions (Li⁺, Na⁺, K⁺, Ca^2 +, Mg^2 +, Zn^2 +, Cu^2 +, Co^2 +, Ni^2 +, Pb^2 +, and Hg^2 +) in organic media. The recognition of Cu^2 + by L lead to red/dark red colored complexes, one emissive L₂Cu and another LCu, less emissive. In regards to fluorescent quantum yield in both cases an increase respective to L was visualized (2 fold for LCu and 7 fold for L₂Cu). The paramagnetic nature of both complexes was proved by the synthesis of both complex species, as well as, through ¹H NMR and FTIR. Compound L demonstrate to be able to detect and quantify the minimal amounts of 1.3 μM/3.3 μM of Cu^2 +.     

Separation and determination of cadmium in water by foam column prior to inductively coupled plasma optical emission spectrometry

The sorption profile of cadmium (II) ions from aqueous iodide media onto procaine hydrochloride (PQ⁺·Cl⁻) treated polyurethane foams (PUFs) solid sorbent was studied. PQ⁺·Cl⁻ treated PUFs solid sorbent was found suitable and fast for Cd²⁺ uptake as [CdI4]_aq²⁻. Thus, removal of Cd²⁺ at trace levels by the sorbent packed columns was achieved. The sorbed Cd²⁺ species onto packed column were recovered with HNO₃ (10.0 mL, 1.0 mol L⁻¹) prior determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). Plot of Cd²⁺ ions concentration was linear in the range 0.05–15 μg L⁻¹. The limits of detection and quantification of Cd²⁺ were found 0.01 μg L⁻¹ and 0.033 μg L⁻¹, respectively. Such limits could be improved to lower values by retention of Cd²⁺ species from large sample volumes of the aqueous phase at the optimized conditions. The relative standard deviation of the packed column for the extraction and recovery of standard aqueous solutions (0.1 L) containing 1.0 and 5.0 μg L⁻¹ (n = 3) of Cd²⁺ ions at flow rate of 5.0 mL min⁻¹ were 1.98 and 2.9%, respectively. The method was validated by analysis of Cd in certified reference materials (CRMs) IAEA-Soil-7 and TMDW water and wastewater samples.     

Improved electrochemical performances of reduced graphene oxide based supercapacitor using redox additive electrolyte

Reduced graphene oxide (rGO) is prepared by simple and eco-friendly hydrothermal reduction method. X-ray photoelectron spectroscopy and Ultraviolet–visible analysis corroborated the reduction of graphene oxide into rGO in basic medium. The flexibility of the prepared rGO is inferred from transmission electron micrographs. Further, the identification of suitable electrolyte is carried out using different anions (SO₄²⁻, Cl⁻, OH⁻) and cations (K⁺, Na⁺) for the superior performance of the rGO based supercapacitors. The electrochemical performance revealed that K⁺ and OH⁻ ions are more active species in aqueous solutions. Subsequently, an effort was taken to improve the specific capacitance in the optimized 1 M KOH electrolyte by KI as redox additive at different concentrations (0.025, 0.05, 0.075 and 0.1 M). The calculated specific capacitance and energy density of rGO electrode in the optimized 1 M KOH + 0.05 M KI electrolyte is 500 F g⁻¹ and 44 Wh kg⁻¹, respectively. On the other hand, it exhibited the specific capacitance of 298 F g⁻¹ at 0.83 A g⁻¹ in non-aqueous polymer gel (PVA + KOH + KI) electrolyte. Finally, the charged aqueous device is utilized to glow the light emitting diode.     

A highly selective and sensitive Schiff-base based turn-on optical sensor for Cu2 + in aqueous medium and acetonitrile

A simple “turn-on” fluorescence chemosensor L (E)-2-((4-(diphenylamino)benzylide-ne)amino)phenol has been synthesized, which displays a rapid, highly sensitive and selective detection for Cu^2 + ions amongst other metal ions. The association constant for L-Cu^2 + complex determine from Benesi–Hildbrand plot was found as 1.96 × 10⁷ M^− 1 and 5.43 × 10⁷ M^− 1 with the detection limit of 1.8 × 10^− 7 M and 8.5 × 10^− 7 M in CH₃CN and CH₃CN/H₂O (v/v = 4/6, pH = 7.4) HEPES buffer, respectively. Potential application of L for Cu^2 + detection in real water samples was also investigated.     

A highly sensitive and selective fluorescent probe for Hg2 + and its imaging application in living cells

Two rhodamine-based Hg^2 + probes L1 and L2 were prepared and confirmed by NMR, MS and crystal data. The sensing behavior of these probes was studied by UV–visible and fluorescence spectroscopy. The probe L1 couldn't be widely applied in aqueous media or mixed media because of its poor solubility. However, the probe L2 displayed selective and sensitive fluorescence enhancement response to Hg^2 + at physiological pH value for biological use. The selectivity of this system for Hg^2 + over other metal ions was remarkably high, and its sensitivity was at ppb level. The probe L2 responded rapidly to Hg^2 + in aqueous solutions with a 1:1 stoichiometry and was successfully applied to image Hg^2 + in living cells.     

Surface acidity study of Mn+-montmorillonite clay catalysts by FT-IR spectroscopy: Correlation with esterification activity

A simple method for evaluating the surface acidity of different cation-exchanged montmorillonite (mont) clay catalysts, Mⁿ⁺-mont (Mⁿ⁺=Al³⁺, Fe³⁺, Cr³⁺, Zn²⁺, Ni²⁺, Cu²⁺, and H⁺), involving treatment with pyridine is described. After treating with pyridine, the samples were heated at 120 °C and the FT-IR spectra were directly recorded in the region 1650 and 1350 cm⁻¹. The data obtained show the presence of both Lewis and Brønsted acid sites. The activities of the catalysts to bring about Brønsted acid catalysed esterification of succinic acid with iso-butanol to yield di-(iso-butyl) succinate have been studied. The Brønsted acidity data obtained for Mⁿ⁺-mont correlated well with activity in the esterification reaction. The activities of the catalysts were found to decrease in the order of exchange ions Al³⁺ > Fe³⁺ > Cr³⁺ > Zn²⁺ > Ni²⁺ > Cu²⁺ > Na⁺-mont. They also correlated well with the charge to radius ratio of the cations. The catalysts exchanged with trivalent cations showed stronger absorption bands attributed to Brønsted acidity (1540 cm⁻¹) whereas those exchanged with divalent cations showed an increased Lewis acidity (1450 cm⁻¹) and reduced Brønsted acidity along with charge to radius ratio. Zn²⁺-, Cu²⁺- and Ni²⁺-exchanged clays showed an additional peak around 1605 cm⁻¹ which is attributed to the pyridine adsorption on surface sites through its π electrons. The method suggested here to evaluate the acidity is suitable for active sites which are thermally unstable such as water molecules in the hydration shell of a cation in exchanged clay.     

Synthesis and chemosensory properties of terpyridine-containing diblock polycarbazole through RAFT polymerization

This paper describes the synthesis of a terpyridine-containing diblock copolymer, poly(N-vinylcarbazole)-block-poly[4′-((4-vinylphenyl) phenyl)-2,2′:6′,2″- terpyridine] (poly(VK₁₅-b-TPY₄)), using the macro-chain transfer agent VK macro-CTA, and employing two-step reverse addition-fragmentation transfer (RAFT) polymerization. We examined the effect of terpyridine units on sensory characteristics of fluorescent chemosensors. VK macro-CTA and diblock copolymer poly(VK₁₅-b-TPY₄) both exhibited moderate thermal stability, with thermal decomposition temperatures of 5% weight losses at approximately 307 °C and 378 °C, respectively, suggesting that the enhancement of thermal stability was attributed to the incorporation of terpyridine segments into the block copolymer. Poly(VK₁₅-b-TPY₄) exhibited higher sensitivities to Ni^2 + and Mn^2 + ions, with Stern–Volmer constants (K_sv) of 2.58 × 10⁵ M^− 1 and 2.57 × 10⁵ M^− 1, respectively. Adding a Zn^2 + ion not only caused partial fluorescence enhancement (3.2-fold quantum efficiency) but also induced a bathochromic shift of emission peak by approximately 56 nm (from 429 nm to 485 nm), indicating that the Zn^2 +-terpyridine complex reduced the twist and vibration of the C–C polymer backbone and enhanced the charge transfer from donors to acceptors because of the more planar and rigid structure. Our results suggest that poly(VK₁₅-b-TPY₄) is a promising material for chemosensory applications.     

Dependence of dielectric properties on structural characteristics of (Zn1/3A2/3)0.5 (Ti1−xBx)0.5O2 (A = Nb5+, Ta5+, B = Ge4+, Sn4+) ceramics at microwave frequencies

The effects of structural characteristics on the dielectric properties of (Zn_1/3A_2/3)_0.5(Ti_1?xB_x)_0.5O₂ (A = Nb⁵⁺, Ta⁵⁺, B = Ge⁴⁺, Sn⁴⁺) (0.1 ≤ x ≤ 0.3) ceramics were investigated at microwave frequency. The sintered specimens showed solid solutions with a tetragonal rutile structure within the solid solution range of compositions. With an increase of BO₂, the temperature coefficient of resonant frequency (TCF) and dielectric constant (K) decreased with a decrease of oxygen octahedral distortion and dielectric polarizabilites, respectively. However, the quality factor (Qf) of the sintered specimens was increased with BO₂ due to the reduction of Ti⁴⁺ ions. The Qf value of the specimens with A = Ta was higher than that of the specimens with A = Nb.     

A new stable Cd(II)-framework for sensitive and selective detection of Cu2 + ions

A new water-stable 3D metal–organic framework (MOF), [Cd₂L₂]·NMP·MeOH (1, H₂L = 2-(3,5-dimethyl-1H-pyrazol-4-yl)-1,3-dioxoisoindoline-5,6-dicarboxylic acid, NMP = 1-methyl-2-pyrrolidinone) has been solvothermally synthesized and structurally characterized. 1 exhibits a 3D open-framework with a 2D metallic plane pillared by L^2 − fragments. Meanwhile, luminescent studies indicate that the luminescence intensity of 1 was strongly dependent on different metal ions. Most interestingly, 1 exhibited significantly quenching effect toward Cu^2 +, which implies that it may be used as a luminescent probe for the detection of Cu^2 +.