An integrated reaction-retention and spectrophotometric detection flow system for the determination of nickel

An integrated flow-through photometric sensor for the determination of nickel in real samples of various origins has been developed. The sensor is based on the reaction of Ni(II) with 1-(2-pyridylazo)-2-naphthol (PAN) immobilized on a cationic resin which was placed in a flow-cell using a spectrophotometer tuned at 566 nm as detector. The Ni(II) ion from the sample injected into the carrrier stream (pH = 5.0) of a monochannel continuous flow system reacts with the immobilized chromogenic reagent to form a red chelate which remains on the active solid support and generates the analytical signal. When this reached its maximum value the Ni(II)-PAN chelate was destroyed using 1 M H₂SO₄ as eluents, leaving the sorbed PAN untouched. The response of the sensor was linear in the three concentration ranges assayed: 0.3–4.0, 0.1–1.6 and 0.05–0.8 μg mL^–1 for sample volumes of 100, 400 and 800 μL, respectively, and the R.S.D.(%) (n = 10) were 1.80(100 μL), 3.04(400 μL) and 2.29(800 μL). The sensor showed an excellent selectivity which could also be increased with a simple on-line modification to avoid interference from copper. It was applied to a variety of real samples with very good results in all cases. Received: 15 April 1998 / Revised: 29 June 1998 / Accepted: 3 July 1998     

Investigation of Methanol Behavior at the Designed Electrochemical Sensor based on Ni(II) Complex and Graphene Nanosheets

In this work, the electrochemical oxidation of methanol was investigated by different electrochemical methods at a carbon paste electrode (CPE) modified with (N‐5‐methoxysalicylaldehyde, N´‐2‐hydroxyacetophenon‐1, 2 phenylenediimino nickel(II) complex (Ni(II)–MHP) and reduced graphene oxide (RGO), which is named Ni(II)‐MHP/RGO/CPE, in an alkaline solution. This modified electrode was found to be efficient for the oxidation of methanol. It was found that methanol was oxidized by the NiOOH groups generated by further electrochemical oxidation of nickel(II) hydroxide on the surface of the modified electrode. Under optimum conditions, some parameters of the analyte (MeOH), such as the electron transfer coefficient (α), the electron transfer rate constant) k_s), and the diffusion coefficient of species in a 0.1 M solution (pH = 13), were determined. The designed sensor showed a linear dynamic range of 2.0–100.0 and 100.0–1000.0 μM and a detection limit of 0.68 μM for MeOH determination. The Ni(II)‐MHP/RGO/CPE sensor was used in the determination of MeOH in a real sample.     

Quantum-chemical modeling of the molecular structures of (555)macrotricyclic chelates in M(II) ion–thiooxamide–glyoxal ternary systems (M = Mn,Fe, Co,Ni, Cu,Zn)

The thermodynamic and geometric parameters of isomeric macrotricyclic Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes that can form upon the complexation of the corresponding hexacyanoferrates( II) with thiooxamide H₂N–C(=S)–C(=O)–NH₂ and glyoxal HC(=O)–CH(=O) in gelatin-immobilized matrices have been calculated by the OPBE/TZVP DFT method with the use of the Gaussian09 program package. It has been found that a complex with the MN₄ chelate core is most stable for M = Mn, Fe, Co, Ni, and Zn, and the MN₂S₂ core is most stable for M = Cu. Bond lengths and bond angles have been reported, and it has been noted that in all complexes, except the Zn(II) one, the chelate core and three fivemembered chelate rings are almost planar.     

An Unprecedented Trinuclear Nickel(II) Complex Assembled from an Asymmetric Salamo-Type Ligand

An unprecedented trinuclear Ni(II) complex assembled from an asymmetric Salamo-type ligand 6-ethoxy- 4′,6′-dichloro-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol (H₂L) is synthesized. The Ni(II) complex with the general formula [Ni₃(L)₂(μ₃-OAc)₂]·3CH₃CN is characterized by IR, UV-vis, and fluorescence spectra and the single crystal X-ray analysis. All the Ni(II) atoms are hexacoordinated with slightly distorted octahedral symmetries. Interestingly, each Ni(II) atom is not located on the N₂O₂ cavity of the asymmetric Salamo-type (L)^2– unit, and two μ₃-OAc ions adopt an uncommon μ₃-η²:η¹ binding mode connecting the Ni1, Ni2, and Ni3 atoms. Furthermore, the crystallizing acetonitrile molecules successfully assemble into an infinite 2D network by hydrogen bonding and C–H···π interactions.     

Development of a disposable miniature l-lysine sensor

A hybrid l-lysine sensor consisting of an immobilized l-lysine decarboxylase and a miniature bacterial CO₂ sensor was fabricated using semiconductor techniques. The bacteria was immobilized in a calcium alginate gel in a miniature oxygen electrode cell together with the electrolyte. The enzyme was immobilized in a bovine serum albumin matrix on a gas-permeable membrane. The cell was formed on a silicon substrate by anisotropic etching and had a two-gold-electrode configuration. The response time of the l-lysine sensor was 1–3 min. The optimum pH was 6.0 and the optimum temperature was 33°C. The response to l-lysine concentration was linear from 25 to 400 μM. Reproducible responses were obtained by adding more than 1 μM pyridoxal-5′-phosphate. The sensor had excellent selectivity for l-lysine and a stable response for more than 25 repetitive operations.     

A modern technique for preparation of zinc(II) and nickel(II) nanometric oxides using Schiff base compounds: synthesis,characterization, and antibacterial properties

The purpose of the work reported in this paper was the preparation and characterization of Zn(II) and Ni(II) nanometric oxides by using a simple Schiff compound as precursor for complexation then thermal degradation at 600 °C. Metal complexes [Ni(L)₂(Cl)₂] and [Zn(L)₂](NO₃)₂, where L is the Schiff base formed by condensation of 2-thiophenecarboxaldehyde with phenylhydrazine, were prepared and characterized by elemental analysis and by magnetic and spectroscopic measurements (infrared, Raman, X-ray powder diffraction, and scanning electron microscopy). Elemental analysis of the chelates suggests the stoichiometry is 1:2 (metal–ligand). Infrared spectra of the complexes are indicative of coordination of the nitrogen of the phenylhydrazine (–Ph–NH–) group and the sulfur atom of the thiophene ring with the central metal atom. Magnetic susceptibility data and electronic and ESR spectra suggest a distorted octahedral structure for the Ni(II) complex and tetrahedral geometry for the Zn(II) complex. The Schiff base and its metal chelates were screened for in-vitro activity against four bacteria, two Gram-positive (Bacillus subtilis and Staphylococcus aureus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa), and two strains of fungus (Aspergillus flavus and Candida albicans). The metal chelates were shown to have greater antibacterial activity than the free Schiff-base chelate.     

Acicular Nickel on Carbon Nanofiber as Electrochemical Sensor Electrode for the Rapid Detection of Aqueous and Gaseous Formaldehyde at Room Temperature

The rapid and straightforward detection of formaldehyde (FA) in the environment is crucial for preventing the accidental inhalation of FA and limiting skin exposure to FA. In this study, we developed a simple nickel-based electrocatalytic electrode on carbon nanofibers (CNFs−Ni), which is suitable for rapidly detecting FA at room temperature. Centrifugal electrospinning was used to obtain polyacrylonitrile (PAN) nanofibers, which was subsequently stabilized and carbonized to fabricate the CNFs. Carbonization of the CNFs occurred at various temperatures (T_c=1200, 1300, 1400, and 1500 °C). PAN CNFs served as a highly conductive template for electroless plating under a magnetic field of 500 G to grow acicular nickel. The amperometric responses of the CNFs−Ni to aqueous FA were then measured. A lab-built amperometric gas sensor (CNFs−Ni 1–8), which comprised CNFs with a reduced Ni loading, was used as the electrode for detecting gaseous FA. Scanning electron microscopy (SEM), linear sweep voltammetry (LSV), cyclic voltammetry (CV), and chronoamperometry were used to evaluate the sensitivities of the electrodes. Within the linear range of 0.05–91.5 mM, the CNFs1400-Ni electrode was highly sensitive for detecting aqueous FA (2592 μA mM⁻¹ cm⁻²), as evidenced by the fast response time (6 s). At a low concentration of gaseous FA (0.5 ppm), the laboratory-built FA gas sensor was stable (98.3 %) and had a fast response time (5 s) after 9 h of continuous operation.     

Determination of cyanides in electroplating solutions as Ni(CN)42– and analysis by capillary electrophoresis

A CE method was developed for the determination of total (free and weakly bound) cyanide in electroplating solutions based on the use of a cationic surfactant (TTAB) and complexation with Ni(II)-NH₃ solutions to Ni(CN)₄ ^2–. Both direct complexation and cyanide distillation combined with complexation were tested. Under optimized conditions, this method is time-saving compared to standard methods. Total cyanide determined by CE had detection limits (with respect to the initial sample concentration) of 0.5 μg/mL for direct complexation and 50 ng/mL for distillation combined with complexation. Total cyanide and cyanide not amenable by chlorination (CNAC) were determined in real samples from spent electroplating baths.     

Polymethacrylate Colorimetric Sensor for Evaluation of Total Antioxidant Capacity

A new colorimetric sensor using an immobilized chromogenic redox reagent was devised for measuring the total antioxidant level in a liquid sample without requiring sample pretreatment. The reagent, Fe(III) – 1,10-phenanthroline (Fe(III)-phen), was immobilized into a polymethacrylate matrix (PMM), and the absorbance changes associated with the formation of the highly colored Fe(II)-phen chelate as a result of reaction with antioxidants was measured at 510 nm. The developed optical sensor was used to screen total antioxidant capacity of some black and green teas, red and white wines.     

Heterogeneous kinetic studies of the hydrogen peroxide decomposition with some transition metal‐heterocyclic complexes

The heterocyclic compounds piperidine (Pip), piperazine (Pz), morpholine (Morph), and N‐methyl piperazine (N‐MPz) were used as ligands to form transition metal complexes with Ni(II), Cu(II), and Co(II) ions. These complexes were supported on Dowex‐50W resin so as to form new potential active catalysts for H₂O₂ decomposition in an aqueous medium. In all cases the reaction showed a first‐order kinetics with respect to H₂O₂ concentration, except with Co(II) complexes, the reaction showed a second‐order kinetics with 2% divinyl benzene (DVB) (50–100 mesh and 200–400 mesh). The rate constant k (per gram dry resin) was evaluated with a resin of cross‐linkage 2 and 8% DVB (50–100 mesh) and 2% DVB (200–400 mesh) over temperature range 25–40°C. With a given resin cross‐linkage, the rate constant has the following order: Ni(II) complexes < Co(II) complexes < Cu(II) complexes. With Pz ligand, k increased in the following sequence: Ni(II) complexes < Cu(II) complexes < Co(II) complexes. The reaction mechanisms of the first‐ and second‐order kinetics were discussed and the activation parameters were deduced. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 617–624, 2001     

Efficient chemiluminescence by aptamer – reactant platform combination with activated Ag–Au alloy nanoparticles for cobalt detection

This article deals with the detection of Co(II) in real water sample using aptamer – reactant platform combination with activated Ag–Au alloy nanoparticles (NPs) by chemiluminescence (CL) method. CL is attributed to a catalytically enhanced decomposition of H₂O₂ by aptamer conjugated Ag–Au alloy NPs to produce reactive oxygen species. The Ag–Au alloy NPs were prepared by chemical method using double reducing agent (i.e. trisodium citrate and polyethylenimine) and used for detection of Co(II) from water by CL method. CL experiments were carried out with the variation of different parameters such as pH, concentration of luminol, concentration of H₂O₂ and Ag–Au alloy NPs. We found that Ag–Au alloy NPs have very good efficiency towards Co(II) detection. Analytical parameters and kinetics were studied in detail to know the nature and mechanism of CL in presence of aptamer conjugated Ag–Au alloy NPs. The linear range of the CL sensor of Co(II) is covered concentration from 0.01 to 10 µg/L with detection limit of 0.001 µg/L. The relative standard deviation for determination of Co(II) was 6.65 in 10 replicated measurements. CL method is first time applied to detect the Co(II) in real water samples at very low level using aptamer conjugated Ag–Au NPs as a catalyst.     

Syntheses,characterization, in vitro antiglycation and DPPH radical scavenging activities of isatin salicylhydrazidehydrazone and its Mn (II), Co (II), Ni (II), Cu (II), and Zn (II) metal complexes

2-Hydroxy salicylhydrazide isatin hydrazone (L) and its Mn (II), Co (II), Ni (II), Cu (II), and Zn (II), metal complexes were synthesized. ¹H NMR, UV–Vis, IR spectroscopy and elemental (CHN/S) analysis techniques were applied for characterization. TG/DTA techniques revealed that all the synthetic compounds are thermally stable up to 300 °C. They were found non-electrolytes in nature. Furthermore, all these complexes were evaluated for antiglycation and DPPH radical scavenging activities. They showed varying degree of activity with IC₅₀ values between 168.23 and 269.0 μM in antiglycation and 29.63–57.71 μM in DPPH radical scavenging activity. Mn (II), Co (II), Ni (II), Cu (II), and Zn (II), metal complexes showed good antiglycation as well as DPPH radical scavenging activity. The IC₅₀ values for antiglycation activity are 168.23 ± 2.37, 234.27 ± 4.33, 257.1 ± 6.43, 267.7 ± 8.43, 269.0 ± 8.56 Ni for Co, Zn, Mn, Cu, and Ni complexes, respectively, while IC₅₀ value were found to be 29.63 ± 2.76, 31.13 ± 1.41, 35.16 ± 2.45, 43.53 ± 3.12, 57.71 ± 2.61 μM for Cu, Zn, Mn, Co and Ni complexes, respectively, for DPPH radical scavenging activity. These synthesized metal complexes were found to be better active than standards Rutin (IC₅₀ = 294.46 μM) for anti-glycation, and tert-butyl-4-hydroxyanisole (IC₅₀ = 44.7 μM) for DPPH radical scavenging activity.     

Development of Electrochemical Impedance Spectroscopy Based Malaria Aptasensor Using HRP‐II as Target Biomarker

Current demand for a stable, low cost and sensitive malaria sensor has prompted to explore novel recognition systems that can substitute widely used protein based labile biorecognition elements to be used in point of care diagnostic devices. Here, we report a novel ssDNA aptamer of 90 mer sequence developed by SELEX process against HRP‐II, a specific biomarker for Plasmodium falciparum strains. High stability of the secondary structure of the isolated aptamer was discerned from its free energy of folding of −20.40 kcal mole⁻¹. The binding constant (K_d) of the aptamer with HRP‐II analysed by isothermal titration calorimetry was ∼1.32 μM. Circular dichroism studies indicated B form of the aptamer DNA. The aptamer was chemically immobilized on a gold electrode surface through a self‐assembled monolayer of dithio‐bis(succinimidyl) propionate to produce the aptasensor. The step wise modification of the layers over the gold electrode during fabrication of the aptasensor was confirmed by cyclic voltammetry. The aptasensor was then challenged with different concentration of HRP‐II and analysed the interaction signals through electrochemical impedance spectroscopy. The impedance signal behaved reciprocally with the increasing concentrations of the target in the sample from which a dynamic range of 1 pM–500 pM (R²=0.99) and LOD of ∼3.15 pM were discerned. The applicability of the developed aptasensor to detect HRP‐II in mimicked real sample was also validated.     

Solution Equilibria of Ternary Systems Involving Nickel(II) Ion,Picolinic Acid,and the Amino Acids Histidine,Cysteine, Aspartic and Glutamic Acids

Solution equilibria of the ternary systems Ni(II)–picolinic acid (Hpic) and the amino acids aspartic acid (H₂asp), glutamic acid (H₂glu), cysteine (H₂cys) and histidine (Hhis), where the amino acids are denoted as H _i L, have been studied pH-metrically. The formation constants of the resulting mixed ligand complexes have been determined at 25 °C using a ionic strength 1.0 mol·dm^?3 NaCl. In the Ni(II)–Hpic–H₂asp and Ni(II)–Hpic–H₂glu systems, the complexes [Ni(pic)H₂L]⁺, Ni(pic)HL, [Ni(pic)L]^? and [Ni(pic)L(OH)]^2? were detected. In the Ni(II)–Hpic–H₂cys system the complexes [Ni(pic)H₂L]⁺ and [Ni(pic)L]^? are present. Additionally, in the Ni(II)–Hpic–Hhis system the species [Ni(Hpic)HL]²⁺, Ni(pic)L and [Ni(pic)L(OH)]^? were identified. The species distribution diagrams as functions of pH are briefly discussed.     

Highly Sensitive and Selective Detection of Pb(II) by NH2−SiO2/Ru(bpy)32+−UiO66 based Solid‐state ECL Sensor

In this study, a novel electrochemiluminescence (ECL) sensor for highly sensitive and selective detection of Pb(II) was developed based on Ru(bpy)₃²⁺ encapsulated UiO66 metal‐organic‐framework (Ru(bpy)₃²⁺?UiO66 MOF) and ?NH₂ group functionalized silica (NH₂?SiO₂). The NH₂?SiO₂ with large surface area provided an excellent platform for the ECL sensor. As numerous exposed carboxyl groups were present on UiO66 backbone, the Ru(bpy)₃²⁺?UiO66 could be steadily immobilized to NH₂?SiO₂ by forming amide bonds. Meanwhile, the introduced UiO66 MOF which used for the encapsulation of Ru(bpy)₃²⁺, significantly enhanced the ECL efficiency of the proposed sensor, as it possessed a large specific surface area and porosity for the loading of Ru(bpy)₃²⁺. Moreover, a high quenching effect on ECL intensity was obtained in the presence of Pb(II) in the electrolyte. Under the optimal conditions, the quenched ECL intensity showed a good linear relationship within Pb(II) concentration in the range from 1.0×10^?6 to 1.0×10² μM, with a detection limit of 1.0×10^?7 μM (S/N=3). The proposed sensor for Pb(II) detection was simple in operation, rapid in testing, stable in signal, and showed a good anti‐interference ability to some other metal ions. Besides, its application for detecting Pb(II) in a real sample was also investigated here. This work provides a potential platform for metal ions detection in environmental monitoring field.     

Dispersive liquid–liquid microextraction using the freezed floating organic drop for rapid,fast, and sensitive determination of lead

A rapid, simple, and sensitive method was developed for lead preconcentration and separation in various real samples by dispersive liquid–liquid microextraction based on the freezing of floating organic drop. In this method, a suitable extraction solvent dissolved in a dispersive solvent was quickly syringed into the water sample so that the solution became turbid. Then, two phases were separated by centrifugation. The floating extractant droplet can be easily solidified on an ice bath and taken out of the water sample. Then, it can be liquefied instantly at room temperature, and analyte can be determined in it. In the creation of a hydrophobic complex with lead, 1-(2-pyridylazo)-2-naphthole (PAN) was used as the chelating agent. 1-Undecanol and acetone were used as extraction and disperser solvent. To achieve the highest recovery, some factors (type and volume of dispersive and extraction solvent, pH, PAN concentration, and salt concentration) were optimised. Under optimised conditions (pH = 9, 1.0 × 10^–3 mol L^?1 PAN, 15% w/v NaCl, 100 µL 1-undecanol, and 0.3 mL acetone), the lead calibration graph was linear from 1.5 to 80 μg L^?1. The detection limit and preconcentration factor were 0.5 μg L^?1 and 50, respectively. Lead was successfully determined in water and food (spinach, rice, potato, carrot, and black tea bag) samples by this method.     

Complexation of 2,3-dihydroxyquinaline with some bivalent <Emphasis Type="Italic">d</Emphasis> metals. Crystal and molecular structures of 2,3-dihydroxyquinoline

The reactions of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Cd with 2,3-dihydroxyquinoline (H₂L) were used to synthesize and identify the complexes M(HL)₂ · 2H₂O (M = Mn, Ni, Cu), Fe(HL)OH · 2H₂O, Co(HL)OH · H₂O, Cd(H₂L)Cl₂, where H₂L participates in the coordination in the monoanionic or neutral forms with the formation of the chelate cycles. Single crystal was isolated and the crystal structure of H₂L was determined. The spectral characteristics of a neutral and anionic form of the ligand were measured, and its complexation with MCl₂ was studied in the ethanol solutions. The acidity constant of H₂L and the formation constants of the complexes in solutions were calculated.     

Synthesis and structure of the disc-like cluster C72H102N12Ni13O40

The disc-like cluster C₇₂H₁₀₂N₁₂Ni₁₃O₄₀ is first time synthesized based on N-(2-pyridyl)methyliminodipropionic acid. Single crystal X-ray diffraction is used to determine its atomic structure. The cluster consists of seven-nuclear core: nickel(II) hydrocomplex (Ni...Ni distance 3.012–3.032 Å) and six nickel chelates of the corresponding acid arranged around its perimeter (Ni...Ni distance 2.981–3.164 Å). In the chelate part of the complex, the ligand is pentadentate owing to the formation of a bridging bond, thus organizing a coordination geometry of the metal center as a distorted square bipyramid (4+2). Liquid chromatography-mass spectrometry is employed to study the structure of the obtained nickel(II) complexes.     

Flow injection-solid phase spectrofluorimetric determination of pyridoxine in presence of group B-vitamins

A flow-through optosensor has been prepared for the sensitive and selective determination of pyridoxine (vitamin B₆) in aqueous solutions. The sensor was developed in conjunction with a monochannel flow-injection analysis system with fluorimetric detection using Sephadex SP-C25 resin as an active sorbent substrate. This method of determination is carried out without any derivatization. The wavelengths of excitation and emission were 295 and 385 nm, respectively. When a HCl (10^–3 mol L^–1) / NaCl (3 × 10^–2 mol L^–1) solution is used as carrier solution, the sensor responds linearly in the measuring range of 5–200, 10–400 and 50–1800 ng mL^–1 with detection limits of 0.33, 0.67, and 5.70 ng mL^–1 for 2000, 1000 and 200 μL of sample volume, respectively. The relative standard deviation for ten independent determinations is less than 0.75% for 0.2 and 1.0 mL of sample volumes used, and 1.31% for 2.0 mL of sample volume used. The method was satisfactorily applied to the determination of vitamin B₆ in pharmaceutical preparations.     

A tetradentate bisoxime and its supramolecular nickel(II) cluster: synthesis,crystal structure,and spectral properties

Salen-type bisoxime 5,5′-dimethoxy-2,2′-[(ethylenedioxy)bis(nitrilomethylidyne)]diphenol (H₂L) and its trinuclear Ni(II) cluster {[(NiL)(n-BuOH)]₂(μ-OAc)₂Ni}?·?n-BuOH have been synthesized and structurally characterized. The structure of H₂L adopts an L-shape conformation where the two salicylaldoxime moieties are well separated. In the trinuclear Ni(II) cluster, two acetates coordinate to three Ni(II)'s through Ni–O–C–O–Ni bridges, four μ-phenoxos from two [NiL(n-BuOH)] units also coordinate to Ni(II), and two n-butanols coordinate to two terminal Ni(II)'s forming a distorted octahedral geometry. The Ni–O–C–O–Ni and μ-phenoxo bridges play important roles in assembling Ni(II) and the ligands. H₂L forms a rectangle-like large cave structure through O–H?···?N, C–H?···?O, and C–H?···?π hydrogen-bond interactions, whereas its trinuclear Ni(II) cluster exhibits a 3-D supramolecular network structure through intermolecular O–H?···?O, C–H?···?O, and C–H?···?π hydrogen-bond interactions.