Complexation Conditions Research Articles

Radiation-induced pink nickel oligomeric clusters in water. Pulse radiolysis study.

γ-rays and pulse radiolysis of aqueous solutions of Ni(2+) ions in the presence of polyacrylate (PA(-)) and 2-propanol leads to the formation of metastable species absorbing at 540 nm that are ascribed to "pink" oligomeric clusters of a few nickel atoms only. The molar absorption coefficient is evaluated as ε540 nm = 3300 ± 300 L mol(-1) cm(-1) per Ni(0) atom. The successive steps from the reduction of Ni(2+) into Ni(+) ions to the formation of the pink clusters at 540 nm under conditions of complexation by PA(-) are investigated by pulse radiolysis. The yield of the formation of pink clusters increases markedly with the irradiation dose rate, demonstrating the occurrence of the disproportionation of the [Ni(+), PA(-)] complex after a single electron pulse. The reduction and nucleation mechanisms, including rate constants, in competition with the back oxidation by protons, particularly at low dose rate, are discussed.

Biodiesel production by combined fatty acids separation and subsequently enzymatic esterification to improve the low temperature properties

The poor low-temperature properties of biodiesel, which provokes easy crystallization at low temperature, can cause fuel line plugging and limits its blending amount with petro-diesel. This work aimed to study the production of biodiesel with a new process of improving the low temperature performance of biodiesel. Waste cooking oil was first hydrolyzed into fatty acids (FAs) by 60g immobilized lipase and 240g RO water in 15h. Then, urea complexation was used to divide the FAs into saturated and unsaturated components. The conditions for complexation were: FA-to-urea ratio 1:2 (w/w), methanol to FA ratio 5:1 (v/v), duration 2h. The saturated and unsaturated FAs were then converted to iso-propyl and methyl esters by lipase, respectively. Finally, the esters were mixed together. The CFPP of this mixture was decreased from 5°C to -3°C. Hydrolysis, urea complexation and enzymic catalyzed esterification processes are discussed in this paper.

Synthesis of (Pyridin-2-YL)Hydrazone Rhenium(I) Tricarbonyl Complexes that Exhibit pH-Sensitive Fluorescence

There is great potential for novel diagnostic and therapeutic agents that combine multiple imaging modalities. The combination of optical and radionuclide imaging systems is particularly promising for the improved management of cancer. We describe a new heteroorganometallacyclic system containing the (2-pyridyl)hydrazono-Re(CO)3 that exhibits pH-sensitive photophysical properties. This optical reporter group was easily incorporated into a novel synthetic probe for targeting estrogen receptors in cancer. The efficient complexation conditions are expected to be compatible with 99mTc-radiolabeling to obtain dual function imaging probes.

Rational Design of Ligand Precursors to Prepare Abnormal (Mesoionic) and Normal Carbene Complexes and Zwitterionic CX‐Type Palladacycles (X = C, N)

AbstractThe preparation of a series of ligand precursors that feature imidazo[1,2‐a]pyridine and amido functional groups is reported. The reactions between the new ligand precursors, pyridine, and palladium acetate in DMF afforded monodentate PdII abnormal (mesoionic) carbene complexes. An isomeric PdII normal carbene complex with a formally identical steric environment to that of the abnormal carbene counterpart was also prepared. The isomeric pairs were characterized by X‐ray structural studies. Under different complexation conditions, in which PdCl2 was employed as metal precursor, a zwitterionic CC‐type palladacycle formed by the C–H activation at the ortho‐N‐phenyl and methylene carbon atoms was obtained. The use of a similar ligand precursor with an NH instead of an NMe group produced a zwitterionic palladalactam complex. In contrast to the previous work in the literature, owing to the rigidity of the fused heterocyclic ring, the palladalactam complex did not undergo intramolecular proton transfer through the coordinated N atom. Overall, we demonstrated that proper modification of the structures of ligand precursors and complexation conditions allowed us to obtain a full range of intriguing PdII complexes including normal and abnormal carbene complexes, and zwitterionic palladalactam and CC‐type palladacycles by means of A–H bond (A = N, C) activations.

Determination of gold and palladium in environmental samples by FAAS after dispersive liquid–liquid microextraction pretreatment

A new dispersive liquid–liquid microextraction (DLLME) method is proposed for rapid separation, simultaneous extraction and preconcentration of gold and palladium at ultra trace amounts. The extraction of the analytes was performed in the presence of 5-[(E)-(2,6-diaminopyridine-3-yl)diazenyl]-1,3,4-thiadiazole-2-thiol (DAT) as chelating agent. Chloroform and acetone were used as extraction and dispersive solvents, respectively. The variables affecting the complexation and extraction conditions were optimized. The calibration curves were linear in the range of 1.1–85 and 0.9–124 μg L−1 with the detection limits of 0.4 and 0.6 μg L−1, and with the enrichment factors of 94 and 113 for Au and Pd, respectively. The precision (RSD%) was better than 2.4%. The accuracy of the method was verified by analysing the certified standard reference material (CDN–PGMS-10). The results show that the dispersive liquid–liquid microextraction pretreatment is a sensitive, rapid, simple and safe method for the separation/preconcentration of gold and palladium.

Synthesis and Characterisation of Poly (Vinylpyrrolidone) – Nickel (II) Complexes

Main use of polymer - metal complexes lies in their ability to act as catalysts. In the proposed work we have selected poly (vinyl pyrrolidone) as ligand for complexing with nickel. Poly (vinyl pyrrolidone) is a water soluble polymer having a large number of consumer and environment friendly uses which are the consequences of its unique properties like biological compatibility, low toxicity, film forming ability, complexing ability, resistance to thermal degradation in solution and relatively inert behavior towards salts and acids. Nickel, being a transition metal, shows very good catalytic properties. Nickel based catalysts meet the criteria required for the catalysis of a wide range of chemical reactions. Polymer-metal complexes of poly (vinylpyrrolidone) and nickel were prepared by using aqueous solution of PVP (30K) and alcoholic solution of nickel chloride hexahydrate (NiCl2 ∙ 6H2O) at room temperature with different molar compositions. The polymer-metal complexes were obtained in crystalline form by evaporation of the solvent. They were characterized by solubility studies, FTIR, 1 H - NMR and 13 C - NMR. Procedure was repeated with aqueous solution of the salt also. The spectral analysis of the reactants and the polymer-metal complexes confirmed the formation of expected complexes. The conditions for better complexation were optimized.

Preconcentration and Determination of Cadmium in Water and Food Samples byin situSurfactant-Based Solid-Phase Extraction and Flame Atomic Absorption Spectrometry

In situ surfactant-based solid-phase extraction (ISS-SPE) is proposed as a preconcentration procedure for the determination of cadmium in water and food samples by flame atomic absorption spectrometry. In the present work, cetyltrimethylammonium bromide was used as a cationic surfactant, hexafluorophosphate ion as an ion-pairing agent and 4-benzylpiperidinedithiocarbamate potassium salt (K-4-BPDC) as a chelating agent. Several variables that affect the extraction efficiencies such as pH, type and amount of surfactant, concentration of ion-pairing agent, concentration of chelating agent, ionic strength and extraction time were investigated and optimized. After optimization of the complexation and extraction conditions, an enrichment factor of 40 was obtained. The calibration curve was linear in the range of 1-50 µg L-1 and the limit of detection was 0.3 µg L-1. The relative standard deviation for 20 µg L-1 of cadmium was lower than 2.2%. Validation of the methodology was performed by standard addition method and analysis of certified reference materials. The method was successfully applied to the determination of cadmium in various food and water samples.

Pre-treatment of the paper pulp in the bleaching process using biodegradable chelating agents

The aim of this work was to study the application of two biodegradable chelating agents, pyridine-2,6-dicarboxylic acid (PDA) and methylglycinediacetic acid (MGDA), in the treatment of the pulp, prior to hydrogen peroxide bleaching. Such compounds must remove transition metals (Mn, Fe and Cu) from pulp, that catalyze the degradation of hydrogen peroxide, and Ca, which is also problematic due to the formation of precipitates that accumulate in the equipment. Computer simulations were first performed to study the best conditions for metal complexation, and optimum pH was defined as 5–5.5 for PDA and 6.5–7 for MGDA. Metals removal from the pulp, as well as the subsequent bleaching process (Q-P1-Paa-P2), were tested experimentally, and performances were compared to ethylenediaminetetracetic acid (EDTA). PDA removed both Mn and Ca efficiently, leaving most Mg in the pulp after first chelation stage, while MGDA had a lower Ca removal, even using a higher pH and concentration. Residual hydrogen peroxide and kappa number after peroxide stages showed a similar bleaching efficiency between the studied compounds and EDTA.

A green and efficient procedure for the preconcentration and determination of cadmium, nickel and zinc from freshwater, hemodialysis solutions and tuna fish samples by cloud point extraction and flame atomic absorption spectrometry

Cloud point extraction (CPE) was used to simultaneously preconcentrate trace-level cadmium, nickel and zinc for determination by flame atomic absorption spectrometry (FAAS). 1-(2-Pyridilazo)-2-naphthol (PAN) was used as a complexing agent, and the metal complexes were extracted from the aqueous phase by the surfactant Triton X-114 ((1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol). Under optimized complexation and extraction conditions, the limits of detection were 0.37μgL(-1) (Cd), 2.6μgL(-1) (Ni) and 2.3μgL(-1) (Zn). This extraction was quantitative with a preconcentration factor of 30 and enrichment factor estimated to be 42, 40 and 43, respectively. The method was applied to different complex samples, and the accuracy was evaluated by analyzing a water standard reference material (NIST SRM 1643e), yielding results in agreement with the certified values.

Nanosheet-Stacked Chiral Silica Transcribed from Metal Ion- and pH-Tuned Supramolecular Crystalline Complexes of Polyamine-D-Glucarate

D-glucaric acid (D-Glc) associates with linear poly(ethyleneimine) (PEI) through hydrogen bonding and electrostatic interactions in aqueous media to form nanostructured crystalline PEI/D-Glc/H2O complexes with PEI/D-Glc/H2O ratios of 2:1:2. These complexes can serve as templates for silica depositions from hydrolytic condensation of tetramethoxysilane to guide morphologically duplicated silica under very mild conditions. Their microscale morphologies are tunable by use of the crystalline complexes regulated in the different pH of the PEI/D-Glc solutions. It was also found that some metal ions added in the PEI/D-Glc complexation process could have a synergistic effect under a certain pH regimes, bringing about remarkable changes in the hierarchy of the resulting complexes. Especially, the complexes formed through fine-tuning of the complexation conditions could direct torsionally stacked silica nanosheets, in which the nanosheets are composed of orderly-bundled nanofibrils. Final elimination of organic components of the templates afforded chiral inorganic silica while retaining the morphologically higher-order structures. The chirality of the silica, which was obtained after calcination at 600 °C, was characterized by means of diffused reflectance circular dichroism (DRCD) spectroscopy with a remote confirmation of the appearance of induced-CD (ICD) signals of achiral or racemic chromophores covalently linked on the silica frames. Interestingly, the shapes and signs of these ICD signals are dramatically changed depending on the pH-tuned templates used in silicification and are strongly correlated to that of the CD signals of the complex templates, indicating that the chiral transcription proceeds accurately with imprinting the higher-order chirality of the complexes on the morphologically structured silica networks.

Preliminary study to determine the optimal conditions for the simultaneous complexation of siRNA and plasmid DNA

We investigated the complexation ratio of siRNA and plasmid DNA combined with Lipofectamine for the effective delivery of genetic materials. First, the amount of Lipofectamine was varied with a fixed amount of DNA or siRNA to determine in which proportions they would form an optimal combination. Finally, to investigate the effect of DNA or siRNA on the co-complexation of both DNA and siRNA, the co-complex of DNA and siRNA was prepared at the various ratios with a fixed amount of DNA. All complexation was confirmed by gel retardation of DNA or siRNA on agarose gels. The effects of siRNA complexes on mRNA expression from plasmid DNA were explored post-transfection, while the influence of plasmid DNA complexes on the transfection of siRNA was determined in GFP-expressing H4IIE cells. The complex between DNA and Lipofectamine was formed at a weight ratio of 0.8:1, whereas the light band of siRNA/Lipofectamine disappeared at a weight ratio of 4:1. When the amounts of DNA, siRNA, and the mixture were fixed, the optimal ratio of nucleic acids and Lipofectamine in our composition was 110:80:350 (ng). Confocal images and flow cytometry showed that inhibition of GFP expression by siRNA was not interfered with by co-complexed plasmid DNA. Moreover, mRNA expression of adiponectin was not hampered by the addition of siRNA; rather, it was increased. Thus, co-complexation of siRNA and plasmid DNA may have a synergistic effect on delivery of the therapeutic gene and siRNA.

Ion mobility spectrometry focusing on speciation analysis of metals/metalloids bound to carbonic anhydrase

In the present work, traveling wave ion mobility spectrometry-mass spectrometry (TWIMS-MS) was applied to speciation analysis of metalloproteins. The influence of pH on complexation conditions between some metals and bovine carbonic anhydrase was evaluated from pH 6 to 9, as well as the time involved in their complexation (0-24h). Employing TWIMS-MS, two conformational states of bovine carbonic anhydrase were observed with charge states of +12 and +11; these configurations being evaluated in terms of the folded state of the apo form and this protein (at charge state +11) being linked to barium, lead, copper, and zinc in their divalent forms. Metalloprotein speciation analysis was carried out for copper (Cu(+) and Cu(2+)), lead (Pb(2+) and Pb(4+)), and selenium (Se(4+) and Se(6+)) species complexed with bovine carbonic anhydrase. Mobilities of all complexed species were compared, also considering the apo form of this protein.

Elaborate Metallosupramolecular Architectures through Desymmetrization Self-assembly of Symmetric Building Blocks

Abstract Desymmetrization self-assembly of symmetric building blocks is a powerful method to construct elaborate metallosupramolecular architectures. Herein several examples are given to discuss how to build up self-assembled complexes with low symmetry, focusing on 1) stabilization of local structural motifs by template molecules and/or interligand interactions, 2) rigidity regulation of ligand scaffolds, and 3) control of intermediate complexation conditions. Unsymmetrically assembled supramolecular host complexes exhibit unique functions reflecting their structural frameworks.

Cloud Point Extraction and Flame Atomic Absorption Spectrometric Determination of Cadmium and Nickel in Drinking and Wastewater Samples

A simple method for the preconcentration of cadmium (Cd) and nickel (Ni) in drinking and wastewater samples was developed. Cloud point extraction has been used for the preconcentration of both metals, after formation of complexes with 8-hydroxyquinoline (8-HQ) and extraction with the surfactant octylphenoxypolyethoxyethanol (Triton X-114). Dilution of the surfactant-rich phase with acidified ethanol was performed after phase separation, and the Cd and Ni contents were measured by flame atomic absorption spectrometry. The experimental variables, such as pH, amounts of reagents (8-HQ and Triton X-114), temperature, incubation time, and sample volume, were optimized. After optimization of the complexation and extraction conditions, enhancement factors of 80 and 61, with LOD values of 0.22 and 0.52 microg/L, were obtained for Cd and Ni, respectively. The proposed method was applied satisfactorily for the determination of both elements in drinking and wastewater samples.

Synthesis of tricarbonylchromium complexes of 4-aryl-1,4-dihydropyridines

Tricarbonylchromium complexes of 4-aryl-1,4-dihydropyridines have been synthesized both under standard thermodynamic conditions using Cr(CO)6 and under milder complexation conditions using more labile [Cr(CO)3(NH3)3] and (η6-naphthalene)Cr(CO)3. Selective complexation of the Cr(CO)3 on the aryl ring in the presence of a 1,4-dihydropyridine ring was achieved.

Uranium (VI) Complexation with Siderophores-pyoverdine Produced by Pseudomonas Fluorescens SHA 281

Fluore sce nt Pseudomonas species produce pyove rdine -type siderophores with a high pote ntial to dissolve ; bind and transport uranium in the e nvironment. Ide ntification of Pseudomonas fluorescens SHA 281 was confirme d by 16S rDNA sequ e ncing. The pyoverdine produce d by the tested strain was e xtracte d and purifie d using XAD-4 Ambe rlite re sin and its chemical structure was confirme d using NMR and CA-MS analyses. The ge l e lectrophoresis of pyoverdine appeare d low molecular we ight with one prote in band at ~12.5 kDa. The ge ne responsible for pyoverdine production was ide ntifie d using PCR technique . Unde r optimum conditions for comple xation, it was found that pyoverdine comple xe d with about 90.48 % and 86.41 % of U (VI) from monazite and (Th-U) concen trate, respectively.

Complexation and flotation of nonferrous metal ions from alkaline solutions with N-acyl-N′-(p-toluenesulfonyl)hydrazines

Surfactant properties and complexation conditions of Cu(II), Co(II), Ni(II), Zn(II), and Cd(II) ions in alkaline media with N-acyl-N′-(p-toluenesulfonyl)hydrazines, which enable their use in ion flotation processes, were studied. The efficiency of the compounds under study as collectors in aftertreatment of alkaline wastewater to remove milligram amounts of Cu(II) and other metals by ion flotation was demonstrated.

Determination of Trace Amounts of Palladium in Water Samples by Graphite Furnace Atomic Absorption Spectrometry after Dispersive Liquid‐Liquid Microextraction

A simple, rapid, and powerful microextraction technique was used for determination of palladium (II) ion in water samples using dispersive liquid‐liquid microextraction (DLLME) followed by graphite furnace atomic absorption spectrometry (GF AAS). The different variables affecting the complexation and extraction conditions such as extraction and disperser solvent type, extraction time, pH, and concentration of chelating agent were optimized. Under the optimum conditions, the calibration graph was linear in the ranges of 0.05–1 μg L−1 with detection limit of 0.02 μg L−1. The precision (RSD %) for ten replicate determination at 0.2 μg L−1 of palladium was better than 3.5% and the enrichment factor 166.5 was obtained from only 5.0 mL of sample. Under the presence of foreign ions, no significant interference was observed. Finally, accuracy and application of the method were estimated by using test samples of natural waters spiked with different amounts of palladium.

Samples of Kidney Failure Patients by Cloud Point Extraction and Electrothermal Atomic Absorption Spectroscopy

A method has been developed for the determination of arsenic (As) in pharmaceutical and scalp hair samples of kidney failure patients by cloud point extraction (CPE). The scalp hair samples were subjected to microwave-assisted digestion in nitric acid-hydrogen peroxide (2 + 1, v/v). Then, dialysate and digested scalp hair solutions were preconcentrated by CPE using pyronine B as a complexing agent. The resulting complex was entrapped in nonionic surfactant (Triton X-114) prior to its determination by electrothermal atomic absorption spectroscopy. The validity of the CPE method for As was checked by analysis of a certified reference material of human hair and a standard addition method for dialysate solution. The chemical variables affecting the analytical performance of the CPE methods were studied and optimized. After optimization of the complexation and extraction conditions, a preconcentration factor of 52 was obtained for As in 10 mL of dialysate solution and acid digested samples of scalp hair. Under the optimum experimental conditions, the LOD and LOQ of As for the preconcentration of 10 mL of solution were 0.022 and 0.073 microg/L, respectively. The level of As in scalp hair samples of kidney failure patients was higher than in healthy controls.

Complexation of zirconium(IV), thorium(IV) and uranium(VI) malonates with Arsenazo III and Arsenazo M on fiber ion exchangers

The adsorption of zirconium, thorium, and uranium malonate complexes on fiber materials filled with AV-17, EDE-10p, and AN-31 anion exchangers and ANKB-50 polyampholite is studied by diffuse reflection spectroscopy, and their complexation with Arsenazo III and Arsenazo M in the solid phase is studied. The influence of the basicity of the bulk agent, concentration of malonic acid, and adsorption and complexation conditions in the analytical signal is demonstrated. Conditions for the determination of 0.02–0.025 μg/mL zirconium in the presence of 5- to 6-fold excesses of thorium and uranium, and 0.008–0.12 μg/mL of uranium(VI) in the presence of thorium and zirconium in equal concentrations are formulated.