Study of Complex Formation between N-Phenylaza-15-Crown-5 with Mg2+, Ca2+, Ag+ and Cd2+ Metal Cations in Some Binary Mixed Aqueous and Non-aqueous Solvents using the Conductometric Method

The complexation reactions between Mg²⁺, Ca²⁺, Ag⁺ and Cd²⁺ metal cations with N-phenylaza-15-crown-5 (Ph-N15C5) were studied in acetonitrile (AN)–methanol (MeOH), methanol (MeOH)–water (H₂O) and propanol (PrOH)–water (H₂O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stochiometry of all of the complexes with Mg²⁺, Ca²⁺, Ag⁺ and Cd²⁺ cations is 1:1 (L:M). The stability of the complexes is sensitive to the solvent composition and a non-linear behaviour was observed for variation of log K _f of the complexes versus the composition of the binary mixed solvents. The selectivity order of Ph-N15C5 for the metal cations in neat MeOH is Ag⁺>Cd²⁺>Ca²⁺>Mg²⁺, but in the case of neat AN is Ca²⁺>Cd²⁺>Mg²⁺>Ag⁺. The values of thermodynamic parameters (ΔH _c ^o , ΔS _c ^o ) for formation of Ph-N15C5–Mg²⁺, Ph-N15C5–Ca²⁺, Ph-N15C5–Ag⁺ and Ph-N15C5–Cd²⁺ complexes were obtained from temperature dependence of stability constants and the results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents.     

Effect of Solvent on Competitive Bulk Membrane Transport of Transition and Post Transition Metal Cations Using Decyl-18-crown-6

A series of competitive metal ion transport experiments have been performed. Each involved transport from an aqueous source phase across an organic membrane phase into an aqueous receiving phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), cupper(II), zinc(II), cadmium(II), silver(I) and lead(II) metal cations. The membrane phase incorporated ionophore, decyl-18-crown-6. The membrane solvents include: chloroform, dichloromethane, 1,2-dichloroethane, nitrobenzene and chloroform–nitrobenzene binary solvents. A good transport efficiency and selectivity of Pb²⁺ transport from aqueous solutions are observed in this investigation. The selectivity order for competitive bulk liquid membrane transport of the studied transition and post transition metal cations through chloroform is: Pb²⁺>Co²⁺>Ni²⁺>Ag⁺>Cd²⁺, but in the case of dichloromethane, 1,2-dichloroethane and nitrobenzene as liquid membranes, the selectivity sequences were found to be: Pb²⁺>Co²⁺>Cd²⁺>Cu²⁺>Ag⁺>Ni²⁺>Zn²⁺, Pb²⁺>Co²⁺>Ag⁺>Ni²⁺>Zn²⁺ and Pb²⁺>Co²⁺>Ni²⁺>Zn²⁺>Cd²⁺>Ag⁺, respectively. The transport rate of the metal cations in chloroform–nitrobenzene binary solvents is sensitive to the solvent composition. The transport processes were studied in absence and presence of the stearic acid and the results show that the sequence of selectivities and ion transport rates change in the presence of stearic acid.     

A Conductometric Study of Complexation Reactions Between Dibenzo-18-Crown-6 (DB18C6) with Cu2+, Zn2+, Tl+ and Cd2+ Metal Cations in Dimethylsulfoxide–Ethylacetate Binary Mixtures

The complex formation between Cu²⁺, Zn²⁺, Tl⁺ and Cd²⁺ metal cations with macrocyclic ligand, dibenzo- 18-crown-6 (DB18C6) was studied in dimethylsulfoxide (DMSO)–ethylacetate (EtOAc) binary systems at different temperatures using conductometric method. In all cases, DB18C6 forms 1:1 complexes with these metal cations. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, Genplot. The non-linear behaviour which was observed for variations of log K _f of the complexes versus the composition of the mixed solvent was discussed in terms of changing the chemical and physical properties of the constituent solvents when they mix with one another and, therefore, changing the solvation capacities of the metal cations, crown ether molecules and even the resulting complexes with changing the mixed solvent composition. The results show that the selectivity order of DB18C6 for the metal cations in pure ethylacetate and pure dimethylsulfoxide is: Tl⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺ but the selectivity order is changed with the composition of the mixed solvents. The values of enthalpy changes (ΔH°_C) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard enthalpy (ΔS°_C) were calculated from the relationship: ΔG°_C,298.15=ΔH°_C − 298.15 ΔS°_C. The obtained results show that in most cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ΔH°_C and ΔS°_C depend strongly on the nature of the medium.     

基于多肽与金属离子作用的一种高选择性Cd2+荧光比率传感器

利用固相多肽合成法合成了一种新的多肽,将该多肽与荧光基团Dansyl偶联制备了一种新的荧光化学比率传感器:Dansyl-Cys-Pro-Pro-Cys-Trp-NH₂。利用荧光光谱研究了它与金属离子的相互作用。结果表明,与其它13种金属离子相比该多肽对金属Cd²⁺有很好的选择性。它能特异性识别Cd²⁺,具有水溶性好,响应时间快等优点。该肽对Cd²⁺具有很强的键合作用,其结合常数为3.0×10¹¹ L²·mol^-2,检出限为11.5 nmol·L^-1。     

A Simple Fluorometric Method Using Chlorophyll a for Determination of Hg2+ Ion

A simple and green analytical procedure based on chlorophyll a is presented for the determination of Hg²⁺ ion. Chlorophyll a was extracted and purified from the leaves of pea and is employed as a reagent for analysis of Hg²⁺ ion. It displays remarkable fluorescence emission at 674 nm when excited at 412 nm. The emission intensity decreased significantly on exposure to various concentrations of Hg²⁺ ion. This forms the basis for the determination of Hg²⁺ ion. The proposed method was evaluated for sensitivity and selectivity. The linear concentration range was found to be 2.0–10 μM with r² = 0.997 and the limit of detection for Hg²⁺ ion was 1.3 μM. Ions including Pb²⁺, Cd²⁺, Ag⁺, Zn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Mg²⁺, Mn²⁺, Ru³⁺, Er³⁺, K⁺, Na⁺, NH₄⁺, Cl⁻, NO₃⁻, CH₃COO⁻ and SO₄²⁻ did not interfere with the measurement of Hg²⁺ ion even at 500-fold excess. Since chlorophyll a is widely available in the leaves of most plants, and the extraction and purification process is simple, this technique can provide an alternative, sensitive and economical way to determine Hg²⁺ ion.     

Complex Formation of 1,10-Dibenzyl-1,10-diaza-18-crown-6 with Ni2+, Cu2+, Ag+ and Cd2+ Metal Cations in Acetonitrile–dimethylformamide Binary Solutions

Conductance measurements are reported for nickel(II), cupper(II), silver(I) and cadmium(II), salts in acetonitrile (AN)–dimethylformamide (DMF) binary solvents containing macrocyclic ligand, 1,10-dibenzyl-1,10-diaza-18-crown-6 (DBDA18C6) at different temperatures. The changes in molar conductance caused by addition of DBDA18C6 to solutions were analyzed by non-linear least squares to give stability constants of 1:1 metal cation–DBDA18C6 complexes. The results show that the stabilities of the complexes are sensitive to solvent composition and in some cases the sequence of stabilities is changed with changing the composition of the mixed solvents. The values of thermodynamic quantities (ΔH°c and ΔS°c) for formation of DBDA18C6-Ni²⁺, DBDA18C6-Cu²⁺, DBDA18C6-Ag⁺ and DBDA18C6-Cd²⁺ complexes were obtained from temperature dependence of the stability constants and the results show that the values of ΔH°c and ΔS°c for these complexes are sensitive to the nature and composition of AN–DMF binary solutions, but they do not vary monotonically with the solvent composition.     

Combination of <Superscript>13</Superscript>C/<Superscript>113</Superscript>Cd NMR,potentiometry, and voltammetry in characterizing the interactions between Cd and two models of the main components of soil organic matter

This work allowed the characterization of the Cd-binding sites of two compounds taken as models for exudates, the main components of soil organic matter (SOM). The studied compounds were exopolysaccharides (EPS), specifically exudates of roots (polygalacturonic acid) and of soil bacteria (Phytagel). Potentiometric acid–base titrations were performed and fitting of the obtained results indicated the presence of two main classes of acidic sites, defined by their pK _a values, for both EPS but of a different nature when comparing the two compounds. The two studied exopolysaccharides presented different acidic/basic site ratios: 0.15 for Phytagel and 0.76 for polygalacturonic acid. Spectroscopic techniques (¹³C/¹¹³Cd NMR, FTIR) distinguished different Cd surroundings for each of the studied EPS, which is in agreement with the titration results. Furthermore, these analyses indicated the presence of –COOH and –OH groups in various proportions for each exopolysaccharide, which should be linked to their reactivity towards cadmium. Cadmium titrations (voltammetric measurements) also differentiated different binding sites for each compound and allowed the determination of the strength of the Cd-binding site of the EPS. Fitting of the results of such voltammetric measurements was performed using PROSECE (Programme d’Optimisation et de Speciation Chimique dans l’Environnement), a software coupling chemical speciation calculation and binding parameter optimization. The fitting, taking into account the Cd²⁺/H⁺ competition towards exopolysaccharides, confirmed the acid-base titrations and spectroscopic analyses by revealing two classes of binding sites: (i) one defined as a strong complexant regarding its Cd²⁺–EPS association (logK = 9–10.4) and with basic functionality regarding H⁺–EPS association (pK _a = 11.3–11.7), and (ii) one defined as a weak complexant (logK = 7.1–8.2) and with acidic functionality (pK _a = 3.7–4.0). Therefore the combination of spectroscopic analyses, voltammetry, and fitting allowed the precise characterization of the binding sites of the studied exopolysaccharides, mimicking the main SOM components. Furthermore, the binding parameters obtained by fitting can be used in biogeochemical models to better define the role of key SOM compounds like exudates of roots and of soil bacteria on trace metal transport or assimilation.     

Complexes of αω-bis(3,3-dialkyldiaziridin-1-yl)alkanes and their bis(2-arylcarbamoyl) derivatives with cadmium and nickel salts

Complexes of αω-bis(3,3-dialkyldiaziridin-1-yl)alkanes and their bis(2-arylcarbamoyl) derivatives with Cd²⁺ and Ni²⁺ salts were synthesized. The X-ray diffraction study showed that only one molecule of the starting bis-diaziridine is involved in the complexation. The Cd²⁺ complexes have octahedral geometry. The Ni²⁺ complexes are either square-planar or octahedral. One of the octahedral Ni²⁺ complexes crystallizes in the chiral space group P2₁. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 53–59, January, 2008.     

Sodium polyacrylate as a binding agent in diffusive gradients in thin-films technique for the measurement of Cu and Cd in waters

An aqueous solution containing sodium polyacrylate (PA, 0.0030 M) was used in diffusive gradients in thin-films technique (DGT) to measure DGT-labile Cu²⁺ and Cd²⁺ concentrations. The DGT devices (PA DGT) were validated in four types of solutions, including synthetic river waters containing metal ions with or without complexing EDTA, natural river water (Hun River, Shenyang, China) spiked with Cu²⁺ and Cd²⁺, and an industrial wastewater (Shenyang, China). Results showed that only free metal ions were measured by PA DGT, recovery = 98.79% for Cu²⁺ and recovery = 97.80% for Cd²⁺ in solutions containing only free metal ions, recovery = 51.02% for Cu²⁺ and recovery = 51.92% for Cd²⁺ in solution with metal/EDTA molar ratio of 2:1 and recovery = 0 in solutions with metal/EDTA molar ratio of 1:1 and 1:2. These indicated that the complexes of Cu-EDTA and Cd-EDTA were DGT-inert or not DGT-labile. The DGT performance in spiked river water (recovery = 8.47% for Cu²⁺ and recovery = 27.48% for Cd²⁺) and in industrial wastewater (recovery = 14.16% for Cd²⁺) were also investigated. Conditional stability constants (log K) of PA-Cu and PA-Cd complexes were determined as 6.98 and 5.61, respectively, indicating strong interaction between PA and the metals.     

Naked eye detection of cadmium using inorganic–organic hybrid mesoporous material

A novel and low-cost optical sensor for the naked eye detection of Cd²⁺in aqueous media based on mesoporous silica containing 4-(2-pyridylazo)resorcinol (PAR) as a probe molecule anchored by N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAC) was prepared. The effects of various factors such as pH, solvent volume, temperature, reaction time, amount of the material, and the presence of various ions were studied in order to optimize operating conditions. The detection was based on the color change of PAR from orange-yellow to purple as a result of complexation with Cd²⁺. The intensity of the Cd-PAR complex varies linearly with the Cd²⁺concentration, from zero to 1.78×10⁻⁷ mol dm⁻³. The detection and quantification limits for the method when determining Cd²⁺ were 1.75×10⁻⁸ and 5.77×10⁻⁸ mol dm⁻³, respectively, with a correlation coefficient of 0.99. Good chemical stability of the material was observed for a period of five months. The developed sensor was applied to the analysis of various industrial effluents and tap water samples. Electronic supplementary material Supplementary material is available for this article at     

Study of Bulk Membrane Transport of Some Heavy Metal Cations Using Three Macrocyclic Ligands Containing Oxygen and Nitrogen Heteroatoms

The transport experiments of Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ag⁺ and Pb²⁺ metal cations were carried out by dibenzo-18-crown-6 (DB18C6), dibenzyl-diaza-18-crown-6 (Dibenzyl-diaza-18C6) and di-tert-butyl-dibenzo-18-crown-6 (Di-tert-butyl-DB18C6) using chloroform (CHCl₃), 1,2-dichloroethane (1,2-DCE) and nitrobenzene (NB) organic solvents as liquid membranes. The source phase contained equimolar concentration of these metal cations and the source and receiving phases being buffered at pH=5 and pH=3, respectively. The obtained results show that the selectivity and the efficiency of transport for these heavy metal cations change with the nature of the ligand and also the organic solvents, which were used as liquid membranes in these experiments. A good selectivity was observed for silver (I) ion by dibenzyl-diaza-18C6 in all membrane systems. Dibenzo-18C6 and di-tert-butyl-DB18C6 showed the highest transport efficiency for cobalt (II) ion. The effect of stearic acid on transport efficiency was also investigated and the results show that the efficiency of transport of the heavy metal cations increases in the presence of this organic acid.     

Dissociation and coordinating ability of 1,2,3,4-tetrahydro-8-hydroxyquinoline in aqueous solution

The state of 1,2,3,4-tetrahydro-8-hydroxyquinoline is studied spectrophotometrically in the near-UV and visible regions at different pH in an aqueous solution in the presence and absence of Cu²⁺, Zn²⁺, and Cd²⁺ cations. The dissociation constant (pK ₁ ≈ 5.6 (293 K)) is (293 K)) is estimated from the pH-metric data. The stability of the complexes formed decreases in the series Cu²⁺ > Zn²⁺ ≥ Cd²⁺. The influence of tetrahydro atoms on the dissociation, complexation, and change in the state of 1,2,3,4-tetrahydro-8-hydroxyquinoline in an aqueous solution is discussed.     

Effect of non-aqueous solvents on stoichiometry and selectivity of complexes formed between 4′-nitrobenzo-15-crown-5 with Fe3+, Y3+, Cd2+, Sn4+, Ce3+ and Au3+ metal cations

The complexation processes between Fe³⁺, Y³⁺, Cd²⁺, Sn⁴⁺, Ce³⁺ and Au³⁺ metal cations with macrocyclic ligand, 4′-nitrobenzo-15-crown-5 (4′NB15C5), were studied in acetonitrile (AN), methanol (MeOH) and nitromethane (NM) solvents at different temperatures using conductometric method. The conductance data show that the stoichiometry of the complexes formed between this macrocyclic ligand and Cd²⁺, Au³⁺ cations is 1: 1 (ML), but in the case of Fe³⁺, Y³⁺ and Ce³⁺ metal cations, 2: 1 (M₂: L) and 2: 2 [M₂: L₂] complexes are formed in nitromethane solutions. The results show, that the selectivity of 4’NB15C5 for the studied metal cations in methanol solutions at 15°C is: Sn⁴⁺ > Cd²⁺ > Y³⁺ > Fe³⁺ ∼ Ce³⁺ > Au³⁺, but in the case of acetonitrile, the stability order was found to be: Y³⁺ > Au³⁺ > Fe³⁺ > Cd²⁺. The values of stability constants of the 1: 1 [M: L] complexes were determined from conductometric data using a GENPLOT computer program. The values of thermodynamic parameter (ΔH _c ^o and ΔH _c ^o) for formation of the complexes were obtained from temperature dependence of the stability constants, using the van’t Hoff plots. The results show that the values of standard enthalpy (ΔH _c ^o) and standard entropy (ΔH _c ^o) change with the nature of the non aqueous solvents.     

13C, 15N and 113Cd NMR and Molecular Orbital Studies of Novel Bile Acid N-(2-aminoethyl)amides and Their Cd2+-complexes

Lithocholic acid N-(2-aminoethyl)amide (1) and deoxycholic acid N-(2-aminoethyl)amide(2) have been prepared and characterized by¹H, ¹³C and ¹⁵N NMR. The accurate molecular masses of 1 and 2 have been determined by ESI MS. The formation of the Cd²⁺-complexes (1+Cd and 2+Cd) in CD₃OD solution have been detected by ¹H,¹³C, ¹⁵N and ¹¹³Cd NMR. The ¹³C NMR chemical shift assignments of 1 and 2 and their Cd²⁺-complexes are based on DEPT-135 and z-GS ¹H,¹³C HMQC experiments as well as comparison with the assignments of the related structures. The ¹⁵N NMR chemical shiftassignments of the ligands and theirCd²⁺-complexes are based on z-GS¹H,¹⁵N HMBC experiments. ¹³C NMR chemical shift differences between 1and its 1:1 Cd²⁺-complex based on ab initiocalculations at Hartree-Fock SCI-PCM level using3-21G(d) basis set are in agreement with theexperimental shift changes observed onCd²⁺-complexation.     

Tuned Cd2+ Selectivity: Showcase of Electronic and Regio-Effect of π-Extended Di-2-Picolylamine-Substituted Quinoline-Based Tolans

π-Extended di-2-picolylamine (DPA)-substituted 8-hydroxyquinoline (8-HQ) tolans (2) were synthesized for testing electronic and regio-effects. The electron-poor CN-tolan (2b) showed clear selectivity for Cd²⁺ (>>Zn²⁺) over other metal ions via turn-on fluorescence, while the electron-rich MeO-tolan (2a) displayed no clear metal selectivity. Furthermore, considering that there was no significant energy difference between the Cd²⁺ complexes of 1 and 2b, the intended regio-effect (7- vs. 5-substituted effect) did not induce steric hindrance. Thus, the regio-effect is mainly electronic. Considering the above, 2a and 2b constitute a complete showcase in which electronic and regio-effects modulate the metal selectivity. The fluorescence titration of 2b (10 mM) with Cd²⁺ showed that the limit of detection (LOD) of the Cd²⁺-selective 2b was 158 nM in PBS (phosphate-buffered saline) (10 mM, pH 7.2) containing 50% MeOH.     

Extraction of Ba<Superscript>2+</Superscript>, Pb<Superscript>2+</Superscript> and Cd<Superscript>2+</Superscript> into nitrobenzene by using strontium dicarbollylcobaltate in the presence of tetramethyl <Emphasis Type="Italic">p-tert</Emphasis>-butylcalix[4]arene tetraketone

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M²⁺(aq)+SrL²⁺(nb)⇔ML²⁺(nb)+Sr²⁺(aq) taking place in the two-phase water-nitrobenzene system (M²⁺ = Ba²⁺, Pb²⁺, Cd²⁺; L = tetramethyl p-tert-butylcalix[4]arene tetraketone; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the ML²⁺ complexes in water saturated nitrobenzene were calculated; they were found to increase in the order Ba²⁺<Cd²⁺<Pb²⁺.     

基于多肽与金属离子作用的一种高选择性Cd2+荧光比率传感器

利用固相多肽合成法合成了一种新的多肽,将该多肽与荧光基团Dansyl偶联制备了一种新的荧光化学比率传感器:Dansyl-Cys-Pro-Pro-Cys-Trp-NH₂。利用荧光光谱研究了它与金属离子的相互作用。结果表明,与其它13种金属离子相比该多肽对金属Cd²⁺有很好的选择性。它能特异性识别Cd²⁺,具有水溶性好,响应时间快等优点。该肽对Cd²⁺具有很强的键合作用,其结合常数为3.0×10¹¹L²·mol^-2,检出限为11.5nmol·L^-1。     

Dimethylcyclam based fluoroionophore having Hg- and Cd-selective signaling behaviors

Diametrically disubstituted bis(anthrylmethyl) derivative of 1,8-dimethylcyclam exhibited pronounced Hg²⁺- and Cd²⁺-selective fluorogenic behaviors in aqueous acetonitrile solution. A distinctive OFF-ON type signaling was observed for Hg²⁺ and Cd²⁺ ions in aqueous acetonitrile (CH₃CN-H₂O = 90:10, v/v) solution, while a selective ON-OFF type switching behavior toward Hg²⁺ ions was observed in solution having higher water content (CH₃CN-H₂O = 50:50, v/v). The detection limit for the analysis of Hg²⁺ ions in 50% aqueous acetonitrile was found to be 3.8 × 10⁻⁶ M. The selective OR logic gate behavior of the prepared compound toward two toxic heavy metal ions of Hg²⁺ and Cd²⁺ ions in CH₃CN-H₂O (90:10, v/v) suggests the possibility as a new chemosensing device for the two important target metal ions.     

Electrochemical studies of cytochrome c on gold electrodes with promotor of humic acid and 4-aminothiophenol

p-Aminothiophenol (PATP) and humic acids (HA or HAs) were applied jointly as the electron transfer accelerants of redox reactions of cytochrome c (Cyt c) on gold electrodes. The electrochemical properties of the modified electrodes were studied by field emission scanning electron microscope, ultraviolet-visible spectroscopy, electrochemical impedance spectroscopy, Raman spectroscopy and cyclic voltammetry. The immobilized Cyt c displayed a couple of stable and well-defined redox peaks with a formal potential of −0.101 V (vs. SCE) in pH 7.0 phosphate buffer solution. Cyt c adsorption is in the form of a monolayer with average surface coverage of 5.28 pmol cm⁻². The electron transfer rate constant was calculated to be 2.14 s⁻¹. It indicate that the HA film acted as a good adsorption matrix for Cyt c and an excellent accelerant for the redox of Cyt c. The Cyt c-HA modified gold electrode showed a new couple of well-marked redox peaks when 2,4-dichlorophenol was added to the test solution.     

Determination of Cytochrome <Emphasis Type="Italic">c</Emphasis> in Human Serum and Pharmaceutical Injections Using Flow Injection Chemiluminescence

It was found that the complex of cytochrome c (Cyt c) and hydrogen peroxide could significantly catalyze the chemiluminescence (CL) reaction from luminol–hydrogen peroxide, and a sensitive, rapid, and simple CL procedure was proposed for the determination of Cyt c in a flow injection system for the first time. The increment of CL intensity was linear over the concentration of Cyt c ranging from 5 to 700 ng ml⁻¹, with a detection limit of 2 ng ml⁻¹ (3σ). At a flow rate of 2.0 ml min⁻¹, a complete analytical process could be performed in 30 s with a relative standard deviation of less than 4.0%. The proposed method was applied successfully for the assay of Cyt c in pharmaceutical injections and human serum, and the recoveries were from 98.0% to 108.8% and 92.5% to 109.0%. The possible mechanism of Cyt c enhanced CL reaction was also discussed.