SCN Complex Research Articles

Synthesis, spectroscopic findings, SEM/EDX, DFT, and single-crystal structure of Hg/Pb/Cu–SCN complexes: In silico ADME/T profiling and promising antibacterial activities

This work contemplates synthesizing M-SCN crystal compounds (M = Hg/Pb/Cu) in the presence of respective metal salts and exogenous ancillary SCN− ion by slowly evaporating the mixed solvent (CH3OH + ACN). The complexes were characterized by spectroscopy, SEM/EDX, and X-ray crystallography. The Hg-Complex, Pb-Complex, and Cu-Complex crystallize in the monoclinic space group (Z = 2/4). The crystal packing fascinatingly consists of weak covalent bonding and Pb⋯S contacts of tetrel type bond. Here are the incredible supramolecular topographies delineated by the Hirshfeld surface and 2D fingerprint plot. The B3LYP/6–311++G (d, p) level calculations in the gas phase optimized the compound's geometry. The energy difference (Δ) between HOMO-LUMO and global reactivity parameters investigates the complex's energetic activity. MESP highlights the electrophilic/nucleophilic sites and H-bonding interactions. Molecular docking was conceded with the Gram- + ve bacterium Bacillus Subtilis (PDB ID: 6UF6) and the Gram-ve bacterium Proteus Vulgaris (PDB ID: 5HXW) to authenticate the bactericidal activity. ADME/T explains the various pharmacological properties. In addition, we studied the antibacterial activity with MIC (μg/mL) values and time-kill kinetics against Staphylococcus aureus (ATCC 25923) and Bacillus subtilis (ATCC 6635) as Gram-positive, Pseudomonas aeruginosa (ATCC 27853) and Escherichia coli (ATCC 25922) as Gram-negative bacteria.

Surface Plasmon Resonance Identifies High-Affinity Binding of l-DOPA to Siderocalin/Lipocalin-2 through Iron–Siderophore Action: Implications for Parkinson’s Disease Treatment

l-3,4-Dihydroxyphenylalanine (l-DOPA), the dopamine precursor, remains the frontline treatment for Parkinson's disease (PD). With the treatment progress, l-DOPA efficacy decreases, necessitating higher and more frequent doses, with higher risks of dyskinesia. l-DOPA chelates iron through its catechol group, forming the l-DOPA:Fe complex; however, the fate of this complex is unknown. Catechol siderophore-like compounds are known to bind siderocalin (Scn)/lipocalin-2 to form stable siderophore:Fe:Scn complexes. Scn is upregulated in PD patients' substantia nigra and may play a role in PD pathophysiology. Therefore, in this study, we used the surface plasmon resonance (SPR) technique to examine the binding properties of l-DOPA to Scn. We found that l-DOPA formed a stable complex with Scn in the presence of Fe3+. Our analysis of the binding properties of l-DOPA precursors and metabolites indicates that the catechol group is necessary but not sufficient to form a stable complex with Scn. Finally, the affinity constant (Kd) of DOPA:Fe3+ binding with Scn (0.8 μM) was lower than l-DOPA plasma peak concentrations in l-DOPA preparations in the past six decades. Our results speculate a significant role for the l-DOPA-Scn complex in the decreased bioavailability of l-DOPA with the progress of PD.

Open-Source Portable Device for the Determination of Fluoride in Drinking Water.

The prolonged exposure to fluorides results in the development of several diseases, from dental fluorosis to crippling deformities of the spine and major joints. The population exposed to high fluoride concentration is located in developing countries where the assurance of water quality is difficult to perform. Addressing this challenge, an open-source system for the determination of fluoride in natural water was developed using the equilibrium between the red Fe-SCN complex and the colorless Fe-F. The reaction develops in cotton substrates to reduce the manipulation of liquid reagents and reduce the errors by nontrained operators. The system was optimized by image analysis and implemented in an open-source Arduino-based device and data was acquired through the serial port of a cell phone, which is also used as a power source, avoiding the use of a battery and reducing production costs. The device showed a detection limit of 0.7 mg L-1 and a linear range of up to 8 mg L-1. This extended detection limit makes the device useful for the application in regions where the fluoride concentration in drinking water is far higher than the United Nations limit (1.5 mg L-1), e.g., the United Republic of Tanzania, where the upper limit of F- was extended to 4 mg L-1 or in USA, where the Environmental Protection Agency established the Maximum Contaminant Level of F- in drinking water at 4 mg L-1. The method was tested with natural waters from the Arusha region in the northeast of Tanzania and validated against the results from ion chromatography showing a good correlation. The developed device exhibits chemical stability of 5 days, allowing it to be manufactured and distributed in local areas and, also, modified according to the requirements of the water composition due to Industry 4.0 concepts used in the design.

Nano silica particles loaded with CYANEX-921 for removal of iron(III) from phosphoric acid

A simple route for preparation of organically modified spherical silica (SiO 2 ) nanoparticles with CYANEX 921 has been discussed. These modified particles has been used to remove Fe 3+ -SCN complex from 9M phosphoric acid. SEM, XRD, IR and EDS have been used to Characterized the powder in its several stages. The effect of SiO 2 weight, thiocyanate concentration, initial Fe (III) concentration, H 3 PO 4 concentration, stirring time, temperature and loaded SiO 2 weight have been used to study the removal percent. The loaded silica succeeded in removal of 70% of Fe (III). Langmuir isotherm model well fit the experimental data with maximum sorption capacity 45.45 mg/g. The reaction kinetic is found to follow the pseudo second order kinetic model the adsorption reaction shows exothermic behavior.

High-sensitivity thiocyanate spectrophotometric method for determination of perrhenate, an analogue of radioactive pertechnetate, under acidic condition

Spectrophotometric method is a simple and effective in situ analytical method for contaminants monitoring, but further improvement of its sensitivity and detection limit for radionuclides determination remains highly desirable. Herein, we report a simple and highly sensitive thiocyanate spectrophotometric method for the determination of radioactive Tc(VII) by studying its chemical analogue Re(VII) in different aqueous media. The colorless thiocyanate reacted with Re(VII) in hydrochloric acid solution in the presence of SnCl2 producing a stable colored Re(IV)-SCN complex, which was extracted into ethyl acetate and then measured at 427 nm. Under optimized conditions, a strong linear relationship can be obtained in the range of 0.25–10 mg L−1 for Re(VII) with R2 value > 0.9942, and the sensitivity of the method was found to be 0.004 μg cm−2 with detection limit of 0.027 mg L−1. This assay provides highly sensitive detection of Re(VII) in environmental media that is high in NO3−, Cu2+, and Fe3+. We applied it to the determination of Re(VII) in the wide range of background solutions, including deionized water, groundwater, and seawater, and analysis results showed that none of the molar absorptivities for both groundwater and seawater backgrounds was statistically different from the deionized water background when the paired Student’s t test, at 95% confidence level, was applied. The operational simplicity, accuracy, and precision of the proposed method suggest that it can be a good alternative for the in situ analysis of pertechnetate in environmental media.

Penerapan Metode Sonikasi terhadap Adsorpsi Fe(III) pada Zeolit Alam Teraktivasi

<p>Iron (III) (Fe (III)) is widely used in the industry such us water treatment, the sugar cane, the concrete industry and coal mining. Industrial activity using Fe(III) has potential impact to environmental pollution problems due to that industry produces Fe waste that one of hazardous waste. Fe content excess might toxic effect to human health and the environment. Zeolite as adsorbent has been evaluated extensively for Fe and other heavy metal. Sonication method has been widely developed in polymer preparation. The method is more effective in operation time because the reaction rate increased and also more efficient on the usage of chemical reagens. The optimization of reaction time, the ratio of Fe(III) with activated zeolite, the influence of pH, and temperature has been assessed for Fe(III) adsorption with an activated zeolite by sonication technique. The formation of Fe(III)-SCN complex assay was used for determination of Fe(III) adsorbed by the activated zeolite with using spectrophotometer. The results showed a relatively short operation time (15 minutes), at pH of 4, temperature of 30 °C with the ratio of 1:50 (weight/volume) for the activated zeolite and Fe(III). </p>

Synthesis, characterization, and determination of genotoxic effect of a novel dimeric 8-hydroxyquinoline Cd(II) SCN complex

In this study, a Cd(II) complex was synthesized using 8-hydroxyquinoline and thiocyanate as the ligands and structurally characterized with the combination of FTIR, 1H-NMR, 13C-NMR, UV–vis, and MS spectral data. Then, genotoxic effects of the prepared complex were investigated. Genotoxic properties of the dimeric 8-hydroxyquinolinthiocyanatoCd(II) [Cd2(8Q)2(SCN)2] complex synthesized as drug raw material were analyzed in human peripheral blood lymphocytes. Concentrations of 1, 2, 4, 6, and 8 μg/mL [Cd2(8Q)2(SCN)2] were used for 24 and 48 h durations. [Cd2(8Q)2(SCN)2] significantly increased chromosomal aberrations (CAs) at 4, 6, and 8 μg/mL concentrations after a 24- h period and 2 and 4 μg/mL after a 48-h period. [Cd2(8Q)2(SCN)2] significantly decreased the mitotic index (MI) at all concentrations, both at 24 and 48 h. Micronuclei frequency (MN) was not affected by [Cd2(8Q)2(SCN)2] treatment compared with the control. After application for a 48 h period, 6 and 8 μg/mL concentrations showed toxic effects both in chromosomal abnormality and in micronucleus tests. It also decreased the cytokinesis-block proliferation index (CBPI), but this result was statistically significant only at 6 and 8 μg/mL concentrations. In the comet assay (single-cell gel electrophoresis (SCGE)), significant increases in comet tail length, tail moment, and tail intensity were observed at all concentrations. [Cd2(8Q)2(SCN)2] displays clastogenic effect in the concentrations used in human peripheral lymphocytes at chromosomal abnormality, micronucleus tests, and cytokinesis-block proliferation index parameters. Further studies should be conducted in other test systems to evaluate the complete genotoxic potential of [Cd2(8Q)2(SCN)2].

A Zinc Morpholine Complex Prevents HCl/Ethanol-Induced Gastric Ulcers in a Rat Model.

Zinc is a naturally occurring element with roles in wound healing and rescuing tissue integrity, particularly in the gastrointestinal system, where it can be detected in the mucosal and submucosal layers. Zinc chelates are known to have beneficial effects on the gastrointestinal mucosa and in cases of gastric ulcer. We synthesized complexes of zinc featuring a heterocyclic amine binding amino acids then investigated their ability to enhance the gastric self-repair. Zinc-morpholine complex, Zn(L)SCN, namely showed strong free-radical scavenging, promotion of the DNA and RNA polymerases reconstruction and suppression of cell damage. The complex’s mode of action is proposed to involve hydrogen bond formation via its bis(thiocyanato-k)zinc moiety. Zn(L)SCN complex had potent effects on gastric enzymatic activity both in vitro and in vivo. The complex disrupted the ulcerative process as demonstrated by changes in the intermediate metabolites of the oxidative pathway – specifically, reduction in the MDA levels and elevation of reduced glutathione together with an attenuation of oxidative DNA damage. Additionally, Zn(L)SCN restored the gastric mucosa, inhibited the production of pro-inflammatory cytokines (IL-6, TNF and the caspases), and preserved the gastric mucous balance. Zn(L)SCN thus exhibited anti-oxidative, anti-inflammatory and anti-apoptotic activities, all of which have cytoprotective effects on the gastric lining.

Solid phase extraction–spectrophotometric determination of fluoride in water samples using magnetic iron oxide nanoparticles

A new, sensitive, fast and simple method using magnetic iron oxide nanoparticles (MIONs), as an adsorbent has been developed for extraction, preconcentration and determination of traces of fluoride ions. The determination method is based on the discoloration of Fe(III)–SCN complex with extracted fluoride ions which was subsequently monitored spectrophotometrically at λ max = 458 nm. Various parameters affecting the adsorption of fluoride by the MIONs have been investigated, such as pH of the solution, type, volume and concentration of desorbing reagent, amount of adsorbent and interference effects. A linear response for the determination of fluoride was achieved in the concentration range of 0.040–1.250 μg mL −1. The limit of detection (LOD) and limit of quantification (LOQ) for fluoride based on 3 times and 10 times the standard deviation of the blank (3S b, 10S b) were 0.015 and 0.042 μg mL −1 ( n = 20) for fluoride ion, respectively. A preconcentration factor of 50 was achieved in this method. The proposed procedure has been applied for determination of fluoride concentration in various water samples. The results obtained from this method were successfully compared with those provided by standard SPADNS method.

Determination of stability constants between complexing agents and At(I) and At(III) species present at ultra-trace concentrations

A competition method is proposed to determine the complexation constants between At(I) and At(III) species and complexing agents. The method, tested with an inorganic ligand, thiocyanate ion (SCN −), and an organic macromolecule, thiacalix[4]arenetetrasulfonate (LH 4) is based on solid/liquid separation or liquid/liquid extraction. For the solid/liquid separation, the cationic exchanger Dowex 50X8 was used. The interaction of At(I) and At(III) with the cationic exchanger is specific but could not be described by the expected cation exchange process. Most probably, At(I, III) interacts with a “strong” site (in weak amount) to form a surface complex at the surface of the resin organic skeleton. For the liquid/liquid separation, chloroform, toluene and hexane were used. All solvents extract astatine species with distribution coefficients varying between 0.7 and 120. The extraction process was shown to be independent of aqueous phase characteristics (pH, ionic strength) and was explained by the solvation of astatine species by the organic solvent. The effect of the addition of the thiacalix[4]arenetetrasulfonate on the solid/liquid or liquid/liquid distribution coefficients could be well described by the formation of a 1:1 complex with stability constants of log β 1 = 4.5 ± 0.4 and 3.3 ± 0.3 for At(I) and At(III), respectively. For the thiocyanate ion, the data measured in the presence of the organic solvents could be explained by the formation of both 1:1 and 1:2 At:SCN complexes. In the case of the solid/liquid separation, data analysis was hampered by the probable formation of a ternary complex between At(I, III), SCN − and the functional groups of the resin. As for the calixarene, the interaction strength appeared slightly higher for At(I) (log β 2 = 5.9 ± 0.3 and log β 1 = 3.8 ± 0.2 for 1:2 and 1:1 complexed species, respectively) than for At(III) (log β 2 = 5.3 ± 0.2 and log β 1 = 2.8 ± 0.2 for 1:2 and 1:1 complexed species, respectively).

Adsorption profile of preheated Cr(III)-SCN complexes on polyurethane foam

The accumulation of preheated chromium(III)-thiocyanate complexes onto polyurethane foam (PUF) has been studied. The maximum sorption of Cr(III) (7.01.10-5M) is occurred at pH 2 from 1.2M thiocyanate solution in 10 minute agitation time using 7.25 mg/ml PUF. The sorption data have been investigated by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The Freundlich parameters 1/n = 0.31 and of KF = 9.7.10-4 mol.g-1, Langmuir constants M = 7.03.10-5 mol.g-1 and of b = 1.5.105 l.mol-1 and of D-R constants, Cm = 1.91.10-4 mol.g-1, affinity coefficient b = -0.0023 mol2.kJ-2 and sorption energy E = 14.7 kJ.mol-1 have been evaluated. Thermodynamic parameters of enthalpy, entropy and Gibbs free energy suggest the endothermic and spontaneous adsorption of Cr(III)-SCN complex onto PUF at higher temperature. The influence of common anions and cations on the accumulation of chromium-thiocyanate on PUF and possible sorption mechanism of [Cr(SCN)4]- species on PUF is discussed.

Rate effected adsorption profile of selenium-thiocyanate complex onto polyurethane foam

Summary The sorption of preheated selenium-thiocyanate complexes onto polyurethane (PUR) foam has been studied as a function of equilibration time (1–60 min), concentration of selenium (3.80 × 10−4 −4.39 × 10−3 M) and amount of PUR foam. Maximum sorption (> 98%) has been achieved from 0.5 M hydrochloric acid solution within 20 minutes using 7.25 mg/cm3 PUR foam in the presence of 3.75 × 10−2 M thiocyanate ions. The sorption data have been subjected to Langmuir, Freundlich and Dubinin-Radushkevich (D–R) isotherms. The Freundlich parameters 1/n = 0.25 ± 0.02 and of K F = 1.7 ± 0.2 mmole g−1, Langmuir constants M = 0.23 ± 0.01 mmole g−1 and of b = 23 ± 2 dm3 mmole−1 and of D-R constants, C m = 0.82 ± 0.04 mmole g−1, β = −0.0032 ± 0.0002 mole2 kJ−2 and of E = 12.5 ± 0.2 kJ mole−1 have been evaluated. The kinetic data have been subjected to Morris-Weber, Lagergren and Reichenberg equations and rate constants of intraparticle transport and first order have been computed. Thermodynamic parameters of enthalpy, entropy and Gibbs free energy suggest the endothermic and spontaneous adsorption of Se(IV)-SCN complex onto PUR foam at higher temperature. The influence of common anions and cations on the accumulation of selenium-thiocyanate onto PUR foam has been carried out. The possible sorption mechanism has also been discussed.

Sorption and thermodynamic behavior of zinc(II)-thiocyanate complexes onto polyurethane foam from acidic solutions

The uptake of Zn(II)-SCN complex onto polyurethane foam (PUF) has been investigated in detail with respect to different composition and variable concentration of electrolyte, zinc, thiocyanate ions and PUF, and equilibration time. The sorption data followed both Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms over the entire concentration range of zinc investigated whereas Freundlich sorption isotherm is obeyed upto 13.6.10-3M concentration. The Langmuir constants Q = 202±7 mmole.g-1 and of b = (1.78±0.31.104 dm3.mole-1 and of D-R paraneter X m = 493±1 mmole.g-1, b = activity coefficient = -0.028±0.0002 and of sorption energy E = 13.2±0.5 kJ.mole-1 and Freundlich constants 1/n = 0.42±0.03 and c m = 6.47±1.7 mmole.g-1 were evaluated. The influence of temperature variation on sorption have yielded DH = -77.5±2.9 kJ.mole-1, DS = -5±0.09 J.mole-1.K-1 and DG = -6.67±0.05 kJ.mole-1. The effect of common anions and cations on the sorption has been examined. Sulphate, ascorbate and bromide ions enhances the sorption to some extent whereas nitrite, Pb(II), Fe(III), Al(III), Cu(II) and Co(II) decrease to sorption significantly. A possible mechanism has been envisaged for Zn(II)-SCN sorption onto PUF.

Effect of excessive amount of Cd(II) cations on surface morphology of prismatic {1 1 0} faces of cadmium mercury thiocyanate crystals

Surface morphologies of cadmium mercury thiocyanate crystals grown from synthesized mother solutions with excessive amount of Cd(II) cations (5%, 20% and 50% in molar ratio) are investigated by atomic force microscopy. Unlike our previous observations, strong anisotropic growths occur at the large two-dimensional nuclei as well as at steps generated by 2D nuclei. These steps are highly bunched macrosteps varying from 1.6 up to 35 nm in height with distinctly well-oriented protuberance trains at the step fronts while regular elementary steps are hardly observed. These protuberances, however, become fewer and less distinct with the increase of excessive Cd(II) cations in the solution and even disappear at a much higher concentration of 50%. Steps also vary from macrosteps to dominant substeps with the height of 1 3 and 2 3 elementary steps of 0.81 nm at this high concentration. These distinct surface morphological variations are assumed to result from the effect of Cd–SCN complex anions as either growth units or impurities under different growth conditions.

Stability and kinetics of decomposition of binuclear Cu(II) complexes with a symmetrical hexaaza macrocycle: the effect of SCN − as ancillary ligand

The effect of added KBr and KSCN on the stability constants of the mono and binuclear Cu(II) complexes with a symmetrical hexaazamacrocycle L has been examined in 0.1 M KNO 3. The presence of these salts does not cause any change in the ligand protonation constants, which indicates that, in the presence of 0.1 M KNO 3, there is not preferential interaction of the Br − and SCN − anions with the highly protonated forms of the ligand. No ternary CuLBr complexes are detected in the potentiometric study of the equilibrium, but several mono and binuclear CuLSCN complexes are formed at significant amounts and their stabilities are reported. The kinetics of decomposition of the binuclear CuL and CuLSCN complexes upon addition of an excess of acid has been also measured. The results obtained for the CuL complexes agree well with those previously reported in 1.0 M KNO 3, and they indicate that the release of both Cu(II) ions is statistically controlled. The existence of some differences between the kinetic data corresponding to decomposition of solutions at different starting pH is interpreted in terms of parallel decomposition of the binuclear Cu 2L 4+, Cu 2L(OH) 3+ and Cu 2L(OH) 2 2+ complexes, the kinetic parameters for the three complexes being slightly different. This interpretation is also supported by the kinetics of decomposition of the CuLSCN − complexes that also reveals differences between the several complexes in solution. If the present data are interpreted in terms of the classical mechanism for decomposition of Cu(II)-polyamine complexes, they suggest that the nature of the ancillary ligands does not cause large changes in the lability of the CuN bonds but it largely affects to the relative rates of attack by H + and water.

Adsorption Isotherms and Thermodynamic Profile of Co(II)—SCN Complex Uptake on Polyurethane Foam

Sorption of cobalt(II)–thiocyanate complex onto polyurethane foam (PUF) has been investigated in detail with respect to the equilibrating time between Co(II)-thiocyanate complex in solution and foam, and concentrations of cobalt(II) and sorbent. The sorption was optimized with respect to the composition of electrolyte. Maximum sorption has been achieved from 0.1 M HCl solution containing 0.5 M SCN after 10 minutes of shaking time. The kinetics and thermodynamics of sorption are studied in detail. The kinetics follow a first-order rate equation with the rate constant, k, equal to 9.57 × 10−2 min.−1 The variation of equilibrium constant K c with temperature (15–50°C) yields values of ΔH = −64 ± 4.6 kJ·mol−1, ΔS = −192.6 ± 15.6 J·mol−1·K−1, and ΔG = −8.71 kJ·mol−1 at 298 K. The sorption of Co(II)-thiocyanate onto PUF in the presence of common anions and cations has also been measured. The sorption data studied in the concentration range of Co(II) 1.12 × 10−4 to 1.20 × 10−3 M follow Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms. Freundlich parameters 1/n = 0.35 ± 0.02 and A = 0.85 ± 0.2 mmol·g−1, Langmuir constants Q = (5.54 ± 0.12) × 10−5 mol·g−1 and b = (3.55 ± 0.74) × 104 dm3·mol−1 and D–R isotherms β = −0.002999 ± 0.000189 kJ2·mol−2, C m = 10.66 ± 0.16 × 10−4 mol·g−1 and E = 12.9 ± 0.4 kJ·mol−1 have been evaluated. The possible sorption mechanism of cobalt–thiocyanate complex onto PUF is also discussed.

Dimeric and polymeric copper(I) complexes. Synthesis and characterization of copper(I) complexes of di-2-pyridyl ketone oxime (DPKox) and crystal structures of [Cu(DPKox)Cl] 2·2H 2O and [Cu(DPKox)(NCS)] n

Copper(I) complexes with di-2-pyridylketone oxime (DPKox) of the type CuLX·nH 2O, n=1 for X=Cl and Br, and n=0 for X=I and SCN, have been synthesized and characterized. The overall physical results suggest tridentate and bidentate DPKox ligand in the Cl, Br and I, SCN complexes, respectively, and terminal X in the former but bridging X in the later. These complexes display MLCT bands in the visible region, but they do not fluoresce at room temperature. The structure determination has shown the chloride complex ( 1) to have a centro-symmetrically related dimeric unit, in which each copper atom is coordinated by Cl(1), N(1), N(2) and N(3) (of the second ligand molecule) in a distorted tetrahedral environment. Hydrogen bonds are formed by the O(1) of the oxime group and a lattice water molecule, and between different lattice water molecules and Cl(1). The structure of the thiocyanate complex ( 2) features tetrahedral geometry around copper atoms, a chelating bidentate DPKox ligand coordinating via one of the two pyridyl nitrogens, N(1), and N(oxime) only and μ-1,3-thiocyanate group forming zigzag chains along the c-axis of the unit cell.

Adsorption and thermodynamic characteristics of Hg(II)-SCN complex onto polyurethane foam

The sorption of Hg(II) in the presence of sodium thiocyanate solution onto polyurethane (PUR) foam, an excellent sorbent, has been investigated in detail. Maximum sorption of Hg(II) is achieved from 0.1 M hydrochloric acid solution containing 7.5×10 −2 M sodium thiocyanate in 5 min. The sorption data followed both Freundlich and Langmuir adsorption isotherms. The Freundlich constants 1/ n and sorption capacity, C m, are evaluated to be 0.44±0.02 and (3.86±0.89)×10 −3 mol g −1. The saturation capacity and adsorption constant derived from Langmuir isotherm are (6.88±0.28)×10 −5 mol g −1 and (5.6±0.37)×10 4 dm 3 mol −1 respectively. The mean free energy ( E) of Hg(II)-SCN sorption onto PUR foam computed from D–R isotherm is 12.4±0.3 kJ mol −1 indicating ion-exchange type mechanism of chemisorption. The variation of sorption with temperature yields thermodynamic parameters of Δ H=−30.7±1.2 kJ mol −1, Δ S=−70.1±4.1 J mol −1 K −1 and Δ G=−9.86±0.77 kJ mol −1 at 298 K. The negative value of enthalpy and free energy reflects the exothermic and spontaneous nature of sorption. On the basis of the sorption data, sorption mechanism has been proposed.

Sequential liquid–liquid extraction graphite furnace atomic absorption spectrometric (GFAAS) and spectrophotometric determination of zirconium(IV) with calixarene hydroxamic acid

A new calixarene hydroxamic acid, 25,26,27,28-tetrahydroxy-5,11,17,23-tetrakis ( N- p-chlorophenyl) calix[4]arene hydroxamic acid (CPCHA) is synthesized and used for the extraction and graphite furnace atomic absorption determination of zirconium(IV). The extract is also determined spectrophotometrically as CPCHA–SCN complex having maximum absorbance at 447 nm with molar absorptivity 9.4×10 3 l mol −1 cm −1. The Beer's law obeys in the range of 1.0–9.5 ppm of zirconium. The graphite atomic absorption (GFAAS) increases the sensitivity by about 50 folds. The method is applied to the trace determination of zirconium(IV) in standard samples.

Flow injection-assisted optical sensor for determination of iron(II) and iron(III) in natural water

An approach for speciation of iron (as Fe(II) and Fe(III)) based on integration of retention of the Fe(III)-SCN complex with detection using a conventional spectrophotometer is proposed here. The device (namely, a flow-cell packed with an exchange resin) has been coupled to a flow-injection manifold with inner-coupled injection valves which enables discrimination between Fe(III) and Fe(II) taking advantage of a redox minicolumn housed in the loop of one of the valves. The method thus proposed has good selectivity with a determination limit of 80 μgl −1 and affords a determination range of 80–500 μgl −1 for Fe(II) plus Fe(III). Application to synthetic and real samples containing both the oxidation states of iron lead to average recoveries of 103% and 101% for Fe(II) and total iron ( Fe( II)+ Fe( III)), respectively, thus showing the usefulness of the overall approach.