Complexation Of Chromium Research Articles

Experimental and Molecular Modeling Studies on the Complexation of Chromium(III) with the Angiotensin-Converting Enzyme Inhibitor Captopril.

Captopril (CPT) is an inhibitor of angiotensin I converting enzyme, used as a medication for the treatment of people with high blood pressure, renal insufficiency, and cardiovascular diseases. It inhibits the angiogenesis process, vasoconstriction, and tumor metastasis. Some metal–captopril complexes exhibit antimicrobial activities. In the current work, the formation of the CrIII–CPT complex was studied spectrophotometrically and potentiometrically in aqueous solution. Kinetics of CrIII–CPT complex formation was spectrophotometrically studied over the pH range 3.20–4.20, at an ionic strength of 0.3 M at 30–50 °C. CrIII–CPT complex formation was potentiometrically studied at 25 °C, where ligand protonation constants and complexes’ overall stability constants were calculated. UV–vis absorption spectra were executed to confirm the complex formation. Density functional theory and molecular dynamics simulation were performed to search the geometries of the CrIII–CPT complex. Atoms in molecules and interaction region indicator calculations are used to investigate intermolecular interactions for the formation of CrIII–CPT complex. The antimicrobial activity of the CPT ligand and CrIII–CPT complex on the prevention and control of environmental pathogenic bacteria, as tested on both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative bacteria Escherichia coli (E. coli) via agar disc diffusion method, assess the ability to use as an antimicrobial agent. CPT had shown good antimicrobial activity against both types of bacteria, which had increased slightly the zone of inhibition in Cr-CPT that indicates the increased efficacy due to Cr(III) antimicrobial activity via its oxidative damage to the bacterial cell wall. No previous study tested the CPT antimicrobial activity against Gram-positive ones such as S. aureus

Surface Complexation of Chromium(VI) on Iron(III) Hydroxide: Mechanisms and Stability Constants of Surfaces Complexes

The adsorption of chromate ions H2-yA (y = 1, 2, and A = CrO42–) on iron(III) hydroxide was conducted as a function of adsorbent mass, solution pH, and hydration time. The surface complexation technique, based on the examination of the chromate distribution between the solid and liquid phases, was adopted to predict the adsorption mechanism. To specify stoichiometry of the chromate surface complexes, the proton (n > 0), and hydroxyl (n < 0) ion-exchange was evaluated at a pH range of 2–12. The obtained “n” values are ranging between -1 and 1. As a result, the sorption process involved specific chemical interaction with surface sites, resulting in 1H+ and 1OH– release of the adsorbate molecule. The surface species identified were ; ; ; ; ; ; ; and . The logarithmic values of their complexing constants were: log K00 = 1.81 ± 0.04; log K11 = -3.53 ± 0.07; log K21 = -1.03 ± 0.23, log K1-1 = 7.15 ± 0.14 and log K2-1 = 9.62 ± 0.53. The results showed that the chromate adsorption on Fe(III) hydroxide was of electrostatic and chemical nature at pH lower than 5.5, and only of chemical nature at pH superior to 5.5. Taking into account these considerations, Fe(III) hydroxide could be considered an excellent sorbent for the removal of Cr(VI) from wastewater solutions.

Complexation of chromium (III) with the antifibrinolytic drug tranexamic acid: Formation, kinetics, and molecular modeling studies

Tranexamic acid (TXA) is widely used as an antifibrinolytic drug, inhibits fibrinolysis by blocking lysine-binding sites on plasminogen, limiting the activation of plasmin; and therefore, prevents excessive blood loss from trauma, surgery (e.g., cardiac, orthopedic, liver transplantation), postpartum bleeding, nosebleeds, and heavy menstruation. Tranexamic acid complexes of some metal ions have shown significant microbiological and anticancer activities. Here, the formation of tranexamate‑chromium (III) complex in aqueous solution has been spectrophotometrically and potentiometrically studied. Kinetics of formation of tranexamate‑chromium(III) complex has been spectrophotometrically studied under pseudo order conditions over the 303–323 K range, pH (3.20–4.56) range, and ionic strength of 0.30 M for a set of TXA concentrations. The formation of this complex was studied potentiometrically at (298.2 ± 0.1) K, in which the overall stability constant and TXA protonation constants were calculated. The UV–visible spectroscopic measurements were carried out to confirm the formation of the Cr(III)–TXA complex. The density functional theory (DFT) and molecular dynamics (MD) simulation were used to illustrate the geometries of the Cr(III)–TXA complex in gas and water phases, as well as the interactions among the involved species.

Special Issue on Wastewater Treatment and Reuse Technologies

Wastewater treatment allows for the safe disposal of municipal and industrial wastewater to protect public health and the ecosystem[...]

Characterization and quantification of chromate adsorption by layered porous iron oxyhydroxide: An experimental and theoretical study

The inner structure of iron oxyhydroxide agglomerates (IOAs) prepared from hydrolysis of ferric chloride was characterized and correlated to surface complexation of hexavalent chromium, Cr(VI), in a broad range of pH (3–12) and ionic strengths (0.0–5.0M). Evolution of particle size, morphology, and surface activity, combined with density functional theory (DFT) calculations, support the condensation reaction initiated formation of IOAs in three levels: iron nanoparticles to nanolayers to agglomerates. This agglomeration process led to a layered porous structure for aqueous-phase IOAs resulting in a rapid and high removal of Cr(VI) in batch tests. By integrating adsorption results, thermodynamic modeling, and quantum chemical calculations for the adsorption reactions, a quantitative distribution profile for each surface coordination of Cr(VI) ions (i.e., monodentate, bidentate, and hydrogen-bonding) was established. Results of this study are important to understand the fundamental mechanism of IOAs formation in aqueous phase and the intrinsic nature of surface complexations at the mineral-water interface for optimal Cr(VI) removal in hypersaline waste streams.

Adsorption of Chromium (VI) on Calcium Phosphate: Mechanisms and Stability Constants of Surface Complexes

The adsorption of chromate on octacalcium phosphate (OCP) was investigated as a function of contact time, surface coverage, and solution pH [...]

Study of a polymer optical microring resonator for hexavalent chromium sensing

This work presents a design method for an Optical Microring Resonator (OMR) dedicated to specific heavy metal species sensing. A Top-Down design approach is used to create an OMR specifically designed for hexavalent chromium sensing, and suitable to a final Lab on Chip integration. Its operating principle is based on optical absorption measurement. This spectral absorption is induced by the colorimetric metallic complexation of hexavalent chromium with 1,5 diphenylcarbazide (DPC).The light enhancement at resonance wavelengths in an OMR allows highly sensitive measurements of the fluid optical absorbance by enhancing the effective path length. Chromate ions react with DPC at visible range. Singular red–violet complex is formed and induce a significant change of light intensity in the transmission spectrum. The intrinsic maximum absorption of metallic complex around 545nm makes the polymer ring resonator parameters changing namely its effective index and attenuation value at resonance. The design considerations of the OMR have been analyzed to optimize critical parameters regarding the polymer ring resonator geometry. Simulations results have been investigated which lead to the geometry of a prototype device.

Nanoparticles and whiskers-based chitosan films for Cr complexation

Though it is known that chitosan films are able to complex metallic ions, underlying molecular mechanisms are poorly understood. Here, we studied the complexation of chromium (III) ions using three films: chitosan films, biocomposites formed from chitosan with nanoparticles, and chitosan with whiskers. Fourier transform infrared spectroscopy revealed the presence of interactions between chromium (III) ions and either chitosan film, or biocomposites of chitosan–chitosan nanoparticles and chitosan–chitosan whiskers. Scanning electron microscopy showed the presence of Cr (III) on the surface of chitosan film and chitosan biocomposites. The surface tension of chitosan film and chitosan biocomposites increased after Cr (III) complexation, according to contact angle data. Kinetic studies show that chitosan–chitosan whiskers biocomposite is the best ligand with complexation of 18 % of chromium (III) ions in 60 min.

Characterization of Cr-Curcumin Complex by Differential Pulse Voltammetry and UV-Vis Spectrophotometry

Differential Pulse Voltammetry (DPV) and UV-Vis techniques were used in characterizing the complexation of chromium with curcumin. It was observed that chromium complexed with curcumin in a 1 : 3 ratio. The experimental values that were used to calculate this ratio were independently determined by the two techniques used. The values obtained from each technique agree with each other reasonably well, within limits of experimental error. The stability constant or formation constant, Kf, of the complex, 1.58×1010, was determined using the Lingane equation and Gibb’s free energy of formation was calculated as −58.18 kJ.

Chromium(III) Complexation to Natural Organic Matter: Mechanisms and Modeling

Chromium is a common soil contaminant, and it often exists as chromium(III). However, limited information exists on the coordination chemistry and stability of chromium(III) complexes with natural organic matter (NOM). Here, the complexation of chromium(III) to mor layer material and to Suwannee River Fulvic Acid (SRFA) was investigated using EXAFS spectroscopy and batch experiments. The EXAFS results showed a predominance of monomeric chromium(III)-NOM complexes at low pH (<5), in which only Cr···C and Cr-O-C interactions were observed in the second coordination shell. At pH > 5 there were polynuclear chromium(III)-NOM complexes with Cr···Cr interactions at 2.98 Å and for SRFA also at 3.57 Å, indicating the presence of dimers (soil) and tetramers (SRFA). The complexation of chromium(III) to NOM was intermediate between that of iron(III) and aluminum(III). Chromium(III) complexation was slow at pH < 4: three months or longer were required to reach equilibrium. The results were used to constrain chromium-NOM complexation in the Stockholm Humic Model (SHM): a monomeric complex dominated at pH < 5, whereas a dimeric complex dominated at higher pH. The optimized constant for the monomeric chromium(III) complex was in between those of the iron(III) and aluminum(III) NOM complexes. Our study suggests that chromium(III)-NOM complexes are important for chromium speciation in many environments.

Influence of solution chemistry on Cr(VI) reduction and complexation onto date-pits/tea-waste biomaterials

Tea waste (TW) and Date pits (DP) were investigated for their potential to remove toxic Cr(VI) ions from aqueous solution. Investigations showed that the majority of the bound Cr(VI) ions were reduced to Cr(III) after biosorption at acidic conditions. The electrons for the reduction of Cr(VI) may have been donated from the TW and DP biomasses. The experimental data obtained for Cr(VI)-TW and Cr(VI)-DP at different solution temperatures indicate a multilayer type biosorption, which explains why the Sips isotherm accurately represents the experimental data obtained in this study. The Sips maximum biosorption capacities of Cr(VI) onto TW and DP were 5.768 and 3.199 mmol/g at 333 K, respectively, which is comparatively superior to most other low-cost biomaterials. Fourier transform infrared spectroscopic analysis of the metal loaded biosorbents confirmed the participation of –COOH, –NH2 and O–CH3 groups in the reduction and complexation of chromium. Thermodynamic parameters demonstrated that the biosorption of Cr(VI) onto TW and DP biomass was endothermic, spontaneous and feasible at 303–333 K. The results evidently indicated that tea waste and date pits would be suitable biosorbents for Cr(VI) in wastewater under specific conditions.

Organometallic chemistry of extended periodic π-electron systems: hexahapto-chromium complexes of graphene and single-walled carbon nanotubes

We demonstrate the organometallic hexahapto complexation of chromium with graphene, graphite and carbon nanotubes. All of these extended periodic pi-electron systems exhibit some degree of reactivity toward the reagents CrCO)6 and (eta6-benzene)Cr(CO)3, and we are able to demonstrate the formation of (eta6-rene)Cr(CO)3 or (eta6-arene)2Cr, where arene = single-walled carbon nanotubes (SWNT), exfoliated graphene (XG), epitaxial graphene (EG) and highly-oriented pyrolytic graphite (HOPG). We find that the SWNTs are the least reactive presumably as a result of the effect of curvature on the formation of the hexahapto bond; in the case of HOPG, (eta6-HOPG)Cr(CO)3 was isolated while the exfoliated graphene samples were found to give both (eta6-graphene)2Cr, and (eta6-graphene)Cr(CO)3 structures. We report simple and efficient routes for the mild decomplexation of the graphene-chromium complexes which appears to restore the original pristine graphene state. This study represents the first example of the use of graphene as a ligand and is expected to expand the scope of graphene chemistry in connection with the application of this material in organometallic catalysis.

Feasibility study on the recovery of chromium (III) by polymer enhanced ultrafiltration

The viability of recovering chromium (III) was studied by polymer enhanced ultrafiltration (PEUF) and its application to tannery wastewater treatment. Four polymers with different functional group, molecular weight and acid–basic equilibrium were tested at 40 and 60 °C in order to investigate the complexation and decomplexation of chromium (III) ions on the polymer chains: polyvinyl alcohol (PVA), polyacrylic acid-co-maleic acid (PACM), polyethylenimine (PEI) and ethoxylated polyethylenimine (EPEI). The reversibility of the polymer metal binding was studied by operating in a dead-end PEUF system. The best chromium (III) rejections for both reactions were obtained by EPEI. The feasibility of recovering chromium (III) with EPEI was also studied in a cross-flow PEUF system. Chromium ions were complexed by EPEI chains at pH = 5 and decomplexed at pH = 1. Membrane fouling due to conformational variations of EPEI was observed at high ionic strengths.

Ethylene Oligomerization Using First-Row Transition Metal Complexes Featuring Heterocyclic Variants of Bis(imino)pyridine Ligands

This report examines the replacement of the imine and pyridine functionalities of the ubiquitous bis(imino)pyridine ligand with various heterocycles. The synthesis of a new class of ligand based around thiazole is described; 2,4-bis[1-(arylimino)ethyl]thiazole (aryl = Ph, 1a; Dipp, 1b) and 2,5-bis[1-(arylimino)ethyl]thiazole (aryl = Ph, 1c; Dipp, 1d) have been prepared in good yield and fully characterized. The coordination chemistry of these ligands with chromium, iron, and cobalt is explored, and the potential of these complexes as ethylene oligomerization initiators is assessed. The chromium complex 2a shows an extremely unusual alternating distribution of higher α-olefin products, which has been previously observed on only one occasion. Both series of products, C4n and C4n+2, show Schulz−Flory behavior but with distinctly different k values. The new ligand 2,5-bis[1-(phenylimino)ethyl]-1-methylpyrrole (1e) is reported along with the attempted synthesis of some corresponding iron complexes. The complexation of chromium by 2,5-bis(phenyliminomethyl)thiophene (1f) is also described, and this material was screened for ethylene oligomerization activity, detailed studies indicating that the ligand may be labile under catalytic conditions. A number of other known heterocyclic ligands incorporating pyrazolyl and benzimidazole functionalities have also been explored with iron, and for the first time their potential to facilitate ethylene oligomerization was assessed. All complexes have been tested via activation with MMAO-3A and AlEt3/[Ph3C][Al(OtBuF)4].

Speciation determination of chromium(III) and (VI) using preconcentration cloud point extraction with flame atomic absorption spectrometry (FAAS)

bis-[2-Hydroxy-1-naphthaldehyde] thiourea was synthesized and preconcentration cloud point extraction (CPE) for speciation determination of chromium(III) and (VI) in various environmental samples with flame atomic absorption spectrometry (FAAS) has been developed. Chromium(III) complexes with bis-[2-hydroxynaphthaldehyde] thiourea is subsequently entrapped in the surfactant micelles. After complexation of chromium(III) with reagent, the analyte was quantitatively extracted to the surfactant-rich phase in the non-ionic surfactant Triton X-100 after centrifugation. The effect of pH, concentration of chelating agent, surfactant, equilibration temperature and time on CPE was studied. The relative standard deviation was 2.13% and the limits of detection were around 0.18 μg L −1.

Fluoride Speciation in Stainless Steel Pickling Liquor

Mixtures of hydrofluoric and nitric acids are used in the pickling of stainless steels, in order to remove oxide scale, generating pickling waste liquors with high HF concentration. Species appearing in this mixed acid solution are fluoride-metal complexes with high stabilization constants. This work discusses about the modelling of equilibrium reactions that could take place, like complexation of iron and chromium. As observed in the literature, 31 species could be present in pickling liquor with 25 equilibrium reactions. Activity coefficients are calculated using Bromley's methodology that depends on cation–anion interaction parameter B. New parameters at 25°C have been calculated, using Nelder and Mead Simplex Algorithm. The new model shows that FeF3, CrF2+ and Ni2+ are the main metallic forms in the solution and undissociated hydrofluoric acid has a high relative concentration, while free fluoride practically does not exist in solution. In neutralization processes, free fluoride is released from undisocciated hydrofluoric acid. Therefore, high fluoride complexes are formed, which could precipitate instead of metal hydroxides.

Complexation of Chromium, Aluminum, and Iron Ions with Monocarboxy Cellulose

Complexation of iron(III), aluminum(III), and chromium(III) cations with monocarboxy cellulose was studied by potentiometric titration and IR spectroscopy. The composition and stability constants of the complexes were determined.

Study of the Complexation, Adsorption and Electrode Reaction Mechanisms of Chromium(VI) and (III) with DTPA Under Adsorptive Stripping Voltammetric Conditions

AbstractThe complexation of Cr(III) and Cr(VI) with diethylenetriaminepentaacetic acid (DTPA), the redox behavior of these complexes and their adsorption on the mercury electrode surface were investigated by a combination of electrochemical techniques and UV/vis spectroscopy. A homogenous two‐step reaction was observed when mixing Cr(III), present as hexaquo complex, with DTPA. The first reaction product, the electroactive 1 : 1 complex, turns into an electroinactive form in the second step. The results indicate that the second reaction product is presumably a 1 : 2 Cr(III)/DTPA complex. The electroreduction of the DTPA‐Cr(III) complex to Cr(II) was found to be diffusion rather than adsorption controlled.The Cr(III) ion, generated in‐situ from Cr(VI) at the mercury electrode at about −50 mV (vs. Ag|AgCl) (3 mol L−1 KCl), was found to form instantly an electroactive and adsorbable complex with DTPA. By means of electrocapillary measurements its surface activity was shown to be 30 times higher than that of the complex built by homogenous reaction of DTPA with the hydrated Cr(III). Both components, DTPA and the in‐situ built complex Cr(III) ion were found to adsorb on the mercury electrode.The effect of nitrate, used as catalytic oxidant in the voltammetric determination method, on the complexation reaction and on the adsorption processes was found to be negligible.The proposed complex structures and an overall reaction scheme are shown.

Synthesis and Physicochemical Properties of Some Transition Metal Complexes with 3-Hydroxypyridine

The complexes ML2 · 2H2O and CrL3 · 8H2O were synthesized by the reaction of Cu(II), Ni(II), Co(II), Cd(II), and Cr(III) nitrates with 3-hydroxypyridine (HL) and identified. The spectroscopic characteristics of neutral, anionic, and cationic forms of the ligand were determined. It was shown that 3-hydroxypyridine enters the complex as an anion to give polymeric chains due to the ligand coordination through the N and O atoms. Complexation of copper, cobalt, and chromium nitrates with 3-hydroxypyridine in ethanol solutions was studied, and the formation constant of the copper complex was calculated. It was found that Cu(II) and Cr(III) complexes are formed in the solid state and in solutions (M : L = 1 : 2 and 1 : 3, respectively; in the case of Cu(II), the M : L ratio is 1 : 3).

Spectrophotometric study of the complexation and extraction of chromium(VI) with cyanine dyes

Solvent extraction of chromium(VI) ion associates with symmetric cyanine dyes including the heterocyclic radicals of 1,3,3-trimethyl-3 N-indoline, benzooxazol, benzothiazol and quinoline has been studied by means of spectrophotometric method. In the acidic medium in the presence of chloride ions, extractable by aromatic hydrocarbons and esters of acetic acids, chromium(VI) ion associates are formed. The molar absorptivities of ion associates are 2.5–3.6×10 5 l mol −1 cm −1 in dependence on extractant and dye. The absorbance of the coloured extracts obeys the Beer's law in the range 0.01–2.1 mg l −1. The extraction of chromium is the highest during extraction from the sulphuric acid medium in the range 0.05–03 M H 2SO 4. It was found that the Cr(VI):Cl:R molar ratio is 1:1:1. A novel procedure of chromium(VI) extraction and spectrophotometric determination in various types of soils and sewage doped with chromium(VI) was examined.