Complex Formation Reactions Research Articles

Terpyridine-containing 5-(2-pyridylmethylene)-2-thioimidazolones and their coordination compounds with copper(II) chloride: synthesis and cytotoxicity

Methods for the synthesis of new ditopic organic ligands containing coordinating fragments of two types, terpyridine and thiohydantoin, have been developed. The synthesized ligands were studied in complex formation reactions with copper(II) chloride. As a result, two types of coordination compounds were isolated and characterized by electron spectroscopy, elemental analysis, and cyclic voltammetry: bis-ligand tetranuclear mixed-valent complexes of copper(I, II) and a monoligand binuclear complex containing two copper(II) ions. The cytotoxic activity of the obtained coordination compounds with respect to the MCF7, A549, and HEK293 cell lines was studied.

Complexes of 1,10-phenanthroline-mono-N-oxides with copper(II) and nickel(II) in aqueous solution and solid phase

Thorough equilibrium and spectroscopic studies are reported on the complexes formed between copper(II) or nickel(II) and derivatives of phenanthroline-mono-N-oxides (1,10-phenanthroline-1-N-oxide (phenO), 2,9-dimethyl-1,10-phenanthroline-1-N-oxide (DMPO) and 3,4,7,8-tetramethyl-1,10-phenanthroline-1-N-oxide (TMPO)). PhenO exhibits excellent metal binding ability, both copper(II) and nickel(II) form bis complexes in which the ligands coordinate to the metal ions via the (N,O) donor set. In the case of copper(II), a square-pyramidal complex forms, where the phenO-s coordinate at the corners of the square and the remaining site is occupied by the water molecule. The bis complex formed between nickel(II) and phenO possesses square-planar geometry in solution, however, the Ni(II) ion exhibits a distorted octahedral geometry in solid phase. DMPO forms relatively stable complexes with copper(II), but the coordination of this ligand to nickel(II) could not be confirmed. Because of precipitate formation in the entire studied pH range (pH = 2.0 – 11.0), well defined complexes could not be identified in the copper(II) – TMPO system. In contrast, this ligand forms stable water soluble nickel(II) complexes. The noted selectivity of these ligands in complex formation reactions is explained by considering the plasticity of copper(II), the rigid, square-planar geometry of nickel(II) and the enhanced steric repulsion of the methyl substituents of DMPO.

Peroxymonosulfate activation by a bimetallic catalyst with Fe nanoclusters and Co single-atoms on C3N4 (FeNCCoSA-C3N4) for oxidation of organic pollutants via radical and nonradical pathways

Catalysts with metal nanocluster and single-atom sites have been used extensively to activate persulfate to remove recalcitrant pollutants while the bimetallic catalyst remains limited researches. Here, a bimetallic C3N4 catalyst with relatively high Fe nanocluster and single-atom Co loadings (7.6% and 3.7%, respectively) (FeNCCoSA-C3N4) was successfully synthesized. FeNCCoSA-C3N4 showed a synergistic coefficient of 7.8 relative to Fe-C3N4 and Co-C3N4 for degrading paracetamol, remarkedly outperforming the counterpart monometallic heterogeneous catalysts, metal ions homogeneous catalyst, or previously reported catalysts in terms of peroxymonosulfate (PMS) activation and paracetamol mitigation. The FeNCCoSA-C3N4/PMS complex contributed to > 60% of paracetamol degradation, whereas radical species and high-valent metal-oxo species contributed 13.3%–15.6% of paracetamol degradation. FeNCCoSA-C3N4/PMS preferentially oxidizes organic pollutants containing electron-donating moieties but may be negatively affected by inorganic carbon and chloride ions. Synthesizing the bimetallic cluster/atom catalyst offers a new way of achieving efficient PMS activation and pollutant oxidation via catalyst/PMS complex formation and electron-transfer reactions.

Silicas with Polyoxyethylene Branches for Modification of Membranes Based on Microporous Block Copolymers.

We have synthesized cubic and linear polysiloxanes containing polyoxyethylene branches (ASiP-Cu) using tetraethoxysilane, polyoxyethylene glycol, and copper chloride as precursors; the products are stable to self-condensation. The effect of copper chloride content on the chemical structure of ASiP-Cu has been established. A special study was aimed at defining the modifying effect of ASiP-Cu on the sorption characteristics of membranes based on microporous, optically transparent block copolymers (OBCs). These OBCs were produced using 2,4-toluene diisocyanate and block copolymers of ethylene and propylene oxides. The study demonstrated significantly increased sorption capacity of the modified polymers. On the basis of the modified microporous block copolymers and 1-(2-pyridylazo)-2-naphthol (PAN) analytical reagent, an analytical test system has been developed. Additionally, the modified OBCs have the benefit of high diffusion permeability for molecules of organic dyes and metal ions. It has been shown that the volume of voids and structural features of their internal cavities contribute to the complex formation reaction involving PAN and copper chloride.

Impedance data as a possible basis for finding stability constants of cucurbituril complexes with inorganic cations

An analysis of the array of impedance data for the interface the Hg-electrode/salt solutions of macrocyclic cavitands of the cucurbituril family containing their supramolecular cationic complexes was performed. A significant change in the properties of the adsorption layer was established with a change in the charge of the electrode surface and the concentrations of the components of the complex formation reaction. The existence of two types of adsorption layer was found, one of which (with positive charges on the electrode surface) is formed with the participation of neutral cavitand molecules. The high sensitivity of the impedance data to the presence of these molecules in solution made it possible to establish the corresponding quantitative dependences for systems with known values of the stability constants of cationic complexes. It is shown that these data can be used to find previously unknown stability constants of cationic complexes of a given cavitand formed in other similar salt systems. The applicability of the proposed method was demonstrated using impedance data for systems with known stability constants of cationic complexes (cucurbit[6]uril + Me2 SO4, Me+ = K+, Na+).

Direct electron transfer kinetics of histamine dehydrogenase at air plasma-treated graphite nanofibers

As histamine is one of the important mediators for allergic reactions, its efficient detection methods and real-time monitoring systems are required for food analyses and drug discoveries to suppress allergic reactions. Although histamine dehydrogenase (HmDH) is a promising candidate for developing enzyme-based electrochemical biosensors, some electron mediators are frequently employed to observe electrocatalytic currents for histamine oxidation. Here, direct electrochemistry of HmDH was studied at the surface of graphite nanofibers (GNFs), which provide active reaction sites for redox species. Air plasma-treated GNFs were used for constructing a three-dimensional network that works both as an electrical nanowire and an enzyme support. Even though the amount of oxygen-containing functional groups didn’t significantly increase at the GNF surface with increase in the air plasma treatment time, direct electron transfer from reduced HmDH by histamine to the GNFs was improved probably due to capped and curvature of the graphite edge sites with oxygen-containing functional groups, which were generated by the air plasma treatment. The air plasma-treated GNFs also allowed enhancement of the complex-formation reaction rate of HmDH with histamine, as the air plasma treatment time increased.

PH-metric titration technique for the study of metal-complexes of substituted 2- Oxo-2H-Chromene-3-Carbohydrazide derivatives in solution: calculation of stability constants

Background: In coordination chemistry, the stability of complexes is expressed in terms of the formation constant of complexes. In coordination complexes, the temperature is very important. It plays an important role in complex formation reaction. Temperature affects metal-ligand stability constant (log K) and proton-ligand stability constant (pK). The metal ion Mn2+, Co2+, Ni2+, and Cu2+ at different temperatures form complexes with 4-sulfamethoxazoleazo-3-methyl-2-pyrazolin-5-one are reported. The metal-ligand stability constant (logK) and proton-ligand stability constant (pK) of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) with organic ligand n-[2-hydroxy-1-napthalydene]-2-methylanilline at 0.1 M ionic strength in 60% dioxane-water medium is studied. The study of thermodynamic parameters and stability constant of complexes of substituted thiazole Schiff bases with rare earth metal ions in mixed solvent is reported. Objective: The study of coordination compounds and a lot of work has been done on metal-ligand stability constant. The same transition metal ion form complexes with substituted pyrazole for this metal-ligand stability constant are determined. Method: Pointwise Calculation Method Half Integral Method. Result: The values of logK1 and logK2 are determined from the metal-ligand formation curve at formation numbers 0.5 and 1.5. In all cases, logK1 is greater than logK2. The ratio logK1/logK2 is positive and greater than one in all systems. This implies that there is little or no steric hindrance to the addition of the secondary ligand molecules. The difference between logK1 - logK2 is usually positive. If the difference between logK1 and logK2 is less than 2.5, simultaneous formation of 1:1 and 1:2 complexes occurs and if it is more than 2.5, then stepwise complex formation occurs. In the present case, in all systems, it is less than 2.5. This indicates the simultaneous formation of 1:1 and 1:2 complexes takes place. Conclusion: A pH-metric study of Substituted 2-oxo-2H-chromene-3-carbohydrazide derivatives with metal ions Fe(III), and Mn(II) occurs. The graphical representation of the curve shows that the acid + ligand curve is separated from the corresponding acid + ligand + metal curve in this system. The formation of a complex is indicated. Half integral method and pointwise calculation method give nearly similar results. The values of stability constants for all systems indicate that the complexes formed in these processes are stable.

Complex formation of halogen substituted tetraphenylporphyrins and Cd(II)-tetraphenylporphyrins with MnCl2 in DMF

Reactions of complex formation of 5,10,15,20-tetra-(2,6-dichlorophenyl)porphyrin, 5,10,15,20-tetra-(2,6-difluorophenyl)porphyrin and metal exchange of their cadmium complexes with manganese chloride(II) in dimethylformamide were investigated. ortho -Substituted manganese complexes were synthesized by prolonged refluxing of the corresponding porphyrins with an excess of MnCl2 in dimethylformamide. Using the metal exchange reaction of Cd(II)-5,10,15,20-tetra-(2,6-dichlorophenyl)porphyrin and Cd(II)-5,10,15,20-tetra-(2,6-difluorophenyl) porphyrin, the corresponding Mn(III)-tetraphenylporphyrins were obtained. On the contrary, the coordination reactions of porphyrins substituted at the pyrrole and phenyl rings with manganese chloride in dimethylformamide proceed under mild conditions with the formation of complexes Mn(II)-2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetra-(2,6-dichlorophenyl)porphyrin [the compound oxidizes in air to a mixture of Mn(II) and Mn(III)-porphyrins] and Mn(II)-2,3,7,8,12,13,17,18-octachloro-5,10,15,20-tetra-(2,6-difluorophenyl)porphyrin. The synthesized compounds were identified using UV-Vis, 1H NMR spectroscopy and mass-spectrometry. Metal exchange reaction of ortho -substituted Cd(II)-porphyrins and complex formation of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetra-(2,6-dichlorophenyl)porphyrin with manganese chloride in dimethylformamide were studied by the spectrophotometric method. The kinetic parameters of the reactions were calculated. A strong effect of β- and ortho -substitution on the reactions of complex formation and metal exchange of the studied compounds was found.

C-C Bond Formation Reaction Catalyzed by a Lithium Atom: Benzene-to-Biphenyl Coupling.

Transition-metal-catalyzed carbon-carbon (C-C) bond formation is an important reaction in pharmaceutical and organic chemistry. However, the reaction process is composed of multiple steps and is expensive owing to the presence of transition metals. This study proposes a lithium-catalyzed C-C coupling reaction of two benzene molecules (Bz) to form a biphenyl molecule, which is a transition-metal-free reaction, based on ab initio and direct ab initio molecular dynamics (AIMD) calculations. The static ab initio calculations indicate that the reaction of two Bz molecules with Li- ions (reactant state, RC) can form a stable sandwiched complex (precomplex), where the Li- ion is sandwiched by two Bz molecules. The complex formation reaction can be expressed as 2Bz + Li - → Bz(Li -)Bz, where the C-C distance between the Bz rings is 2.449 Å. This complex moves to the transition state (TS) via the structural deformation of Bz(Li-)Bz, where the C-C distance is shortened to 2.118 Å. The barrier height was calculated to be -9.9 kcal/mol (relative to RC) at the MP2/6-311++G(d,p) level. After TS, the C(sp3)-C(sp3) single bond was completely formed between the Bz rings (the C-C bond distance was 1.635 Å) (late complex). After the dissociation of H2 from the late complex, a biphenyl molecule was formed: the C(sp2)-C(sp2) bond. The calculations suggest that the C-C bond coupling of Bz occurred spontaneously from 2Bz + Li-, and biphenyl molecules were directly formed without an activation barrier. Direct AIMD calculations show that the C-C coupling reaction also takes place under electron attachment to Li(Bz)2: Li(Bz)2 + e- → [Li-(Bz)2]ver → precomplex → TS → late complex, where [Li-(Bz)2]ver is the vertical electron capture species of Li(Bz)2. Namely, the C-C coupling reaction spontaneously occurred in Li(Bz)2 owing to electron attachment. Similar C-C coupling reactions were also observed for halogen-substituted benzene molecules (Bz-X, X = F and Cl). Furthermore, this study discusses the mechanism of C-C bond formation in electron capture based on the theoretical results.

COMPLEX FORMATION OF GOLD (I) WITH 2-METHYLIMIDAZOLE

The complex formation process of Au (I) with 2-methylimidazole was studied by potentiometric titration. When 2-methylimidazole is added to the [AuCl2]-/Au system, the potential gradually decreases without any jumps. The nonlinearity of the dependence of E on –lg[2MI] indicates the stepwise nature of the complex formation between [AuCl2]- and 2-methylimidazole. The general and thermodynamic stability constants of the complexes were determined in the temperature range of 278-318 K (at T=298 K, lgβ0[AuСl(Н2МИ)]+=13.84±0.03; lgβ10[Au2МИCl]=5.38±0.05; lgβ20[Au(2МИ)2]+=10.60±0.03). The reliability of the determination of the constants is proved by the satisfactory agreement between the experimentally found values of the potentials (Eex.) with theoretical ones (Etheor.). As the temperature increases, the stability of the complexes increases. A change in the ionic strength of the solution has little effect on the stability of the complexes. Comparison of the process of complexation of gold (I) and gold (III) with 2-methylimidazole shows that the stability of the complexes of trivalent gold is superior to similar complexes of gold (I). The thermodynamic functions of the complex formation reaction were calculated by the temperature coefficient method. In this case, the value of ΔrН0 was determined from the tangent of the slope of the direct dependence lgβ0=f(1/T), and the value of ΔrS0 was determined from the segment cut off by this straight line on the y-axis. The change in the isobaric-isothermal potential was calculated by the equation ΔrG0= ΔrН0-TΔrS0. The substitution of chloride ions for a 2MI molecule is accompanied by a positive change in ΔН, which has a negative contribution to the spontaneous course of reactions. For the [AuCl2]- - 2MI system, the number of particles participating in the reaction remains unchanged and the positive change in ΔS is most likely due to the release of water molecules from the hydration shell of the initial substances and reaction products.

Development and Validation of New Spectrophotometric Methods for the Quantitative Estimation of Naftopidil in Bulk and Pharmaceutical Formulation

Four simple, sensitive, precise and accurate spectrophotometric methods A, B, C and D have been developed for the quantitative estimation of Naftopidil. UV method (A) has been developed by using alcohol as the solvent. The wavelength of maximum absorbance selected was 269nm. The method was linear between the range of 2-10g/ml with correlation coefficient of 0.9999. %RSD of precision was calculated and found to be 0.965. Colorimetric Methods B, C and D have been developed by oxidation followed by complex formation reaction using 1,10- phenanthroline, 2,2’- bipyridyl and Potassium ferricyanide respectively, using ferric chloride as oxidizing agent. Regression analysis for the methods was carried out and the correlation coefficient was found to be between the range of 0.99969-0.9999 depicting very good linear relationship between the concentration of the drug and corresponding absorbance values. % RSD of precision for the three colorimetric methods was calculated and found between the range of 0.4126-1.1354 showing that the methods are precise. Accuracy studies were carried out at three different levels and the results fall between the range of 99.89 to 99.96.

Liquid Dynamics Determine Transition Metal-N-Heterocyclic Carbene Complex Formation.

The mechanism of metal-N-heterocyclic carbene (NHC) complex formation from imidazolium salts in the presence of weak bases was investigated through theoretical methods. Quantum chemical calculations revealed that the two bases considered here, sodium acetate and trimethylamine, both facilitate complex formation. In contrast to previous experiments, these calculations indicated a slightly lower barrier with the amine. Molecular dynamics simulations showed that the ionic nature of the [AuCl2 ]- and imidazolium ions, as well as the sodium acetate base keep these species associated in the reaction mixture through ion pairing. This pre-association of the components produces those clusters that are essential for the metal complex formation reaction. The neutral amine, however, remains mostly separated from the other reaction partners, making it a significantly less effective base.

Complex formation of molybdenum (V) with 1-phenyl-2,3-dimethylpyrazoline-5-thion in 4 mol/L HCI medium at 273-338 K

The process of complexation of molybdenum (V) with 1-phenyl-2,3-dimethylpyrazolin-5-thione in a 4 mol/l HCI medium in the temperature range 273-338 K was studied by the potentiometric method. It has been shown that the reduced form of the 1-phenyl-2,3-dimethylpyrazolin-5-thione molecule is involved in the complex formation reaction. Using the data of potentiometric studies, the change in the energy value (ΔE) of the (NH4)2[MoOCI5]2-1-phenyl-2,3-dimethylpyrazolin-5-thione-4 mol/l HCl system, the equilibrium concentrations of 1-phenyl-2,3-dimethylpyrazolin-5-thione, formation function values, step and general stability constants of oxochloro-1-phenyl-2,3-dimethylpyrazolin-5-thione complexes of molybdenum (V) formed in HCl solutions in the temperature range 273-338 K. The stability constants of oxochloro-1-phenyl-2,3-dimethylpyrazolin-5-thione complexes of molybdenum (V) were refined using the Bjerrum graphical method. The temperature coefficient method was used to estimate the thermodynamic functions of complex formation processes in the (NH4)2[MoOCI5]-1-phenyl-2,3-dimethylpyrazolin-5-thione - 4 mol/L HCI system. The domains of dominance and the maximum yield of each complex form are found. It has been established that in the studied system (NH4)2[MoOCI5]-1-phenyl-2,3-dimethylpyrazolin-5-thione - 4 mol/l HCI during the interaction of the MoO3+ ion with 1-phenyl-2,3-dimethylpyrazolin- 5-thione in the entire temperature range of the experiment forms 5 mononuclear coordination compounds containing from one to five coordinated molecules of the organic ligand. It was found that with increasing temperature, the values of the general stability constants of coordination compounds decrease, which confirms the exothermicity of the reaction of formation of oxochloro-1-phenyl-2,3-dimethylpyrazoline-5-thione compounds of molybdenum (V). The experimentally found values of enthalpy made it possible to assume that the reaction of complex formation between the MoO3+ ion and the molecules of nitrogen- and sulfur-containing heterocyclic 1-phenyl-2,3-dimethylpyrazolin-5-thione proceeded exothermically spontaneously. Based on the above equations, all calculations were carried out using a computer in the Excel programming language, Borland Delphi, Windows 7 operating system.

Разработка спектрофотометрической методики определения ионов меди (II) с N-бензилоил-N'-(фенилсульфонил)гидразином

The results of studying the processes of complex formation of N-benzyloyl-N'-(phenylsulfonyl)hydrazine (BPSH) with Cu(II) ions in ammonia media are presented. The complex formation reaction was studied by spectrophotometric method. The maximum light absorption of the studied complex compound was determined. The optimal conditions for the complex formation of BFSH with Cu(II) ions were studied: the time for the development of the color of the complex; pH range of complex formation, amount of photometric reagent. The optimal ratios [Cu(II)]:[BFSH]=2:1 and 1:1 were determined by the saturation method. Under optimal conditions, a calibration curve was constructed for the determination of Cu(II) ions with BFSH in an ammonia medium. Methods of mathematical statistics determined the convergence and correctness of the spectrophotometric method of determination. Approbation of the technique was carried out on the product of flotation enrichment of sulfide copper-nickel ore of the Murmansk deposit.

Evaluation of Selectivity of Rare Earth Metals by Hexane-1,6-diyl bis(4,4,4-trifluoro-3-oxobutanoate)

Using hexane-1,6-diyl bis (4,4,4-trifluoro-3-oxobutanoate) (H2hdfob), the mechanism for extracting rare earth metal ions to the organic phase was evaluated. From slope analysis, it was clarified that one divalent metal hydroxide ion reacts with two H2hdfob where one of the protons is dissociated from each ligand. Such a complexation formed the 1 : 2 metal–ligand neutral complex. Such a complex formation reaction is very similar to that of Co2+ or Ni2+, which form a 1 : 1 metal–ligand neutral complex.

Галогенидные комплексы циркония. Синтез, строение, возможности практического применения

Obtaining methods, some reactions, and structural features of zirconium halide complexes, as well as examples of their possible applications have been systematized and described, based on the analysis of the literature published mainly from 2018 until 2021. In discussion of the synthetic methods the main attention is focused on the most effective approaches for preparing such compounds. Reactions of zirconium complex formation are studied. Information about biological and catalytic activity of some zirconium derivatives is given.

Development of Quality Control Parameters for Standardization of Herb of the Cultivated Plant <i>Alchemilla mollis</i> (Buser) Rothm.

Introduction. Alchemilla herb is proposed for introduction into pharmaceutical practice, for obtaining extracts with various pharmacological activity. To expand, resource base of Alchemilla it has been proposed to use a high biomass cultivated plant – Alchemilla mollis (Buuser) Rothm. In terms of qualitative and quantitative characteristics of the chemical composition Alchemilla mollis herb is comparable to the samples of raw materials of wild-growing Alchemilla. The presence of chemotaxonomic features necessitates the preparation of regulatory documentation for the introduction of this plant as a source of medicinal raw materials.Aim. Development of a methodology for assessing the main group of biologically active substances and the quantitative determination of flavonoids in Alchemilla mollis herb.Materials and methods. As objects of study, we used Alchemilla mollis herb harvested from plants cultivated in the Perm Krai. The chromatographic parameters of raw material authenticity were determined by thin layer chromatography (TLC). To develop the parameters for the quantitative determination of flavonoids in Alchemilla mollis herb, a modification of the method proposed for Alchemilla herb was carried out.Results and discussion. During chromatographic study of Alchemilla mollis herb were identified cinaroside, rutin, and quercetin. Cynaroside was referred to the marker substances. Ethyl acetate : acetic acid (85 : 15) was chosen as the optimal chromatographic system. A modification and validation of the method for the quantitative determination of flavonoids in Alchemilla herb was carried out. The change of the extractant, particle size, time and frequency of extraction for sample preparation and the optimal use of cynaroside as a standard substance are substantiated. The optimal conditions for the reaction of complex formation with aluminum chloride are established.Conclusion. To determine the authenticity of Alchemilla mollis herb, it was proposed to use the identification of cynaroside by TLC. The modified method for the quantitative determination of flavonoids in terms of cynaroside for the Alchemilla mollis herb, reproducible, correct and can be used for standardization. When testing the methodology on samples of raw materials harvested in the Perm region, a range of values for the content of flavonoids was 3.14–4.84 %, with an average level of variability.

Synthesis and application of a thiol functionalized clay for borewell water purification: Microchemical characteristics and adsorption studies

This study was conducted to ascertain the effect of heavy metals on the general quality of borewell water in a municipality near Kollam District, Kerala state, India. Red-water iron contamination in borewell water has been a major concern for many years that has not been fully resolved. This research introduces an innovative, reliable, and efficient organoclay scavenger for the adsorptive removal of Fe(III) ions from watersheds, by grafting MBO onto Na-MMT clay (MBO/Na-MMT), which was produced via one-pot oxidation reaction using H2O2 to introduce the active functional groups, like the -SOH group, onto the montmorillonite clay. This special alteration of this material improved Na-MMT’s capacity to adsorb ferric ions. To evaluate the material's characteristics, X-ray diffraction, SEM-EDS, FTIR, CHNS, TG, and Zeta potential were used. Batch adsorption tests with different solution pH, Fe(III) ion concentrations, agitation periods, adsorbent dose and temperatures were conducted in order to optimise the adsorption procedure. The MBO/Na-MMT exceeded several of the reported adsorbent materials in the literature with an impressive adsorption capacity of 83.33 mg/g and efficiency (97.9%), which was accomplished by spontaneous complexation reaction. Fe(III) spontaneously attached to MBO/Na-MMT by a complex formation reaction mechanism with PSO kinetics and the variability of the adsorption process was highlighted by Elovich kinetic model because of heterogeneity of the surface. The adsorbent material demonstrated a remarkable capability for regeneration, ensuring the material's stability and reusability.

EXTRACTION AND ATOMIC-ABSORPTION DETERMINATION OF TUNGSTEN (VI) WITH 2-HYDROXY-5-T-BUTYLPHENOL-4'-NITROAZOBENZENE

The complexation of tungsten (VI) with an azo compound synthesized from para-tret-butylphenol (2-hydroxy-5-Tr-butylphenol-4-nitro-asobenzene) has been studied spectrophoto¬metrically. The optimum pH values of the solution are 2.0-3.0. The maximum light absorption of the complexes in n-butanol is in the range 460-470nm, and that of the reagent at 360-370; complex formation is accompanied by a bathochromic shift. The spectrophotometric characteristics of the complex have been calculated and the composition of the complex was determined by various methods. Using the equilibrium shift and isomolar series methods it has been found that the W:R ratio is 1:2. By the Sommer method it has been found that during complex formation one proton is released from each reagent molecule. The complex stability constant βk = 9.04·108 and the complex formation reaction equilibrium constant (4.2·104) have been calculated by the method of Komar. The molar absorption coefficient is (3.44.2).104. The graduation diagram is linear at a tungsten concentration of 1.0-10 µg/ml, n-butanol has been used as an extractant. A single extraction with n-butanol 97% of tungsten as a complex is extracted. Methods of extraction-atomic-absorption and extraction-photometric determination of tungsten have been developed and the influence of a number of extraneous ions on the determination of tungsten has been revealed. The correctness of the results obtained has been controlled by analysing the State Standard Alloy Reference Materials

Pocket test for instantaneous quantification of starch adulterant in milk using a counterfeit banknote detection pen

This work presents a paper-based analytical device for instantaneous detection of adulterant starch in commercial milk. A highly efficient strategy was based on the well-established starch/iodine complex formation reaction by using a commercial counterfeit detection pen (CDP). Employing the CDP as a user-friendly and reagent-free approach to modify confined regions of a paper substrate readily promotes the reaction with starch in milk. The resulting color change can be analyzed by a digital scanner or via portable smartphone cameras. The proposed device provided a linear behavior in the concentration range between 0.05 and 1 %, with limits of detection and quantification equal to 0.05 % and 0.17 %, respectively. The sensor shows a very stable readout for many interferents, except for sodium hydroxide at higher concentrations (>1.0 %). Recovery tests performed at different concentration levels yielded values from 96.2 to 116.8 %, demonstrating its potential for quantitative analysis.