Solution equilibria and stability of the complexes of pyridinecarboxylic acids: Complexation reaction of mercury(II) with 2-hydroxynicotinic acid

Summary The solution equilibria of 2-hydroxynicotinic acid (hyna) complexes with mercury(II) have been studied spectrophotometrically in 50% (v/v) ethanol at 20°C and an ionic strength of 0.1mol dm^–3 (NaClO₄). Three mercuric complexes are formed in solution in dependence on the acidity of the medium. The basic characteristics of the different complexes are determined and the analytical aspects of the complexation reaction are demonstrated. A critical investigation has also been presented of the solution equilibria and stability of the mixed complex of mercury(II) withhyna and thiosalicylic acid (tsa). The various complex transitions leading to the formation of the 1 : 1 : 1 Hg(tsa)(hyna) ternary complex in solution are investigated. The non-charged mono-ligand complex Hg(hyna) is used for UV-spectrophotometric determination of mercury atpH 4.5–5 (_max=325nm, =0.8·10⁴lmol^–1cm^–1). The system obeyed Beer's law up to 36.1 µg ml^–1 of Hg(II). The optimum concentration range (Ringbom) is between 6 and 28.5µg ml^–1. Interference caused by a number of ions was masked by the addition of fluoride ions.

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Lösungsgleichgewichte und Stabilitätskonstanten von Komplexen der Pyridincarbonsäuren: Die Komplexierungsreaktion von Quecksilber(II) mit 2-Hydroxynikotinsäure

Zusammenfassung Die Lösungsgleichgewichte von 2-Hydroxynikotinsäure (hyna) mit Hg(II) wurde spektrophotometrisch in 50% (v/v) Ethanol bei 20°C und einer Ionenstärke von 0.1 mol dm^–3 (NaClO₄) untersucht. In Abhängigkeit von der Acidität des Mediums werden drei Quecksilberkomplexe gebildet. Die grundlegenden Charakteristika der Komplexe wurden bestimmt und die analytischen Aspekte aufgezeigt. Die gemischten Komplexe von Hg(II) mithyna und Thiosalicylsäure (tsa), insbesondere die verschiedenen Komplexübergänge zum ternären 1 : 1 : 1 Hg(tsa)(hyna)-Komplex, wurden ebenfalls untersucht. Der ungeladene Monoligandenkomplex Hg(hyna) kann beipH 4.5–5 zur UV-spektroskopischen Quecksilberbestimmung eingesetzt werden (_max=325nm, =0.8·10⁴lmol^–1cm^–1). Das System gehorcht bis zu einer Hg(II)-Konzentration von 36.1µgml^–1 dem Beerschen Gesetz. Der optimale Konzentrationsbereich (Ringbom) liegt zwischen 6 und 28.5µgml^–1. Interferenzen mit einer Reihe anderer Ionen konnten durch Maskierung mit Fluoridionen umgangen werden.

     

Spectrophotometric determination of ascorbic acid using copper(II)-neocuproine reagent in beverages and pharmaceuticals

The proposed method for ascorbic acid (Vitamin C) (AA) determination is based on the oxidation of AA to dehydroascorbic acid with a Cu(II)-2,9-dimethyl-1,10-phenanthroline (neocuproine (Nc)) reagent in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450 nm. This chelate was formed immediately and the apparent molar absorptivity for AA was found to be 1.60 × 10⁴ dm³ mol⁻¹ cm⁻¹. Beer's law was obeyed between 8.0 × 10⁻⁶ and 8.0 × 10⁻⁵ M concentration range. The relative standard deviation for 90 μg AA was 3%. The Cu(II)-Nc reagent is a milder and therefore more selective oxidant than the conventional Fe(III)-1,10-phenanthroline (phen) reagent used for the same assay. This feature makes the proposed method superior for real samples such as fruit juices containing weak reductants such as citrate, oxalate and tartarate that otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to a number of commercial fruit juices, pharmaceutical preparations containing Vitamin C, and red wine. The meta-bisulfite content of wine was removed with an anion exchanger at pH 3 prior to analysis, and a difference extractive–spectrophotometric method of AA assay in wine was developed so as to suppress the interferences caused by wine anthocyanins and polyphenols. The findings of the developed method for fruit juices and pharmaceuticals were also statistically compared with those of HPLC so as to establish it as a reliable novel method.     

Spectrophotometric study of coproporphyrin-I complexes of copper(II) and cobalt(II)

The reagent 3,8,13,18-tetramethyl-21H,23H-porphine-2,7,12,17-tetrapropionic acid or coproporphyrin-I (CPI) was used for the spectrophotometric determination of copper(II) and cobalt(II) in the presence of pyridine and imidazole catalysts. Optimum conditions were investigated and the methods were applied to the determination of parts per billion levels of copper(II) and cobalt(II). The Sandell sensitivities of the recommended procedures were 0.568 μm cm⁻² and 0.464 μg cm⁻² (for A = 0.001) for copper and cobalt, respectively. The relative standard deviations were 2.0% for copper and 1.0% for cobalt. The kinetics of the reaction of CPI with copper(II) and cobalt(II) in the presence of the catalysts and the influence of the temperature were studied, and their kinetic constants determined.The influence of light on the photodecomposition of CPI was also studied.     

Spectrophotometric investigation of the complexation equilibria of zirconium(IV) withlawsone and determination of zirconium

Summary The complexation equilibria of zirconium(IV) withlawsone (2-hydroxy-1,4-naphthoquinone) have been studied spectrophotometrically in 40% (v/v) ethanol at 20°C and at an ionic strength of 0.1M (NaClO₄). A complete picture of the solution equilibria in thepH range 1.5–4.0 is presented. The absorbance vs.pH graphs were analyzed to characterize the complexation equilibria in solution. A simple, rapid, selective, and sensitive method for the spectrophotometric determination of zirconium is proposed based on the formation of Zr(lawsone)₂ atpH 3.3(_max=450 nm, =1.13×10⁴l · mol^–1 · cm^–1). The interference caused by a number of ions can be masked by the addition of cyanide. The method has been applied to the determination of zirconium in some synthetic samples.

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Spektrophotometrische Untersuchung der Komplexierungsgleichgewichte von Zirkonium(IV) mitLawsone und Bestimmung von Zirkonium

Zusammenfassung Die Komplexierungsgleichgewichte von Zirkonium(IV) mitLawsone (2-Hydroxy-1,4-naphthochinon) wurden spektrophotometrisch in 40%igem Ethanol (v/v) bei 20°C und einer Ionenstärke von 0.1M (NaClO₄) untersucht. Ein vollständiges Bild der Gleichgewichte in Lösung impH-Bereich von 1.5 bis 4.0 wird präsentiert. Die Extinktions-pH-Kurven wurden analysiert, um die Komplexierungsgleichgewichte in Lösung zu charakterisieren. Eine einfache, schnelle, selektive und empfindliche Methode zur spektrophotometrischen Zirkoniumbestimmung auf der Basis der Bildung des Zr (lawsone)₂-Komplexes beipH=3.3(_max=450 nm, =1.13×10⁴l · mol · cm^–1) wird vorgestellt. Eine Anzahl störender Ionen kann durch Zugabe von Cyanid maskiert werden. Die Methode wurde zur Zirkoniumbestimmung in einigen synthetischen Proben eingesetzt.

     

Spectrophotometric determination of molybdenum based on charge transfer complexes sensitized by copper(II)

A new high sensitive spectrophotometric determination of trace molybdenum was investigated. The sensitivity of the determination of molybdenum, which based on the color charge transfer complex of molybdotungstophosphate-3,3′,5,5′-tetramethylbenzidine, was greatly enhanced by copper(II) ions in the presence of polyvinyl alcohol. The improved method maintained the features of simplicity, rapidity and selectivity, especially eliminating the interference from tungsten. Under the optimum conditions, Beer's law was obeyed over the range from 2 to 32 ng ml⁻¹ molybdenum with molar absorptivity being 4.92×10⁵ l mol⁻¹ cm⁻¹ at 660 nm. The relative standard deviation was 1.2% under nine determinations for 16 ng ml⁻¹ Mo(VI). The present method had been applied to the determination of trace molybdenum in tungsten ores with satisfactory results.     

Spectrophotometric determination of the soil fumigant: dazomet with copper(II)-neocuproine reagent

A spectrophotometric method has been developed for the assay of dazomet, a soil fumigant effective for the control of nematodes, germinating weeds and soil fungi, using the copper(II)-neocuproine (2,9-dimethyl-1,10-phenanthroline) oxidizing reagent. A highly colored copper(I)-neocuproine chelate formed immediately in ammonium acetate-buffered solution a result of the redox reaction with dazomet, and its concentration measured from the absorbance at 453 nm using a molar absorptivity of (3.35±0.15)×10⁴ l mol⁻¹ cm⁻¹ for dazomet, the LOD for soil being 1-2 ppm. Dazomet in commercial formulations (such as Basamit, BASF) and soil extract could be measured by the developed method which was rapid (color development took 5 min), and cost-effective. The developed method was as precise as the CIPAC HPLC method (at 95% confidence level) using a nucleosil 100-5 C₁₈ column with UV detection. The degradation of dazomet in different types of forestry soil, i.e. sandy, loamy and clay soils to which moisture and Basamit in recommended doses were applied, was followed kinetically using the developed procedure. The proposed method is much simpler than the US-EPA and CIPAC methods of dazomet assay, and is applicable to on-site colorimetry for field use (via retention of the colored copper(I)-neocuproine cation on an acidic cation exchanger) where rapid detection of dazomet residues and breakdown products is required. The method was not interfered with common soil ions and 1,3-dichloropropene (1,3-D), a fumigant used in combination with dazomet.     

Solution equilibria of pyridinecarboxylic acids: Complexation reaction of 2-mercaptonicotinic acid-copper (II) complex with thiosalicylic acid

The reaction of 2-mercaptonicotinic-copper (II) complex (Cu²⁺-MENA, 1 3n 1) with thiosalicylic acid (TSA) has been investigated spectrophotometrically in ethanol-water solution (50%, v/v) at I=O.IM (NaClO₄) and 25°C. Under the acidic conditions encountered in this study, there are competing equilibria between protonation of the Cu²⁺-MENA binary chelate, the formation of the Cu(MENA)(TSA) ternary complex and protonation of the second ligand (TSA). The equilibrium constants for the complexation reactions and the stability of the mixed-ligand complex are determined. The optimum conditions for the predominance of the ternary complex are established and the enhancement of this complex over binary complex formation is evaluated. Complex-forming equilibria have also been examined by potentiometric-pH titrations and the experimental data are discussed in relation to various equilibria existing in solution. Structural and bonding features of the mixed-ligand complex are illustrated from considerations of the IR spectral data.     

Spectrophotometric total protein assay with copper(II)-neocuproine reagent in alkaline medium

Total protein assay was made using copper(II)–neocuproine (Nc) reagent in alkaline medium (with the help of a hydroxide-carbonate-tartarate solution) after 30 min incubation at 40 °C. The absorbance of the reduction product, Cu(I)–Nc complex, was recorded at 450 nm against a reagent blank. The absorptivity of the developed method for bovine serum albumin (BSA) was 0.023 l mg⁻¹ cm⁻¹, greater than that of Lowry assay (0.0098), and much greater than that of Cu(II)–bicinchoninic acid (BCA) assay (0.00077). The linear range of the developed method (8–100 mg l⁻¹ BSA) was as wide as that of Lowry, and much wider than that of BCA (200–1000 mg l⁻¹ BSA) assay. The sensitivity of the method was greater than those of Cu-based assays (biuret, Lowry, and BCA) with a LOD of 1 mg l⁻¹ BSA. The within-run and between-run precisions as RSD were 0.73 and 1.01%, respectively. The selectivity of the proposed method for protein was much higher than those of dye-binding and Lowry assays: Most common interferents to other protein assays such as tris, ethanolamine, deoxycholate, CsCl, citrate, and triton X-100 were tolerated at 100-fold concentrations in the analysis of 10 mg l⁻¹ BSA, while the tolerance limits for other interferents, e.g., (NH₄)₂SO₄ and acetylsalicylic acid (50-fold), SDS (25-fold), and glycerol (20-fold) were at acceptable levels. The redox reaction of Cu(II)–Nc as an outer-sphere electron transfer agent with the peptide bond and with four amino acid residues (cystine, cysteine, tryptophan, and tyrosine) was kinetically more favourable than that of Cu(II) alone in the biuret assay. Since the reduction product of Cu(II) with protein, i.e., Cu(I), was coordinatively saturated with Nc in the stable Cu(Nc)₂⁺ chelate, re-oxidation of the formed Cu(I) with Fenton-like reactions was not possible, thereby preventing a loss of chromophore. After conventional protein extraction, precipitation, and redissolution procedures, the protein contents of the minced meat (veal and turkey), sardine, various milk products, and egg white were analyzed with the proposed and Lowry methods, and the results correlated appreciably (r = 0.98). The method was validated by Kjeldahl analyses of the tested samples; the data sets of complex samples assayed by Cu(II)–Nc and Lowry correlated to the findings of Kjeldahl yielded correlation coefficients r = 0.96 and 0.97, respectively, with slopes being close to 1. Interferences of glucose and thiol compounds at relatively low concentrations could be compensated for by selecting a lower alkaline pH (i.e., pH 10) at a cost of slightly reduced sensitivity and adding an identical amount of interferent to the reagent blank, respectively, since the absorbances due to BSA and interferent were additive. Thus a novel spectrophotometric method for total protein assay using a stable reagent and chromophore, which was simple, rapid, sensitive, flexible, and relatively selective, was developed, and applied to a variety of food products.     

Spectrophotometric determination of ascorbic acid by the modified CUPRAC method with extractive separation of flavonoids-La(III) complexes

The proposed method for ascorbic acid: AA (Vitamin C) determination is based on the oxidation of AA to dehydroascorbic acid with the CUPRAC reagent of total antioxidant capacity assay, i.e., Cu(II)-neocuproine (Nc), in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450 nm. The flavonoids (essentially flavones and flavonols) normally interfering with the CUPRAC procedure were separated with preliminary extraction as their La(III) chelates into ethylacetate (EtAc). The Cu(I)-Nc chelate responsible for color development was formed immediately with AA oxidation. Beer's law was obeyed between 8.0 × 10⁻⁶ and 8.0 × 10⁻⁵ M concentration range, with the equation of the linear calibration curve: A_450 nm = 1.60 × 10⁴C (mol dm⁻³) − 0.0596. The relative standard deviation (R.S.D.) in the analysis of N = 45 synthetic mixtures containing 1.25 × 10⁻² mM AA with flavonoids was 5.3%. The Cu(II)-Nc reagent is a lower redox-potential and therefore more selective oxidant than the Fe(III)-1,10-phenanthroline reagent conventionally used for the same assay. This feature makes the proposed method superior for real samples such as fruit juices containing weak reductants such as citrate, oxalate and tartarate that may otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to some commercial fruit juices and pharmaceutical preparations containing Vitamin C + bioflavonoids. The findings of the developed method for fruit juices and pharmaceuticals were statistically alike with those of HPLC. The proposed spectrophotometric method was practical, low-cost, rapid, and could reliably assay AA in the presence of flavonoids without enzymatic procedures open to interferences by enzyme inhibitors.     

Studies on the mixed-ligand complexes of copper(II) with gallic acid and pyridine carboxylic acids and their benzologues

Summary The ternary complex formation of copper(II) with gallic acid (gal) and 2-hydroxy nicotinic acid (hyna), 2-mercapto nicotinic acid (mena), salicylic acid (sa) or thiosalicylic acid (tsa) as a second ligand in a 1:1:1 molar ratio has been investigated in 40% (v/v) ethanol using spectrophotometric andpH titration methods. The solution equilibria of the ternary systems have been determined and the stability constants of the mixed complexes has been evaluated. Considering all parameters, the Cu-gal-sa ternary system was proved as a suitable, rapid, and sensitive spectrophotometric indicator for determining traces of copper.The ternary system containingsa obeysBeer's law up to 3.4 µg·ml^–1 copper. The optimum range for the determination of copper (Ringbom) atpH 6.0 ranges from 0.63 to 1.74 µg·ml^–1 of copper. The molar absorptivity of the ternary complex is 1.3×10⁴l·mol^–1·cm^–1.

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Untersuchungen anmixed-ligand — Komplexen von Kupfer(II) mit 3,4,5-Trihydroxybenzoesäure und Pyridincarbonsäuren und ihren C-Homologen

Zusammenfassung Die Bildung ternärer Komplexe von Kupfer(II) mit 3,4,5-Trihydroxybenzoesäure (gal) und 2-Hydroxynicotinsäure (hyna), 2-Mercaptonicotinsäure (mena), Salicylsäure (sa) oder Thiosalicylsäure (tsa) in einem molaren Verhältnis von 1:1:1 wurde mittels spektrophotometrischer und potentiometrischer Methoden in 40% (v/v) Ethanol untersucht. Die Lösungsgleichgewichte der termären Systeme und die Stabilitätskonstanten der gemischten Komplexe wurden bestimmt. Unter Berücksichtigung aller Parameter erwies sich das termäre System Cu-gal-sa als geeigneter schneller und empfindlicher Indikator zur Spurenanalyse von Kupfer.Dassa enthaltende ternäre System gehorcht demBeerschen Gesetz bis zu einer Kupferkonzentration von 3.4 µg·ml^–1. Der optimale Bereich zur Bestimmung von Kupfer (Ringbom) beipH 6.0 erstreckt sich von 0.63 bis 1.74 µg Cu pro ml. Die molare Extinktion des ternären Komplexes beträgt 1.3×10⁴l·mol·cm^–1.

     

A simple and selective flow-injection spectrophotometric determination of copper(II) by using acetylsalicylhydroxamic acid

A new simple, and rapid flow-injection spectrophotometric method is developed for the determination of trace amounts of Cu(II) by using a new chromogenic reagent acetylsalicylhydroxamic acid (AcSHA). The method is based on the formation of colored Cu(II)-(AcSHA)₂ complex. The optimum conditions for the chromogenic reaction of Cu(II) with AcSHA is studied and the colored (green) complex is selectively monitored at λ_max 700 nm. With the reagent carrier solvent (dimethylsulfoxide (DMSO) and acetate buffer, pH 4.2) flow-rate of 1 ml min⁻¹, a detection limit (2S) of 1 μg l⁻¹ Cu(II) was obtained at a sampling rate of 80 sample h⁻¹. The calibration graph was linear in the Cu(II) concentration range 5-120 μg l⁻¹. The relative standard deviation (n=10) was 0.64% for a sample containing 60 μg l⁻¹ Cu(II). The detailed study of various interferences confirmed the high selectivity of the developed method. The method was successfully applied to determine trace amounts of copper(II) in river and seawater samples. The accuracy of the method was demonstrated by the analysis of standard reference materials C12X3500 and C14XHS 50.     

Spectrophotometric determination of microamounts of quercetin based on its complexation with copper(II)

The complexation process of the transition metal Cu(II) with quercetin was studied. The investigation was conducted spectrophotometrically in ethanol at the maximum absorption wavelength of 458.5 nm. Cu(II)—quercetin complex composition (1: 1) was determined using the Job, Harvey—Manning, and mole ratio methods. Complex stability constant was calculated by the Job and mole ratio methods and the respective logarithm values were 7.53 ± 0.25 and 7.44 ± 0.03. A new method for quantitative determination of the quercetin content in solution was developed in this work. At the optimal conditions quercetin was determined in concentrations ranging from 0.202 to 1.006 μg cm⁻³ with relative standard error of 2.5 % to 5.5 %. The lower detection limit was 0.067 μg cm⁻³. The method was found very accurate, reproducible, and sensitive, capable to determine microamounts of quercetin in pharmaceutical preparations.     

A study of complex equilibria of phenylglycine with nickel(II), copper(II) and zinc(II) in water and in water - methanol solution

The complex equilibria of the systems phenylglycine — nickel(II), copper(II) and zinc(II) in water and in water — methanol solution have been studied by computer analysis of potentiometric data. The mode of coordination has been established by¹³C-NMR and IR studies.

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Gleichgewichtsuntersuchungen der Komplexbildung von Phenylglycin mit Nickel(II), Kupfer(II) und Zink(II) in Wasser und Wasser - Methanol-Lösung

Zusammenfassung Anhand einer Computer-Analyse von potentiometrischen Daten wurden die Bildungsgleichgewichte in den Systemen Phenylglycin — Nickel(II), Kupfer(II) und Zink(II) untersucht. Der Koordinationstyp wurde mittels¹³C-NMR und IR festgestellt. Die Lösungsmittel waren Wasser und Wasser — Methanol.

     

Complex formation equilibria of some β-amino-alcohols with lead(II) and cadmium(II) in aqueous solution

A study of complex formation equilibria of some β-amino-alcohols with lead(II) and cadmium(II) ions at 25°C and in 0.5 M KNO₃ is reported. The amino-alcohols considered are 2-amino-1-propanol, 2-amino-1-butanol, 2-amino-1-pentanol and 2-amino-1,3-propanediol. sec-Buthylamine and 2-amino-1-methoxy-propane have been also considered for comparison. The results are discussed in terms of ligand structure, paying attention to the number of hydroxyl groups and to the length of the alkyl residual. A weak contribution of the alcoholic oxygen in the coordination of cadmium(II) and the presence of a mixed hydroxyl species in lead(II) containing systems are hypothesized.     

Analytical Use of Copper (II)-Neocuproine in The Spectrophotometric Determination of Hydrazines

Abstract

This work characterizes a newly developed, sensitive and convenient spectrophotometric procedure for determination of sub-ppm concentrations of hydrazine and its organic derivatives. The method is based on formation of the cuprous neocuproine chelate after reaction of hydrazines with a prepared aqueous solution of the copper (II)-neocuproine complex. The cuprous chelate is then directly measured in aqueous solution at 458 nm. The effect of several experimental conditions influencing the reaction are presented and the method was employed for the analyis of 5 different hydrazine compounds. The standard deviation did not exceed ± 0.47%.     

Spectrophotometric Determination of Copper in Natural Waters and Pharmaceutical Samples with Chloro(Phenyl) Glyoxime

A simple method for the determination of trace amounts of copper by spectrophotometry is described based on the formation of the copper‐chloro‐(phenyl) glyoxime complex. The molar absorptivities of the complexes at pH 4.0 at 290.5 nm were 0.8 × 10⁴l/mol cm. Optimal conditions such as reagent amounts and pH for the copper determination were reported. The effects of the foreign ions were also investigated. The method was successfully applied for determinations of copper in some natural waters and pharmaceutical samples.     

Structure of the nitrosoguanidine complexes of nickel(II) and copper(II) by X-ray crystallography and computational analysis

Using the X-ray structure of solid nitrosoguanidine (ngH), potential structures of its complex with aqueous nickel(II) were surmised. A single-crystal X-ray diffraction determination of the Ni(II) complex confirmed one of these configurations. The X-ray structural parameters were compared with the most stable gaseous configurations derived from ab initio-MO calculations. The lowest energy calculated configuration of the nickel(II) complex and the X-ray crystal structure are in excellent agreement. The neutral diamagnetic, planar, red-colored [bis(nitrosoguanidate)nickel(II)] complex, [Ni(ng)₂]°, is nitrogen coordinated in the trans configuration. It is highly insoluble in all solvents investigated, and has essentially the same crystal symmetry and unit-cell dimensions as the free ligand. In ligand crystals, two molecules have four nitrogen atoms aligned in a plane such that they are suitable for coordination to a nickel ion (1.945, 2.064?Å), when it is at the 1/2,?1/2,?1/2 unit-cell position. Furthermore, the complexes stack, as in [Ni(dmg)₂]°, placing the nickel ions in nearly perfect positions for weak metal–metal bonding between adjacent layers at the near optimum distance of 3.65(1)?Å. This results in a tight, linear macromolecule having low volatility and the extremely low solubility observed. As far as we are aware this is the first instance in which a ligand crystal structure is essentially the same as the complex it forms, with minor differences in bond distances, angles and torsion angles, and suggests some potentially unique properties and applications for this material.     

桑色素褪色光度法测定茶叶中的锰

锰是人体必需的微量元素,具有重要的生理功能和营养作用.茶树对锰有富集现象,茶叶是人们常用的饮料[1].因此,建立一种灵敏而又简便的测定痕量锰的分析方法,具有重要的实用价值.