EQUILIBRIA INVOLVING COBALT(II) HALIDES AND PHOSPHINE OXIDES I. A SPECTROPHOTOMETRIC STUDY OF THE COBALT(II) CHLORIDE — TRIPHENYLPHOSPHINE OXIDE SYSTEM IN ACETONE MEDIUM

Abstract

The CoCl₂-triphenylphosphine oxide system was studied in anhydrous acetone medium, at 25.00 · 0.05 ° C, by spectrophotometry. It was found that the system comprises at least three complex species, whose over-all stability constants are: β₁ = (1.40 · 0.10) · 10⁴ M^?1, β₂ = (6.77 · 0.95) · 10⁶ M^?2, β₃ = (1.77 · 0.40) · 10⁹ M^?3. The composition of the system as well as the values of the stability constants of the complex species are in a marked disagreement with the literature data. The compatibility between the experimental data and the results obtained in the present work was confirmed by different methods.     

AUTOCATALYTIC REDUCTION OF PYRIDINECOBALOXIME(III) BY MOLECULAR HYDROGEN

Abstract

In the presence of added cobaloxime(II), hydroxopyridinecobaloxime(III) is autocatalytically reduced by molecular hydrogen in methanol at 20°C. The sigma-shaped volumetric curves were evaluated by computer simulation of the system of differential equations corresponding to a 4-step mechanism. The key reduction step is presumably H-atom transfer from hydridocobaloxime(III) to cobaloxime(III). The lower limit of its rate constant is k₄=(5.0 ± 0.5) × 10⁴ M^?1 sec^?1 at 20°C. Hydridopyridinecobaloxime(III) is thermodynamically unstable, its estimated formation equilibrium constant being (3.9 ± 0.6) × 10^?4 M^?1. The possible role of cobaloxime(I) species is discussed.     

Preconcentration and Spectrophotometric Determination of Chromium (VI) and Total Chromium in Drinking Water by the Sorption of Chromium Diphenylcarbazone with Surfactant Coated Alumina

Abstract

A simple and inexpensive method for determining chromium (VI) in drinking water by spectrophotometry after preconcentration with sodium dodecyl sulphate (SDS) coated alumina column is described. Chromium(VI) is reacted with diphenylcarbazide (DPC) and the Cr-DPC complex is quantitatively adsorbed onto a SDS coated alumina column from 800 ml of sample solution. The complex is then eluted with a 8 ml mixture of methanol, acetone and hydrochloric acid and determined by spectrophotometry. Total chromium can be determined after oxidation of chromium (III) to chromium (VI) by KMnO₄. The relative standard deviation (10 replicate analyses) at the 10 μg l^?1 of chromium (VI) and 10 μg l^?1 of total chromium were 3.5% and 3.4% and corresponding limits of detection (based on 3 σ) were 0.040 μg l^?1 and 0.033 μg l^?1, respectively.     

Spectrophotometric and potentiometric study of the cobalt(II)-thiocyanate system in aqueous medium

The cobalt(II)—thiocyanate system was spectrophotometrically studied at 2.0 M ionic strength (NaClO₄) and 25°C. The following formation constants were obtained: β₁ = 6.9 M^?, β₂ = 28.9 M^?2, β₃ = 12.1 M^?3 and β₄ = 1.30 M^?4. Three wavelengths were considered, 515, 590 and 615 nm, and the molar absorptivities of each species were calculated. Linear relationships were obtained for $\text{ε}$ vs $\text{n}$ and α_i. There is strong evidence that the tetrahedral [Co(SCN)₄]^2? is virtually the only species absorbing at 590 and 615 nm. An indirect potentiometric method led to comparable equilibrium constants. The cadmium(II)—thiocyanate formation constants used in the indirect method, under the same conditions, were found to be β₁ = 21.51 ± 0.09 M^?1, β₂ = 123 ± 1 M^?2, β₃ = 130 ± 3 M^?3 and β₄ = 173 ± 1.2 M^?4, in good agreement with earlier literature data.     

Synthesis,characterization, DNA-binding,and antioxidant activities of four copper(II) complexes containing N-(3-hydroxybenzyl)-amino amide ligands

Four new substituted amino acid ligands, N-(3-hydroxybenzyl)-glycine acid (HL₁), N-(3-hydroxybenzyl)-alanine acid (HL₂), N-(3-hydroxybenzyl)-phenylalanine acid (HL₃), and N-(3-hydroxybenzyl)-leucine acid (HL₄), were synthesized and characterized on the basis of ¹H NMR, IR, ESI-MS, and elemental analyses. The crystal structures of their copper(II) complexes [Cu(L₁)₂]·2H₂O (1), [Cu(L₂)₂(H₂O)] (2), [Cu(L₃)₂(CH₃OH)] (3), and [Cu(L₄)₂(H₂O)]·H₂O (4) were determined by X-ray diffraction analysis. The ligands coordinate with copper(II) through secondary amine and carboxylate in all complexes. In 2, 3, and 4, additional water or methanol coordinates, completing a distorted tetragonal pyramidal coordination geometry around copper. Fluorescence titration spectra, electronic absorption titration spectra, and EB displacement indicate that all the complexes bind to CT-DNA. Intrinsic binding constants of the copper(II) complexes with CT-DNA are 1.32?×?10^6?M^?1, 4.32?×?10^5?M^?1, 5.00?×?10^5?M^?1, and 5.70?×?10^4?M^?1 for 1, 2, 3, and 4, respectively. Antioxidant activities of the compounds have been investigated by spectrophotometric measurements. The results show that the Cu(II) complexes have similar superoxide dismutase activity to that of native Cu, Zn-SOD.     

THE INTERACTION OF 2-AMINO-2-HYDROXYMETHYL-1,3-PROPANEDIOL WITH COBALT(II) AND MANGANESE(II) IONS

Abstract

The stepwise complex formation between 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) with Co(II) and Mn(II) was studied by potentiometry at constant ionic strength 2.0 M (NaClO₄) and T = (25.0 ± 0.1)°C, from pH measurements. Data of average ligand number (Bjerrum's function) were obtained from such measurements followed by integration to obtain Leden's function, F ₀(L). Graphical treatment and matrix solution of simultaneous equations have shown two overall stability constants of mononuclear stepwise complexes for the Mn(II)/TRIS system (β₁ = (5.04 ± 0.02) M^?1 and β₂ = (5.4 ± 0.5) M^?2) and three for the Co(II)/TRIS system (β₁ = (1.67 ± 0.02) × 10² M^?1, β₂ = (7.01 ± 0.05) × 10³ M^?2 and β₃ = (2.4 ± 0.4) × 10⁴ M^?3). Slow spontaneous oxidation of Co(II) solutions by dissolved oxygen, accelerated by S(IV), occurs in a buffer solution TRIS/HTRIS⁺ 0.010/0.030 M, with a synergistic effect of Mn(II).     

Sensitive spectrophotometric determination of palladium with tin(II) chlorided and rhodamine-6g after flotation

Palladium is determined by reaction with tin(II) chloride and rhordamine-6G in hydrochloric acid medium, flotation of the ion-association complex, [(R6G⁺)₂Pd (SnCl^?₃)₄]·[(R6G⁺) (SnCl^?₃] with di-isopropyl ether, and dissolution in acetone for spectrophotometry. The molar absorptivity is 2.84 x 10⁵ l mol^?1 cm^?1 at 530 nm; Beer's law is obeyed in the range 0.05–0.35 μg Pd ml^?1. Other platinum metals and silver interfere. Traces of palladium in silver metal are determined after extraction of palladium with dimethylglyoxime in chloroform.     

Electrochemical and spectrophotometric determination of the formation constants of the ascorbic acid-��-cyclodextrin and dopamine-��-cyclodextrin inclusion complexes

From UV?Cvis spectrophotometry and cyclic voltammetry it is demonstrated the interaction of dopamine, DA, and ascorbic acid, AA, with ??-cyclodextrin, ??CD, in aqueous media at pH 3.0. The formation constants of the respective inclusion complexes were also determined. The spectrophotometry data fed into the data processing software SQUAD, allowed calculation of the said constants for the AA?C??CD complex (H₂AA?C??CD) giving a value of 3236 M^?1, while for the dopamine complex DA?C??CD (H₃DA+??CD) this was 5888 M^?1. From these results, the theoretical absorption spectra were generated which fitted quite well the experimental ones, thus indicating clearly that the constants are reliable. Moreover, from the cyclic voltammetry data, the stated constants were also calculated whereby that of the H₂AA?C??CD gave a value of 3981 M^?1 while for the dopamine complex DA?C??CD (H₃DA+??CD) it was 4898 M^?1. It is noteworthy to say that these values were similar to those found through spectrophotometry.     

Zero-Order and Third-Derivative Spectrophotometric Determination of Iron(III) with 4-(2-Pyridylazo)-Resorcinol in the Presence of N-Hexadecylpyridinium Chloride

Abstract

The complex formation reaction between iron(III) and 4-(2-pyridylazo) resorcinol(PAR) in the presence of various water soluble surfactants((N-hexadecylpyridinium chloride (HPC), poly(vinylalcohol)(PVA), sodium dodecylsulfate(SDS), sodium N-lauroylsarcosine(SL)) alone or in combination at weakly acidic media was systematically investigated. An improved and more sensitive spectrophotometric method for the determination of iron was proposed by zero-order and third-derivative spectrophotometry using the PAR-iron(III)-HPC ternary complex system at about pH 5.2. The calibration curve was rectilinear in the ranges of 0 – 15.0 μg iron(III) in a final 10-ml on the zero-order spectrophotometry. Also, upon the third-derivative spectrophotometry, Beer's law was obeyed in the range of 0 – 8.0 μg iron(III)/10 ml by measuring the distance between the absorbance peak(λ₁ = 527 nm) and the valley (λ₂ = 560 nm). The apparent molar absorptivity was 4.8 × 10⁴ 1 mol^?1 cm^?1 in zero-order spectrophotometry, and 1.36 × 10⁵ mol^?1 cm^?1 in third-derivative spectrophotometry. The effect of foreign ions was decreased within ½ – ¼-fold in comparison with the method in the presence of PVA without HPC. Especially, the third-derivative spectrophotometric method was sensitive and selective, and made possible to assay mixed sample solution containing iron(III) and copper(II), etc.     

Consecutive determination of rutin and quercetin by spectrophotometric measurements

The consecutive determination of rutin and quercetin without any pretreatment for separation was examined in methanol solutions by a conventional and a two-wavelength spectrophotometry. Based the tendency of quercetin to form more stable metal complexes compared to rutin, quercetin can be determined through the tin(II) complex formation without interference from rutin. The method was applied to the determination of quercetin in the concentration range of 3.0 × 10^?6 to 2.0 × 10^?5M.Quercetin is apt to be oxidized by oxygen rather than rutin, especially in the presence of copper(II), whereas rutin is not decomposed under such a condition. After removal of quercetin through copper(II)-catalyzed oxidation, rutin ranging in concentration from 2.0 × 10^?6 to 2.0 × 10^?M was determined by the absorbance measurement of rutin-copper(II) complex in slightly alkaline methanol media.Both rutin and quercetin were determined directly by two-wavelength spectrophotometry, without adding any complex forming metals; the lower limit of detection was about 1.0 × 10^?5M. The method was extended to the determination of a smaller amounts of rutin and quercetin using the absorption peaks of their zirconium(IV) complexes, and the determination of both components in the range of 5.0 × 10^?6 to 3.0 × 10^?5M was made with a relative error of within ±4%.     

Two new heteroleptic ruthenium(II) dithiocarbamates: synthesis,characterization, DFT calculation and DNA binding

Two ruthenium(II) dithiocarbamates, cis-[Ru(DMP)₂L](BF₄), where L = 4-(4-methoxy-phenyl)piperazine-1-carbodithioate (1) and 4-(3-methoxyphenyl)piperazine-1-carbodithioate (2) and DMP = 2,9-dimethyl-1,10-phenanthroline, have been synthesized and characterized. The DNA-binding affinity of these metal complexes was investigated by UV–visible spectrophotometry with DNA-binding constants of 6.2 × 10⁴ M^?1 (1) and 1.2 × 10⁵ M^?1 (2) and electrostatic binding mode was confirmed by viscometric measurements. For insight into the structural differences, both complexes were studied computationally. B3LYP/LANL2DZ level of Density Functional Theory was used for the computational studies in Gaussian 09. The optimized bond lengths are in agreement with the reported values. Comparative computational studies reveal interesting transformations in bond lengths, angles, Natural Bond Orbital charges, molecular orbitals, Molecular Electro Static Potentials, and global chemical reactivity indices. Based on quantum chemical results a structure–activity relationship has been attempted.     

First Example of Schiff Bases Containing Poly(Acryl Amid) in the Synthesis and Characterization

A novel polymeric‐Schiff base derived from the condensation reaction poly(acryl amid) and indole‐3‐carboxaldehyde has been synthesized and their Co(II) and Ni(II) complexes have been prepared. Mol ratio of acrylamid group and Schiff bases group was estimated by means of height of ‐CH multiple peaks and –CH=N‐ peak in ¹H‐NMR spectrum. The studied substances were characterized by molar conductance, magnetic susceptibility, electronic and IR spectral studies. In addition, main units have been suggested with elemental analysis for these substances, and than the weight average molecular weight (M_w) has been suggested. The number average molecular weight (M_n) was determined with a vapor pressure osmometer. Polydispersity index (PDI) found to be ca 1.7 from M_w/M_n for poly‐Schiff bases and their Co(II) and Ni(II) complexes. PAA‐Schiff bases were found to have the highest thermal stablility compared to that of the Co(II) and Ni(II) complexes. The conductivities of the PAA‐Schiff bases and their complexes were measured by the four‐probe technique and were found in the range 10^?5?10^?6 S cm^?1.     

Nuclease activity of redox/non-redox active binuclear transition metal mixed-polypyridine complexes: [M2(1,4-tpbd)(diimine)2(H2O)2]4+, M = Zn,Co, Ni,Cd, diimine = phen,bpy, dafo

Seven new transition metal complexes formulated as [M₂(1,4-tpbd)(diimine)₂(H₂O)₂]⁴⁺ [M = Zn, Co, Ni, Cd; 1,4-tpbd = N,N,N′,N′-tetrakis(2-pyridylmethyl)benzene-1,4-diamine; diimine is a N,N-donor heterocyclic base like 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), 4,5-diazafluoren-9-one (dafo)] have been synthesized and structurally characterized by X-ray crystallography: [Zn₂(1,4-tpbd)(phen)₂(H₂O)₂]⁴⁺ (1), [Zn₂(1,4-tpbd)(bpy)₂(H₂O)₂]⁴⁺ (2), [Co₂(1,4-tpbd)(phen)₂(H₂O)₂]⁴⁺ (3), [Ni₂(1,4-tpbd)(phen)₂(H₂O)₂]⁴⁺ (4), [Ni₂(1,4-tpbd)(bpy)₂(H₂O)₂]⁴⁺ (5), [Ni₂(1,4-tpbd)(dafo)₂(H₂O)₂]⁴⁺ (6) and [Cd₂(1,4-tpbd)(phen)₂(H₂O)₂]⁴⁺ (7). Single crystal diffraction reveals that the metals in the complexes are all in a distorted octahedral geometry. The interactions of the seven complexes with calf thymus DNA (CT-DNA) have been investigated by UV absorption, fluorescence, circular dichroism spectroscopy and viscosity measurements. The apparent binding constants (K_app) are calculated to be 5.2?×?10⁵ M^?1 for 1, 1.05?×?10⁵ M^?1 for 2, 5.76?×?10⁵ M^?1 for 3, 4.57?×?10⁵ M^?1 for 4, 1.29?×?10⁵ M^?1 for 5, 1.7?×?10⁵ M^?1 for 6, 2.53?×?10⁵ M^?1 for 7, the binding propensity to the calf thymus DNA in the order: 3 (Co-phen) > 1 (Zn-phen) > 4 (Ni-phen) > 7 (Cd-phen) > 6 (Ni-dafo) > 5 (Ni-bpy) > 2 (Zn-bpy). Furthermore, these complexes display efficient oxidative cleavage of supercoiled DNA; the Zn(II)/H₂O₂ and Cd(II)/H₂O₂ systems efficiently cleave DNA attributed to the peroxide ion coordinated to the Zn(II) and Cd(II), which enhanced their nucleophilicity, this is rare.     

Absolute rate constants for hydrogen abstraction from hydrocarbons by the trichloromethylperoxyl radical

Absolute rate constants have been measured for the reactions of trichloromethylperoxyl radicals with cyclohexane, cyclohexene, and hexamethylbenzene. The CCl₃O₂ radicals were produced by pulse radiolysis of air-saturated CCl₄ solutions containing various amounts of the hydrocarbons. The rate constants were determined by competition with the one-electron oxidation of metalloporphyrins, using the rate of formation of the metalloporphyrin radical cation absorption to monitor the reaction by kinetic spectrophotometry. The rate constants for hydrogen abstraction from cyclohexane, cyclohexene, and hexamethylbenzene were found to be 1 × 10³, 1.0 × 10⁵, and 7.5 × 10⁴ M^?1 s^?1, respectively.     

Kinetic and mechanistic study of N-aminopiperidine formation via the raschig process

Formation of N-aminopiperidine (NAPP) in the reaction of monochloramine with piperidine was studied by varying the reagents concentrations, pH and temperature. The study was carried out in diluted solutions, recording simultaneously monochloramine concentration by UV spectrophotometry at 243 nm and hydrazine concentration at 237 nm after treatment with formaldehyde. The presence of two competitive reactions: formation of NAPP and a complex parallel reaction limiting the yield of hydrazine, was established. Reaction products were characterized by GC/MS analysis. The rate constant of NAPP formation and activation parameters were determined, k ₁ = 56 × 10^?3 M^?1 s^?1 (25°C) and k ₁ = 9.3 × 10⁶ exp(?46.5/RT) M^?1 s^?1, respectively.     

Synthesis and spectral studies of some new dimeric [(μ-Cl)2M2(L)2 · xTHF] [M = Zn(II) and Hg(II)] complexes containing Schiff-base ligands

A series of binuclear Schiff-base complexes of zinc(II) and mercury(II) containing bidentate ligands (HL) [HL?=?salicylidene-2-methyl-1-aminobenzene (HL¹), salicylidene-2-aminopyridine (HL²), and salicylidene-3-nitro-1-aminobenzene (HL³)] with “N” and “O” donors have been synthesized by simple metathetic reactions of anhydrous metal chlorides with sodium salts of Schiff bases (in tetrahydrofuran (THF)/MeOH) in equimolar ratio to produce [(µ-Cl)₂M₂(L)₂?·?xTHF] [where M?=?Zn(II) and Hg(II); L?=?HL¹, HL², and HL³; x?=?0 for (1), (4), (6) and x?=?2 for (2), (3), (5)]. The main emphasis on the complexes [(µ-Cl)₂M₂(L)₂?·?2THF] (2), (3), and (5) is given due to their five-coordinate environment around metal ions. The complexes have been characterized by elemental analyses (M, Cl, C, H, N), melting point, and spectral (FT-IR, ¹H-NMR, and ¹³C-NMR) studies. The structural composition of the complexes has been determined by FAB-MS spectral studies. FAB-MS showed the isotopic molecular ion peak [M⁺] and fragments supporting the formulation. Powder X-ray diffraction study of 6 is also reported showing the crystallite size (404.5?Å) of the complex.     

The effect of additives of strong inorganic acids on IR-spectroscopic determination of water in organic solutions

The possibility of the quantitative determination of water in organic solvents containing strong acids by IR spectrophotometry at 3500–3700 cm^?1 was studied. The molar absorption coefficients at the maximum of the most intense absorption bands of water in acetonitrile, chloroform, and 1,2-dichloroethane were 115, 43, and 88 M^?1 cm^?1, respectively. The study of the effect of acid additions to acetonitrile showed that hydrochloric and nitric acids had little on the shape and intensity of the IR spectra of water. The presence of perchloric acid reduces the intensity (for 0.027 M HClO₄, by 40% at 3618 cm^?1), which was due to the state of acids in the solvents. Conductometric measurements showed that, under these conditions, HCl and HNO₃ were unionized, while HClO₄ dissociated almost completely.     

Reactivity of selected volatile organic compounds (VOCs) toward the sulfate radical (SO4−)

Rate constants for a series of alcohols, ethers, and esters toward the sulfate radical (SO₄^?) have been directly determined using a laser photolysis set‐up in which the radical was produced by the photodissociation of peroxodisulfate anions. The sulfate radical concentration was monitored by following its optical absorption by means of time resolved spectroscopy techniques. At room temperature the following rate constants were derived: methanol ((1.6 ± 0.2) × 10⁷ M^?1 s^?1); ethanol ((7.8 ± 1.2) × 10⁷ M^?1 s^?1); tert‐butanol ((8.9 ± 0.3) × 10⁵ M^?1 s^?1); diethyl ether ((1.8 ± 0.1) × 10⁸ M^?1 s^?1); MTBE ((3.13 ± 0.02) × 10⁷ M^?1 s^?1); tetrahydrofuran (THF) ((2.3 ± 0.2) × 10⁸ M^?1 s^?1); hydrated formaldehyde ((1.4 ± 0.2) × 10⁷ M^?1 s^?1); hydrated glyoxal ((2.4 ± 0.2) × 10⁷ M^?1 s^?1); dimethyl malonate (CH₃OC(O)CH₂C(O)OCH₃) ((1.28 ± 0.02) × 10⁶ M^?1 s^?1); and dimethyl succinate (CH₃OC(O)CH₂CH₂C(O)OCH₃) ((1.37 ± 0.08) × 10⁶ M^?1 s^?1) where the errors represent 2σ. For the two latter species, we also measured the temperature dependence of the corresponding rate constants. A correlation of these kinetics with the bond dissociation energy is also presented and discussed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 539–547, 2001     

An Ion-Selective Electrode for Dibasic Phosphate Ion

Abstract

A phosphate-selective electrode is developed based on a silver coordination reaction. The electrode responds linearly toward HPO₄ ⁼ in the concentration range of 10^?4 to 10^?1 M (slope = 27 mV/dec.). The electrode also shows good selectivity over sulfate, nitrate, perchlorate and acetate.     

Determination of Methimazole and Carbimazole Using Polarography and Voltammetry

Abstract

Anodic waves of methimazole (I) (1-methylimidazole-2-thiol) and carbimazole (II) (1-ethoxycarbonyl-3-methyl-2-thio-4-imidazoline) on mercury electrodes correspond to mercury salt formation. Both compounds form in the thiono form a soluble complex at pH < 6, compound (I) at higher pH-values a slightly soluble salt of the thiol form. Electrode processes involving the thiol form are complicated by adsorption. Oxidation at solid electrodes occurs only at potentials more than 0.5 V more positive. For compound (I) spectrophotometry indicated pK_a=12.0 ± 0.2. By d.c. polarography in 0.1 M H₂SO₄ containing 10% ethanol the determination of both compounds is possible between 4 × 10^? and 1 × 10^?3 M, by differential pulse polarography between 1 × 10^? and 1 × 10^?4 M, by differential pulse voltammetry at HMDE between 5 × l0^?7 and 6 × 10^? M.