Spectrophotometric and polarographic study of pyridine-2-aldehyde guanylhydrazone-Cu(II) complex

The reaction between Cu(II) and pyridine-2-aldehyde guanylhydrazone nitrate (PAG) was investigated by using the techniques of spectrophotometry and polarography.A spectrophotometric determination of Cu(II) with PAG can be performed in a concentration range varying from 0.39–5.50 ppm of copper; the molar absorptivity is 1.2 × 10⁴ liters mole^?1 cm^?1 at 380 nm and the relative error is ±0.6%.The complex gave rise to a single well defined cathodic wave ($\text{E}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= ?0.34 V}\text{for pH}\text{= 8.1}$). The reduction process is diffusion controlled, involves two electrons, and is irreversible.The stoichiometry 1:1 of the complex was established by different methods and by both techniques. The apparent stability constants were computed as log K = 4.4 ± 0.1 and 4.7 from spectrophotometric and polarographic techniques, respectively.     

Numerical evaluation of complex stability constants from polarographic data for quasi-reversible processes

Stability constants of copper(II) butyrate complexes were determined by polarography. Numerical treatment of polarographic data for quasi-reversible electrode processes was developed and yielded good estimates of reversible E_{$\text{1}\text{2}$} values. An improved three-electrode polarographic apparatus was constructed based on operational amplifiers.     

Direct current and differential pulse polarographic behaviour of benzylpenicilloic acid

The differential pulse and direct current polarographic behaviour of benzylpenicilloic acid (BPA) is discussed. In pH 9.2 borate buffer, the single anodic wave (E_{$\text{1}\text{2}$} = -0.25 V) obtained is diffusion-controlled at concentrations less than 2 × 10^-5 M but adsorptioncontrolled in 10^-4 M solution. Cyclic voltammetry at a hanging mercury drop electrode shows that the electrode reaction is reversible at pH 9.2. The differential pulse peak current is linearly related to concentration in the range 10^-6—2 × 10^-5 M. Penicillamine yields an anodic peak well separated from the BPA peak. Both substances may be determined in each other's presence. Intact penicillin decreases the BPA peak but the linearity between i_p and BPA concentration is maintained.     

Zum einfluss des leitelektrolyten auf die polarographi- sche reduktion des methylbromids

The irreversible polarographic reduction of methyl bromide was studied in aqueous solution in the presence of various base electrolytes.E_{$\text{1}\text{2}$} values became more positive with increasing charge density and surface activity of the cations. Mixed electrolytes with alkali metal salts and tetraalkylammonium salts or cationic surfactants suppressed this increase inE_{$\text{1}\text{2}$} values. With such mixed electrolytes containing highly active surfactants of sufficient charge density, a normal polarographic determination of methyl bromide is possible. The final diffusion rate of the active component has also a considerable effect on E_{$\text{1}\text{2}$} values so that the E_{$\text{1}\text{2}$} values of such systems cannot be characterized by the solution composition alone.     

Acid—base equilibria of some benzhydryl piperazine derivatives

The ultraviolet spectral and polarographic behaviour of several benzhydryl piperazine derivatives is described. Attempts have been made to associate the pK data obtained with protonations at various nitrogen atoms in the molecules. Analysis of the plots of E_{$\text{1}\text{2}$} vs. pH have yielded direct polarographic methods for determining some of these compounds in the presence of possible metabolic products.     

Voltammetric determination of agriculturally-significant benzenearsonic acids

Direct current and differential pulse polarographic measurements are reported on a series of substituted benzenearsonic acid compounds that are important in agricultural applications. Compounds studied were o-aminobenzenearsonic acid, p-aminobenzene-arsonic acid, p-nitrobenzenearsonic acid, p-ureidobenzenearsonic acid, and 3-nitro-4-hydroxybenzenearsonic acid. Polarographic reduction potentials varied with pH for all compounds, shifting to more negative values as the pH was increased. Although diffusion-controlled reduction waves were observed in all cases, some compounds exhibited a dependence of E$\text{1}\text{2}$ on concentration, especially at relatively high concentrations. Differential pulse polarographic peak currents were proportional to concentration from 10^-4 M to 10^-6 M.     

Studies in polarographic analysis : Determination of manganese after oxidation to the manganic state stabilized by triethanolamine

The manganic complex with triethanolamine, prepared by the oxidation of manganous solution in presence of 0.5M NaOH and 4% by volume triethanolamine with atmospheric oxygen, is found suitable for the polarographic determination of manganese. Under these conditions, the diffusion current is proportional to the Mn⁺² concentration from 2.10^-4·7.10^-3ME$\text{1}\text{2}$,for the Mn⁺³/Mn⁺² wave = — 0.5 V vs S.C.E. The temperature coefficient for the diffusion current 1.2% per degree I and D° decrease by increasing the alkali or triethanolamino concentration. They amount in presence of NaOH = 0.5M and 4% triethanolamine to I = 1.27 and D° = 4.18·10^-6 cm²/sec.     

Inverse polarographic determination of creatinine with alkaline picrate and 3,5-dinitrosalicylic acid

A selective and highly sensitive inverse polarographic method for the determination of creatinine has been developed, involving the measurement of disappearance of diffusion current for the picric acid wave ($\text{E}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= ?0.501}\text{V}$) when creatinine is added. Creatinine levels of 0–5 μg/ml can be measured accurately.Investigation of 3,5-dinitrobenzoic acid and 3,5-dinitrosalicylic acid revealed the latter to be more reactive and useful for the inverse polarographic determination of creatinine at levels of 0–30 μg/ml.     

Electrochemical study and polarographic determination of ranitidine

In the polarographic reduction of ranitidine, an H₂-antagonist of histamine, three waves are observed; their half-wave potentials and limiting currents depend strongly on the pH of the solution. The first and second waves are due to reduction of teh protonated, CHNO₂H⁺, and unprotonated, CHNO₂, nitroethene group of ranitidine, respectively; the origin of the third wave is unknown. The characteristics of the second and third waves are studied in acetic acid/acetate buffer at pH 5.5; the first wave does not appear at this pH. The second wave (E_{$\text{1}\text{2}$} = ?0.90 V, vs. Ag/AgCl) is useful for determining ranitidine in the range 2.4–4.9 × 10^?4 M by direct current polarography and in the range 2.5 × 10^?7?2.05 × 10^?5 M by differential pulse polarography.     

Dosage de l'histidine: Étude polarographique et dosage du dinitrofluorobenzene

After polarographic study and determination of dinitrofluorobenzene at varying pH and determination of a number of electron exchanges (n), standardization curves have been constructed at pH 5 and 10. They allow the estimation of DNFB to a concentration of 1γ/ml with a precision of 4–7%. The curve shows 2 or 3 leaps, according to pH.. The E_{$\text{1}\text{2}$} of the first two are less than 1 volt.     

Analytical application of triethylenetetraaminehexa- acetic acid: Part 2. Polarographic Investigation of the reactions of TTHA at the dropping mercury electrode

TTHA gives an anodic d.c. wave and s.w. peak corresponding to oxidation of mercury at the d.m.e. surface with formation of a Hg(II)—TTHA complex. Similar processes are known for other ligands, e.g. EDTA and DCTA, but the greater stability of the Hg(II)—TTHA complex gives a significant improvement in the shapes of the anodic wave and s.w. peak. An increase in pH shifts the E_{$\text{1}\text{2}$} and E_p values towards more negative values because the conditional stability constant of the Hg(II)—TTHA complex is increased. Although the half–wave potentials of the reduction wave of Hg(II)—TTHA and of the anodic wave of TTHA, are the same, other criteria for the reversibility of polarographic reactions suggest that the anodic TTHA process at the d.m.e. is not completely reversible. The temperature coefficient of the wave and s.w. peak as well as the dependence of the wave height on the square root of the mercury head prove that the process is diffusion–controlled. Supporting electrolytes are given for which the d.c. wave and the s.w. peak of TTHA are well-shaped, with linear dependence between the wave or peak height and the concentration of TTHA in the ranges 5 × 10^-5–5 × 10^-4 M (d.c.) and 1 0^-5–1 × 10^-4 M (s.w.).     

The riboflavin—dihydroriboflavin system in acidic medium on mercury: Part II. A polarographic investigation

Polarographic current—potential characteristics and current—time curves for the reduction of riboflavin (RF) to dihydroriboflavin (DRF) in 0.01 M HClO₄ + 0.09 M NaClO₄ have been examined in detail. It has thus been shown that the RF adsorption prewave is due to the formation of two overlapping adsorbed monolayers of DRF molecules. Lateral interactions of RF molecules between themselves, of DRF molecules between themselves and of RF with DRF molecules in the first adsorbed monolayer are weak, whereas vertical interactions between overlapping DRF molecules are relatively strong. This explains the abrupt increase in the slope of the RF adsorption prewave and its shift towards more positive potentials as soon as the second adsorbed monolayer of DRF starts to form. The so-called “normal” wave for RF reduction has a half-wave potential E^II_{$\text{1}\text{2}$} = ?0.180 V/SCE, practically coinciding with the formal potential of the RF/DRF couple, and a slope corresponding to a reversible two-electron reduction unaffected by semiquinone formation. The shape of polarographic mean current vs. potential curves has been accounted for through an approximate solution of the corresponding diffusional problem.     

Electrochemical studies of organometallic compounds : III. The polarographic determination of the CH acidity of metallocenes

The polarographic reduction of the tree sets of compounds, i.e. organomercury salts, symmetrical organomercury compounds and σ-derivatives of π-cyclopentadienyliron dicarbonyl, have been investigated. The polarographic parameters obtained have been correlated with the pK_a values of RH. A least squares treatment of the results and a comparison of the accuracy of the determination for the new pK_a values of RH obtained for the three sets of reactions investigated show that the best correlation is obtained for a plot of the half-wave reduction potentials E_{$\text{1}\text{2}$} of π-C₅H₅Fe(CO)₂-σ-R and the pK_a values of RH. The pK_a values for ferrocene, cyclopentadienylmanganese and rhenium tricarbonyls as CH acids have been determined.     

The lowest quartet state of copper porphin: Zeeman experiments at 4.2 K

Zeeman experiments in a magnetic field of 75 kG on copper porphin in a single crystal of n-octane prove the lowest metastable state to be a quartet as predicted by Gouterman and colleagues. In zero magnetic field this quartet is split into two degenerate pairs, the ±$\text{1}\text{2}$ components lying at about 0.7 cm^?1 higher energy than the ±$\text{3}\text{2}$ components.     

Heterodiene syntheses—XIX: Correlation of the kinetic data with lumo energies in the reaction between 1-aryl-4-benzylidene-5-pyrazolones and isopropyl vinyl ether

The kinetics of the reaction between 1-p-substituted phenyl-4-benzylidene-5-pyrazolones and isopropyl vinyl ether have been studied by quantitative spectroscopic analysis and liquid chromatography. The rate increases with the electron attracting character of the substituents and a correlation is obtained with σ- constants. The polarographic one-electron half-wave reduction potentials E^red_{$\text{1}\text{2}$}, which represent an experimental measure for the relative energy of the lowest unoccupied molecular orbital (LUMO), were measured. Good correlations were obtained between these and the kinetic data, thus demonstrating the frontier-controlled character of the cycloaddition and the dominant interaction between the LUMO of the pyrazolone and the highest occupied molecular orbital (HOMO) of the vinyl ether.     

Étude du comportement polarographique de Ge(IV)

A reduction wave of Ge(IV) is observed at pH valvest greater than 7. The study of the wave has shown that the reduction is irreversible and occurs from Ge⁺⁴ to Ge° and that its height is strongly dependend on the pH. We have shown that the second wave observed by Das Gupta and Nair in the medium NH₄CI-NH₄OH cannot be ascribed to Ge. From an analytical point of view, it should be operated in the pH-regiXXXn. from 8 to 9, wliere the height of the wave can be considered as constant ; the diffusion current constant equals 6.82. In the KCl 0.05M medium, we have measured D = 0.79.1O^-5 cm²/sec and E$\text{1}\text{2}$ = —1.50 volt v/SCE; where as NH₄Cl-NH₄OH, medium. D = 0.89–10^-5 cm²/sec and E$\text{1}\text{2}$ = —1.56 volt v/SCE,     

Structure cristalline de Cu4(PO4)2O

Cu₄(PO₄)₂O is a new copper-rich phosphate. The preparation is described. The unit cell is triclinic, $\text{P}\text{1}$, with a = 7.528 Å, b = 8.090 Å, c = 6.272 Å; α = 113.68°, β = 81.56°, γ = 105.77°. The structure was solved from 1526 independent reflections using Patterson and Fourier syntheses. The final R value is 0.041 for the 1217 strongest reflections. Copper sites form a three-dimensional framework. The structure consists of homogeneous layers of copper and oxygen atoms parallel to the (012) plane. Phosphorus atoms are inserted between copper and oxygen layers.     

Electrochemical oxidation of α-hyponitrate ion and its analytical applications

α-Hyponitrate ion is electrochemically oxidized at mercury electrodes: the reaction proceeds by an initial 1-electron oxidation to give an anion radical which decomposes to give nitrogen oxide and nitrite as the ultimate products. The d.c. polarographic wave of α-hyponitrate (E_{$\text{1}\text{2}$} = -0.325 V vs. SCE) in 0.1 M sodium hydroxide can be used for the determination of α-hyponitrate in the range 0.08–1.3 mM; a.c. polarography (E_p = -0.30 V vs. SCE) is useful in the range 0.075–1.0 mM. Amperometric titration with 0.05 M hexacyanoferrate(III) is suitable for determinations of 5–20 mg of sodium α-hyponitrate. A.c. polarography at pH 11.0 allows α-hyponitrate to be determined in the presence of 50-fold amounts of hydroxylamine.     

Analytical applications of azoisoxazoles. III. Complexes of cobalt,copper, and cadmium with 2-(5′-methyl-2′-isoxazolylazo)-4-methoxyphenol

2-(5′-methyl-2′-isoxazolylazo)-4-Methoxyphenol has been synthesized and its ionization constant (pK_a = 7.98 ± 0.08) spectrophotometrically determined in a 4% ($\text{v}\text{v}$) ethanol-water medium at μ = 0.25 M (NaClO₄). The reagent originates water soluble complexes with cobalt (log β₂ = 11.45 ± 0.16), copper (log β₁ = 7.15 ± 0.10), and cadmium (log β₁ = 3.96 ± 0.12), and can be used for the spectrophotometric determination of cobalt and copper as well as metallochromic indicator for copper.     

The crystal structure of strontium tetraiododiargentate octahydrate,SrAg2I4 · 8H2O

Crystals of strontium tetraiododiargentate octahydrate, SrAg₂I₄ · 8H₂O belong to the tetragonal space group I422(D⁹₄), with a = 12.86 ± 0.03, c = 5.56 ± 0.02Å, and Z = 2. The structure may be described as having, in one-to-one ratio, columns formed by [Sr(H₂O)₈]²⁺ entities centered at (0, 0) and ($\text{1}\text{2}\text{,}\text{1}\text{2}$) and chains of edge-sharing AgI₄ tetrahedra centered at ($\text{1}\text{2}$, 0) and (0, $\text{1}\text{2}$), the chains being linked to each other through water molecules by hydrogen bonding and through van der Waals forces between iodide ions. The crystals are obtained from a saturated aqueous solution of SrI₂ which is then saturated with AgI; dilution of this solution or addition of water to the crystals precipitates β-AgI. This demonstrates the ease with which the three-dimensional corner-sharing tetrahedra of the β-AgI transform to the edge-sharing chain arrangement of tetrahedra and vice versa. It is probable that the saturated solution itself contains [Sr(H₂O)₈]²⁺ and AgI₄-chain entities.Anhydrous compounds of strontium and barium halides with silver and copper halides appear to be unattainable at atmospheric pressure. It is speculated that this is associated with the particular coordination requirements of the alkaline earth ions.