Dichloramine-B as redox titrant in non-aqueous or partially aqueous media

Dichloramine-B is proposed as a redox titrant in glacial acetic acid medium. The general conditions for its use and the procedures for estimating hydrazine, ascorbic acid, ferrocyanide, hydroquinone, oxine, antimony(III) and thallium(I) potentiometrically and allyl, crotyl and cinnamyl alcohols by a back-titration procedure are described.     

Dibromamine-B as a new redox titrant in non-aqueous or partially aqueous media

A new redox titrant, dibromamine-B (N,N'-dibromobenzene sulphonamide) is introduced for use in acetic acid medium. Direct potentiometric determinations of hydrazine, ascorbic acid, aniline, thiourea and its metal complexes and oxine and its metal complexes have been described.     

Complexes formed in solution between vanadium(IV)/(V) and the cyclic dihydroxamic acid putrebactin or linear suberodihydroxamic acid

An aerobic solution prepared from V(IV) and the cyclic dihydroxamic acid putrebactin (pbH(2)) in 1:1 H(2)O/CH(3)OH at pH = 2 turned from blue to orange and gave a signal in the positive ion electrospray ionization mass spectrometry (ESI-MS) at m/z(obs) 437.0 attributed to the monooxoV(V) species [V(V)O(pb)](+) ([C(16)H(26)N(4)O(7)V](+), m/z(calc) 437.3). A solution prepared as above gave a signal in the (51)V NMR spectrum at δ(V )= -443.3 ppm (VOCl(3), δ(V) = 0 ppm) and was electron paramagnetic resonance silent, consistent with the presence of [V(V)O(pb)](+). The formation of [V(V)O(pb)](+) was invariant of [V(IV)]:[pbH(2)] and of pH values over pH = 2-7. In contrast, an aerobic solution prepared from V(IV) and the linear dihydroxamic acid suberodihydroxamic acid (sbhaH(4)) in 1:1 H(2)O/CH(3)OH at pH values of 2, 5, or 7 gave multiple signals in the positive and negative ion ESI-MS, which were assigned to monomeric or dimeric V(V)- or V(IV)-sbhaH(4) complexes or mixed-valence V(V)/(IV)-sbhaH(4) complexes. The complexity of the V-sbhaH(4) system has been attributed to dimerization (2[V(V)O(sbhaH(2))](+) ? [(V(V)O)(2)(sbhaH(2))(2)](2+)), deprotonation ([V(V)O(sbhaH(2))](+) - H(+) ? [V(V)O(sbhaH)](0)), and oxidation ([V(IV)O(sbhaH(2))](0) -e(-) ? [V(V)O(sbhaH(2))](+)) phenomena and could be described as the sum of two pH-dependent vectors, the first comprising the deprotonation of hydroxamate (low pH) to hydroximate (high pH) and the second comprising the oxidation of V(IV) (low pH) to V(V) (high pH). Macrocyclic pbH(2) was preorganized to form [V(V)O(pb)](+), which would provide an entropy-based increase in its thermodynamic stability compared to V(V)-sbhaH(4) complexes. The half-wave potentials from solutions of [V(IV)]:[pbH(2)] (1:1) or [V(IV)]:[sbhaH(4)] (1:2) at pH = 2 were E(1/2) -335 or -352 mV, respectively, which differed from the expected trend (E(1/2) [VO(pb)](+/0) < V(V/IV)-sbhaH(4)). The complex solution speciation of the V(V)/(IV)-sbhaH(4) system prevented the determination of half-wave potentials for single species. The characterization of [V(V)O(pb)](+) expands the small family of documented V-siderophore complexes relevant to understanding V transport and assimilation in the biosphere.     

Spectrophotometric determination of vanadium(IV) in the presence of vanadium(V) using Br-PADAP

In the present paper, a simple and sensitive method is proposed for vanadium(IV) determination in the presence of vanadium(V). This is based on the oxidation of vanadium(IV) present in the sample to vanadium(V) by addition of iron(III) cation, followed by a complexation reaction of iron(II) with the spectrophotometric reagent 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP). The iron(II) reacts with Br-PADAP immediately, forming a stable complex with a large molar absorptivity. The vanadium(IV) determination is possible, with a calibration sensitivity of 0.549 g ml^–1, for an analytical curve of 18.8 ng ml^–1 to 2.40 g ml^–1, molar absorptivity of 2.80 × 10⁴ 1 mole^–1 cm^–1 and a detection limit of 5.5 ng ml^–1. Selectivity was increased with the use of EDTA as a masking agent. The proposed method was applied for the vanadium(IV) determination in the presence of several amounts of vanadium(V). The results revealed that 200 g of vanadium(V) do not interfere with determination of 5.00 g of vanadium(IV). The precision and the accuracy obtained were satisfactory (R. S. D.<2%).     

Hydrolytic precipitation of calcium polyvanadates from vanadium(IV) and vanadium(V) solutions

The effect of VO²⁺ ions on the composition and kinetics of calcium polyvanadate precipitation from solutions with 1.5 ≤ pH ≤ 9 at 80–90°C has been studied. For 1,5 ≤ pH < 3 and V⁴⁺/V⁵⁺ = 0.11–9, the precipitated compounds have the general formula Ca _x V _y ⁴⁺ V _12?y ⁵⁺ O_31?δ · nH₂O (0.8 ≤ x ≤ 1.06, 2 ≤ y ≤ 3, 0.94 ≤ δ ≤ 1.5). The maximum vanadium(IV) proportion (y = 3) in the precipitates is achieved when V⁴⁺/V⁵⁺ = 0.5?1.0 in the solution and pH is 3. Polyvanadate precipitation at pH 1.7 has a long induction period (up to 30 min), which is not observed for V⁴⁺/V⁵⁺ > 0.1. Precipitation in solutions with pH 3 occurs only when VO²⁺ ions are added, with a maximum rate near V⁴⁺/V⁵⁺ = 0.2 and in presence of chloride ions. The processes are controlled by a secondorder reaction on the polyvanadate surface.     

Spectrophotometric determination of vanadium as vanadium(IV) pyridine thiocyanate

A spectrophotometric determination of vanadium as vanadium(IV) pyridine thiocyanate is described. The blue complex is formed in acidic aqueous solution and extracted into pyridine-chloroform. Absorbance is measured at 7.40 mμ. The range of best accuracy for 1-cm cells is from about 80 to 240 μg of vanadium per ml, and sensitivity is 0.4 μg of vanadium per cm² at 7.40 mμ. The vanadium may be present initially as vanadium(IV) or vanadium(V), which is reduced to vanadium(IV) by the large excess of thiocyanate ion added. Several elements interfere in the determination ; a separation procedure involving mercury cathode electrolysis is suggested.     

Binuclear vanadium(V) and vanadium(IV,V) complexes of dihydrocaffeic,caffeic and ferulic acids

Summary Binuclear complexes of dihydrocaffeic, caffeic and ferulic acids with vanadium were prepared and studied. The suggested square-pyramidal structures with catecholic-type coordination are supported by various spectroscopic, magnetic and thermogravimetric data.     

o,o′-Alkylene dithiophosphato complexes of vanadium(IV) and vanadium(V)

Reactions of VO(acac)₂ with alkylene dithiophosphoric acids, POGOS₂H, and of VOCl₃ with the ammonium salts NH₄(POGOS₂) in 1:2 molar ratio gave the oxovanadium(IV) alkylene dithiophosphates, [VO(POGOS₂)₂], and monochloroxovanadium(V) alkylene dithiophosphates, [VOCl(POGOS₂)₂], respectively, where G = —CH₂CMe₂-CH₂—, —CH₂CEt₂CH₂—, —CHMeCH₂CMe₂— or —CMe₂CMe₂—. These complexes are green solids, soluble in common organic solvents and sensitive to moisture. They were characterized by elemental analysis, molecular weight and spectral studies including i.r. and n.m.r. (¹H, ¹³C and ³¹P), which suggested bidentate bonding of the POGOS₂ ligands to give a square pyramidal for the V^IV complexes and an octahedral geometry for the V^V complexes.     

Vanadium(IV) and vanadium(V) complexes of salicyladimine ligands

The synthesis and characterization of a V(IV) and a V(V) complex of the salicyladimine ligand system are described. The reaction of salicylaldehyde and 1,3-diaminohydroxypropane with vanadyl sulfate produced a monomer (VOL1) which, upon heating in methanol, crystallized as a V(V) complex (VO(2)L1). The reaction of 3-methoxysalicylaldehyde, 1,3-diaminohydroxypropane, and vanadyl sulfate resulted in a binuclear complex held together by hydrogen bonding (VOL2). VOL1 was determined to catalyze the epoxidation of cyclohexene better than VOL2. The synthesis and characterization of VOL1, VOL2, and VO(2)L1 are described. The role of each complex as a catalyst for the epoxidation of cyclohexene is investigated. Results indicate that the V(V) complex performs better than either of the V(IV) complexes.     

Kinetic-catalytic determination of vanadium(IV) using methyl orange-bromate redox reaction.

Determination of V(IV) based on its catalytic effect on the reaction between Methyl Orange and bromate in thepresence of citric acid was studied. The calibration curve obtained by fixed-time method was linear in the range of 2.5-300 ng ml(-1). By use of slope method, a calibration curve containing two linear portions were obtained. Using fixed-time and slope methods, we obtained detection limits of 0.8 and 1.5 ng ml(-1), respectively. Fe2+, As(III), V(V) and Hg2+ interfered. The method was successful for analysis of water samples.     

Joint extraction of vanadium(V) and vanadium(IV) with di(2-ethylhexyl) hydrogen phosphate

The organic extracts formed in joint extraction of vanadium(V) and vanadium(IV) with di(2-ethylhexyl) hydrogen phosphate from weakly acidic aqueous solutions were characterized by IR and electronic spectroscopy and chemical analysis.     

Selective and sensitive extraction spectrophotometric method for the determination of vanadium (V) as a mixed ligand complex withN-phenyl benzohydroxamic acid and 4-(2-pyridylazo)resorcinol in non-aqueous media

A selective, sensitive and direct method for the spectrophotometric determination of vanadium in steels is developed in which vanadium is extracted withN-phenyl benzohydroxamic acid (PBHA) into chloroform from 5M hydrochloric acid medium followed by colour development by addition of 4-(2-pyridylazo)resorcinol (PAR) inN,N-dimethyl formamide (DMF). The vanadium(V)-PBHA-PAR mixed ligand complex shows maximum absorbance at 560 nm with a molar absorptivity 3.6 × 10⁴ l mol^–1 cm^–1 and obeys Beer's law up to 2.0 g/ml of vanadium. The composition of the mixed ligand complex is determined by Job's method of continuous variations which revealed a 1 1 1 ratio for V(V) PBHA PAR. This method can be directly applied for the determination of vanadium in steels, while in the case of titanium base alloys, after separation of titanium matrix it gives good results even at 50–200 g of vanadium per gram level.     

Cyclic voltammetric study of the redox system of glutathione using the disulfide bond reductant tris(2-carboxyethyl)phosphine

The stabilization of the reduction state of proteins and peptides is very important for the monitoring of protein-protein, protein-DNA and protein-xenobiotic interactions. The reductive state of protein or peptide is characterized by the reactive sulfhydryl group. Glutathione in the reduced (GSH) and oxidized (GSSG) forms was studied by cyclic voltammetry. Tris(2-carboxyethyl)phosphine (TCEP) as the disulfide bond reductant and/or hydrogen peroxide as the sulfhydryl group oxidant were used. Cyclic voltammetry measurements, following the redox state of glutathione, were performed on a hanging mercury drop electrode (HMDE) in borate buffer (pH 9.2). It was shown that in aqueous solutions TCEP was able to reduce disulfide groups smoothly and quantitatively. The TCEP response at -0.25 V vs. Ag/AgCl/3 M KCl did not disturb the signals of the thiol/disulfide redox couple. The origin of cathodic and anodic signals of GSH (at -0.44 and -0.37 V) and GSSG (at -0.69 and -0.40 V) glutathione forms is discussed. It was shown that the application of TCEP to the conservation of sulfhydryl groups in peptides and proteins can be useful instrument for the study of peptides and proteins redox behavior.     

Hydrolytic precipitation of magnesium polyvanadates in vanadium (IV, V) solutions

The phase and chemical composition of precipitates formed in Mg(VO₃)₂-VOSO4-H₂O system at initial pH from 1 to 7 and temperature from 80 to 90°C was studied. Polyvanadates of variable composition Mg _x V _y ⁴⁺V_12-y ⁵⁺¹O_31–δ · nH₂O (0.7 ≤ x ≤ 1.3, 1.2 ≤ y ≤ 2.4, 0.7 ≤ δ = 1.4) were formed at pH from 1 to 4 and V⁴⁺/V⁵⁺ ratio from 0.43 to 9. Compounds with the general formula Mg _x V _y ⁴⁺V_6-y ⁵⁺O_16-δ · nH₂O (0.7 ≤ x ≤ 0.65, y = 1.0, 0.8 ≤ δ ≤ 0.85) were formed at pH from 6.0 to 7.0 and V⁴⁺/V⁵⁺ ratios from 0.11 to 0.25. The maximum V⁴⁺ concentration (y = 2.4) in the precipitates was achieved at the VV⁴⁺/V⁵⁺ solution ratio of 1.0 and pH = 3. The precipitates in solutions with pH 3 were formed only upon addition of VO²⁺ ions with the maximum rate at a V⁴⁺/V⁵⁺ ratio of 0.33. These processes were limited by second-order reactions on the surface of polyvanadates.     

Synthesis,spectroscopic, theoretical study,and biological activities of vanadium(IV) and vanadium(V) complexes with isonipecotic acid

Russian Journal of General Chemistry - Vanadium(IV) and vanadium(V) complexes 1–7 have been synthesized by the reaction of isonipecotic acid with VOSO4 · 3 H2O, VCl3(THF)3, and NH4VO3 at...     

Liquid-liquid extraction of vanadium(V) from sulfate media with diisododecylamine

The liquid-liquid extraction of vanadium(V) from sulfate media with diisododecylamine (DIDA), a new reagent providing an alternative to the well-known trioctylamine-based extractant, has been investigated at 22°C with toluene and kerosene as diluents. DIDA efficiently recovers vanadium(V) from weakly acidic solutions (pH 5–6), yielding a DIDA: V = 1: 2.5 (mol/mol) complex in the organic phase. Vanadium is completely reextractable from the organic phase with an NH₄OH solution (1: 1). IR spectroscopic studies and Karl Fisher determination of the water content of the extracts have demonstrated that vanadium extraction is due an interfacial anion-exchange reaction (log K _ex = 1.6–1.7) yielding amine association species containing inverse micelles.