Low-temperature UV-visible and NMR spectroscopic investigations of O(2) binding to ((6)L)Fe(II), a ferrous heme bearing covalently tethered axial pyridine ligands

In this report, we describe the reversible dioxygen reactivity of ((6)L)Fe(II) (1) [(6)L = partially fluorinated tetraphenylporphyrin with covalently appended TMPA moiety; TMPA = tris(2-pyridylmethyl)amine] using a combination of low-temperature UV-vis and multinuclear ((1)H and (2)H) NMR spectroscopies. Complex 1, or its pyrrole-deuterated analogue ((6)L-d(8))Fe(II) (1-d(8)), exhibits downfield shifted pyrrole resonances (delta 28-60 ppm) in all solvents utilized [CH(2)Cl(2), (CH(3))(2)C(O), CH(3)CN, THF], indicative of a five-coordinate high-spin ferrous heme, even when there is no exogenous axial solvent ligand present (i.e., in methylene chloride). Furthermore, ((6)L)Fe(II) (1) exhibits non-pyrrolic upfield and downfield shifted peaks in CH(2)Cl(2), (CH(3))(2)C(O), and CH(3)CN solvents, which we ascribed to resonances arising from the intra- or intermolecular binding of a TMPA-pyridyl arm to the ferrous heme. Upon exposure to dioxygen at 193 K in methylene chloride, ((6)L)Fe(II) (1) [UV-vis: lambda(max) = 433 (Soret), 529 (sh), 559 nm] reversibly forms a dioxygen adduct [UV-vis: lambda(max) = 422 (Soret), 542 nm], formulated as the six-coordinate low-spin [delta(pyrrole) 9.3 ppm, 193 K] heme-superoxo complex ((6)L)Fe(III)-(O(2)(-)) (2). The coordination of the tethered pyridyl arm to the heme-superoxo complex as axial base ligand is suggested. In coordinating solvents such as THF, reversible oxygenation (193 K) of ((6)L)Fe(II) (1) [UV-vis: lambda(max) = 424 (Soret), 542 nm] also occurs to give a similar adduct ((6)L)Fe(III)-(O(2)(-)) (2) [UV-vis: lambda(max) = 418 (Soret), 537 nm. (2)H NMR: delta(pyrrole) 8.9 ppm, 193 K]. Here, we are unable to distinguish between a bound solvent ligand or tethered pyridyl arm as axial base ligand. In all solvents, the dioxygen adducts decompose (thermally) to the ferric-hydroxy complex ((6)L)Fe(III)-OH (3) [UV-vis: lambda(max) = 412-414 (Soret), 566-575 nm; approximately delta(pyrrole) 120 ppm at 193 K]. This study on the O(2)-binding chemistry of the heme-only homonuclear ((6)L)Fe(II) (1) system lays the foundation for a more complete understanding of the dioxygen reactivity of heterobinuclear heme-Cu complexes, such as [((6)L)Fe(II)Cu(I)](+), which are models for cytochrome c oxidase.     

Determination of doxorubicin hydrochloride by visible spectrophotometry

Four simple and sensitive visible spectrophotometric methods (A-D) have been described for the assay of doxorubicin hydrochloride either in pure form or in pharmaceutical formulations. Method A was developed based on oxidation of the drug with Fe(III) to produce Fe(II), which subsequently reacts with 1.10-ortho-phenanthroline to form a red colored complex (lambda(max): 510 nm) at pH 4.6. Method B involves the reduction of Folin-Ciocalteu (F-C) reagent by the drug and the reduced species formed possesses a characteristic intense blue color (lambda(max): 770 nm). In methods C and D. oxidation of the drug with periodate at specified experimental conditions yields formaldehyde and dialdehyde, which in turn react either with 3-methyl-2-benzothiazolinone hydrazone hydrochloride to form an intensely brilliant blue cationic dye (lambda(max): 620-670 nm. method C) or by condensation with phenylhydrazine hydrochloride (PHH) to form orange-red colored product (lambda(max): 510 nm, method D) in the presence of potassium ferricyanide. All of the variables have been optimized and the reaction mechanisms presented. The concentration measurements are reproducible within a relative standard deviation of 1.0%.     

Spectrophotometric determination of Fe(III) in alkaline solutions without neutralization

Spectrometric study on the complexation of Fe(III) with an organic reagent obtained by coupling 3-methyl-1-phenyl-5-pyrazolone with diazotized 3-hydroxy-4-amino-benzene sulphonic acid was carried out in alkaline solutions. A 1:2 Fe(III): reagent water soluble complex is formed. The optimum pH is 9.0-11.8. The maximum absorbance of the complex lies at lambda = 560 nm, where the absorbance of the reagent is low. The molar absorptivity is 9000 l.mole(-1).cm(-1) at pH = 11.6. The value of the stability constant determined at 20 +/- 1 degrees C, pH = 11.6 and lambda = 560 nm is 4 x 10(5)M. The Beer-Lambert law is followed for iron concentration in the 0.2-5.0 mug/ml range. The spectrophotometric method was tested on synthetic solutions and thus applied for determination of traces of Fe(III) in several samples of alkaline hydroxides and carbonates without the neutralization of the solutions.     

Complexation equilibria and spectrophotometric determination of iron(III) with 1-amino-4-hydroxyanthraquinone

The complex equilibria of iron(III) with 1-amino-4-hydroxyanthraquinone (AMHA) were studied spectrophotometrically in 40% (v/v) ethanol and an ionic strength of 0.1M (NaClO(4)). The complexation reactions were demonstrated and characterized using graphical logarithmic analysis of the absorbance-pH graphs. A simple, rapid, selective and sensitive method for the spectrophotometric determination of trace amounts of Fe(III) is developed based on the formation of Fe(AMHA) complex at pH 2.5 (lambda(max) = 640 nm, epsilon approximately = 2.1 x 10(4) L. mol(-1) . cm(-1)) in the presence of a large number of foreign ions. Interferences caused by palladium(II) was masked by the addition of cyanide ions. The method has been applied to the determination of iron in some synthetic samples and polymetallic iron ores.     

Molecular and electronic structure of square-planar nickel II, nickel III and nickel III pi-cation radical complexes with a tetradentate o-phenylenedioxamidate redox-active ligand

The molecular and electronic structures of the electron transfer series of four-coordinate square-planar nickel complexes with the ligand o-phenylenebis(N'-methyloxamidate), [NiL]z (z = 2-, 1-, 0), have been evaluated by DFT and TDDFT calculations, and most of their experimentally available structural and spectroscopic properties (X. Ottenwaelder et al., Dalton Trans., 2005, DOI: 10.1039/b502478a) have been reasonably reproduced at the B3LYP level of theory. The anionic species [NiL]2- and [NiL]- are genuine low-spin nickel II and nickel III complexes with diamagnetic singlet (S = 0) and paramagnetic doublet (S = 1/2) states, respectively. The nickel III complex presents shorter Ni-N(amidate) bond distances (1.85-1.90 A) than the parent nickel II complex (1.88-1.93 A) and characteristic LMCT bands in the NIR region (lambda max = 794 and 829 nm) while the analogous MLCT bands for the nickel(II) complex are in the UV region (lambda max = 346 and 349 nm). The neutral species [NiL] is a nickel III o-benzosemiquinonediimine pi-cation radical complex with a diamagnetic singlet (S = 0) and a paramagnetic triplet (S = 1) states fairly close in energy but fundamentally different in orbital configuration. The singlet metal-radical ground state results from the antiferromagnetic coupling between the 3d(yz) orbital of the Ni III ion (S(M) = 1/2) and the pi(b) orbital of the benzosemiquinone-type radical ligand (S(L) = 1/2), which have a large overlap and thus strong covalent bonding. The triplet metal-radical excited state involves the ferromagnetic coupling between the Ni III 3d(zx) orbital and the benzosemiquinone-type pi(b) orbital, which are orthogonal to each other. The singlet and triplet states of the nickel III pi-cation radical complex possess characteristic quinoid-type short-long-short alternating sequence of C-C bonds in the benzene ring, as well as intense MLCT transitions in the VIS (lambda max = 664 nm) and NIR (lambda max = 884 nm) regions, respectively.     

Heme/non-heme diiron(II) complexes and O2, CO, and NO adducts as reduced and substrate-bound models for the active site of bacterial nitric oxide reductase

As a first generation model for the reactive reduced active-site form of bacterial nitric oxide reductase, a heme/non-heme diiron(II) complex [(6L)Fe(II)...Fe(II)-(Cl)]+ (2) {where 6L = partially fluorinated tetraphenylporphyrin with a tethered tetradentate TMPA chelate; TMPA = tris(2-pyridyl)amine} was generated by reduction of the corresponding mu-oxo diferric compound [(6L)Fe(III)-O-Fe(III)-Cl]+ (1). Coordination chemistry models for reactions of reduced NOR with O2, CO, and NO were also developed. With O2 and CO, adducts are formed, [(6L)Fe(III)(O2-))(thf)...Fe(II)-Cl]B(C6F5)4 (2a x O2) {lambda(max) 418 (Soret), 536 nm; nu(O-O) = 1176 cm(-1), nu(Fe-O) = 574 cm(-1) and [(6L)Fe(II)(CO)(thf)Fe(II)-Cl]B(C6F5)4 (2a x CO) {nu(CO) 1969 cm(-1)}, respectively. Reaction of purified nitric oxide with 2 leads to the dinitrosyl complex [(6L)Fe(NO)Fe(NO)-Cl]B(C6F5)4 (2a x (NO)2) with nu(NO) absorptions at 1798 cm(-1) (non-heme Fe-NO) and 1689 cm(-1) (heme-NO).     

On-line dilution flow injection manifold for the selective spectrophotometric determination of ascorbic acid based on the Fe(II)-2,2'-dipyridyl-2-pyridylhydrazone complex formation

A new simple and rapid FI method for the accurate and precise spectrophotometric determination of ascorbic acid (AsA) in pharmaceutical formulations is reported. The method is based on the reduction of Fe(III) to Fe(II) by the analyte, and the subsequent reaction of the produced Fe(II) with 2,2'-dipyridyl-2-pyridylhydrazone (DPPH) in acidic medium (pH ca. 2.5) to form a colored complex (lambda(max)=535 nm). An on-line dilution mode using a binary inlet static mixer (BISM) was incorporated in the FI system, allowing the determination of the analyte in a wide concentration range. The calibration graph was linear in the range of 5.7-600.0 mg l(-1) AsA, at a sampling rate of 120 injections h(-1). The method was found to be very precise [s(r)=0.1% at 300 mg l(-1) AsA (n=12)] and the 3delta detection limit (c(L)=1.7 mg l(-1)) was quite satisfactory. The detailed study of various interferences confirmed the high selectivity of the proposed method. Its application to a variety of pharmaceuticals produced excellent results, with a mean relative error of e(r)<1.0%.     

Complexation and determination of palladium (II) ion with para-Cl-phenylazo-R-acid spectrophotometrically

The complexation of para-Cl-phenylazo-R-acid azo dye with Pd(II) has been studied spectrophotometrically. Protonation constant (pK(a)) of the ligand has been calculated and the stability conditional constants of para-Cl-phenylazo-R-acid ligand with palladium ion has been determined at a constant temperature (25.0 degrees C), where the molar ratio of this complex is 1:1 (metal:ligand) with logbeta(1)=3.75, and 1:2 with logbeta(2)=8.55. Solid complex of para-Cl-phenylazo-R-acid has been prepared and characterized on the basis of elemental analysis and FTIR spectral data. A procedure for the spectrophotometric determination of Pd(II) using para-Cl-phenylazo-R-acid as a new azo chromophore is proposed where it is rapid, sensitive and highly specific. Beer's law was obeyed in the range 0.50-10.00 ppm at pH 5.0-6.0 to form a violet-red complex (epsilon=7.7 x 10(4) l(-1) mol(-1) cm(-1) at lambda(max)=560 nm). Metal ions such as Cu(II), Cr(III), La(III), Yb(III), Y(III), and Rh(III) interfere with the complex. Ammonium salt of trimellitic acid is used to precipitate some of the interfering ions and a scheme for separation of Pd(II) from a synthetic mixture similar in composition to platinum ore or deposit was made.     

Spectrophotometric determination of cobalt(II) with 2-[di-(2-pyridyl)-methylidenehydrazino]quinoline

A simple, rapid and selective procedure for spectrophotometric determination of cobalt has been developed. Cobalt(II) forms two water-soluble complexes with 2-[di-(2-pyridyl)methylidenehydrazino]quinoline, an orange-yellow complex (lambda(max) 510 nm) in the pH range 2-12 and a pink complex (lambda(max) 530 nm) in 0.1-6M perchloric acid medium. The molar absorptivities for the orange-yellow and pink complexes are 3.65 x 10(4) and 4.1 x 10(4) 1.mole(-1).cm(-1) and Beer's law is obeyed up to 1.84 and 2.0 ppm of cobalt(II) respectively. Cobalt(II) has also been determined in alloys.     

Colorimetric recognition of Cu(II) by (2-dimethylaminoethyl)amino appended anthracene-9,10-diones in aqueous solutions: deprotonation of aryl amine NH responsible for colour changes

Chromogenic receptors 2 and 3 undergo distinct colour changes from magenta to blue on gradual addition of Cu(II) and can be used as colorimetric probes for spectrophotometric and visual analysis of Cu(II) in the presence of biological metal ions Na(I), K(I), Mg(II), Ca(II), Fe(II), Zn(II) etc. in aqueous solution (methanol-water 1 : 1 v/v). On addition of Cu(II), both 2 and 3 exhibit a bathochromic shift of Delta lambda(max) = 114 nm for 2 and Delta lambda(max)= 150 and 265 nm for receptor 3. The protonation constants and formation constants of Cu(II) complexes of receptors 2 and 3 (at pH 7) and the effect of pH on formation of these complexes has been determined by the combination of UV-vis-pH titrations of receptors 2 and 3 and their Cu(II) complexes. These results and the emergence of only one peak at 610 nm for 2 and two distinct absorption peaks at 715 and 800 nm for 3 on addition of Cu(II) unambiguously point to mono- and di-deprotonation for 2 and 3, respectively.     

Extractive-spectrophotometric determination of molybdenum with 4-unsubstituted-5-pyrazolones

A fairly sensitive and selective method for rapid determination of tracer amounts of molybdenum(V) as mixed-ligand complexes with thiocyanate and 4-unsubstituted-5-pyrazolones is described. The red complexes are extractable into chloroform from 1-5M hydrochloric or perchloric acid or 1-3M sulphuric arid media. The molar absorptivities are in the range 1.72-2.15 x 10(4)l.mole(-1).cm(-1) at 455 nm (lambda(max)). The method has been applied to the estimation of molybdenum in various synthetic and alloy-steel samples. In presence of excess of the reagent, Cu(II), Co(II), Mn(II), Fe(II), Fe(III), Al(III), Cr(III), Cr(VI), Ti(III), Ti(IV), Zr(IV), Hf(IV), V(III), V(IV), V(V), Nb(V), Ta(V), W(VI) and U(VI) do not interfere.     

Fe(III)Fe(III) and Fe(II)Fe(III) Complexes as Synthetic Analogues for the Oxidized and Reduced Forms of Purple Acid Phosphatases

Novel Fe(III)Fe(III) and Fe(II)Fe(III) complexes [Fe(2)(BBPMP)(&mgr;-OAc)(&mgr;-X)](n)() (1, X = OAc(-), n = 1+; 2, X = OH(-), n = 1+; 3, X = OAc(-), n = 0; 4, X = OH(-), n = 0), where BBPMP(3)(-) is the anion of 2,6-bis[(2-hydroxybenzyl)(2-pyridylmethyl)aminomethyl]-4-methylphenol, and OAc(-) is acetate, were prepared in order to provide models for the active site of purple acid phosphatases (PAPs). Complex 1 was obtained by the reaction of H(3)BBPMP with Fe(ClO(4))(2).6H(2)O in methanol and sodium acetate trihydrate under ambient conditions, while complex 3 was synthesized as described for 1, under an argon atmosphere with low levels of dioxygen. 2 was isolated from 1in acetonitrile by a substitution of the bridging acetate group by hydroxide, while 4 was generated in solution during a spectropotentiostatic experiment on 2, under argon. Complex 1, [Fe(III)(2)(BBPMP)(&mgr;-OAc)(2)]ClO(4).H(2)O, has been characterized by X-ray crystallography. Crystal data: monoclinic, space group P2(1)/n, a = 14.863(5) ?, b = 12.315(3) ?, c = 20.872(8) ?, beta = 90.83(3) degrees, Z = 4. IR, M?ssbauer, magnetic, electronic absorption, and electrochemical properties of 1-3 have been investigated, and some of these properties represent a contribution to the understanding of the dinuclear iron center of PAPs. Complexes 2, [Fe(III)(2)(BBPMP)(&mgr;-OAc)(&mgr;-OH)]ClO(4) (lambda(max) = 568 nm/epsilon = 4760 M(-)(1) cm(-)(1)), and 4 [Fe(II)Fe(III)(BBPMP)(&mgr;-OAc)(&mgr;-OH)] (lambda(max) = 516 nm/epsilon = 4560 M(-)(1) cm(-)(1)), constitute good synthetic analogues for the chromophoric site for the oxidized and reduced forms, respectively, of the enzyme.     

Kinetic determination of microamounts of some sulphur-containing ligands

Some sulphur-containing ligands have been shown to inhibit the Hg(II)-catalysed substitution of p-nitrosodiphenylamine (p-NDA) for cyanide in hexacyanoferrate(II), by binding the mercury(II). This effect is used for determination of microamounts of cysteine, thioglycollic acid and thiosulphate. The reactions are followed spectrophotometrically at 640 nm (lambda(max) of [Fe(CN)(5).p-NDA](3-)). The determination range depends on the amount of mercury(II) added and the stability of the Hg(II)-ligand complex. Under specified conditions, the detection limits are: thioglycollic acid 1 x 10(-7)M, cysteine 1 x 10(-6)M and thiosulphate 4 x 10(-7)M.     

Synthesis, structure, spectroscopy and redox chemistry of square-planar nickel(II) complexes with tetradentate o-phenylenedioxamidates and related ligands

A series of four-coordinate square-planar nickel(II) complexes of o-phenylenebis(N'-methyloxamidate)(L1) and related o-phenylene(N'-methyloxamidate)oxamate (L2) and o-phenylenebis(oxamate)(L3) tetradentate ligands have been synthesized and characterized structurally, spectroscopically and electrochemically. The parent nickel(II)-L1 complex presents an intense MLCT band in the UV region (lambda max = 357 nm) and a distinctive 1 s --> 4p CT satellite in the Ni K-edge XANES spectrum (E = 8339.2 eV). These features together with the short Ni-N(amidate) bond lengths (1.85-1.93 A) as revealed by the analysis of the Ni K-edge EXAFS spectrum and confirmed by single-crystal X-ray diffraction are typical of square-planar low spin (S = 0) Ni(II) ions. The dianionic nickel(II) complexes, [Ni(II)L(i)](2-)(i = -3), experience two redox processes in acetonitrile at 25 degrees C. The first redox process, at moderately low potentials (E1 = 0.12-0.52 V vs. SCE), is a reversible one-electron metal-centered oxidation to the corresponding monoanionic nickel(III) complexes, [Ni(III)L(i)]-. The second redox process, at relatively high potentials (E2 = 0.86-1.04 V vs. SCE), is a quasireversible to irreversible one-electron oxidation largely centered on the o-benzenediamidate fragment of the non-innocent ligand, yielding the corresponding neutral nickel(iii) complexes with a o-benzosemiquinonediimine pi-cation radical ligand, [Ni(III)(L(i))*+]. The singly and doubly oxidized species of the parent nickel(II)-L1 complex have been prepared by chemical oxidation and characterized spectroscopically in acetonitrile at -40 degrees C. The stable singly oxidized nickel(III)-L1 species presents an intense LMCT band in the NIR region (lambda max = 910 nm) and a rhombic X-band EPR spectrum (g1 = 2.193, g2 = 2.080 and g3 = 2.006) characteristic of square-planar low spin (S = 1/2) Ni(III) ions. The unstable double oxidized nickel(III)-L1 pi-cation radical species exhibits a rather intense visible band (lambda max = 645 nm) that is tentatively assigned as a MLCT transition from the Ni(III)-benzosemiquinone type ground state to the Ni(IV) excited state.     

High-valent nonheme iron. Two distinct iron(IV) species derived from a common iron(II) precursor

The reaction of [Fe(II)(beta-BPMCN)(OTf)2] (1, BPMCN = N,N'-bis(2-pyridylmethyl)-N,N'-dimethyl-trans-1,2-diaminocyclohexane) with tBuOOH at low-temperature yields alkylperoxoiron(III) intermediates 2 in CH2Cl2 and 2-NCMe in CH3CN. At -45 degrees C and above, 2-NCMe converts to a pale green species 3 (lambda(max) = 753 nm, epsilon = 280 M(-1) cm(-1)) in 90% yield, identified as [Fe(IV)(O)(BPMCN)(NCCH3)]2+ by comparison to other nonheme [Fe(IV)(O)(L)]2+ complexes. Below -55 degrees C in CH2Cl2, 2 decays instead to form deep turquoise 4 (lambda(max) = 656, 845 nm; epsilon = 4000, 3600 M(-1) cm(-1)), formulated to be an unprecedented alkylperoxoiron(IV) complex [Fe(IV)(BPMCN)(OH)(OOtBu)]2+ on the basis of M?ssbauer, EXAFS, resonance Raman, NMR, and mass spectral evidence. The reactivity of 1 with tBuOOH in the two solvents reveals an unexpectedly rich iron(IV) chemistry that can be supported by the BPMCN ligand.     

Functional mimic of dioxygen-activating centers in non-heme diiron enzymes: mechanistic implications of paramagnetic intermediates in the reactions between diiron(II) complexes and dioxygen

Two tetracarboxylate diiron(II) complexes, [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(C(5)H(5)N)(2)] (1a) and [Fe(2)(mu-O(2)CAr(Tol))(4)(4-(t)BuC(5)H(4)N)(2)] (2a), where Ar(Tol)CO(2)(-) = 2,6-di(p-tolyl)benzoate, react with O(2) in CH(2)Cl(2) at -78 degrees C to afford dark green intermediates 1b (lambda(max) congruent with 660 nm; epsilon = 1600 M(-1) cm(-1)) and 2b (lambda(max) congruent with 670 nm; epsilon = 1700 M(-1) cm(-1)), respectively. Upon warming to room temperature, the solutions turn yellow, ultimately converting to isolable diiron(III) compounds [Fe(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (L = C(5)H(5)N (1c), 4-(t)BuC(5)H(4)N (2c)). EPR and M?ssbauer spectroscopic studies revealed the presence of equimolar amounts of valence-delocalized Fe(II)Fe(III) and valence-trapped Fe(III)Fe(IV) species as major components of solution 2b. The spectroscopic and reactivity properties of the Fe(III)Fe(IV) species are similar to those of the intermediate X in the RNR-R2 catalytic cycle. EPR kinetic studies revealed that the processes leading to the formation of these two distinctive paramagnetic components are coupled to one another. A mechanism for this reaction is proposed and compared with those of other synthetic and biological systems, in which electron transfer occurs from a low-valent starting material to putative high-valent dioxygen adduct(s).     

Reduction of the ferrous alpha-verdoheme-cytochrome b5 complex

The ferrous alpha-verdoheme-cytochrome b(5) complex, [Fe(II)(verdoheme)](+), has been prepared and characterized spectroscopically. Anaerobic addition of excess sodium dithionite to [Fe(II)(verdoheme)](+) at pH 10 produces a one-electron-reduced species with spectroscopic characteristics that suggest a ferrous hexacoordinated verdoheme pineutral radical best formulated as a [Fe(II)(verdoheme*)] --> [Fe(I)(verdoheme)] resonance hybrid. At lower pH values (7.0 and 8.0) the one-electron-reduced species is shown to disproportionate to produce the resting state [Fe(II)(verdoheme)](+) complex and the two-electron-reduced [Fe(II)(verdoheme:)](-) anion. The latter might also be formulated as a resonance hybrid [Fe(I)(verdoheme*)](-) --> [Fe(II)(verdoheme:)](-). The disproportionation reaction becomes very slow as the pH is raised above 9.0. Exposure of the one-electron- or two-electron-reduced verdoheme complexes of cytochrome b(5) to O(2) results in rapid and quantitative reoxidation to the resting state [Fe(II)(verdoheme)](+) complex.     

Spectrophotometric determination of Fe(II) with 2,4,6-tri(2'-pyridyl)-1,3,5-triazine in the presence of large quantities of Fe(III) and complexing ions

A spectrophotometric method for the determination of Fe(II) in the presence of large amounts (up to 800 mg/l.) of Fe(III) is suggested. The Fe(III) is effectively masked by complexing with fluoride at pH 2.0-2.4 before development of the violet Fe(II) complex with 2,4,6-tri(2'-pyridyl)-1,3,5-triazine. The absorbance is measured at 595 nm. Various commonly occurring ions which complex with Fe(II) and/or Fe(III) do not interfere.     

Spectrophotometric determination of vanadium in different oxidation states with pyrogallol

Determination of vanadium at low concentrations is easily performed with pyrogallol as a ligand which forms a bluish-violet complex with vanadium(III), (IV) or (V). The colour of the bluish-violet complex (lambda(max) = 580 nm) contrasts well with the colour of both pyrogallol and vanadium. The complexes are stable for several hours. Beer's law is obeyed over the range 0-14 mug/ml vanadium at pH 6. The apparent molar absorptivity at 580 nm is (7.75 +/- 0.25) x 10(3)1.mole(-1).cm(-1). The effects of diverse ions on the determination of vanadium have been fully studied. Only Mo(VI) and W(VI) interfere seriously. The method is selective, sensitive and can be applied to the determination of total vanadium in a variety of samples.     

Disulphides of dithiophosphinic acids as analytical reagents-I Extractive spectrophotometric determination of palladium with some bis(dialkylthiophosphoryl)- and bis(diarylthiophosphoryl)disulphides

The disulphides of dithiophosphinic acids (DS) with the general formula R(2)P(S)SSP(S)R(2), where R = C(2)H(5), C(3)H(7), C(5)H(11), C(6)H(5) (I-IV) form coloured complexes of 1:3 stoichiometry with Pd(II). The absorption maxima and molar absorptivities are: a lambda(I) = 302 nm, epsilon(I) = 2.04 x 10(4) 1.mole(-1).cm(-1); lambda(II) = 305 nm, epsilon(II) = 2.58 x 10(4); lambda(III) = 303 nm, epsilon(III) = 2.60 x 10(4); lambda(IV) = 315 nm, epsilon(IV) = 3.25 x 10(4). The reaction takes about 3 min at room temperature, and the colour is stable for 24 hr. The influence of time, pH, reagent concentration, organic solvents and interferences have been studied. An extractive photometric method of determination of Pd(II) is described and applied to the determination of Pd(II) in a mixture of platinum metals.