Formation of cobalt(III) compounds with some peptides

Summary The complexes formed from cobalt(III) and dipeptides such as glycylglycine, glycylaspartic acid, glycylthreonine, glycyltyrosine and glycylproline were studied. The formation process of cobalt(III)-dipeptide species was investigated by spectrophotometry after oxidizing the cobalt(II) complexes by sodium peroxide. The formation of the cobalt(III) complexes occurs through an oxo-intermediate, as shown by the spectral behaviour, and depends on the pH of the solutions.Complex stoichiometries, molar absorptivities and concentration ratios at the equilibrium of the cobalt(III)-dipeptide complexes were determined at pH 2.2 to avoid the formation of binuclear dioxygen-cobalt complexes.     

Optical and chromaticity parameters of transition metal complexes with 1-nitroso-2-naphthol-3,6-disulfonic acid in the presence of surfactants

Optimal conditions for the complexation of transition metal ions [Cu(II), Ni(II), Co(II, III), and Fe(II, III)] with 1-nitroso-2-naphthol-2,6-disulfonic acid have been determined by spectrophotometry in the presence of cationic (cetylpyridinium and cetyltrimethylammonium bromides) and nonionic (OP-10, neonol) surfactants. The introduction of nonionic surfactants does not influence the optical parameters of the system, while the introduction of cationic ones leads to hyperchromic and hypsochromic (for the system Fe(III)-NRS-surfactant) effects. The stoichiometric ratios determined by the method of isomolar series and treatment of the saturation curves of cationic surfactants at pH 4.0 are Me(II): R: surfactant = 1: 2: 4, Me(III): R: surfactant = 1: 3: 6. The molar absorption coefficients and chromaticity parameters of ternary complexes have been determined. A 2–5-fold increase in the molar absorption coefficients and chromaticity functions as compared to binary systems has been revealed.     

The stability constants of some metal chelates of triethylenetetraminehexaacetic acid (ttha)

Stability constants for Al(III), Cd(II), Co(II), Cu(II), Fe(III), Hg(II), La(III), Nd(III), Er(III), Mg(II). Mn(II), Ni(II), Pb(II), Th(IV) and Zn(II) complexes of triethylenetetraminehexaacetic acid (TTHA) have been evaluated from data obtained by pH and pM measurements. The pM method based on measurements with the mercury electrode and the redox system Fe(III)/Fe(II) proved to be very useful when binuclear complexes are formed.     

Characterization of metal-deferoxamine complexes by continuous variation method: A new approach using capillary zone electrophoresis

Siderophores are low molecular weight non-ribosomal peptides with extremely high affinity by iron. However, other metals present affinity for siderophores but to a smaller degree. Deferoxamine is an example of a bacterial hydroxamic siderophore, which was investigated herein. Capillary zone electrophoresis (CZE) was used as a new approach in the continuous variation method for the characterization of metal-deferoxamine complexes. A set of samples containing both metal (e.g., Fe(III), Fe(II) or Ni(II)) and siderophore with different molar ratios was prepared and analyzed by both CZE and UV-vis spectrophotometry. A phosphate buffer pH 8.0 was used as the background electrolyte in the first case due to best complex and free ligand peaks resolution. The Job's plots obtained from complex peak areas (complex concentration) versus metal molar fraction revealed complexes stoichiometries of M : L of 2 : 3, 1 : 2 and 1 : 1 for Fe(III), Fe(II) and Ni(II) complexes, respectively. Conditional formation constants could also be calculated for Fe(III) and Fe(II) complexes as K_f = 1.03 × 10¹³ and 2.47 × 10⁴, respectively. UV-visible spectrophotometric analysis confirmed the data obtained for Fe(III)-complex.     

Thermodynamic stability and kinetic inertness of MS-325, a new blood pool agent for magnetic resonance imaging

Stability constants were measured for complexes formed between a modified DTPA ligand and the metal ions Gd(III), Eu(III), Fe(III), Ca(II), Cu(II), and Zn(II) at 25 degrees C in 0.1 M NaClO4. The gadolinium complex of this ligand is MS-325, a novel blood pool contrast agent for magnetic resonance imaging currently undergoing clinical trials. Stability constants were determined by 4 different methods: direct pH titration, pH titration with competition by EDTA, competition with DTPA using an HPLC-MS detection system, and competition with Eu(III) by monitoring equilibrium by luminescence spectroscopy. The 1:1 stability constants, log beta101, are the following: Gd, 22.06 (23.2 in 0.1 M Me4NCl); Eu, 22.21; Fe, 26.66; Ca, 10.45; Cu, 21.3; Zn, 17.82. The exchange kinetics of the Gd complex, MS-325, with the radioactive tracer (152,154)Eu were studied at 25 degrees C in 0.1 M NaClO4. The exchange reaction has acid-dependent and acid-independent terms. The rate expression is given by the following: R = k(a)[GdL][H]2 + kb[GdL][Gd][H] + kc[GdL][Gd]. The rate constants were determined to be the following: k(a) = 1.84 x 10(6) M(-2) x min(-1), kb = 2.87 x 10(3) M(-2) x min(-1), kc = 3.72 x 10(-3) M(-1) x min(-1). MS-325 is 2-3 times more stable than GdDTPA at pH 7.4 and is 10-100 times more kinetically inert.     

Spectrophotometric study of etodolac complexes with copper (II) and iron (III)

A rapid, simple, and selective method was developed for the determination of etodolac. The method depends on complexation of etodolac with copper (II) acetate and iron (III) chloride followed by extraction of complexes with dichloromethane and then measuring the extracted complexes spectrophotometrically at 684 and 385 nm in case of Cu (II) or Fe (III), respectively. Different factors affecting the reaction, such as pH, reagent concentration, and time, were studied. By use of Job's method of continuous variation, the molar ratio method, and elemental analysis, the stoichiometry of the reaction was found to be in the ratio of 1:2 and 1:3, metal:drug in the case of Cu (II) and Fe (III), respectively. The method obeys Beer's law in a concentration range of 2.00-9.00 and 0.50-2.00 mg/mL in case of Cu (II) and Fe (III), respectively. The stability of the complexes formed was also studied, and the reaction products were isolated for further investigation. The complexes have apparent molar absorptivities of about 32.14 +/- 0.97 and 168.32 +/- 1.12 for Cu (II) and Fe (III), respectively. The suggested procedures were successfully applied to the analysis of pure etodolac and its pharmaceutical formulations. The validity of the procedures was further ascertained by the method of standard additions, and the results were compared with other reported spectrophotometric methods and showed no significant difference in accuracy and precision.     

Salicylic acid derivatives form stable complexes with scandium(III) ion in aqueous solution

The stability constants of 5-nitrosalicylic acid (5-NSA) and 5-sulfosalicylic acid (5-SSA) complexes of Sc(III) were determined by potentiomeric pH titration. ML and ML2 type first and second complexes were observed in the solutions of 5-NSA and 5-SSA with Sc(III) at 25 degrees C in I=0.1 M ionic medium. The stability constants of Sc(III)-5NSA and Sc(III)-5SSA systems were also investigated by spectrophotometry to determine the stoichiometries of the complexes formed in the reactions. Our results showed that Sc(III)-5SSA complexes are more stable than the Sc(III)-5NSA complexes in aqueous solutions.     

Speciation of dissolved iron(II) and iron(III) in environmental water samples by gallic acid-modified nanometer-sized alumina micro-column separation and ICP-MS determination

A method has been developed for the speciation of trace dissolved Fe(II) and Fe(III) in water by coupling gallic acid (GA) modified nanometer-sized alumina micro-column separation with inductively coupled plasma mass spectrometry (ICP-MS). The separation of Fe(II) and Fe(III) was achieved based on the obvious difference in reaction kinetics between Fe(II) and Fe(III) with GA. Fe(III) was selectively retained on the micro-column at pH 5.5-6.5, while Fe(II) could not be retained by the micro-column at the whole tested pH range of 1.0-6.5, and passed through the micro-column. The Fe(II) can be determined by ICP-MS directly without preconcentration/separation procedure, while Fe(III) retained on the micro-column was then eluted with 1.0 mL of 1 mol L(-1) HCl and determined by ICP-MS. The parameters affecting the separation of Fe(II) and Fe(III) were investigated systematically and the optimum separation conditions were established. Under the optimized conditions, the detection limits of 0.48 microg L(-1) and 0.24 microg L(-1) with relative standard deviation of 5.6% and 4.3%(C= 5 microg L(-1), n= 7) for Fe(II) and Fe(III) were found, respectively. No obvious effect on the speciation of Fe(II) and Fe(III) was found with the change of the ratio of Fe(II) and Fe(III) from 0 ratio 10 to 10 ratio 0. The proposed method was applied for the determination of trace Fe(II) and Fe(III) in environmental water and the recoveries for spiked samples were found to be in the range of 97-105%.     

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.     

Synthesis, spectroscopic and thermal characterization of some transition metal complexes of folic acid

Compounds having general formula: [M(FO)(Cl)(x)(H(2)O)(y)].zH(2)O, where (M=Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II), FO=folate anion, x=2 or 4, y=2 or 4 and z=0, 1, 2, 3, 5 or 15) were prepared. The obtained compounds were characterized by elemental analysis, infrared as well as electronic spectra, thermogravimetric analysis and the conductivity measurements. The results suggested that all folate complexes were formed by 2:1 molar ratio (metal:folic acid) as a bidentate through both of the two carboxylic groups. The molar conductance measurements proved that the folate complexes are electrolytes. The kinetic thermodynamic parameters such as: E*, DeltaH*, DeltaS* and DeltaG* were estimated from the DTG curves. The antibacterial evaluation of the folic acid and their complexes was also done against some Gram positive/negative bacteria as well as fungi.     

Equilibrium studies on chromium(III) complexes of salicylic acid and salicylic acid derivatives in aqueous solution

The complexes of chromium(III) ion formed by salicylic acid, SA(H(2)L), and its derivatives (H(2)L): 5-nitrosalicylic acid (5-NSA), 5-sulphosalicylic acid (5-SSA) were investigated by means of potentiometry and spectroscopy, at 25 degrees C and in ionic strength of 0.1 M KNO(3) and 0.1 M KCl, respectively. Over the acidic pH range, the coordination of Cr(III) ion to SA and its derivatives in 1 : 1 mole ratio occurs, CrL(+) type complex is formed. In the excess of ligand, the coordination of the second ligand molecule is somewhat hindered; as a result CrL(HL) type complex occurs. Their existences were verified and their formation constants were determined. At near neutral pH, CrL(OH) and CrL(HL)(OH)(-) type hydroxo complexes formed by hydrolytic equilibria and their formation constants were also defined. The stabilities of Cr(III) complexes of SA and its derivatives decrease in the following order: SA>5-SSA>5-NSA. The formation constants of Cr(III) complexes of SA and its derivatives are in comparable ranges with the corresponding complexes of the 2,x-dihydroxybenzoic acid (2,x-DHBA) of Cr(III) ion. The stabilities of SA complexes for V(IV), Cr(III) and Fe(III) ions that have similar ionic radii, increase in the order VOL相似文献   

Effect of Pyruvate on the Redox Behavior of the Iron (III)-(II) Couple

Abstract

Evidence for the formation of Fe(III) and Fe(II) complexes with pyruvate ion is presented. Complexes with a 1:2 ratio of Fe(II) to pyruvate and 1:1 ratio of Fe(III) to pyruvate were identified by spectrophotometry. The complexation results in partial kinetic control of the electrochemical oxidation of Fe(II) in citrate buffer. In addition, Fe(III) was found to be chemically reduced by pyruvate. The apparent first order rate constant at 25[ddot]C is 7.12 × 10^?2 s ^?1in pH 4.0 pyruvate buffer and 1.24 × 10^?1 s ^?1 in pH 3.2 pyruvate buffer. In pH 4.0 citrate buffer the reaction is not first order and is significantly slower.     

Spectrophotometric determination of cationic surfactants by formation of ternary complexes with Fe(III) and chrome azurol

An extraction-free spectrophotometric method for the determination of cationic surfactants, such as cetylpyridinium chloride, cetyltrimethylammonium bromide and zephiramine is proposed, which is based on the formation of ternary complexes with Fe(III) and chrome azurol S. The molar ratio of the complex is 2:1:1 (Fe(III):chrome azurol S: cationic surfactant). The method is simple, rapid and sensitive, giving an apparent molar absorptivity of 4.5×10⁴ L·mol^?1-cm^?1 and a linear range of 0.1–6.0 μmol/L cationic surfactants. The total cationic surfactant content can be determined directly in aqueous solutions by measuring the absorbance at 680 nm (pH 5.8). The method has been successfully applied to water samples.     

Determination of iron(II) with bipyridylglyoxal dithiosemicarbazone

Bipyridylglyoxal dithiosemicarbazone reacts with iron(II) or (III). The Fe(III) complex is yellow (lambda(max) 400 nm). Fe(II) forms a red-violet 1:2 complex at pH 2.5 (lambda(max) 550 nm) and a green-blue 1:1 complex at pH 5-10 (lambda(max) 590-610 nm). Both ferrous complexes can be oxidized to the ferric complex; this reaction is reversible. The quantitative application of the ferrous complex has been studied.     

Ion-interaction chromatography of several metallocyanide complexes stabilized by adding cyanide in a neutral mobile phase.

Standard solutions (at 10(-5) M levels) of Cu(I)- and Fe(II)-cyanide complexes were stabilized for at least 5 h using 0.5 mM cyanide solution (around pH 9) as a medium. Complexes of Cu(I)- and Fe(III)-cyanide also could be stabilized without any dissociation by adding 1 mM cyanide to an acetonitrile-water (18:82, v/v) mobile phase (pH 7.0) containing 10 mM tetra-n-propylammonium salt (TPA). Under the optimal conditions, the six complexes of Cu(I)-, Ag(I)-, Ni(II)-, Fe(II)-, Fe(III)- and Au(I)-cyanides were resolved from their mixtures within about 45 min, with well-shaped chromatographic peaks.     

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.     

Simultaneous determination of Fe(II) and Fe(III) by kinetic spectrophotometric H-point standard addition method

The H-point standard addition method (HPSAM) for simultaneous determination of Fe(II) and Fe(III) is described. The method is based on the difference in the rate of complex formation of iron in two different oxidation states with Gallic acid (GA) at pH 5. Fe(II) and Fe(III) can be determined in the range of 0.02–4.50 μg ml⁻¹ and 0.05–5.00 μg ml⁻¹, respectively, with satisfactory accuracy and precision in the presence of other metal ions, which rapidly form complexes with GA under working conditions. The proposed method was successfully applied for simultaneous determination of Fe(II) and Fe(III) in several environmental and synthetic samples with different concentration ratios of Fe(II) and Fe(III).     

Radiometric studies on the reaction of some metals with potassium pentacyanonitrosyl manganate

The nature and composition of complexes formed by the reaction of Fe(III), Cr(III), Zn(II), and Co(II) with potassium pentacyanonitrosyl manganate K₃ [Mn(CN)₅NO] has been investigated by radiometric method. The metals form 1∶1 complexes with K₃ [Mn(CN)₅NO], the optimum pH for maximum precipitation being 3.6 for Fe(III), 7.3 for Cr(III), 5.4 for Zn(II), and 8.3 for Co(II). The solubility of the complexes as computed from activity at maximum precipitation point follows the order: chromium complex > iron complex > cobalt complex > zinc complex. The radiometric titration curves also show the formation of colloidal precipitates with dilute Zn(II) solutions.     

Supramolecular spin-crossover iron complexes based on imidazole-imidazolate hydrogen bonds

The [Fe(II)(H(3)L)](BF(4))(2).3H(2)O (1) complex was synthesized, where H(3)L (tris[[2-[(imidazole-4-yl)methylidene]amino]ethyl]amine) is a tripodal ligand obtained by condensation of tris(2-aminoethyl)amine and 4-formylimidazole (fim) in a 1:3 molar ratio. Starting from 1, a series of complexes, [Fe(II)(H(1.5)L)](BF(4))(0.5) (2) (=[Fe(II)(H(3)L)][Fe(II)(L)]BF(4)), [Fe(H(1.5)L)]BF(4) (3) (=[Fe(II)(H(3)L)][Fe(III)(L)](BF(4))(2)), [Fe(III)(H(3)L)](BF(4))(3).fim.H(2)O (4), and [Fe(III)(L)].2.5H(2)O (5), has been synthesized and characterized. The single-crystal X-ray structure of each complex has been determined. The Fe(II) compound, 2, and a mixed valence Fe(II)-Fe(III) compound, 3, involve formally hemi-deprotonated ligands, H(1.5)L. The structure of 3 consists of a homochiral two-dimensional assembled sheet, arising from the intermolecular hydrogen bonds between [Fe(II)(H(3)L)](2+) and [Fe(III)(L)](0) (3). All but 5 exhibit spin crossover between low-spin (LS) and high-spin (HS) states. This is a rare case where both Fe(II) and Fe(III) complexes containing the same ligand exhibit spin-crossover behavior. Magnetic susceptibility and M?ssbauer studies showed that 3 has three accessible electronic states: LS Fe(II)-LS Fe(III), HS Fe(II)-LS Fe(III), and HS Fe(II)-HS Fe(III). Compounds 1-3 show the light-induced excited spin-state trapping effect at the Fe(II) sites upon irradiation with green light. The solution magnetic properties, electronic spectra, and electrochemical properties of 1, 4, and 5 were also studied.     

Spectrophotometric Investigation of Iron(III)-N-Phenylcin-namohydroxamic Acid System

Abstract

N-Phenylcinnamohydroxamic acid, PCHA, was found to react with iron (III) to form complex species of different colour depending upon the reaction environment. The reaction conditions for the formation of the complex species were studied in aqueous-ethanolic medium. The general spectral properties of the species were investigated. The absorption curves were found to have two isobestic points. The number and composition of the complexes were determined and found to have composition 1:1, 1:2, 1:3 (Fe: PCHA). The wavelengths of the maximum absorbances were figured out to be 535, 495, and 445 nm for the I, II, and III complex species, respectively. It was verified that the Beer's law holds for these complexes at all wavelengths, and for the mixtures at the wavelengths of the isobestic points in a wide range of pH. The stepwise stability constants have been determined by the method of isobestic point and found to be log K₁ = 11.55, log K₂ = 10.11, and log Kg₃ = 7.44 for the I, II, and III complex species, respectively. The distribution diagrams (nomograms) of the complex species as a function of pH were constructed and the molar extinction coefficients of the three consecutive complexes have also been determined.