Separation and direct UV detection of lanthanides complexed with pyridine-2-carboxylic acid by capillary electrophoresis

Separation and detection of lanthanides by capillary zone electrophoresis in the presence of pyridine-2-carboxylic acid (picolinic acid) as UV-absorbing complexing agent were investigated. The resolution of partially complexed positively charged complexes is improved by using two buffer ligands competing with picolinic acid for metal ions. When hydroxyisobutyric acid (HIBA) and formic acid are used together as competing ligands, this provides complete separation of all 14 lanthanides with good peak shapes. An on-column separation of 14 lanthanides was achieved in only 9 min using 0.8 mmol/l picolinic acid, 10 mmol/l HIBA and 25 mmol/l formic acid at pH 4.7. Determination of lanthanide complexes was performed by direct detection at 210 nm. Detection limits (signal-to-noise ratio=3) are ca. 0.53-0.96 microg/ml.     

含三芳胺基的吡啶甲酸衍生物及其环金属铱配合物的合成与性能

通过Ullmann反应和Negishi偶联反应, 合成了一种含三芳胺功能基的吡啶-2-甲酸衍生物; 并以此为辅助配体、1-苯基异喹啉为环金属配体, 设计合成了一种新型环金属铱配合物. 该配合物的二氯甲烷溶液, 在391～461 nm范围呈现了强烈的金属-配体电荷转移(MLCT)电子跃迁吸收带; 其最大发光波长为609 nm. 与传统的二(1-苯基异喹啉)(吡啶-2-甲酸)合铱配合物相比, 设计的环金属铱配合物具有增强的MLCT电子跃迁吸收和低的氧化电位, 是一种有发展潜力的红色磷光材料.     

Minimization of Cu and Ni interferences in the determination of Sb by hydride generation atomic absorption spectrometry: the use of picolinic acid as masking agent and the influence of l-cysteine

The minimization of copper and nickel interference on the determination of antimony by hydride generation atomic absorption spectrometry using picolinic acid and l-cysteine as masking agents was studied. Concentrations up to 4000 and 1000 mg l⁻¹ of nickel and copper respectively were found to be tolerable in the presence of picolinic acid. The simultaneous presence of both transition metals could be tolerated by using a mixture of picolinic acid and l-cysteine. In the analysis of a nickel oxide certified reference material good agreement between the recommended and found values was verified. A detection limit (3 s, n=10) of 0.1 μg Sb g⁻¹ in the original sample was estimated.     

1H NMR studies of solvent and substituent effects on strong intramolecular hydrogen bonds

Chemical shifts of H-bonded protons in tetrabutylammonium hydrogen maleate and 14-substituted picolinic acid N-oxides have been measured in a number of dry solvents, of different activity, in order to distinguish between symmetrical single minimum and asymmetrical hydrogen bonds. In tetrabutylammonium hydrogen maleate the resonance was observed at 20.70 ppm and its was independent of the nature of the solvent used. The chemical shift value of picolinic acid N-oxide varies with the solvent. These observations suggest that the hydrogen bond is symmetrical in tetrabutylammonium hydrogen maleate but that it is asymmetrical in picolinic acid N-oxide. The chemical shifts of substituted picolinic acid N-oxides were correlated with σ_p, σ_m and Δ_pK_a. The substituent and solvent effects are compared and the position of the intramolecular H-bonded protons in picolinic acid N-oxides are estimated and discussed.     

Formation constants of binary chelates of Cu(II)/Ni(II) with 4-chloro and 4-amino picolinic acid N-oxide in aquo organic media

The proton ligand constants of 4-chloro and 4-amino picolinic acid N-oxide and the formation constants of corresponding binary chelates of Cu(II) and Ni(II) have been measured at 30°C and 0.1M ionic strength in varying percentages of dioxane-water, acetone-water, ethanol-water and isopropanol-water. The results are discussed with reference to the change in dielectric constants of water in the presence of organic solvent, change in the structuredness of water, change in hydrogen bonding ability of the organic solvent in water, solvent basicity and proton solvation by organic solvent. The values have been compared with aqueous and mixed aqueous systems of picolinic acid N-oxide and 4-methoxy picolinic acid N-oxide.     

N nuclear quadrupole resonance of picolinic,nicotinic, isonicotinic and dinicotinic acids

The ¹⁴N nuclear quadrupole resonance (NQR) quadrupole coupling tensors of picolinic, nicotinic, isonicotinic and dinicotinic acids have been determined. Two different ¹⁴N quadrupole coupling constants 1007 kHz and 4159 kHz have been observed for picolinic acid demonstrating the presence of both protonated and non-protonated nitrogen atoms in this system in the solid. Only one set of non-protonated ¹⁴N NQR lines has been observed in other pyridinecarboxylic acids demonstrating the absence of the protonated zwitter ion forms observed in picolinic acid. The non-protonated ¹⁴N quadrupole coupling constant is the highest for the non-protonated nitrogen in picolinic acid and decreases to 3774 kHz in nicotinic acid and 3570 kHz in isonicotinic acid. It is the lowest in dinicotinic acid where the corresponding ¹⁴N quadrupole coupling constant is 2794 kHz. The observed anomalous decrease in the ¹⁴N quadrupole coupling constant of dinicotinic acid with decreasing temperature is tentatively explained as reflecting the increase in the residence time of the N–H?O bonded proton in the potential well close to the nitrogen.     

Improved Large-Scale Preparation of 4-Iodopicolinic Acid

Dimethylformamide showed a dramatic catalytic effect in the chlorination of picolinic acid with thionyl chloride. Methyl 4-chloropicolinate was directly transformed to 4-iodopicolinic acid in a good yield.     

6-Phosphoryl picolinic acids as europium and terbium sensitizers

Three 6-phosphoryl picolinic acid (6PPA) derivatives were synthesized and used as europium and terbium sensitizers. Two of the three ligands (6-diethoxyphosphoryl picolinic acid (Hdeppa) and 6-monoethoxyphosphoryl picolinic acid (H(2)meppa)) are water-soluble, once complexed to lanthanide ions, while the third (6-dihydroxyphosphoryl picolinic acid (H(3)dhppa)) forms a precipitate. The stability constants of the phosphoryl-based complexes were found to be higher than the carboxylate analogue (dipicolinic acid, H(2)dpa). The main species are the [LnL(3)] complexes under strict stoichiometric conditions, confirmed by (31)P NMR spectroscopy, mass spectrometry and lifetime analyses. The photophysical measurements reveal that the emission intensity of [Eu(deppa)(3)] is maximal at pH 4.8, whereas for [Eu(meppa)(3)](3-), the optimum pH is observed at 9.0. The lifetimes are all in the millisecond range and have confirmed the absence of water molecules in the first coordination sphere. The emissions of the terbium are always brighter than the corresponding europium within this phosphoryl series. The quantum yields of the phosphoryl containing complexes are lower than the carboxylate analogue ([Ln(dpa)(3)](3-)), except for [Tb(deppa)(3)], which exhibits an interesting quantum yield of 40% in aqueous solution.     

Separation of electronic and steric effects: Oxidation of ortho -substituted phenyl methyl sulphides by peroxoanions, chromium(VI) and picolinic acid catalysed chromium(VI)

The kinetics of oxidation ofortho-substituted phenyl methyl sulphides by peroxoanions, Cr(VI) and picolinic acid catalysed Cr(VI) have been investigated. Regression analyses of the rate data by using Taft and Charton equations to separate steric effect from electronic effects have been carried out. In peroxoanion oxidations, the localized electronic effect plays a major role. In the uncatalysed and picolinic acid catalysed Cr(VI) oxidations, both localized and delocalized effects are significant. Steric effect plays a minor role in all the oxidations     

Magnetic and electronic characterization of 2:1 copper(II) complexes of a series of aminocarboxylic acids

Copper(II) complexes with L-(—)-proline, pipecolinic acid, picolinic acid, anthranilic acid, 4-chloranthranilic acid, 3,5,-dichloroanthranilic acid, 4-nitroanthranilic acid, N-phenyl-anthranilic acid, and flufenamic acid anions were prepared and characterized. The copper complexes of the anions of proline, pipecolinic acid, and picolinic acid are soluble in polar solvents and display frozen solution EPR spectra with axial resonance parameters. The copper complexes of the ring-substituted anthranilates are highly insoluble or only slightly soluble in a few solvents. The EPR spectra of the copper-doped zinc(II) analogues of these complexes display various degrees of rhombicity in their EPR parameters. The N-substituted anthranilates form insoluble complexes in aqueous solution which readily dissolve in organic solvents and undergo dimerization.     

Kinetic Studies of Picolinic Acid Catalyzed Chromic Acid Oxidation of Cyclohexanone

The chromic acid oxidation of cyclohexanone catalyzed by picolinic acid in water undergoes a change from first-to zero-order dependence in both cyclohexanone and acidity. The mechanism proposed indicates the formation of an intermediate C₁ by picolinic acid and chromic acid. Then C₁ would react with enol form of cyclohexanone to give another intermediate C₂. C₂ finally cleaves into products.     

Nachweis,Strukturaufklärung und Synthese bisher unbekannter Aminosäurekonjugate aus menschlichem Harn I

The conjugates of glycine with furan 2,5-dicarboxylic acid and of picolinic acid as well as a conjugate of pyroglutamic acid with phenylacetic acid, previously unknown as natural metabolites, were detected to be normal metabolites in human urine.     

An electrochemical study on interaction of copper ions with three isomers,picolinic, nicotinic and isonicotinic acids at physiological pH

The electrochemical behaviors of copper ions complexed with picolinic, nicotinic and isonicotinic acids (2-, 3- and 4-pyridinecarboxylic acids) in Britton–Robinson buffer (pH 7.4) was studied by polarographic and voltammetric techniques on a mercury electrode. This study showed that the reduction of complexed copper ions in the presence of nicotinic acid (NA) was carried out in two one-electron steps [Cu(II)/Cu(I) and Cu(I)/Cu(0)] whereas this cathodic process in the presence of picolinic acid (PA) or isonicotinic acid (INA) occurred in one two-electron step [Cu(II)/Cu(0)]. The stability of the Cu(I) complex can be sourced from the positions of carboxylate substituents on these isomeric ligands, binding to the copper center.     

Experimental and theoretical IR and Raman spectra of picolinic, nicotinic and isonicotinic acids

The experimental and theoretical (B3PW91/6-311++G**) vibrational (IR and Raman) spectra of picolinic, nicotinic and isonicotinic acids (pyridine-2-, -3-, and -4-carboxylic acid, respectively) were studied. Three stable calculated structures were found for picolinic acid: the structure with intramolecular hydrogen COOH?N bond, and the two without hydrogen bond. For the nicotinic acid two stable theoretical structures differ in orientation of the COOH group with respect to the nitrogen atom, whereas for the isonicotinic acid only one form was stable. The theoretical vibrational spectra of the three acids were interpreted by means of potential energy distributions (PEDs) using VEDA 3 program. Next, selected experimental bands were assigned based on the scaled theoretical wavenumbers. Finally, the wavenumbers and intensities for the three isomeric acids were compared and discussed in terms of location of the carboxylic group.     

A Short Synthesis of Fusaric Acid and Analogues

Fusaric acid (5-n-butyl-pyridine-2-carboxylic acid) and other substituted picolinic acid derivatives are synthesized in two steps from readily available α,β-unsaturated hydrazones and 2-chloroacrylonitrile in high yield.     

Dosage electrochimique du cobalt: I. Etude des Courbes Intensité— Potentiel du Système cobalt(III)/cobalt(II) en Milieu Picolique

Electrochemical determination of cobalt. Part I. Studies of current—voltage curves of the cobalt(III)/cobalt(II) system in picolinic acid mediaAs a preliminary to the development of electrochemical determinations of cobalt in steels, current—voltage curves at a platinum electrode were studied for the systems coblt(III)/cobalt(II) and iron(III)/iron(II) in media containing picolinic acid as complexing agent. Iron(III) oxidizes cobalt(II) in this complexmg medium, and the iron-(II) formed can be determined by an oxidant such as cerium(IV).     

南海柳珊瑚Menella Spinifera Kukenthal化学成分的研究(二)

从中国南海针小月柳珊瑚（MenellaSpiniferaKukenthal）中分离到一种内盐，其结构经UV、IR、MS、1HNMR和13CNMR分析确定为：N-甲基吡啶羧酸内按盐。本文是首次报导这个化合物的波谱数据。     

Attaining control by design over the hydrolytic stability of Fe-TAML oxidation catalysts

The iron(III) complexes of tetra amidato macrocyclic ligands (TAMLs) ([Fe{1-X1-2-X2C6H2-4,5-(NCOCMe2NCO)2CR2}(OH2)]- , 1: X1 = X2 = H, R2 = Me2 (a), R2 = (CH2)2 (b); X1 = X2 = Cl, R2 = F2 (c), etc.), which the proton is known to demetalate at pH < 3, are also subject to catalyzed demetalation by Br?nsted acid buffer components at pH 4-9 such as H2PO4-, HSO3-, and CH3CO2H, HO2CCH2CO2-. Buffers based on pyridine (py) and tris(hydroxymethyl)aminomethane (TRIS) are catalytically inactive. Where reactions proceed, the products are demetalated TAMLs and iron species of variable composition. Pseudo-first-order rate constants for the demetalation (kobs) are linear functions of the acid concentrations, and the effective second-order rate constants k1,eff have a hyperbolic dependence on [H+] (k1,eff = a1[H+]/(b1+[H+]). The rate of demetalation of 1a in H2PO4-/HPO42- buffer is appreciable, but the kobs values for 1b and 1c are immeasurably low, showing that the rates are strongly affected by the CR2 or "tail" fragments, which are known to potently affect the TAML basicity. The reactivities of 1 depend insignificantly on the aromatic ring or "head" group of 1. The proposed mechanism involves precoordination of the acidic buffer species followed by hydrolysis. The demetalating abilities of buffer species depend on their structures and acidities. Thus, although pyridine-2-carboxylic (picolinic) acid catalyzes the demetalation, its 3- and 4-isomers (nicotinic and isonicotininc acids) are inactive. The difference is rationalized to result from the ability that only coordinated picolinic acid has to deliver a proton to an amidato nitrogen in an intramolecular manner. The reaction order in picolinic acid equals one for 1a and two for 1b. For 1b, "inactive" pyridine and nicotinic acid speed up the demetalation in the presence of picolinic acid, suggesting that the second order arises from the axial binding of two pyridine molecules, one of which must be picolinic acid. The binding of pyridine- and imidazole-type ligands was confirmed by UV/vis equilibrium measurements and X-ray crystallography. The implications of these mechanistic findings for designing superior Fe-TAML oxidation catalysts and catalyst formulations are discussed using the results of DFT calculations.     

Dosage electrochimique du cobalt : II. Applications aux Aciers à Faible ou à Moyenne Teneurs

Electrochemical determination of cobalt. Part I. Studies of current—voltage curves of the cobalt(III)/cobalt(II) system in picolinic acid mediaAs a preliminary to the development of electrochemical determinations of cobalt in steels, current—voltage curves at a platinum electrode were studied for the systems coblt(III)/cobalt(II) and iron(III)/iron(II) in media containing picolinic acid as complexing agent. Iron(III) oxidizes cobalt(II) in this complexmg medium, and the iron-(II) formed can be determined by an oxidant such as cerium(IV).     

Metal ion-assisted transformations of 2-pyridinealdoxime and hexafluorophosphate

Metal-ion mediated reactions of 2-pyridinealdoxime and hexafluorophosphate lead to Zn(II) complexes containing picolinic acid, picolinamide and monofluorophosphate (-2) as ligands.