Preparation and study of new poly-8-hydroxyquinoline chelators for an anti-Alzheimer strategy

Fourteen different ligands have been synthesized with two covalently linked 8-hydroxyquinoline motifs that favor metal complexation. These bis-chelators include different bridges at the C2 positions and different substituents to modulate their physicochemical properties. They can form metal complexes in a ratio of one ligand per metal ion with Cu II and Zn II, two metal ions involved in the formation of amyloid aggregates of the toxic Abeta-peptides in the Alzheimer disease. The apparent affinity of all bis-8-hydroxyquinoline ligands for Cu II and Zn II are similar with logK Cu II approximately 16 and logK Zn II approximately 13 and are 10,000 times more efficient than for the corresponding 8-hydroxyquinoline monomers. Their strong chelating capacities allow them to inhibit more efficiently than the corresponding monomers the precipitation of Abeta-peptides induced by Cu II and Zn II and also to inhibit the toxic formation of H2O2 due to copper complexes of Abeta. The best results were obtained with a one-atom linker between the two quinoline units. X-ray analyses of single-crystals of Cu II, Zn II or Ni II complexes of 2,2'-(2,2-propanediyl)-bis(8-hydroxyquinoline), including a one-atom linker, showed that all heteroatoms of the bis-8-hydroxyquinoline ligand chelate the same metal ion in a distorted square-planar geometry. The Cu II and Zn II complexes include a fifth axial ligand and are pentacoordinated.     

Application of the zone melting technique to metal chelate systems-V Zone chromatographic separation of metal chelates on columns of some inert solid solvents

Binary mixtures of acetylacetone and 8-hydroxyquinoline chelates of copper(II), nickel(II), cobalt(II) and cobalt(III) were processed by zone-chromatography on columns of some naphthylalkyl ethers as inert solid solvents. The metal chelates were separated to give chromatograms on the columns according to the ratio of their distribution coefficients. Distribution coefficients of metal ions varied with the type of chelating agent used and the solid solvent, and were found to be strongly affected by operating conditions, especially zone length, zone travelling speed and initial concentration of the metal chelate.     

Structure and behavior of organic analytical reagents : Heats and entropies of formation of several divalent metal chelates of 2- and 4-methyl-8-hydroxyquinoline1

The Calvin-Bjerrum titration technique for the determination of chelate formation constants has been applied to the Cu(II), Ni(II), Co(II), Zn(II) and Mn(II) chelates of 2- and 4-methyl-8-hydroxyquinoline. Measurements were made at several temperatures in order to evaluate ΔH and ΔS values of chelation. The results obtained were interpreted in terms of steric hindrance of the 2-methyl group. In all cases the heats of formation of the chelates of 2-methyl-8-hydroxyquinoline were remarkably morepositive than those for the corresponding chelates of 4-methyl-8-hydroxyquinoline. This large difference in the strengths of the metal-chelate bonds is apparently due to the hindrance of the methyl groups which prevent the close grouping of the two reagent molecules around the metal in chelates of 2-methyl-8-hydroxyquinoline. The lower bond strength in chelates of 2-methyl-8-hydroxy-quinoline is partially compensated by a relatively larger entropy of formation. This is attributed to decreased solvent chelate interaction caused by the shielding of the polar O, N, and metal atoms by the 2-methyl groups. The determination of chelate fortmation constants of 2-phenyl-8-hydroxyqumoline has been carried out to further extend our study of steric effects in metal chelates.     

Application of the zone melting technique to metal chelate systems-II Concentration of a trace amount of metal acetylacetonate in chromium(III) acetylacetonate

The zone melting process was applied to tris(acetylacetonato) chromium(III) which contained a trace amount of aluminium(III), iron(III), copper(II), manganese(III), nickel(II) cobalt(III) and rhodium(III) in the forms of their acetylacetonates, and the highly purified chromium chelate was found in the top portion of a column, while the minor components except the rhodium chelate were concentrated in the bottom portion. The rhodium chelate was concentrated in the top portion. Ease of migration of the minor components during the zone melting process decreased in the order Cu, Fe, Mn, Co, Ni, Al and Rh, and was accounted for in terms of their crystal structures. Extremely slow speed of zone travel caused an increase of the distribution coefficient; this was due to back diffusion of minor components into a congealed solid phase from a molten zone.     

Complexing properties of 2-(2'-hydroxyphenyl)8-hydroxyquinoline

The reactions of the new ligand, 2-(2'-hydroxyphenyl)-8-hydroxyquinoline with selected metal ions have been studied. With Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), 1:1 complexes are formed in solution which are considerably more stable than the corresponding complexes of 8-hydroxyquinoline. With AI(III) stable 1:1 and 2:1 complexes are formed. With the aid of molecular models, the enhanced stability is attributed to the formation of a strain-free 5,6 bicyclic chelate-ring system.     

Aromatic properties of 8-hydroxyquinoline and its metal complexes

Chelatoaromaticity (aromaticity of chelate complexes) has been recently recognized as an important property influencing the stability of chelate compounds. In this paper, aromaticity of various forms of 8-hydroxyquinoline (anion, neutral molecule, zwitterion and cation) as well as its chelate complexes with magnesium and aluminium ions are investigated. Aromatic properties of these compounds are analyzed using several aromaticity indices based on energetic, geometric, magnetic and electronic physical manifestations of this phenomenon. Results of performed calculations have shown different aromatic properties for the two rings (pyridine and benzene) occurring in the studied ligand. Aromaticity of these rings in metal complexes of 8-hydroxyquinoline is significantly higher than that in corresponding ligand anion. This means that during complexation the aromaticity of the ligand increases and the chelatoaromatic effect stabilizes the studied metal complexes. In contrast, metallocyclic rings of studied metal complexes have non-aromatic properties, and, consequently, the metallocyclic ring is not stabilized by chelatoaromaticity. We conclude that, in the complex, every 8-hydroxyquinoline unit and the metal ion are separated p-electronic systems.      

Synthesis and characterization of 5-substituted 8-hydroxyquinoline derivatives and their metal complexes

5-Aminomethyl-8-hydroxyquinoline (QN) was synthesized as a scaffold to generate dimers, trimers, and tetramer metalloquinolates. Starting from QN, a series of 5-substituted 8-hydroxyquinoline derivatives conjugated with small bioactive molecules were synthesized. Absorption and emission spectra indicate that these QN derivatives chelate well with metal ions, which may serve as a new platform to explore the applications of metalloquinolates for a variety of potential applications.     

8-羟基喹啉重量法快速测定钨铁合金中钨

8-羟基喹啉与许多金属元素(除碱金属外),在弱酸性或弱碱性溶液中能形成螯合物沉淀,这种沉淀分子量大,组成恒定。试样以硝酸和氢氟酸溶解,EDTA为掩蔽剂,在乙酸铵-乙酸(pH=6.5)的缓冲溶液中,8-羟基喹啉与钨生成黄色沉淀,灼烧称重无水WO3。分别对沉淀时pH值、陈化时间、沉淀剂的用量进行选择,研究出了一种快速、准确、经济的分析方法。分析准确度好、精密度高,完全能够满足生产分析要求。     

Comparative study of 8-hydroxyquinoline derivatives as chelating reagents for flow-injection preconcentration of cobalt in a knotted reactor

8-Hydroxyquinoline (HQ), 2-methyl-8-hydroxyquinoline (CH₃-HQ), 5,7-dichloro-2-methyl-8-hydroxyquinoline (Cl₂-CH₃-HQ), 5,7-dibromo-8-hydroxyquinoline (Br₂-HQ), 5-sulfo-7-iodo-8-hydroxyquinoline (ferron) and 5-sulfo-8-hydroxyquinoline (SO₃H-HQ) were compared as chelating reagents for on-line sorption preconcentration of cobalt in a knotted reactor (KR) precoated with the reagent. The results obtained with the different HQ derivatives reveal those properties of the chelating reagent responsible for the processes taking place in the KR. The influence of hydrophobicity, acidity, stability of the cobalt chelate and type of substituents in the HQ ring system on the separate steps of the flow injection (FI) preconcentration procedure are discussed. According to the performance characteristics of the different HQ derivatives, the most important parameters for on-line preconcentration in a KR are the hydrophobicity of the reagent and the stability of the chelate complex with the analyte.     

Extraction of tungsten with 8-hydroxyquinoline and some of its derivatives

The extraction of tungsten by chloroform solutions of 8-hydroxyquinoline(I), 2-methyl-8-hydroxyquinoline(II), 5,7-dibromo-8-hydroxyquinoline(III) and 8-mercaptoquinoline(IV), as a function of the concentration of tungsten and reagent and the acidity of the aqueous phase, has been studied. Evidence was obtained for the quantitative extraction of tungsten over a wide range of acidity. The degree of extraction of tungsten at 10(-5)M concentration with I,III and IV gives two maxima when plotted against acidity. The extraction maximum for the more acidic solutions lies in the region where the reagents exist in the protonated form and its position depends on the reagent used. It is suggested that different tungsten complexes are extracted, depending on the acidity of the aqueous phase.     

Size-exclusion chromatographic behaviour of metal chelates of 8-hydroxyquinoline

Analytical and Bioanalytical Chemistry - The size-exclusion chromatographic behaviour of 8-hydroxyquinoline (abbreviated as HOx) and its metal(II, III) chelates on Fractogel PVA 2000 in p-dioxane...     

Properties of 8-hydroxyquinoline immobilized on a silica surface

The ionization constants of benzeneazo-8-hydroxyquinoline grafted to a silica surface were determined by potentiometric titration. The spectrophotometric measurements showed that with increase in pH, deprotonation of the grafted 8-hydroxyquinoline nitrogen takes place. The dynamic capacity of the sorbent obtained with respect to the Cu²⁺, Co²⁺, and Ni²⁺ ions at various pH was determined. The immobilized benzeneazo-8-hydroxyquinoline is suitable for removing trace amounts of metal ions from solutions and for their chromatographic separation. It was found that the metal complexes of Cu²⁺ and Co²⁺ with grafted benzeneazo-8-hydroxyquinoline exhibit catalytic activity in the oxidation of hydrazine by molecular oxygen in aqueous solutions.Translated from Teoreticheskaya i Ékperimental'naya Khimiya, Vol. 25, No. 1, pp. 108–112, January–February, 1989.     

Solvent extraction of zinc with 5,7-dichloro-2-methyl-8-hydroxyquinoline into chloroform

The distribution equilibria of the zinc complex with 5,7-dichloro-2-methyl-8-hydroxyquinoline in the water-chloroform system have been studied at 25 degrees . The influence of pH, reagent and metal concentrations, and the presence of sodium perchlorate in the aqueous phase has been determined. From quantitative evaluation of the extraction equilibrium data, it has been deduced that the complex extracted is the simple 1:2 chelate, ZnR(2), although at ligand concentrations higher than 0.3M, the self-adduct complex seems to begin to form. The extraction constant of the ZnR(2) species, refined by means of the program Letagrop-Distribution, has the value log K(ex) = - 6.15 +/- 0.07.     

Extraction of copper(II) with the APCD/DIBK system from concentrated hydrochloric and nitric acid media: estimation of true limit of acidity for the extraction

The extraction of copper(II) from strongly acidic solution (0.01-8M hydrochloric and 0.01-5M nitric acid) with ammonium 1-pyrrolidinecarbodithioate in di-isobutyl ketone has been studied. Compared with the hydrochloric acid system, a considerably larger amount of the reagent is needed for complete extraction of copper chelate from nitric acid solution as the extract is more unstable in the nitric acid system. The decomposition of copper chelates extracted from nitric acid is based on the oxidation of the reagent and the chelate; the spectral change of the extract from nitric acid suggests that the copper(II) chelate is initially oxidized to copper(II) and then decomposes. The upper limit of the acidity of both acids from which the copper chelate can be quantitatively extracted strongly depends on the reagent concentration; the limit with 8 x 10(-2)M APCD (500-fold reagent: metal molar ratio) was taken as 8 and 4M for hydrochloric and nitric acid, respectively.     

Silica-modified magnetic nanoparticles functionalized with cetylpyridinium bromide for the preconcentration of metals after complexation with 8-hydroxyquinoline

Magnetically driven separation technology has received considerable attention in recent decade for its great potential application. In this study, we investigate the application of silica-modified magnetite nanoparticles (NPs) coated with a cationic surfactant as adsorbent for microextraction and determination of trace amounts of Cu(II), Ni(II), Co(II), Cd(II), Pb(II) and Mn(II) from environmental water samples. The synthesized silica-coated NPs in combination with cetylpyridinium bromide have the ability to adsolubilize the metal ions after complexation with 8-hydroxyquinoline. The NPs bearing the target metals are easily separated from the aqueous solution by applying an external magnetic field and the complexed metals were desorbed using acidic methanol. The desorbed analytes are introduced into the graphite furnace of an atomic absorption spectrometer. The effect of pH, complexing agent, amount of cetylpyridinium bromide, microextraction time, desorption conditions, ionic strength on extraction efficiency of the metal ions are investigated and optimized. Under the optimized conditions, the detection limits for Cu(II), Ni(II), Co(II), Cd(II), Pb(II) and Mn(II) are 4.7, 9.1, 9.5, 2.3, 7.4 and 15.3 ng L⁻¹, respectively and the relative standard deviations (n = 6) are less than 3.6%. The accuracy of the method was evaluated by recovery measurements on the spiked samples and good recoveries (93-113%) with low RSDs were achieved.     

Differential-pulse voltammetric determination of molybdenum in nitrate medium in the presence of 8-hydroxyquinoline

The determination of Mo(VI) by differential-pulse voltammetry based on catalytic currents in nitrate medium is described. The existence of catalytic currents in the system Mo(VI)NO₃^? in the presence of 8-hydroxyquinoline was proved by various polarographic techniques. The optimum background electrolyte is 20 ml 0.5 M KNO₃?0.005 M HNO³ with the addition of 1 ml of 1 × 10^?2 M 8-hydroxyquinoline. The detection limit is 7 × 10^?10 M under these conditions. Cr(VI), Cu(II), Cd(II) and Pb(II) interfere when present at higher concentrations then Mo(VI) and W(VI) interferes at an equal concentration to Mo(VI). The method was successfully used in analyses of environmental samples.     

The chromatographic behavior of group (IIB) metal ions on polyurethane foam functionalized with 8-hydroxyquinoline

Polyurethane foam functionalized with 8-hydroxyquinoline has been prepared by coupling the foam matrix with 8-hydroxyquinoline (oxine) through an azo spacer. The oxine-bonded foam (Ox PUF) was characterized by use of different tools (UV–Vis spectra, IR spectra, density, and stability). Ox PUF was found to be very suitable for separation and preconcentration of trace metals, e.g. Zn(II), Cd(II), and Hg(II) ions, from wastewater in the pH ranges 2–12, 9–12, and 3–6, respectively. Various conditions influencing the sorption of these metal ions on to Ox PUF were optimized. Extraction of the metal ions was accomplished in 15 to 20 min. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for H, S, and G of 41.99, 158.23, and –5.1 kJ mol^–1, respectively. The capacities of the foam material were 0.27, 0.16, and 0.09 mmol g^–1 for Zn(II), Cd(II), and Hg(II), respectively. Preconcentration factors >50 were achieved (RSD6.18). The quantitative results were obtained from experiments performed using certified reference materials.     

Chloromethylation of 8-hydroxyquinoline

The reaction of formaldehyde on a hydrochloric acid solution of 8-hydroxyquinoline, in the presence of hydrochloric acid gas, gave a chloromethyl derivative which is probably 7-chloromethyl-8-hydroxyquinoline hydrochloride. This compound is readily converted into the 7-hydroxymethyl derivative in alkaline solution. The 7-chloromethyl compound has been investigated as an analytical reagent for metal ions in acid solutions.     

Complexation of transition metals with 8-hydroxyquinoline chemically immobilized on the surface of a silica gel-polyaniline composite

The complex-forming properties of a silica gel-polyaniline composite with 8-hydroxyquinoline covalently immobilized by the Mannich reaction with respect to Pb(II), Cd(II), Cu(II), Ni(II), Co(II), Al(III), Fe(III), and Mo(VI) ions were studied. The resulting adsorbent had a high sorption capacity and satisfactory kinetic characteristics, which allowed us to use it for the separation or preconcentration of transition metal ions. Data on the composition and structure of the test metal complexes with 8-hydroxyquinoline immobilized on the composite surface were obtained from an analysis of electronic diffuse reflectance spectra and corresponding adsorption isotherms.     

Spectrophotometric determination of zirconium with 5,7-dibromo-8-hydroxyquinoline in presence of thiocyanate

The characteristics of the ternary complex formed between zirconium(IV) and 5,7-dibromo-8-hydroxyquinoline in presence of thiocyanate have been studied with an analytical point of view. The resulting colored species is extractable into chloroform with absorption maximum at 416 nm, which leads to the determination of the trace amounts of the metal ion. The method obeys Beer’s law in the range 0.2–9.0 μg Zr/mL having molar absorbitivity and Sandell’s sensitivity values of 1.05 × 10⁴ L/mol cm and 0.0087 μg Zr/cm², respectively. The ratio of zirconium(IV), 5,7-dibromo-8-hydroxyquinoline and thiocyanate in the extracted species is found to be 1: 2: 2. A large number of foreign ions do not interfere in the proposed method. The applicability of the procedure is tested by carrying out satisfactorily the analysis of a wide variety of samples.