Metal ions 8-hydroxyquinoline

Metal ions 8-Hydroxyquinoline Org DTPA Complexes Charged complexes [53]... 

The extraction of metal ions depends on the chelating ability of 8-hydroxyquinoline. Modification of the stmcture can improve its properties, eg, higher solubility in organic solvents (91). The extraction of nickel, cobalt, copper, and zinc from acid sulfates has been accompHshed using 8-hydroxyquinohne in an immiscible solvent (92). In the presence of oximes, halo-substituted 8-hydroxyquinolines have been used to recover copper and zinc from aqueous solutions (93). Dilute solutions of heavy metals such as mercury, ca dmium, copper, lead, and zinc can be purified using quinoline-8-carboxyhc acid adsorbed on various substrates (94). 

Despite the ubiquity of aluminum hydroxyquinolinate chelates as ETMs, other metal chelates of substituted 8-hydroxyquinoline, such as Group II metal ions of Zn2+ and Be2+ have also been used as the ETM in OLEDs (Scheme 3.28) [131-133],... 

B.J. Chen, X.W. Sun, and Y.K. Li, Influences of central metal ions on the electroluminescence and transport properties of tris-8-hydroxyquinoline metal chelates, Appl. Phys. Lett., 82 3017-JO 19 (2003). 

The use of complexing reagents containing two functional groups is an effective method employed for metal ion determination by fluorescence measurement. For example, 8-hydroxyquinoline (3) (Figure 4.8) forms complexes with a large number of metal ions. 

There are many interesting derivatives of quinoline and acridine obtained by substitution. In particular, 8-hydroxyquinoline (oxine) is the second complexing agent in importance after EDTA. Sulfonation in position 5 leads to a compound which is soluble in water and that exhibits outstanding fluorogenic properties (i.e. fluorescence enhancement) on complexation with metal ions (e.g. aluminum). 

An extractive spectrophotometric procedure based on the complexation of reduced Iron(II) with 5-Chloro-7-iodo-8-hydroxyquinoline (CIHQ) for the estimation of micro amounts of vitamin C. The resulting brown colored complex was extracted into chloroform to give a reddish brown extract which shows an absorption band at 485 nm. This chelate was formed immediately and the apparent molar absorptivity and Sandell s sensitivity for vitamin C was found to be 8.5 x 105 dm3 mol"1 cm 1 and 2.072xl0 4g cm 2. Linear relationship between absorbance and concentration of ascorbic acid is observed up to 0.8 pg ml"1. Interference studies of different substances including sugars, vitamins and amino acids, metal ions and organic acids were carried out. The utility of the method was tested by analysing some of the marketed products of vitamin C... 

Figure 3.7 Test for trace metal ions on the surface of octadecyl-bonded silica gel. Column A, 5 pm octadecyl-bonded silica gel, 15 cm x 4.6 mm i.d. B, octadecyl-bonded silica gel, 15 cm x 4.6 mm i.d. C, octadecyl-bonded 10 pm silica gel, 30 cm x 4.0 mm i.d. eluent, 50% aqueous acetonitrile flow rate, 1 ml min-1 temperature, ambient detection, UV 220 nm (the scales of A, B, and C are not the same) sample, 8-hydroxyquinoline. Columns, A, metal ion free B, low proportion of metal ions C, high level of metal ions.

If a hydroxyester function is incorporated into a potential chelating system then the ability even of a labile metal ion to catalyze the hydrolysis can be assessed. The 8-hydroxyquinoline 17 and 2,2 -phenanthroline 18 frameworks have proved popular for this purpose. 

Hydroxyquinoline, whose chemistry has been reviewed (56CRV271), has found wide application as an analytical reagent, and is known as oxine . It forms insoluble complexes with a great many metal ions, coordinating at O and N, and can be used for the estimation of Mg, Zn, Al, Cu, Bi, Fe, Mn, Ni and others. 

Extraction of transition metals from low grade ores. Factor (c) (formation of a chargeless chelate complex) can be illustrated by considering the formation of complexes between 8-hydroxyquinoline (HQ) and a mixture of metal ions, say, M2+ = Fe2+, Co2+, Ni2+, and Cu2+. This is in fact the order of increasing stability constants of the complexes MQ2 (equilibrium constants /J2 for Eq. 17.14) log 2 = 15.0, 17.2, 18.7, and 23.4, respectively, in dilute solution at 20 °C. This commonly encountered sequence for complex formation by the divalent Fe, Co, Ni and Cu ions is known as the Irving-Williams order (cf. the susceptibility of Ni2+ and Cu2+ to complexing by NTA3-, noted in Sections 14.4 and 16.5). 

Figure 12.3—Fluorescent aromatic compounds. The compound names are followed by their fluorescent quantum yields, whose values are obtained by comparison to compounds of known fluorescence. Measurements were made at 77 K. 8-hydroxyquinoline is representative of many molecules that form fluorescent chelates with certain metal ions.

Why is the extraction of a metal ion into an organic solvent with 8-hydroxyquinoline more complete at higher pH ... 

Hydroxyquinoline (oxine, 6), one of the earliest analytical reagents, also is one of the most widely studied N—O bidentates. Its early coordination chemistry was reviewed by Phillips.19 Its use as an in vivo agent in microbiological systems has been reviewed by Schulman and Dwyer.20 The extensive use of oxine and substituted forms, and closely related bidentates, for the analytical solvent extraction and colorimeteric determination of metal ions has been comprehensively reviewed.21 An unusual bridged bonding mode for oxine has been reported in which N monodentate and O... 

As carboxylic esters of 8-hydroxyquinoline are readily hydrolyzed in the presence of metal ions, it has been possible to develop the carbo(8-quinoloxy) substituent as an amino-protecting group for peptide synthesis (Scheme 14). 

Metal ions have quite marked effects on the hydrolysis of methyl 8-hydroxyquinoline-2-carboxylafe (50)218 and ethyl l,10-phenanthroline-2-carboxylate (51).219 Base hydrolysis of the 8-hydroxyquinoline derivative (50) was studied over the pH range 9.2-12.1 and values of fcoH determined for HA and the anion A-. Formation constants KMA+ were determined at 25 °C for the equilibrium M2+ + A MA+, as were the rate constants fcOH for the base hydrolysis of the MA+ complexes (Table 19). Quite large rate accelerations are observed (103-106) when comparisons are made with the base hydrolysis of A . The charge carried by the complex does not appear to be a major factor in determining base hydrolysis rates. Thus at 25 °C the complex CuA+ undergoes base hydrolysis (kOH= 6.3xl05 s 1) at a very similar rate to the corresponding... 

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