Zinc oxinate

It is noteworthy that the Be—O distance (1.60 A) is of the same order as that found for other coordination compounds of beryllium and leads to the value of 1.0—1.1 A for the covalent radius of beryllium in this type of coordination.26 Clearly arguments based on relative ionic radii are invalid. Thus the dihydrate of zinc oxinate has been shown to form a distorted tetrahedron with two long Zn—H20 bonds while the lengths Zn—O and Zn—N to the ligand are 2.05 and 2.06 A respectively, whence the zinc radius is 1.38 A. Clearly the use of an ionic radius (Zn2+ = 0.74 A) would be misleading. Similarly the Cu—N bond in compounds of Cu11 with ammonia and ethylenediamine (1.99,2.05,2.01 A) implies a radius of 1.3-1.4 A in these coordination compounds, a value considerably larger than the ionic radius of 0.7 A.23... 

When 8-hydroxyquinoline (oxine) (I) is added to an ammonical or caustic alkaline solution of a zinc salt, there is quantitative precipitation of the light yellow crystalline zinc oxinate(II), which displays a yellow-green fluorescence in ultraviolet light. The precipitate is readily soluble in excess mineral acid. Consequently, the precipitation of zinc oxinate from neutral solutions of zinc salts is incomplete because of the rapid establishment of the equilibrium ... 

Accordingly, if a solution of a zinc salt is treated with an excess of hydroxy-quinoline and the precipitate is removed by filtration, the clear filtrate consists of the zinc oxinate equilibrium solution, from which fluorescent zinc oxinate can be precipitated by hydroxyl ions and consequently also by contact with ammonia vapors. Quantities of zinc oxinate which are too slight to give a visible turbidity nevertheless yield an easily discernible fluorescence. 

Reagent Zinc oxinate equilibrium solution 1 % aqueous solution of zinc chloride is treated with excess 1 % alcoholic solution of 8-hydroxyquinoline and the precipitate is filtered off. The reagent solution keeps. 

Zinc ions, like many other di-and trivalent ions, are precipitated by 8-hydroxyquinoline (oxine) forming the oxinates [M(oxinate)J where n is the valence of the metal ion and the number of chelate rings formed. Precipitation starts at a characteristic pH value and is complete with in a range of higher pH s, these being pH 3.3 and >4.4 respectively for zinc oxinate. 

Like Al and Cd, zinc oxinate fluoresces when irradiated with a medium pressure mercury lamp. The intensity of the fluorescence can be used for the determination of zinc ions in solution. The formation of the oxinate is similar to the above method. The addition of gum arabic solution stabilises the suspension. 

The reference in Sec.4.5.2.1 gives fluorescence spectra of zinc oxinate. 

Discussion. Various metals (e.g. aluminium, iron, copper, zinc, cadmium, nickel, cobalt, manganese, and magnesium) under specified conditions of pH yield well-defined crystalline precipitates with 8-hydroxyquinoline. These precipitates have the general formula M(C9H6ON) , where n is the charge on the metal M ion [see, however, Section 11.11(c)]. Upon treatment of the oxinates with dilute hydrochloric acid, the oxine is liberated. One molecule of oxine reacts with two molecules of bromine to give 5,7-dibromo-8-hydroxyquinoline ... 

Fluorimetry is generally used if there is no colorimetric method sufficiently sensitive or selective for the substance to be determined. In inorganic analysis the most frequent applications are for the determination of metal ions as fluorescent organic complexes. Many of the complexes of oxine fluoresce strongly aluminium, zinc, magnesium, and gallium are sometimes determined at low concentrations by this method. Aluminium forms fluorescent complexes with the dyestuff eriochrome blue black RC (pontachrome blue black R), whilst beryllium forms a fluorescent complex with quinizarin. 

The zinc complex of oxine fluoresces in ultraviolet light, and this forms the basis of the following method. 

Spectrophotometers Units of length, 646, 647 of mass, 75 of volume, xxix, 78 Universal indicators 268 Uranium, D. of by cupferron, (g) 471 by oxine, (g) 474 Uranyl zinc acetate 467 Urea in homogeneous pptn., 426, 453... 

Copper quinolinolate (oxine copper) is the chelate of divalent copper and 8-hydroxyquinoline and shares most of its market with copper naphthenate, which is a complex copper salt of mixed naphthenic acids. The principal uses are in wood treatments and some military textiles, where the green color is not objectionable. Copper naphthenate has an odor but is cheaper than oxine. Both copper naphthenate and zinc naphthenate have performed well in environment tests, with exposure to soil above-ground, as well as concrete (33). 

The interest in oxines has now moved from antimicrobial therapy to nuclear medicine and the chemotherapy of malaria. A few other applications have also been found 5,7-diiodo-oxinate enhances gastrointestinal uptake of zinc, an element whose deficiency may cause acrodermatis enteropathica1905 several halogenated oxines - 5-chloro-7-iodooxine (Entero-Vioform), 5,7-diiodooxine (Diodoquin) - have been used in the treatment of amoebic dysentry but this is now a discontinued therapy. 5-Methyloxine has proved an effective therapy in the treatment of cholera in humans191,1925. 

Zinc can be separated from Cd and Pb in the iodide system [17,18]. It can also be separated from other metals as the chelate complex with oxine (CHCI3, 1,2-dichloroethane) [19-22], diphenylcarbazone [23] HTTA [24], and A-phenylcinnamoylhydroxamic acid (chloroform in the presence of stearylamine) [25]. Zn has been separated from the excess of Cd with the use of l-phenyl-3-methyl-4-stearoyl-5-pyrazolone in benzene solutions [26]. 

Since fef for complex formation is compounded of 2 and fe2 3, the net effect is not readily predictable. It should be noted that the observed value for fef has to be corrected for a reduction in the number of replaceable water molecules (by multiplying by a factor of 6/(6 — n) where n is the number of coordination positions occupied by the bound ligand). The net effect observed is a negative one, the reactivity order with NSA being Mg + > Mg(TP) > Mg(NTA) > Mg(ATP) whereas that for oxine [66] is more expectedly Mg > Mg(NTA) > Mg(ATP) > Mg(TP) ". Similar studies have been made with manganese(II), cobalt(II), zinc(II), and nickel(II) [70b]. 

A class of zinc ion (Zn2+) sensors, which utilized an unnatural amino acid that included the chelation-sensitive fluorophore, 8-hydroxy-4-(Af,Af-dimethylsulfonamido)-2-methylquinoline (sulfonamido oxine (Sox), Figure 1.3a), provided inspiration for a second class of kinase activity sensors [12-14]. The Sox amino acid was prepared via asymmetric synthesis and converted to the fluorenylmethyloxycarbonyl (Fmoc)-protected derivative and incorporated via SPPS into a peptide containing a proline-mediated fi-turn sequence [13]. The fl-turn was flanked by both Zn-chelating amino acids and the Sox fluorophore (Figure 1.3b). In this case, the fi-turn was included to provide preorganization... 

Walkup, G.K. and Imperiali, B. (1998) Stereoselective synthesis of fluorescent a-amino acids containing oxine (8-hydroxyquinoline) and their peptide incorporation in chemosensors for divalent zinc. /. Org. Chem., 63,... 

Solid phase extraction of zinc could be an alternative in zinc sample pretreatment. Adsorption of the oxinate complex on microcrystalline naphthalene is a recently suggested possibility [73]. 

The antimicrobial activity described here is only valid for 8-hydroxyquinoline and not for the seven other possible hydroxyquinolines which are widely inactive and do not, as does 8-hydroxyquinoline, chelate metal cations, e.g. copper, iron and zinc. Contrary to Oxine the corresponding chelation complexes, e.g. copper 8-hydroxyquinoline (Section 11.5) possess considerable lipid solubility enabling the complex to pass through the cell membrane and then to dissociate into the toxic 8-hydroxyquinoline. However, according to the findings of Block (1983)... 

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