METAL COMPLEXES OF THE ALKALOID 4-FORMYL-8-HYDROXY-QUINOLINE OCCURRING IN THE TIMBER OF BROUSSONETIA

: Several complexes of the li and 4-formy'l-8-hydrox quinoline with the metal ions. ~i'+, 2n2*, CU". Cd8+. A4n2+. MI2'. *13+. FeY+ and Moo12+ have been synthesized. Their compositions have been charactcrised from elemen- tal analyses and spectroscopic data. These studies may bear some relevance to the role of naturally occurring ligands in the metal ion translocation in plants.


Introduction
Chelating ligands from plants and their metal complexes have received some attention as possible models for metal ion translocation in ' The role of carrier molecules4 in metal ion absorption and transport is attractive to explain the mechanism of the movement of metal ions into plants. In the case of bacteria, water soluble ligands such as ferrichromes and siderochromes fulfill this role.7 The presence of several classes of natural prodxcts with chelating ability prompted our investigations in this Broussonetia zeylanich is an endemic plant t o Sri Lanka belonging t o the Moraceae family. The first naturally occurring 8-hydroxyquinoline derivative was isolated5 from the timber extracts of this plant (I).
On account of the well known complexing ability of 8-hydroxyquinoline, we have investigated the complexes of this ligand (I) with some biologically important metal ions.

Experimental
The isolation of the ligand 4-formyl-8-hydroxyquinoline is reported elsewhere5 and a sample was kindly provided by Prof. A, A. L. Gunatilaka of this Department. ,The complexes of ~e~+ , ~i~' , zn2+, c d 2 + , ~n~+ ~1~ + , c u 2 + and ~g ' + were prepared by the following procedure. A solution of the metal chloride (0.5 m mole) in 5 ml of water, l m l of 5N acetic acid and 0.5 g of sodium acetate was warmed t o 70-80°C. A solution of the ligand (in the appropriate molar ratio) in 10 ml of ethanol was then added and the reaction mixture was boiled. In the case of the molybdenum cornplex, molybidic acid was used in place of the metal chloride. The resultant dark coloured solution was cooled and the precipitate obtained was filtered, washed with ethanol, ether and dried in vacuo. The yields obtained were in the range of 50-80% (based on the metal). The yields were in general lower than in the case of 8-hydroxyquinoline complexes since the complexes appear to be more soluble in aqueous media. The colours of the complexes persisted in solution and in the case of the iron complex, further evaporation was necessary to separate the complex as a precipitate.
Infrared spectra were obtained in KBr discs using a Perkin-Elmer 257 spectrophotometer. The UV-VIS spectra were recorded on a PyeUnicam model SP 8000 spectrophotometer. The' complexes were analyzed for the oxine by the standard titration technique9, with KBr03 and the metal by standard gravimetric techniques. During gravimetry it wds necessary to remove the ligand in some cases by extracting it into chloroform.

Composition of the complexes
From the analytical data it was possible to derive the composition of these complexes. Table 1 summarizes the analytical data and the formulae of the complexes obtained.
Analysis of the oxine content in these complexes also confirm the stoichiometries proposed for them in Table 1.

Infrared Spectra
The IR spectrum of the free ligand showed the presence of a broad band at ca. 3200cm-' due to the OH group and a band at 1690 cm-' due t o the -CHO group. The IR spectra of the metal complexes showed the disappearance of the broad band at 3200 cm-' indicative of coordination via the hydroxyl group. Since the ' H NMR spectrum of the free -1igand in CDC1, showed the appearance of an acetal proton upon addition o f CD30D, the IR spectra of metal complexes were closely examined for the presence of the -CHO group. All complexes showed the presence of the -CHO group intact with the v = shifted6 to ca. 1710 cm-' . The IR spectrum of the molybdenum complex showed two strong absorption bands around 900 cm-I and 925 cm-' indicating the presence of a cis-MoQ2 group.

Electronic Spectra
All complexes are intensely coloured and distinctly more so than the analo-' gous 8-hydroxyquinoline complexes ( Table 2). The increased intensity of

Conclusion
Chemical analysis and spectroscopic data confirm the composition and the nature of these complexes. These complexes are more soluble in aqueous media than the corresponding 8-hydroxyquinoline complexes. They remain in ethanollwater solution at physiological pH values. This feature is important in assessing the role of naturally occurring ligands in the metal ion translocation in plants.
The enhanced activity of some drugs as their metal complexes is well, . d o~u m e n t e d . ' ,~ The antibacterial action of 8-hydroxyquinoline has been explained on the transport and subsequent release of ~e~+ in the medium across the cell membranes of certain types of bacteria.' O Thus the metal chelates studied above may also have some relevance in explaining the observed antibacterial activity of 4-formyl-8-hydroxyquinoline.