Attempt to protect wood using copper(II) complex with 1,7-diphenyl-1,6-heptadiene-3,5-dione, a non-phenolic curcuminoid A. Sundaryono, A. Nourmamode, C. Gardrat, S. Grelier, O. Despeyroux, A. Castellan Abstract For the first time, curcuminoids known for their antioxidant and sunscreen properties were used for photoprotection of lignocellulosics. It was shown that complex between copper(II) and non-substituted curcu- min 2, displaying remarkable photostability in ethyl ace- tate/ethanol solution, is able to photostabilize in some extend a-carbonyl b-O-4 lignin model and more efficiently spruce wood. Der Versuch, Holz mit einem Kupfer(II) Komplex mit 1.7-Diphenyl-1.6-Heptadien-3.5-Dion, einem nicht phenolischen Curcumin, zu schu ¨tzen Zusammenfassung Zum ersten Mal wurde Curcumin, das fu ¨r seine antioxidante und sonnenschu ¨tzende Wirkung bekannt ist, fu ¨r den Lichtschutz von Lignin- Cellulosen eingesetzt. Es wurde gezeigt, dass der Kupfer(II)-Komplex mit einem unsubstituierten Curcu- min 2, das in einer Lo ¨sung aus Ethylacetat/Ethanol u ¨ber eine bemerkenswerte Photostabilita ¨t verfu ¨gt, die Fa ¨- higkeit besitzt, a-Carbonyl b-O-4 Lignin-Moleku ¨le und noch effizienter Fichtenholz gegen Lichtabbau zu stabilisieren. 1 Introduction Color modification of wooden materials on UV-visible light exposure was mainly attributed to lignin (De ´glise and Merlin 1994). This phenomenon is enhanced by the presence of water and micro-organisms (Feist and Hon 1984). The action of light leads to degradation of lignin and carbohydrates, decreasing physical, chemical and biological properties of the material (Hon and Feist 1992). Abstraction of benzylic hydrogen by peroxides, followed by cleavage of b-O-4 bonds, is the major pathway of lignin depolymerization (Scaiano et al. 1991, Palm et al. 1992). The cleavage generates phenoxy radicals, which are further oxidized into colored chromophores (Leary 1968). Among them, ortho and para quinones were involved (Argyro- poulos et al. 1995, Agarwal 1998, Be ´arnais-Barbry et al. 2001). Phenoxy radicals might be formed by direct pho- tolysis of absorbing phenols (Castellan et al. 1990). Wood protection against UV-visible light is well documented (De ´glise, Merlin 1994; Feist, Hon 1984). Coating is one of the most effective treatments to protect wood (Feist 1988, Podgorski et al. 1994), whereas chemical modification of wood by esterification met some success (Imamura 1993, Rowel et al. 1993), photooxidation of lignin phenols being preserved. For clear woods, combined action of hydroxy- benzophenone or hydroxyphenylbenzotriazole UV absorbers and antioxidants such as hindered amine light stabilizers or polyethylene glycols appear quite efficient (Castellan et al. 1996), especially when the additives are retained by grafting at the surface of the wood (Grelier et al. 1997). Chromium, iron or copper ions were found to confer some photoprotection to wood (Evans 1994). Wood treatment with inorganic additives such as a copper- chromium-arsenic (CCA) mixture or with boron, a sub- stitute of arsenic, was developed for outdoor applications (Ross, Feist 1991, Pizzi, Baecker 1996); nevertheless copper(II) treated woods were found to be very sensitive to light (Grelier 2000). Recently, we have developed new transition metal complexing molecular systems incorporating curcumin entities as a complexing element (Sundaryono 2003a). Curcumin 1 is known to complex boron and transition metals (Spicer, Strickland 1952, Kuhlwein et al. 1997). It is a powerful antioxidant and is able to transfer protec- tion to light-sensitive drugs in formulations for soft gelatin capsules (Tonnesen and Karlsen 1987). It was also used in cosmetic compositions as natural sunscreen (Nambudiry, Natraj 1991). We have studied the photo- degradation mechanism of curcuminoids and showed, that their quantum yield is very low (2·10 )5 ) (Sun- daryono et al. 2003b). It was observed that the b-dike- tone moiety in curcuminoids is involved both in capturing hydroxyl radicals and in redox reactions (Tonnesen and Greenhill 1992). According to the potentiality of curcuminoid molecules, we have investi- gated the ability of complexes B/2 and Cu(II)/2 to photoprotect lignocellulosic surfaces. Curcuminoid 2 was chosen for its easy synthesis from cheap compounds, benzaldehyde and acetylacetone. The photostability of the complexes was first evaluated and the action of the copper(II) complex, which was found to be very photo- stable, was studied on a b-O-4 lignin model compound and on spruce wood. Holz als Roh- und Werkstoff 61 (2003) 377–381 Ó Springer-Verlag 2003 DOI 10.1007/s00107-003-0401-x 377 Published online: 9 August 2003 A. Sundaryono, A. Nourmamode, C. Gardrat, S. Grelier, O. Despeyroux, A. Castellan (&) Laboratoire de Chimie des Substances Ve ´ge ´tales, UPRES EA-494, Universite ´ Bordeaux 1, 351 cours de la Libe ´ration, 33405 Talence, France E-mail: a.castellan@lcsv.u-bordeaux1.fr Originalarbeiten Æ Originals