DNA binding of mixed-metal supramolecular Ru, Pt complexes Zhenglai Fang, Shawn Swavey, Alvin Holder, Brenda Winkel 1 , Karen J. Brewer * Department of Chemistry, Virginia Polytechnic Institute, Blacksburg, VA 24061-0212, USA Received 2 August 2002; accepted 21 September 2002 Abstract The mixed-metal supramolecular complexes ½ðtpyÞRuðPEt 2 PhÞðdppÞPtCl 2 ðPF 6 Þ 2 and ½ðtpyÞRuðPEt 2 PhÞðbpmÞPtCl 2 ðPF 6 Þ 2 are of interest in that they couple light absorbing ruthenium centers to a reactive metal site through a communicative bridge (tpy ¼ 2; 2 0 :6 0 ; 2 00 -terpyridine, bpm ¼ 2; 2 0 -bipyrimidine and dpp ¼ 2,3-bis(2-pyridyl)pyrazine). These systems have been studied and shown to avidly bind to DNA, greatly reducing its mobility through an agarose gel. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Supramolecular; Ruthenium; Platinum; DNA binding; Mixed-metal 1. Introduction Ruthenium complexes of polyazine ligands have been extensively studied showing interesting redox and photophysical properties. ½RuðbpyÞ 3  2þ is a good chro- mophore and its 3 MLCT excited state undergoes both intermolecular energy and electron transfer (bpy ¼ 2; 2 0 - bipyridine and MLCT ¼ metal to ligand charge transfer) [1–3]. Interest in extending this chemistry has led to the rapid development and study of polyazine bridged su- pramolecular complexes [3–7]. One group of interesting multifunctional supramolecular complexes couples Ru(II) light absorbers (LA) to reactive metal (RM) centers. Polyazine bridging ligands (BL) are commonly used for the construction of polymetallic complexes [3–7]. These BLs serve to connect two metal centers and, by virtue of their p systems, are spectroscopically and redox active. One commonly used BL, 2,3-bis(2-pyridyl)pyr- azine (dpp), possesses a lower lying p* orbital than bpy [3–6,8–10]. The BL bpm (bpm ¼ 2; 2 0 -bipyrimidine) has been less explored even though it binds to each metal center through equivalent donor atoms, eliminating the stereoisomerization associated with the AB chelate na- ture of dpp [3,4,7]. The properties of supramolecular complexes are also modulated by the choice of terminal ligands (TL). Using 2; 2 0 :6 0 ; 2 00 -terpyridine (tpy) as a terminal ligand results in some stereochemical control of supramolecular com- plexes by eliminating the D and K isomeric mixtures present in tris-bidentate systems. Although the Ru ! tpy MLCT excited state in ½RuðtpyÞ 2  2þ is short lived [11–13], polymetallic complexes incorporating the Ru II (tpy) chromophore can have long excited state lifetimes [14–23]. Ruthenium and platinum tpy complexes are known which display interactions with DNA. The chromo- phores, ½Ru IV ðtpyÞðbpyÞO 2þ and ½Ru III ðtpyÞðbpyÞOH 2þ , have been shown to site-selectively cleave DNA [24,25]. ½PtðtpyÞðOHÞ þ is known to be a bifunctional DNA binding agent [26]. Coupling Ru(II) to Pt(II) through polyazine bridging ligands has been of recent interest. The supramolecular Inorganic Chemistry Communications 5 (2002) 1078–1081 www.elsevier.com/locate/inoche * Corresponding author. Tel.: +1-540-231-6579; fax: +1-540-231- 3255. E-mail address: kbrewer@chemserver.chem.vt.edu (K.J. Brewer). 1 Department of Biology, Virginia Tech, Blacksburg, VA 24061- 0406, USA. 1387-7003/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S1387-7003(02)00648-2