We have compared the cancer cell cytotoxicity, cell uptake, and DNA binding properties of the isomeric terphenyl complexes [(eta(6)-arene)Ru(en)Cl](+), where the arene is ortho- (2), meta- (3), or para-terphenyl (1) (o-, m-, or p-terp). Complex 1, the X-ray crystal structure of which confirms that it has the classical "piano-stool" geometry, has a similar potency to cisplatin but is not cross-resistant and has a much higher activity than 2 or 3. The extent of Ru uptake into A2780 or A2780cis cells does not correlate with potency. Complex 1 binds to DNA rapidly and quantitatively, preferentially to guanine residues, and causes significant DNA unwinding. Circular and linear dichroism, competitive binding experiments with ethidium bromide, DNA melting, and surface-enhanced Raman spectroscopic data are consistent with combined intercalative and monofunctional (coordination) binding mode of complex 1. This unusual DNA binding mode may therefore make a major contribution to the high potency of complex 1.

The synthesis and characterization of ruthenium(II) arene complexes [(eta(6)-arene)Ru(N,N)Cl](0/+), where N,N = 2,2'-bipyridine (bipy), 2,2'-bipyridine-3,3'-diol (bipy(OH)(2)) or deprotonated 2,2'-bipyridine-3,3'-diol (bipy(OH)O) as N,N-chelating ligand, arene = benzene (bz), indan (ind), biphenyl (bip), p-terphenyl (p-terp), tetrahydronaphthalene (thn), tetrahydroanthracene (tha) or dihydroanthracene (dha), are reported, including the X-ray crystal structures of [(eta(6)-tha)Ru(bipy)Cl][PF(6)] (1), [(eta(6)-tha)Ru(bipy(OH)O)Cl] (2) and [(eta(6)-ind)Ru(bipy(OH)(2))Cl][PF(6)] (8). Complexes 1 and 2 exibit CH (arene)/pi (bipy or bipy(OH)O) interactions. In the X-ray structure of protonated complex 8, the pyridine rings are twisted (by 17.31 degrees). In aqueous solution (pH = 2-10), only deprotonated (bipy(OH)O) forms are present. Hydrolysis of the complexes was relatively fast in aqueous solution (t(1/2) = 4-15 min, 310 K). When the arene is biphenyl, initial aquation of the complexes is followed by partial arene loss. Complexes with arene = tha, thn, dha, ind and p-terp, and deprotonated bipyridinediol (bipy(OH)O) as chelating ligands, exhibited significant cytotoxicity toward A2780 human ovarian and A549 human lung cancer cells. Complexes [(eta(6)-bip)Ru(bipy(OH)O)Cl] (7) and [(eta(6)-bz)Ru(bipy(OH)O)Cl] (5) exhibited moderate cytotoxicity toward A2780 cells, but were inactive toward A549 cells. These activity data can be contrasted with those of the parent bipyridine complex [(eta(6)-tha)Ru(bipy)Cl][PF(6)] (1) which is inactive toward both A2780 ovarian and A549 lung cell lines. DFT calculations suggested that hydroxylation and methylation of the bipy ligand have little effect on the charge on Ru. The active complex [(eta(6)-tha)Ru(bipy(OH)O)Cl] (2) binds strongly to 9-ethyl-guanine (9-EtG). The X-ray crystal structure of the adduct [(eta(6)-tha)Ru(bipy(OH)O)(9-EtG-N7)][PF(6)] shows intramolecular CH (arene)/pi (bipy(OH)O) interactions and DFT calculations suggested that these are more stable than arene/9-EtG pi-pi interactions. However [(eta(6)-ind)Ru(bipy(OH)(2))Cl][PF(6)] (8) and [(eta(6)-ind)Ru(bipy)Cl][PF(6)] (16) bind only weakly to DNA. DNA may therefore not be the major target for complexes studied here.

We have used ion mobility-mass spectrometry combined with molecular modeling for the separation and configurational analysis of three low-molecular-weight isomeric organoruthenium anticancer complexes containing ortho-, meta-, or para-terphenyl arene ligands. The isomers were separated using ion mobility based on traveling-wave technology and the experimentally determined collision cross sections were compared to theoretical calculations. T he application of electrospray ionization (ESI) mass spectrometry (MS) to organometallic chemistry and its development toward the characterization of organometallic species has been the focus of previous studies [1][2][3]. ESI is a gentle ionization technique, capable of transferring preformed ions from solution into the gas phase, and has been used in previous investigations of the interaction of organometallic-based anticancer drugs and biomolecules [4,5]. The platinum-based drug, cisplatin [cis-diamminedichloridoplatinum(II)], for example, falls into this category and is one of the leading drugs used in the fight against cancer. DNA is a potential target for many metal-based anticancer drugs and distortions of DNA structure often correlate with anticancer activity. Other metal-based anticancer drugs, such as those based on ruthenium, are being developed as alternative treatments to combat cancer. In particular, the aim is to widen the spectrum of anticancer activity, reduce unwanted side effects, and avoid crossresistance with cisplatin and related drugs. Insights into the physical size and shape of these novel Ru-based drugs are important for elucidation of structureactivity relationships and for optimizing key interactions such as intercalation into DNA [6,7]. Here we explore three novel isomeric Ru-based anticancer drugs using a combined ion mobility and mass spectrometry (IM-MS) approach.As a stand-alone technique, MS cannot separate isomeric species or provide bulk structural conformational information. However, IM has the ability to rapidly separate isomeric species (on the MS acquisition timescale) based on differences in their collision cross sections (CCSs; physical size and shape) in the gas phase, thus providing specific information on ionic configuration [8 -11]. The combination of IM with MS provides an extremely powerful analytical tool.To investigate the possible benefits of the IM-MS technique, an instrument that is based around "travelingwave" (T-wave) mobility separation [12][13][14] has been used for the first time to analyze a mixture of three low-molecular-weight isomeric ruthenium terphenyl anticancer complexes (m/z 427.1 based on 102 Ru, labeled 1, 2, and 3 in Figure 1a). The study has allowed us to probe the individual differences in shape in an attempt to correlate them with differences in anticancer activity. Molecular modeling was also used to generate a range of possible structures and the theoretical CCSs for these structures were calculated for comparison with experimentally derived T-wave values. Excellent agreement was observed between the e...