No abstract

The kinetics of oxidation of cyclohexene, cyclohexen-1-ol, and indene by cis-[Ru IV (bpy) 2 (py)(O)] 2+ (bpy ) 2,2′-bipyridine and py ) pyridine) have been studied in CH 3 CN. The reactions are first-order in both Ru IV )O 2+ and substrate in an initial, rapid stage in which Ru(IV) is reduced to Ru(III). The rate constants are 0.16 ( 0.01, 1.10 ( 0.02, and 5.74 ( 0.74 M -1 s -1 for cyclohexene, cyclohexen-1-ol, and indene, respectively. A k(R,R′-H 4 )/k(R,R′-D 4 ) kinetic isotope effect of 21 ( 1 is observed for the oxidation of cyclohexene. At a 2:1 ratio of Ru IV dO 2+ to olefin, the reactions of Ru IV dO 2+ with either cyclohexene or indene give Ru II -NCCH 3 2+ and the 4-electron ketone products, 2-cyclohexen-1-one and indenone, respectively, as identified by GC-MS. As the ratio of cyclohexene to Ru IV dO 2+ is increased, cyclohexen-1-ol becomes an increasingly competitive product. The mechanisms of these reactions are highly complex. They involve two distinct stages and the formation and subsequent reactions of Ru III -substrate bound intermediates.

The comproportionation reaction between [RuIV(bpy)2(py)(0)]2+ and [Ruu(bpy)2(py)(OH2)]2+ in acetonitrile (CH3-CN) to form 2 equiv of [Rum(bpy)2(py)(OH)]2+ (bpy = 2,2'-bipyridine, py = pyridine) was investigated by means of rapid-scan, stopped-flow kinetics, yielding the rate constant keom = (4.07 ± 0.13) x 103 M_1 s_1 at 25 °C. Under the same conditions in 1% w/v H2O or D2O in CH3CN the rate constants were (3.10 ± 0.12) x 103 M_1 s-1 and (2.13 ± 0.02) x 102 M-1 s_1, respectively. The solvent isotope effect fc(H2o/&(D20) = 14.6 ± 0.7 provides evidence for proton-coupled electron transfer. The long term instability of [Rum(bpy)2(py)(OH)]2+ in CH3CN was investigated by following the changes in the UV-vis spectrum over periods up to 2 x 105 s. Principal factor analysis of the spectral changes by singular value decomposition revealed the presence of four colored components during the reaction. The application of global kinetic analysis methods allowed the data to be fit to a model involving initial disproportionation to Ruiv=02+ and Ru11-OH22+ (£disp = 81 ± 8 M_l s-i, 25 °C), followed by irreversible substitution of the aqua complex by CH3CN to give [Run(bpy)2(py)(NCCH3)]2+ (U0iv = (1.66 ± 0.02) x 10-3 s-1, 25 °C). Further reaction of RuIV=02+ with solvent or impurities also occurred to give [Run(bpy)2(py)(NCCH3)]2+ (k ~5 x 10~6 s_1, 25 °C). An independent study of the loss of [RuIV(bpy)2(py)(0)]2+ in CH3CN revealed that Ru111-OH2+ was formed as an intermediate during this reaction. The rate constants from the global kinetic analysis also provided an estimate of the equilibrium constant for comproportionation, KCOm = 50 ± 5 in CH3CN. The dependence of ksou on [H2O] for solvolysis of the aqua complex by CH3CN is consistent with a dissociative (D) mechanism. The competition ratio for capture of the 5-coordinate intermediate by H20 or CH3CN is kAQ/kAS = 18.4 ± 0.6 at 25 °C.

The anticancer ruthenium complex trans-[tetrachlorobis(1H-indazole)ruthenate(III)], otherwise known as KP1019, has previously been shown to inhibit proliferation of ovarian tumor cells, induce DNA damage and apoptosis in colon carcinoma cells, and reduce tumor size in animal models. Notably, no doselimiting toxicity was observed in a Phase I clinical trial. Despite these successes, KP1019's precise mechanism of action remains poorly understood. To determine whether Saccharomyces cerevisiae might serve as an effective model for characterizing the cellular response to KP1019, we first confirmed that this drug is internalized by yeast and induces mutations, cell cycle delay, and cell death. We next examined KP1019 sensitivity of strains defective in DNA repair, ultimately showing that rad1D, rev3D, and rad52D yeast are hypersensitive to KP1019, suggesting that nucleotide excision repair (NER), translesion synthesis (TLS), and recombination each play a role in drug tolerance. These data are consistent with published work showing that KP1019 causes interstrand cross-links and bulky DNA adducts in mammalian cell lines. Published research also showed that mammalian cell lines resistant to other chemotherapeutic agents exhibit only modest resistance, and sometimes hypersensitivity, to KP1019. Here we report similar findings for S. cerevisiae. Whereas gain-of-function mutations in the transcription activator-encoding gene PDR1 are known to increase expression of drug pumps, causing resistance to structurally diverse toxins, we now demonstrate that KP1019 retains its potency against yeast carrying the hypermorphic alleles PDR1-11 or PDR1-3. Combined, these data suggest that S. cerevisiae could serve as an effective model system for identifying evolutionarily conserved modulators of KP1019 sensitivity.