Published: September 09, 2011 r2011 American Chemical Society 8145 dx.doi.org/10.1021/ac201646z | Anal. Chem. 2011, 83, 8145–8151 ARTICLE pubs.acs.org/ac Electrospray Ionization Tandem Mass Spectrometry Analysis of the Reactivity of Structurally Related Bromo-methyl-benzoquinones toward Oligonucleotides Janna Anichina, †,‡ Yuli Zhao, † Steve E. Hrudey, † Andre Schreiber, ‡ and Xing-Fang Li* ,† † Division of Analytical and Environmental Toxicology, Department of Laboratory Medicine and Pathology, Faculty of Medicine and Dentistry, University of Alberta, 10-102 Clinical Sciences Building, Edmonton, Alberta, Canada T6G 2G3 ‡ AB SCIEX, 71 Four Valley Drive, Concord, Ontario, Canada L4K 4V8 H alobenzoquinones are a class of disinfection byproducts (DBPs) recently discovered in drinking water treated with common disinfection methods, such as chlorination or chloramination. 1 These compounds have been predicted to be highly toxic and to have lowest observed adverse effect levels (LOAEL) up to 10 000 times lower than the regulated DBPs such as chloroform. 2 Disinfection of drinking water has been proven to be the most efficient measure for preventing water- borne disease by inactivation of pathogenic microorganisms. However, unintended reactions between disinfectants and nat- ural organic matter (NOM), anthropogenic contaminants, and bromide and iodide present in raw water lead to generation of DBPs in the treated water. Epidemiological studies have found an association between the consumption of chlorinated water and an increased risk of bladder cancer. 1,3,4 The regulated DBPs, such as halomethanes and haloacetic acids, are easily detectable, but the carcinogenic potency of these DBPs is insufficient to explain epidemiological observations. Other DBPs, yet to be identified, may have higher toxicity. Recently, significant attention was given to the origin of the brominated and iodinated DBPs formed upon chloramination disinfection treatment. 4,5 Overall, the toxicity of the established brominated and iodinated disinfection byproducts significantly exceeds that of the chlorinated DBPs. We have also found that 2,6-dibromo-1,4-benzoquinone exhibited a much higher affinity toward oligonucleotides (ODNs) than the chlorobenzoquinones. 6 The toxicological effects of haloquinone compounds are unclear due to limited information. A previous study examined the cytotoxicity of substituted benzoquinones, including methyl, chloro, and bromo substituents with rat and human hepatocytes. 7 A correlation was found between the electron-withdrawing strength of the substituents on the benzoquinone ring and the cytotoxicity of the corresponding compounds. No study has examined the effects of halo and methyl groups on a quinone ring on their ability to interact with DNA. Benzoquinones are well-documented as caus- ing DNA damage. The mechanisms of DNA damage by quinones have been suggested to involve one-electron reduction of the quinone ring to produce an unstable semiquinone radical that auto-oxidizes by O 2 , initiating the cascade of formation of a wide range of reactive oxygen species that may eventually cause Received: June 27, 2011 Accepted: September 9, 2011 ABSTRACT: We report the use of electrospray ionization tandem mass spectrometry (ESI-MS/MS) as a tool for rapid screening of structurally related chemicals toward oligonucleotides using the binding of five bromobenzoquinones with single-stranded (ss) and double-stranded (ds) oligonucleotides (ODNs) as a model. We found that these compounds interact differentially with oligonucleotides depending on the extent of their bromination and methylation. Three dibromobenzoquinones, 2,6-dibromo- 1,4-benzoquinone (2,6-DBBQ), 2,5-dibromo-1,4-benzoquinone (2,5-DBBQ), and 2,5- dimethyl-3,6-dibromo-1,4-benzoquinone (DMDBBQ), bound to ssODN to form 1:1 adducts, and the binding constant of DMDBBQ bound to ssODN was 100-fold lower than those of 2,6-DBBQ and 2,5-DBBQ to ssODN, indicating that methyl groups hindered interactions of the bromoquinones with ODNs. Collision-induced dissociation (CID) of the 1:1 and 1:2 adducts of ODN with 2,6-DBBQ and 2,5-DBBQ demonstrated neutral loss of DBBQ and charge separations. Incubation of two tetrabromobenzo- quinones (TBBQ), 2,3,5,6-tetrabromo-1,4-benzoquinone and 3,4,5,6-tetrabromo-1,2-benzoquinone, with the same ODNs did not form any adducts of TBBQ with ssODN or dsODN; however, bromideODNs were detected. Fragmentation of the bromide ODN adducts showed loss of the HBr molecule, supporting the presence of bromide on ODNs. High-resolution MS and MS/MS analysis of the mixtures of dinucleotides (AA, GG, CC, and TT) and TBBQ confirmed the presence of bromide on the dinucleotides, supporting the transfer of bromide to ODNs through interaction with TBBQ. This study presents evidence of differential interactions of structurally related bromo and methyl-benzoquinones with oligonucleotides and demonstrates a potential application of ESI-MS/MS analysis of chemical interactions with ODN for rapid screening of the reactivity of other structurally related environmental contaminants toward DNA.