Protonated adenine: Tautomers, solvated clusters, and dissociation mechanisms

Turecček, František; Chen, Xiaohong

doi:10.1016/j.jasms.2005.06.010

Cited by 76 publications

(107 citation statements)

References 43 publications

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“…There is general agreement with earlier theoretical studies of the purine bases [36][37][38][39][40] and of cytosine [34,41]. The measured proton affinity of aniline is 874 kJ/mol (208.8 [42] and 209.5 kcal/mol [43] )and experimental [44] and theoretical [45] studies showed almost equal propensity for protonation at the amino-N-and the para-C-atoms.…”

Section: Site Of Protonation and Mode Of Initial Fragmentationsupporting

confidence: 88%

“…Data for guanine reported in reference [38]. Compare also [34,36] for proton affinities of cytosine and adenine, respectively. b Exp.…”

Section: Experimental and Computationalmentioning

confidence: 82%

“…McCloskey et al studied the CID spectra of protonated adenine [33b] and protonated guanine [33c]. More recently, Tureček et al [34] and Wang et al [35] reported on their experimental and computational studies of protonated cytosine, Tureček et al [36] explored the dissociation mechanisms of protonated adenine in detail, and we will refer to these reports in the Discussion.…”

Section: Esi and Deglycationmentioning

confidence: 99%

“…There is hardly any barrier to the back-reaction of 63 via transition-state structure 62 to 16, this feature is the hallmark of pseudopericyclic reactions [52], and the relative energy of 63 with regard to 16 is 268.7 kJ/mol. Tureček et al [36] showed that 63 plays a crucial role to exchange the N1-and the amino-N atoms in …”

Section: Esi-ms/ms Of Adenosinementioning

confidence: 99%

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Ammonia elimination from protonated nucleobases and related synthetic substrates

Qian

Yang

et al. 2007

J. Am. Soc. Mass Spectrom.

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The results are reported of mass-spectrometric studies of the nucleobases adenine 1h (1, R ϭ H), guanine 2h, and cytosine 3h. The protonated nucleobases are generated by electrospray ionization of adenosine 1r (1, R ϭ ribose), guanosine 2r, and deoxycytidine 3d (3, R ϭ deoxyribose) and their fragmentations were studied with tandem mass spectrometry. In contrast to previous EI-MS studies of the nucleobases, NH 3 elimination does present a major path for the fragmentations of the ions [1h ϩ H] ϩ , [2h ϩ H] ϩ , and [3h ϩ H] ϩ . The ion [2h ϩ H Ϫ NH 3 ] ϩ also was generated from the acyclic precursor 5-cyanoamino-4-oxomethylenedihydroimidazole 13h and from the thioether derivative 14h of 2h (NH 2 replaced by MeS). The analyses of the modes of initial fragmentation is supported by density functional theoretical studies. Conjugate acids 15-55 were studied to determine site preferences for the protonations of 1h, 2h, 3h, 13h, and 14h. The proton affinity of the amino group hardly ever is the substrate's best protonation site, and possible mechanisms for NH 3 elimination are discussed in which the amino group serves as the dissociative protonation site. The results provide semi-direct experimental evidence for the existence of the pyrimidine ring-opened cations that we had proposed on the basis of theoretical studies as intermediates in nitrosative nucleobase deamination. [1,2]. This chemistry has been studied extensively because of the dietary and environmental exposure of humans to these substances [3][4][5]. Toxicological studies of deamination became more significant when it was recognized that endogenous nitric oxide [6,7] causes nitrosation [8,9], and that this process is accelerated by chronic inflammatory diseases [10,11]. It has been known for a long time that deamination of adenine 1, guanine 2, and cytosine 3 (Scheme 1) results in the formation of hypoxanthine, xanthine, and uracil, respectively, and these products are thought to result from DNA base diazonium ions 4-6, respectively, by direct nucleophilic dediazoniation. The discovery of oxanine formation [12][13][14] in the nitrosative deamination of guanine challenged the generality and completeness of this mechanism. Theoretical studies revealed that unimolecular dediazoniation of guaninediazonium ion 5 is accompanied or immediately followed by pyrimidine ringopening [15,16] and that cytosine-catalysis promotes the process [17,18]. The resulting 5-cyanoimino-4-oxomethylene-4,5-dihydroimidazole is a highly reactive intermediate and undergoes acid-catalyzed 1,4-addition via cyano-N or imino-N protonated 5-cyanoimino-4-oxomethylene-4,5-dihydroimidazoles, 9 and 10, respectively [19].Labeling studies support this reaction mechanism for oxanine formation [20]. Moreover, we synthesized 5-cyanoamino-4-imidazolecarboxamide and studied its cyclization chemistry [21] and its proficiency for cross-link formation [22]. The unimolecular dediazoniation of the diazonium ions of adenine and cytosine can proceed without ring-opening but the cations 7 and 11 formed in this...

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Section: Site Of Protonation and Mode Of Initial Fragmentationsupporting

confidence: 88%

“…Data for guanine reported in reference [38]. Compare also [34,36] for proton affinities of cytosine and adenine, respectively. b Exp.…”

Section: Experimental and Computationalmentioning

confidence: 82%

Section: Esi and Deglycationmentioning

confidence: 99%

Section: Esi-ms/ms Of Adenosinementioning

confidence: 99%

See 2 more Smart Citations

Ammonia elimination from protonated nucleobases and related synthetic substrates

Qian

Yang

et al. 2007

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

show abstract

“…1). However, the mechanistic details have not been explored (apart from an ab initio mechanistic study of the HCN dimerization and adenine protonation) (19,20). Experimental investigations would be very difficult because adenine is not formed cleanly, yields are small, and many steps are involved.…”

mentioning

confidence: 99%