1997 Alfred Bader Award Lecture Reactivities of arylnitrenium ions with guanine derivatives and other nucleophiles

Transient Resonance Raman and Density Functional Theory Investigation of 4-Methoxyphenylnitrenium and 4-Ethoxyphenylnitrenium Ions

“…The oxocarbocation character of the 4-alkoxyphenylnitrenium ions also appears to influence the chemical reactivity of these ions toward nucleosides such as 2‘deoxyguanosine. For example, the biphenyl-4-yl-nitrenium and the 4‘-methoxybiphenyl-4-ylnitrenium ions exhibited significant selectivity toward reaction with 2‘-deoxyguanosine even in the nucleophilic solvent water, whereas this selectivity was not found for the 4-alkoxyphenylnitrenium ions. , This was suggested to be due to greater charge at the oxocarbo group in the alkoxyphenylnitrenium ions and hence a lesser charge and reactivity at the nitrenium moiety . Our present results are reasonably consistent with this hypothesis in that there does appear to be a noticeable localization of charge at the oxocarbo moiety at the expense of the nitrenium ion moiety.…”

“…These types of reactions are thought to result in carcinogenic mutations. − ,, Arylnitrenium ions are reactive short-lived species that are difficult to study. Several photochemical methods have been developed to enable laser spectroscopy techniques to be used to directly probe arylnitrenium ions in room-temperature solutions. − The lifetimes of arylnitrenium ions and their rate constants for reactions with other molecules have been measured using time-resolved transient absorption experiments. − ,, Recently, time-resolved infrared (TRIR) absorption spectroscopy and time-resolved resonance Raman (TR 3 ) spectroscopy have been used to investigate the structure and properties of several arylnitrenium ions. ,− These studies showed that the arylnitrenium ions have significant iminocyclohexadienyl character to varying degrees depending on their structure and substituents. ,− Several alkoxyphenylnitrenium ions including 4-methoxyphenylnitrenium and 4-ethoxyphenylnitrenium ions have been examined using time-resolved transient absorption spectroscopy and found to have relatively long lifetimes on the order of a millisecond. , We note that the 4-ethoxyphenylnitrenium ion is of particular interest because it would be formed from the carcinogen phenacetin that had found use as an analegesic until it was banned for use.…”

Transient Resonance Raman and Density Functional Theory Investigation of the 4-Acetamidophenylnitrenium Ion

“…The properties and chemical reactions of arylnitrenium ions have long been of intense interest because they are thought to be key intermediates in chemical carcinogenesis. − Aromatic amines may be enzymatically transformed into sulfate esters of the corresponding N -hydroxylamines and in aqueous environments will spontaneously produce an arylnitrenium ion and a sulfate ion. , Arylnitrenium ions such as the 2-fluorenylnitrenium ion can be selectively trapped by guanine bases in DNA and make adducts, and these kinds of reactions are believed to lead to carcinogenic mutations. − ,, Arylnitrenium ions are very reactive and hence short-lived species that are generally difficult to study. Several photochemical methods have been developed in order to allow laser spectroscopic techniques to directly probe the spectroscopy and kinetics of arylnitrenium ions in room-temperature solutions. − The rate constants for reactions with other molecules and the lifetimes of arylnitrenium ions have been obtained for a number of systems using time-resolved transient absorption spectroscopy. − ,, More recently, time-resolved vibrational spectroscopic techniques such as time-resolved infrared (TRIR) absorption spectroscopy and time-resolved resonance Raman (TR 3 ) spectroscopy have been used to directly probe the structure of arylnitrenium ions in both organic and largely aqueous solvents. ,− These investigations showed that severa...…”

Generation ofN,N-Di(4-bromophenyl)nitrenium Ion under Acidic Conditions: Search for a Nitrenium Dication

“…Due to their role in DNA damaging reactions, the arylnitrenium ions have been extensively characterized. [4][5][6][7][8] In general, it has been shown that there is significant delocalization of positive charge from the nitrenium ion center into the aromatic ring as illustrated in Scheme 1. For this reason, it is possible to form a nitrenium dication through protonation of the nitrogen lone pair.…”