The reactive intermediates N,N-di(4-chlorophenyl)nitrenium ion and N,N-di(4-bromophenyl)nitrenium ion were generated through photolysis of the corresponding N-amino(2,4,6,-collidinium) ions. The behavior of these diarylnitrenium ions was characterized by laser flash photolysis, analysis of the stable photoproducts, and ab initio calculations with density functional theory. The latter predict these species to have singlet ground states. The halogenated diarylnitrenium ions are significantly longer lived than the unsubstituted diphenylnitrenium ion. Specifically, cyclization to form carbazole derivatives occurs negligibly, if at all, with the halogenated derivatives. They do, however, carry out most of the characteristic reactions of singlet arylnitrenium ions, including combining with nucleophiles on the aryl rings, adding to arenes, and accepting electrons from readily oxidized traps. Interestingly these species also abstract H atoms from 1,4-cyclohexadiene and various phenol derivatives. The implication of the latter process in relation to the computed singlet-triplet energy gaps of ca. -12.5 kcal/mol is discussed.
[reaction: see text] Laser flash photolysis experiments, chemical trapping studies, and time-dependent density functional theory calculations demonstrate that photolysis of protonated 1,1-diarylhydrazines generates N,N-diarylnitrenium ions.
Laser flash photolysis was used to examine the reaction of N-methyl-N-(4-biphenylyl)nitrenium ion with various amino acids and proteins in aqueous media. This nitrenium ion was found to react rapidly (>10 8 M À1 s À1 ) with tryptophan, tyrosine, methionine and cysteine, more slowly (10 7 -10 8 M À1 s À1 ) with lysine, histidine, and arginine. Rapid reaction was also seen with several representative proteins including bovine serum albumin, lysozyme, and chymotrypsin. These results suggest that reaction with proteins is likely to be a significant pathway in the reactions of nitrenium ions generated in vivo.
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