Photochemistry of protonated nitrosamine: chemical inertia of NH2NOH+ versus reactivity of NH3NO+.
The photochemical behavior of the protonated simplest nitrosamine [NH2NO-H](+) has been addressed by means of the CASPT2//CASSCF methodology in conjunction with the ANO-L basis sets. The relative stability of the different tautomers, namely, (1) NH2NOH(+), (2) NH3NO(+), and (3) NH2NHO(+), has been considered, and the corresponding tautomerization transition states have been characterized. With respect to the most chemically relevant species, it has been found that NH2NOH(+) corresponds to a bound structure, while NH3NO(+) corresponds to an adduct between NH3 and NO(+) at both CASSCF and CASPT2 levels of theory. Vertical transition calculations and linear interpolations on the homolytic dissociation of NH3NO(+) in combination with previous results on neutral nitrosamine [J. Chem. Phys. 2006, 125, 164311] and neutral N,N-dimethylnitrosamine [J. Org. Chem. 2007, 72, 4741] indicate that, in acidic diluted solutions, the protonation of nitrosamine takes place on the excited surface. The N-N dissociation channels have been studied both in ground and first excited singlet state. An S1/S0 conical intersection is found to be responsible for the photostability of NH2NOH(+). On the contrary, NH3NO(+) is photochemically unstable as its first excited state is purely dissociative. The latter species is characterized by a twofold reactivity: the formation of nitrosyl cation (NO(+)) in the ground state and the photorelease of physiologically relevant nitric oxide radical (NO) in its first excited state.
Peláez
Daniel
D
Department of Physical Chemistry, Faculty of Sciences, University of Málaga, E-29071 Málaga, Spain.
Arenas
Juan F
JF
Otero
Juan C
JC
Avila
Francisco J
FJ
Soto
Juan
J
D000641:Ammonia / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D009569:Nitric Oxide / Q000737:chemistry*; D009602:Nitrosamines / Q000737:chemistry*; D010777:Photochemistry; D010782:Photolysis; D011522:Protons; D012996:Solutions / Q000737:chemistry; D013816:Thermodynamics
D005609:Free Radicals; D009602:Nitrosamines; D011522:Protons; D012996:Solutions; D009569:Nitric Oxide; D000641:Ammonia