title: Structure, stability, and substituent effects in aromatic S-nitrosothiols: the crucial effect of a cascading negative hyperconjugation/conjugation interaction.
abstract: Aromatic S-nitrosothiols (RSNOs) are of significant interest as potential donors of nitric oxide and related biologically active molecules. Here, we address a number of poorly understood properties of these species via a detailed density functional theory and the natural bond orbital (NBO) investigation of the parent PhSNO molecule. We find that the characteristic perpendicular orientation of the -SNO group relative to the phenyl ring is determined by a combination of the steric factors and the donor-acceptor interactions including, in particular, a cascading orbital interaction involving electron delocalization from the oxygen lone pair to the σ-antibonding S-N orbital and then to the π*-aromatic orbitals, an unusual negative hyperconjugation/conjugation long-range delocalization pattern. These interactions, which are also responsible for the relative weakness of the S-N bond in PhSNO and the modulation of -SNO group properties in substituted aromatic RSNOs, can be interpreted as a resonance stabilization of the ionic resonance component RS(-)/NO(+) of the RSNO electronic structure by the aromatic ring, similar to the resonance stabilization of PhS(-) anion. These insights into the chemistry and structure-property relationships in aromatic RSNOs can provide an important theoretical foundation for rational design of new RSNOs for biomedical applications.
authors.affiliation: Department of Chemistry, Marquette University , P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, United States.
authors.forename: Matthew
authors.initials: M
authors.lastname: Flister
authors.forename: Qadir K
authors.initials: QK
authors.lastname: Timerghazin
mesh_terms: D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D026403:S-Nitrosothiols / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D026403:S-Nitrosothiols