Sulfur K-edge X-ray absorption spectroscopy as an experimental probe for S-nitroso proteins

Nature of S-N Bonding in Sulfonamides and Related Compounds: Insights into π-Bonding Contributions from Sulfur K-Edge X-ray Absorption Spectroscopy

Molecules containing sulfur-nitrogen bonds, like sulfonamides, have long been of interest because of their many uses and interesting chemical properties. Understanding the factors that cause sulfonamide reactivity is important, yet there continues to be controversy regarding the relevance of S-N π bonding in describing these species. In this paper, we use sulfur K-edge X-ray absorption spectroscopy (XAS) in conjunction with density functional theory (DFT) to investigate the role of S_3p contributions to π-bonding in sulfonamides, sulfinamides, and sulfenamides. We explore the nature of the electron distribution of the sulfur atom to its nearest neighbors and widen our scope to its effects on rotational barriers along the sulfur-nitrogen axis. The experimental XAS data together with time-dependent DFT calculations confirm that sulfonamides-and the other sulfinated amides in this series-have essentially no S-N π bonding involving S_3p contributions and that electron repulsion is the dominant force affecting rotational barriers along the S-N axis.

Electronic structure of S-nitrosothiols from sulfur K-edge X-ray absorption spectroscopy

Sulfur K-edge X-ray absorption spectroscopy (S K-edge XAS) was applied to investigate the electronic structure of primary and tertiary S-nitrosothiols. Our experimental data, supported by density functional calculations, indicate that changes at Cα affect the S-nitroso group through both inductive and direct orbital effects. Furthermore, our data are consistent with a weakening of the S–N bond in tertiary S-nitrosothiols as compared to their primary S-nitroso analogues. These results support existing computational models and suggest that the reactivity of S-nitrosothiols is not dominated by the electronics of the S–N bond.