Properties of Gaseous Deprotonated L-Cysteine S-Sulfate Anion [cysS-SO<sub>3</sub>]<sup>−</sup>: Intramolecular H-Bond Network, Electron Affinity, Chemically Active Site, and Vibrational Fingerprints
L-cysteine S-sulfate, Cys-SSO<sub>3</sub>H, and their derivatives play essential roles in biological chemistry and pharmaceutical synthesis, yet their intrinsic molecular properties have not been studied to date. In this contribution, the deprotonated anion [cysS-SO<sub>3</sub&g...
| Main Authors: | , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2023-01-01
|
| Series: | International Journal of Molecular Sciences |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1422-0067/24/2/1682 |
| Summary: | L-cysteine S-sulfate, Cys-SSO<sub>3</sub>H, and their derivatives play essential roles in biological chemistry and pharmaceutical synthesis, yet their intrinsic molecular properties have not been studied to date. In this contribution, the deprotonated anion [cysS-SO<sub>3</sub>]<sup>−</sup> was introduced in the gas phase by electrospray and characterized by size-selected, cryogenic, negative ion photoelectron spectroscopy. The electron affinity of the [cysS-SO<sub>3</sub>]<sup>•</sup> radical was determined to be 4.95 ± 0.10 eV. In combination with theoretical calculations, it was found that the most stable structure of [cysS-SO<sub>3</sub>]<sup>−</sup> (<b>S<sub>1</sub></b>) is stabilized via three intramolecular hydrogen bonds (HBs); i.e., one O−H⋯⋯N between the –COOH and –NH<sub>2</sub> groups, and two N−H⋯⋯O HBs between –NH<sub>2</sub> and –SO<sub>3</sub>, in which the amino group serves as both HB acceptor and donor. In addition, a nearly iso-energetic conformer (<b>S<sub>2</sub></b>) with the formation of an O−H⋯⋯N−H⋯⋯O−S chain-type binding motif competes with <b>S<sub>1</sub></b> in the source. The most reactive site of the molecule susceptible for electrophilic attacks is the linkage S atom. Theoretically predicted infrared spectra indicate that O−H and N−H stretching modes are the fingerprint region (2800 to 3600 cm<sup>−1</sup>) to distinguish different isomers. The obtained information lays out a foundation to better understand the transformation and structure–reactivity correlation of Cys-SSO<sub>3</sub>H in biologic settings. |
|---|---|
| ISSN: | 1661-6596 1422-0067 |