VUV Photoelectron Spectroscopy of Cysteine Aqueous Aerosols: A Microscopic View of Its Nucleophilicity at Varying pH Conditions.
Cysteine (Cys) is unique due to its highly reactive thiol group. It often regulates the biological function of proteins by acting as the redox site. Despite its biological significance, however, the valence electronic structure of Cys under the aqueous environments remains unavailable. Here, we report the VUV photoelectron spectroscopy of Cys aqueous aerosols via a newly built aerosol VUV photoelectron spectroscopy apparatus. The photoelectron spectra of Cys show distinct band shapes at varying pH conditions, reflecting the altered molecular orbital characters when its dominating form changes. The ionization energy of Cys is determined to be 8.98 ± 0.05 eV at low pH. A new feature at a binding energy of 6.97 ± 0.05 eV is observed at high pH, suggesting that the negative charge on the thiolate group becomes the first electron to be removed upon ionization. This work implies that when Cys is involved in redox processes, the charge transfer mechanism may be entirely altered under different pH conditions.
†Department of Chemistry, National Sun Yat-sen University, 80424 Kaohsiung, Taiwan, Republic of China.
Chien-Cheng
CC
Su
†Department of Chemistry, National Sun Yat-sen University, 80424 Kaohsiung, Taiwan, Republic of China.
Youqing
Y
Yu
†Department of Chemistry, National Sun Yat-sen University, 80424 Kaohsiung, Taiwan, Republic of China.
Po-Chiao
PC
Chang
†Department of Chemistry, National Sun Yat-sen University, 80424 Kaohsiung, Taiwan, Republic of China.
Yu-Wei
YW
Chen
†Department of Chemistry, National Sun Yat-sen University, 80424 Kaohsiung, Taiwan, Republic of China.
I-Ying
IY
Chen
‡National Synchrotron Radiation Research Center, 30076 Hsinchu, Taiwan, Republic of China.
Yin-Yu
YY
Lee
†Department of Chemistry, National Sun Yat-sen University, 80424 Kaohsiung, Taiwan, Republic of China.
Chia C
CC
Wang
D000336:Aerosols; D003545:Cysteine / Q000737:chemistry*; D056951:Photoelectron Spectroscopy / Q000379:methods*
D000336:Aerosols; D003545:Cysteine
VUV photoelectron spectroscopy; aerosols; cysteine; ionization energy; nucleophilicity; pH dependence; thiol oxidation