Surface-Altered Protonation Studied by Photoelectron Spectroscopy and Reactive Dynamics Simulations.
The extent to which functional groups are protonated at aqueous interfaces as compared to bulk is deemed essential to several areas in chemistry and biology. The origin of such changes has been the source of intense debate. We use X-ray photoelectron spectroscopy and all-atom reactive molecular dynamics simulations as two independent methods to probe, at the molecular scale, both bulk and surface distributions of protonated species of cysteine in an aqueous solution. We show that the distribution of the cysteine species at the surface is quite different from that in the bulk. We argue that this finding, however, cannot be simply related to a change in the extent of proton sharing between the two conjugate acid/base pairs that may occur between these two regions. The present theoretical simulations identify species at the surface that are not present in the bulk.
†Institute of Physics, Brasilia University, Box 4455, 70910-970 Brası́lia, Distrito Federal, Brazil.
Áderson Miranda
ÁM
da Silva
†Institute of Physics, Brasilia University, Box 4455, 70910-970 Brası́lia, Distrito Federal, Brazil.
Alexandra
A
Mocellin
‡CNR-ICCOM, Institute of Chemistry of Organometallic Compounds, via G. Moruzzi 1, I-56124 Pisa, Italy.|§Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
Susanna
S
Monti
§Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.|∥CNR-IPCF, Institute of Chemical and Physical Processes, via G.Moruzzi 1, I-56124 Pisa, Italy.
Cui
C
Li
⊥Institute of Physics, Federal University of Bahia, 40210-340 Salvador, Bahia, Brazil.
Ricardo R T
RR
Marinho
⊥Institute of Physics, Federal University of Bahia, 40210-340 Salvador, Bahia, Brazil.
Aline
A
Medina
§Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
Hans
H
Agren
∥CNR-IPCF, Institute of Chemical and Physical Processes, via G.Moruzzi 1, I-56124 Pisa, Italy.
Vincenzo
V
Carravetta
#Institute of Physics "Gleb Wataghin", University of Campinas (Unicamp), 13083-859 Campinas, São Paulo, Brazil.
Arnaldo Naves
AN
de Brito
D056004:Molecular Dynamics Simulation / Q000706:statistics & numerical data*; D056951:Photoelectron Spectroscopy / Q000379:methods*; D011522:Protons
D011522:Protons
XPS; aqueous solution; chemical indicator; cysteine; molecular dynamics; protonated species surface and bulk