TY - JOUR
T1 - Modeling the Weak pH Dependence of Proton-Coupled Electron Transfer for Tryptophan Derivatives
AU - Cui, Kai
AU - Soudackov, Alexander V.
AU - Hammes-Schiffer, Sharon
N1 - Publisher Copyright:
© 2023 American Chemical Society.
PY - 2023/12/14
Y1 - 2023/12/14
N2 - The oxidation of tryptophan (Trp) is an important step in many biological processes and often occurs by sequential or concerted proton-coupled electron transfer (PCET). The apparent rate constants for the photochemical oxidation of two Trp derivatives in water have been shown to be pH-independent at low pH and to exhibit weak pH dependence at higher pH. Herein, these systems are investigated with a general, multi-channel model that includes sequential and concerted mechanisms as well as various proton donors and acceptors. This model can reproduce the kinetic data for both Trp derivatives with physically meaningful parameters and suggests that the weak pH dependence may arise from the competition between OH- and H2O as proton acceptors in concerted PCET. Deprotonation of an ammonium group for one of the systems leads to a more complex pH dependence at higher pH. This work demonstrates the importance of considering multiple competing channels for the analysis of the pH dependence of apparent PCET rate constants.
AB - The oxidation of tryptophan (Trp) is an important step in many biological processes and often occurs by sequential or concerted proton-coupled electron transfer (PCET). The apparent rate constants for the photochemical oxidation of two Trp derivatives in water have been shown to be pH-independent at low pH and to exhibit weak pH dependence at higher pH. Herein, these systems are investigated with a general, multi-channel model that includes sequential and concerted mechanisms as well as various proton donors and acceptors. This model can reproduce the kinetic data for both Trp derivatives with physically meaningful parameters and suggests that the weak pH dependence may arise from the competition between OH- and H2O as proton acceptors in concerted PCET. Deprotonation of an ammonium group for one of the systems leads to a more complex pH dependence at higher pH. This work demonstrates the importance of considering multiple competing channels for the analysis of the pH dependence of apparent PCET rate constants.
UR - http://www.scopus.com/inward/record.url?scp=85179616512&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85179616512&partnerID=8YFLogxK
U2 - 10.1021/acs.jpclett.3c02282
DO - 10.1021/acs.jpclett.3c02282
M3 - Article
C2 - 38039095
AN - SCOPUS:85179616512
SN - 1948-7185
VL - 14
SP - 10980
EP - 10987
JO - Journal of Physical Chemistry Letters
JF - Journal of Physical Chemistry Letters
IS - 49
ER -