TY - JOUR
T1 - Electron Transfer in Binary Hemin-Modified Alkanethiol Self-Assembled Monolayers on Gold
T2 - Hemin's Lateral and Interfacial Interactions
AU - Sosna, Maciej
AU - Ferapontova, Elena E.
N1 - Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.
PY - 2022/9
Y1 - 2022/9
N2 - Orientated coupling of redox enzymes to electrodes by their reconstitution onto redox cofactors, such as hemin conjugated to self-assembled monolayers (SAMs) formed on the electrodes, poses the requirements for a SAM design enabling reconstitution. We show that the kinetics of electron transfer (ET) in binary SAMs of alkanethiols on gold composed of in situ hemin-conjugated 11-amino-1-undecanethiol (AUT) and diluting OH-terminated alkanethiols with 11, 6, and 2 methylene groups (MC11OH, MC6OH, and MC2OH) depends on both the SAM composition and surface density of hemin, Γheme. In AUT/MC11OH SAMs composed of equal linker/diluent lengths, the heterogeneous ET rate constant ksdecreased with the Γhemeand varied between 70 and 500 s-1. For shorter diluents, the ksof 245-330 s-1(C6) and 300-340 s-1(C2) showed a little (if any) Γhemedependence. In AUT/MC11OH SAMs, the increasing Γhemeresulted in the steric crowding of hemin species and their neighboring lateral interactions in the plane of hemin localization, affecting the potential distribution at the SAM/electrode interface and inducing local electrostatic effects interfering with hemin oxidation. In AUT/MC6OH and AUT/MC2OH SAMs, hemin discharged at the plane of the closest approach to the gold surface, equal to the diluent length and permeable to electrolyte ions, which lessened those effects. All studied binary SAMs provided steric hindrance for protein reconstitution on the hemin cofactor conjugated to the extended AUT linker. Further use of SAM-modified electrodes with the covalently attached hemin as interfaces for heme proteins' reconstitution should consider SAMs with loosely dispersed redox centers terminating more rigid molecular wires. Such wires place hemin at fixed distances from the electrode surface and thus ensure the interfacial properties required for the effective on-surface reconstitution of proteins and enzymes.
AB - Orientated coupling of redox enzymes to electrodes by their reconstitution onto redox cofactors, such as hemin conjugated to self-assembled monolayers (SAMs) formed on the electrodes, poses the requirements for a SAM design enabling reconstitution. We show that the kinetics of electron transfer (ET) in binary SAMs of alkanethiols on gold composed of in situ hemin-conjugated 11-amino-1-undecanethiol (AUT) and diluting OH-terminated alkanethiols with 11, 6, and 2 methylene groups (MC11OH, MC6OH, and MC2OH) depends on both the SAM composition and surface density of hemin, Γheme. In AUT/MC11OH SAMs composed of equal linker/diluent lengths, the heterogeneous ET rate constant ksdecreased with the Γhemeand varied between 70 and 500 s-1. For shorter diluents, the ksof 245-330 s-1(C6) and 300-340 s-1(C2) showed a little (if any) Γhemedependence. In AUT/MC11OH SAMs, the increasing Γhemeresulted in the steric crowding of hemin species and their neighboring lateral interactions in the plane of hemin localization, affecting the potential distribution at the SAM/electrode interface and inducing local electrostatic effects interfering with hemin oxidation. In AUT/MC6OH and AUT/MC2OH SAMs, hemin discharged at the plane of the closest approach to the gold surface, equal to the diluent length and permeable to electrolyte ions, which lessened those effects. All studied binary SAMs provided steric hindrance for protein reconstitution on the hemin cofactor conjugated to the extended AUT linker. Further use of SAM-modified electrodes with the covalently attached hemin as interfaces for heme proteins' reconstitution should consider SAMs with loosely dispersed redox centers terminating more rigid molecular wires. Such wires place hemin at fixed distances from the electrode surface and thus ensure the interfacial properties required for the effective on-surface reconstitution of proteins and enzymes.
UR - http://www.scopus.com/inward/record.url?scp=85138041253&partnerID=8YFLogxK
U2 - 10.1021/acs.langmuir.2c01064
DO - 10.1021/acs.langmuir.2c01064
M3 - Journal article
C2 - 36062334
AN - SCOPUS:85138041253
SN - 0743-7463
VL - 38
SP - 11180
EP - 11190
JO - Langmuir
JF - Langmuir
IS - 37
ER -