Visualizing and tuning thermodynamic dispersion in metalloprotein monolayers.
In coupling the redox state of an adsorbed molecule to its spectral characteristics redox profiles can be directly imaged by means of far-field fluorescence. At suitable levels of dilution, on optically transparent electrode surfaces, reversible interfacial electron transfer processes can be followed pixel by pixel down to scales which approach the molecular. In mapping out switching potentials across a surface population, thermodynamic dispersion, related to variance in the orientation, electronic coupling, protein fold, electric field drop, and general surface order, can be quantified. The self-assembled monolayer buffering the protein from the underlying metallic electrode surface not only acts to tune electronic coupling between the two but also potentially provides a variable more easily segmented from other contributions to molecular dispersion. We have, specifically, considered the possibility that the supporting monolayer crystallinity is a significant contributor to the subsequently observed spread in half-wave potentials. We report here that this is indeed the case and that this spread diminishes from 17 to 12 mV for the blue copper protein azurin as the supporting alkanethiol layer crystallinity increases. The work herein, then, presents not only a direct determination of submonolayer scale variance in redox character but also a means of tuning this through gross surface and entirely standard chemical means.
Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
Amol Virendra
AV
Patil
Jason John
JJ
Davis
D001400:Azurin / Q000737:chemistry* / Q000378:metabolism*; D004563:Electrochemistry / Q000379:methods*; D004579:Electron Transport; D008856:Microscopy, Fluorescence / Q000379:methods*; D008958:Models, Molecular; D016011:Normal Distribution; D011487:Protein Conformation; D011550:Pseudomonas aeruginosa; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013816:Thermodynamics
D013438:Sulfhydryl Compounds; D001400:Azurin