Cooperative Binding of 1-Phenylimidazole to Cobalt(II) Octaethylporphyrin on Graphite: A Quantitative Imaging and Computational Study at Molecular Resolution
2020
Korpany, Katalin V. | Chilukuri, Bhaskar | Hipps, K. W. | Mazur, Ursula
Cooperative interactions play a critical role in the stability and reactivity of biological systems and are an increasingly important consideration in the synthesis of functional materials, but quantitative single-molecule measurements of this phenomenon are rare. Many of these cooperative interactions necessarily occur on surfaces, making the study of cooperative effects at interfaces of particular importance. Here, we report a quantitative experimental and theoretical study of the cooperative binding of 1-phenylimidazole (PhIm) to cobalt(II) octaethylporphyrin (CoOEP) on highly oriented pyrolytic graphite (HOPG) at the solution–solid interface. Scanning tunneling microscopy (STM) confirmed and monitored the binding of PhIm to HOPG-supported CoOEP with single-molecule resolution. Nearest-neighbor analysis of these STM images revealed positive cooperative binding behavior. Periodic plane-wave density functional theory (DFT) calculations of PhIm/CoOEP/HOPG and cobalt(II) porphine (CoP)/HOPG systems support the experimental observations of positive cooperativity. DFT calculations revealed that the binding energy of PhIm to Co-porphyrin increases as PhIm binds to more neighboring molecules. Calculations also suggest that the presence of HOPG is crucial to observe positive cooperativity in this system.
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