Primitive Molecular Recognition Effects in Electron Transfer Processes: Modulation of ((Trimethylammonio)methyl)ferrocenium/ferrocene Self-Exchange Kinetics via Hydrophobic Encapsulation

Roger M. Nielson, L. Andrew Lyon, Joseph T Hupp

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32 Citations (Scopus)

Abstract

1H NMR line broadening measurements show that the electron self-exchange rate constant for ((trimethylamino)methyl)ferrocenium/ferrocene (TMAFc2+/+) in D2O as solvent is decreased by ca. 20-50 fold in the presence of excess β-cyclodextrin. The rate effect is associated with the selective hydrophobic encapsulation of the ferrocene form of the redox couple (i.e., the ferrocenium form is not significantly encapsulated). Selective encapsulation leads to a coupling of electron transfer to host (cyclodextrin) transfer. Optical intervalence absorption measurements for a closely related mixed-valence system strongly suggest that the coupling decreases the self-exchange rate by increasing the thermal activation barrier - an inference that is corroborated by activation parameter measurements. The barrier increase ultimately can be understood in terms of a redox asymmetry effect upon the isolated electron transfer event, where the overall exchange mechanism likely entails sequential electron and host transfer.

Original languageEnglish
Pages (from-to)970-973
Number of pages4
JournalInorganic Chemistry
Volume35
Issue number4
Publication statusPublished - 1996

Fingerprint

Molecular recognition
Encapsulation
electron transfer
Modulation
modulation
Kinetics
Electrons
Cyclodextrins
kinetics
activation
Chemical activation
inference
optical absorption
asymmetry
Light absorption
valence
Rate constants
Ion exchange
nuclear magnetic resonance
Nuclear magnetic resonance

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

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title = "Primitive Molecular Recognition Effects in Electron Transfer Processes: Modulation of ((Trimethylammonio)methyl)ferrocenium/ferrocene Self-Exchange Kinetics via Hydrophobic Encapsulation",
abstract = "1H NMR line broadening measurements show that the electron self-exchange rate constant for ((trimethylamino)methyl)ferrocenium/ferrocene (TMAFc2+/+) in D2O as solvent is decreased by ca. 20-50 fold in the presence of excess β-cyclodextrin. The rate effect is associated with the selective hydrophobic encapsulation of the ferrocene form of the redox couple (i.e., the ferrocenium form is not significantly encapsulated). Selective encapsulation leads to a coupling of electron transfer to host (cyclodextrin) transfer. Optical intervalence absorption measurements for a closely related mixed-valence system strongly suggest that the coupling decreases the self-exchange rate by increasing the thermal activation barrier - an inference that is corroborated by activation parameter measurements. The barrier increase ultimately can be understood in terms of a redox asymmetry effect upon the isolated electron transfer event, where the overall exchange mechanism likely entails sequential electron and host transfer.",
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T1 - Primitive Molecular Recognition Effects in Electron Transfer Processes

T2 - Modulation of ((Trimethylammonio)methyl)ferrocenium/ferrocene Self-Exchange Kinetics via Hydrophobic Encapsulation

AU - Nielson, Roger M.

AU - Andrew Lyon, L.

AU - Hupp, Joseph T

PY - 1996

Y1 - 1996

N2 - 1H NMR line broadening measurements show that the electron self-exchange rate constant for ((trimethylamino)methyl)ferrocenium/ferrocene (TMAFc2+/+) in D2O as solvent is decreased by ca. 20-50 fold in the presence of excess β-cyclodextrin. The rate effect is associated with the selective hydrophobic encapsulation of the ferrocene form of the redox couple (i.e., the ferrocenium form is not significantly encapsulated). Selective encapsulation leads to a coupling of electron transfer to host (cyclodextrin) transfer. Optical intervalence absorption measurements for a closely related mixed-valence system strongly suggest that the coupling decreases the self-exchange rate by increasing the thermal activation barrier - an inference that is corroborated by activation parameter measurements. The barrier increase ultimately can be understood in terms of a redox asymmetry effect upon the isolated electron transfer event, where the overall exchange mechanism likely entails sequential electron and host transfer.

AB - 1H NMR line broadening measurements show that the electron self-exchange rate constant for ((trimethylamino)methyl)ferrocenium/ferrocene (TMAFc2+/+) in D2O as solvent is decreased by ca. 20-50 fold in the presence of excess β-cyclodextrin. The rate effect is associated with the selective hydrophobic encapsulation of the ferrocene form of the redox couple (i.e., the ferrocenium form is not significantly encapsulated). Selective encapsulation leads to a coupling of electron transfer to host (cyclodextrin) transfer. Optical intervalence absorption measurements for a closely related mixed-valence system strongly suggest that the coupling decreases the self-exchange rate by increasing the thermal activation barrier - an inference that is corroborated by activation parameter measurements. The barrier increase ultimately can be understood in terms of a redox asymmetry effect upon the isolated electron transfer event, where the overall exchange mechanism likely entails sequential electron and host transfer.

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