The electronic properties of a model active site for blue copper proteins as probed by Stark spectroscopy

Arindam Chowdhury, Linda A. Peteanu, Patrick L. Holland, William B Tolman

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A complex that mimics many of the properties of the blue copper protein center that was synthesized by Holland and Tolman1 is studied using Stark spectroscopy to determine the values of two electronic properties, the change in the dipole moments (|Δ→Μ|) and the average change in the polarizability (〈Δα〉) for excitation into the ligand-to-metal charge transfer (LMCT) band. Measurements at 77 K in methylcyclohexane yield a value for |Δ→μ| of between 1.3 and 1.9 D for the lowest energy LMCT band, which has been assigned as a predominantly thiolate (Sπ) → Cu(dx2-y2) transition.2 The value of |Δ→μ| is remarkably similar to that we have measured earlier for the type-1 blue copper protein azurin in a glycerol-water glass. The sensitivity of Stark spectroscopy to charge-transfer transitions is utilized to identify and, in some cases, to confirm the assignment previously made via magnetic circular dichroism (MCD)2 of several higher-energy charge-transfer bands. Values for the electron-transfer matrix element (Hab) and the effective charge-transfer distance (Rab) derived from our measurements on this complex are also reported. These parameters are likewise found to be quite similar to those previously determined for azurin.

Original languageEnglish (US)
Pages (from-to)3007-3012
Number of pages6
JournalJournal of Physical Chemistry B
Issue number11
StatePublished - Mar 21 2002


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