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SORPTION AND DIRECT ELECTROCHEMISTRY OF MITOCHONDRIAL CYTOCHROME C ON HEMATITE SURFACES

Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA

View larger version (20K): [in a new window]   Figure 1. (a) Sorption isotherms of µmoles of Hcc sorbed/g of hematite vs. µmoles of dissolved Hcc/L of supernatant solution at pH 4.0 ± 0.05, 6.83 ± 0.07, and 9.5 ± 0.10. (b) Sorption of Hcc on hematite as a function of pH (filled circles, right-hand axis). Black dotted and dashed curves give overall repulsive (positive) or attractive (negative) forces between hematite and Hcc (references for Hcc isoelectric point and hematite point of zero charge are given in the text; Hamaker constant for van derWaals calculation from Schudel et al. (1997) and Neal et al.(1999)). The thick dashed horizontal line gives the amount of sorption corresponding to one monolayer of Hcc on hematite in hexagonal close packing. The vertical lines show the zero crossing points for the force calculations with and without van der Waals forces for easier comparison to the sorption data.

View larger version (30K): [in a new window]   Figure 2. UV-visible absorption spectra showing the Soret band as a function of pH; (a)molar absorptivity of Hcc solutions; (b) absorbance of supernatant solutions of Hcc sorbed on hematite. Because the concentration of Hcc in the supernatant solutions was based on molar absorptivity in solutions, the molar absorptivity of the supernatant solutions could not be compared independently.

View larger version (19K): [in a new window]   Figure 3. (a) Sorption kinetics forHcc sorbing on hematite over a period of 1–120 h for pH 2.9, 7.0 and 9.7; (b) wavelength position of Soret bands in supernatant solutions from sorption experiments as a function of time at pH 2.9, 7.0 and 9.7.

View larger version (40K): [in a new window]   Figure 4. (a) Ionic strength dependence of Hcc sorption on hematite at pH 3.0, 6.7 and 9.5; (b) UV-visible spectra for Hcc in solution at pH 3.0 and 9.5 at 100, 300 and 500 mM background electrolyte (KCl) concentration showing changes in molar absorptivity with ionic strength at pH 9.5.

View larger version (24K): [in a new window]   Figure 5. Cyclic voltammograms (current vs. potential) of Hcc solution at pH 9.5 using a hematite working electrode, Pt wire counter electrode and an Ag wire pseudo-reference calibrated to an Ag/AgCl reference electrode.