Biomedical Engineering Reference
In-Depth Information
reductant side to the oxidant side and is independent of direction of illumination (from the
reductant side to the oxidant side or the other way around). Similar observations have
been reported using other types of redox reactions (reviewed by Tien [39]).
Upon illumination with a brief (microsecond or shorter) light pulse, a transient
photocurrent initially flows in the direction expected by vectorial electron transfers but
250
200
150
100
50
0
50
0
50
100
150
200
(A)
Time (
µ
s)
8
6
4
2
0
3
2
1
0
0
0.5
1.0
1.5
2.0
2.5
3.0
Time (
µ
s)
(B)
FIGURE 15.2
Comparison of experimentally measured with predicted photoelectric responses. The BLM contained about 5
mM magnesium mesoporphyrin IX di- n -amyl ester. Both aqueous phases contained 1 M NaCl and 10 mM phos-
phate buffer at pH 7.2. In addition, the oxidant side contained 20 mM potassium ferricyanide and 0.5 mM potas-
sium ferrocyanide whereas the reductant side contained 20 mM potassium ferrocyanide (the omission of
potassium ferrocyanide at the reductant side has no major effect). The access impedance was 5.1 k
in Record A
and 380
s in Record A and 150 ns in Record B. The pho-
toemf has the time course of the power (intensity) of the dye laser pulse (output 590 nm, shown as the bottom
trace in Record B). See text for further explanation. (From Hong, F. T., Mauzerall, D. (1974). Interfacial photore-
actions and chemical capacitance in lipid bilayers. Proc. Natl. Acad. Sci. USA 71:1564-1568. (A) and Hong, F. T.,
Mauzerall, D. (1976). Tunable voltage clamp method: application to photoelectric effects in pigmented bilayer
lipid membranes. J. Electrochem. Soc. 123:1317-1324. (B))
in Record B. The instrumental time constant was 1.5
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