Additions and Corrections
2776 The Journal of Physical Chemistry, Vol. 96, No. 6, 1992
+
AV2+ e(C1) AV+
+ DODAC-H
hv
AV+
AV+-H hu
+
AV2+ e(E)
EH+
hv
vts~clesolution
AV+
e
+ DAC
+ e(E)
-+ + -
a-tocopherol F=r EH+
(1)
AV+
EO
AV
H+
(2) (3) (4) (5)
(6) AVZ+reacts with an electron, e, which probably comes from the chloride counterion to produce A V (eq 1). The radical conversion from AV+ to the DAC radical occurs in the presence of DODAC vesicles under photoirradiation (eq 2). (ii)a-Tocopherol(1-3 mol %), Photoreduction of AV2+to AV+ is accelerated by electrons released from a-tocopherol (eqs 3 and 4). The AV+ concentration increases with an increase of a-tocopherolconcentration, and the radical conversion from AV+ to the DAC radical is accelerated by the high concentration of AV+ (eq 2). EH+is produced by electrons released from a-tocopherol (eq 3) followed by deprotonation of EH+ in the vesicle solution under photoirradiation to result in EO (eq 5). (iii) a-Tocopherol (9-23 mol %). AV+ produced by primary photoreduction of AV2+(ap 1 and 4) reacts with electrons releastd from a-tocopherol at high concentrations (eq 3) to give AV (eq 6), which is not detected by ESR. The radical is depressed by the low concentration of AV+. Finally, EH+converts to EO by H+transfer to the vesicle solution under photoirradiation (q5). E f W of a-Tocoplerol Addition 011 the Photoreduction Yield ia DODAC Vesidea Yields of MV+, EO, of and the sum of MV+ and EO (total yield) from MV2+in DODAC vesicles with a-tocopherol (+3 mol %) are obtained by double integration of the simulated spectra and normalized to the yield of CI6V2+in DODAC vesicles without a-tocopherol (Figure 8). These yields can be compared. The yield of MV+ in DODAC ( i ) a-Tocopherol (0 mol
5%).
vesicles increases slightly with increasing a-tocopherol to about 3 mol % a-tocopherol and then decreases with further increase of a-tocopherol. The initial increase of the MV+ yield is due to an additional photoreduction process by electrons released from a-tocopherol (eq 3). Above 9 mol % a-tocopherol, the decrease of the MV+ yield is due to its conversion from MV+ to MV. The yield of the EO in DODAC vesicles increases with a-tocopherol until about 17 mol 9%. This increase of EO yield suggests that the deprotonation of EH+ is promoted by DODAC molecules under photoirradiation. The total yields from AV2+in DODAC vesicles with a-tocopherol increase with increasing alkyl chain length of AVZ+at a-tocopherol concentrations up to 3 mol 96 (Figure 6). This increase is greater for AV2+with longer alkyl chains due to a location in less hydrated r e g i ~ n s , which ~ ~ . ~promotes ~ an increase of the DAC radical. For 9 mol 46 and greater a-tocopherol, the total yields remain almost constant versus alkyl chaii length. The constant yield may be due to a balance of electron back reaction via eq 3 and the scavenging effects of DODAC molecules. The total yields versus a-tocopherol concentration (Figure 8) show an increase to 9 mol % and then an approximate plateau. The yield fmm a4cqherol(23 mol 96) only in hexane is lower than that from a-tocopherol (23 mol 96) in DODAC vesicles (Figures 6 and 7). This suggests that DODAC vesicle solutions act to stabilize the EO radical. These results do demonstrate that one can "tune" the magnitude of the alkyl chain length effect of AV2+on the total photoreduction yield by the addition of a-tocopherol in DODAC vesicles. However, the tuning range is rather narrow. This limited tuning range is related to the secondary photoreduction of AV+ to AV and the photoinduced conversion of a-tocopherol. Acknowledgment. We thank Professor H.Kashiwabara for use of the Melcom Cosmo 700 I11 computer at the Nagoya Institute ofTechndogy. This research was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, US.Department of Energy. P.B. thanks CNR for partial financial support.
ADDITIONS AND CORRECTIONS 1991, Volume 95
Kevin AsBley,* Frederick Weinert, M.beab C.Samant, H.W, and M.R.PMlpott*: Infrared Spectroelectrochemicl Study of Cyanide Adsorption on Palladium Surfaces. Pages 7411 and 7412. Figures 4 and 6 were inadvertently switched. The figure captions are correct, but the figures themselves should be exchanged.
