In situ spectroelectrochemical measurements have been carried out to probe the charge injection from excited Ru(bpy) 2 (dcbpy) 2+ , Ru(II), into the SnO 2 nanocrystallites. The dependence of luminescence yield and lifetime at various applied potentials suggests that the heterogeneous electron transfer from excited sensitizer into the semiconductor can be controlled by the externally applied electrochemical bias. The maximum quenching is seen at positive potentials while an increase in the luminescence yield and lifetime is seen at negative potentials. Laser flash photolysis of Ru(II)-modified SnO 2 nanocrystalline film has been carried out to record the transient absorption spectra at different applied potentials. The yield of electron transfer product, Ru(III), decreases as the applied bias is switched to negative potentials. At an applied bias of -0.7 V the only observable transient is the excited Ru(II) complex (Ru(II)*). The maximum apparent electron transfer rate constant, k et (∼4 × 10 8 s -1 ), observed at positive bias agrees with the previously determined electron transfer rate constants from emission lifetime and microwave conductivity experiments. The apparent rate constant for heterogeneous electron transfer is dependent on the applied bias, and it decreases as the difference between the pseudo-Fermi level of SnO 2 and oxidation potential of Ru(II)* decreases. These results suggest that the decreased rate of charge injection is responsible for lower IPCE (incident photon-to-photocurrent efficiency) observed in photoelectrochemical cells under negative bias. No significant change in the rate of reverse electron transfer was observed at potentials greater than -0.4 V.

ErratumRyu HJ, Kim DY, Park JY, Chang HY, Lee MH, Han K-H, Chon CY, Ahn SH. Clinical features and prognosis of hepatocellular carcinoma with respect to pre-S deletion and basal core promoter mutations of hepatitis B virus genotype C2.

No abstract

The absorption spectra of pure spread films of C60 and C70 as well as mixtures of C60 or C70 with 1,2-dioleoylsn-glycerol, DOG (Cao/DOG or G O / D O G = 1/1, 1/4, 1/20), have been measured at the nitrogen-water interface. These spectra resemble those of C60 and C70 solid films rather than spectra reported in nonaqueous solvents. The data suggest that aggregates of fullerene molecules form in spread films on the water surface. Even in (or C70/DOG) 1 /20 mixed spread films, the fullerene molecules exist in microdomains rather than homogeneous 2-dimensional solutions. Aggregate formation for Cw and c70 in DMSO/water mixed solvents has also been investigated. At low water volume fraction, cp (<0.10), the spectrum of C60 (1 X lW M) is that of monomer as observed in cyclohexane or benzene. Increasing cp to >0.10 leads to spectra resembling those of spread films. At a constant cp of 0.40, an increase in C60 concentration above M gives similar results.

No abstract

No abstract

To gain an understanding of the mechanism by which the hydroxyl free radical can arise in superoxide generating systems and learn how different chelaters of iron can inhibit this reaction, a pulse radiolysis kinetic study of the reaction of O;-with Fe(III)EDTA, Fe(III)HEDTA and Fe(III)DETAPAC (or DTPA) was undertaken. Superoxide reacts readily with Fe(III)EDTA and Fe(III)HEDTA with a pH-dependent second-order rate constant having values of 1.9 x lo6 M-l. s-' and 7.6 x 16 M-'. s-' at pH 7, respectively. However, the rate constant for the reaction of O;-with Fe(III)DETAPAC was found to be much slower, the upper limit for the rate constant being 104 M-l. s-l. These results in conjunction with spin-trapping experiments with Fe(II)EDTA, Fe(II)HEDTA, Fe(II)DETAPAC and Hz02 suggests that DETAPAC inhibits the formation of 'OH by slowing the reduction of Fe(II1) to Fe(I1) and not by inhibiting the Fenton reaction.

No abstract