A new method has been proposed to determine the equilibrium between the bulk and the surface by directly
measuring surface concentrations using laser two-photon ionization. This method has been applied to
pyrenebutyric acid. The surface concentrations depended on the pH of the solution and were analyzed on the
basis of two equilibrium constants and two distribution coefficients. Most pyrenebutyric acid stays on the
surface at pH = 2.2. The equilibrium constant, pK
a, of pyrenebutyric acid on the water surface was determined
to be 7.85 ± 0.13, and this value is shifted to higher value than that in the bulk (4.76). The distribution
coefficient of the neutral pyrenebutyric acid was determined as (5.9 ± 2.8) × 10-2 m, and that of pyrenebutyric
anion as (4.82 ± 0.1) × 10-5 m. The ratio of the distribution coefficient of the neutral pyrenebutyric acid to
that of pyrenebutyric anion was determined to be (1.2 ± 0.6) × 103. These findings indicate that the equilibrium
shifts toward the neutral form on the water surface. Laser two-photon ionization was found to be a sensitive
and powerful technique to analyze equilibrium on the surface and that between the surface and the bulk.
Heptamethyl cobyrinate, hydrophobic vitamin B12, was reduced to its Co(I) species by a reaction with sodium tetrahydroborate, which reacted with various organic halides, such as CH2Cl2, CHCl3, CCl4, CHBrCl2, CHBr3, CCl3CH3, CFCl3, and BrCH2CH2CH3, to form the corresponding alkylated complexes with dehalogenation. The alkylated complexes were characterized by elemental analyses and ESI-MS, and the photo-lability of the alkylated complexes was confirmed by the UV–vis absorption spectral change. The fashion for cleavage of the cobalt–carbon bond under irradiation with visible light was investigated by an ESR spin-trapping technique. The redox behavior of a series of alkylated complexes was investigated by cyclic voltammetry. The alkylated complexes showed an irreversible reduction peak at −1.21 to −1.29 V vs Ag–AgCl, which showed cleavage of the cobalt–carbon bond by electrolysis.
The cell performances under low or high relative humidity were examined for Pt / C cathode catalysts of various kinds of carbon support. No significant difference of cell performance were observed among Vulcan XC-72, Graphitized Vulcan XC-72, HSAC-1 (Surface Area = c.a. 800 m2 g-1, particle size = c.a. 30 nm), and HSAC-2 (Surface Area = c.a. 800 m2 g-1, particle size = c.a. 10 nm). Heat treatment process to improve the stability decreased the cell performance especially under low relative humidity. It was suggested by the titration of catalysts that the loss of hydrophilic organic group on the surface of carbon support by the heat treatment of catalysts was one of the reasons. The effect of the weight ratio of ionomer to carbon (I / C) was also examined. For example, in the case of Vulcan XC-72 support, the best I / C for the cell performance was 0.9.
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