An aqueous silver sol (mean particle size: 6 nm) is mixed with KI and NaSH solution, and the changes in optical absorption and light scattering are recorded. When iodide adsorbs on the silver particles, the 225-nm band of I-disappears concurrently with the decreasing of the silver plasmon absorption band. In the same time range, the intensity of light scattering slightly decreases, which is explained as a detachment of the colloidal particles from the polyphosphate stabilizer. At a later stage, the silver plasmon band is red-shifted and the light scattering finally increases again, which is understood in terms of loose cluster formation of the particles. The adsorption of H*S leads to damping and a simultaneous blue shift of the plasmon absorption band. The adsorption of H2S is faster than that of SH-, as there is no Coulomb repulsion between the adsorbant and the negatively charged metal particles.

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The plasmon absorption band of 6-nm silver particles in aqueous solution is blue-shift4 and strongly broadened upon the adsorption of phosphine, PH3. The effects are more pronounced in alkaline than acidic solution. In alkaline solution, the adsorption is completely irreversible. Upon aging of the silver solutions containing PH3, hydrogen and phosphate are generated in the mole ratio 4: 1. A mechanism is proposed for the catalytic action of the silver particles in the reaction of phosphine with water, in which donation of electron density from absorbed phosphine into the silver particles is an important step. Conductivity measurements indicate that phosphine in alkaline solution is adsorbed as PH2-. It is shown in coadsorption experiments that phosphine is more strongly adsorbed than I-and that SH-and phosphine are about equally strongly adsorbed.

The rate of ATP hydrolysis catalyzed by the membrane-bound CF,,F, ATP synthase from chloroplasts served as a probe for the determmatton of the reduction grade of the enzyme treated with dithiothreitol (DTT) or thioredoxin. Rate constants for reduction were obtamed. It turns out that reduction by thioredoxin IS about a factor of 6,000 more effective than DTT reduction. The activation profiles with respect to dpH were obtained for reduced and oxidized ATPases. The activation curve of reduced enzyme turns out to have its half-maximum degree of activation at dpH = 1.65, which is considerably lower than reported hitherto. The corresponding value of the oxidtzed enzyme has been obtained from the rate of ATP hydrolysis m the case of incomplete reduced ATPases, taking into account the aforementioned rate constants, and comes to dpH = 3.35.

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