Protons uptake

Acrylonitrile or methyl acrylate readily inserts into allylnickel bonds (example 34, Table HI). A trans double bond is formed by loss of a proton. Insertion of acetylene followed by oxidative elimination with allyl halides gives cis double bonds (example 32, Table III). Insertion of methyl propiolate, followed by proton uptake, leads to a trans double bond (example 33, Table III). Norbomene has been shown to insert stereoselectively cis.exo into an allylnickel bond (example 35, Table III). 

The effectiveness of betaine can be explained better by its blocking proton uptake from solution. Betaine lessened the amount of protonated phenolic hydroxyl groups at any pH and consequently the intermolecular association between kraft lignin molecules. The chemical reactions can be shown as follows ... 

First, injection occurs from the photoexcited dye into the tin oxide conduction band, but is followed by very rapid trapping at a site that is energetically close to the conduction band and physically close to the dye. Trapping is accompanied by rapid, charge-compensating uptake of a proton—either from a hydronium ion or from a water molecule. Perhaps because of the proton uptake, the trapped electron remains proximal to the dye for at least a few hundred nanoseconds. The proximity enables each electron to return precisely to the dye that initially injected it. In other words, the recombination is geminate and the process is first... 

Are the mechanisms described here applicable to cells operating in nonaque-ous environments It is conceivable that the sequence described by Eqs. (12)-( 14) occurs under certain conditions. The more complex sequence involving coupled electron and cation transfer probably does not. Although Li+ (the electrolyte cation most often used in Gratzel-type cells) is known to intercalate into high-area metal oxide semiconductors [49,90,108-111], the rate is probably too slow to be coupled to injection and back ET in the same way that aqueous proton uptake and release are coupled to these processes. The ability to use water itself as a proton source means that solution-phase diffusional limitations on proton uptake are absent. Alkali metal ion uptake from nonaqueous solutions, on the other hand, clearly is subject to diffusional limitations. 

Figure 16-22 (A) Structure of the active site of iron superoxide dismutase from E. coli. From Carlioz et al m Courtesy of M. Ludwig. (B) Interpretive drawing illustrating the single-electron transfer from a superoxide molecule to the Fe3+ of superoxide dismutase and associated proton uptake. Based on Lah et al.376...

C. Measurement of proton uptake—1 to 2 hours, depending on the choice of experiments. 

Other optional experiments may be completed if time allows. For example, the effectiveness of various redox dyes may be analyzed. In addition to those listed in the text, FMN, ferricyanide, and dichlorophenolindophe-nol may be tested (Neumann and Jagendorf, 1964). It has been shown that NH4C1 and amines stimulate proton uptake. If a potassium ion-specific electrode is available, the light-induced efflux of K+ from spinach chloroplasts may be studied (Dilley, 1972). 

Experimental arrangement for measuring proton uptake by illuminated chloroplasts. See text for details. 

Compare the relative rates of proton uptake for each experimental condition and explain any differences. Did the addition of light-sensitive redox cofactor affect the rate of pH shift What is the effect of the addition of... 

Explain the effect, if any, of the redox cofactor on the rate of proton uptake. 

B 9. Would you expect the rate of proton uptake in this experiment to be dependent on the wavelength of light used What wavelength(s) is most effective Explain. 

Proton uptake is most efficient when light is absorbed by chlorophyll in the ranges 400-500 nm and 650-700 nm. 

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