Flow cell experiments

In order to check the survival of methanol adsorbate to the transfer conditions, the following experiment was performed. After adsorption of methanol and solution exchange with base electrolyte, the Pt electrode was transferred to the UHV chamber over a period of ca. 10 min, then back to the cell where it was reimmersed into the pure supporting electrolyte. A voltammogram was run and compared with that of an usual flow cell experiment. The results, (see Fig. 2.5a,b), show that the transfer procedure is valid. The areas under the oxidation curve are the same. As in the case of adsorbed CO on Pt (see Fig. 1.4), the change in the double peak structure indicates that some surface re-distribution may occur. 

Figure 9. Comparison of the release of 10 pm glass microspheres from a glass surface between a flow cell experiment and a centrifuge experiment.

The third approach to solving this problem (Farber, 1999) involves the preparation of an enzyme-intermediate complex at high substrate concentration for X-ray data collection. Under such a condition active sites in the crystal lattice will be filled with intermediates. Using a combination of flow cell experiments and equilibrium experiments, it is possible to obtain the structure of important intermediates in an enzyme reaction (Bolduc et al., 1995). It was also discovered that some enzyme crystals can be transformed from their aqueous crystallization buffer to nonaqueous solvents without cross-linking the crystals before the transfer (Yennawar et. al., 1995). It is then possible to regulate the water concentration in the active site. The structure of the first tetrahedral intermediate, tetrapeptide -Pro-Gly-Ala-Tyr- in the y-chymotrypsin active site obtained by this method is shown in Fig. 1.1. 

For comparison, the measured adsorption rate for PNP to the air/water interface gave a rate constant of it = 4.4 0.2 x 10 s but a desorption rate of 6 2 s [52]. The rapid adsorption to the air/water interface is quite consistent with the very rapid establishment of the SHG signal from PNP at the dodecane/water interface observed in these flow cell experiments. However, the observed decay rate constant in the presence of TBP of ca. 0.5 s is much faster than the desorption rate constant that would be implied from the air/water experiments. This further implicates a reorganization process involving bonding between TBP and PNP as the cause of the loss of SHG intensity, which results in an overall loss of orientational order. 

Qiu F, Compton RG, Coles BA, Marken F (2000) Thermal activation of electrochemical processes in a Rf-heated channel flow cell experiment and finite element simulation. J Electroanal Chem 492 150-155... 

The current/potential behavior of CO on a porous Pt surface is demonstrated after CO adsorption in a flow cell experiment [22] via a potential scan in a solution free of CO, starting at 50 mV versus RHE[23. Figure 2 shows a first low current region (peak I) between 0.3 and 0.55 V, in the upper part, well below oxide formation on platinum. The following three peaks. 

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