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An approximate theory for the feedback mode of the scanning electrochemical microscope (SECM) is developed to interpret the effects of substrate shielding on an ultramicroelectrode tip during a recording of iT versus d curves (approach curves) for reversible and quasireversible kinetics at a substrate surface. The resulting expressions for the tip current, iT, show a good fit to more accurate SECM simulations as well as to the experimental response of a reversible and quasireversible reaction. SECM shielding experiments thus give an interesting new insight into SECM approach curves over electrodes at different potentials, which suggest possible applications to measuring heterogeneous kinetics for fast reactions and diffusion coefficient determination.

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Cry11Aa and Cyt1Aa of Bacillus thuringiensis are active against mosquitoes and show synergism. Cyt1Aa functions as a membrane receptor inducing Cry11Aa oligomerization. Here we characterized Cry11Aa helix ␣-3 mutants impaired in oligomerization and toxicity against Aedes aegypti, indicating that oligomerization of Cry11Aa is important for toxin action. Cyt1Aa did not recover the insecticidal activity of Cry11Aa mutants.