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and a systematically larger event amplitude (up to 10 pA) was observed. The measured rate constant suggests that the coordination of a single ion with an amino acid follows hard-soft-acid-base theory, which has never been systematically validated in the case of a single molecule. By adjusting the measurement pH from 6.8 to 8.0, the duration of a single ion binding event could be modified with a ∼46-fold time extension. The phenomena reported suggest MspA to be a superior engineering template for probing a variety of extremely small analytes, such as monatomic and polyatomic ions, small molecules or chemical intermediates, and the principle of hard-soft-acid-base interaction may be instructive in the pore design.
Wang et al. (Tue,) studied this question.