| Abstract
| - Various amino acid-carrying amphiphiles were synthesized, and the pK values of the attachedamino acid residues were investigated at the air−water interface and in aqueous vesicles using π−A isothermmeasurements, 1H NMR titration, and IR spectroscopy in reflection−adsorption mode. The ε-amino groupof the Lys residue embedded at the air−water interface displays a significant pK shift (4 or 5 unit) comparedwith that observed in bulk water, while the pK shift in aqueous vesicles was not prominent (ca. 1 unit).Moreover, pK values of the amino acids at the air−water interface can be tuned simply by control of thesubphase ionic strength as well as by molecular design of the amphiphiles. A simple equation based onthe dominant contribution by the electrostatic energy to the pK shift reproduces well the surface pressuredifference between protonated and unprotonated species, suggesting a reduction in the apparent dielectricconstant at the air−water interface. Hydrolysis of a p-nitrophenyl ester derivative was used as a modelreaction to demonstrate the use of the Lys-functionalized monolayer. Efficient hydrolysis was observed,even at neutral pH, after tuning of pK for the Lys residue in the monolayer, which is a similar case to thatoccurring in biological catalysis.
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