Journal
ACS NANO
Volume 6, Issue 2, Pages 1314-1321Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn204111w
Keywords
single-molecule force spectroscopy; force-clamp spectroscopy; silyl ester; acyloxysilane; hydrolysis; mechanochemistry
Categories
Funding
- German Excellence Initiative via Nanosystems Initiative Munich (NIM)
- Deutsche Forschungsgemeinschaft [Sonderforschungsbereich 677]
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We have investigated the strength of silyl ester bonds formed between carboxymethylated amylose (CMA) molecules and silane-functionalized silicon oxide surfaces using AFM-based single-molecule force spectroscopy in the force-clamp mode. Single tethered (MA molecules were picked up, and bond lifetimes were determined at constant clamp forces of 0.8, 1.0, and 1.2 nN at seven temperatures between 295 and 320 K at pH 2.0. The results reveal biexponential rupture kinetics. To obtain the reaction rate constants for each force and temperature individually, the results were analyzed with a biexponential kinetic model using the maximum likelihood estimation (MLE) method. The force-independent kinetic and structural parameters of the underlying bond rupture mechanisms were extracted by fitting the entire data set with a parallel MLE fit procedure using the Zhurkov/Bell model and, alternatively, an Arrhenius kinetics model combined with a Morse potential as an analytic representation of the binding potential. With activation energies between 37 and 40 kJ mol(-1), and with Arrhenius prefactors between 5 x 10(4) and 2 x 10(6) s(-1), the results point to the hydrolysis of the silyl ester bond.
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