Anisotropy of Pairwise Interactions between Hexadecanes in Water Measured by AFM Force Spectroscopy

摘要: The pulling coordinate dependence of hexadecane dimer dissociation in water was studied using AFM-based single molecule force spectroscopy. Hexadecanes were covalently bound to both the AFM cantilever and glass substrates through hydrophilic poly-(ethylene glycol) tethers. polymer tether attached either end or middle molecule. Experimentally configurations hexadecanes tethered probe substrate include a symmetric end-attached configuration (EE), an asymmetric vs middle-attached (ME), (MM). Kinetic parameters distance transition state barrier (barrier width) activation energy extracted from statistical analysis double rupture events. employs recently introduced two-bond model that corrects for errors induced by potential multiple simultaneous events accounts stiffening effects. Effects shape intermolecular considered Bell−Evans Hummer−Szabo spectroscopy models. energies similar all while width significantly shorter MM ME than EE configurations. Primitive models touching merging spherical cylindrical shapes considered. These inconsistent with kinetic parameters. It is suggested observed anisotropy may be result conformational extended collapsed during dimerization. A flexible four-bead account flexibility. Using length solvent accessible surface area hexadecane, gave molecular consistent experimental data. This suggests flexibility important factor hydrophobic interactions between alkane chains.