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Pairwise Interactions between Linear Alkanes in Water Measured by AFM Force Spectroscopy

Ray, Chad and Brown, Jason R. and Kirkpatrick, Andrea and Akhremitchev, Boris B. (2008) Pairwise Interactions between Linear Alkanes in Water Measured by AFM Force Spectroscopy. Journal of the American Chemical Society, 130 (30). pp. 10008-10018. ISSN 0002-7863.

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Pairwise interactions between n-alkanes from decane to octadecane in water have been studied by single-molecule force spectroscopy. The interacting molecules are covalently tethered to the glass substrate and to the probe of an atomic force microscope by water-soluble linkers to facilitate single-molecule detection. However, the measured distribution of rupture forces deviates significantly from the distribution predicted by theoretical models for rupture of individual bonds. To describe the statistics of rupture forces, an analytical model that considers near-simultaneous rupture of two bonds loaded by tethers with different lengths is introduced. The common most probable force analysis approach is used for comparison. In both data analyses, the possible systematic errors due to nonlinear elasticity of polymeric tethers and variations in the shape of the potential of mean force were considered. Experimental distributions of rupture forces are well-fit by the two-bond rupture model using a single set of kinetic parameters for different experiments, while the most probable force approach yields parameters that vary significantly for different samples. The measured activation energies for dissociation of alkanes are close to the free energies predicted by cavity models of hydrophobic interactions. The surface free-energy density is estimated to be ∼21 kJ/(mol nm^2) and is close to the upper limit of free energies used in the computer simulations of hydrophobic interactions in proteins. In contrast to the predictions of the cavity models, the measured activation energy does not increase monotonically with increase in alkane chain size. To explain this discrepancy and the measured distance to the transition-state barrier (∼0.6 nm), it is suggested that alkanes undergo conformational transition to the collapsed state upon dimerization. Change in the alkane conformation from extended to helical has been observed previously for binding of alkanes in water to hydrophobic synthetic receptors. Here, however, conformational change is suggested without geometrical constraints imposed by small cavitands. The proposed collapsed state of the alkane dimers has implications for the kinetics of self-assembly of surfactant micelles.

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Additional Information:© 2008 American Chemical Society. Received March 2, 2008. Publication Date (Web): July 3, 2008. We thank Duke University and the National Science Foundation (Grant CHE-0719043) for financial support.
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Duke UniversityUNSPECIFIED
Issue or Number:30
Record Number:CaltechAUTHORS:20170509-133949889
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Official Citation:Pairwise Interactions between Linear Alkanes in Water Measured by AFM Force Spectroscopy Chad Ray, Jason R. Brown, Andrea Kirkpatrick, and Boris B. Akhremitchev Journal of the American Chemical Society 2008 130 (30), 10008-10018 DOI: 10.1021/ja801568y
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77307
Deposited By: Tony Diaz
Deposited On:16 May 2017 22:00
Last Modified:03 Oct 2019 17:56

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