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Covalent Attachment of Single Molecules for AFM-based Force Spectroscopy
Published on: March 16, 2020
Pairwise interactions between linear alkanes in water measured by AFM force spectroscopy
Chad Ray1, Jason R Brown, Andrea Kirkpatrick
1Department of Chemistry, Duke University, Durham, North Carolina 27708, USA.
Journal of the American Chemical Society
|July 4, 2008
Summary
Single-molecule force spectroscopy reveals n-alkane interactions in water. A two-bond rupture model accurately describes rupture forces, suggesting alkanes collapse upon dimerization, impacting micelle formation.
Area of Science:
- Physical Chemistry
- Biophysics
- Surface Science
Background:
- Understanding hydrophobic interactions is crucial for molecular self-assembly and biological processes.
- Previous models for molecular rupture forces often simplify bond dynamics.
- n-alkanes serve as model systems for studying hydrophobic effects in aqueous solutions.
Purpose of the Study:
- To investigate pairwise interactions between n-alkanes (decane to octadecane) in water using single-molecule force spectroscopy.
- To develop and validate a theoretical model that accurately describes the distribution of rupture forces observed in these interactions.
- To explore the thermodynamic and kinetic aspects of alkane dimerization and its implications for hydrophobic interactions.
Main Methods:
- Single-molecule force spectroscopy (SMFS) was employed to measure rupture forces between n-alkanes.
- Molecules were tethered to an atomic force microscope probe and a substrate using water-soluble linkers.
- An analytical model considering near-simultaneous rupture of two bonds and a most probable force analysis were used to interpret the data.
Main Results:
- Experimental rupture force distributions were well-described by a two-bond rupture model with consistent kinetic parameters.
- The most probable force analysis yielded varying parameters, indicating limitations in its application here.
- Measured activation energies for alkane dissociation align with cavity models, but do not increase monotonically with chain length.
- A transition-state barrier distance of approximately 0.6 nm was determined.
Conclusions:
- The two-bond rupture model provides a superior description of n-alkane interactions in water compared to simpler models.
- Alkane dimerization likely involves a conformational transition to a collapsed state, deviating from simple extended models.
- This conformational change offers insights into the kinetics of surfactant micelle self-assembly.
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