Issue Date: October 28, 2013
Van der Waals Force Measured In Solution
Van der Waals dispersion forces are attractive forces between atoms and molecules that arise from fluctuations in electron distribution. The weakness of the forces makes them particularly hard to study in solution to understand their important roles in protein folding and assembly of nanostructured materials. A group led by Scott L. Cockroft of the University of Edinburgh, in Scotland, has devised a way to measure the attraction between alkyl chains in solution: by using NMR spectroscopy to monitor the structure of a self-folding organic compound (Nat. Chem. 2013, DOI: 10.1038/nchem.1779). The structural equilibrium of the compound between its folded and unfolded states is governed by intramolecular van der Waals forces between its alkyl chains as well as by solvent interactions. From the position of the equilibrium, Cockroft and colleagues extracted the contributions of the various forces, yielding experimental values for alkyl-alkyl van der Waals dispersion forces in 31 solvents and solvent mixtures. The results suggest that solvent cohesion rather than van der Waals dispersion forces drives association of alkyl groups.
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