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Materials

Immobilized For Hydrophobic Interactions

Chemical heterogeneity could be used to tune forces in molecular recognition or self-assembly

by Celia Henry Arnaud
January 19, 2015 | A version of this story appeared in Volume 93, Issue 3

Theory and simulations have suggested that nanometer-scale chemical heterogeneity affects hydrophobic interactions that are important to molecular recognition and self-assembly processes. Nicholas L. Abbott, Samuel H. Gellman, and coworkers at the University of Wisconsin, Madison, have now experimentally tested the effect of such heterogeneity. The researchers used chemical force microscopy to measure the adhesive forces between two alkyl-functionalized surfaces and how immobilized cations affect those forces on the nanometer scale (Nature 2015, DOI: 10.1038/nature14018). They made the measurements in aqueous triethanolamine buffer with and without 60% methanol, which eliminates most of the hydrophobic adhesion. The attachment of amine/ammonium or guanidine/guanidinium groups dramatically changed the hydrophobic interaction strength. Protonation of amine groups doubled the hydrophobic interaction strength, whereas guanidine/guanidinium groups eliminated measurable hydrophobic interactions independent of the degree of protonation. The team observed similar effects in β-peptides with amine- and guanidine-containing regions. The measurements show that short-range chemical heterogeneity does greatly affect hydrophobic interactions and could be used as a strategy to tune molecular recognition or self-assembly.

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