Mapping hydrophobicity at the nanoscale: Applications to heterogeneous surfaces and proteins

Abstract

Approaches to quantify wetting at the macroscale do not translate to the nanoscale, highlighting the need for new methods for characterizing hydrophobicity at the small scale. We use extensive molecular simulations to study the hydration of homo and heterogeneous self-assembled monolayers (SAMs) and of protein surfaces. For homogeneous SAMs, new pressure-dependent analysis shows that water displays higher compressibility and enhanced density fluctuations near hydrophobic surfaces, which are gradually quenched with increasing hydrophilicity, consistent with our previous studies. Heterogeneous surfaces show an interesting context dependence--adding a single -OH group in a CH3 terminated SAM has a more dramatic effect on water in the vicinity compared to that of a single CH3 group in an -OH background. For mixed -CH3/-OH SAMs, this asymmetry leads to a non-linear dependence of hydrophobicity on the surface concentration. We also present preliminary results to map hydrophobicity of protein surfaces by monitoring local density fluctuations and binding of probe hydrophobic solutes. These molecular measures account for the behavior of protein's hydration water, and present a more refined picture of its hydrophobicity map. At least for one protein, hydrophobin-II, we show that the hydrophobicity map is different from that suggested by a commonly used hydropathy scale.

Super-resolution surface mapping using the trajectories of molecular probes

“…Recent molecular simulations have suggested that single-molecule interactions can potentially identify nanoscale differences in hydrophobicity 22 . Here, we use a photo-patterned hydrophobically modified surface 23 as a model system to prepare spatially well-defined areas of varying hydrophobicity, and a fluorescently labelled fatty acid (BODIPY-labelled dodecanoic acid) as a probe molecule.…”

Strong Coupling between Nanofluidic Transport and Interfacial Chemistry: How Defect Reactivity Controls Liquid–Solid Friction through Hydrogen Bonding

“…On the GRA-2H and the BN-2H defects, the OH group of the dissociated water molecule can act both as a donor and an acceptor, leading to stronger interactions with the liquid film. [57][58][59] For instance the GRA-2H defect accepts ca. 1.1 bonds and donates ca.…”

Indirect Evidence for Self Association of Muscle Fatty Acid Binding Protein from Locusta migratoria

“…The contribution of the hydrophobic amino acids becomes more important as the patch size increases. The polar amino acids expose an approximately constant fraction of their non-polar area independent of patch size [30]. Though the mobility of residues on the surface is generally higher, it decreases for the polar residues with increasing patch size [31].…”