Nanoconfined water can orient and cause long-range dipolar interactions with biomolecules

Dirk Hegemann,Nicolas Hocquard,Manfred Heuberger

doi:10.1038/s41598-017-18258-1

Dirk Hegemann, Nicolas Hocquard + Show 1 more

Open Access

https://doi.org/10.1038/s41598-017-18258-1

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Abstract

Surface properties are generally determined by the top most surface layer also defining how molecules adsorb onto it. By exploring effects due to interactions with deeper subsurface layers, however, long-range interaction forces were found to also significantly contribute to molecular adsorption, in which hydration of the subsurface region is the key factor. Water molecules confined to a subsurface amphiphilic gradient are confirmed to cause these long-range dipolar interactions by preferential orientation, thus significantly changing the way how a protein interacts with the surface. These findings imply future exploitation of an additional factor to modulate adsorption processes.

Highlights

The interactions of water with solid surfaces are essential for a manifold of biochemical, chemical and physical processes[1]
Amphiphilic gradients are well known to exist naturally inside self-assembled structures, the here used artificial nano-gradients are made of plasma polymers[6,13] and are fundamentally different because they are stabilized by a network of covalent crosslinks rather than amphiphilic equilibrium interactions
The matrix was generated by initial deposition of a nominally 50 nm thick hydrophilic base layer with the dosed addition of O2 gas, followed by a hydrophobic cover layer of varying thickness, D, of several nanometers[6]

Summary

Results and Discussion

A very high stability of the confining plasma polymer (pp) matrix, in the hydrated state, is prerequisite to designing a defined subsurface gradient. The independence of this effect on a significant change of Debye length (screening depth) by replacing water (~300 nm) with PBS (~0.86 nm) rules out a simple electrostatic interaction, while the water structure at the surface is affected[21,22] At this point we note a small difference in amount of adsorbed protein on the plain hydrophilic ppSiOx matrix as a function of salt concentration; this is expected due to the acquisition of a negative charge hindering the adsorption of negatively charged BSA molecules[9,23]. The data clearly suggest that the effect is caused by a dipolar interaction, involving oriented molecular dipoles

Type of interaction

Methods

Additional Information