From Microtornadoes to Facial Rejuvenation: Implication of Interfacial Water Layers

Abstract

Crystalline interfacial water layers have been observed at room temperature on both hydrophobic and hydrophilic surfaces - in air and subaquatically. Their implication in biology (and evolution) was postulated in a visionary paper in 1971 by Szent Gyorgyi. Today, they are believed to play a fundamental role in protein folding. A recent X-ray diffraction study reports on their presence on crystals in contact with their growth solution. Their subaquatic persistence on hydrophobic solids was reported in 2007. Their relevance in nanoscale phenomena is reflected by the multidisciplinary focus in their study. In the course of a systematic exploration of interfacial water layers on solids we discovered microtornadoes, found a complementary explanation to the surface conductivity on hydrogenated diamond, and arrived at a practical method to repair elastin degeneration using light. The result was rejuvenated skin, reduced wrinkle levels, juvenile complexion, and lasting resilience. Conforming to an extreme sensibility of interfacial water layers to direct observation techniques, a major part of the existing data stems from computer models. Experimentally, interfacial water layers have been studied by X-rays and neutron scattering, 1,2 atomic force microscopy (AFM), 3-5 near-field scanning optical microscopy (NSOM), 6 atomic force acoustic microscopy (AFAM), 7 drop evaporation experiments, 8 and recently on hydrogen-terminated nanocrystalline diamond. 9 A synoptic analysis of all these perspec- tives provides an increasingly clear picture of the nature of interfacial water: The central and probably generalizable result seems to be that the structural difference between water layers on a solid surface exposed to air, and water layers that prevail at the interface between the same solid surface and bulk water, is less pronounced than that between water layers on a hydrophobic and a hydrophilic surface, studied under identical conditions. The practical importance of this insight is enormous: Extracting information on water structures in air is simpler than probing water layers at the interface between a solid and bulk water, and we are justified to use the structural information (molecular order, density, or viscosity of the water) acquired in simple systems for modeling complex systems. In practice, this means that structural information obtained for instance by AFM in air on a certain model substrate could be transferred for modeling aspects in biological systems. The relevance of the partial approach becomes clear from realizing that biological surfaces are inhomogeneous: Their dynamic nature, with nanoscopic patches varying in polarity and topography, exclude a macroscopic perspective and complicate distinctive experimental insight. Thus, the requirement for model surfaces, which permit us to mimic specific biosystem aspects, is clear. Obviously, biocompatible materials based model surfaces are the best choice here. The themes investigated have one aspect in common: The substrates impose their order to the interfacial water layer - in other words the water layers may be looked upon as informational blueprints. The recently reported synthesis of high density carbon nanocrystals 10 might enrich our perception of interfacial water layers. In explaining the synthesis, the authors arrived at the conclusion that the new nanocrystals were formed in a process in which the crystalline interfacial water imposed its order to the metastable (solidifying) carbon nanocrystals. Clearly, this possibility implies evidence for an active function of interfacial water. In the era of think small the realization of this aspect deserves our attention and merits further study. Subaquatic Interfacial Water Layers on Nanocrystalline Diamond. We are currently using nanocrystalline diamond to extract information on interfacial water layers. Minimal corrosion, extensive biocompatibility, and a precisely adjustable nanostructure promote this material to an ideal model platform for getting structural insight into water layers contacting biological surfaces. Specifically on hydrogen-terminated diamond (hydrophobic), we found that interfacial water is crystalline, and thereby proton