Direct experimental evidence reaffirming these theoretical predictions was achieved through a combination of techniques using static compression X-ray diffrac-tion and inelastic X-ray scattering on deeply supercritical argon in a diamond anvil cell. Specifically, the theory predicts the existence of phonon gaps in vibrational spectra of liquids and a thermodynamic boundary in the supercritical state. In this Viewpoint, we derive the phonon theory of liquids and biological fluids stemming from Frenkel's microscopic picture of the liquid state. We will also mention techniques that may be of use in the future (i.e., cryo-EM, droplet interface bilayers, inelastic X-ray scattering, and neutron reflectometry), which can further our understanding of the different and unique physicochemical properties of nanoscopic lipid domains.Īmong the three basic states of matter, solid, liquid, and gas, the liquid state has always eluded general theoretical approaches for describing liquid energy and heat capacity.

In this review article we will discuss studies which have used techniques that are inherently sensitive to nanoscopic structural features (i.e., neutron scatting, nuclear magnetic resonance, and Förster resonance energy transfer). Since most commonly used techniques are sensitive to microscale structural features, it is therefore not surprising that it took some time to reach a consensus regarding their existence.

This ambiguity surrounding lipid domains could be partly attributed to the fact that they are highly dynamic, nanoscopic structures. Although the notion of functional lipid domains, also known as 'lipid rafts', is now widely accepted, this was not always the case.

For the past 50 years, evidence for the existence of functional lipid domains has been steadily accumulating.

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