Hydrodynamics of molecular rotors in lipid membranes

TL;DR

This paper develops a theoretical framework to accurately interpret molecular rotor fluorescence relaxation times, accounting for both membrane viscosity and interleaflet friction, improving viscosity measurements in lipid membranes.

Contribution

It introduces a theory that corrects molecular rotor measurements by including interleaflet friction, enhancing the accuracy of membrane viscosity assessments.

Findings

Relaxation time depends on viscosity and interleaflet friction.

A correction factor improves viscosity measurement accuracy.

Molecular rotors can estimate interleaflet friction if viscosity is known.

Abstract

Molecular rotors form twisted conformations upon photoexcitation, with their fluorescent relaxation time serving as a measure of viscosity. They have been used to assess membrane viscosities but yield higher values compared to other methods. Here, we show that the rotor's relaxation time is influenced by a combination of membrane viscosity and interleaflet friction. We present a theory for the relaxation time and obtain a correction factor that accounts for the discrepancy. If the membrane's viscosity is known, molecular rotors may enable the extraction of the elusive interleaflet friction.