Elucidation of small molecule passive permeation across lipid membranes using conventional solution state NMR methods

Quantifying small molecule uptake across a biological membrane in any cell system is crucial for the development of efficacious and selective drugs. However, obtaining such data is not trivial, especially in bacterial systems. Herein, we present an assay which enables the determination of the degree of passive permeation and membrane interaction of mixtures of small molecules in vesicles of a desired lipid composition, including that of bacterial membranes. The assay employs highly accessible conventional solution NMR experiments, exploiting the paramagnetic relaxation enhancement effect, and allows the measurement of membrane permeation on mixtures of any number of small molecules which do not exhibit heterogeneous molecular signal overlap in under 20 minutes. As a proof-of -principle we apply this methodology to candidates from a class of supramolecular self-associating amphiphiles, members from which have been shown to interact with biological phospholipid membranes and elicit an antimicrobial effect, allowing the determination and comparison of their membrane permeability and membrane interaction properties.