SAXS measurements of azobenzene lipid vesicles reveal buffer-dependent photoswitching and quantitative Z->E isomerisation by X-rays

The study focuses on photoresponsive lipid membranes containing azobenzene, which can be controlled by light to reversibly change membrane shape, permeability, and fluidity. Although the light-driven behavior is visible at the macroscopic level, the authors note that it was unclear how much the trans/cis ratio actually changes during illumination, and whether that switching could be improved. Using small-angle X-ray scattering, the authors measure membrane thickness and relate it to trans/cis ratios, finding an unexpected dependence on the aqueous buffer composition. They report smaller-than-expected photoswitching with deionized water and larger thickness variations than previously observed. They also state that soft X-rays can quantitatively isomerise photolipid membranes to the all-trans state, supporting stronger X-ray-based membrane control and emphasizing the role of high-energy X-rays for observation-only soft matter experiments.