Novel sterol-spiropyran derivatives: synthesis and photoactivity in Langmuir monolayers

We describe the synthesis of novel sterol-spiropyran conjugates based on either cholesterol or ergosterol and designed to easily incorporate in lipid membranes. We demonstrate that these compounds, in mixtures with a lipid, form stable and light-responsive Langmuir monolayers on aqueous surfaces. Large differences in the monolayer pressure-area isotherms are observed upon light-induced conformational switch of the spiropyran moiety of the sterol-spiropyran compound in the monolayer. We present evidence that the kinetics of monolayer response to photoisomerisation is controlled by the monolayer compressional (dilatational) elasticity. The results suggest that these sterol-spiropyran conjugates would likely readily incorporate in more complex lipid systems such as bilayers and could provide a coupling mechanism to control their properties, lateral organisation and morphology by light.