Investigating how biological membrane parameters influence the ring opening of Provitamin D

Ultrafast photochemical transformations of 7-Dehydrocholesterol (DHC, Provitamin D₃), DHC-Acetate and Ergosterol (Ergo, Provitamin D₂) to previtamin (D₃, D₃-acetate and D₂) occurs upon a ring-opening reaction in the excited state where a Cyclohexadiene (CHD) chromophore embedded within the molecules opens to form a previtamin D species. In isotropic environments, the ring opening reaction occurs within 1-2ps therefore it is necessary to use ultrafast techniques such as transient absorption to capture the kinetics. However, in the lipid bilayer this reaction is slowed to 11ps. Here we are studying DHC and its analogs in lipid bilayers as a simple model for biologically relevant skin membrane models. To investigate the 6 fold slow down, the ring opening of DHC will be discussed in terms of lipid properties such as Van der Waals interactions, Hydrogen Bonding and membrane ridgidity.