Foreign molecules in biomembranes : Molecular effects on intact stratum corneum and model lipid systems

This thesis mainly explores how the molecular mobility of lipid and protein components in the outermost layer of the skin, the stratum corneum (SC), varies with different conditions and upon adding foreign compounds. These studies require methods that makes it possible to detect and characterize the minor amount of fluid components in the highly ordered solid SC sample with resolved molecular information. 13C polarization transfer solid-state nuclear magnetic resonance (PT ssNMR) is well suited for this task, and was employed as the main method through this thesis. The aims of this thesis were achieved by studies on well-controlled systems of intact SC, extracted corneocyte, and model lipid systems, and by combining PT ssNMR with different complementary biophysical techniques.A general conclusion from the presented studies of different foreign compounds is that apolar compounds mainly affect SC lipids, while more polar compounds affect both SC lipid and protein components. The effects strongly depend on the identity of the additive, and on the hydration conditions, and they vary with concentrations and temperatures. One interesting finding is the essential role of water in the mobility of keratin filaments. Apart from the effects on SC components, one can also simultaneously characterize the molecular mobility of the additves that are incorporated in the complex SC matrix by using PT ssNMR.We also demonstrate a clear correlation between the molecular mobility in SC lipids and proteins and the skin permeability upon additives, which forwards the understanding of the skin macroscopic barrier function at a molecular level. The findings of this research can be applied in topical formulations for, e.g., drug delivery and skin care products