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Abstract
Lipid molecules in the stratum corneum (SC) play a crucial role in the barrier function of the skin by preventing water loss while also binding to water molecules to maintain hydration. In the American Alligator (Alligator mississippiensis), the SC’s lipid composition closely resembles that of birds, reflecting their shared evolutionary history. However, it is unclear whether these lipids interact with water in a manner similar to birds. In this study, we investigate the effects of hydration on SC lipids by exposing samples (n=9) to 0%, 75%, and 100% relative humidity (RH) at 33oC for 24 hours. We used infrared spectroscopy to analyze the relative strength of hydrogen bonding and the prevalence of gauche defects in lipid chains. Furthermore, we analyzed the same variables in samples exposed to 100% RH comprised of deuterated water (D2O). Exposing the samples to D2O allowed us to precisely differentiate the hydrogen bond strength in water from the hydrogen bonding contributions of other hydroxyl groups in the SC because -OH stretching absorbance peaks are located in a different region of the infrared spectrum. We found that the strength of hydrogen bonding in the SC decreased after exposure to 100% RH, but analysis of the -OD stretching region confirmed that elements of the SC continue to influence hydrogen bond strength even at high water content. Additionally, the number of gauche defects in lipid chains did not
change in response to hydration with H2O or D2O, with lower variability in gauche defects upon exposure to D2O. Taken together, our results indicate that polar lipids bind with and sequester water molecules outside lipid layers in a manner similar to that observed in bird SC and may play a role in hydrating the skin.