Thermal dependence of Raman descriptors of ceramides. Part II: effect of chains lengths and head group structures

Abstract

The outermost layer of the mammalian skin, the stratum corneum (SC), represents the main skin barrier. The SC lipids have a very exceptional composition, as the main lipid classes are ceramides (CER), long-chain fatty acids and cholesterol. Information on the function of each CER subclass and on the relation between CER lipid organisation and composition is of great importance to unravel the mechanism controlling the skin barrier function. Raman spectroscopy has been increasingly used for the study of intra- and inter-molecular structures of long-chain lipid compounds. In this study, we employed Raman spectroscopy to evaluate the effect of (1) the chain length and (2) the polar head architecture on the conformational order and organisational behaviour of CERs. The relation between the structure and the stability of the organisation was studied by monitoring the thermotropic response of each CER in the temperature range between 25 and 95 °C. This work enabled the determination of a correlation between the gauche/trans ratio in the νCC region and the state of the lateral packing. Moreover, it was shown that -OH groups in the α position of the fatty acids reduce the stability while long alkyl chains reinforces the intra- and inter-chains order.

In vivo Raman Microspectroscopy: Intra- and Intersubject Variability of Stratum Corneum Spectral Markers

“…material). Generally, our Raman assignments correlate with those in the literature [26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46]. The Raman spectrum of the SC is dominated by vibrational bands of its structural proteins, lipids, and tissue water.…”

“…The trans/gauche conformer ratio was analyzed by calculating the S1130 + S1060/S1085 ratio. High values of this ratio are associated with a compact state in lipid packing while a decrease is indicative of loosening [43]. …”

Examination of the effect of Stratum Corneum isolation process on the integrity of the barrier function: a confocal Raman spectroscopy study

“…The trans‐gauche conformers ratio were analyzed by calculating S 1130+1060 /S 1080 ratio. High values of this ratio are associated with a compact state in the lipid packing while a decrease is indicative of loosening . the δ(CH 2 ) twisting (1288–1314 cm −1 ). The position of this band shifts to higher wavenumbers with the conformational disorder. the ν asym CH 2 (2882 cm −1 )/ν sym CH 2 (2852 cm −1 ) ratio, generally used as an indicator for both conformational state and lateral packing.…”

Comparison of structure and organization of cutaneous lipids in a reconstructed skin model and human skin: spectroscopic imaging and chromatographic profiling

“…The main differences are observed in the composition of ceramides. The use of Raman spectroscopy to examine the lateral packing and conformational order in SC lipids is well established (22,(26)(27)(28)(29)(30). The secondary structure and folding of keratin has similarly been assessed using Raman spectroscopy (22).…”