Combined in vivo confocal Raman spectroscopy and density functional theory to detect carboxymethyl(lysine) in the human stratum corneum

Abstract A set of thirty confocal Raman spectra of the stratum corneum of women classified as healthy young, healthy elderly and diabetic elderly were acquired and analyzed, focusing the identification of the advanced glycation ends products (AGEs), specifically the N(6)-Carboxymethyllysine (CML), also named as 2-Amino-6-(carboxymethylamino)hexanoic acid. The analysis was done considering that CML in the skin of young pH values can exists principally in two forms: as zwitterion and as a monoanionic species. Identification of CML in the set of experimental confocal Raman spectra. The acidic form may only exist in lower or in negligible concentrations compared with the other species present in solution at the skin pH. Simulated Raman spectra through the DFT/B3LYP/6-311 G (d, p) procedure were obtained for the CML-zwitterion and for CM-monoanionic species. Identification of CML in the set of experimental confocal Raman spectra of the skin of young, healthy elderly and diabetic elderly women was done by comparison with the confocal Raman spectrum of CML; by comparison between the calculated B3LYP/6-311 G spectrum of CML with the second derivative spectrum of the mean value of the confocal Raman spectra of skin of the three groups of participants; by comparison between the second derivative spectrum of the three groups of participants with the confocal Raman spectrum of CML. Differences between the three groups of spectra was analyzed through band deconvolution analysis (BDA) and the corresponding Gaussian fitting, indicating the following relative concentration of the CML spectral coincident bands for each group: 33% (healthy young women - HYW), 35% (healthy elderly women - HEW) and 32% for (elderly diabetic women-EDW).