Spectroscopic Active Probes for Investigation of Lipid Transformation in Cells and Membranes

Deuterium-labeled lipids provide a powerful means to probe lipid organization, dynamics, and molecular interactions in complex biological systems. In this work, systematic spectroscopic characterization of deuterated fatty acids, sterols, phospholipids, and sphingolipids using Raman and infrared (IR) spectroscopies is presented. Importantly, this study establishes a fundamental spectroscopic reference framework and analytical guidelines for investigating lipid transformation processes in cells and membranes, as all data presented herein are acquired from well-defined lipid standard compounds. The unique C-D stretching region (2300-2000 cm^-1), located within the spectroscopically "silent" window and absent in endogenous cellular components, was exploited for selective detection and semiquantitative assessment of lipid probes. Integration of C-D band intensities enables the estimation of the probe content in complex matrices as the signal correlates with the degree of deuterium substitution. While the C-D spectral region remained largely invariant with respect to the lipid backbone structure, other vibrational modes, particularly those associated with headgroups or specific functional moieties, exhibited lipid-class-dependent intensity variations upon deuteration, reflecting differences in the molecular environment and vibrational coupling. Importantly, deuteration does not significantly interfere with biological function, as replacing hydrogen with deuterium only marginally increases the atomic mass without altering the chemical structure, polarity, or overall molecular interactions, thereby preserving the native lipid behavior. The reference spectra presented here provide an essential foundation for interpreting hyperspectral vibrational data acquired from cellular and membrane systems, supporting future applications of label-free Raman and IR imaging aimed at monitoring lipid remodeling, metabolic regulation, and therapeutic modulation in biological contexts.