Raman spectroscopic investigation of pressure-induced transitions in 5-methyluridine hemihydrate crystal

The structural flexibility of modified nucleosides is closely related to the stability and adaptability of RNA architectures. High pressure introduces a unique thermodynamic perturbation that can reveal hidden conformational states and subtle intermolecular interactions in these molecular systems. This work presents a comprehensive investigation of the structural and vibrational properties of 5-methyluridine hemihydrate (5 mU) under high hydrostatic pressure up to 7.1 GPa using Raman spectroscopy. Rietveld refinement at ambient conditions confirms an orthorhombic structure with space group P2 1 2 1 2 1 . High-pressure Raman spectra exhibit significant changes over the entire spectral range (100–3500 cm −1 ), providing clear evidence of two pressure-induced conformational transition regions centered near ~1 and ~ 3 GPa. The first transition region is predominantly associated with CH and CH 3 vibrations, ribose banding modes, and the emergence of a new band at the lattice modes. The second transition region involves distortions of ribose and uracil moieties and changes in C O, NH, and OH modes, as well as the appearance of a new band in the lattice region, reflecting hydrogen-bond rearrangement. Principal Component Analysis applied to selected spectral regions provides quantitative support for these findings, revealing distinct clustering across the corresponding pressure ranges. A comparative analysis with unmodified uridine demonstrates that methylation, together with the hydrogen-bonding network involving water molecules, plays a key role in modulating the crystal response to pressure by tuning intermolecular interactions, highlighting the potential of 5 mU as a promising system for investigating molecular adaptability under extreme conditions.