Spectroscopic Probing of Solute–Solvent Interactions in Aqueous Methylsulphonylmethane (MSM) Solutions: An Integrated ATR-FTIR, Chemometric, and DFT Study

The widespread use of methylsulphonylmethane (MSM) as a dietary supplement highlights the need to understand its fundamental behaviour in aqueous solutions. In this paper, we investigate changes in the MSM band shape as a function of its concentration using Attenuated Total Reflection FTIR (ATR-FTIR) spectroscopy. ATR spectra may be complicated by significant optical artefacts arising from refractive index changes. These can be misinterpreted as genuine vibrational shifts, leading to erroneous conclusions. Here, we systematically investigate aqueous MSM solutions using three different internal reflection elements. Applying a rigorous ATR correction procedure, validated by transmission measurements and PARAFAC (Parallel Factor Analysis) analysis, decouples physical phenomena from optical distortions. The corrected spectra reveal a crucial finding: the primary effect of MSM is not a shift in the sulphone band position, but a distinct change in its shape. This result, supported by DFT (Density Functional Theory) calculations, indicates increased heterogeneity of local hydration environments and demonstrates the criticality of proper ATR correction.