Unveiling Possible Interactions between Tetramethylammonium Hydroxide and Caffeine in an Aqueous Medium via Volumetric and IR Spectroscopic Techniques

The objective of the present investigation is to explore the molecular interactions between tetramethylammonium hydroxide (TMAH) and caffeine (CAF), two neurologically active compounds, in aqueous solutions using volumetric and IR spectroscopic techniques, aiming to understand their hydration behavior, solvation dynamics, and impact on water structure. Volumetric parameters such as apparent and partial molar volume (Vϕ andVϕ0), limiting molar expansibility (Eϕ0), isobaric thermal expansion coefficient (αP), and Hepler’s constant (∂Eϕ0/∂T)P were determined across varying concentrations and temperatures. Positive magnitudes and ascending trends of Vϕ0 and Eϕ0 with increasing CAF concentration and temperature suggest strong ion–hydrophilic and hydrogen-bonding interactions that restructure water networks. Additionally, transfer volumes (ΔtrVϕ0) and ion-pair and triplet interaction coefficients (VAB and VABB) confirmed significant ion–ion and ion–hydrophilic interactions between TMAH and CAF. FTIR spectroscopy corroborated the presence of polar-hydrophilic and hydrogen-bonding interactions in binary and ternary systems. The novelty lies in bridging a research gap on the physicochemical interactions of TMAH and CAF, both amphiphilic neuroactive agents, with relevance to biochemistry, pharmaceuticals, and chemical engineering. The findings enhance the understanding of hydration dynamics and solvation behavior, providing useful insights for drug delivery systems, material design, and toxicity assessment involving structurally active solutes.