Tamsulosin–water interactions and electronic absorption in aqueous solution: Insights from first-principles molecular dynamics

Understanding the interactions between biologically relevant molecular species and water is crucial for drug design and assessing their impact on living organisms and the environment. In this study, we investigate the molecular behavior of tamsulosin (TAMS) in aqueous solution, focusing on its dynamics, interactions with water, and electronic absorption properties.

The amphiphilic nature of TAMS is highlighted by its sulfonamide–water interaction energy, which is predicted to be stronger than water–water interactions. Structural analyses, including radial distribution functions and coordination numbers, confirm that TAMS is primarily stabilized in water through interactions involving its hydrophilic sulfonamide group.

Another key aspect of this study is the electronic absorption spectrum of TAMS in water, which plays a crucial role in understanding its photodegradation—an important factor in its pharmaceutical application as an alpha-blocker. Experimental studies on TAMS absorption spectra often exhibit strong dependence on variables such as concentration and thermodynamic conditions, complicating definitive conclusions. Theoretical calculations also present challenges, best addressed through a first-principles approach.

Here, we employ time-dependent density functional theory (TD-DFT) to investigate the electronic absorption spectrum of TAMS in aqueous solution. An accurate description is achieved by tuning the ω parameter of LC-ωPBE to match CASPT2 excitation energies of phenol. The computed spectrum shows excellent agreement with recent experimental data. Additionally, the semiempirical ZINDO/S method, despite its lower computational cost, captures key spectral features of TAMS in water.