Atrazine and ametryne inclusion complexes with 2-hydroxypropyl-β/γ-cyclodextrin: Spectroscopic studies and molecular dynamics simulation

Atrazine (ATZ) and ametryne (AME) inclusion complexes with 2-hydroxypropyl-β/γ-cyclodextrin (2-HP-β/γ-CD) in aqueous media and solid state were studied. Electrospray ionization mass spectrometry (ESI-MS), 1D (¹H), and 2 D (DOSY, ROESY) nuclear magnetic resonance spectroscopy (NMR) were utilized to investigate and characterize the inclusion complexes in aqueous media. The solid complexes prepared by freeze-drying methods were subsequently subjected to characterization by Fourier transform infra-red spectroscopy (FT-IR) and powder X-ray diffraction (PXRD) technique. The formation constants were obtained by 2D DOSY NMR in DMSO‑d₆, and were found to be 55 and 149 M⁻¹, for ATZ@HPβ-CD and ATZ@HPγ-CD, respectively. For AME@HPβ-CD and AME@HPγ-CD, the formation constants were found to be 92 and 132 M⁻¹, respectively. Molecular Dynamics (MD) simulations were performed to shed more light on the mode of guest inclusion into the hosts and to demarcate factors that affect the stability of these complexes in aqueous media. All complexes were found to be highly stable in aqueous media along the simulation run, which is in agreement with the experimental findings. The stability of these complexes is driven by the hydrophobic effects where both hosts encapsulate the guests deeply into the hydrophobic cavity. Furthermore, a number of hydrogen bonds between the hosts and the guests were found to contribute to the stability of these complexes.