Inclusion of diuron, neburon, and linuron into β-CD a multi-equilibrium GFN2-xTB study

Distinct association constants related to including the phenylurea herbicide diuron into β-CD were reported along experiments carried out over the years. From the literature, we found association constants for this particular system corresponding to 125 M⁻¹ (2002), 750 ± 50 M⁻¹(2004), 175.86 ± 4.21 M⁻¹(2012), and 269.73 M⁻¹ (2019). Since the association constants are essential parameters for CD-based systems, we decided to apply the recently developed theoretical multi-equilibrium GFN2-xTB quantum approach to determine the most representative value for diuron included in β-CD. Within the additional investigation of linuron and neburon, other phenyl urea herbicides comprising chlorine atoms attached to the aromatic ring investigated within the experimental study published in 2002, we apply our theoretical approach to treat 16,308 arrangements in aqueous media. We concluded that an experimental binding constant equal to 750 ± 50 M⁻¹ is coherent to the diu@β-CD system. Furthermore, the GFN2-xTB/multi-equilibrium approach suggests that K (lin@β-CD) < K(neb@β-CD) < K (diu@β-CD) and distinct guest orientations contribute to each binding constant in solution.

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