Posted by The combination of sulfamethoxazole (SMX) and trimetorphan (TMP) produces a synergistic effect by sequentially inhibiting two critical enzymatic steps in folic acid synthesis, which impedes the development of bacterial resistance. No data are currently available regarding the ternary mutual diffusion coefficients of the pharmaceutical compounds SMX and TMP in aqueous solutions containing CDs. This study aims to fill this gap by presenting experimental diffusion coefficient data obtained via the Taylor dispersion method at 298.15 K for aqueous ternary systems—SMX/CDs (α–, β–, and γ–CD) and TMP/CDs (α–, β–, and γ–CD)—at different carrier concentrations. These measurements are complemented by the quantification of other thermodynamic and transport parameters, such as density and viscosity, and by spectroscopy studies.
The equilibrium binding constants (K) for these interactions were estimated as follows: for SMX:α–CD and SMX:γ–CD, approximately 10 M−1 and 100 M−1, respectively; and for SMX:β–CD, within the range of 500–1000 M−1. Interactions between TMP and all three cyclodextrins (α–CD, β–CD, and γ–CD) were also observed. In this case, the estimated K value for TMP:α–CD falls within the 500–1000 M−1 range, while for TMP:β–CD and TMP:γ–CD, the binding constants are K ≥ 1000 M−1.
These results were further supported by complementary viscosity, density, and UV-Vis spectroscopy measurements, all of which consistently confirmed the formation of host–guest complexes. For instance, UV-Vis spectral analysis revealed a possible association between SMX and β–CD, with an estimated association constant (K) of 982 M−1.
Importantly, these interactions have environmental relevance: CDs offer a dual advantage by combining selective retention of pharmaceutical contaminants with the potential for regeneration of the encapsulating agents. This makes them promising candidates for application in water treatment technologies aimed at mitigating antibiotic pollution.