Study of the physicochemical properties of trimethoprim with β-cyclodextrin in solution

The behavior of trimethoprim (TMP) in aqueous solutions containing different concentration of β-cyclodextrin (β-CD) was characterized by the solubility method, UV spectrophotometry and differential scanning calorimetry (DSC). The UV spectra enhancement of TMP as result of complex with β-CD was investigated. Complexation with β-CD increase the TMP aqueous solubility and the phase solubility diagram was AL type. Thermodynamic parameters of the complex process, K, ΔG, ΔH and ΔS, were determined from the phase solubility diagram at 298 and 318 K, respectively. The experimental results indicated that the complex process was an enthalpy-driven process. Mechanism of the complex of β-CD with TMP was further discussed using the molecular model program. Results showed that the 3,4,5-trimethoxybenzyl group of the TMP was partly embedded in the cavity of β-CD.