## 3 Results and Discussion
### Thermodynamic Parameters and Binding Modes
If \(\Delta H\) does not vary significantly in the range of temperatures studied, both \(\Delta H\) and \(\Delta S\) can be evaluated from the Van 't Hoff equation (Equation (4)):  
\[\ln K_{\text{a}}=-\Delta H/\text{RT}+\Delta S/\text{R} \tag{4}\]  
where \(K_{\text{a}}\) is analogous to the associative binding constants at the relevant temperature. \(R\) is the gas constant. \(\Delta H\) and \(\Delta S\) were calculated using the Van 't Hoff plots (Table 4). The Gibbs' free energy change (\(\Delta G\)) was then estimated from the following relationship (Equation (5)):  
\[\Delta G=\Delta H-T\Delta S \tag{5}\]  
The negative \(\Delta G\) values listed in Table 5 indicated that the complexation of PDQL and HSA occurred spontaneously in the aqueous solution. The signs of \(\Delta H\) and \(\Delta S\) for the binding reaction were both found to be positive, which revealed that hydrophobic forces played the chief role in the process of PDQL binding to HSA. With 3-(benzylideneamino)-6-chloro-1-(3,3-dimethylbutanonyl)-2-phenyl-2,3-dihydroquinazolin -4(\(1H\))-one as a reference compound, the changes in \(\Delta H\) and \(\Delta S\) were compared and studied after \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Compound** & **Van ’t Hoff** & **R 12** & **SD 23** \\ \hline R=H & \(Y=12.88527-866.16/T\) & 0.99975 & 0.00264 \\ R=CF3 & \(Y=12.26971-536.08/T\) & 0.99971 & 0.00175 \\ R=CCH3 & \(Y=12.74821-675.57/T\) & 0.99845 & 0.00509 \\ R = CH(CH\({}_{3}\))\({}_{2}\) & \(Y=11.84592-296.08/T\) & 0.99944 & 0.00133 \\ R=CH3 & \(Y=11.43527-282.37/T\) & 0.99742 & 0.00274 \\ R=CN & \(Y=11.80447-305.68/T\) & 0.99949 & 0.00132 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Van ’t Hoff plots of PDQL-HSA systems. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Compound** & **T (K)** & **K 12** & **K 12** & **K 23** & **\(\Delta H\) 23** & **\(\Delta S\) 23** \\ \hline R=CH & 298 & 2.15794 & 0.99949 & & \(-24.7229\) & \\ R=H & 307 & 2.34365 & 0.99969 & 7.20125 & \(-25.6871\) & 107.1281 \\  & 316 & 2.54637 & 0.99963 & & \(-26.6513\) & \\ \hline R=CF3 & 298 & 3.52395 & 0.99985 & & \(-25.9421\) & \\  & 307 & 3.72392 & 0.99994 & 4.45697 & \(-26.8602\) & 102.0104 \\  & 316 & 3.90369 & 0.99980 & & \(-27.7783\) & \\ \hline R=OCH3 & 298 & 3.57039 & 0.99965 & & \(-25.9679\) & \\  & 307 & 3.79393 & 0.99944 & 5.61669 & \(-26.9218\) & 105.9886 \\  & 316 & 4.06275 & 0.99961 & & \(-27.8757\) & \\ \hline R=CH(CH\({}_{3}\))\({}_{2}\) & 298 & 5.16790 & 0.99977 & & \(-26.9330\) & \\  & 307 & 5.31304 & 0.99984 & 2.41609 & \(-27.8194\) & 98.4869 \\  & 316 & 5.46879 & 0.99990 & & \(-28.7058\) & \\ \hline R=CH3 & 298 & 3.58307 & 0.99954 & & \(-25.9841\) & \\  & 307 & 3.69690 & 0.99958 & 2.34762 & \(-26.8397\) & 95.0728 \\  & 316 & 3.78131 & 0.99925 & & \(-27.6954\) & \\ \hline R=CN & 298 & 4.79585 & 0.99987 & & \(-26.7050\) & \\  & 307 & 4.95109 & 0.99968 & 2.54142 & \(-27.5883\) & 98.1424 \\  & 316 & 5.08399 & 0.99959 & & \(-28.4716\) & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Thermodynamic parameters of PDQL-HSA binding systems at different temperatures. the introduction of the five familiar substituents on the benzene ring. The signs of the \(\Delta H\) change (\(\Delta\Delta H\)) and the \(\Delta S\) change (\(\Delta\Delta S\)) listed in Table 6 showed that the binding affinities were enhanced by van der Waals or hydrogen bonding forces after the introduction of the substituted groups, which was indicated by the analysis based on the laws of thermodynamics, as summarized by [PERSON] and [PERSON] [43]. The fluorine atoms of the trifluoromethyl group and the nitrogen atoms of the cyano group may provide separated electron pairs, to form hydrogen bonds.