# Study on Dicyandiamide-Imprinted Polymers with Computer-Aided Design
## 2 Results and Discussion
### Selection of Functional Monomer Based on Theoretical Calculations  
AM, MAA, MBA, and IA have been considered as the functional monomers. As shown in Figure 3, the models of the complexes constructed by DCD and the functional monomers (AM, MAA, MBA, and IA) were calculated, respectively. The calculated results indicate that the optimal molar ratios for DCD to AM, MAA, MBA, and IA are 1:5, 1:5, 1:3, and 1:4, respectively. Applying these imprinting molar ratios, the complexes exhibited the lowest energies and the maximum number of bonds between DCD and the functional monomers, respectively. The numbers of bonds between DCD and AM, MAA, MBA, and IA are respectively 10, 10, 6, and 7 in the complexes. The lengths of these bonds are all within the range of H-bond length (0.1622\(\sim\)0.2279 nm) [22]. Additionally, the roles of the reactive sites of DCD and the functional monomers are consistent with the results of the MEP analysis. For example (see Figure 3B), when MAA acted as the functional monomer, the proton donors (H4, H5, H6, and H10) of DCD form the H-bonds with the proton acceptors (O19, O67, O31, and O43 (O55)) of MAA, respectively. Moreover, the N3 and N9 atoms (proton acceptors) of DCD form the H-bonds with the H21 and H33 (H45, H57) atoms (proton donors) of MAA, respectively. The values of binding energies of DCD and different functional monomers (\(\Delta E_{\rm B1}\)) were listed in Table 2. As shown in Table 2, the values of \(\Delta E_{\rm B1}\) are in the order of \(\Delta E_{\rm B1}\)(DCD-MAA) \(<\)\(\Delta E_{\rm B1}\)(DCD-AM) \(<\)\(\Delta E_{\rm B1}\)(DCD-IA) \(<\)\(\Delta E_{\rm B1}\)(DCD-MBA), which may indicate that the interaction between DCD and MAA has the highest strength among the complexes formed from DCD and the functional monomers. As a result, among  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Species** & **wB97 XD** & **B3 LYP** & **PBE1 PBE** & **LC-wPBE** & **M062X** & **Experimental** \\ \hline  & & & & \(R\)(Å) & & \\ N1–C2 & 1.27 & 1.27 & 1.27 & 1.27 & 1.28 & 1.34 \\ N3–C2 & 1.37 & 1.37 & 1.36 & 1.36 & 1.37 & 1.37 \\ N7–C2 & 1.42 & 1.42 & 1.42 & 1.42 & 1.42 & 1.36 \\ N7–C8 & 1.33 & 1.33 & 1.33 & 1.33 & 1.33 & 1.28 \\ N9–C8 & 1.16 & 1.17 & 1.16 & 1.16 & 1.18 & 1.22 \\ \hline  & & & \(\Phi\)(\({}^{\circ}\)) & & & \\ N1–C2–N3 & 123 & 123 & 123 & 123 & 123 & 124 \\ N1–C2–N7 & 121 & 121 & 121 & 121 & 121 & 120 \\ N3–C2–N7 & 115 & 115 & 115 & 115 & 115 & 116 \\ C2–N7–C8 & 121 & 121 & 121 & 121 & 121 & 120 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The calculated (at the wB97 XD, B3 LYP, PBE1 PBE, LC-wPBE, and M062X levels with the 6-31G(d,p) basis set) and experimental structural parameters of DCD.  
Figure 2: MEP populations of DCD, AM, MAA, MBA, and IA.  
these functional monomers, MAA should be the best one for the preparation of the MIPs with the properties of recognizing DCD, and the best imprinting molar ratio should be 1:5.  
As shown in Figure 3B, one DCD molecule is surrounded by five MAA molecules. There are a large number of interactions between the DCD molecule and the MAA molecules. For example, the H4, H5, H6, and H10 atoms of the DCD molecule interact with the O19, O67, O31, and O43 (O55) atoms (proton accepters) of the MAA molecules, respectively. The N1, N3, and N9 atoms (proton accepters) of the DCD molecule interact with the H69, H21, and H33 (H45, H57) atoms of the MAA molecules. From Figure 3B, it could be found that there is no self-association of the MAA functional monomer in the concentration range studied in the work. This is in agreement with the conclusion that the self-association might not appear in the low concentration of the functional monomer [32].