3.1 Interaction Between Cordycepin and the Functio...
The properties of molecularly imprinted polymer depend on the formation of a stable complex between cordycepin and the functional monomer.In general，the interaction force is formed by hydrogen bonding in a noncovalent polymerized reaction.To determine the molecular recognition mechanism，the interaction between cordycepin and alpha-methylacrylic acid was investigated by ultraviolet-visible and infrared spectroscopy.When the template binds with the monomer，the characteristic adsorption peaks of the template typically shift.
The ultraviolet absorption spectra of cordycepin and a mixture of cordycepin and alpha-methylacrylic acid in methanol were determined to evaluate the interaction.The results are shown in Figure 1.The mixture of cordycepin and alphamethylacrylic acid had absorption peaks at 216nm and 260nm.The 216nm was shifted to 223nm with increased alpha-methylacrylic acid in the mixture，and was accompanied with the increasing absorbance，whereas the peak of 260nm did not shift.These changes were caused by the interactions between cordycepin and alpha-methylacrylic acid.Higher monomer ratios increased the interactions.The complex of cordycepin and alpha-methylacrylic acid was probably formed through hydrogen bonding between the amine group of the former with the carboxylic acid group of the latter.
Figure 1 Ultraviolet adsorption spectra of different ratios of cordycepin and alpha-methylacrylic acid in tetrahydrofuran(https://www.daowen.com)
Figure 2 Infrared spectra of(1)nonimprinted polymer；(2)molecularly imprinted polymer；(3)lycol dimethyl acrylate；and(4)alpha-methylacrylic acid
Infrared spectra of the cordycepin molecularly imprinted polymer and nonimprinted polymer are shown in Figure 2.The 3606cm—1 adsorption peak was the hydroxy stretching vibration absorption of the carboxylic acid group in the nonimprinted polymer spectrum.The results showed that the adsorption peak strength decreased and shifted to 3602cm—1.The vibration frequency of the hydroxyl group decreased，which indicated that the hydrogen bonding was present between cordycepin and alpha-methylacrylic acid.