## 5 Analysis of Template-Monomer Functional Interactions
### Proton-Nuclear Magnetic Resonance (\({}^{1}\)H-Nmr)
As for MIP, which is formed non-covalently with electrostatic (ionic) interactions, for example, 2,4-D herbicide, with 4-vinyl pyridine as a functional monomer, and synthesized using methanol/water solvent so that the nature of the interaction that will form is impossible for hydrogen bonds to form but possible for the electrostatic interaction. An NMR titration study of the system revealed that the primary interaction is based on the electrostatic effect. The basic pyridine molecule and the 2,4-D acid molecule form an ionic pair, and a solvent is also used. Controls use a non-polar solvent (deuterated chloroform); this solvent is used because observing interactions in the solvent (methanol) is complicated due to the exchange process between the labile protons of the analyte and the deuterium atom of the solvent takes place rapidly [124]. The acidic proton signal of the carboxylic acid migrates strongly upwards as the titration progresses for a higher concentration of 4-VP, as the 4-VP in solution is progressively protonated. The electrostatic interactions supported by the imprinted polymer show the most excellent affinity for the structural analogs of phenoxy acetic acid and 2,4-dichlorobenzoic acid. Both compounds can interact electrostatically with their carboxylic substituents, and both contain an aromatic group so that the affinity for 2,4-dichlorobenzoic acid shows steric [125]. Suspended-State High Resolution/Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy (STD HR/MAS NMR)  
Analysis using Suspended-State STD HR/MAS NMR involves solids (MIP) suspended or dispersed in a liquid. Suspended state NMR can be used to investigate the interaction between templates/analytes and MIP [85]. In this technique, the protons in the MIP are saturated. Energy will be transferred from the MIP protons to the protons in the analyte, and an increased signal in the analyte protons will occur. This increase in the signal can provide information about the possible interactions of MIP with the analyte [126]. Like the study of [PERSON] et al., who researched the interaction of MIP and template (bupivacaine) using suspended-state STD HR/MAS NMR. The MIP-bupivacaine interaction was observed from the increase in proton signaling of bupivacaine. Interaction observations were carried out on monolithic MIP (mMIP), and monolithic non imprinted polymer (mNIP). The mMIP showed significantly stronger interactions with aromatic protons and twice as many with nitrogen-bound protons than mNIP, thus indicating that mMIP-bupivacaine interacts via a polar interaction. While mNIP showed a signal twice as strong as the methyl group on the alkyl chain (non-polar interaction). The analysis results using STD NMR were following the chromatography results, namely bupivacaine in mMIP formed a specific binding site with the polar group of the functional monomer (MAA) [85]. Another study was from [PERSON] et al. [127], who used STD HR/MAS NMR to investigate the interaction of 9-ethyladenine (9 EA) as a template/analyte and MIP. From the STD HR/MAS NMR spectrum, it was known that the signal increase occurs in several hydrogen atoms (H-2, H-8, H-10, and H-12), indicating that H-12 has the most prominent signal increase. From the observations, it was also known that the primary interaction of EA and MIP occurs through hydrogen bonds, namely through the amino group in 9 EA. From the spectrum, there may be multiple hydrogen bonds between 9 EA and MIP, including N-1 and N-3 (affecting H-2); N-7 (affecting H-8) [127]. Therefore, STD HR/MAS NMR is useful to see the type of interaction, whether polar or non-polar interaction between MIP and its template.