NMR spectroscopy for assessing cocaine-functional monomer interactions when preparing molecularly imprinted polymers

Study on the affinity sites of cadmium's binding to ligands by thermodynamics and nuclear magnetic resonance spectroscopy

The affinity sites of cadmium (Cd(II)) when binding to cysteine (Cys) and glutathione (GSH) were studied via thermodynamics and nuclear magnetic resonance (NMR) spectroscopy methods. The results showed that the Cd(II) binding sites of Cys and GSH were -SH (exothermic), -NH2 (endothermic) and -COOH (endothermic). The thermodynamic behaviour of Cd(II) binding to Cys/GSH in boric acid and HEPES buffers differed, with the former being mainly endothermic and the latter mainly exothermic. It could be inferred that, in the boric acid system, the main binding site of Cd(II) with Cys and GSH is changed from -SH in HEPES to -COOH and -NH2 in boric acid. This was confirmed by the results of NMR experiments of Cd(II) with Cys/GSH. 1D 1H-NMR experiments showed that, after the combination of Cd(II) and Cys, the changes in the chemical shifts and peak strengths of protons near the -SH group for the reaction in HEPES were greater than when boric acid buffer was used. Changes in the chemical shift and peak strength of the -NH2 protons due to the binding of Cd(II) to GSH were evident in the boric acid buffer but not in HEPES. The screening of functional monomers is very important in the process of preparation of cadmium ion-imprinted materials. This research provides important theoretical and experimental guidance for the screening of functional monomers.

Synthesis of molecularly imprinted polymer by precipitation polymerization for the removal of ametryn

Ametryn (AME) is a triazine herbicide which is mainly used to kill unwanted herbs in crops. Despite its importance in agriculture, the usage of AME also poses a risk to humans and the ecosystem due to its toxicity. Hence, it is important to develop a method for the effective removal of AME from various water sources which is in the form of molecular imprinting polymer (MIP). In this study, MIP of AME was synthesized via precipitation polymerization using AME as the template molecule with three different functional monomers including methacrylic acid (MAA), acrylamide (AAm) and 2-vinylpyridine (2VP). The three different synthesized polymers namely MIP (MAA), MIP (AAm) and MIP (2VP) were characterized using Fourier Infra-red spectroscopy (FTIR) and Field Emission Electron Microscopy (FESEM). Then, the batch binding study was carried out using all three MIPs in which MIP (MAA) attained the highest rebinding efficiency (93.73%) among the synthesized polymers. The Energy-Dispersive X-ray spectroscopy (EDX) analysis, Brunauer-Emmett-Teller (BET) analysis and thermogravimetric analysis (TGA) were also conducted on the selected MIP (MAA). Adsorption studies including initial concentration, pH and polymer dosage were also conducted on MIP (MAA). In this study, the highest adsorption efficiency was attained at the optimum condition of 6 ppm of AME solution at pH 7 with 0.1 g of MIP (MAA). MIP (MAA) was successfully applied to remove AME from spiked distilled water, tap water and river water samples with removal efficiencies of 95.01%, 90.24% and 88.37%, respectively.

Molecularly Imprinted Carriers for Diagnostics and Therapy-A Critical Appraisal

Simultaneous diagnostics and targeted therapy provide a theranostic approach, an instrument of personalized medicine-one of the most-promising trends in current medicine. Except for the appropriate drug used during the treatment, a strong focus is put on the development of effective drug carriers. Among the various materials applied in the production of drug carriers, molecularly imprinted polymers (MIPs) are one of the candidates with great potential for use in theranostics. MIP properties such as chemical and thermal stability, together with capability to integrate with other materials are important in the case of diagnostics and therapy. Moreover, the MIP specificity, which is important for targeted drug delivery and bioimaging of particular cells, is a result of the preparation process, conducted in the presence of the template molecule, which often is the same as the target compound. This review focused on the application of MIPs in theranostics. As a an introduction, the current trends in theranostics are described prior to the characterization of the concept of molecular imprinting technology. Next, a detailed discussion of the construction strategies of MIPs for diagnostics and therapy according to targeting and theranostic approaches is provided. Finally, frontiers and future prospects are presented, stating the direction for further development of this class of materials.

Recyclable nanoparticles based on a boronic acid-diol complex for the real-time monitoring of imprinting, molecular recognition and copper ion detection

Molecularly imprinted polymers (MIPs) have now become one of the most remarkable materials in the field of molecular recognition. Although many efforts have been made to study the process and mechanism of molecular imprinting, it has not been possible to monitor the interactions between the template and the growing polymer chains under real-time experimental conditions. The behavior of the template-monomer complex during the whole polymerization process has remained largely unknown. In this work, we introduce a fluorescence technique that allows monitoring of the template-functional monomer complex during an actual imprinting process, as well as the real-time signaling of template binding and dissociation from the imprinted polymer. For the first proof-of-principle, we select Alizarin Red S (ARS) and 4-vinylphenylboronic acid as the template and functional monomer, respectively, to synthesize MIP particles via precipitation polymerization. As the formation of the template-functional monomer complex leads to strong fluorescence emission, it allows the status of the template binding to be monitored throughout the whole reaction process in real time. Using the same fluorescence technique, the kinetics of template binding and dissociation can be studied directly without particle separation. The hydrophilic MIP particles can be used as a scavenger to remove ARS from water. In addition, the MIP particles can be used as a recyclable sensor to detect Cu ions. As the Cu ion forms a stable complex with ARS, it causes ARS to dissociate from the MIP nanoparticles, leading to effective fluorescence quenching. The non-separation analytical method based on fluorescence measurement provides a convenient means to study molecular imprinting reactions and the kinetics of molecular recognition using imprinted polymers. The recyclable nanoparticle sensor allows toxic Cu ions to be detected directly in water in the range of 0.1-100 μM with a recovery of 84-95%.

A miniaturized analytical method based on molecularly imprinted absorbents for selective extraction of (S)-1,1'-binaphthyl-2,2'-diamine and combinatorial screening of polymer precursors by computational simulation

Chiral resolution of binaphthylamine is often a toilful conundrum in the field of analytical chemistry and biomedicine. The work puts forward a selective, sensitive, and miniaturized analytical method based on molecularly imprinted polymers (MIPs) as adsorbent for miniaturized tip solid-phase extraction (MTSPE) in the separation of binaphthylamine enantiomer. This method combines the advantages of MIPs (high selectivity), MTSPE (low consumption), and high-performance liquid chromatography (HPLC, high sensitivity). A simple synthesis methodology of MIP (P2) was conducted through bulk polymerization with (S)-(-)-1,1'-binaphthyl-2,2'-diamine (S-DABN) as template together with methacrylic acid monomer, and ethylene glycol dimethacrylate as cross-linker in proper porogen, realizing a selective recognition and efficient enrichment for S-DABN. The method exhibited appreciable linearity (0.06-1.00 mg ml^-1 ), low quantification limit (0.056 mg ml^-1 ), good absolute recoveries (45.70%-69.29%), and high precision (relative standard deviations ≤ 3.54%), along with low consumption (0.50 ml sample solution and 25.0 mg adsorbent). Based on the density functional theory, computational simulation was used to make a preliminary prediction for rational design of MIPs and gave a reasonable elaboration involving the potential mechanism of templates interacting with functional monomers. The adsorption kinetics and thermodynamics were investigated to evaluate the recombination process of substrates. In addition, the selectivity of MIPs for S-DABN was obtained by MIP-MTSPE coupled with HPLC, which supports the feasibility of this convenient design process. The proposed method was employed for selective extraction of S-DABN and exhibited promising potential in the application of chiral analysis.

β-Cyclodextrin Derivative Grafted on Silica Gel Represents a New Polymeric Sorbent for Extracting Nitisinone from Model Physiological Fluids

Nitisinone (NTBC) is used in the treatment of disorders affecting the tyrosine pathway, including hereditary tyrosinemia type I, alkaptonuria, and neuroblastoma. An inappropriate dosage of this therapeutic drug causes side effects; therefore, it is necessary to develop a rapid and sensitive method to monitor the content of NTBC in patients' blood. This study aimed to develop anew polymeric sorbent containing β-cyclodextrin (β-CD) derivatives grafted on silica gel to effectively extract NTBC from model physiological fluids. The inclusion complex formed between β-CD and NTBC was examined by proton nuclear magnetic resonance spectroscopy. The novel sorbents with derivatives of β-CD were prepared on modified silica gel using styrene as a comonomer, ethylene glycol dimethacrylate as a crosslinking agent, and 2,2'-azo-bis-isobutyronitrile as a polymerization initiator. The obtained products were characterized via Fourier transform infrared spectroscopy and then used as sorbents as part of a solid phase extraction technique. High NTBC recovery (70%indicated that the developed polymeric sorbent may be suitable for extracting this compound from patients' blood samples.

Factors Affecting Preparation of Molecularly Imprinted Polymer and Methods on Finding Template-Monomer Interaction as the Key of Selective Properties of the Materials

Molecular imprinting is a technique for creating artificial recognition sites on polymer matrices that complement the template in terms of size, shape, and spatial arrangement of functional groups. The main advantage of Molecularly Imprinted Polymers (MIP) as the polymer for use with a molecular imprinting technique is that they have high selectivity and affinity for the target molecules used in the molding process. The components of a Molecularly Imprinted Polymer are template, functional monomer, cross-linker, solvent, and initiator. Many things determine the success of a Molecularly Imprinted Polymer, but the Molecularly Imprinted Polymer component and the interaction between template-monomers are the most critical factors. This review will discuss how to find the interaction between template and monomer in Molecularly Imprinted Polymer before polymerization and after polymerization and choose the suitable component for MIP development. Computer simulation, UV-Vis spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Proton-Nuclear Magnetic Resonance (¹H-NMR) are generally used to determine the type and strength of intermolecular interaction on pre-polymerization stage. In turn, Suspended State Saturation Transfer Difference High Resolution/Magic Angle Spinning (STD HR/MAS) NMR, Raman Spectroscopy, and Surface-Enhanced Raman Scattering (SERS) and Fluorescence Spectroscopy are used to detect chemical interaction after polymerization. Hydrogen bonding is the type of interaction that is becoming a focus to find on all methods as this interaction strongly contributes to the affinity of molecularly imprinted polymers (MIPs).

Theoretical Insight into the Interaction between Chloramphenicol and Functional Monomer (Methacrylic Acid) in Molecularly Imprinted Polymers

Molecular imprinting technology is a promising method for detecting chloramphenicol (CAP), a broad-spectrum antibiotic with potential toxicity to humans, in animal-derived foods. This work aimed to investigate the interactions between the CAP as a template and functional monomers required for synthesizing efficient molecularly imprinted polymers for recognition and isolation of CAP based on density functional theory. The most suitable monomer, methacrylic acid (MAA), was determined based on interaction energies and Gibbs free energy changes. Further, the reaction sites of CAP and MAA was predicted through the frontier molecular orbitals and molecular electrostatic potentials. Atoms in molecules topology analysis and non-covalent interactions reduced density gradient were applied to investigate different types of non-covalent and inter-atomic interactions. The simulation results showed that CAP was the main electron donor, while MAA was the main electron acceptor. Moreover, the CAP–MAA complex simultaneously involved N-H···O and C=O···H double hydrogen bonds, where the strength of the latter was greater than that of the former. The existence of hydrogen bonds was also confirmed by theoretical and experimental hydrogen nuclear magnetic resonance and Fourier transform infrared spectroscopic analyses. This research can act as an important reference for intermolecular interactions and provide strong theoretical guidance regarding CAP in the synthesis of molecularly imprinted polymers.

Effective preparation of magnetic molecularly imprinted polymer nanoparticle for the rapid and selective extraction of cyfluthrin from honeysuckle

Cyfluthrin is a widely used pesticide. In this study, a sensitive and efficient magnetic molecularly imprinted polymer (MMIP) was prepared by surface molecular imprinting, which used functionalized Fe₃O₄ particles as magnetic cores. Cyfluthrin was extracted and enriched using magnetic molecularly polymer for analyzing pesticide residue of Chinese herbal medicines. The crystal type, microstructure, particle size, saturation magnetization, and characteristic functional groups of the synthesized MMIPs were analyzed by analysis equipment. The results of isothermal adsorption and kinetic adsorption indicated that MMIPs reached adsorption equilibrium at 30 min, with a maximum capacity of 4.9 mg g^-1, which had good adsorption performance, while selective adsorption experiments showed that MMIPs had higher affinity for cyfluthrin. Under the optimized conditions, the limit of detection (LOD) and the limit of quantification (LOQ) were 32.987 ng ml^-1 and 109.955 ng ml^-1, respectively. And linear range (30-3000ng ml^-1) of cyfluthrin with correlation coefficient R²=0.9979, and MMIPs were used in honeysuckle, the recoveries were 91.5%∼97.2%, and RSD was 5.35%∼8.32% (n = 3). It is indicated that the magnetic molecularly imprinted polymer can be used as an effective material for the specific separation of cyfluthrin from honeysuckle.

An Investigation of the Intermolecular Interactions and Recognition Properties of Molecular Imprinted Polymers for Deltamethrin through Computational Strategies

Deltamethrin (DM) is a toxic pesticide that is nonetheless widely used to control insect pests in agricultural production. Although the number of DM molecularly imprinted polymers (MIPs) is increasing in many scientific applications, the theoretical aspects of the participating intramolecular forces are not fully understood. This paper aims to explore the intermolecular interactions between the template molecule DM and the functional monomer acrylamide (AM) through density functional theory (DFT), analysis of hydrogen nuclear magnetic resonance (¹H-NMR), Fourier transform infrared spectroscopy (FTIR), and adsorption thermodynamics. The results indicated that there is strong hydrogen bonding between O19 of DM and H9 of AM, suggesting that it is the preferable site for the binding of the target molecule. The existence of interaction sites was found to play an important role in the recognition process. The results from selective adsorption experiments showed that the DM MIPs exhibited the highest adsorption capacity for DM (Q = 75.72 mg g⁻¹) as compared to the five structural analogs. Furthermore, the recovery rates of spiked DM from various teas using the DM MIPs as solid-phase extraction filler also possessed a high value (all greater than 83.68%), which enables them to be used as separate and recognition functional materials.

Electrochemical sensing of cocaine in real samples based on electrodeposited biomimetic affinity ligands

A selective electrochemical sensor for direct detection of cocaine was developed based on molecularly imprinted polymers electropolymerized onto graphene-modified electrodes. Palladium nanoparticles were integrated in the sensing layer for the benefit of enhancing the communication between the imprinted sites and the electrode and improving their homogeneous distribution. The molecularly imprinted polymer was synthesized by cyclic voltammetry using p-aminobenzoic acid as a high affinity monomer selected by computational modeling, and cocaine as a template molecule. Experimental parameters related to the electrochemical deposition of palladium nanoparticles, pH, composition of the electropolymerization mixture, extraction and rebinding conditions were studied and optimized. Under optimized conditions, the oxidation peak current varied linearly with cocaine concentration in the range of 100-500 μM, with a detection limit of 50 μM (RSD 0.71%, n = 3). The molecularly imprinted sensor was able to detect cocaine in saliva and river water with good recoveries after sample pretreatment and was successfully applied for screening real street samples for cocaine.