Improving the Selectivity of the C-C Coupled Product Electrosynthesis by Using Molecularly Imprinted Polymer─An Enhanced Route from Phenol to Biphenol.

We developed a procedure for selective 2,4-dimethylphenol, DMPh, direct electro-oxidation to 3,3',5,5'-tetramethyl-2,2'-biphenol, TMBh, a C-C coupled product. For that, we used an electrode coated with a product-selective molecularly imprinted polymer (MIP). The procedure is reasonably selective toward TMBh without requiring harmful additives or elevated temperatures. The TMBh product itself was used as a template for imprinting. We followed the template interaction with various functional monomers (FMs) using density functional theory (DFT) simulations to select optimal FM. On this basis, we used a prepolymerization complex of TMBh with carboxyl-containing FM at a 1:2 TMBh-to-FM molar ratio for MIP fabrication. The template-FM interaction was also followed by using different spectroscopic techniques. Then, we prepared the MIP on the electrode surface in the form of a thin film by the potentiodynamic electropolymerization of the chosen complex and extracted the template. Afterward, we characterized the fabricated films by using electrochemistry, FTIR spectroscopy, and AFM, elucidating their composition and morphology. Ultimately, the DMPh electro-oxidation was performed on the MIP film-coated electrode to obtain the desired TMBh product. The electrosynthesis selectivity was much higher at the electrode coated with MIP film in comparison with the reference nonimprinted polymer (NIP) film-coated or bare electrodes, reaching 39% under optimized conditions. MIP film thickness and electrosynthesis parameters significantly affected the electrosynthesis yield and selectivity. At thicker films, the yield was higher at the expense of selectivity, while the electrosynthesis potential increase enhanced the TMBh product yield. Computer simulations of the imprinted cavity interaction with the substrate molecule demonstrated that the MIP cavity promoted direct coupling of the substrate to form the desired TMBh product.

Polytyramine Film-Coated Single-Walled Carbon Nanotube Electrochemical Chemosensor with Molecularly Imprinted Polymer Nanoparticles for Duloxetine-Selective Determination in Human Plasma.

We devised, fabricated, and tested differential pulse voltammetry (DPV) and impedance spectroscopy (EIS) chemosensors for duloxetine (DUL) antidepressant determination in human plasma. Polyacrylic nanoparticles were synthesized by precipitation polymerization and were molecularly imprinted with DUL (DUL-nanoMIPs). Then, together with the single-walled carbon nanotube (SWCNT) scaffolds, they were uniformly embedded in polytyramine films, i.e., nanoMIPs-SWCNT@(polytyramine film) surface constructs, deposited on gold electrodes by potentiodynamic electropolymerization. These constructs constituted recognition units of the chemosensors. The molecular dynamics (MD) designing of DUL-nanoMIPs helped select the most appropriate functional and cross-linking monomers and determine the selectivity of the chemosensor. Three different DUL-nanoMIPs and non-imprinted polymer (nanoNIPs) were prepared with these monomers. DUL-nanoMIPs, synthesized from respective methacrylic acid and ethylene glycol dimethyl acrylate as the functional and cross-linking monomers, revealed the highest affinity to the DUL analyte. The linear dynamic concentration range, extending from 10 pM to 676 nM DUL, and the limit of detection (LOD), equaling 1.6 pM, in the plasma were determined by the DPV chemosensor, outperforming the EIS chemosensor. HPLC-UV measurements confirmed the results of DUL electrochemical chemosensing.

Cilostazol-imprinted polymer film-coated electrode as an electrochemical chemosensor for selective determination of cilostazol and its active primary metabolite.

An electrochemical chemosensor for cilostazol (CIL) determination was devised, engineered, and tested. For that, a unique conducting film of the functionalized thiophene-appended carbazole-based polymer, molecularly imprinted with cilostazol (MIP-CIL), was potentiodynamically deposited on a Pt disk electrode by oxidative electropolymerization. Thanks to electro-oxidation potentials lower than that of CIL, the carbazole monomers outperformed pyrrole, thiophene, and phenol monomers, in this electropolymerization. The pre-polymerization complexes quantum-mechanical and molecular dynamics analysis allowed selecting the most appropriate monomer from the three thiophene-appended carbazoles examined. The electrode was then used as a selective CIL chemosensor in the linear dynamic concentration range of 50 to 924 nM with a high apparent imprinting factor, IF = 10.6. The MIP-CIL responded similarly to CIL and CIL's pharmacologically active primary metabolite, 3,4-dehydrocilostazol (dhCIL), thus proving suitable for their determination together. Simulated models of the MIP cavities binding of the CIL, dhCIL, and interferences' molecules allowed predicting chemosensor selectivity. The MIP film sorption of CIL and dhCIL was examined using DPV by peak current data fitting with the Langmuir (L), Freundlich (F), and Langmuir-Freundlich (LF) isotherms. The LF isotherm best described this sorption with the sorption equilibrium constant (KLF) for CIL and dhCIL of 12.75 × 10-6 and 0.23 × 10-6 M, respectively. Moreover, the chemosensor cross-reactivity to common interferences study resulted in the selectivity to cholesterol and dehydroaripiprazole of 1.52 and 8.0, respectively. The chemosensor proved helpful in determining CIL and dhCIL in spiked human plasma with appreciable recovery (99.3-134.1%) and limit of detection (15 nM).

Selective Impedimetric Chemosensing of Carcinogenic Heterocyclic Aromatic Amine in Pork by dsDNA-Mimicking Molecularly Imprinted Polymer Film-Coated Electrodes.

Inspired by the easy intercalation of quinoxaline heterocyclic aromatic amines (HAAs) in double-stranded DNA (dsDNA), we synthesized a nucleobase-functionalized molecularly imprinted polymer (MIP) as the recognition unit of an impedimetric chemosensor for the selective determination of a 2-amino-3,7,8-trimethyl-3H-imidazo[4,5-f]quinoxaline (7,8-DiMeIQx) HAA. HAAs are generated in meat and fish processed at high temperatures. They are considered to be potent hazardous carcinogens. The MIP film was prepared by potentiodynamic electropolymerization of a pre-polymerization complex of two adenine- and one thymine-substituted bis(2,2'-bithien-5-yl)methane functional monomer molecules with one 7,8-DiMeIQx template molecule, in the presence of the 2,4,5,2',4',5'-hexa(thiophene-2-yl)-3,3'-bithiophene cross-linking monomer, in solution. The as-formed MIP chemosensor allowed for the selective impedimetric determination of 7,8-DiMeIQx in the 47 to 400 µM linear dynamic concentration range with a limit of detection of 15.5 µM. The chemosensor was successfully applied for 7,8-DiMeIQx determination in the pork meat extract as a proof of concept.

Valorization of Brewery Wastes for the Synthesis of Silver Nanocomposites Containing Orthophosphate.

Brewery wastes from stage 5 (Wort precipitate: BW5) and stage 7 (Brewer's spent yeast: BW7) were valorized for the synthesis of silver phosphate nanocomposites. Nanoparticles were synthesized by converting silver salt in the presence of brewery wastes at different temperatures (25, 50, and 80 °C) and times (10, 30, and 120 min). Unexpectedly, BW7 yielded Ag3PO4 nanoparticles with minor contents of AgCl and Ag metal (Agmet). Contrastingly, BW5 produced AgCl nanoparticles with minor amounts of Ag3PO4 and Agmet. Nanocomposites with different component ratios were obtained by simply varying the synthesis temperature and time. The morphology of the nanocomposites contained ball-like structures representative of Ag3PO4 and stacked layers and fused particles representing AgCl and Agmet. The capping on the nanoparticles contained organic groups from the brewery by-products, and the surface overlayer had a rich chemical composition. The organic overlayers on BW7 nanocomposites were thinner than those on BW5 nanocomposites. Notably, the nanocomposites exhibited high antibacterial activity against Escherichia coli ATCC 25922. The antibacterial activity was higher for BW7 nanocomposites due to a larger silver phosphate content in the composition and a thin organic overlayer. The growth of Agmet in the structure adversely affected the antimicrobial property of the nanocomposites.

Molecularly imprinted polymer nanoparticles-based electrochemical chemosensors for selective determination of cilostazol and its pharmacologically active primary metabolite in human plasma.

Molecularly imprinted polymer (MIP) nanoparticles-based differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) chemosensors for antiplatelet drug substance, cilostazol (CIL), and its pharmacologically active primary metabolite, 3,4-dehydrocilostazol (dhCIL), selective determination in human plasma were devised, prepared, and tested. Molecular mechanics (MM), molecular dynamics (MD), and density functional theory (DFT) simulations provided the optimum structure and predicted the stability of the pre-polymerization complex of the CIL template with the chosen functional acrylic monomers. Moreover, they accounted for the MIP selectivity manifested by the molecularly imprinted cavity with the CIL molecule complex stability higher than that for each interference. On this basis, a fast and reliable method for determining both compounds was developed to meet an essential requirement concerning the personalized drug dosage adjustment. The limit of detection (LOD) at the signal-to-noise ratio of S/N = 3 in DPV and EIS determinations using the ferrocene redox probe in a "gate effect" mode was 93.5 (±2.2) and 86.5 (±4.6) nM CIL, respectively, and the linear dynamic concentration range extended from 134 nM to 2.58 µM in both techniques. The chemosensor was highly selective to common biological interferences, including cholesterol and glucose, and less selective to structurally similar dehydroaripiprazole. Advantageously, it responded to dhCIL, thus allowing for the determination of CIL and dhCIL together. The EIS chemosensor appeared slightly superior to the DPV chemosensor concerning its selectivity to interferences. The CIL DPV sorption data were fitted with Langmuir, Freundlich, and Langmuir-Freundlich isotherms. The determined sorption parameters indicated that the imprinted cavities were relatively homogeneous and efficiently interacted with the CIL molecule.

Electrochemical sensor for selective tyramine determination, amplified by a molecularly imprinted polymer film.

A molecularly imprinted polymer (MIP) film based electrochemical sensor for selective determination of tyramine was devised, fabricated, and tested. Tyramine is generated in smoked and fermented food products. Therefore, it may serve as a marker of the rottenness of these products. Importantly, intake of large amounts of tyramine by patients treated with monoamine oxidase (MAO) inhibitors may lead to a "cheese effect", namely, a dangerous hypertensive crisis. The limit of detection at S/N = 3 of the chemosensor, in both differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) determinations, with the use of the Fe(CN)64-/Fe(CN)63- redox probe, was 159 and 168 µM tyramine, respectively. The linear dynamic concentration range was 290 µM to 2.64 mM tyramine. The chemosensor was highly selective with respect to the glucose, urea, and creatinine interferences. Its DPV determined apparent imprinting factor was 5.6. Moreover, the mechanism of the "gate effect" in the operation of the polymer film-coated electrodes was unraveled.

Low-oxidation-potential thiophene-carbazole monomers for electro-oxidative molecular imprinting: Selective chemosensing of aripiprazole.

New thiophene-carbazole functional and cross-linking monomers electropolymerizing at potentials sufficiently low for molecular imprinting of an electroactive aripiprazole antipsychotic drug were herein designed and synthesized. Numerous conducting molecularly imprinted polymer (MIP) films are deposited by electropolymerization at relatively low potentials by electro-oxidation of pyrrole, aniline, phenol, or 3,4-ethylenedioxythiophene (EDOT). However, their interactions with templates are not sufficiently strong. Hence, it is necessary to introduce additional recognizing sites in these cavities to increase their affinity to the target molecules. For that, functional monomers derivatized with substituents forming stable complexes with the templates are used. However, oxidation potentials of these derivatives are often, disadvantageously, higher than that of parent monomers. Therefore, we designed and synthesized new functional and cross-linking monomers, which are oxidized at sufficiently low potentials. The deposited MIP and non-imprinted polymer (NIP) films were characterized by PM-IRRAS and UV-vis spectroscopy and imaged with AFM. The structure of the aripiprazole pre-polymerization complex with functional monomers was optimized with density functional theory (DFT), and aripiprazole interactions with imprinted cavities were simulated with molecular mechanics (MM) and molecular dynamics (MD). MIP-aripiprazole film-coated electrodes were used as extended gates for selective determination of aripiprazole with the extended-gate field-effect transistor (EG-FET) chemosensor. The linear dynamic concentration range was 30-300 pM, and the limit of detection was 22 fM. An apparent imprinting factor of the MIP-1 was IF = 4.95. The devised chemosensor was highly selective to glucose, urea, and creatinine interferences. The chemosensor was successfully applied for aripiprazole determination in human plasma. The results obtained were compared to those of the validated HPLC-MS method.

Protein Determination with Molecularly Imprinted Polymer Recognition Combined with Birefringence Liquid Crystal Detection.

Liquid crystal-based sensors offer the advantage of high sensitivity at a low cost. However, they often lack selectivity altogether or require costly and unstable biomaterials to impart this selectivity. To incur this selectivity, we herein integrated a molecularly imprinted polymer (MIP) film recognition unit with a liquid crystal (LC) in an optical cell transducer. We tested the resulting chemosensor for protein determination. We examined two different LCs, each with a different optical birefringence. That way, we revealed the influence of that parameter on the sensitivity of the (human serum albumin)-templated (MIP-HSA) LC chemosensor. The response of this chemosensor with the (MIP-HSA)-recognizing film was linear from 2.2 to 15.2 µM HSA, with a limit of detection of 2.2 µM. These values are sufficient to use the devised chemosensor for HSA determination in biological samples. Importantly, the imprinting factor (IF) of this chemosensor was appreciable, reaching IF = 3.7. This IF value indicated the predominant binding of the HSA through specific rather than nonspecific interactions with the MIP.

"Gate Effect" in p-Synephrine Electrochemical Sensing with a Molecularly Imprinted Polymer and Redox Probes.

The "gate effect" mechanism for conductive molecularly imprinted polymer (MIP) film coated electrodes was investigated in detail. It was demonstrated that the decrease of the DPV signal for the Fe(CN)64-/Fe(CN)63- redox probe with the increase of the p-synephrine target analyte concentration in solution at the polythiophene MIP-film coated electrode did not originate from swelling or shrinking of the MIP film, as it was previously postulated, but from changes in the electrochemical process kinetics. The MIP-film coated electrode was examined with cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and surface plasmon resonance (SPR). The MIP-film thickness in the absence and in the presence of the p-synephrine analyte was examined with in situ AFM imaging. Moreover, it was demonstrated that doping of the MIP film was not affected by p-synephrine binding in MIP-film molecular cavities. It was concluded that the "gate effect" was most likely caused by changes in radical cation (polaron) mobility in the film.

Selective PQQPFPQQ Gluten Epitope Chemical Sensor with a Molecularly Imprinted Polymer Recognition Unit and an Extended-Gate Field-Effect Transistor Transduction Unit.

A molecularly imprinted polymer (MIP) recognition system was devised for selective determination of an immunogenic gluten octamer epitope, PQQPFPQQ. For that, a thin MIP film was devised, guided by density functional theory calculations, and then synthesized to become the chemosensor recognition unit. Bis(bithiophene)-based cross-linking and functional monomers were used for this synthesis. An extended-gate field-effect transistor (EG-FET) was used as the transduction unit. The EG-FET gate surface was coated with the PQQPFPQQ-templated MIP film, by electropolymerization, to result in a complete chemosensor. X-ray photoelectron spectroscopy analysis confirmed the presence of the PQQPFPQQ epitope, and its removal from the MIP film. The chemosensor selectively discriminated between the octamer analyte and another peptide of the same number of amino acids but with two of them mismatched (PQQQFPPQ). The chemosensor was validated with respect to both the PQQPFPQQ analyte and a real gluten extract from semolina flour. It was capable to determine PQQPFPQQ in the concentration range of 0.5-45 ppm with the limit of detection (LOD) = 0.11 ppm. Moreover, it was capable of determining gluten in real samples in the concentration range of 4-25 ppm with LOD = 4 ppm, which is a value sufficient for discriminating between gluten-free and non-gluten-free food products. The gluten content in semolina flour determined with the chemosensor well correlated with that determined with a commercial ELISA gluten kit. The Langmuir, Freundlich, and Langmuir-Freundlich isotherms were fitted to the epitope sorption data. The sorption parameters determined from these isotherms indicated that the imprinted cavities were quite homogeneous and that the epitope analyte was chemisorbed in them.

Electrochemically synthesized molecularly imprinted polymer of thiophene derivatives for flow-injection analysis determination of adenosine-5'-triphosphate (ATP).

Two selective chemosensors for adenosine-5'-triphosphate (ATP) determination featuring molecularly imprinted polymer (MIP) film recognition units were fabricated. For imprinting, three different thiophene derivatives were used as functional monomers. That is, the uracil substituent of bis(2,2'-bithienyl)methane 2 complementarily H-bond paired the adenine moiety of ATP, the boronic acid substituent of thiophene 3 covalently bound vicinal diols of the ribofuranose moiety, and amide substituents of bis(2,2'-bithienyl)methanes 4 bound to the pyrophosphate moieties. Different binding motifs adopted for the ATP recognition and the structure of the supramolecular pre-polymerization complex were optimized with the DFT computing at the B3LYP/3-21G((*)) level. MIP films were prepared by potentiodynamic electropolymerization of this complex with the imprinting factor of 9.47±0.2. An analytical signal was transduced with a 10-MHz resonator of EQCM and a Pt electrode for the piezoelectric microgravimetry (PM) and capacitive impedometry (CI) determination of ATP, respectively, under FIA conditions. Analytical properties of the MIP film were unraveled by spectroscopic ellipsometry, XPS, IRRAS, and DPV. The limit of detection was 0.1 and 0.2 µM for the PM and CI chemosensor, respectively, being an order of magnitude lower than the ATP concentration in biological systems. Moreover, cross-selectivity was demonstrated with the adenosine-5'-diphosphate (ADP) imprinting and ATP discrimination.