Computational design and development of a novel voltammetric sensor for minoxidil detection based on electropolymerized molecularly imprinted polymer

Novel quantum dots-based assay for the determination of anti-hypertensive drugs minoxidil and timolol in different matrices

The present work reports a sensitive, affordable, and ecologically friendly spectrofluorimetric method for the assessment of two antihypertensive medications, namely minoxidil and timolol. Blue-emitting sulfur and nitrogen co-doped carbon quantum dots (S,N-CQDs) were generated by exposing soluble starch and thiourea to a 15-minute microwave treatment. The so- prepared nanodots displayed fluorescence at 276/430 nm with a quantum yield of 22 %. Inspection of the so-prepared nano-sensor verified their doping with nitrogen and sulfur, and their size was in the range of 4.5-9.03 nm. The proposed method was found to be rectilinear in the range of 0.20-5.0 and 2.0-30.0 µg/mL, with LOQs of 0.16 and 0.82 µg/mL for minoxidil and timolol, respectively. The developed method was employed to assess the concentrations of minoxidil and timolol in their pharmaceutical formulations, with %recoveries varying between 99.00 % and 101.94 %, and low RSD values (less than 2 %). The high sensitivity of the developed method allowed its use for timolol measurement in artificial aqueous humor, with % recoveries between 97.60 %.and 101.57 %. The study further examined how each analyte interacted with the prepared dots, leading to a quenching of their fluorescence. Additionally, an interference study was utilized to evaluate the specificity of the proposed approach through determining analyte levels in the existence of common additives, co-formulated drugs, and co-administered drugs. The analytical eco-scale, GAPI and AGREE assessment techniques were utilized to confirm the suggested method greenness.

A disposable homemade screen printed electrode for famotidine analysis using a computer-designed molecularly imprinted polymer based on the MWCNT-Fe3O4 nanocomposite in simulated real samples

A home-made screen printed electrode (SPE) was designed with a magnetic multi-walled carbon nanotube composite (MWCNT-Fe3O4) and a molecularly imprinted polymer (MIP) for sensitive and selective electrochemical analysis of famotidine (FAM). The SPE was fabricated using non-commercial conductive inks such as carbon and silver inks. The electrodes were printed by a painting technique on polyvinyl chloride (PVC) sheets as a substrate. To optimize the composition of the carbon ink, a mixture design methodology was employed. A computational approach was used to select the functional monomer. The imprinted layer was synthesized by electropolymerization of FAM (template) and pyrrole (PY) (monomer) using cyclic voltammetry (CV) on the working electrode surface modified with the MWCNT-Fe3O4 nanocomposite. Differential pulse voltammetry (DPV) was applied to characterize the template removal and rebinding processes. The Plackett-Burman design (PBD) and central composite design (CCD) investigated the effect of parameters on the MIP/MWCNT-Fe3O4/SPE performance. The sensor exhibited a linear dynamic range of 1-1000 μM (R2 = 0.9919) with a limit of detection (LOD) of 0.027 μM (3sb, n = 3). It demonstrated good repeatability and reproducibility, with relative standard deviations (RSD) of 3.6 and 4.2, respectively. This disposable and cost-effective sensor successfully detected FAM in simulated real samples and correlated well with high-performance liquid chromatography (HPLC) results.

Atenolol-imprinted polymer: a DFT study

The purpose of this work was to investigate, via DFT calculations, the molecularly imprinted polymer (MIP) for atenolol (ATL) β-blocker evaluating distinct functional monomers (FMs), solvents, and cross-linker agents (CLAs). As the main result, we could determine from structural and thermodynamic data the best MIP synthesis protocol as being: p-vinyl benzoic acid (APV) as FM, toluene as solvent, and pentaerythritol triacrylate (PETRA) as CLA. We believe this rational design can be very useful for experimentalists in an attempt to perform an efficient synthesis of a MIP for this important β-blocker drug.

Nano optical and electrochemical sensors and biosensors for detection of narrow therapeutic index drugs

For the first time, a comprehensive review is presented on the quantitative determination of narrow therapeutic index drugs (NTIDs) by nano optical and electrochemical sensors and biosensors. NTIDs have a narrow index between their effective doses and those at which they produce adverse toxic effects. Therefore, accurate determination of these drugs is very important for clinicians to provide a clear judgment about drug therapy for patients. Routine analytical techniques have limitations such as being expensive, laborious, and time-consuming, and need a skilled user and therefore  the nano/(bio)sensing technology leads to high interest.

A novel electrochemical sensor for the determination of histidine based on a molecularly imprinted copolymer

The present study aimed to report a novel electrochemical sensor through electropolymerization of o-aminophenol (o-AP) and m-dihydroxy benzene (m-DB) as monomers on the surface of the glassy carbon electrode (GCE) for the determination of histidine (His) as a template molecule. The developed sensor exhibited satisfactory sensitivity and high selectivity, and also offered a linear range between 0.005 and 10.0 μM with a detection limit of 0.9 nM. Finally, it is worth mentioning that we also aimed at employing the proposed sensor for the detection of His in blood serum samples.

The Use of Computational Methods for the Development of Molecularly Imprinted Polymers

Recent years have witnessed a dramatic increase in the use of theoretical and computational approaches in the study and development of molecular imprinting systems. These tools are being used to either improve understanding of the mechanisms underlying the function of molecular imprinting systems or for the design of new systems. Here, we present an overview of the literature describing the application of theoretical and computational techniques to the different stages of the molecular imprinting process (pre-polymerization mixture, polymerization process and ligand-molecularly imprinted polymer rebinding), along with an analysis of trends within and the current status of this aspect of the molecular imprinting field.

Development, validation, and application of an RP-HPLC method for concurrent quantification of Minoxidil and Finasteride in a topical solution for hair regrowth

A topical solution comprising of Minoxidil (MXL) and Finasteride (FNS) for alopecia is formulated in the present work, which essentially contains a lipid-Lauroglycol FCC as a penetration enhancer. The objective of the proposed work was to develop a rapid, simple, and robust reverse phase high performance liquid chromatographic (RP-HPLC) method to determine MXL and FNS in the said formulation. Herein, the chromatographic conditions were optimized based on the theoretical principles of separation and physicochemical properties such as pKa and log P of both the Active Pharmaceutical Ingredients (APIs). The separation was accomplished on an Inertsil® ODS-3 C18 column (150mm×4.6mm; 5μm of particle size) at 25°C by using a mobile phase composed of 70:30 v/v ratio of Methanol and Milli-Q water along with 0.5% Triethylamine at pH 6.4 adjusted with Ortho Phosphoric Acid. Drug peaks showed a good resolution at 210nm. The retention times for MXL and FNS were found to be 2.40min and 6.39min, respectively. The developed method was found to be linear (R²≥0.998) in a concentration range of 5-100μg/mL for both the drugs. The method was validated according to the ICH guidelines Q2 (R1). The ability of the method to differentiate between the types formulations was demonstrated by the in vitro diffusion data performed using a highly sophisticated Strat-M® membrane. The cumulative amount of drug released (MXL and FNS) at the end of 24hours was maximum for the topical formulation containing lipids prepared using isopropyl alcohol and propylene glycol as the base.

Mechanism of Nanocomposite Formation in the Layer-by-Layer Single-Step Electropolymerization of π-Conjugated Azopolymers and Reduced Graphene Oxide: An Electrochemical Impedance Spectroscopy Study

This work presents a study of the formation mechanism of electrochemically deposited alternating layers of azopolymer and graphene oxide, as well as a systematic study of the physicochemical characteristics of the resulting nanocomposite films by electrochemical impedance spectroscopy. The nanocomposite films were constructed by cyclic electropolymerization, which allowed for the assembly of thin films with alternating azopolymers and reduced graphene oxide (rGO) layers in one step. Morphological characterizations were performed by atomic force microscopy and scanning electron microscopy and verified that the electrodeposition of the poly(azo-BBY) polymeric film occurred during the anodic sweep, and the deposition of graphene oxide sheets took place during the cathodic sweep. By analyzing the electrochemical impedance spectra using equivalent circuit models, variations in the resistance and capacitance values of the system were monitored as a function of the amount of electrodeposited material on the fluorine doped tin oxide electrode. In addition, the interfacial phenomena that occurred during the electroreduction of the rGO sheets were monitored with the same method.

Electrochemical Detector for Liquid Chromatography: Determining Minoxidil in Hair-Growth Pharmaceuticals

Background:

The electrochemical behavior of minoxidil on gold (Au), Glassy Carbon (GCEs), and Carbon Paste Electrodes (CPEs) was investigated in an aqueous supporting electrolyte (phosphate buffer [pH 2.0-6.5], acetate buffer [pH 4.3], and Britton and Robinson buffer [pH 2.0-7.4]).

Methods:

For cyclic voltammetric measurements with suitable methodical parameters, CPEs catalyze electrooxidation of minoxidil more efficiently than do other electrodes. Minoxidil was detected using high-performance liquid chromatography with an electrochemical (carbon paste) detector (HPLCECD). For direct current mode, with the current at a constant potential, and measurements with suitable experimental parameters, a linear concentration from 0.02 to 2.6 mg L-1 was found. The detection limit was approximately 20 ng m L-1.

Results:

The developed method detected minoxidil samples.

Conclusion:

Findings using HPLC-ECD and HPLC with an ultraviolet detector were comparable.

Rational design of a molecularly imprinted polymer for dinotefuran: theoretical and experimental studies aimed at the development of an efficient adsorbent for microextraction by packed sorbent

In this work, we studied theoretically the formation process of a molecularly imprinted polymer (MIP) for dinotefuran (DNF), testing distinct functional monomers (FM) in various solvents through density functional theory calculations. The results revealed that the best conditions for MIP synthesis were established with methacrylic acid (MAA) as FM in a 1 : 4 stoichiometry and with chloroform as the solvent. This protocol showed the most favourable stabilization energies for the pre-polymerization complexes. Furthermore, the formation of the FM/template complex is enthalpy driven and the occurrence of hydrogen bonds between the DNF and MAA plays a major role in the complex stability. To confirm the theoretical results, MIP was experimentally synthesized considering the best conditions found at the molecular level and characterized by scanning electron microscopy and thermogravimetric analysis. After that, the synthesized material was efficiently employed in microextraction by packed sorbent combined with high-performance liquid chromatography in a preliminary study of the recovery of DNF from water and artificial saliva samples.

Preparation and application of a carbon paste electrode modified with multi-walled carbon nanotubes and boron-embedded molecularly imprinted composite membranes

An innovative electrochemical sensor was fabricated for the sensitive and selective determination of tinidazole (TNZ), based on a carbon paste electrode (CPE) modified with multi-walled carbon nanotubes (MWCNTs) and boron-embedded molecularly imprinted composite membranes (B-MICMs). Density functional theory (DFT) calculations were carried out to investigate the utility of template-monomer interactions to screen appropriate monomers for the rational design of B-MICMs. The distinct synergic effect of MWCNTs and B-MICMs was evidenced by the positive shift of the reduction peak potential of TNZ at B-MICMs/MWCNTs modified CPE (B-MICMs/MWCNTs/CPE) by about 200 mV, and the 12-fold amplification of the peak current, compared with a bare carbon paste electrode (CPE). Moreover, the coordinate interactions between trisubstituted boron atoms embedded in B-MICMs matrix and nitrogen atoms of TNZ endow the sensor with advanced affinity and specific directionality. Thereafter, a highly sensitive electrochemical analytical method for TNZ was established by different pulse voltammetry (DPV) at B-MICMs/MWCNTs/CPE with a lower detection limit (1.25 × 10^-12 mol L^-1) (S/N = 3). The practical application of the sensor was demonstrated by determining TNZ in pharmaceutical and biological samples with good precision (RSD 1.36% to 3.85%) and acceptable recoveries (82.40%-104.0%).

Molecularly imprinted electrochemical sensor based on an electrode modified with an imprinted pyrrole film immobilized on a β-cyclodextrin/gold nanoparticles/graphene layer

A novel molecularly imprinted electrochemical sensor was constructed for the sensitive detection of quercetin (Qu) based on a glassy carbon electrode (GCE) modified with β-cyclodextrin (β-CD), gold nanoparticles(AuNPs) and graphene (GR).