Turghun Muhammad

Rational design and synthesis of water-compatible molecularly imprinted polymers for selective solid phase extraction of amiodarone

Novel water-compatible molecularly imprinted polymers (MIPs) selective for amiodarone (AD) were designed via a new methodology which relies on screening library of non-imprinted polymers (NIPs). The NIP library consisted of eighteen cross-linked co-polymers synthesized from monomers commonly used in molecular imprinting. The binding capacity of each polymer in the library was analyzed in two different solvents. Binding in water was used to assess non-specific (hydrophobic) interactions and binding in an appropriate organic solvent was used to assess specific interactions. A good correlation was found between the screening tests and modeling of monomer-template interactions performed using computational approach. Additionally, analysis of template-monomer interactions was performed using UV-vis spectroscopy. As the result, 4-vinylpyridine (4-VP) was selected as the best monomer for developing MIP for AD. The 4-VP-based polymers demonstrated imprinting factor equal 3.9. The polymers performance in SPE was evaluated using AD and its structural analogues. The recovery of AD was as high as 96% when extracted from spiked phosphate buffer (pH 4.5) solution and 82.1% from spiked serum samples. The developed MIP shown as a material with specific binding to AD, comparing to its structural analogues, 1-(2-diethylaminoethoxy)-2,6-diiodo-4-nitrobenzene and lidocaine, which shown 9.9% and 25.4% of recovery from the buffer solution, correspondingly. We believe that the screening of NIP library could be proposed as an alternative to commonly used computational and combinatorial approaches.

Rational design of molecularly imprinted polymer: the choice of cross-linker

The paper describes a rational approach for the selection of cross-linkers during the development of molecularly imprinted polymers (MIPs). As a model system for this research MIPs specific for the drug zidovudine (AZT) were designed and tested. Three cross-linkers trimethylolpropane trimethacrylate (TRIM), ethylene glycol dimethacrylate (EGDMA) and divinylbenzene (DVB) were studied. The analogue of zidovudine (AZT) ester (AZT-ES) was used as a dummy template. The imprinting factors for all of the polymers in the static adsorption experiments were calculated. The data on the AZT adsorption by control polymers (CP), which were prepared with different cross-linkers without a functional monomer, was also analyzed. DVB was found to be more inert towards zidovudine than EGDMA and TRIM, which was confirmed by both molecular modelling and adsorption experiments. It was demonstrated that DVB-based polymers had a higher imprinting factor (I = 1.85) compared with other tested cross-linked polymers. It was suggested that the selection of the cross-linker should be based on the strength of the interaction with the template: the cross-linker which displays lower binding of the template should be preferential because it generates MIPs with lower non-specific binding and a higher imprinting factor, and therefore specificity. Which cross-linker to use for the preparation of any particular MIP can be determined by analysis of the interactions between the cross-linker and template. This could be done either virtually using computational modelling or by template adsorption using a small library of polymers prepared using different cross-linkers.

Mesostructured Co–Ce–Zr–Mn–O composite as a potential catalyst for efficient removal of carbon monoxide from hydrogen-rich stream

Mesostructured CoxCe0.85Zr0.15MnyOe composites were firstly prepared by a simple one-pot surfactant-assisted co-precipitation (SACP) method and then employed to catalyze the CO preferential oxidation (CO PROX) reaction in an H2-rich stream. Effects of the Co and Mn contents (x and y, respectively) in the formula, as well as the presence of H2O and CO2 in feed were investigated. The as-synthesized Co0.4Ce0.85Zr0.15Mn0.10Oe catalyst showed excellent catalytic performance in the CO PROX reaction: 100% CO conversion could be observed in a wide temperature range of 140–200 °C; even in the simulated syngas, the almost complete CO removal could still be achieved at 175–225 °C; no obvious change in both CO conversion and CO2 selectivity over the catalyst took place during the CO PROX process with simulated syngas as feed. N2 physisorption (BET), temperature-programmed reduction (TPR), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopic (XPS) characterization techniques were employed to reveal the relationship between the catalyst nature and catalytic performance. The outstanding catalytic performance in CO PROX reaction was remarkably dependent on a larger specific surface area, more reducible Co3+ and the high dispersity of the Co3O4, affected by the Co and Mn contents through strong Co–Ce–Zr–Mn interactions. The mesostructured Co0.4Ce0.85Zr0.15Mn0.10Oe catalyst prepared by the simple one-pot SACP protocol can be a promising candidate for CO PROX reaction in excess H2.

Monitoring Dissolution Rate of Amiodarone Tablets by a Multiple Fiber-Optic Sensor System

Afiber-optic dissolution testing (FODT) system for solid pharmaceutical formulations has been constructed. The system is based on a charge-coupled device (CCD) detector and includes six fiber-optic probes. Light is produced by a small deuterium arc lamp illuminating an optical fiber bundle. Six fiber-optic dipping probes were constructed with reflection geometry. The light passes back and forth through the flow-through cuvette backed by a coated aluminum mirror. The sampling interval was typically 30 sec for all probes. The system was tested for different tablet and capsule formulations. Amiodarone is a Class III anti-arrhythmic agent. It is used for treatment of many ventricular and supraventricular arrhythmias, including arterial fibrillation. It is a highly hydrophobic drug, and factors of its formulation, including constitutional heterogeneity, surface membrane, and production technology, influence its absorption. The dissolution of marketed amiodarone tablets was tested by the system, and dissolution parameters were directly obtained from the dissolution curves. It was found that there were significant differences in the dissolution of these products.

Determination of total polyphenols in tea by a flow injection-fiber optic spectrophotometric system

ABSTRACT A flow injection-fiber optic spectrophotometric system was established for the online determination of total polyphenol content in tea samples. The method was based on the chromogenic reaction between the phenolic compounds (gallic acid) and ferrous tartrate which was used as the colorimetric reagent and the absorption was determined at the maximum absorption wavelength of 540 nm at 20°C and pH 7.5. The calibration curve from standard solutions of gallic acid was linear in the range from 0.010 to 0.100 mg/mL with a correlation coefficient of 0.9970. The relative standard deviation of polyphenol measurements for eight tea samples was between 0.55 and 3.18%. It can be concluded that the proposed method has allowed simple, fast, and accurate determination of total polyphenol content in tea products.

In Situ Liquid-Phase-Adsorption Measurement System Based on Fiber-Optic Sensing with the Aid of Membranes

At present, liquid phase adsorption (LPA) is still being quantitatively characterized in the way of manual sampling and off-line determination because of the complexity of the system comparing to gas adsorption. This paper describes a novel method for in situ, real-time measurement of LPA in general based on fiber-optic sensing (FOS) with the aid of membranes for the first time. A self-made measurement vessel was assembled from an adsorption bag, thermostatic devices with a stirrer, and a fiber-optic dipping probe. Also, macroporous adsorption resins (MARs) and rutin were chosen as model adsorbent and adsorbate to establish the FOS system. Here, in situ light absorption measurement was achieved by eliminating interference of adsorbent particles via encapsulating them with a membrane into the adsorption bag. In situ LPA measurement of rutin solution on MARs was obtained by detecting light absorption at 353 nm using dipping probe, in the broad concentration range from 0.3 to 60 mg/L with excellent linearity (R2 = 0.9996). In situ measurements of adsorption and desorption kinetics on five kinds of MARs with different polarities were systematically carried out, showing that the adsorption process obeyed the pseudo-second-model. As well as, the system was proved to be highly accurate and reproducible. More importantly, this method enabled to study the initial stage of the adsorption process, starting from the time of the first second, which is the most important part in the adsorption kinetics, and this is impossible for traditional sampling methods. The successful application of FOS to in situ measurement of LPA not only contributes to fast, automatic, and real-time monitoring of LPA process but also enriches the research connotation of adsorption.

In-situ measurement of the adsorption thermodynamics of rutin on macroporous adsorption resins by fiber-optic sensing

Abstract This paper describes instrumentation of a spectrophotometric system and its application for in-situ, real-time measurement of adsorption thermodynamics in aqueous solution by use of laboratory-constructed fiber-optic measurements. A measurement vessel was assembled from an adsorption bag, stirring and thermostatic devices, and a fiber-optic dipping probe. A macroporous adsorption resin and rutin were selected as the model adsorbent and adsorbate. In-situ liquid phase adsorption measurement of the system was achieved through monitoring of the absorption by dipping the probe in a broad range of concentrations. In-situ measurement of the AB-8 resin adsorption at temperatures from 303 K to 323 K was systematically carried out, showing that temperature was an influencing factor for the adsorption capacity and initial adsorption rate. The adsorption thermodynamic parameters for AB-8 indicated that the results well fitted the Freundlich model. In addition, a favorable, exothermic, spontaneous, physical process of rutin was demonstrated on AB-8. The obtained results showed that this method was successful at keeping the adsorption temperature constant. The application of fiber-optic sensing to the in-situ measurement of liquid phase adsorption enables automated and real-time monitoring of adsorption thermodynamics.

A Simple and Selective Fluorescent Sensor Chip for Indole-3-Butyric Acid in Mung Bean Sprouts Based on Molecularly Imprinted Polymer Coatings

In this paper, we report the preparation of molecularly imprinted polymer coatings on quartz chips for selective solid-phase microextraction and fluorescence sensing of the auxin, indole-3-butyric acid. The multiple copolymerization method was used to prepare polymer coatings on silylated quartz chips. The polymer preparation conditions (e.g., the solvent, monomer, and cross-linker) were investigated systemically to enhance the binding performance of the imprinted coatings. Direct solid-phase fluorescence measurements on the chips facilitated monitoring changes in coating performance. The average binding capacity of an imprinted polymer coated chip was approximately 152.9 µg, which was higher than that of a non-imprinted polymer coated chip (60.8 µg); the imprinted coatings showed the highest binding to IBA among the structural analogues, indicating that the coatings possess high selectivity toward the template molecule. The developed method was used for the determination of the auxin in mung bean extraction, and the recovery was found to be in the range of 91.5% to 97.5%, with an RSD (n = 3) of less than 7.4%. Thus, the present study provides a simple method for fabricating a fluorescent sensor chip for selective analysis.