FakhrEldin O. Suliman

Computational modeling of capillary electrophoretic behavior of primary amines using dual system of 18-crown-6 and β-cyclodextrin

Using capillary electrophoresis (CE) three chiral primary amine compounds 1-aminoindan (AI), 1-(1-naphthyl)ethylamine (NEA) and 1,2,3,4-tetrahydro-1-naphthylamine (THAN), exhibited only partial or no separation when β-cyclodextrin (βCD) was used as chiral selector. The use of 18-crown-6 (18C6) as a second additive with βCD resulted in an enhanced separation. A molecular modeling study, using molecular mechanics and the semiempirical PM6 calculations, was used to help explaining the mechanism of the enantiodifferentiation and to predict the separation process. Optimization of the structures of the complexes by the PM6 method indicate that the poor separation obtained in the presence of the βCD chiral selector alone is due to the small binding energy differences (ΔΔE) of 4.7, 1.1 and 1.2 kcal mol(-1) for AI, NEA and THAN, respectively. In the presence of 18C6 it was suggested that a sandwich compound between 18C6, amine and βCD is formed. Theoretical calculations show that a significant increase in the binding energy is obtained for the sandwich compounds indicating strong hydrophobic and van der Waals interactions that show enhanced enantiodifferentiation.

Study on the spectral and inclusion properties of a sensitive dye, 3-naphthyl-1-phenyl-5-(5-fluoro-2-nitrophenyl)-2-pyrazoline, in solvents and β-cyclodextrin

3-Naphthyl-1-phenyl-5-(5-fluoro-2-nitrophenyl)-2-pyrazoline (NPFP), a fluorogenic probe and its derivative NPFP-Phenylephrine were synthesized and their absorption and fluorescence properties were recorded in solvents of varying polarity. Spectroscopic studies reveal that, the solvatochromic behavior of the compounds depend not only on the polarity but also on the hydrogen-bonding properties of the solvents. The effects of β-cyclodextrin on the fluorescence properties of both compounds were studied. It was found that there is an enhancement in the fluorescence intensity of labeled drug (NPFP-Phenylephrine) in the presence of β-cyclodextrin. In the present study, the molecular motions of NPFP-Phenylephrine embedded in a β-cyclodextrin cavity have been investigated by fluorescence techniques in steady-state and time resolved modes.

A novel microfluidic device for estimating the total phenolic/antioxidant level in honey samples using a formaldehyde/potassium permanganate chemiluminescence system

A microfluidic device has been investigated as a tool for the estimation of the total phenolic content/antioxidant level in honey using an acidic potassium permanganate chemiluminescence (KMnO4-CL) detection system. Selected phenolic antioxidants, including quercetin, catechin, gallic acid, caffeic acid and ferulic acid, produced analytically useful chemiluminescence signals, with detection limits ranging between 2.4 nmol L−1 for gallic acid and 34.0 nmol L−1 for o-coumaric acid. The parameters that affect the chemiluminescence intensities of each antioxidant were carefully optimized, including chip geometry, volume and area of the detection chip, pH, and concentrations of reagents used and flow rates. The effect of formaldehyde and other enhancers on CL signal intensity was extensively investigated. The method was applied to honey samples. Nine different honey samples exhibited total phenolic/antioxidant levels of 41.2 to 765.4 mg kg−1 with respect to gallic acid. The Folin–Ciocalteu (FC) assay results were well correlated with the chemiluminescence results. The method was found to be selective, rapid and sensitive when used to estimate the total phenolic/antioxidant level, producing good agreement with reported results for honey samples.

Synthesis, characterization and DFT calculation of 4-fluorophenyl substituted tris(8-hydroxyquinoline)aluminum(III) complexes.

New 4-fluorophenyl substituted 8-hydroxyquinoline derivatives, 5-(4-fluorophenyl)quinolin-8-ol and 5,7-bis(4-fluorophenyl)quinolin-8-ol, were synthesized and characterized by spectroscopic methods. The aluminum complexes of 5-(4-fluorophenyl)quinolin-8-ol (AlQF) and of 5,7-bis(4-fluorophenyl)quinolin-8-ol (AlQF2) exhibit strong fluorescence emission centered at 525 nm and 530 nm respectively. The quantum yield of both complexes were enhanced compared to the parent tris(8-hydroxyquinolinato)aluminum(III) complex. Electronic structures and photophysical properties of the new complexes were investigated theoretically by ab initio and density functional theory (DFT) and time dependent DFT (TD-DFT). Geometries of the ground state (S0) and the first excited state (S1) of the new complexes were optimized at the B3LYP/6-31G(d) functional and configuration interaction singles (CIS) method respectively. The aryl substituents were found to contribute significantly to the frontier molecular orbitals (FMOs). We have observed that in both cases the lowest occupied molecular orbital (LUMO) energy decreases while the energy of the highest occupied molecular orbital is slightly increased. The most significant increase was observed for AlQF2.

An enhanced cerium(IV)-rhodamine 6G chemiluminescence system using guest-host interactions in a lab-on-a-chip platform for estimating the total phenolic content in food samples.

Two chemiluminescence-microfluidic (CL-MF) systems, e.g., Ce(IV)-rhodamine B (RB) and Ce(IV)-rhodamine 6G (R6G), for the determination of the total phenolic content in teas and some sweeteners were evaluated. The results indicated that the Ce(IV)-R6G system was more sensitive in comparison to the Ce(IV)-RB CL system. Therefore, a simple (CL-MF) method based on the CL of Ce(IV)-R6G was developed, and the sensitivity, selectivity and stability of this system were evaluated. Selected phenolic compounds (PCs), such as quercetin (QRC), catechin (CAT), rutin (RUT), gallic acid (GA), caffeic acid (CA) and syringic acid (SA), produced analytically useful chemiluminescence signals with low detection limits ranging from 0.35 nmol L(-1) for QRC to 11.31 nmol L(-1) for SA. The mixing sequence and the chip design were crucial, as the sensitivity and reproducibility could be substantially affected by these two factors. In addition, the anionic surfactant (i.e., sodium dodecyl sulfate (SDS)) can significantly enhance the CL signal intensity by as much as 300% for the QRC solution. Spectroscopic studies indicated that the enhancement was due to a strong guest-host interaction between the cationic R6G molecules and the anionic amphiphilic environment. Other parameters that could affect the CL intensities of the PCs were carefully optimized. Finally, the method was successfully applied to tea and sweetener samples. Six different tea samples exhibited total phenolic/antioxidant levels from 7.32 to 13.5 g per 100g of sample with respect to GA. Four different sweetener samples were also analyzed and exhibited total phenolic/antioxidant levels from 500.9 to 3422.9 mg kg(-1) with respect to GA. The method was selective, rapid and sensitive when used to estimate the total phenolic/antioxidant level, and the results were in good agreement with those reported for honey and tea samples.

Determination of the pseudoephedrine content in pharmaceutical formulations and in biological fluids using a microbore HPLC system interfaced to a microfluidic chemiluminescence detector

A novel automated precolumn derivatization followed by separation using liquid chromatography for the determination of pseudoephedrine (PSE) by a microfluidic chemiluminescence detector has been developed. An on-line derivatization procedure was utilized by converting PSE into a highly light emitting species in a Ru(bipy)3(2+)-peroxydisulphate chemiluminescence (CL) system by derivatizing it with a 1.0 M formaldehyde solution. The derivatized analyte was directly injected into a microbore high-performance liquid chromatography (HPLC) system coupled to an on-chip chemiluminescence detector. The newly developed highly selective, sensitive and fast HPLC-CL method was validated and successfully applied for the analysis of PSE in pharmaceutical formulations and a human urine sample. The selectivity of the method is not only due to the HPLC separation but is also due to the highly selective detection principle of the Ru(bipy)3(2+)-peroxydisulphate CL system used. There was no interference observed from the common preservatives and excipients used in pharmaceutical preparations, which did not show any significant CL signal. The retention time of PSE was less than 3 min, and the detection limits and quantification limits were found to be 5.7 and 26.0 µg L(-1), respectively.

HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY DETERMINATION OF ANILINES WITH FLUORESCENT DETECTION AND PRE-COLUMN DERIVATIZATION

A simple, sensitive, and rapid reverse-phase high-performance liquid chromatography (RP-HPLC) method for the determination of anilines in water is proposed. The use of 2,7-diethylamino-2-oxo-2H-chromen-3-yl-benzothiazole-6-sulfonylchloride (coumarin 6-SO2Cl) as a fluorigenic-labeling reagent was investigated. The label reacted with aniline within 30 min under mild conditions (ambient temperature, pH 9.0) to give sulfonamides that were separated by RP-HPLC employing fluorescence detection with an excitation wavelength of 470 nm and an emission wavelength of 520 nm. The optimum conditions for fluorescence, derivatization, and chromatographic separation were established. The calibration curves were linear for the range 0–800 ppb. The proposed method was applied for the determination of anilines in spiked drinking water samples and irrigation water samples with recoveries of 90.0–103.9% and relative standard deviations of 1.2–4.7%, respectively. This method showed good accuracy and repeatability that can be used for the quantification of aniline in real samples.

3(2H)-Furanone as a promising scaffold for the synthesis of novel fluorescent organic dyes: an experimental and theoretical investigation

3(2H)-Furanones are a type of five-membered heterocyclic compounds of synthetic and biological importance. For exploring the utilities of this “sweet” aroma component for bio-analytical purposes we have prepared and characterized two novel fluorophores (2Z)-2-(5-fluoro-2-ntro benzylidene)-5-phenyl-3(2H)-furanone (FNPF) and (2Z)-2-(4-carboxy benzylidene)-5-phenyl-3-(2H)-furanone (CBPF) on a 3-furanone skeleton. In order to expand their application potential, the photophysical properties have been investigated using absorption and emission spectroscopy, in combination with quantum chemical calculations. As expected, both compounds showed efficient solvatochromic properties and the excited state dipole moments are larger than those of the ground state. Solvent dependent spectral data using TD-DFT calculations on the optimized ground and excited state structures of both compounds were found to correlate well with the experimental findings.

Unveiling a versatile heterocycle: pyrazoline – a review

The design and synthesis of novel fluorescent heterocyclic dyes is a “hotspot” research area, due to their favourable photophysical properties and crucial role in charge transfer processes, which could allow huge advances in the fields of physics, chemistry and biology. One group of electron-rich nitrogen carriers, pyrazolines, are enjoying brisk growth, since they combine exciting electronic properties with the potential for dynamic applications. Concerning multi-functional applications, pyrazolines could provide a new range of applications that would revolutionize various fields. As reported in many studies, the potential applications of pyrazolines are vast and ever growing, but they have yet to make in-roads into real-life applications. This review provides an overview on the current status of pyrazoline derivatives in terms of synthesis, physico-chemical properties and various applications in order to realize their full potential for practical applications, and to trigger the synthesis and study of novel pyrazoline based compounds with much promise. We also present our conclusions and outlook for the future.

Determination of Common Adulterants in Herbal Medicine and Food Samples using Core-shell Column Coupled to Tandem Mass Spectrometry

High-performance liquid chromatography coupled to tandem mass spectrometry was used to develop and validate a rapid method to qualitatively and quantitatively analyse 18 common adulterants in herbal medicine and food samples. Initially, the mobile phase composition was optimized in three different columns: core-shell, monolithic and standard 3.5-µm-particle-size columns. The results show that the core-shell column provides the best separation. Moreover, the tandem mass spectrometry was optimized. The linear range for all adulterants was 0.5-500 μg mL-1. Finally, the samples that were supplied by the Public Authority of Customer Protection, Ministry of Health, and those collected from the local market were analysed. The results indicate that 7 of 33 analysed samples contained adulterants. The adulterated samples mainly contain sildenafil, tadalafil or vardenafil. The concentrations of these three adulterants in the samples were 0.18-39 wt%. This study is the first report in the Sultanate of Oman about adulteration in herbal medicine and food samples. The results clearly raise some concern and require proper plan of action to increase public awareness about this serious issue.