Sol-gel immobilized cyano-polydimethylsiloxane coating for capillary microextraction of aqueous trace analytes ranging from polycyclic aromatic hydrocarbons to free fatty acids

Sol-gel coating containing highly polar cyanopropyl and nonpolar poly(dimethylsiloxane) components (sol-gel CN-PDMS coating) was developed for capillary microextraction (CME). The sol-gel chemistry provided an efficient means to immobilize the CN-PDMS coating by establishing chemical anchorage between the coating and the fused silica capillary inner surface. This chemical bond provided excellent thermal and solvent stability to the created sol-gel coating. For the extraction of polar and nonpolar analytes, the upper allowable conditioning temperatures were 330 degrees C and 350 degrees C, respectively. To our knowledge, this is the first time when a CN-PDMS thick coating survived such a high operation temperature. The prepared sol-gel CN-PDMS coating provided effective extraction of polar and nonpolar analytes simultaneously from aqueous samples. The cyanopropyl moiety in sol-gel CN-PDMS coatings provided effective extraction of highly polar analytes such as free fatty acids, alcohols, and phenols without requiring derivatization, pH adjustment or salting out procedures. The PDMS moiety, on the other hand, provided efficient extraction of nonpolar analytes. The extraction properties of the sol-gel CN-PDMS coatings can be fine tuned via manipulation of relative proportions of 3-cyanopropyltriethoxysilane and hydroxy-terminated PDMS in the sol solution used to create the coatings. Detection limits of nanogram/liter (ng/L) were achieved for both highly polar and nonpolar analytes directly extracted from aqueous media using sol-gel CN-PDMS coated microextraction capillaries followed by GC analysis.     

Instant nano-hydroxyapatite: a continuous and rapid hydrothermal synthesis

Nano-particle hydroxyapatite (HA) rods, were rapidly synthesised using a three pump continuous hydrothermal process (using a water feed at up to 400 degrees C and at 24 MPa): the product was obtained as a highly crystalline and phase pure material, without the need for an ageing step or subsequent heat treatment.     

Use of solid-phase extraction, reverse osmosis and vacuum distillation for recovery of aromatic sulfonic acids from aquatic environment followed by their determination using liquid chromatography-electrospray ionization tandem mass spectrometry

Three different sample preparation techniques (i) solid-phase extraction, (ii) reverse osmosis and (iii) vacuum distillation have been investigated and the recoveries were compared for determination of highly water-soluble benzene and stilbene sulfonic acids in aqueous environment by liquid chromatography with photodiode array (PDA) and electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The recoveries were quite high using vacuum distillation (>90%) compared to solid phase extraction and reverse osmosis. The negative ion ESI mass spectra containing the peaks of quasimolecular ion [M-H]- allow the molecular mass determination of unknown compounds whereas the structures were proposed using fragments obtained from MS/MS analysis of [M-H]- ions. At lower fragmentation voltages only the quasimolecular ion [M-H]- was observed and as fragmentation voltages increased, it led to the formation of fragment ions corresponding to [M-H-SO3]-, [M-H-SO2]-, and SO3-. The detection limits were 1-28 microg/L with LC-ESI-MS. The sample collected from wastewater treatment plant was found to contain 21.1, 13.3, 12.1, 41.8 and 9.9 microg/L of cis-4,4(l)-diaminostilbene-2,2(l)-disulfonic acid (cis-DASDA), trans-4,4(l)-diaminostilbene-2,2(l)-disulfonic acid (trans-DASDA), 3-amino acetanilide-4-sulfonic acid (3-AASA), 4-chloroaniline-2-sulfonic acid (4-CASA), 2-chloroaniline-5-sulfonic acid (2-CASA), respectively.     

A new tetrasubstituted α-fluoro cyclohexanone bearing a fluoroisopropyl group at C5

A new tetrasubstituted cyclohexanone 5 fluorinated at C2 and having a fluoroisopropyl group at C5 has been synthesized in five steps from 3-methyl cyclohexenone and the structure of both diastereomers fully assigned. It is shown that diastereomer Ia having the fluorine atom at C2 in the axial position (in the most populated conformer of this diastereomer) is major and is a good catalyst for epoxidation of trans-olefins by oxone while diastereomer IIe is not. Moreover, only 0.3 equiv. of 5-Ia are necessary and the ketone is totaly recovered after reaction (no Baeyer-Villiger).     

Optimal control of the obstacle problem: optimality conditions

^** E-mail: k.aithadi{at}ucam.ac.ma In this paper, we investigate optimal control problem governedby variational inequality of the obstacle type. Existence ofsolution for the problem is proved and we also show how to obtainoptimality conditions for a penalized problem issued from theoriginal one.     

Spectral studies of Fe(III) complexes of dipodal tridentate chelating agents

The dipodal ligands (Im) and (BIm) as well as complexes [FeLCl₃] [L = Im (1) and BIm (2)] have been prepared and studied using spectroscopic techniques. The magnetic moment, IR, electronic (ligand field), FAB-mass and NMR spectral data indicate a hexa-coordinate geometry around high-spin state Fe³⁺ where the ligands coordinate as a tridentate [N,N,N] chelating agent. ⁵⁷Fe-Mössbauer spectral data confirmed the presence of a ligand asymmetry around Fe³⁺ in a high-spin state electronic configuration (t_2g³,e_g², S = 5/2) with nuclear transition Fe(±3/2 → ±1/2) exhibiting Kramer's double degeneracy. The molecular computations provided the optimum energy perspective plots for the molecular geometries giving the important structural data.     

Synthesis and characterization of new poly(ester-amide)s containing diarylidenecyclohexanone in the main chain. Part: II

A new category of poly(ester-amide)s based on diarylidenecyclohexanone in the main chain were synthesized via interfacial polycondensation of two monomers namely: 2,6-bis(4-hydroxybenzylidene) cyclohexanone I and 2,6-bis(4-hydroxy-3-methoxybenzylidene) cyclohexanone II with diacid chlorides IIIa–c. The model compounds were synthesized by reacting one mole of compounds IVa–c with two monomers I and II. The structure of the model compounds was confirmed by correct elemental and spectral analyses. The various characteristics of the resulting polymers including: solubility, viscosity, thermal analysis, and X-ray diffraction analysis were determined and discussed. The majority of the polymers were insoluble in most common organic solvents. The viscosity measurements in dimethylsulfoxide showed the values 0.58–0.79 dl/g. Thermal analysis showed that they were thermally stable up to 500 °C. X-ray analysis showed that the polymers had some degree of crystallinity in the region 2θ = 5–50°.     

Quick bioanalytical method of quantification and validation of sulbactam in plasma using high performance liquid chromatography

A quick method of quantitative determination of sulbactam in human plasma, using liquid chromatography-UV spectroscopy, has been developed and validated. After derivatization with imidazole, plasma samples were treated by direct deproteinization with acetonitrile as an extraction solvent. After ultracentrifugation, sulbactam extract was directly injected onto the LC column. Chromatographic separation was performed on TSK Gel Super ODS (50 mm × 4.6 mm i.d., 2 μm) using methanol and phosphate buffer with tetrabutylammonium hydroxide solution as a mobile phase. Gradient elution was employed. The method was fully validated according to the United States Food and Drug Administration requirements (linearity, precision, trueness, quantification limit, detection limit, recovery, specificity and stability). The calibration curves were linear within the concentration range of 0.05–4.0 μg mL⁻¹. Good method/system precision and accuracy of the method were demonstrated.      

Spectral characteristics and fluorescence quenching of N,N′-bis(4-pyridyl)-3,4:9,10-perylenebis(dicarboximide) (BPPD)

The photophysical properties such as electronic absorption, molar absorptivity, emission spectra, fluorescence quantum yield and fluorescence lifetime of N,N′-bis(4-pyridyl)-3,4:9,10-perylene bis(dicarboximide) (BPPD) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity, while the fluorescence quantum yield (?_f) is solvent dependent. The ground state geometry has been computed by using density functional theory (DFT), the transition from HOMO to LUMO from perylene core with maximum absorption at 512 nm and HOMO–LUMO energy difference equal 2.53 eV. BPPD dye undergoes molecular aggregation to dimmer or higher aggregates in dimethyl sulfoxide (DMSO). Crystalline solids of BPPD gives excimer-like emission at 676 nm. The fluorescence quenching of BPPD is also studied using hydrated ferric oxide nanoparticle (FeOOH), and the Stern–Volmer rate constants (K_sv) were calculated as 8×10⁶ and 9.2×10⁶ M^?1 in ethanol and ethylene glycol, respectively.     

Dystrophin Protein Quantification as a Duchenne Muscular Dystrophy Diagnostic Biomarker in Dried Blood Spots Using Multiple Reaction Monitoring Tandem Mass Spectrometry: A Preliminary Study

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder characterized by progressive muscle loss, leading to difficulties in movement. Mutations in the DMD gene that code for the protein dystrophin are responsible for the development of DMD disorder, where the synthesis of this protein is completely halted. Therefore, circulating dystrophin protein could be a promising biomarker of DMD disease. Current methods for diagnosing DMD have sensitivity, specificity, and reproducibility limitations. Herein, a quantitative liquid chromatography–tandem spectrometry (LC–MS/MS) technique in multiple reaction monitoring (MRM) mode was designed and validated for accurate dystrophin protein measurement in a dried blood spot (DBS). The method was successfully validated on the basis of international guidelines regarding calibration curves, precision, and accuracy. In addition, patients and healthy controls were used to test the amount of dystrophin protein circulating in DBS samples as a potential biomarker for DMD disorders. DMD patients were found to have considerably lower levels than controls. To the best of our knowledge, this is the first study to report dystrophin levels in DBS through LC–MS/MS as a diagnostic marker for DMD to the proposed MRM method, providing a highly specific and sensitive approach to dystrophin quantification in a DBS that can be applied in DMD screening.