A validated spectrofluorometric method for the determination of celecoxib in capsules

A rapid, selective, sensitive and simple fluorescence method was developed for the direct determination of celecoxib in capsules. The capsules were emptied, pulverized and dissolved in either ethanol or acetonitrile, sonicated and filtered. Direct fluorescence emission was measured at 355±5 nm (exciting at 272 nm). The method was fully validated and the recoveries were excellent, even in presence of excipients.     

On-line determination of organophosphorus pesticides in water by solid-phase microextraction and gas chromatography with thermionic-selective detection

This paper describes the extraction of 49 organophosphorus pesti-cides (OPPs) from water samples using solid-phase microextraction (SPME). Three fibers, including a 15-μm XAD-coated fiber, a 85-μm polyacrylate-coated fiber, and a 30-μm polydimethylsilox-ane-coated fiber (PDMS), were evaluated here. The effects of stirring and the addition of NaCl to the sample were examined for the polyacrylate-coated fiber. The precision of the technique was examined for all three fibers and the extraction kinetics were investigated using the XAD- and polyacrylate-coated fibers. With some exceptions, the XAD- and polyacrylate-coated fibers performed better than the PDMS-coated fiber. The superiority of the XAD-nd polyacrylate-coated fiber. The superiority of the XAD- and polyacrylate-coated fibers over the PDMS-coated fibers can be attribuibuted to the aromatic functionalities of the XAD and the polar functionalities in the polyacrylate. The relatively high percent RSDs indicate that the SPME technique needs to be further refined before it can be used for anything other than screening. A more effective form of agitation than mechanical stirring may be neccessary to reduce variability and achieve a faster equilibrium between the sample and the SPME fiber.     

Surface activity of thymol: implications for an eventual pharmacological activity

In the present work, we studied the ability of thymol to affect the organization of model membranes and the activity of an intrinsic membrane protein, the GABA(A) receptor (GABA(A)-R). In this last aspect, we tried to elucidate if the action mechanism of this terpene at the molecular level, involves its binding to the receptor protein, changes in the organization of the receptor molecular environment, or both. The self-aggregation of thymol in water with a critical micellar concentration approximately = 4 microM and its ability to penetrate in monomolecular layers of soybean phosphatidylcholine (sPC) at the air-water interface, even at surface pressures above the equilibrium, lateral pressure of natural bilayers were demonstrated. Thymol affected the self-aggregation of Triton X-100 and the topology of sPC vesicles. It also increased the polarity of the membrane environment sensed by the electrochromic dye merocyanine. A dipolar moment of 1.341 Debye was calculated from its energy-minimized structure. Its effect on the binding of [3H]-flunitrazepam ([3H]-FNZ) to chick brain synaptosomal membranes changed qualitatively from a tendency to the inhibition to a clear activatory regime, up on changing the phase state of the terpene (from a monomeric to a self-aggregated state). Above its CMC, thymol increased the affinity of the binding of [3H]-FNZ (K(d-control)= 2.9, K(d-thymol)= 1.7 nM) without changing the receptor density (B(max-control)= 910, B(max-thymol)= 895 fmol/mg protein). The activatory effect of thymol on the binding of [ [3H]-FNZ was observed even in the presence of the allosteric activator gamma-aminobutyric acid (GABA) at a concentration of maximal activity, and was blocked by the GABA antagonist bicuculline. Changes in the dipolar arrangement and in the molecular packing of GABA(A)-R environment are discussed as possible mediators of the action mechanism of thymol.     

Analysis of compounds of environmental concern: II. Diphenyl ethers

Nineteen halogenated and/or nitrated diphenyl ethers (currently listed in EPA Method 8111) have been separated on a DB-5/ DB-1701 column pair connected to an inlet splitter and separate electron capture detectors. Retention times are included for 10 additional compounds evaluated for their suitability as internal standards or surrogate compounds for incorporation into Method 8111. Method reproducibility and linearity are discussed, and results are presented for extracts of two real samples spiked with the 19 diphenyl ethers and analyzed using the dual-column dual-detector arrangement.     

Computationally-assisted approach to the vibrational spectra of molecular crystals: study of hydrogen-bonding and pseudo-polymorphism.

A new computationally-assisted methodology (PiMM), which accounts for the effects of intermolecular interactions in the crystal, is applied to the complete assignment of the Raman and infrared vibrational spectra of room temperature forms of crystalline caffeine, theobromine, and theophylline. The vibrational shifts due to crystal packing interactions are evaluated from ab initio calculations for a set of suitable molecular pairs, using the B3LYP/6-31G* approach.The proposed methodology provides an answer to the current demand for a reliable assignment of the vibrational spectra of these methyl-xanthines, and clarifies several misleading assignments. The most relevant intermolecular interactions in each system and their effect on the vibrational spectra are considered and discussed. Based on these results, significant insights are obtained for the structure of caffeine in the anhydrous form (stable at room temperature), for which no X-ray structure has been reported. A possible structure based on C((8))--H...N((9)) and C((1,3))--H...O intermolecular interactions is suggested.     

Chemical transformations of 3‐amino‐2‐quinolones

In order to find new antimalarial drugs, an exploration about the chemical properties of the starting compounds 3‐amino‐6‐chloro‐4‐phenyl‐1H‐quinolin‐2‐one ( 1 ) and 3‐amino‐4‐methyl‐1H‐quinolin‐2‐one ( 2 ) was developed. Acylation with acyl chloride, sulfonyl chloride and acetic anhydride were carried out. Despite a previous report [2], when acetyl chloride or acetic anhydride were assayed on 1 , only the diacetyl derivative 7 was obtained. When this compound was heated at reflux temperature in a mixture of acetic acid and acetic anhydride, it was transformed in the oxazoloquinoline 8 . Further reactions of the acyl derivatives with diazomethane afforded 1‐methylated compounds. Compound 2 gave the imine 16 by condensation with 4‐nitrobenzaldehyde.     

A new method for reversible immobilization of thiol biomolecules based on solid-phase bound thiolsulfonate groups

A new method for the reversible immobilization of thiol bimolecules, e.g., thiolpeptides and thiolproteins, to beaded agarose and other solid phases is reported. The method consists of an activation and a coupling step. The activation is based on oxidation of disulfides (or thiol groups via disulfides) present in a solid phase by hydrogen peroxide at moderately acidic pH. This oxidation leads to disulfide oxides (thiolsulfinate groups of which the majority are further oxidized to thiolsulfonate). The thiolsulfonate groups react easily with thiol compounds, which become immobilized via disulfide bonds. The pH range for thiol coupling is wide (pH 5-8), but for most thiols the reaction seems to proceed faster at pH>7. The stability of the reactive group to hydrolysis, especially at neutral and weakly acidic pH, is very high. The activated gel, therefore, can be stored as a suspension at pH 5 for extended periods. The method has been used to reversibly immobilize glutathione, β-galactosidase, alcohol dehydrogenase, urease, and papain, all with exposed thiol groups as well as thiolated bovine serum albumin and sweet-potato β-amylase. Depending on the thiol content of starting thiol-agarose, thiol-sulfonate-agarose derivatives with different binding capacities can be obtained. Thus, up to 5.0 mg (16 μmol) glutathione and 15 mg thiol-protein/mL gel derivative have been immobilized.     

Determination of organochlorine pesticides (OCPs) in breast milk from Rio Grande do Sul,Brazil, using a modified QuEChERS method and gas chromatography-negative chemical ionisation-mass spectrometry

ABSTRACT

The food chain is the main source of exposure to humans by organochlorine pesticides (OCPs) due to the bioaccumulation. Breast milk can accumulate OCPs, so this matrix is often used as an environmental bioindicator. The currently available methods for the determination of several OCPs and metabolites in breast milk involve, in general, multi-step sample preparation and quantification techniques with low selectivity, high cost and much time and labour. Thus, a fast and efficient method based on sample preparation using the quick, easy, cheap, effective, rugged and safe (QuEChERS) method combined with gas chromatography coupled to mass spectrometry with negative chemical ionisation (GC-NCI-MS) was developed, validated and applied for determination of 16 OCPs and metabolites in breast milk samples. The extract was cleaned by dispersive solid-phase extraction (d-SPE) using MgSO₄ and C18, evaporated in a Turbovap® system, redissolved and analysed by GC-NCI-MS. The method was validated showing acceptable recoveries (72–118%) and precision (RSD <19%). Method limits of detection (LODs) and quantification (LOQs) ranged from 0.75 to 7.5 ng g^?1 and from 2.5 to 25 ng g^?1 lipid, respectively. The method was successfully applied to 20 samples of breast milk from different regions of the Rio Grande do Sul state, Brazil, of which 75% contained residues below the LOQs.     

A concise and stereoselective chemoenzymatic synthesis of Sitophilate,the male-produced aggregation pheromone of Sitophilus granarius (L.)

(2S,3R)-Sitophilate, the male-produced aggregation pheromone of the granary weevil Sitophilus granarius (L.) was prepared stereoselectively using a novel chemoenzymatic approach in 50% overall yield. The synthetic design was based on an enantioselective fungal reduction of ethyl 2-methyl-3-oxopentanoate with a strain of Aureobasidium pullulans (CCM H1), followed by a Mitsunobu inversion at C3. The last step in the synthetic sequence was a lipase-mediated transesterification using the commercially available Candida antarctica B lipase (CaL B, Novozym 435) using microwave irradiation under solvent-free conditions.     

A green-emitting α-substituted β-diketonate Tb3+ phosphor for ultraviolet LED-based solid-state lighting

The α-substituted β-diketonate [Ln(3Cl-acac)₃(H₂O)₂] [Ln = Tb, Gd] complexes (with 3Cl-acac^– being 3-chloro-2,4-pentanedionate) were characterized by elemental analysis, infrared, ultraviolet (UV)-visible and photoluminescence spectroscopies. For comparison purposes regarding photoluminescence, the well-known [Tb(acac)₃(H₂O)₂] complex was also synthesized. By considering the phosphorescence spectra of [Gd(3Cl-acac)₃(H₂O)₂], the effect of chloride replacement of hydrogen on the triplet state energy of the 3Cl-acac ligand was revealed. To support the interpretation and rationalization of the experimental results, Time-dependent DFT calculations were performed on Tb(3Cl-acac)₃(H₂O)₂. Additionally, the possibility of Tb(3Cl-acac)₃(H₂O)₂ to be used as potential green-emitting phosphor material for solid-sate light emitting diodes was evaluated. A prototype was successfully fabricated coating a near-UV LED (370 nm) with the Tb(3Cl-acac)₃(H₂O)₂ complex.