Determination of psilocybin in hallucinogenic mushrooms by reversed-phase liquid chromatography with fluorescence detection

The determination of psilocybin was carried out by reversed-phase liquid chromatography (HPLC) with fluorescence (FL) detection. Psilocybin was labeled with 5-dimethylaminonaphthalene-1-[N-(2-aminoethyl)]sulfonamide (DNS-ED) at 60 °C for 4 h in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) as the activation reagent. The resulting derivative was separated on a Mightysil RP-18 GP column (150 mm × 4.6 mm, i.d. 3 μm) with the mixture of 50 mM ammonium acetate (AcONH₄) and CH₃CN, and detected at 539 nm (excitation at 321 nm). The structure of the derivative was identified by HPLC-ESI-MS. A good linear relation of the calibration curve of psilocybin was observed under the proposed conditions for labeling, separation and detection. The quantification limit was 4.4 ng in 1 mg dried mushroom. The proposed procedure was successfully used for the determination of psilocybin in real samples. The contents of psilocybin in six magic mushrooms by the proposed HPLC-FL method were less than 20.0 ng in 1 mg dried samples.     

Ultra-performance liquid chromatographic-electrospray mass spectrometric determination (UPLC-ESI-MS) of O-demethylated metabolite of paeonol in vitro: Assay development, human liver microsome activities and species differences

A simple and sensitive method for determination of the O-demethylation activity of rat, dog, minipig, and human liver micrsomes toward paeonol using ultra-performance liquid chromatography with mass detection (UPLC-MS) has been developed. The method uses chemically synthesized O-demethylated metabolite of paeonol (2,4-dihydroxyacetophenone, DHA) as a standard for method validation. Validation was done with respect to specificity, linearity, detection limit, recovery, stability, precision and accuracy. The chromatographic separation was achieved on a UPLC BEH C₁₈ column (50 mm × 2.1 mm i.d., 1.7 μm), with phase of acetonitrile-water (ratio 30:70). Selective ion reaction (SIR) monitor was specific for paeonol, DHA and I.S. The method was specific since there were no interference peaks from the reaction matrix. The calibration curve for DHA was linear from 0.5-100 μM with r² = 0.9999. The newly developed method has good precision and accuracy. The method was successfully used to determine the kinetics of DHA activities toward paeonol in liver microsomes from different species. Dog liver microsomes (DLMs) were the most active in paeonol O-demethylation (709.7 pmol/min/mg protein) followed by rat liver microsomes (RLMs) (579.6 pmol/min/mg protein), HLMs (569.3 pmol/min/mg protein), and then minipig liver microsomes (PLMs) (417.3 pmol/min/mg protein). The developed method was appropriated for rapid screening paeonol O-demethylation activity in liver microsomes from different species.     

Fast method for monitoring phospholipase A2 activity by liquid chromatography–electrospray ionization mass spectrometry

A new liquid chromatography–electrospray ionization mass spectrometry (LC–ESI-MS) method for the fast determination of phospholipase A₂ (PLA₂) activity has been developed. For the first time, the method allows the parallel detection of glycerophosphatidylcholine (GroPCho) as PLA₂ substrate as well as of its products fatty acid (FA) and lyso-GroPCho. ESI-MS was carried out in negative ion mode, detecting the FA as [M − H]⁻ ions and the lyso-GroPCho and GroPCho as acetate adducts [M + Ac]⁻. Utilizing a fast gradient on a short C₅-modified silica gel column with 3 μm particles, five GroPChos, five FAs and six lyso-GroPChos could be separated according to their chain length in less than 3 min. A very high average chromatographic efficiency of 41,200 theoretical plates (plate height 0.5 μm) was achieved for the separation of the GroPChos. The method was applied for monitoring the release of arachidonic acid (20:4 FA) and 1-stearoyl-lyso-sn-GroPCho (18:0 GroPCho) from unilamellar vesicles of 1-stearoyl-2-arachidonoyl-sn-GroPCho (18:0/20:4 GroPCho). With a limit of detection of 0.5 pmol (total amount injected on column) for the FAs and lyso-GroPChos and 1.5 pmol for the GroPChos as well as a linear range of 1.5 decades, the method has proven to be suitable for the monitoring of different secretory PLA₂ (sPLA₂) conversions. Furthermore, it was applied to screen a small library of PLA₂ inhibitors for their activity towards sPLA₂ type V and snake venom of Bothrops moojeni. In both cases, active samples could be directly identified. With its short analysis time, its high chromatographic efficiency and the parallel detection of substrate and all products, the developed LC–ESI-MS method is well suited for the analysis of PLA₂ activity.     

Development of a microbioreactor with ecto-nucleoside triphosphate diphosphohydrolase 2 (NTPDase2) immobilized on a polyacrylamide-coated capillary at the outlet

A simple and fast method of immobilization of cell membrane suspension containing human ecto-nucleoside triphosphate diphosphohydrolase 2 (NTPDase2) on a polyacrylamide-coated capillary was developed. The enzyme microbioreactor was prepared by hydrodynamic injection of a small plug of the polycationic electrolyte hexadimethrine bromide (HDB) followed by a suspension of an enzyme-containing membrane preparation. In order to shorten the enzyme assay time and to increase the throughput of the assay, the capillary was coated from the outlet end and all injections were performed from the outlet end of the capillary. For the monitoring of the enzymatic reaction, the substrate ATP dissolved in reaction buffer (140 mM NaCl, 5 mM KCl, 1 mM MgCl₂, 2 mM CaCl₂, and 10 mM Hepes, pH 7.4, internal standard: 10 μM UMP) in the absence or presence of inhibitor was injected electrokinetically and incubated in the microbioreactor for 1 min with 1 kV of applied voltage. Then, the electrophoretic separation of the reaction products was initiated by applying a constant current of 60 μA. A 50 mM phosphate buffer (pH 6.5) was used for the separations and the products were detected by UV absorbance at 260 nm. The new method was compared with an at-capillary-inlet method without immobilization of the enzyme. The results (K_m values, K_i values for inhibitor) obtained with both methods were similar and comparable with literature data. The developed outlet immobilized enzyme microreactor using a coated capillary is very fast, simple and most economic allowing multiple use of the enzyme.     

Enzyme sensor for the electrochemical detection of the marine toxin okadaic acid

An enzyme sensor for the electrochemical detection of the marine toxin okadaic acid (OA) has been developed. The strategy was based on the inhibition of immobilised protein phosphatase (PP2A) by this toxin and the electrochemical measurement of the enzyme activity by the use of appropriate enzyme substrates, electrochemically active after dephosphorylation by the enzyme. Colorimetric inhibition assays have demonstrated the PP2A from human red blood cells to be more sensitive and to provide a wider linear range than the one produced by genetic engineering. Catechyl monophosphate (CMP) and p-aminophenyl phosphate (p-APP) have been tested as enzyme substrates, the former providing higher electrochemical currents at convenient working potentials (+450 mV vs. Ag/AgCl). Biosensors with 19.1 and 5.0 U of immobilised enzyme have been applied to the OA detection. Whereas the 19.1-U biosensor has provided higher electrochemical currents and more reliable determinations, the 5.0-U one has attained a lower 50% inhibition coefficient (IC₅₀) value (22.19 in front of 154.84 μg L⁻¹) and a larger working range (2.69-171.87 in front of 42.97-171.87 μg L⁻¹). The analysis of toxicogenic dinoflagellate extracts with both biosensors and the comparison with the colorimetric assay and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) have demonstrated the applicability of the developed electrochemical devices as screening biotools for the assessment of the toxicity of a sample.     

Novel methods for the quantification of (2E)-hexadecenal by liquid chromatography with detection by either ESI QTOF tandem mass spectrometry or fluorescence measurement

Sphingosine-1-phosphate lyase (SPL) is the only known enzyme that irreversibly cleaves sphingosine-1-phosphate (S1P) into phosphoethanolamine and (2E)-hexadecenal during the final step of sphingolipid catabolism. Because S1P is involved in a wide range of physiological and diseased processes, determining the activity of the degrading enzyme is of great interest. Therefore, we developed two procedures based on liquid chromatography (LC) for analysing (2E)-hexadecenal, which is one of the two S1P degradation products. After separation, two different quantification methods were performed, tandem mass spectrometry (MS) and fluorescence detection. However, (2E)-hexadecenal as a long-chain aldehyde is not ionisable by electrospray ionisation (ESI) for MS quantification and has an insufficient number of corresponding double bonds for fluorescence detection. Therefore, we investigated 2-diphenylacetyl-1,3-indandione-1-hydrazone (DAIH) as a derivatisation reagent. DAIH transforms the aldehyde into an ionisable and fluorescent analogue for quantitative analysis. Our conditions were optimised to obtain the outstanding limit of detection (LOD) of 1 fmol per sample (30 μL) for LC–MS/MS and 0.75 pmol per sample (200 μL) for LC determination with fluorescence detection. We developed an extraction procedure to separate and concentrate (2E)-hexadecenal from biological samples for these measurements. To confirm our new methods, we analysed the (2E)-hexadecenal level of different cell lines and human plasma for the first time ever. Furthermore, we treated HT-29 cells with different concentrations of 4-deoxypyridoxine (DOP), which competitively inhibits pyridoxal-5-phosphate (P5P), an essential cofactor for SPL activity, and observed a significant decrease in (2E)-hexadecenal relative to the untreated cells.     

Hydrogen peroxide-sodium hydrosulfite chemiluminescence system combined with high-performance liquid chromatography for determination of 1-hydroxypyrene in airborne particulates

In this research, a highly sensitive chemiluminescence method based on a sodium hydrosulfite (NaHSO₃)-hydrogen peroxide (H₂O₂) reaction for the determination of 1-hydroxypyrene (1-OHP) was developed. The response of this system was linear in the range from 0.5 to 50 pmol (R² = 0.9983). The limit of detection for 1-OHP was 100 fmol (S/N = 3). 1-OHP in airborne particulates was well separated from interfering compounds using an ODS column with 75% methanol as the mobile phase in isocratic mode. The proposed method was successfully applied to determine the 1-OHP in airborne particulates collected in Kanazawa, Japan. The average concentration of 1-OHP in the atmosphere was 2.0 pg/m³ (9.2 fmol/m³).     

Carbamidocyclophanes F and G with anti-Mycobacterium tuberculosis activity from the cultured freshwater cyanobacterium Nostoc sp.

Two new (1 and 2) and three known (3–5) carbamidocyclophanes were isolated from a cultured freshwater cyanobacterium Nostoc sp. (UIC 10274) obtained from a sample collected at Des Plaines, Illinois. Their planar structures and stereoconfigurations were determined by extensive spectroscopic analysis including 1D/2D NMR experiments, HRESIMS as well as CD spectroscopy. Carbamidocyclophane F (1) showed potent anti-Mycobacterium tuberculosis activity in the microplate Alamar blue assay and low-oxygen-recovery assay with MIC values of 0.8 and 5.4 μM, respectively. Carbamidocyclophane F (1) also displayed antimicrobial activities against the gram positive bacteria Staphylococcus aureus and Enterococcus faecalis with MIC values of 0.1 and 0.2 μM, respectively. Carbamidocyclophane F (1) and Carbamidocyclophane G (2) both showed antiproliferative activity against MDA-MB-435 and HT-29 human cancer cell lines with IC₅₀ values in the range from 0.5 to 0.7 μM.     

Aqua bridged Cu2 dimer of a heptadentate N4O3 coordinating ligand: Synthesis,structure and magnetic properties

The N₄O₃ coordinating heptadentate imidazolidinyl phenolate ligand, H₃L (2-(2′-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) forms with Cu(II) a rare aqua bridged complex [{Cu₂(μ-L)(μ-H₂O)}₂](ClO₄)₂ · 4.5H₂O (1 · 4.5H₂O). Complex 1 · 4.5H₂O contains two crystallographically different but chemically equivalent dinuclear [Cu₂(μ-L)(μ-H₂O)]⁺ cationic units in the asymmetric unit. The copper atoms of each dinuclear unit are in a distorted square-pyramidal environment and are held together by phenolate, imidazolidinyl and aqua bridges with a Cu···Cu separation of av. 3.34 Å. The compound exhibits a very weak antiferromagnetic exchange interaction (J = −0.77 cm⁻¹, ? = −2 J?₁?₂) between the two copper(II) (S = 1/2) ions. The ¹H NMR spectrum of the complex shows a total of 17 hyperfine shifted peaks, as expected from the idealized C_s symmetry of the compound, spread over a very large window of chemical shift, spanning about 250 ppm. The complex, having an appropriate intermetallic separation for catechol binding, shows catecholase like activity in MeCN at 25 °C, with the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ).     

Real time monitoring uracil excision using uracil-containing molecular beacons

As a highly conserved damage repair protein, UDG excises uracil bases through its glycosylase activity. We report here an alternative fluorescence method for UDG assay with high accuracy and sensitivity by applying uracil-modified molecular beacons as substrates. The detection limit of UDG is 0.005 U mL⁻¹. The K_M and k_cat are 0.89 ± 0.1 μM and 210 ± 10 min⁻¹, respectively. The method is applied to screening inhibitors and the results indicate that both of the 5-FU and cisplatin can inhibit UDG activity with the IC₅₀ values of 6.1 ± 0.52 mM and 3.2 ± 0.24 mM, respectively. Furthermore, the combination of uracil-modified molecular beacons and nuclease inhibitor makes the new method possible to specifically detect UDG activity in cell-free extracts and serum. Taken together, the simple, rapid and sensitive method has potential relevance for a variety of applications, such as molecular diagnosis and screening of UDG inhibitors.     

Synthesis of a liposome incorporated 1-carboxyalkylxanthine-phospholipid conjugate and its recognition by an RNA aptamer

RNA or DNA aptamers have received much attention in recent literature as therapeutic agents and chromatographic matrices, however, their use in analytical methodologies is relatively unexplored. We describe here investigations aiming to combine this promising technology with versatile liposomes in a competitive assay format. Thus, a phospholipid derivative of an unsymmetrical 1,3-disubstituted xanthine (1-carboxyethyl-3-methylxanthine-DPPE) was prepared for incorporation into the lipid bilayers of dye-encapsulating liposomes. Its synthesis and characterization using GC-MS, ¹H NMR, and HPLC are described. Equilibrium filtration experiments using enzyme linked immunosorbent assays (ELISAs) were completed to assess the affinity for theophylline of an unmodified RNA aptamer and one that had been modified on the 3′ end with biotin. A dissociation constant (K_d) for theophylline with the unmodified RNA aptamer of 0.9 μM and biotinylated aptamer of 1.0 μM was determined which showed that this modification did not affect the aptamer's affinity using this technique. The observed K_d values correlated well to the previously reported value of 0.6 μM. Experiments were also carried out in a competitive manner with the prepared 1-carboxypropyl-3-methylxanthine intermediate, and the final 1-carboxypropyl-3-methylxanthine-DPPE conjugate once it had been incorporated into the bilayers of liposomes. The K_d value for 1-carboxypropyl-3-methylxanthine was approximately 2.7 μM. Finally, successful binding to theophylline-analog-tagged liposomes in a competitive assay format was shown versus liposomes prepared without the tag.     

An easy-to-use excimer fluorescence derivatization reagent, 2-chloro-4-methoxy-6-(4-(pyren-4-yl)butoxy)-1,3,5-triazine,for use in the highly sensitive and selective liquid chromatography analysis of histamine in Japanese soy sauces

In this study, a novel pre-column excimer fluorescence derivatization reagent, 2-chloro-4-methoxy-6-(4-(pyren-4-yl)butoxy)-1,3,5-triazine (CMPT), was developed for polyamines, specifically histamine. By CMPT derivatization, the polyamines, histamine and tyramine were converted to polypyrene derivatives, and emitted intra-molecular excimer fluorescence at 475 nm. This could clearly be distinguished from the normal fluorescence emitted from reagent blanks at 375 nm. Unlike conventional excimer fluorescence derivatization reagents, CMPT is chemically stable and its reactivity sustained over at least 36 days even in solution state. We successfully applied this reagent to the sensitive and selective analysis of histamine in different kinds of Japanese commercial soy sauces. The detection and quantification limits of histamine were 15 and 50 μg L⁻¹, respectively, equating to 1.35 pmol and 4.5 pmol for a 6 μL injection. This sensitivity helped the direct analysis of soy sauce samples only treated by one-step liquid–liquid extraction without concentration. The histamine levels of commercial soy sauce samples (koikuchi, usukuchi and saishikomi) investigated were 1.24–768.5 mg L⁻¹.     

On-bead fluorescent DNA nanoprobes to analyze base excision repair activities

DNA integrity is constantly threatened by endogenous and exogenous agents that can modify its physical and chemical structure. Changes in DNA sequence can cause mutations sparked by some genetic diseases or cancers. Organisms have developed efficient defense mechanisms able to specifically repair each kind of lesion (alkylation, oxidation, single or double strand break, mismatch, etc). Here we report the adjustment of an original assay to detect enzymes’ activity of base excision repair (BER), that supports a set of lesions including abasic sites, alkylation, oxidation or deamination products of bases. The biosensor is characterized by a set of fluorescent hairpin-shaped nucleic acid probes supported on magnetic beads, each containing a selective lesion targeting a specific BER enzyme. We have studied the DNA glycosylase alkyl-adenine glycosylase (AAG) and the human AP-endonuclease (APE1) by incorporating within the DNA probe a hypoxanthine lesion or an abasic site analog (tetrahydrofuran), respectively. Enzymatic repair activity induces the formation of a nick in the damaged strand, leading to probe's break, that is detected in the supernatant by fluorescence. The functional assay allows the measurement of DNA repair activities from purified enzymes or in cell-free extracts in a fast, specific, quantitative and sensitive way, using only 1 pmol of probe for a test. We recorded a detection limit of 1 μg mL⁻¹ and 50 μg mL⁻¹ of HeLa nuclear extracts for APE1 and AAG enzymes, respectively. Finally, the on-bead assay should be useful to screen inhibitors of DNA repair activities.     

Preconcentration and determination of ultra trace amounts of arsenic(III) and arsenic(V) in tap water and total arsenic in biological samples by cloud point extraction and electrothermal atomic absorption spectrometry

A new approach for developing a cloud point extraction-electrothermal atomic absorption spectrometry has been described and used for determination of arsenic. The method is based on phase separation phenomenon of non-ionic surfactants in aqueous solutions. After reaction of As(V) with molybdate towards a yellow heteropoly acid complex in sulfuric acid medium and increasing the temperature to 55 °C, analytes are quantitatively extracted to the non-ionic surfactant-rich phase (Triton X-114) after centrifugation.To decrease the viscosity of the extract and to allow its pipetting by the autosampler, 100 μl methanol was added to the surfactant-rich phase. An amount of 20 μl of this solution plus 10 μl of 0.1% m/v Pd(NO₃)₂ were injected into the graphite tube and the analyte determined by electrothermal atomic absorption spectrometry.Total inorganic arsenic(III, V) was extracted similarly after oxidation of As(III) to As(V) with KMnO₄. As(III) was calculated by difference. After optimization of the extraction condition and the instrumental parameters, a detection limit (3σ_B) of 0.01 μg l⁻¹ with enrichment factor of 52.5 was achieved for only 10 ml of sample. The analytical curve was linear in the concentration range of 0.02-0.35 μg l⁻¹. Relative standard deviations were lower than 5%. The method was successfully applied to the determination of As(III) and As(V) in tap water and total arsenic in biological samples (hair and nail).     

Development of an HPLC method for the determination of mexiletine in human plasma and urine by solid-phase extraction

A sensitive and specific high-performance liquid chromatography (HPLC) method has been developed and validated for the quantification of mexiletine (MEX) in human plasma and urine. It uses solid-phase extraction (SPE) followed by an automated reversed-phase HPLC with a pre-column derivatization with 4-chloro-7-nitrobenzofurazan (NBD-CI) and UV-vis Absorbance detection. The process was set as: the UV-vis Absorbance wavelength was set at 458 nm. Chromatographic separation was performed on a Phenomenex-C₁₈ Column (Aqua, 150 mm × 4.6 mm i.d. with 5 μm particle size) with the mobile phase consisting of acetonitrile and water (80:20, v/v), and the flow rate was set at 1.0 mL min⁻¹. Calibration of the overall analytical procedure gave a linear signal (r > 0.9998) over a MEX concentration range of 0.2-2.0 μg mL⁻¹ in human plasma and urine. The detection limit in plasma and urine was 0.1 μg mL⁻¹. Intra- and inter-day precision of the assay at three concentrations within this range were 0.31-2.50%. The high specificity and sensitivity have been achieved by this fast method (total run-time <6 min). The method has been successfully validated in human plasma and urine and it has been shown to be precise, accurate and reliable.     

The measurement of cyclic nucleotide phosphodiesterase 4 activities via the quantification of inorganic phosphate with malachite green

A spectrometric method was investigated to measure the activities of recombinant human cyclic nucleotide phosphodiesterase 4 (PDE4), based on the use of malachite green (MLG) to quantify phosphate released from adenosine-5′-monophosphate (AMP) by the action of calf intestinal alkaline phosphatase (CIAP). Glycerol at 2% stabilized the complex between MLG and phosphomolybdate, whose absorbance at 630 nm was proportional to phosphate concentrations with resistance to common substances in PDE4 reaction mixtures except papaverine. CIAP had the Michaelis-Menten constant (K_m) of (12.0 ± 2.1) μM (n = 3) for AMP at pH 7.4, and was resistant to EDTA below 0.20 mM. By the coupled end-point assay at 30.0 U L⁻¹ CIAP with reaction durations within 30 min, the rates to release phosphate in PDE4 reaction mixtures containing 10.0 mM MgCl₂ and 0.10 mM EDTA linearly responded to the amounts of PDE4 over wide ranges. Meanwhile, K_m of PDE4 was (8.8 ± 0.2) μM (n = 2), zinc ion inhibited PDE4 and rolipram had the inhibition constant about 10 nM. These results supported that by the coupled end-point assay, this method was promising to screen of PDE inhibitors that had no interference with the MLG assay of phosphate.     

Development of a class selective immunoassay for the type II pyrethroid insecticides

A general and broad class selective enzyme-linked immunosorbent assay was developed for the type II pyrethroid insecticides, such as cypermethrin, deltamethrin, cyhalothrin, cyfluthrin, fenvalerate, esfenvalerate and fluvalinate. Polyclonal antibodies were generated by immunizing with a type II pyrethroid immunogen ((RS)-α-cyano-3-phenoxybenzyl (RS)-cis,trans-2,2-dimethyl-3-carboxyl-cyclopropanecarboxylate) conjugated with thyroglobulin. Antisera were screened against nine different coating antigens. The antibody-antigen combination with the most selectivity for type II pyrethroids such as cypermethrin was further optimized and tested for tolerance to co-solvent, pH and ionic strength changes. The IC₅₀s of the optimized immunoassay were 78 μg l⁻¹ for cypermethrin, 205 μg l⁻¹ for cyfluthrin, 120 μg l⁻¹ for cyhalothrin, 13 μg l⁻¹ for deltamethrin, 6 μg l⁻¹ for esfenvalerate, 8 μg l⁻¹ for fenvalerate and 123 μg l⁻¹ for fluvalinate. No cross-reactivity was measured for the type I pyrethroids such as permethrin, bifenthrin, phenothrin, resmethrin and bioresmethrin. This assay can be used in monitoring studies to distinguish between type I and II pyrethroids.     

Analysis of salicylic acid based on the fluorescence enhancement of the As(III)-salicylic acid system

A new, simple and sensitive spectrofluorimetric method for the determination of salicylic acid (λ_ex = 315 nm, λ_em = 408 nm) using As(III) as a sensitizing reagent has been investigated by measuring the increase of fluorescence intensity of salicylic acid due to the complexation of As(III)-salicylic acid in presence of sodium dodecyl sulfate (SDS) 10⁻³ M. Under optimum conditions, a significant relationship was obtained between the fluorescence intensity and salicylic acid concentration. A linear calibration curve was obtained in the range 13.8-13812 μg l⁻¹ with product-moment correlation coefficient (R) 0.99985 and detection limit 4.2 μg l⁻¹. The R.S.D. is 2.35% (n = 5).The method was applied successfully to the determination of salicylic acid in human serum.     

Synthesis, structure and optical limiting properties of organoruthenium-chalcogenide clusters

Treatment of Ru₃(CO)₁₂ with Ph₃PS affords the compounds [Ru₃(μ₃-S)₂(CO)_9 − n(PPh₃)_n] (n = 1 (1a), 2 (2a)) and [Ru₃(μ₃-S)(μ₃-CO)(CO)₇(PPh₃)₂] (3a) as the major products. Single crystal X-ray diffraction studies of [Ru₃(μ₃-S)₂(CO)₈(PPh₃)] and [Ru₃(μ₃-S)(μ₃-CO)(CO)₇(PPh₃)₂] show these two classes of compounds to contain square pyramidal Ru₃S₂ and trigonal pyramidal Ru₃S metal cores, respectively, with the latter being isostructural to the analogous selenide cluster compound. The clusters [Ru₃(μ₃-E)₂(CO)_9 − n(PPh₃)_n] (E = S, n = 1; E = Se, n = 2) readily undergo ligand displacement reactions with PPh₃ to afford the compounds [Ru₃(μ₃-E)₂(CO)₆(PPh₃)₃] (E = S, 5a; E = Se 5b). The mixed chalcogenide cluster, [Ru₃(μ₃-S)(μ₃-Se)(CO)₇(PPh₃)₂] (6), was prepared from the reaction of [Ru₃(μ₃-S)(μ₃-CO)(CO)₇(PPh₃)₂] and SePPh₃. The optical limiting properties of the complexes 1a,b, 2a,b, 5a,b have been measured by the Z-scan technique employing 40 ns pulses at 523 nm; power limiting was observed for all clusters under our experimental conditions.     

Mesoporous TiO2 nanoparticles for highly sensitive solid-phase microextraction of organochlorine pesticides

Mesoporous TiO₂ nanoparticles were synthesized with the hydrothermal method and characterized by powder X-ray diffraction (PXRD) and transmission electron microscope (TEM). Then a superior solid-phase microextraction (SPME) fiber was fabricated by sequentially coating the stainless steel fiber with silicone sealant film and mesoporous TiO₂ powder. The developed fiber possessed a homogeneous surface and a long life-span up to 100 times at direct immersing (DI) extraction mode. Under the optimized conditions, the extraction efficiencies of the self-made 17 μm TiO₂ fiber for six organochlorine pesticides (OCPs) were higher than those of the two commercial fibers (65 μm PDMS/DVB and 85 μm PA fibers) which were much thicker than the former. As for analytical performance, low detection limits (0.08–0.60 ng L⁻¹) and wide linearity (5–5000 ng L⁻¹) were achieved under the optimal conditions. The repeatabilities (n = 5) for single fiber were between 2.8 and 12.3%, while the reproducibilities (n = 3) of fiber-to-fiber were in the range of 3.7–15.7%. The proposed fiber was successfully applied to the sensitive analysis of OCPs in real water samples and four of the six analytes were detected from the rainwater and the lake water samples.