Acetonitrile Solution Research Articles

Rapid determination of five halobenzoquinones in aquatic products by QuEChERS-ultra performance liquid chromatography-tandem mass spectrometry

Halobenzoquinones (HBQs), which are emerging chlorinated disinfection byproducts (DBPs), have attracted increasing attention because they are frequently detected in treated tap water, entrainment water, etc. These compounds are mainly generated during the water treatment process using chlorine, chloramine, and chlorine dioxide as disinfectants, and display more toxic effects than regulated DBPs, such as trihalomethane and haloacetic acid. HBQs have been recognized as potential bladder carcinogens and are harmful to the nervous system. Additionally, they can exert genotoxic effects and cause oxidative damage to DNA and proteins. The risk of HBQs in aquatic products is expected to rise because the disinfection of public facilities has significantly increased in recent years. Therefore, developing a sensitive and accurate analytical method to detect HBQs in aquatic products is of great importance. Several analytical methods, including gas chromatography, gas chromatography-mass spectrometry, electrochemical methods, liquid chromatography, and liquid chromatography-tandem mass spectrometry, can be used to identify and quantify HBQs in water. However, to the best of our knowledge, no reports on the determination of HBQ levels in aquatic products are yet available. Further, pretreatment is essential for HBQ determination because of the complex matrix effects of aquatic products. Herein, a sensitive and accurate method based on the QuEChERS technique coupled with ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed for the simultaneous determination of five HBQs in aquatic products. For the QuEChERS procedure, the pretreatment conditions, such as the extraction solvent and adsorbent species, were systematically optimized. The sample was extracted with 10 mL of 10% methanol acetonitrile solution (containing 0.1% formic acid), dehydrated, and centrifuged with sodium chloride and anhydrous magnesium sulfate. The supernatant was purified using a QuEChERS packing material consisting of 50 mg N-propylethylenediamine (PSA), 30 mg of graphitized carbon black (GCB), and 30 mg of neutral alumina (Al2O3), dried with nitrogen, and concentrated. The five HBQs were separated on a Waters ACQUITY UPLC BEH C18 column (100 mm×2.1 mm, 1.7 μm) using 0.25% acetonitrile formate solution and 0.25% formic acid aqueous solution as the mobile phase under a gradient elution program and then detected using UPLC-MS/MS with negative electrospray ionization (ESI-) under multiple reaction monitoring (MRM) mode. Quantitative analysis was performed using a matrix-matched external standard method. The five HBQs achieved rapid separation within 6 min, indicating that the proposed method has a much shorter separation time compared with previous studies. The matrix effect was evaluated by establishing a matrix-matched calibration curve. The results showed that 2,5-dichloro-1,4-benzoquinone (2,5-DCBQ) presented a matrix-enhancing effect, whereas the other HBQs displayed matrix-inhibiting effects. In particular, tetrachlorobenzoquinone (TCBQ) exhibited strong inhibitory effects. Under the optimized experimental conditions, the five HBQs demonstrated good linear relationships in the range of 1.0-50.0 μg/L, with correlation coefficients (r)≥0.9992. The detection limits of the method were 0.15-0.8 μg/kg, and the recoveries of the target compounds were 85.9%-116.5%. The relative standard deviations were 1.4%-8.2%, which indicates good reproducibility. The proposed method was successfully applied to actual sample detection, and 2,6-dichloro-3-methyl-1,4-benzoquinone (2,6-DCMBQ) was detected in grass carp. The proposed method is convenient, sensitive, accurate, and suitable for the simultaneous determination of five HBQs in aquatic products. Moreover, the developed method provides a reliable reference for the routine monitoring of trace HBQs in food samples.

Photoredox-HAT Catalysis for Primary Amine α-C-H Alkylation: Mechanistic Insight with Transient Absorption Spectroscopy.

The synergistic use of (organo)photoredox catalysts with hydrogen-atom transfer (HAT) cocatalysts has emerged as a powerful strategy for innate C(sp3)-H bond functionalization, particularly for C-H bonds α- to nitrogen. Azide ion (N3-) was recently identified as an effective HAT catalyst for the challenging α-C-H alkylation of unprotected, primary alkylamines, in combination with dicyanoarene photocatalysts such as 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN). Here, time-resolved transient absorption spectroscopy over sub-picosecond to microsecond timescales provides kinetic and mechanistic details of the photoredox catalytic cycle in acetonitrile solution. Direct observation of the electron transfer from N3- to photoexcited 4CzIPN reveals the participation of the S1 excited electronic state of the organic photocatalyst as an electron acceptor, but the N3• radical product of this reaction is not observed. Instead, both time-resolved infrared and UV-visible spectroscopic measurements implicate rapid association of N3• with N3- (a favorable process in acetonitrile) to form the N6•- radical anion. Electronic structure calculations indicate that N3• is the active participant in the HAT reaction, suggesting a role for N6•- as a reservoir that regulates the concentration of N3•.

Cleft Receptor for the Recognition and Extraction of Tetrahedral Oxyanions

We report the design and synthesis of a new cleft-shaped bis-urea receptor for the recognition of tetrahedral oxyanions from a foldameric N,N′-dimethyl-N,N′-diphenylurea scaffold. The receptor forms 3:1 host–guest complexes with sulfate, phosphate, and arsenate anions in the solid state by readily binding them through hydrogen bonding. 1H NMR analysis of binding events in a competitive medium (DMSO-d6/H2O, 90:10) revealed that the receptor has a strong and selective affinity for arsenate (Ka(3:1) = 2.41 (±0.79) × 108 M–3) in comparison with phosphate and no affinity for sulfate. The receptor extracts the three oxyanions from water into chlorinated organic solvents when the tetra-n-butyl ammonium ion is used as a cationic support. The receptor also crystallizes out the arsenate anion from water with faster kinetics in acetonitrile solution with a similar cationic support.

Origin of Solvent Stabilization at Superconcentrated Electrolyte/Electrode Interfaces Revealed by Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy

Superconcentrated electrolyte solutions have attracted much attention because of their ability to stabilize solvent molecules for high-voltage rechargeable batteries. However, the stabilization mechanism has not been fully understood because of the lack of an in situ observation of the relevant interface. In the present study, we investigated the interfaces of platinum electrodes and acetonitrile solutions containing dilute and superconcentrated lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) using in situ heterodyne-detected vibrational sum frequency generation as well as ex situ vibrational sum frequency generation spectroscopies. The results showed that the structures of the electrode interfaces are remarkably different with these two solutions and indicate that acetonitrile decomposes in the dilute solution, whereas the TFSI– anion decomposes in the superconcentrated solution.

A Highly Selective and Sensitive Sequential Recognition Probe Zn2+ and H2PO4- Based on Chiral Thiourea Schiff Base.

A series of novel chiral thiourea fluorescent probes HL1-HL6 were designed and synthesized from (1R,2R)-1,2-diphenylethylenediamine, phenyl isothiocyanate, and different substituted salicylic aldehydes. All of the compounds were confirmed by 1H NMR, 13C NMR, and HRMS. They exhibit high selectivity and sensitivity to Zn2+ in the presence of nitrate ions with the detection limit of 2.3 × 10-8 M (HL5). Meanwhile, their zinc (II) complexes (L-ZnNO3) showed continuous response to H2PO4- in acetonitrile solution. The identification processes could further be verified by supramolecular chemistry data analysis, X-ray single-crystal diffraction analysis, and theoretical study. The research provides reliable evidence for an explanation of the mechanism of action of thiourea involved in coordination, which is important for the application of thiourea fluorescent probes. In short, the sensors HL1-HL6 based on chiral thiourea Schiff base will be promising detection devices for Zn2+ and H2PO4-.

Quantification of cefaclor in human plasma using SIL-IS LC-ESI-MS/MS for pharmacokinetics study in healthy Chinese volunteers.

A steady, high-efficiency, and precise liquid chromatography-electrospray ionization-tandem mass spectrometry method was established and validated using cefaclor-d5 as the stable isotope-labeled internal standard for quantification of cefaclor in human plasma. One-step protein precipitation was applied to extract human plasma samples using methanol as precipitant. An Ultimate XB C18 column (2.1 × 50.0mm, 5.0μm) was used to achieve chromatographic separation. Mobile phases of gradient elution were an aqueous solution containing 0.1% formic acid (mobile phase A) and an acetonitrile solution containing 0.1% formic acid (mobile phase B). Electrospray ionization in positive-ion mode was applied to detect under multiple reaction monitoring mode. Target fragment ion pairs of cefaclor and stable isotope-labeled internal standard, respectively, were m/z 368.2 → 191.1 and m/z 373.2 → 196.1. Linear range of this method was between 20.0 and 10,000.0ng/ml, with coefficient of determination (R2 ) >0.9900. Seven concentrations of quality control samples were used: 20.0ng/ml (lower limit of quantitation), 60.0ng/ml (low quality control), 650 ng/ml (middle quality control), 5000 ng/ml (arithmetic average middle quality control [AMQC]), 7500 ng/ml (high quality control), 10,000 ng/ml (upper limit of quantification), and 40,000 ng/ml (dilution quality control [DQC]). The method was validated for selectivity, lower limit of quantitation, linearity, accuracy, precision, recovery, matrix effect, dilution reliability, stability, carryover, and incurred sample reanalysis. This stable isotope-labeled internal standard liquid chromatography-electrospray ionization-tandem mass spectrometry approach has been successfully applied to study the pharmacokinetics of cefaclor dry suspension among healthy Chinese volunteers.

Solid AIE fluorophore molecule with specific response of amide functional group to detect gaseous phosgene

A new solid Aggregation-induced Emission (AIE) fluorophore molecule (Ind-CONH2) for specific response of gaseous phosgene based on the dehydration of primary amide to nitrile was designed. Specially, visible AIE color changes of Ind-CONH2 with phosgene could be observed directly from bright blue to greenish blue on a portable solid-state test-strip under a 365 nm ultraviolet (UV) lamp, which showed inverse color changes from colorless to bright blue in homogeneous acetonitrile solution due to intramolecular charge transfer (ICT) effect. LOD of Ind-CONH2 for phosgene in acetonitrile was 1.52 nM and that for gaseous phosgene was 0.16 ppm (response time was less than 10 s in acetonitrile and 3 min for gas), which had a good development prospect in detecting phosgene. Additionally, Ind-CONH2 was successfully used as an erasable fluorescent anti-counterfeiting ink.

Schottky contact of nano-BiOx thin film synthesized galvanostatically on stainless steel in acetonitrile

In this study, the nanosized-BiOx thin film (mostly Bi2O3 with a trace amount of Bi2O5) is electrochemically synthesized on stainless steel (SS) surface at room temperature. The coating process is carried out using the galvanostatic pulse deposition method in an acetonitrile solution containing bismuth tetrafluoroborate, tartaric acid, tetrabutylammonium hydroxide, and tetrabutylammonium tetrafluoroborate. The structural and morphological characterizations of thin film are performed by XRD, XPS, SEM-EDX, and AFM techniques. Accordingly, α- and δ-Bi2O3-based coating with oxygen vacancies contains a small amount of Bi2O5 on the SS surface. The BiOx thin film exhibits a rough surface with many nano-sized hills homogeneously distributed. Electrical characterization is conducted with electrochemical impedance spectroscopy, current-voltage, and Hall effect measurements. The pseudoresistance with the most drastic change increases with rising potential and decreases again after reaching its maximum value at the open circuit potential. It could be inferred that the composition (oxidation states or oxygen deficiency) of the Bi2O3-based film varies according to the applied potential. The n-type Schottky behavior is observed at the SS/BiOx interface. Furthermore, the n-type SS/BiOx-based Schottky diode tested for endurance shows significant stability over 200 cycles.

Development of the spectrophotometric method for the determination of rosuvastatin in tablets by using bromophenol blue

The aim of the work was to develop a spectrophotometric method for the determination of rosuvastatin in tablets based on the reaction with BPB in compliance with the principles of «green» chemistry.
 Material and methods. Analytical equipment: two-beam UV-visible spectrophotometer Shimadzu model -UV 1800 (Japan), software UV-Probe 2.62, electronic laboratory balance RAD WAG AS 200/C. The following APIs, dosage forms, reagents and solvents were used in work: pharmacopoeial standard sample (CRS) of rosuvastatin calcium (Sigma-Aldrich, (≥ 98 %, HPLC)), BCG (Sigma-Aldrich, (≥ 98 %, HPLC)), "Rosuvastatin" tablets 10 mg, 15 mg, 20 mg, methanol (Honeywell, (≥ 99.9 %, GC)), ethanol (Honeywell, (≥ 99.9 %, GC)), chloroform (Honeywell, (≥ 99.9 %, GC)), acetonitrile (Honeywell, (≥ 99.9 %, GC)), and ethyl acetate (Honeywell, (≥ 99.7 %, GC)).
 Results and discussion. A spectrophotometric method for determining rosuvastatin by reaction with BPB in an acetonitrile solution using the absorption maximum at a wavelength of 595 nm has been developed. Stoichiometric ratios of reactive components were established, which were 1:1. The developed method for the quantitative determination of rosuvastatin was validated following the requirements of the SPhU. The analytical method was linear in the 7.99-23.97 μmol/L concentration range. The LOD and LOQ values were calculated to be 0.77 µmol/L and 2.36 µmol/L. According to the «greenness» pictogram of the analytical method using the AGREE method, the score was 0.77, indicating that the proposed spectrophotometric method for determining rosuvastatin was developed in compliance with the principles of «green» chemistry.
 Conclusions. An eco-friendly spectrophotometric method has been developed to quantitatively determine rosuvastatin in tablets based on the reaction with BPB. The appropriate sulfophthalein dye (BPB) and its concentration (4.00 x 10-4), the optimal eco-friendly solvent (acetonitrile), and the appropriate wavelength (595 nm) were chosen, and the sensitivity of the reaction was calculated. The analytical method was validated, and its possibility for use in the pharmaceutical analysis was shown

Singlet Oxygen Generation via an Electrochemical Reduction Method Assisted by a Ruthenium(II) Complex.

In this work, singlet oxygen (1O2) is unprecedently recorded in the electrochemical reduction of tris(2,2'-bipyridine)ruthenium(II) [Ru(bpy)32+] in an acetonitrile solution with dissolved oxygen, which is well characterized by the specific probe of Singlet Oxygen Sensor Greens and the technique of electron-spin resonance in this work. Importantly, this new electrochemical method to produce 1O2 shows higher efficiency than the conventional photodriven method. Furthermore, taken together with the inherent advantages of electrochemical techniques compared with the photochemical/chemical-driven method, this electrochemical method would inevitably show great promise in reactive-oxygen-species-related studies in the future.

Using the UPLC-QTOF-MS Fingerprinting Coupled with Clustering Analysis to Verify the Quality Control of Fritillaria przewalskii Maxim

Background: A method is proposed as follows to establish the ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) fingerprinting and content determination for Fritillaria przewalskii Maxim. (FPM). Materials and Methods: The separation was developed using an Acquity UPLC CSH C18 column (2.1 mm × 100 mm, 1.7 µm). The gradient elution was carried out with acetonitrile solution with 0.1% acetic acid (containing 0.01 mol L−1 ammonium acetate) as the mobile phase, with the flow rate of 0.4 mL min−1, column temperature of 30°C, and injection volume of 2 µL. Fourteen batches of samples were analyzed under the above chromatographic conditions to ascertain the fingerprint of FPM sourced in different areas. A total of 45 common peaks were selected for analysis. Two chromatographic peaks were identified by comparison with the standard compound, and simultaneous content determination of the two compounds was carried out. These two compounds were identified as two alkaloids, peiminine and peimisine. SPSS 25.0 and SIMCA 14.1 were used for cluster analysis (CA), principal component analysis (PCA), and orthogonal partial least squares discriminant analysis (OPLS-DA) on the peak area of the 45 common peaks of FPM. Results: Results from this showed that samples sourced from different regions could be successfully divided into three groups based on their origin. The contents of peiminine and peimisine in different batches of FPM ranged from 57.92 to 76.01 µg/g and 118.12 to 167.39 µg/g. A quick and convenient identification using UPLC fingerprinting combined with PCA was then established to differentiate among FPM samples from different growing regions. Conclusion: This method may prove to be helpful for the quality evaluation and control of FPM and related medicinal plants in the future.

Preparation, thermal properties and electrical conductivity of solutions of pyridinium ionic liquids with tetrachloroferrate anion

Thermal stability of N -alkylpyridinium tetrachloroferrates(III) [C5H5NR]FeCl4 [R = C4H9, (CH2)3CN, CH2C6H5, C8H17, C10H21] in air in the range of 25-600°C was studied, as well as the thermal stability of N -alkylpyridinium chlorides. The equivalent electrical conductivity of N -alkylpyridinium tetrachloroferrates(III) in acetonitrile solution at 25°C was investigated. The ionic association constants K a , the limiting molar electrical conductivity (λ0) and the standard Gibbs energy of the association (Δ G °) in acetonitrile solutions were calculated based on conductometric data by the Lee-Wheaton method.

Assessment of antioxidant and DPPH free radical scavenging activity of 1,2-dithiole-3-thione derivatives by using cyclic voltammetry, spectroscopic, and molecular docking studies

The antioxidant and the DPPH free radical scavenging activity of 4-phenyl-3H-1,2-dithiole-3-thione (DT1), 5-(4-fluorophenyl)−3H-1,2-dithiole-3-thione (DT2), 5-(4-phenyl-3-thioxo-3H-1,2dithiol-5-yl)-benzo[d]oxazole-2(3H)thione (DT3) and 4-methyl-5-((phenylamino)methyl)−3H-1,2-dithiole-3-thione (DT4) was investigated using cyclic voltammetry (CV) and electronic spectroscopy (ES) assays. The diminution in anodic peak current density of an acetonitrile solution of DPPH in the absence and presence of gradually increasing amounts of 1,2-dithiole-3-thione derivatives (DT) was successfully exploited for measuring the antioxidant activity and the DPPH free radical scavenging activity. The EC50 values obtained from the CV and ES experiments suggested that all compounds had potential DPPH radical scavenging ability with the derivative DT3 possessing the highest potency of 21.5 ± 1.30 from CV and 20.6 ± 1.05 from ES. A molecular docking simulation indicated that all DT derivatives interacted with amino acid residues of glutathione reductase via hydrogen bonding and hydrophobic interactions. Based on the inhibitory concentration and docking score values, compound DT4 was the second inactive compound against the glutathione reductase enzyme having values equal to 41.4 µM and a docking score of −25.6 kJ/mol respectively. Toxicity perdition studies revealed that compounds DT1 and DT2 were non-toxic.

Functionalized Graphene from Electrochemical Exfoliation of Graphite toward Improving Lubrication Function of Base Oil

Electrochemical exfoliation of graphene is an environmentally friendly method, which enables mass production. Herein, three ionic liquids (ILs) with the same imidazole cation were used to exfoliate graphite into functionalized graphene, as a lubricant additive in an acetonitrile solution. Chemical and structural characterization revealed the relationship between the functionalization density of graphene and the concentration of IL, showing higher concentrations with higher densities. The exfoliated graphene hybrid oil displayed good dispersion because of a high functionalization density. More importantly, the different anions affected the tribological properties of the exfoliated graphene. Among them, the exfoliated graphene with 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]) possessed the best tribological performance, and the average friction coefficient and wear volume were reduced by 32% and 39%, respectively. Through the characterization of worn surfaces and wear debris, the lubrication mechanism and structural evolution of the functionalized graphene were illustrated in detail. The good lubrication function was attributed to the formation of a tribo-film and the disorder transformation of the graphene structure. The simultaneous exfoliation and functionalization of graphene offers a promising advanced lubricant for industrial fabrication.

Decorated crown ethers as selective ion traps: Solvent’s role in crown’s preference towards a specific ion

Deviation of sodium and potassium concentrations from their optimal values in living organisms is associated with severe health conditions, thus their precise determination in blood samples requires design of sensitive sensors. Additionally, excess of the two alkali cations should be removed from drinking water. Crown ethers are well-known metal ion traps, as careful choice of crown’s size and its substituents might tune it towards favoring a specific ion. It has been proved experimentally that dibrominated bithiophene crown ethers with five and six oxygen atoms selectively capture the Na+ and the K+ ion, respectively (Giovannitti et al., Adv. Funct. Mater. 26, 2016, 514) in acetonitrile solution. In the present contribution, we analyzed the nature of ion–crown, ion–solvent, and crown–solvent interactions, and demonstrated that the solvent molecules are responsible for the decorated crown’s preference for a particular alkali cation. While past research focused on the ring size and the ion radius compatibillity, which is important for a formation of a stable ion–crown complex, our findings highlight the decisive role of solvent molecules in the selectivity of crown ethers toward particular cations.

Determination of Oseltamivir in Human Plasma by HPLC-MS/MS.

A procedure for the determination of oseltamivir in human plasma by high-performance liquid chromatography( tandem mass spectrometry (HPLC-MS/MS) was proposed and validated. Arapid and easy-to-use method of liquid(liquid extraction with ethyl acetate using venlafaxine as an internal standard was used during sample preparation. The addition of benzoic acid to aqueous acetonitrile solutions of the analyte was shown to prevent its oxidative degradation. The detection limit and limit of quantitation were 0.08 and 0.30 ng/mL, respectively; the calibration range, 0.3-200 ng/mL (R 2 = 0.9937); the total analysis time, 3.2 min. The within- and between-run accuracy ranged from 97 to 105%. The precision was <10%. The proposed procedure was characterized by selective determination of the analyte, the absence of significant matrix effects, the ability to dilute samples with high analyte concentrations, and satisfactory extraction recovery (≥89%). The analyte was stable when stored in plasma samples (4 h at room temperature, 31 d at (80°C, after three freeze(thaw cycles) and extracts under autosampler storage conditions (24 h at 15°C). The procedure was successfully used for oseltamivir quantitation in actual plasma samples from healthy volunteers obtained during a bioequivalence study of the new generic drug.

Studies on Electrochemical Properties of Polycarbazole Prepared Via Self-Support Polymerization and Self-Doping

Mixed glassy zirconium-tin phosphate, g-Zr0.64.Sn.0.36(HPO4)2.3H2O(g-ZrSnP), nano fibrous cerium phosphate, Ce(HPO4)2 2,9H2O(nCePf), and mixed glassy zirconium-tin phosphate / fibrous cerium phosphate nanocomposite membrane, [g-Zr0.64 Sn0.36 (HPO4)2]0.25 [Ce(HPO4)2]0.75 ..4.43H2O, were prepared and characterized. By chemical , x-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform spectroscopy (FTIR), Zirconium tin mole ratio were estimated using (EDAX). Novel [g-Zr0.64 Sn0.36 (HPO4)2]0.25 [Ce(HPO4)2]0.75 / polycarbazole nanocomposite membrane was prepared via self-support polymerization of carbazole, which was promoted by the reduction of Ce(iv) phosphate present in the inorganic matrix. Possible explanation is nCePf present on the surface of the nanocomposite is attacked by carbazole, converted to cerium (III) orthophosphate(CePO4). The resultant polycarbazole was characterized by C,H,N analysis, SEM ,FT-IR. UV-Vis and electrical conductance measurements. From elemental (C,H,N) analysis, the amount of polycarbazole present in the composite found to be (2.15 % in wt.). Polycarbazole is considered as one of modern material used in solar cells, furthermore it has become an important material for optoelectronic applications in recent years. The dc conductivity of polycarbazole nanocomposite membrane at 280C (using RC-Circuit) found to be equal to 3x10-5 Scm-1, range of semi-conductors. We suggest self-doping occurred on polymerization, which is due to H+ present in (O3POH)2 groups of [g-Zr0.64 Sn0.36 (HPO4)2]0.25. The electrochemistry of resultant polycarbazole in acetonitrile solution for a range of concentrations from 1.06 x10-4 to 2.19 x 10–3 mol dm-3 was carried out using CV techniques. Investigation of its electrochemical properties affords insight into the mechanisms for their oxidation and reduction, therefore provides the basis for evaluating the stabilities of the material and for designing novel polycarbazole-derived materials with desired properties as well as new devices. That will be discussed.

Critical Analysis of Association Constants between Calixarenes and Nitroaromatic Compounds Obtained by Fluorescence. Implications for Explosives Sensing.

The binding behaviour of two ureido-hexahomotrioxacalix[3]arene derivatives bearing naphthyl (1) and pyrenyl (2) fluorogenic units at the lower rim towards selected nitroaromatic compounds (NACs) was evaluated. Their affinity, or lack of it, was determined by UV-Vis absorption, fluorescence and NMR spectroscopy. Different computational methods were also used to further investigate any possible complexation between the calixarenes and the NACs. All the results show no significant interaction between calixarenes 1 and 2 and the NACs in either dichloromethane or acetonitrile solutions. Moreover, the fluorescence quenching observed is only apparent and merely results from the absorption of the NACs at the excitation wavelength (inner filter effect). This evidence is in stark contrast with reports in the literature for similar calixarenes. A naphthyl urea dihomooxacalix[4]arene (3) is also subject to the inner filter effect and is shown to form a stable complex with trinitrophenol; however, the equilibrium association constant is greatly overestimated if no correction is applied (9400 M-1 vs 3000 M-1), again stressing the importance of taking into account the inner filter effect in these systems.

Simultaneous Determination of 26 Pesticide Residues in Traditional Chinese Medicinal Leeches by Modified QuEChERS Coupled with HPLC-MS/MS.

A Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) pretreatment technique combined with HPLC-MS/MS was established to detect 26 pesticides in traditional Chinese medicinal leeches. The sample was extracted by acetonitrile solution with sodium acetate-0.1% (v/v) acetic acid as a buffer system, then cleaned up by a mixture of 750 mg of MgSO4, 150 mg of C18, and 150 mg of PSA, separated by an ACQUITY BEH C18 column, and determined in the dynamic multiple reaction mode. Under the optimized conditions, the peak areas of the 26 pesticides in leeches showed good linearity (r > 0.99) between their mass concentrations from 1 to 100 μg/L. At the spike levels of 10, 20, and 100 μg/kg, the recoveries of 26 pesticides in leeches were 72.9-101.6% with an RSD of 1.1-12.8%, an LOQ of 10 μg/kg, and an LOD of 0.1-5.4 μg/kg. This method is easy, rapid, sensitive, and practical and meets the requirements of pesticide residue detection standards.

Structure directing agent assisted solvothermal synthesis of octahedral WO3·nH2O large microcrystals: Study of electrochemical and optical properties

In the present study, the growth of tungsten trioxide crystals by solvothermal method was investigated in the presence of polyethylene glycol (PEG) and L-3,4-dihydroxyphenylalanine (L-dopa) as the structure directing agents in acetonitrile solution. The change of crystal faces consisting of stacked layers to very smooth facets is attributed to the change of the crystal growth mechanism from a three-step mechanism in the absence of PEG and L-dopa to a two-step mechanism in their presence. The rate of formation and growth of crystals in the presence of 5 w% of PEG increases significantly compared to those grown in the absence of PEG. The crystals solvothermally grown in the presence of L-dopa were of the octahedral WO3·0.5H2O with fully smooth faces, and those grown in the presence of PEG were the octahedral and rectangular microcrystals of WO3·H2O The transparency and electro-optical properties of the prepared crystal layers are improved in the presence of PEG. The dynamic potential electropolymerization of aniline and the formation of a thin layer of polyaniline on tungsten trioxide crystals were performed and the properties of the obtained core–shell hybrid film were studied. It was shown that covering the crystals with a very thin layer of polyaniline helps to stabilize their electrochemical and optical properties.