Ammonium Methanol Research Articles

Adsorption and magnetic solid-phase extraction of NSAIDs from pharmaceutical wastewater using magnetic carbon nanotubes: Effect of sorbent dimensions, magnetite loading and competitive adsorption study

Abstract Magnetic carbon nanotubes (MCNT) of different dimensions and different magnetite-to-carbon nanotube (Mag:CNT) ratios were prepared and characterized for magnetic solid phase extraction (MSPE) of some non-steroidal anti-inflammatory drugs (NSAIDs) (ketoprofen (KET), diclofenac sodium (DIC) and ibuprofen (IBU)) from water prior to their HPLC determination. The results revealed that the best mixing ratio of (Mag:CNT) was at (1:1) ratio; long CNT was better than short CNT; the best external diameter was 60–100 nm. This sorbent was labeled as L-MCNT60-100 nm (1:1). The optimum MSPE-HPLC method was as follows: 150 mg of L-MCNT60-100 nm (1:1) sorbent was added to 50 mL solution containing KET, DIC and IBU at pH 5. The solution was shaken for 30 min and the sorbent was separated from the solution using an external magnet. The adsorbed analytes were eluted using 5 mL of 10% ammonia in methanol and the eluent was then injected into HPLC instrument. Figures of merit were estimated to be as follows (KET, DIC and IBU, respectively): detection limits: 0.4, 0.5, 0.5 μ g L−1; sensitivity: 3.13, 3.40, 1.46 L mg−1; %RSD range: [2.6–7.2], [2.2–5.1], [2.7–6.4] %; bias range (%): [(-26.8)–(14.0)], [(-7.4)–(17.0)], [(-8.4)–(17.8)]%. Application on tap water and pharmaceutical wastewater gave spiked recovery as follows: Tap water: KET: 103.7%( ± 5.4); DIC: 110.3%( ± 5.3); IBU: 70.1%( ± 6.5); Pharmaceutical wastewater: KET: 58.8%( ± 7.2); DIC: 48.9%( ± 5.9); IBU: 100.5%( ± 8.2). Adsorption studies were conducted to measure the adsorption capacity of the adsorbents where the effect of MCNT dimensions, magnetite loading and competitive adsorption were investigated.

Simultaneous Determination of Three 5-HT3Receptor Antagonists Accompanied by Stability Study Using Thin-Layer Chromatography–Densitometry

A thin-layer chromatographic (TLC)—densitometric method for the separation and simultaneous determination of 3 5-HT3 receptor antagonists, namely, tropisetron hydrochloride (TRP), granisetron hydrochloride (GRN), and ondansetron hydrochloride dihydrate (OND) was developed. Densitometric measurements were done at 285 nm for TRP and 305 nm for both OND and GRN using the reflectance—absorbance mode. Separation was carried out on silica gel TLC plates using chloroform—methanol—ammonia (10 m) (8:2:0.1, V/V) as the mobile phase. The three drugs have been separated with RF values of 0.23 ± 0.01, 0.63 ± 0.01, and 0.76 ± 0.01 for TRP, GRN, and OND, respectively. The limits of detection and quantification for linear regression analysis of the studied drugs ranged from 2.79 to 12.05 and from 8.45 to 36.50 ng per band, respectively, while for polynomial regression, the limits of detection and quantification for the studied drugs ranged from 3.40 to 15.51 and from 10.31 to 46.99 ng per band, respectively. The developed method was applied for determination of the studied drugs in pharmaceuticals and human plasma with good precision and accuracy. Stability-indicating thin-layer chromatographic method for the determination of OND in the presence of its degradation products under different conditions and subsequent kinetic study had been successfully applied.

Controlled PtIr nanoalloy as an electro-oxidation platform for methanol reaction and ammonia detection

Herein, a surfactant-free, ethylene glycol-mediated synthesis of PtIr nanoalloys was optimized. In particular, a post-synthesis treatment was identified as the key step in order to determine the nanoparticles size and their organization in the nanostructure, depending on the presence of a reducing agent and on pressure conditions. After synthesis, the as-obtained nanomaterials were broadly characterized: SEM and TEM images, EDX maps and XRD spectra showed the formation of nanorods with a few nanometers size and similar quantitative compositions of platinum and iridium. Afterward, the electrocatalytic activity towards the methanol oxidation reaction of the synthesized nanomaterials was tested and the best sample, treated under a hydrogen/nitrogen flow at 10 bar, exhibits a negligible onset potential (0.058 V) and a very high If/Ib ratio (2.5). Moreover, the aforementioned sample was tested as an electrochemical sensor for the detection of small traces of ammonia in an aqueous solution with a limit of detection of 4.88 μM. The sensor was tested also in simulated wastewater coming from the fertilizer industry, showing proper operation and excellent selectivity.

Selective and facile deacetylation of pentacyclic triterpenoid under methanolic ammonia condition and unambiguous NMR analysis

The acetyl ester plays an important role for protection of the hydroxyl groups in carbohydrates synthesis. In the present study, we described an efficient deprotection of acetyl group of pentacyclic triterpenoid by using methanolic ammonia in THF solution. Good selectivity for cleaving gal-C2-OAc group of 3β-hydroxy-olean-12-en-28-oic acid 28-N-2,3,4,6-tetra-O-acetyl-β-d-galactopyranoside (3) was achieved in the presence of methanolic ammonia within 4 h at low temperature (−60 °C) in a yield of 56%. The reaction disclosed here provides a new method for the synthesis of C2 selective modified carbohydrates, which is more useful than conventional synthesis procedure that usually requires many steps including temporary regioselective protection and deprotection. When the reaction temperature was increased from −60 °C to room temperature, the cleavage of the other three acetyl groups of galactose in an order of C4-OAc > C3-OAc > C6-OAc was observed. Based on this study, a plausible route for the deacetylation reaction has been proposed.

Effect of Quercetin Rich Onion Extracts on Bacterial Quorum Sensing.

Quorum sensing (QS) regulates bacterial gene expression and studies suggest quercetin, a flavonol found in onion, as a QS inhibitor. There are no studies showing the anti-QS activity of plants containing quercetin in its native glycosylated forms. This study aimed to evaluate the antimicrobial and anti-QS potential of organic extracts of onion varieties and its representative phenolic compounds quercetin aglycone and quercetin 3-β-D-glucoside in the QS model bacteria Chromobacterium violaceum ATCC 12472, Pseudomonas aeruginosa PAO1, and Serratia marcescens MG1. Three phenolic extracts were obtained: red onion extract in methanol acidified with 2.5% acetic acid (RO-1), white onion extract in methanol (WO-1) and white onion extract in methanol ammonium (WO-2). Quercetin 4-O-glucoside and quercetin 3,4-O-diglucoside were identified as the predominant compounds in both onion varieties using HPLC-DAD and LC-ESI-MS/MS. However, quercetin aglycone, cyanidin 3-O-glucoside and quercetin glycoside were identified only in RO-1. The three extracts showed minimum inhibitory concentration (MIC) values equal to or above 125 μg/ml of dried extract. Violacein production was significantly reduced by RO-1 and quercetin aglycone, but not by quercetin 3-β-D-glucoside. Motility in P. aeruginosa PAO1 was inhibited by RO-1, while WO-2 inhibited S. marcescens MG1 motility only in high concentration. Quercetin aglycone and quercetin 3-β-D-glucoside were effective at inhibiting motility in P. aeruginosa PAO1 and S. marcescens MG1. Surprisingly, biofilm formation was not affected by any extracts or the quercetins tested at sub-MIC concentrations. In silico studies suggested a better interaction and placement of quercetin aglycone in the structures of the CviR protein of C. violaceum ATCC 12472 than the glycosylated compound which corroborates the better inhibitory effect of the former over violacein production. On the other hand, the two quercetins were well placed in the AHLs binding pockets of the LasR protein of P. aeruginosa PAO1. Overall onion extracts and quercetin presented antimicrobial activity, and interference on QS regulated production of violacein and swarming motility.

Regioselective single pot C3-glycosylation of strophanthidol using methylboronic acid as a transient protecting group.

This manuscript describes a single pot protocol for the selective introduction of unprotected sugars to the C3 position of the cardiotonic steroid strophanthidol. These reactions proceed with high levels of regiocontrol (>20:1 rr) in the presence of three other hydroxyl functionalities including the C19 primary hydroxyl group and could be applied to different sugars to provide the deprotected cardiac glycosides upon work up (5 examples, 77-69% yield per single operation). The selective glycosylation of the less reactive C3 position is accomplished by the use of traceless protection with methylboronic acid that blocks the C5 and C19 hydroxyls by forming a cyclic boronic ester, followed by in situ glycosylation and a work up with ammonia in methanol to remove the boronic ester and the carbohydrate ester protecting groups.

Analysis of the retention behavior of selected antiarrhythmics by means of thin-layer chromatography

The retention behavior of ivabradine, its 11 related compounds, diltiazem and verapamil has been examined by thin-layer chromatography using non-polar stationary phase (RP-18) and the following mobile phases: methanol-6.25% aqueous ammonia, tetrahydrofuran - 6.25% aqueous ammonia, and also polar stationary phase (silica gel) with tetrahydrofuran – 6.25% methanolic ammonia as mobile phase. In the examined chromatographic systems, linear relationships were established between the retention coefficients, RM0 and m, and molecular properties of the investigated antiarrhythmic drugs. The Quantitative Structure Retention Relationship (QSRR) modeling was performed with use of the stepwise multiple linear regression, in order to select the most important molecular properties which influence the retention behavior. The developed models revealed that apart from lipophilicity also the molecular volume (V), and the hydrogen bond basicity (B) of the tested compounds are the most important for the retention behavior in the examined chromatographic systems.

ESTIMATION OF SORPTION PROPERTIES OF BOTTOM SEDIMENTS OF THE KUYALNIK ESTUARY

Work is sanctified to research of adsorption descriptions and basic physical and chemical properties and chemical distribution of standards of the ground sedimentations (GS) selected from a superficial layer (0-18 cm) in north part of aquatorium of the Kuyalnik estuary. The sorption of water and methanol vapor, ammonia and sulfur dioxide was determined in the static conditions. Sorption isotherms have been analyzed according to Brunauer-Emmett-Teller theory of polymolecular sorption, the monolayer capacity and the heat of sorption of water molecules and methanol in the first layer have been determined. The essential difference between the values of the specific surface, calculated by different methods (Brunauer-Emmett-Teller theory, Kiselev). The differences in their values are is natural, as for the calculations data are used to measure the sorption of water vapor at different sites of isotherms (for BET - the area at p/ps = 0,01±0,4; Kiselyov at p/ps = 0,55±0,98). Under static conditions the absorption of sulfur dioxide and the ammonia by bottom sediments samples was studied. It is shown the SO2 uptake process, flogoing predominantly through the chemisorption mechanism, occurs only in the presence of «free» water formed after the formation of the monolayer. The maximum sorption capacity on dry samples is 2,6 mg/g. The limiting ammonia sorption capacity (19,1 mg/g at P = 13,3 kPa), unlike sulfur dioxide, in our view, is mainly determined by their organic component, namely the presence in it of humic acids having polyfunctional groups, such as phenolic, hydroxyl groups, carboxylic acid groups that are capable of adsorbing, absorbing and selectively extracting various organic and inorganic substances. The dispersion, organomineral composition, biological, bactericidal activity and sorption characteristics of the samples of bottom sediments (peloids) Kuyalnik estuary in relation to a number of markers of different nature (water vapor, methanol, ammonia, sulfur dioxide) show prospects for use as a cheap natural raw material to expand the range of sorbents for environmental purposes, entero - and vulnerosorbtion (application of sorbents) for medicine, cosmetology.

A Validated Quantification of Sudan Red Dyes in Spicery using TLC and a 16-bit Flatbed Scanner.

We present a video-densitometric quantification method for Sudan red dyes in spices and spice mixtures, separated by TLC. Application was done band-wise in small dots using a 5μL glass pipette. For separation, the RP-18 plates (20 × 20cm with fluorescent dye; Merck, Germany, 1.05559) were developed in a vertical developing chamber without vapor saturation from the starting point to a distance of 70mm by using acetonitrile, methanol, and aqueous ammonia solution (25%; 8 + 1.8 + 0.2, v/v) as mobile phase. The quantification is based on direct measurements using an inexpensive 16-bit flatbed scanner for color measurements (in red, green, and blue). Evaluation of only the green channel makes the measurements very specific. For linearization, an extended Kubelka-Munk expression for data transformation was used. The range of linearity covers more than two magnitudes and lies between 20 and 500ng. The extraction from a 2g sample with acetonitrile, evaporation, and reconstitution to 200μL with methanol and the band-wise application (7mm) of a 10μL sample allows a statistically defined LOD of less than 500ppb of Sudan red dyes. To perform the analysis, a separation chamber, RP-18 plates, 5μL glass pipettes, and a 16-bit flatbed scanner for 105 € are needed; therefore, the separation method is inexpensive, fast, and reliable.

Simultaneous quantification of chlorpheniramine, pseudoephedrine, and ibuprofen in antitussive preparation by high-performance liquid chromatography and thin-layer chromatography–densitometric methods

Simple, accurate, precise, sensitive, and validated high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC)‒densitometric methods were developed for the simultaneous determination of chlorpheniramine maleate (CPM), pseudoephedrine HCl (PSE), and ibuprofen (IBF) in tablet dosage form. In method A, reversed-phase (RP)-HPLC analysis was performed on Zorbax C8 column (150 mm × 4.6 mm, 5 μm particle size i.d.), using a mobile phase consisting of methanol–acetonitrile–distilled water (pH 4) using orthophosphoric acid in the ratio (80:10:10, v/v) and flow rate of 0.7 mL min−1. Quantification was achieved with ultraviolet (UV) detection at 220 nm. In method B, TLC analysis was carried out on an aluminum-backed sheet of silica gel 60 F254 layer using ethyl acetate‒methanol‒ammonia (8:2:0.8, v/v) as the mobile phase. Quantification was carried out with UV detection at 262 nm. The validation of the proposed methods was applied according to the International Conference on Harmonization (ICH)...

Validated stability-indicating high-performance liquid chromatography and thin-layer chromatography methods for the determination of zopiclone in pharmaceutical formulation

Two novel, sensitive, and selective stability-indicating chromatographic methods were described for the analysis of zopiclone (ZOP) in the presence of its degradation products, namely, 7-oxo-6,7-dihydro-5H-pyrrolo[3,4-b]pyrazin-5-yl-4-methylpiperazine-1-carboxylate (hydrolytic DEG) and 5H-pyrrolo[3,4-b]pyrazine-5,7(6H)-dione (oxidative DEG), in drug substance and product. The first method was an isocratic reversed-phase high-performance liquid chromatography (RP-HPLC) using Inertsil ODS3 (250 × 4 mm, 5 μm) column. Upon using HPLC, the run time could be reduced, and actually, the solvents consumption decreased. Quantification was achieved by detection wavelength at 237 nm, based on peak area. Chromatographic separation was performed over the range of 1–10 μg mL−1 with limits of detection (LOD) and quantification (LOQ) of 0.18 and 0.55 μg mL−1 and a mean recovery of 99.98 ± 0.55. The analysis was achieved at 30°C using a mixture of acetonitrile and water (50:50 v/v) as the mobile phase. The second method was thin-layer chromatography (TLC) applied for the separation and analysis of zopiclone in the presence of its alkaline, acidic, and oxidative degradation products. Chromatography was performed on silica gel 60 F254 plates with ethyl acetate–methanol–ammonia 33% (17:2:1 v/v) as the mobile phase. Successful resolution was observed with significant difference in the RF values, followed by densitometric measurement at 303 nm. Evaluation was carried out over the range of 0.1–2 μg per spot with a mean recovery of 100.52% ± 0.24. The developed methods were successfully applied to the analysis of ZOP in bulk powder, laboratory-prepared mixtures containing different percentages of its degradation products, and pharmaceutical dosage form. The degradation products were separated by HPLC as well as identified by TLC, infrared (IR), and mass spectrometry (MS) to confirm its structures and elucidate degradation pathway. The developed methods were validated as per the International Conference on Harmonization (ICH) guidelines. The results obtained by the proposed methods were statistically compared with the reported methods revealing high accuracy and good precision.

The Volatile Composition of Comet C/2017 E4 (Lovejoy) before its Disruption, as Revealed by High-resolution Infrared Spectroscopy with iSHELL at the NASA/IRTF

Abstract In 2017 April, we acquired comprehensive high-resolution spectra of newly discovered comet C/2017 E4 (Lovejoy) as it approached perihelion, and before its disintegration. We detected many cometary emission lines in the range (2.8–5.3) μm, in four customized instrument settings (L1-c, L3, Lp1-c, and M1) of iSHELL—the new near-IR high-resolution immersion echelle spectrograph at NASA/IRTF (Maunakea, Hawaii). We identified 12 molecular species: nine primary volatiles (H2O, HCN, NH3, CO, C2H2, C2H6, CH4, CH3OH, H2CO) and three product species (CN, NH2, OH). We detected 85 H2O emission lines from 12 water vibrational bands across L1-c and M1 settings. The many detected water emission lines enabled retrieval of accurate measures for ortho- and para-H2O independently, thereby reducing systematic uncertainty in the derived ortho–para ratio and nuclear spin temperature. Excitation analyses and emission profile analyses were performed for all species, and molecular abundance ratios relative to water are compared with values found for other Oort Cloud comets in our infrared database. Abundance ratios are consistent for most species, with the exception of underabundant methanol and overabundant ammonia in E4.

Isolation of the anionic toxin monofluoroacetate from a decontamination foam matrix

Oxidizing decontamination agents such as the Vanguard-Allen CASCAD foam can be used to contain the blast from an improvised explosive device and can also be used to decontaminate conventional chemical weapons via hydrolysis or oxidation reactions. However, chemical analysis of such foams remains a challenge due to complex sample matrices that can contain chlorine bleaches (such as dichloroisocyanurate), co-solvents, and surfactants. To overcome this issue, we have developed a combined liquid-liquid extraction and solid phase extraction (SPE) protocol that isolates toxicologically relevant anionic analytes, such as monofluoroacetate (CH2FCO2−), from such a matrix. The protocol development was monitored by 1H decoupled 19F NMR spectroscopy, which gave a limit of detection of 0.1 mM for CH2FCO2− using a 20 min acquisition time. After separation using a strong anion exchange (SAX) SPE column and an eluent of 10% ammonia in methanol, the analyte was derivatised using 2,4-dichloroaniline and dicyclohexylcarbodiimide (DCC) before GC–MS analysis. This resulted in a limit of detection of 5.9 μM for monofluoroacetate in a CASCAD decontamination foam matrix.

A Dedicated Mass Spectrometer Tuning Method for SFC–MS and Evaluation of Two Different Linear Restrictor Types Used in the Operation of a Split Flow Pre-Back Pressure Regulator SFC–MS Interface

The operation of a SFC–MS system has been improved. The SFC–MS interface uses a post-column make-up flow of liquid whose supply line to the SFC–MS interface mixing tee is equipped with an injection valve. Prior to analysis, this arrangement permits a stable flow of a dilute tune solution of analyte(s) for the exact amount of time required to optimize mass spectrometry tuning. Advantageously, with this arrangement tuning is performed in the presence of the exact split flow and same composition of SFC mobile phase and make-up liquid to be used for subsequent SFC–MS operation. The SFC–MS interface was constructed to provide a pre-back pressure regulator split flow to the mass spectrometer using a linear restrictor. Two different linear restrictors constructed from either 50 µm i.d. PEEK tubing or 25 µm i.d. fused silica tubing were evaluated. For best electrospray performance, each restrictor required a different post-column make-up flow rate. The use of either restrictor retained a high degree of chromatographic fidelity for the SFC separation of six pharmaceutical compounds using a cyanopropyl column with a mobile phase of supercritical fluid carbon dioxide modified with methanol and aqueous ammonia solution. Each restrictor provided a different level of SFC–MS performance for each of the six pharmaceutical compounds tested. Based upon overall performance, a linear fused silica restrictor was selected to develop a chromatographic separation using on-line SFC–MS for three structurally very similar monensin sodium salt analogues that are not directly amenable to off-line SFC using UV/Vis detection.

Synthesis of Cyclic and Acyclic Pyrimidine Nucleosides Analogues with Anticipated Antiviral Activity.

A convenient method for preparation of cyclic and acyclic nucleosides was achieved by alkylation of 6-(2,4-dichlorophenoxymethyl) pyrimidine-2,4-dione (1) with a variety of acyclic and cyclic activated sugar analogues, namely (2-acetoxyethoxy)methyl acetate (3), 2-(acetoxymethoxy)propane-1,3-diyl dibenzoate (4), benzyloxymethyl acetate (5), 2-acetoxy-5-(benzoyloxymethyl)tetrahydrofuran-3,4-diyl dibenzoate (12), 5-chloro-2-((4-chlorobenzoyloxy)methyl) tetrahydrofuran-3-yl 4-chlorobenzoate (13) and 2-(acetoxymethyl)-6-bromotetrahydro-2H-pyran-3,4,5-triyl triacetate (14), respectively. Deprotection of the synthesized nucleosides was achieved by using methanolic ammonia. The structures of the newly synthesized nucleoside analogues were fully characterized by analytical methods (mass spectrometry, 1H NMR, 13C NMR, and elemental analysis).

Validated thin-layer chromatographic method for alternative and simultaneous determination of two anti-gout agents in their fixed dose combinations

AbstractA rapid, simple and sensitive thin-layer chromatography (TLC) spectrodensitometric method was developed for the simultaneous determination of colchicine and probenecid in their binary mixtures. The two drugs were quantitatively separated using silica gel 60 F254 as stationary phase and toluene–ethyl acetate–methanol–ammonia (30:20:20:0.1, v/v/v/v) as mobile phase with UV detection at 248 nm for both drugs and at 354 nm for colchicine alone. Both drugs were efficiently separated with Rf values of 0.33±0.03 and 0.60±0.03 for probenecid and colchicine, respectively. The linearity was found to be 16–320 and 120–2400 (ng/band) with quantitation limits of 17.59 and 225.82 ng/band for colchicine and probenecid, respectively, at 248 nm. At 354 nm, the linearity range of colchicine was found 16–240 ng/band with a quantitation limit of 54.03 ng/band. The experimental determination ranges were greatly extended with lower quantitation limits (15.60 and 116.13 ng/band for colchicine and probenecid, respectively at 248 nm, and 13.20 for colchicine at 354 nm) and correlation coefficients were improved when polynomial regression analysis was used. The quadratic model was found to be the best fit for all responses. The method has been validated according to the International Conference on Harmonization (ICH) guidelines providing good correlation coefficients (0.9997-0.9999) for both drugs, and it has been successfully applied in the determination of both drugs in their commercial dosage form without interference from excipients.

Determination of metformin hydrochloride, melamine and dicyandiamide in metformin hydrochloride preparations by tandem dual solid phase extraction cartridges-high performance liquid chromatography-electrospray ionization multi-stage mass spectrometry

A method for the confirmation and quantification of metformin hydrochloride and its relative substances melamine and dicyandiamide using tandem dual solid phase extraction (SPE) cartridges and high performance liquid chromatography-electrospray ionization multi-stage mass spectrometry (HPLC-ESI-MSn) was developed. The samples were extracted with anhydrous ethanol containing 0.1% (v/v) acetic acid under ultrasound-assisted conditions. The extracts were concentrated and purified using Cleanert PCX and C18 tandem dual solid phase extraction cartridges, and eluted with 5% (v/v) ammonia methanol solution. The separation was performed on a Kromasil-C18 column (100 mm×4.6 mm, 3.5 μm) with gradient elution. The detection was performed in selected ion monitoring (SIM) mode using electrospray ionization multi-stage mass spectrometry. The external standard method was used for quantification. The extraction solvents, types of SPE cartridges and eluents were optimized by comparing the recoveries under different conditions. The results showed that the detector response of each target compound was linear in corresponding mass concentration ranges with the correlation coefficients (r2) ≥ 0.9992. The limits of detection (LODs) and the limits of quantification (LOQs) of the three analytes were 1.48-13.61 μg/kg and 5.96-45.67 μg/kg, respectively. The recoveries of the three analytes were 65.02%-118.33% spiked at low, medium and high levels. The relative standard deviations (RSDs) were no more than 13.41%. The method is reliable, easy, and has a better purification effect. The method can be applied to the routine analysis of metformin hydrochloride and its relative substances melamine and dicyandiamide in different preparations of metformin hydrochloride.

Synthesis of β-Nicotinamide Riboside Using an Efficient Two-Step Methodology.

A two-step chemical method for the synthesis of β-nicotinamide riboside (NR) is described. NR has achieved wide use as an NAD+ precursor (vitamin B3) and can significantly increase central metabolite NAD+ concentrations in mammalian cells. β-NR can be prepared with an efficient two-step procedure. The synthesis is initiated via coupling of commercially available 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose with ethyl nicotinate in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf). 1 H NMR showed that the product was formed with complete stereoselectivity to produce only the β-isomer in high yield (>90% versus starting sugar). The clean stereochemical result suggests that the coupling proceeds via a cationic cis-1,2-acyloxonium-sugar intermediate, which controls addition by nucleophiles to generate predominantly β-stereochemistry. The subsequent deprotection of esters in methanolic ammonia generates the desired product in 85% overall yield versus sugar. © 2017 by John Wiley & Sons, Inc.

Determination of Seven Urinary Metabolites of Organophosphate Esters using Liquid Chromatography-Tandem Mass Spectrometry

Abstract A simple method was developed for simultaneous determination of seven urinary metabolites of organophosphate esters (OPs) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Based on different physical and chemical properties of these OP metabolites, their enrichment and clean-up were performed through solid phase extraction to obtain high-efficient solid phase extraction cartridges, and the washing and elution conditions were optimized. At the same time, the kinetic parameters and mass spectrometry parameters were investigated for getting the qualitative and quantitative characteristic ion pairs for analysis of each metabolites. The results showed that the Oasis WAX solid phase extraction cartridge was suitable for sample enrichment and clean-up, and the optimal elution solvents were 2 mL of 5% ammonia in methanol and 2 mL of methanol. The recoveries of six analytes ranged from 60.5 to 104.0%, whereas the recovery of diethyl phosphate ranged from 17.8% to 36.2%. The complete baseline separations of seven analytes were achieved under optimized chromatographic conditions. The limits of detection and limits of quantification of the seven analytes ranged from 0.005 to 0.2 μg L−1 and 0.02 to 0.5 μg L−1, respectively. The intra-day and inter-day precision results (RSD = 15.4%) showed that this method had good stability and reproducibility. This method was subsequently used to determine OP metabolites in 10 urine samples from the general population in Guangzhou city. The concentrations of the seven OP metabolites in urine samples ranged from 0.5 to 6.7 μg L−1.

Synthesis and Characterization of Alkylamine-Functionalized Si(111) for Perovskite Adhesion With Minimal Interfacial Oxidation or Electronic Defects.

We investigated synthetic strategies for the functionalization of Si(111) surfaces with organic species containing amine moieties. We employed the functionalized surfaces to chemically "glue" perovskites to silicon with efficient electron transfer and minimal oxidation leading to deleterious recombination at the silicon substrate. A two-step halogenation-alkylation reaction produced a mixed allyl-methyl monolayer on Si(111). Subsequent reactions utilized multiple methods of brominating the allyl double bond including reaction with HBr in acetic acid, HBr in THF, and molecular bromine in dichloromethane. Reaction with ammonia in methanol effected conversion of the bromide to the amine. X-ray photoelectron spectroscopy (XPS) quantified chemical states and coverages, transient-microwave photoconductivity ascertained photogenerated carrier lifetimes, atomic force microscopy (AFM) quantified perovskite-silicon adhesion, and nonaqueous photoelectrochemistry explored solar-energy-conversion performance. The HBr bromination followed by the amination yielded a surface with ∼10% amine sites on the Si(111) with minimal oxide and surface recombination velocity values below 120 cm s-1, following extended exposures to air. Importantly, conversion of amine sites to ammonium and deposition of methylammonium lead halide via spin coating and annealing did not degrade carrier lifetimes. AFM experiments quantified adhesion between perovskite films and alkylammonium-functionalized or native-oxide silicon surfaces. Adhesion forces/interactions between the perovskite and the alkylammonium-functionalized films were comparable to the interaction between the perovskite and native-oxide silicon surface. Photoelectrochemistry of perovskite thin films on alkylammonium-functionalized n+-Si showed significantly higher Voc than n+-Si with a native oxide when in contact with a nonaqueous ferrocene+/0 redox couple. We discuss the present results in the context of utilizing molecular organic recognition to attach perovskites to silicon utilizing organic linkers so as to inexpensively modify silicon for future tandem-junction photovoltaics.