Proton‐Conductive 3D LnIII Metal–Organic Frameworks for Formic Acid Impedance Sensing

Metal‐organic frameworks (MOFs) as new classes of proton‐conducting materials have been highlighted in recent years. Nevertheless, the exploration of proton‐conducting MOFs as formic acid sensors is extremely lacking. Herein, we prepared two highly stable 3D isostructural lanthanide(III) MOFs, {(M(μ₃‐HPhIDC)(μ₂‐C₂O₄)_0.5(H₂O))?2 H₂O}_n (M=Tb ( ZZU‐1 ); Eu ( ZZU‐2 )) (H₃PhIDC=2‐phenyl‐1H‐imidazole‐4,5‐dicarboxylic acid), in which the coordinated and uncoordinated water molecules and uncoordinated imidazole N atoms play decisive roles for the high‐performance proton conduction and recognition ability for formic acid. Both ZZU‐1 and ZZU‐2 show temperature‐ and humidity‐dependent proton‐conducting characteristics with high conductivities of 8.95×10^?4 and 4.63×10^?4 S cm^‐1 at 98 % RH and 100 °C, respectively. Importantly, the impedance values of the two MOF‐based sensors decrease upon exposure to formic acid vapor generated from formic aqueous solutions at 25 °C with good reproducibility. By comparing the changes of impedance values, we can indirectly determine the concentration of HCOOH in aqueous solution. The results showed that the lowest detectable concentrations of formic acid aqueous solutions are 1.2×10^?2 mol L^?1 by ZZU‐1 and 2.0×10^?2 mol L^?1 by ZZU‐2 . Furthermore, the two sensors can distinguish formic acid vapor from interfering vapors including MeOH, N‐hexane, benzene, toluene, EtOH, acetone, acetic acid and butane. Our research provides a new platform of proton‐conductive MOFs‐based sensors for detecting formic acid.     

Hydrogen bonding in the hydroxysulfinyl radical‐formic acid‐water system: A theoretical study

Quantum chemical methods have been employed to evaluate the possible configurations of the 1:1 and 1:2 HOSO‐formic acid complexes and 1:1:1 HOSO‐formic acid‐water complexes. The first type of complex involves two H bonds, while the other two types comprise three H bonds in a ring. The complexes are relatively stable, with CBS‐QB3 computed binding energies of 14.3 kcal mol^?1, 23.4 kcal mol^?1, and 21.1 kcal mol^?1 for the lowest‐energy structures of the 1:1, 1:2, and 1:1:1 complexes, respectively. Complex formations induce a large spectral red‐shift and an enhancement of the IR intensity for the H‐bonded OH stretching modes relative to those in the parent monomers. TDDFT calculations of the low‐lying electronic excited states demonstrate that the complexes are photochemically quite stable in the troposphere. Small spectral shifts in comparison to the free HOSO radical suggest that the radical and the complexes would not be easily distinguishable using standard UV/vis absorption spectroscopy. © 2016 Wiley Periodicals, Inc.     

Novel Synthesis and Antimicrobial Activity of 3‐Substituted 5‐bromo‐7‐methyl‐1,2,4‐triazolo‐[3,4‐b]‐benzothiazoles

4‐Methyl acetanilide ( 1 ) on treatment with bromine in acetic acid, followed by hydrolysis with dilute HCl/NaOH solution, yielded 2‐bromo‐4‐methyl aniline ( 2 ), which on treatment with sodium thiocyanate in acetic acid afforded 2‐amino‐4‐bromo‐6‐methyl benzothiazole ( 3 ). Compound 3 in ethylene glycol was heated at 150°C with 80% hydrazine hydrate to get 4‐bromo‐2‐hydrazino‐6‐methyl benzothiazole ( 4 ). This hydrazino compound 4 on heating with formic acid for 3 h yielded 4‐bromo‐2‐hydrazinoformyl‐6‐methyl benzothiazole ( 5 ). Same compound 4 when heated independently with formic acid for 6 h/urea for 3 h/carbon disulfide in alkali afforded 5‐bromo‐7‐methyl ( 6 )/5‐bromo‐3‐hydroxy‐7‐methyl ( 7 )/5‐bromo‐3‐mercapto‐7‐methyl ( 8 )‐1,2,4‐triazolo‐[3,4‐b]‐benzothiazoles, respectively. Compound 4 on heating with acetic acid/acetic anhydride gave acetyl benzothiazolyl derivative 9 , which on cyclization with orthophosphoric acid yielded 5‐bromo‐3,7‐dimethyl‐1,2,4‐triazolo‐[3,4‐b]‐benzothiazole ( 10 ). All these newly synthesized compounds were screened for antimicrobial activity against Escherichia coli (Gram ?ve), Bacillus subtilis (Gram +ve), Erwinia carotovora, and Xanthomonas citri using ampicillin, streptomycin, and penicillin as a standard for comparison.     

Photochemically Engineering the Metal–Semiconductor Interface for Room‐Temperature Transfer Hydrogenation of Nitroarenes with Formic Acid

A mild photochemical approach was applied to construct highly coupled metal–semiconductor dyads, which were found to efficiently facilitate the hydrogenation of nitrobenzene. Aniline was produced in excellent yield (>99 %, TOF: 1183) using formic acid as hydrogen source and water as solvent at room temperature. This general and green catalytic process is applicable to a wide range of nitroarenes without the involvement of high‐pressure gases or sacrificial additives.     

Selective Utilization of the Methoxy Group in Lignin to Produce Acetic Acid

Selective transformation of lignin into a valuable chemical is of great importance and challenge owing to its complex structure. Herein, we propose a strategy for the transformation of methoxy group (‐OCH₃) which is abundant in lignin into pure highly valuable chemicals. As an example to apply this strategy, a route to produce acetic acid with high selectivity by conversion of methoxy group of lignin was developed. It was demonstrated that the methoxy group in lignin could react with CO and water to generate acetic acid over RhCl₃ in the presence of a promoter. The conversions of methoxy group in the kraft lignin and organosolv lignin reached 87.5 % and 80.4 %, respectively, and no by‐product was generated. This work opens the way to produce pure chemicals using lignin as the feedstock.     

The Interaction of Zinc(II) and Hydroxamic Acids and a Metal‐Triggered Lossen Rearrangement

The structure and reactivity of a complex of zinc(II), water, acetic acid, and acetohydroxamic acid, in which one of the acids is deprotonated, is investigated by means of mass spectrometry, labeling studies, and density functional calculations to unravel the exceptional binding properties of hydroxamic acids towards zinc‐containing enzymes at the molecular level. It is shown that acetohydroxamic acid is deprotonated in the complex, whereas acetic acid is present in its neutral form. The binding energies of the ligands towards zinc increase in the following order: water<acetic acid<acetohydroxamic acid. The structure of the complex and its fragmentation provide experimental evidence for the proposed mode of operation of drugs based on hydroxamic acids. Furthermore, coordinatively unsaturated complexes of zinc and acetohydroxamic acid undergo a zinc‐assisted Lossen rearrangement followed by elimination of water if acetohydroxamic acid is present as a neutral ligand, or by loss of methylisocyanate if acetohydroxamic acid is deprotonated.     

Different Catalytic Effects of a Single Water Molecule: The Gas‐Phase Reaction of Formic Acid with Hydroxyl Radical in Water Vapor

The effect of a single water molecule on the reaction mechanism of the gas‐phase reaction between formic acid and the hydroxyl radical was investigated with high‐level quantum mechanical calculations using DFT–B3LYP, MP2 and CCSD(T) theoretical approaches in concert with the 6‐311+G(2df,2p) and aug‐cc‐pVTZ basis sets. The reaction between HCOOH and HO has a very complex mechanism involving a proton‐coupled electron transfer process (pcet), two hydrogen‐atom transfer reactions (hat) and a double proton transfer process (dpt). The hydroxyl radical predominantly abstracts the acidic hydrogen of formic acid through a pcet mechanism. A single water molecule affects each one of these reaction mechanisms in different ways, depending on the way the water interacts. Very interesting is also the fact that our calculations predict that the participation of a single water molecule results in the abstraction of the formyl hydrogen of formic acid through a hydrogen atom transfer process (hat).     

Simple and Efficient Synthesis of 2‐Oxo‐2H‐Pyrido[1,2‐a]Pyrimidin‐3(4H)‐Ylidene)Acetic Acid and Its Rearrangement in Presence of Acid Media

A highly efficient one‐pot simple synthesis of 2‐[2‐oxo‐2H‐pyrido[1,2‐a]pyridmidn‐3(4H)‐ylidene)]acetic acid is described. The rearrangement of 2‐[2‐oxo‐2H‐pyrido[1,2‐a]pyridmidn‐3(4H)‐ylidene)]acetic acid in the presence of polyphosphoric acid (PPA) yielded a seven‐membered diazepine with decarboxylation and ring expansion.     

A validated HPLC‐MS/MS method for determination of genipin‐1‐o‐glucuronic acid in rat plasma after administration of genipin and its application to a pharmacokinetic study

A sensitive and specific method was developed and validated for the quantitation of one major metabolite of genipin in rats plasma. The major metabolite was isolated from rat bile via semi‐preparative HPLC technology and its chemical structure was identified as genipin‐1‐o‐glucuronic acid (GNP‐GLU), which was for the first time used as a standard compound for quantitative analysis in rat plasma after administration of genipin. The application of high‐performance liquid chromatography–tandem mass spectrometry in negative mode in multiple reaction monitoring mode was investigated. Chromatographic separation was achieved on an Eclipse XDB‐C₁₈ column using a mobile phase consisting of water with 0.1% formic acid (A)–acetonitrile (B). The limit of detecation was 0.214 ng/mL and the lower limit of quantification was 0.706 ng/mL. The calibration curve was linear from 1.27 to 3810 ng/mL for plasma samples, with a correlation coefficient of 0.9924. The intra‐ and inter‐day precisions and accuracy were all within 15%. The recoveries of GNP‐GLU and puerarin were above 90.0 and 76.2%, respectively. The highly sensitive method was successfully applied to estimate pharmacokinetic parameters of GNP‐GLU following oral and intravenous administration of genipin to rats. Copyright © 2013 John Wiley & Sons, Ltd.     

Simultaneous determination of N‐ethylpentylone,dopamine, 5‐hydroxytryptamine and their metabolites in rat brain microdialysis by liquid chromatography tandem mass spectrometry

N‐Ethylpentylone (NEP) is a popular synthetic cathinone abused worldwide. To obtain more information about its pharmacokinetics and pharmacodynamics, a rapid, simple and sensitive liquid chromatography–tandem mass spectrometry method was developed for the determination of NEP, two important neurotransmitters, dopamine and serotonin, and their metabolites, including 3,4‐dihydroxyphenylacetic acid, 3‐methoxytyramine and 5‐hydroxyindole‐3‐acetic acid, in rat brain microdialysate. The analytes were separated on a Phnomenex Polar C₁₈ column, with a mobile phase of 0.1% formic acid in water (A) and 0.1% formic acid in acetonitrile (B) under gradient elution to shorten the total chromatographic run time. A triple quadruple mass spectrometer coupled with an electrospray ionization source in both positive and negative ion mode was used to detect the analytes. This method showed excellent accuracy (87.4–113.5%) and precision (relative standard deviation <15%) at three quality control levels. The limits of detection were 0.2 ng/mL for NEP and 0.2–50 nm for the others and good linearity was obtained. This study pioneered a method to integrate exogenous drugs and endogenous neurotransmitters as the drugs act on the same determination system, which means that this innovation can provide support for further study of the addictive effects of NEP or other synthetic cathinones on extracellular levels of dopamine and 5‐hydroxytryptamine.     

Crystal transition from hydrated chitosan and chitosan/monocarboxylic acid complex to anhydrous chitosan investigated by X‐ray diffraction

We have studied the crystal transition behaviors from hydrated chitosan to anhydrous chitosan by X‐ray diffraction analyses. Hydrated chitosan prepared by deacetylation of crustacean α‐chitin was subjected to the two conversion methods, hydrothermal treatment and high‐humidity treatment via chitosan/monocarboxylic acid complex. The transition by hydrothermal treatment progressed with increasing treatment temperature and time, and the rapid transition occurred above 200 °C. Chitosan/acetic acid complex and chitosan/formic acid complex were prepared by immersing hydrated chitosan in acid solution. The transition from chitosan/acetic acid complex to anhydrous chitosan in high relative humidity condition proceeded with increasing temperature and was complete at 80 °C for 1 h, whereas chitosan/formic acid complex did not convert to anhydrous chitosan under the same conditions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1065–1069     

Halide–Amine Co‐Passivated Indium Phosphide Colloidal Quantum Dots in Tetrahedral Shape

Wet chemical synthesis of covalent III‐V colloidal quantum dots (CQDs) has been challenging because of uncontrolled surfaces and a poor understanding of surface–ligand interactions. We report a simple acid‐free approach to synthesize highly crystalline indium phosphide CQDs in the unique tetrahedral shape by using tris(dimethylamino) phosphine and indium trichloride as the phosphorus and indium precursors, dissolved in oleylamine. Our chemical analyses indicate that both the oleylamine and chloride ligands participate in the stabilization of tetrahedral‐shaped InP CQDs covered with cation‐rich (111) facets. Based on density functional theory calculations, we propose that fractional dangling electrons of the In‐rich (111) surface could be completely passivated by three halide and one primary amine ligands per the (2×2) surface unit, satisfying the 8‐electron rule. This halide–amine co‐passivation strategy will benefit the synthesis of stable III‐V CQDs with controlled surfaces.     

Simultaneous determination of acetylsalicylic acid and salicylic acid in human plasma by isocratic high‐pressure liquid chromatography with post‐column hydrolysis and fluorescence detection

A selective, sensitive and rapid high‐performance liquid chromatography method with post‐column hydrolysis and fluorescence detection was developed for the simultaneous quantification of acetylsalicylic acid and its metabolite salicylic acid in human plasma. Following the addition of 2‐hydroxy‐3‐methoxybenzoic acid as internal standard and simple protein precipitation with acetonitrile, the analytes were separated on a ProntoSIL 120 C₁₈ ace‐EPS column (150 × 2 mm, 3 µm) protected by a C₈ guard column (5 µm). The mobile phase, 10 mm formic acid in water (pH 2.9) and acetonitrile (70:30, v/v), was used at a flow rate of 0.35 mL/min. After on‐line post‐column hydrolysis of acetylsalicylic acid (ASA) to salicylic acid (SA) by addition of alkaline solution, the analytes were measured at 290 nm (λ_ex) and 400 nm (λ_em). The method was linear in the concentration ranges between 0.05 and 20 ng/μL for both ASA and SA with a lower limit of quantification of 25 pg/μL for SA and 50 pg/μL for ASA. The limit of detection was 15 pg/μL for SA and 32.5 pg/μL for ASA. The analysis of ASA and SA can be carried out within 8 min; therefore this method is suitable for measuring plasma concentrations of salicylates in clinical routine. Copyright © 2012 John Wiley & Sons, Ltd.     

Lanthanide‐IMAC enrichment of carbohydrates and polyols

In this study a new type of immobilized metal ion affinity chromatography resin for the enrichment of carbohydrates and polyols was synthesized by radical polymerization reaction of vinyl phosphonic acid and 1,4‐butandiole dimethacrylate using azo‐bis‐isobutyronitrile as radical initiator. Interaction between the chelated trivalent lanthanide ions and negatively charged hydroxyl groups of carbohydrates and polyols was observed by applying high pH values. The new method was evaluated by single standard solutions, mixtures of standards, honey and a more complex extract of Cynara scolymus. The washing step was accomplished by acetonitrile in excess volumes. Elution of enriched carbohydrates was successfully performed with deionized water. The subsequent analysis was carried out with matrix‐free laser desorption/ionization–time of flight mass spectrometry involving a TiO₂‐coated steel target, especially suitable for the measurement of low‐molecular‐weight substances. Quantitative analysis of the sugar alcohol xylitol as well as the determination of the maximal loading capacity was performed by gas chromatography in conjunction with mass spectrometric detection after chemical derivatization. In a parallel approach quantum mechanical geometry optimizations were performed in order to compare the coordination behavior of various trivalent lanthanide ions. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of 16 phthalic acid esters in food simulants from plastic food contact materials by LC‐ESI‐MS/MS

An RP LC‐ESI‐MS/MS method for the determination of the migration of 16 primary phthalic acid esters from plastic samples has been developed using distilled water, 3% acetic acid, 10% alcohol, and olive oil as food simulants. Detection limits were 1.6–18.5 μg/kg in distilled water, 1.4–17.3 μg/kg in 3% acetic acid, 1.4–19.2 μg/kg in 10% alcohol, and 31.9–390.8 μg/kg in olive oil. The RSDs were in the range of 0.07–11.28%. The real plastic products inspection showed that only few analyzed samples were phthalates contaminated. Bis‐2‐ethylhexyl ester and dibutyl phthalate were the common items migrated from the plastic products into food and feeds, but the migration concentrations were far below the limits set by European Union (1.5 mg/kg for bis‐2‐ethylhexyl ester and 0.3 mg/kg for dibutyl phthalate).     

The effect of different monocarboxylic acids on the gelation behaviour of Cu ethoxide

Cu ethoxide becomes soluble in methoxyethanol when formic, acetic, or acrylic acid is added. For the complete dissolution, the minimum molar ratio of an acid to Cu ethoxide is two for formic acid (HOFA), and one for acetic (HOAC) or acrylic (HOAA) acid. The solutions of Cu ethoxide with any amounts of formic acid are incapable of forming gels. Those with acetic or acrylic acid/Cu ratio of 1 are able to convert to gels. For the range of the water concentration from 1.5 to 10 M, the gelation time is strongly dependent on [H₂O] for the solution with HOAC/Cu ratio of 1, while it is almost independent for the solution with HOAA. It is suggested that the differences in the behaviour of soluble Cu species derived from the three acids are attributed to different coordination forms and the bonding strength between ligands and copper ions.     

Identifying and minimizing buffer interferences in ToF‐SIMS analyses of lignocellulose

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has demonstrated applicability to the analysis of lignocellulosic samples including pulp, paper, plants, and wood. One such application is to use ToF‐SIMS as a tool for detecting the activity of enzymes applied to degrade or modify plant biomass. The use of buffers for pH control of these enzymatic reactions can pose problems due to the nature of the ToF‐SIMS measurement. Specifically, inorganic species (e.g. salts) from buffer components could introduce several concerns for quantitative or semi‐quantitative ToF‐SIMS analysis. First, salts can produce additional peaks in the mass spectra, which may overlap with lignocellulose peaks of interest (mass interference). Second, salts can alter the chemical environment, or ‘matrix’, altering the ionization probability of lignocellulose‐related secondary ions during the sputtering mechanism of the ToF‐SIMS measurement (matrix effects). Third, salts may physically coat the lignocellulose surface, decreasing the signal from the lignocellulose, causing poor signal‐to‐noise in the analysis. The current work presents a simple approach for identifying interferences due to buffers, using both principal component analysis (PCA) and previously established lignocellulose‐relevant peak ratios. Furthermore, a simple acetic acid rinsing protocol is compared to distilled water rinsing and is evaluated and for its effectiveness in removing buffer‐related salts. The data shows that briefly rinsing lignocellulose samples in dilute acetic acid can be effective in restoring the validity of lignocellulose composition interpretations using ToF‐SIMS. Copyright © 2014 John Wiley & Sons, Ltd.     

Selective Hydrogen Generation from Formic Acid with Well‐Defined Complexes of Ruthenium and Phosphorus–Nitrogen PN3‐Pincer Ligand

An unsymmetrically protonated PN³‐pincer complex in which ruthenium is coordinated by one nitrogen and two phosphorus atoms was employed for the selective generation of hydrogen from formic acid. Mechanistic studies suggest that the imine arm participates in the formic acid activation/deprotonation step. A long life time of 150 h with a turnover number over 1 million was achieved.