Reaction mechanism of monoethanolamine with CO₂ in aqueous solution from molecular modeling

We present a theoretical study of the reaction mechanism of monoethanolamine (MEA) with CO? in an aqueous solution. We have used molecular orbital reaction pathway calculations to compute reaction free energy landscapes for the reaction steps involved in the formation of carbamic acids and carbamates. We have used the conductor-like polarizable continuum model to calculate reactant, product, and transition state geometries and vibrational frequencies within density functional theory (DFT). We have also computed single point energies for all stationary structures using a coupled cluster approach with singles, doubles, and perturbational triple excitations using the DFT geometries. Our calculations indicate that a two-step reaction mechanism that proceeds via a zwitterion intermediate to form carbamate is the most favorable reaction channel. The first step, leading to formation of the zwitterion, is found to be rate-determining, and the activation free energies are 12.0 (10.2) and 11.3 (9.6) kcal/mol using Pauling (Bondi) radii within the CPCM model at the CCSD(T)/6-311++G(d,p) and CCSD(T)/6-311++G(2df,2p) levels of theory, respectively, using geometries and vibrational frequencies obtained at the B3LYP/6-311++G(d,p) level of theory. These results are in reasonable agreement with the experimental value of about 12 kcal/mol. The second step is an acid-base reaction between a zwitterion and MEA. We have developed a microkinetic model to estimate the effective reaction order at intermediate concentrations. Our model predicts an equilibrium concentration for the zwitterion on the order of 10?11 mol/L, which explains why the existence of the zwitterion intermediate has never been detected experimentally. The effective reaction order from our model is close to unity, also in agreement with experiments. Complementary ab initio QM/MM molecular dynamics simulations with umbrella sampling have been carried out to determine the free energy profiles of zwitterion formation and proton transfer in solution; the results confirm that the formation of the zwitterion is rate-determining.     

Identification of a novel cannabimimetic phenylacetylindole, cannabipiperidiethanone, as a designer drug in a herbal product and its affinity for cannabinoid CB₁ and CB₂ receptors

A new cannabimimetic phenylacetylindole (cannabipiperidiethanone, 1) has been found as an adulterant in a herbal product which contains two other known synthetic cannabinoids, JWH-122 and JWH-081, and which is distributed illegally in Japan. The identification was based on analyses using GC-MS, LC-MS, high-resolution MS and NMR. Accurate mass spectrum measurement showed the protonated molecular ion peak of 1 at m/z 377.2233 [M+H]? and the molecular formula of 1 was C??H??N?O?. Both mass and NMR spectrometric data revealed that 1 was 2-(2-methoxyphenyl)-1-{1-[(1-methylpiperidin-2-yl)methyl]-1H-indol-3-yl}ethanone. Compound 1 has a mixed structure of known cannabimimetic compounds: JWH-250 and AM-2233. Namely, the moiety of phenylacetyl indole and N-methylpiperidin-2-yl-methyl correspond to the structure of JWH-250 and AM-2233, respectively. However, no synthetic, chemical or biological information about 1 has been reported. A binding assay of compound 1 to cannabinoid receptors revealed that 1 has affinity for the CB? and CB? (IC??=591, 968 nM, respectively) receptors, and shows 2.3- and 9.4-fold lower affinities than those of JWH-250. This is the first report to identify cannabimimetic compound (1) as a designer drug and to show its binding affinity to cannabinoid receptors.     

Phenolics and flavonoids compounds, phenylanine ammonia lyase and antioxidant activity responses to elevated CO₂ in Labisia pumila (Myrisinaceae)

A split plot 3 × 3 experiment was designed to examine the impact of three concentrations of CO? (400, 800 and 1,200 μmol·mol?1) on the phenolic and flavonoid compound profiles, phenylalanine ammonia lyase (PAL) and antioxidant activity in three varieties of Labisia pumila Benth. (var. alata, pumila and lanceolata) after 15 weeks of exposure. HPLC analysis revealed a strong influence of increased CO? concentration on the modification of phenolic and flavonoid profiles, whose intensity depended on the interaction between CO? levels and L. pumila varieties. Gallic acid and quercetin were the most abundant phenolics and flavonoids commonly present in all the varieties. With elevated CO? (1,200 μmol·mol?1) exposure, gallic acid increased tremendously, especially in var. alata and pumila (101-111%), whilst a large quercetin increase was noted in var. lanceolata (260%), followed closely by alata (201%). Kaempferol, although detected under ambient CO? conditions, was undetected in all varieties after exposure. Instead, caffeic acid was enhanced tremendously in var. alata (338~1,100%) and pumila (298~433%). Meanwhile, pyragallol and rutin were only seen in var. alata (810 μg·g?1 DW) and pumila (25 μg·g?1 DW), respectively, under ambient conditions; but the former compound went undetected in all varieties while rutin continued to increase by 262% after CO? enrichment. Interestingly, naringenin that was present in all varieties under ambient conditions went undetected under enrichment, except for var. pumila where it was enhanced by 1,100%. PAL activity, DPPH and FRAP also increased with increasing CO? levels implying the possible improvement of health-promoting quality of Malaysian L. pumila under high CO? enrichment conditions.     

Combinatorial synthesis and characterization of metal-open frameworks in mild and friendly conditions: application to CO₂ adsorption

Combinatorial screening using precipitation methods at room temperature can lead to a great diversity of carboxylate based Metal Organic Frameworks (MOFs) including already known or original porous solids. The investigation of the synthesis of MOFs in different solvent and solvent mixtures includes the use of solvents such as alcohols and tetrahydrofuran (THF) which would greatly facilitate large scale production. We also show the application of Principal Component Analysis (PCA) and clustering techniques on large libraries of XRD diffraction files in order to identify classes of similar phases and peculiar phases. The combinatorial screening of 105 samples in the La/btc system has led to the identification of two phases which are solvent depending. On the La(btc) compound, the CO? adsorption measurements reveal a guest-host interactions as supported by XRD phase transformation upon thermal treatment. The mass transport can be assigned to a "single file diffusion" regime due to the one dimensional channel porous structure associated to small pore size.     

Catalytic synthesis of α-oxoketene S,S-acetals in a wet ionic liquid [Bmim]Cl/H₂O homogeneous system

A clean, practical and environmentally friendly synthesis in a homogeneous system has been developed for α-oxoketene S,S-acetals. A mixture of [Bmim]Cl and water was used as medium. The best economical and practical molar ratio of [Bmim]Cl to substrate was 4 to 1. With various types of 1,3-dicarbonyl compounds as substrate, the corresponding α-oxoketene S,S-acetals have been prepared under mild reaction conditions with yields of 53-74% after purification with silica gel column. [Bmim]Cl/water can be recycled several times.     

Self-Accelerating Effect in a Covalent–Organic Framework with Imidazole Groups Boosts Electroreduction of CO2 to CO

Solvent effect plays an important role in catalytic reaction, but there is little research and attention on it in electrochemical CO₂ reduction reaction (eCO₂RR). Herein, we report a stable covalent-organic framework (denoted as PcNi-im ) with imidazole groups as a new electrocatalyst for eCO₂RR to CO. Interestingly, compared with neutral conditions, PcNi-im not only showed high Faraday efficiency of CO product (≈100 %) under acidic conditions (pH ≈ 1), but also the partial current density was increased from 258 to 320 mA cm⁻². No obvious degradation was observed over 10 hours of continuous operation at the current density of 250 mA cm⁻². The mechanism study shows that the imidazole group on the framework can be protonated to form an imidazole cation in acidic media, hence reducing the surface work function and charge density of the active metal center. As a result, CO poisoning effect is weakened and the key intermediate *COOH is also stabilized, thus accelerating the catalytic reaction rate.     

Densely Packed CO2 Aids Charge,Spin, and Lattice Ordering Partially Fluctuated in a Porous Metal–Organic Framework Magnet

Partial charge fluctuations in the charge-ordered state of a material, often triggered by structural disorders and/or defects, can significantly alter its physical characteristics, such as magnetic long-range ordering. However, it is difficult to post-chemically fix such accidental partial fluctuations to reconstruct a uniform charge-ordered state. Herein, we report CO₂-aided charge ordering demonstrated in a CO₂-post-captured layered magnet, [{Ru₂(o-ClPhCO₂)₄}₂{TCNQ(OMe)₂}] ⋅ CO₂ ( 1⊃CO₂ ; o-ClPhCO₂⁻=ortho-chlorobenzoate; TNCQ(OMe)₂=2,5-dimethoxy-7,7,8,8-tetracyanoquinodimethane). Pristine porous layered magnet 1 had a partially charge-fluctuated ordered state, which provided ferrimagnetic ordering at T_C=65 K. Upon loading CO₂, 1 adsorbed one mole of CO₂, forming 1⊃CO₂ , and raising T_C to 100 K. This was because of the vanishing charge fluctuations without significantly changing the framework structure. This research illustrates the post-accessible host–guest chemistry delicately combined with charge, spin, and lattice ordering in a spongy magnet. Furthermore, it highlights how this innovative approach opens up new possibilities for technology and nanoscale magnetism manipulation.     

Precise generation of dynamic biochemical signals by controlling the programmable pump in a Y-shaped microfluidic chip with a “christmas tree” inlet

The generation of dynamic biochemical signals in a microfluidic control system is of importance for the study of the interaction between biological cells and their niches. However, most of microfluidic control systems are not able to provide dynamic biochemical signals with high precision and stability due to inherent mechanical vibrations caused by the actuators of the programmable pumps. In this paper, we propose a novel microfluidic feedback control system integrating an external feedback control system with a Y-shaped microfluidic chip with a “Christmas tree” inlet. The Proportional Integral Derivative (PID) controller is implemented to reduce the influence of vibrations. In order to regulate the control parameters efficiently, a mathematical model is built to describe the actuator of the programmable pump, in which a fractional-order model is utilized. Both simulation and experimental studies are carried out, confirming that the microfluidic feedback control system can precisely and stably generate desired dynamic biochemical signals.     

High-performance anion-exchange chromatography–mass spectrometry method for determination of levoglucosan, mannosan, and galactosan in atmospheric fine particulate matter

Biomass burning has a strong influence on the atmospheric aerosol composition through particulate organic, inorganic, and soot emissions. When biomass burns, cellulose and hemicelluloses degrade, producing monosaccharide anhydrides (MAs) such as levoglucosan, mannosan, and galactosan. Therefore, these compounds have been commonly used as tracers for biomass burning. In this study, a fast water-based method was developed for the routine analysis of MAs, based on high-performance anion-exchange chromatography with electrospray ionization mass spectrometry detection. This method combines simple sample preparation, fast separation, and the advantages of the selective detection with MS. Analysis run was optimized to the maximum separation of levoglucosan, mannosan, and galactosan with 15-min analysis. The validation results indicated that the method showed good applicability for determination of MA isomer concentrations in ambient samples. The limit of detection was 100 pg for levoglucosan and 50 pg for mannosan and galactosan. Wide determination ranges enabled the analysis of samples of different concentration levels. The method showed good precision, both for standard solutions (3.9–5.9% RSD) and for fine particle samples (4.3–8.5% RSD). Co-elution of internal standard (carbon-13-labeled levoglucosan) and sugar alcohols with levoglucosan decreased the sensitivity of levoglucosan determination. The method was used to determine the MA concentrations in ambient fine particle samples from urban background (Helsinki) and rural background (Hyytiälä) in Finland. The average levoglucosan, mannosan, and galactosan concentrations were 77, 8.8, and 4.2 ng?m^?3 in Helsinki (winter 2008–2009) and 17, 2.3, and 1.4 ng?m^?3 in Hyytiälä (spring 2007), respectively. The interrelation of the three MA isomers was fairly constant in the ambient fine particle samples.     

Facilitated Photocatalytic CO2 Reduction in Aerobic Environment on a Copper-Porphyrin Metal–Organic Framework

Herein, we fabricated a π–π stacking hybrid photocatalyst by combining two two-dimensional (2D) materials: g-C₃N₄ and a Cu-porphyrin metal–organic framework (MOF). After an aerobic photocatalytic pretreatment, this hybrid catalyst exhibited an unprecedented ability to photocatalytically reduce CO₂ to CO and CH₄ under the typical level (20 %) of O₂ in the air. Intriguingly, the presence of O₂ did not suppress CO₂ reduction; instead, a fivefold increase compared with that in the absence of O₂ was observed. Structural analysis indicated that during aerobic pretreatment, the Cu node in the 2D-MOF moiety was hydroxylated by the hydroxyl generated from the reduction of O₂. Then the formed hydroxylated Cu node maintained its structure during aerobic CO₂ reduction, whereas it underwent structural alteration and was reductively devitalized in the absence of O₂. Theoretical calculations further demonstrated that CO₂ reduction, instead of O₂ reduction, occurred preferentially on the hydroxylated Cu node.     

Development of a simplified method for the simultaneous determination of retinol, α-tocopherol,and β-carotene in serum by liquid chromatography–tandem mass spectrometry with atmospheric pressure chemical ionization

A new and simple method for the determination of fat-soluble vitamins (retinol, alpha-tocopherol, and beta-carotene) in human serum was developed and validated by using liquid chromatography-tandem mass spectrometry with atmospheric pressure chemical ionization (LC-APCI-MS-MS). Different solvent mixtures were tested to obtain deproteinization and extraction of the analytes from the matrix. As a result, a volume of 240 microL of a 1:1 (v/v) ethanol/ethyl acetate mixture added to 60 microL of serum was found to be suitable for both protein precipitation and antioxidants solubilization, giving the best recovery for all three analytes. Deproteinized samples (20 microL) were injected after dilution, without the need for concentration or evaporation to dryness and reconstruction of the sample. Vitamins were separated on a C-8 column using a 95:5 (v/v) methanol/dichloromethane mixture and ionized in the positive-ion mode; detection was performed in the selected-reaction monitoring mode. Linearity of the LC-APCI-MS-MS method was established over 5 orders of magnitude for retinol and alpha-tocopherol, whereas in the case of beta-carotene it was limited to 4 orders. Lower limits of quantitation were 1.7, 2.3, and 4.1 nM for retinol, alpha-tocopherol, and beta-carotene, respectively. Serum concentrations of retinol, alpha-tocopherol, and alpha+beta-carotene determined in a group of healthy volunteers were 2.48, 38.07, and 0.50 microM, respectively, in samples collected in winter ( n=122) and 2.69, 45.88, and 0.90 microM during summer ( n=66).     

Structure,dynamics, and solvation in a disordered metal–organic coordination polymer: a multiscale study

Metal–organic coordination polymers are a growing class of technologically-important materials in which transition metal ions are connected by multitopic organic chelators to form a 3-D network structure. While the structures of many highly-ordered metal–organic frameworks have been determined, far less structural information is available about the more common disordered materials. Our study combines pair distribution function analysis from total X-ray scattering, ab initio quantum mechanical calculations, and all-atom molecular dynamics to explore the structure and dynamics of a poorly-ordered branched coordination polymer. The polymer structure is highly flexible and dynamic, and is dramatically affected by its solvation state, a finding with far-reaching implications for the incorporation of coordination polymers into nanocomposite materials.     

Bridge-bonded formate: active intermediate or spectator species in formic acid oxidation on a Pt film electrode?

We present and discuss the results of an in situ IR study on the mechanism and kinetics of formic acid oxidation on a Pt film/Si electrode, performed in an attenuated total reflection (ATR) flow cell configuration under controlled mass transport conditions, which specifically aimed at elucidating the role of the adsorbed bridge-bonded formates in this reaction. Potentiodynamic measurements show a complex interplay between formation and desorption/oxidation of COad and formate species and the total Faradaic current. The notably faster increase of the Faradaic current compared to the coverage of bridge-bonded formate in transient measurements at constant potential, but with different formic acid concentrations, reveals that adsorbed formate decomposition is not rate-limiting in the dominant reaction pathway. If being reactive intermediate at all, the contribution of formate adsorption/decomposition to the reaction current decreases with increasing formic acid concentration, accounting for at most 15% for 0.2 M DCOOH at 0.7 VRHE. The rapid build-up/removal of the formate adlayer and its similarity with acetate or (bi-)sulfate adsorption/desorption indicate that the formate adlayer coverage is dominated by a fast dynamic adsorption-desorption equilibrium with the electrolyte, and that formate desorption is much faster than its decomposition. The results corroborate the proposal of a triple pathway reaction mechanism including an indirect pathway, a formate pathway, and a dominant direct pathway, as presented previously (Chen, Y. X.; et al. Angew. Chem. Int. Ed. 2006, 45, 981), in which adsorbed formates act as a site-blocking spectator in the dominant pathway rather than as an active intermediate.     

Biomonitoring of the atmospheric pollution using lichens in the metropolitan area of São Paulo city,Brazil

The atmospheric pollution of São Paulo city is a serious problem due to the expansion of industrial area, increasing number of vehicles and population density. This work presents results obtained in the analysis of lichens collected in different sites of São Paulo city and in non-polluted areas of Atlantic Forest. Concentrations of twenty elements were determined in Canoparmelia texana species and comparisons were made between the results obtained in lichens from different sites. High concentrations of the elements As, Ba, Cd, Co, Cr, Fe, La, Mn, Sb and Zn were found for samples collected in sites located near industries and petrochemical plant. Br and Sb concentrations were also high in lichens from sites affected by vehicular emissions.     

Residue analysis and kinetics modeling of thiophanate-methyl,carbendazim, tebuconazole and pyraclostrobin in apple tree bark using QuEChERS/HPLC–VWD

Winter is the key period for the control of apple diseases, and fungicides are needed to protect the trunk or main branches. Fungicide residue in apple tree bark is an important basis for the action of the pesticide, but there are no reports on analytical methods or dissipation patterns. In this work, thiophanate-methyl, carbendazim, tebuconazole and pyraclostrobin were selected as typical fungicides and a new QuEChERS–HPLC–VWD(QuEChERS extraction followed by high-performance liquid chromatography detection with a variable wavelength detector) analytical method was developed to estimate their residue kinetics in apple tree bark during the winter months. In the pretreatment step, the sorbent for the clean-up of extracts was optimized as 60 mg/ml primary secondary amine and a gradient-elution model followed by a variable wavelength detection was developed for instrumental analysis. Then this method was validated and applied to the analysis of apple tree bark samples with the linearity range of 0.010–50.00 mg/L, quantification limit range of 0.028–0.080 mg/kg and recovery range of 86.1–101.4%. The dissipation kinetics of thiophanate-methyl and pyraclostrobin could be described by the first-order and two-phase kinetics models, respectively. For carbendazim and tebuconazole, two new models were developed to describe their residue kinetics.     

Selective reduction of nitroarenes to N-arylhydroxylamines by use of Zn in a CO2–H2O system, promoted by ultrasound

The promoting effect of ultrasound on the selective reduction of nitroarenes to N-arylhydroxylamines by use of Zn in an environmentally benign CO₂–H₂O system has been demonstrated. The yield of N-phenylhydroxylamine reaches 95 % when the reaction is carried out with a Zn-to-nitrobenzene molar ratio of 2.2 under ultrasound (40 kHz) at 25 °C and normal pressure of CO₂ for 60 min. Application of ultrasound to the reaction has the advantages of higher yield of N-arylhydroxylamines, shorter reaction time, and consumption of less Zn.