Mechanism of the Water–Gas Shift Reaction Catalyzed by Efficient Ruthenium‐Based Catalysts: A Computational and Experimental Study

Supported ionic liquid phase (SILP) catalysis enables a highly efficient, Ru‐based, homogeneously catalyzed water‐gas shift reaction (WGSR) between 100 °C and 150 °C. The active Ru‐complexes have been found to exist in imidazolium chloride melts under operating conditions in a dynamic equilibrium, which is dominated by the [Ru(CO)₃Cl₃]^? complex. Herein we present state‐of‐the‐art theoretical calculations to elucidate the reaction mechanism in more detail. We show that the mechanism includes the intermediate formation and degradation of hydrogen chloride, which effectively reduces the high barrier for the formation of the requisite dihydrogen complex. The hypothesis that the rate‐limiting step involves water is supported by using D₂O in continuous catalytic WGSR experiments. The resulting mechanism constitutes a highly competitive alternative to earlier reported generic routes involving nucleophilic addition of hydroxide in the gas phase and in solution.     

Tailoring the electrochemical charge storage properties of carbonaceous support by redox properties of heteropoly acids: where does the synergy come from?

Journal of Solid State Electrochemistry - The synergistic effects between two Keggin-type heteropoly acids (HPAs) and carbon surface were examined and elucidated. An improved high rate capability...     

Dispersive micro-solid phase extraction of 16 priority polycyclic aromatic hydrocarbons from water by using thermally treated clinoptilolite,and their quantification by GC-MS

The authors report on a novel sorbent (thermally treated natural zeolite; clinoptilolite) for use in dispersive micro-solid phase extraction (D-μ-SPE) of polycyclic aromatic hydrocarbons (PAHs) from water samples. The method was applied to the D-μ-SPE of 16 priority PAHs which then were quantified by gas chromatography with mass spectrometric detection (GC-MS). The method was validated in terms of specificity and selectivity, linearity and linear range, accuracy, precision, uncertainty, limits of detection and quantification. Figures of merit include (a) linear analytical ranges between 2.08 and 208 ppb, and (b) detection limits in the range from 0.01 to 0.92 ppb. The method was successfully applied to the determination of PAHs in river waters.

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Graphical abstract Schematic representation of dispersive micro-solid phase extraction (D-μ-SPE) of trace levels of PAHs in water samples by using thermally treated clinoptilolite as sorbent prior to gas chromatography-mass spectrometry analysis (GC-MS).

     

Phytochemical analysis of Saponaria officinalis L. shoots and flowers essential oils

Phytochemical analysis by GC and GC/MS of the essential oil samples obtained from fresh shoots and flowers of Saponaria officinalis L. allowed the identification of 96 components in total, comprising 94.7% and 86.0% of the total oils compositions, respectively. Regarding the shoots essential oil, the major of 87 identified volatile compounds were phytol (14.1%), tricosane-6,8-dione (13.4%), patchouli alcohol (7.9%) and tricosane (7.2%), whereas patchouli alcohol (20.0%), heneicosane (11.5%) and tricosane (8.4%) were dominant among the 66 volatiles in the flower oil. Nonterpenoid compounds had the highest contribution in S. officinalis shoots essential oil (53.7%), while in the flower oil, constituents were almost evenly distributed between the oxygenated sesquiterpenoid (41.2%) and nonterpenoid compounds (39.5%).     

Hydrogen Bonding between Metal‐Ion Complexes and Noncoordinated Water: Electrostatic Potentials and Interaction Energies

The hydrogen bonding of noncoordinated water molecules to each other and to water molecules that are coordinated to metal‐ion complexes has been investigated by means of a search of the Cambridge Structural Database (CSD) and through quantum chemical calculations. Tetrahedral and octahedral complexes that were both charged and neutral were studied. A general conclusion is that hydrogen bonds between noncoordinated water and coordinated water are much stronger than those between noncoordinated waters, whereas hydrogen bonds of water molecule in tetrahedral complexes are stronger than in octahedral complexes. We examined the possibility of correlating the computed interaction energies with the most positive electrostatic potentials on the interacting hydrogen atoms prior to interaction and obtained very good correlation. This study illustrates the fact that electrostatic potentials computed for ground‐state molecules, prior to interaction, can provide considerable insight into the interactions.     

Hydrolysis of amide bond in histidine-containing peptides promoted by chelated amino acid palladium(II) complexes: dependence of hydrolytic pathway on the coordination modes of the peptides

Hydrolytic reactions between cis-[Pd( -Ala-N,O)Cl₂]⁻ and cis-[Pd( -Ala-N,O)(H₂O)₂]⁺, in which -Ala is alanine coordinated through N and O atoms, and N-acetylated peptides -histidylglycine (MeCO-His-Gly), glycyl- -histidine (MeCO-Gly-His), glycylglycyl- -histidine (MeCO-Gly-Gly-His) and glycyl- -histidylglycine (MeCO-Gly-His-Gly) were studied by ¹H NMR spectroscopy. All reactions were carried out in the pH range 2.0–2.5 and two different temperatures, 22 and 60°C. In the reactions of these two palladium(II) complexes with MeCO-His-Gly, complete hydrolysis of the amide bond involving carboxylic group of histidine occurs in less than 24 h. The cleavage is regioselective. With peptides containing free a carboxylic group of histidine, MeCO-Gly-His and MeCO-Gly-Gly-His, palladium(II) complex promote the cleavage of the MeCO–Gly and Gly–Gly amide bonds. No cleavage of the Gly–His amide bond was observed. The mechanism of these hydrolytic reactions involves release of -Ala ligand and aquation of the palladium(II) complex chelated to the substrate through the imidazole N-3 atom and deprotonated nitrogen atom of the amide bond involving amino group of histidine. This aqua complex represents a catalytically active form different from the initially added catalytically inactive complex. In the reactions of palladium(II) complexes with tripeptide MeCO-Gly-His-Gly, two amide bonds, MeCO–Gly and His–Gly, were cleaved. The mechanism of the cleavage of these amide bonds is correlated with two different palladium(II)–substrate catalytically active forms. These findings contribute to the better understanding of selective cleavage of peptides and proteins and must be taken into consideration in designing new reagents for this purpose.     

Simultaneous Determination of Hydrochlorothiazide, Cilazapril and Its Active Metabolite Cilazaprilat in Urine by Gradient RP-LC

A rapid and simple liquid chromatographic method with UV detection has been developed for the determination of hydrochlorothiazide (HCTZ), cilazapril (CL) and its active metabolite cilazaprilat (CLT) in urine. Sample preparation for urine consisted of solid-phase extraction using styrene-divinylbenzene (SDB-2) cartridges. The chromatographic system was a Zorbax Eclipse XDB-C₁₈ column with a mixture of methanol and 10 mM phosphate buffer, pH 2.3 with gradient (20 to 60% of methanol) as mobile phase at a flow rate of 1.0 mL min^?1. The detection was performed at the wavelength of 206 nm. Enalapril maleat was used as an internal standard. The detector response was linear in the range of 2.4–30.0, 1.6–15.0 and 1.8–20.0 μg mL^?1 for HCTZ, CL and CLT, respectively. LOQ was determined to be 2.4, 1.6 and 1.8 μg mL^?1 for HCTZ, CL and CLT, respectively. Both intra- and inter-day precision were within acceptable limits. The method has been applied to urine samples obtained from three hypertensive patients after intake of HCTZ and CL therapeutic dose.     

“Wet” Versus “Dry” Folding of Polyproline

When the all-cis polyproline-I helix (PPI, favored in 1-propanol) of polyproline-13 is introduced into water, it folds into the all-trans polyproline-II (PPII) helix through at least six intermediates [Shi, L., Holliday, A.E., Shi, H., Zhu, F., Ewing, M.A., Russell, D.H., Clemmer, D.E.: Characterizing intermediates along the transition from PPI to PPII using ion mobility-mass spectrometry. J. Am. Chem. Soc. 136, 12702–12711 (2014)]. Here, we show that the solvent-free intermediates refold into the all-cis PPI helix with high (>90%) efficiency. Moreover, in the absence of solvent, each intermediate appears to utilize the same small set of pathways observed for the solution-phase PPII → PPI transition upon immersion of PPII_aq in 1-propanol. That folding in solution (under conditions where water is displaced by propanol) and folding in vacuo (where energy required for folding is provided by collisional activation) occur along the same pathway is remarkable. Implicit in this statement is that 1-propanol mimics a “dry” environment, similar to the gas phase. We note that intermediates with structures that are similar to PPII_aq can form PPII under the most gentle activation conditions—indicating that some transitions observed in water (i.e., “wet” folding, are accessible (albeit inefficient) in vacuo. Lastly, these “dry” folding experiments show that PPI (all cis) is favored under “dry” conditions, which underscores the role of water as the major factor promoting preference for trans proline.

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Graphical Abstract ?

     

Nature of the water/aromatic parallel alignment interactions

The water/aromatic parallel alignment interactions are interactions where the water molecule or one of its O? H bonds is parallel to the aromatic ring plane. The calculated energies of the interactions are significant, up to ΔE_{CCSD(T)(limit)} = ?2.45 kcal mol^?1 at large horizontal displacement, out of benzene ring and CH bond region. These interactions are stronger than CH···O water/benzene interactions, but weaker than OH···π interactions. To investigate the nature of water/aromatic parallel alignment interactions, energy decomposition methods, symmetry‐adapted perturbation theory, and extended transition state‐natural orbitals for chemical valence (NOCV), were used. The calculations have shown that, for the complexes at large horizontal displacements, major contribution to interaction energy comes from electrostatic interactions between monomers, and for the complexes at small horizontal displacements, dispersion interactions are dominant binding force. The NOCV‐based analysis has shown that in structures with strong interaction energies charge transfer of the type π → σ*(O? H) between the monomers also exists. © 2014 Wiley Periodicals, Inc.