A primary isotopic gas standard for sulfur in the form of SF6 with Système International d’Unités traceable values for isotopic composition and molar mass

A batch of SF₆ gas prepared by Messer (Germany) was metrologically certified for absolute isotope abundance ratios and molar mass (atomic weight) of sulfur following the ISO/BIPM Guide to the expression of uncertainties in measurements. The certification is based on the “Avogadro II Measurement Procedure” using the “Avogadro II amount comparator,” which was developed in the framework of the redetermination of the Avogadro constant. For the correction of small remaining systematic effects of unknown nature, synthetic isotope mixtures of Ag₂S converted to SF₆ were used in order to obtain “calibrated” or “absolute” values with small combined uncertainty. The values for this sulfur primary isotopic gas standard (PIGS) are traceable to the Système International d’Unités (SI) in the shortest possible way and can therefore serve as a link to SI when used in differential measurements. The PIGS is now commercially available.     

Absolute Brønsted Acidities and pH Scales in Ionic Liquids

Although receiving large interest over the last years, some fundamental aspects of Brønsted acidity in ionic liquids (ILs) have up to now been insufficiently highlighted. In this work, standard states, activity, and activity coefficient definitions for IL solvent systems were developed from general thermodynamic considerations and then extended to a general mixed solvent standard state. By using the bromide/bromoaluminate systems as representative ILs, formulae for thermodynamically consistent pH scales for ILs with simple (Br^?) and complex ([Al_nBr_3n+1]^?) anions were derived on the basis of the chemical potential of the proton. Supported by quantum chemical [ccsd(t)/MP2/DFT/COSMO‐RS] calculations, Gibbs solvation energies of the proton were calculated, which allowed the ILs to be ranked in absolute acidity, that is, pH_abs or μ_abs(H⁺, IL), and additionally allowed their acidity to be compared with molecular Brønsted acid systems. It was shown that bromoaluminate ILs are suited for reaching superacidic conditions. The complexity of autoprotolysis processes in C₆MIM⁺[AlBr₄]^? (C₆MIM=1‐hexyl‐3‐methylimidazolium) with or without the addition of basic (i.e. Br^?) or acidic (AlBr₃ and/or HBr) solutes was examined in detail by model calculations, and they indicated a large thermodynamic influence of small deviations from the exact stoichiometric composition.     

IRRADIATION-ENHANCED PHYTOCHROME PELLETABILITY IN AVENA: IN VIVO DEVELOPMENT OF A POTENTIAL TO PELLET AND THE ROLE OF Mg2+ IN ITS EXPRESSION IN VITRO

The enhanced phytochrome pelletability that results from in vivo irradiation of Avena shoots may be divided into two operationally defined sequential stages: the in vivo development of a “potential to pellet” and the “expression” of this potential in vitro. Kinetic studies confirm previous findings that the generation of this “potential to pellet” is a very rapid (complete in < 10 s, 25°C), genuinely intracellular process, itself photoreversibly induced by P_fr. In addition, it is shown that the sustained development of the “potential to pellet”, that proceeds in the dark at 0°C following a red pulse, requires P_fr continually in the cell over the entire development period. Far red light immediately terminates further development of the red-induced “potential” at any point during the development phase. No immediate reduction is observed, however, in that level of “potential pelletability” already attained at the time of the far red pulse. This indicates that the level of “potential pelletability” established in vivo is insensitive to the form of the pigment at extraction regardless of the level reached. “Expression” of the “potential to pellet” refers to the actual detection in homogenates of an enhanced physical association of phytochrome with pelletable material. Maximum “expression” requires the presence of a divalent cation in the medium during homogenization. Rapid posthomogenization addition of Mg²⁺ to Mg²⁺-free extracts sustains enhanced pelletability but with rapidly declining effectiveness over the fmt 1–2 min after extraction. The rate of decline is faster if the phytochrome is present as P_fr than as P_r in the homogenate. Neither these nor previous data permit a distinction to be made between (a) preservation by the cation of a pre-existing intracellular interaction, and (b) a Mg²⁺-mediated induction of an artifactual, in vitro association predetermined in the cell by a genuine phyto-chrome-controlled process. Various formalistic models are discussed in the context of these and other data.     

Potential energy surface for Li+Li2: AN AB initio valence-bond calculation

A potential energy surface, calculated using the ab initio multistructure valence-bond technique, is reported for the collinear Li + Li₂ system. The ground state potential surface of the system is predicted to have no barrier to reaction and to possess a well of 4.62 kcal/mole (0.200 eV) relative to the infinitely separated reactants with the Li₂ at its equilibrium separation. An analytic potential energy surface is derived, which includes empirical corrections for the “diatomic” errors in the ab initio calculation. The empirically corrected surface dissociates to the experimental Li₂ potential energy curve when any one of the three lithium atoms is removed to a large distance. Cuts in the ab initio potential energy surface of the lowest electronically excited states of the system are also reported.     

Superacidic or Not…︁? Synthesis,Characterisation, and Acidity of the Room‐Temperature Ionic Liquid [C(CH3)3]+ [Al2Br7]−

The room‐temperature ionic liquid (RT‐IL) [C(CH₃)₃]⁺ [Al₂Br₇]^? (m.p. 2 °C) was generated by bromide abstraction from tert‐butyl bromide with the Lewis acid aluminum bromide in the absence of solvent. The crystal structure of the tert‐butyl cation salt was determined by X‐ray diffraction. NMR, IR, and Raman spectroscopy, as well as quantum‐chemical and thermodynamic calculations, confirm the composition of this RT‐IL. Thus, one may consider this RT‐IL to be a readily accessible (and on a large scale) cationic Brønsted acid (protonated isobutene) with the potential for further reactivity. Based on the new absolute Brønsted acidity scale, we calculated an absolute pH_abs value of 171 for liquid bulk [C(CH₃)₃]⁺ [Al₂Br₇]^?. This value is about as acidic as 100 % sulfuric acid (pH_abs=171) and, thus, on the edge of superacidity.     

Kinetics and mechanism of interaction between methanol and adsorbed oxygen on a smooth polycrystalline platinum electrode: Transients of the open-circuit potential

The method of transients of the open-circuit potential, combined with cathodic potentiodynamic pulses, is used for studying the methanol interaction with preliminarily adsorbed oxygen (O_ads) in 0.5 M H₂SO₄. It is established that, for the larger part of the time period required for a full reduction of a monolayer of O_ads in solutions of methanol on polycrystalline platinum, the process occurs at large coverages of the surface by O_ads (?_O). In the region of medium coverages, transients of the open-circuit potential are accurately described by the equation that corresponds to the mechanism of “conjugated reactions.” The mechanism of the methanol interaction with O_ads happens to be close to that for formic acid, which is explained by a dissociative character of these HCO compounds. Kinetic parameters characterizing the methanol reaction with O_ads in the region of large and medium coverages are determined and analyzed.     

The Origin of the Reproduction of Different Nitrogen Uptakes in Covalent Organic Frameworks (COFs)

In order to quantitatively examine the activation level for covalent-organic frameworks (COFs) on gas adsorption, the effect of impurities on nitrogen uptakes in a series of boron-based COFs was investigated by grand canonical Monte Carlo simulation (GCMC), based on accurate force fields derived from high-level B2PLYP-D3/def2-TZVPP calculation. The conformations and the type of impurities were found to have little effect on the gas uptakes, but the quantity of impurities plays a crucial role on N₂ loadings. More important, the terms of “activation mass ratio” and “activation volume ratio” were defined to estimate the realistic pore volume ratio for DBA-COFs (DBA=π-conjugated dehydro-benzoannulene), and predict the potential of gas uptakes in DBA-COFs. Our approach for DBA-COFs materials could also be adopted for high-throughput screening of a much vaster number of porous materials, to evaluate their impurities content and predict their adsorption potential.     

Das Redoxverhalten von Bisbiphenylchrom(I)-jodid in Wasser

Bisbiphenylchromiumiodide [BBCr(I)J] is widely used as a “reference ion” in comparing redox potentials in different solvents. The voltametric behaviour in aqueous solutions however, is complicated by adsorption phenomena of the oxidized as well as the reduced form. Classical polarography, A—C polarography, cyclic voltametry, large scale electrolysis and pulsevoltametric methods have been employed to obtain information about the nature of the electrode reaction, its reversibility and the solubility of the reactants. Based on these data it is shown that the formal standard redox potential corresponds to the reactionBBCr(I)_ads/BBCr(O)_ads and has to be regarded as a “surface redox potential”.     

Determination of the heterogeneity factor in the Frumkin adsorption isotherm from the width of capacity peaks

An appraisal of the various known surface preparations for the single crystal TiO₂ as used in solar photoelectrolysis cells is presented. The results presented are derived from photocurrent-voltage characteristics and interpretations of the surface behaviour are made on the basis of these measurements and their deviations from theoretically “ideal” behaviour. A novel preparation procedure is also introduced, producing results that represent the closest approach to the theoretically ideal surface known to date.     

Scale formation and control in oil and gas fields: A review

The formation of scale poses several serious menaces in oil and gas exploitations. The scaling phenomenon may cause technical problems such as obstruction of equipment and pipes, which causes great damages and results in economic losses; besides, scale is one of the most difficult issues to resolve. Preventing scale formation relies on understanding the composition of the scale, appropriate scale inhibitor, and early pretreatment. The use of chemicals acting as a scale inhibitor is a significantly effective and economical approach in controlling scale deposition. This review mainly studies the mechanism of scale formation, the characteristics of different kinds of scale inhibitors, and the progress of application research in recent years. In particular, some of the green scale inhibitors derived from synthetics and “natural” organic molecules are summed up. Meanwhile, the prospects of scale inhibitors in the future are also described. It is hoped that this review will have potential value for the development of an efficient, economic, and environment-friendly scale inhibitor.     

Molecular modeling of polymers. IV. Estimation of glass transition temperatures

A method is described which allows molecular modeling to be combined with a group additive property model to estimate glass transition temperatures of linear polymers. T_g is assumed to be a function of conformational entropy and mass moments of the polymer. These two molecular properties are estimated in terms of the torsion angle units composing the polymer using conformational energy calculations. A “universal” T_g equation is derived using 30 structurally diverse polymers and multidimensional linear regression analysis. “Designer” T_g equations are also derived specifically for acrylate and methacrylate polymers. The work described here demonstrates how molecular modeling can be combined with group additivity theory to yield open-ended models that are not restricted by lack of requisite group additive parameters and take advantage of three-dimensional molecular information.     

Measurements and Utilization of Consistent Gibbs Energies of Transfer of Single Ions: Towards a Unified Redox Potential Scale for All Solvents

Utilizing the “ideal” ionic liquid salt bridge to measure Gibbs energies of transfer of silver ions between the solvents water, acetonitrile, propylene carbonate and dimethylformamide results in a consistent data set with a precision of 0.6 kJ mol⁻¹ over 87 measurements in 10 half-cells. This forms the basis for a coherent experimental thermodynamic framework of ion solvation chemistry. In addition, we define the solvent independent - and the values that account for the electronating potential of any redox system similar to the value of a medium that accounts for its protonating potential. This scale is thermodynamically well-defined enabling a straightforward comparison of the redox potentials (reducities) of all media with respect to the aqueous redox potential scale, hence unifying all conventional solvents′ redox potential scales. Thus, using the Gibbs energy of transfer of the silver ion published herein, one can convert and unify all hitherto published redox potentials measured, for example, against ferrocene, to the scale.     

Synthesis of OMS Materials and Investigation of Their Acceptor–Donor Characteristics

Three ordered mesoporous siliceous (OMS) materials known as MCM41s—unmodified MCM-41C16 (“C16”), and two MCM41s with different surface functionalities: MCM-41C16-SH (“C16-SH”) and MCM-41C16-NH₂ (“C16-NH₂”)—were synthesized and studied by inverse gas chromatography in order to determine their acceptor–donor properties. The specific retention volumes of nonpolar and polar probes that were chromatographed on these ordered mesoporous silica adsorbents were evaluated under infinite dilution conditions. Two methods were employed to calculate the standard free energy of adsorption, ΔG _ads, of each chromatographed probe on the basis its specific retention volume. These ΔG _ads values were then employed to estimate the van der Waals contribution and the specific contribution of the free surface energy for each MCM41. DN values (donor numbers, based on the Gutmann scale) and AN* values (acceptor numbers, based on the Riddle–Fowkes scale) were employed to determine the values of parameters that characterize the ability of the MCM41s to act as electron acceptors (parameter: K _A) and donors (parameter: K _D). Considering the different compositions of the probes, each of which has different acceptor–donor properties, a new chromatographic test to supplement the Grob test is suggested.     

Synthesis of OMS Materials and Investigation of Their Acceptor–Donor Characteristics

Three ordered mesoporous siliceous (OMS) materials known as MCM41s—unmodified MCM-41C16 (“C16”), and two MCM41s with different surface functionalities: MCM-41C16-SH (“C16-SH”) and MCM-41C16-NH₂ (“C16-NH₂”)—were synthesized and studied by inverse gas chromatography in order to determine their acceptor–donor properties. The specific retention volumes of nonpolar and polar probes that were chromatographed on these ordered mesoporous silica adsorbents were evaluated under infinite dilution conditions. Two methods were employed to calculate the standard free energy of adsorption, ΔG _ads, of each chromatographed probe on the basis its specific retention volume. These ΔG _ads values were then employed to estimate the van der Waals contribution and the specific contribution of the free surface energy for each MCM41. DN values (donor numbers, based on the Gutmann scale) and AN* values (acceptor numbers, based on the Riddle–Fowkes scale) were employed to determine the values of parameters that characterize the ability of the MCM41s to act as electron acceptors (parameter: K _A) and donors (parameter: K _D). Considering the different compositions of the probes, each of which has different acceptor–donor properties, a new chromatographic test to supplement the Grob test is suggested.

     

“Demonstration” vs. “designation” of measurement competence: the need to link accreditation to metrology

Formal acceptance of the results of chemical laboratories is increasingly organized through a) accreditation of measuring laboratories nationally and b) mutual recognition of accreditation internationally (through formal Multilateral Recognition Agreements, MRAs). However, real comparability of results of measurements is realized by using common (internationally agreed) measurement scales which make these results traceable to this scale, i.e. “traceable” to the same (internationally agreed) value of the unit of that scale. In addition, the criterion against which the evaluation is done, should be “external” to the measurement laboratories which are being evaluated. This is realized in IRMM’s International Measurement Evaluation Programme (IMEP) where evaluation is performed against values which are anchored using “metrology”, the science of measurement with its own rules, which offers a sound foundation for measurement in all scientific disciplines. It is argued in this paper that the demonstration of measurement capability against values on such scales provides a result-oriented rather than a procedure-oriented evaluation. Thus, competence can be “demonstrated” rather than just “designated” and this can be shown to both customers and regulators. It inspires more confidence.     

Synthesis of Pt3Ni-based functionalized MWCNTs to enhance electrocatalysis for PEM fuel cells

Nanoscale Pt₃Ni/functionalized multiwalled carbon nanotubes (FMWCNTs) catalysts, successfully synthesized by anchoring nickel–platinum alloy nanoparticles on FMWCNTs, are presented in this paper. Compared with conventional commercial Pt/C catalysts, the preliminary results revealed that the Pt₃Ni/FMWCNTs catalysts demonstrated not only higher specific activity for oxygen reduction reaction (ORR) but also outstanding stability. The enhancement in the stability of the Pt₃Ni/FMWCNTs catalysts is believed to be due to the anchor effects in Pt₃Ni alloy structure, the stronger interaction between Pt₃Ni alloy nanoparticles and FMWCNTs, and the “π sites” anchoring centers for metal nanoparticles from CNTs with high graphite.     

“Cold” Synthesis of a New Antidepressant Drug S 3344

A “cold” synthetic route to 7-(4-fluorobenzylamino)-8-methylnonanoïc acid, a new antidepressant drug, is reported. This method can be used to obtain the tritium labelled compound in C₈-C₉ position. The synthesis involves introduction of double bond on the aliphatic chain, reduction of this and hydrolysis in alkaline medium of the ester function.     

Boron Tunneling in the “Weak” Bond-Stretch Isomerization of N−B Lewis Adducts

Some nitrile-boron halide adducts exhibit a double-well potential energy surface with two distinct minima: a “long bond” geometry (LB, a van der Waals interaction mostly based on electrostatics, but including a residual charge transfer component) and a “short bond” structure (SB, a covalent dative bond). This behavior can be considered as a “weak” form of bond stretch isomerism. Our computations reveal that complexes RCN−BX₃ (R=CH₃, FCH₂, BrCH₂, and X=Cl, Br) exhibit a fast interconversion from LB to SB geometries even close to the absolute zero thanks to a boron atom tunneling mechanism. The computed half-lives of the meta-stable LB compounds vary between minutes to nanoseconds at cryogenic conditions. Accordingly, we predict that the long bond structures are practically impossible to isolate or characterize, which agrees with previous matrix-isolation experiments.     

Evaluation of the matrix‐like effect in multiresidue pesticide analysis by gas chromatography with tandem mass spectrometry

In multiresidue pesticide analysis using gas chromatography, it has long been recognized that an increase in the number of pesticides present in a standard solution can result in an enhancement of the peak responses of certain pesticides. Despite being widely acknowledged, this phenomenon has been rarely studied and is poorly understood. In this study, the authors have tentatively called this phenomenon the “matrix‐like effect” and demonstrated it clearly using gas chromatography with tandem mass spectrometry. Five selected pesticides, namely, omethoate, terbufos, malathion, procymidone, and permethrin, and four internal standard candidates, namely, triphenyl phosphate, naphthalene‐d ₈, phenanthrene‐d ₁₀, and fluoranthene‐d ₁₀, were used to evaluate the matrix‐like effect following the addition of 58, 108, and 166 other pesticides. With the exception of naphthalene‐d ₈, the responses of all evaluated pesticides and internal standard candidates were dramatically enhanced by the addition of up to 166 coexisting pesticides. The relative response factors of the five pesticides to each internal standard candidate were not constant under the conditions studied, meaning that these internal standard candidates did not adequately compensate for the matrix‐like effect, at least for the five evaluated pesticides. The results revealed that the presence of various mixtures of pesticides in standard solutions might act as an unintentional analyte protectant, that is, some sort of troublesome “quasi‐matrix.”     

Determination of Absolute Gas Adsorption Isotherms by Combined Calorimetric and Dielectric Measurements

A new method to determine absolute masses of gas adsorbed on the external and internal surfaces of a porous solid is proposed. It consists on a combination of calorimetric and dielectric measurements. These lead to the enthalpy and the dielectric polarization of the adsorbed phase from which by purely thermodynamic calculations the absolute mass adsorbed can be determined without using the so-called helium volume hypothesis nor any other equivalent assumption.As example adsorption of subcritical carbon dioxide (CO₂) on zeolite (Degussa DAY) at 298 K and pressures up to 0,4 MPa is considered. As expected data of absolute masses adsorbed are always somewhat larger than the corresponding Gibbs excess masses calculated from both volumetric and gravimetric measurements via the helium volume of the zeolite.