One hundred and forty years “Fresenius’ Journal of Analytical Chemistry”

The distribution of rare earth elements (REE) in a pooled soil sample collected from Zhangzhou, Fujian Province, China, was screened by a five-step sequential extraction procedure coupled with ICP–MS determination after preconcentration of REE and removal of the matrix by extraction with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP). The results showed that the distribution of REE in the different fractions of the pooled soil sample studied followed the order soluble species (46.76%) > species bound to organic matter (22.08%) > species in the residue (16.77%) > species bound to Fe–Mn oxides (2.02%). An effective method for speciation of REE, which utilized weak cation-exchange HPLC separation hyphenated with post-column derivatization and visible or on line ICP–MS detection, was, moreover, developed and successfully applied to the speciation of REE in the soluble extract of the pooled soil sample. The stability of known complexes of lanthanum during the HPLC separation was investigated with fluoride, citrate, and ethylenediamine tetraacetic acid (EDTA) chosen as ligands modeling those in the soil. REE in the soluble extract of the pooled soil sample were subsequently classified into three types of species –≤ + 1 charged complexes (negatively charged, neutral, and +1 charged), + 2 charged complexes, and “free” REE species. This method is expected to be useful for identification of bioavailable (or toxic) species of REE in environmental samples.     

The oxygen deficient cubic perovskite SrFe1−xScxO3−δ (x ≤ 0.5; 0.1 ≤ δ ≤ 0.5): Structural features and physical properties

Solid state synthesis method has been used to stabilize oxygen deficient perovskite phases SrFe_1?xSc_xO_3?δ (0 ≤ x ≤ 0.5). The good homogeneity of samples is confirmed by energy dispersive spectroscopy (EDS) analysis performed with a transmission electronic microscope (TEM). By combining X-ray and electronic diffraction (ED), it is demonstrated that the cationic substitution on the B site of the perovskite induces a decrease of the oxygen content but without inducing long range ordering phenomenon. On this basis, X-ray patterns of compounds were indexed in the cubic Pm3m space group. The oxidation states of iron evidenced by Mössbauer spectroscopy, are in good agreement with the oxygen stoichiometries determined by cerimetric titration. In the SrFe_1?xSc_xO_3?δ series, the Fe³⁺/Fe⁴⁺ origin of the electronic conductivity is clearly evidenced. The limit compound SrFe_0.5Sc_0.5O_2.5 is highly resistive and characterized by a cluster glass-like behaviour. Finally, negative magnetoresistivity properties are revealed for the x = 0.1 and x = 0.2 samples, reaching ?10% around the magnetic transition temperature in a 7T magnetic field.     

“Green Star”: a holistic Green Chemistry metric for evaluation of teaching laboratory experiments

Abstract

This paper presents a new semi-quantitative metric, Green Star (GS), for evaluation of the global greenness of chemical reactions used in teaching laboratories. Its purpose is to help choose the more acceptable reactions for implementing Green Chemistry (GC) and to identify suitable modifications of protocols to improve the greenness of the chemistry practiced by students. GS considers globally, in principle, all the Twelve Principles of GC. The metric consists in the evaluation of the greenness of the reaction for each principle by pre-defined criteria, followed by graphical representation of the results in an Excel radar chart – the fuller the chart, the higher degree of greenness. To illustrate the construction and the scope of the metric, a case study is presented – the iron(II) oxalate dihydrate synthesis performed under several sets of conditions to pursue the implementation of greenness.     

Single crystal structure investigation of twinned NaKSi2O5 — a novel single layer silicate

A new synthetic crystalline mixed alkali disilicate of composition NaKSi₂O₅ has been prepared by re-crystallization of a glass of corresponding composition. The compound is monoclinic, space group P2₁/n (a=7.3005(8) Å, b=17.389(2) Å, c=12.353(1) Å, β=91.14(1)°, V=1567.9 Å³, Z=12, D_calc=2.52 g cm⁻³). The crystal used for the data collection showed twinning by pseudo-merohedry according to 2_[001], a feature we took account of in the refinements. The structure was solved by direct methods and refined to a residual of R₁=0.070 (170 parameters). The compound belongs to the group of tetrahedral single layer silicates. Individual sheets are parallel to (001). The stepped layers can be described as being built by the condensation of unbranched dreier double chains. The double chains in turn consist of two unbranched dreier single chains connected via common corners and exclusively containing tertiary (Q³) tetrahedra. The stacking of the layers consisting of four-, six- and eight-membered rings results in a three-dimensional structure in which the alkali cations reside in the voids between neighboring sheets. The sodium and potassium atoms show an ordered distribution among the six symmetrically independent alkali sites. The coordination numbers for Na and K vary between 4 to 5 and 6 to 7, respectively.     

Efficient synthesis of an ε-hydroxy ester in a space–time yield of 1580 g L−1 d−1 by a newly identified reductase RhCR

A new NADH-dependent carbonyl reductase RhCR capable of efficiently reducing the ε-ketoester ethyl 8-chloro-6-oxooctanoate (ECOO) to give ethyl (S)-8-chloro-6-hydroxyoctanoate [(S)-ECHO], an important chiral precursor for the synthesis of (R)-α-lipoic acid, was identified from Rhodococcus sp. ECU1014. Using recombinant Escherichia coli cells expressing RhCR and glucose dehydrogenase used for the regeneration of cofactor, 440 g L⁻¹ (2 M) of ECOO were stoichiometrically converted to (S)-ECHO in a space–time yield of 1580 g L⁻¹ d⁻¹ without the external addition of any expensive cofactor.     

Vibrational relaxation rates for H on a Si(1 0 0):(2×1) surface: a two-dimensional model

The results of calculations based on perturbation theory of vibrational relaxation rates due to coupling to substrate phonons for hydrogen atoms adsorbed on a Si(1 0 0):(2×1) surface are presented. For this purpose a two-dimensional model is adopted in which both the H–Si stretching and bending motions are included. It is shown that within this model the multiphonon emission and absorption processes play a negligible role. The calculated lifetimes agree well with available experimental data.     

Structural and magnetic properties of TbxY3−xFe5O12 (0 ≤ x ≤ 0.8) thin film prepared via sol–gel method

Terbium-doped yttrium iron garnet (Tb_xY_3−x Fe₅O₁₂; x = 0.0, 0.2, 0.4, 0.6 and 0.8) nanoparticles thin films have been prepared onto quartz substrate by sol–gel method followed by spin coating process. Annealing of the films was processed at 900 °C in air for 2 h. The structures were investigated by using an X-ray diffractometer (XRD) and a field emission scanning electron microscope (FE-SEM). The magnetic properties were studied by a vibrating sample magnetometer (VSM). The XRD patterns of the films were consistent with a single phase garnet structure. The lattice parameter was initially increased with Tb³⁺ concentration due to the larger size of the Tb³⁺ ion compared to Y³⁺ ion, but a decrease in lattice parameter was observed at higher Tb³⁺ concentration due to the effect of film’s thickness. FE-SEM micrographs reveal that the particles were highly agglomerated. The grain’s sizes for all films were in the range of 40–59 nm. The magnetic measurements at room temperature (25 °C) show that the saturation magnetization (M_s) of the films was reduced with the increase in Tb³⁺ ions, which due to the antiparallel alignment between Tb³⁺ ions and Fe³⁺ ions. The films illustrate normal shapes of hysteresis loops except Tb_0.2Y_2.8Fe₅O₁₂ and Tb_0.4Y_2.6Fe₅O₁₂ films exhibiting two steps increments before being saturated. The coercivity values (H_c) demonstrate non linear dependency with the terbium concentration (x).     

Establishing a “Ring-Size-Divergent” Synthetic Strategy: Synthesis,Structural Revision,and Absolute Configuration of Feroniellins

Feroniellin analogs isolated from Feroniella lucida possess a furanocoumarin skeleton connected to monoterpenic five- to seven-membered ethereal rings by an ether linkage and exhibit a broad spectrum of biological activities. In this contribution, we intended to establish a “ring-size-divergent” synthetic strategy for the monoterpenic five- to seven-membered ethereal rings through the chemical sythesis of feroniellins. The short and comprehensive synthesis of feroniellins was achieved in only two steps from easily available bergamottin based on the “ring-size-divergent” strategy. In addition, these syntheses resulted in revision of the proposed structures for feroniellins A and B and the determination of all the absolute configurations of feroniellins; their preliminary anti-inflammatory activities were investigated as well.     

Measurement and correlation of the (p, ρ, T) relation of liquid cyclohexane,toluene, and ethanol in the temperature range from 233.15 K to 473.15 K at pressures up to 30 MPa for use as density reference liquids

Comprehensive (p, ρ, T) measurements on cyclohexane, toluene, and ethanol were carried out in the homogeneous liquid phase for temperatures from 233.15 K to 473.15 K at pressures up to 30 MPa. The measurements were performed by using an accurate single-sinker densimeter based on the Archimedes’ buoyancy principle. The total uncertainty of the measurements in density was estimated to be 0.015% (level of confidence 95%). Based on the experimental results, accurate correlation equations for the density of the three liquids have been established; their uncertainty is 0.020%. Comparisons with previous results of other experimentalists and with values calculated from current equations of state are presented. In this context it is also shown that the density of a liquid can vary slightly depending on the batch of the liquid used for the measurements. The purpose of this work was to provide accurate correlation equations for the densities of the three selected liquids so that these liquids can be used as density reference liquids for the calibration of densimeters and, in particular, for the calibration of vibrating-tube densimeters.     

“Just as the Structural Formula Does”: Names,Diagrams, and the Structure of Organic Chemistry at the 1892 Geneva Nomenclature Congress

At the Geneva Nomenclature Congress of 1892, some of the foremost organic chemists of the late nineteenth century crafted a novel relationship between chemical substances, chemical diagrams, and chemical names that has shaped practices of chemical representation ever since. During the 1880s, the French chemist Charles Friedel organised the nomenclature reform effort that culminated in the Geneva Congress; in the disorderly nomenclature of German synthetic chemistry, Friedel saw an opportunity to advance French national interests and his own pedagogical goals. Friedel and a group of close colleagues reconceived nomenclature as a unified field, in which all chemical names ought to relate clearly to one another and to the structure of the compounds they represented. The German chemist Adolf von Baeyer went a step farther, arguing for names that precisely and uniquely corresponded to the structural formula of each compound, tailored for use in chemical dictionaries and handbooks. Baeyer's vision prevailed at the Geneva Congress, which consequently codified rules for rigorously mapping structural formulas into names, resulting in names that faithfully represented the features of these diagrams but not always the chemical behaviour of the compounds themselves. This approach ultimately limited both the number of chemical compounds that the Geneva rules were able to encompass and the breadth of their application. However, the relationship between diagram and name established at the Geneva Congress became the foundation not only of subsequent systems of chemical nomenclature but of methods of organising information that have supported the modern chemical sciences.     

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape‐controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution‐phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape‐controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.     

Sintering kinetics study of mechanically alloyed nanocrystalline Mo–30 wt.% W

The paper details the results of sintering kinetics studies conducted on nanocrystalline Mo–30 wt.% W alloy powders prepared through mechanical alloying route. Both, constant rate of heating method as well as Stepwise Isothermal Dilatometry (SID) technique were used for studying the sintering kinetics. Measured step isothermal shrinkage data were analyzed by Mekipritti-Meng method. The shrinkage data was found to fit well with the rate equation proposed in this method and its validity was established for mechanically alloyed systems. Kinetic parameters were evaluated and sintering was found to occur through two major mechanisms operative successively, which are grain boundary diffusion and lattice diffusion with corresponding energies of activation as 230 kJ/mol and 480 kJ/mol, respectively. The results have been well supported by micro structural evaluation of specimens at different stages of sintering.