Compounds RE Research Articles

Deep Insights into Complicated Superdislocation Dissociation and Core Properties of Dislocation in L1 2 ‐Al 3 RE Compounds: A Comprehensive First‐Principles Study

Deep Insights into Complicated Superdislocation Dissociation and Core Properties of Dislocation in L1 ₂ ‐Al ₃ RE Compounds: A Comprehensive First‐Principles Study

Deep Insights into Complicated Superdislocation Dissociation and Core Properties of Dislocation in L1 2 ‐Al 3 RE Compounds: A Comprehensive First‐Principles Study

The complicated superdislocation dissociation, dislocation core properties, and slip mechanism of L12 structural alloys have been controversial. Herein, the generalized stacking-fault energy surfaces (γ-surfaces) of the {001}, {110}, and {111} planes in L12-Al3RE (RE = Er, Tm, Yb, Lu) compounds are first calculated according to ab initio density functional theory. Based on the γ-surfaces, the superdislocation dissociation modes are preliminarily estimated using the unstable and stable stacking-fault energies and their ratio. The result shows that the possible type of dissociations cannot be determined just from these ratios. Then, the 2D Peierls–Nabarro (PN) model is applied to simulate the ⟨110⟩{111} superdislocation dissociation configuration evolution in L12-Al3RE, and the complete dislocation properties, including the dissociation width, the dislocation movement, and the Peierls energy and stress, are also investigated. The present study indicates that the combination of the γ-surface and the 2D PN model can comprehensively elucidate the superdislocation properties and deformation mechanisms of L12 structural alloys.

Synthesis and Chemistry of Ammonioethenyl and Phosphonioethenyl Ligands in Zwitterionic Dirhenium Carbonyl Complexes.

New zwitterionic dirhenium carbonyl complexes containing ammonioethenyl and phosphonioethenyl ligands have been synthesized and studied. The reaction of Re2(CO)10 with C2H2 and Me3NO yielded the dirhenium complex Re2(CO)9(NMe3) (6) and the new zwitterionic complex Re2(CO)9[η1-E-2-CH═CH(NMe3)] (7). Compound 6 was characterized structurally and was found to have a NMe3 ligand in an equatorial coordination site cis to a long Re-Re single bond, Re-Re = 3.0938(2) Å. Compound 7 can be obtained from the reaction of 6 with ethyne (C2H2) formally by the insertion of ethyne into the Re-N bond to the NMe3 ligand. Compound 7 contains a 2-trimethylammonioethenyl ligand, -CH═CH(+NMe3), that is formally a zwitterion having a positive charge on the nitrogen atom and a negative charge on the terminal carbon atom. When coordinated to rhenium by the terminal ethenyl carbon atom, the negative charge on the -CH═CH(+NMe3) carbon atom is formally transferred to the rhenium atom. The reaction of Re2(CO)10 with C2H2 and NEt3 in the presence of Me3NO yielded the new dirhenium complex Re2(CO)9[η1-E-2-CH═CH(NEt3)] (8) together with some 6 and 7. Compound 8 is structurally similar to 7, but it contains a NEt3 group in the ammonioethenyl ligand in the place of the NMe3 group in 7. Reactions of 7 with PMePh2 and PPh3 yielded the zwitterionic 2-arylphosphonioethenyl-coordinated dirhenium carbonyl complexes, Re2(CO)9[η1-E-2-CH═CH(PPh2Me)] (9a) and Re2(CO)9[η1-E-2-CH═CH(PPh3)] (9b), and the zwitterionic 1-phosphonioethenyl ligand in the dirhenium carbonyl complexes, Re2(CO)9[η1-1-C(PPh2Me)(═CH2)] (10a), Re2(CO)8[μ-η2-1-C(PPh2Me)(═CH2)] (11a), and Re2(CO)8[[μ-η2-1-C(PPh3)(CH2)] (11b). Compound 10a was converted to 11a and the new compound Re2(CO)7(μ-H)[μ-η2-1-(CH2C)P(Ph)(Me)(o-C6H4)], (12) by decarbonylation using Me3NO. Compound 12 contains an ortho-metalated phenyl ring. The new products 6,7, 8, 9b, 10a, 11a, 11b and 12 were characterized structurally by single-crystal X-ray diffraction analyses.

The Polyphenolic Profile and Antioxidant Activity of Five Vegetal Extracts with Hepatoprotective Potential.

Oxidative stress is among the major triggers for many important human functional disorders, which often lead to various metabolic or tissue diseases. The aim of the study is to obtain five standardized vegetal extracts (Cynarae extractum—CE, Rosmarini extractum—RE, Taraxaci extractum—TE, Cichorii extractum—CHE, and Agrimoniae extractum—AE) that contain active principles with an essential role in protecting liver cells against free radicals and quantify their antioxidant actions. The compounds of therapeutic interest from the analyzed extracts were identified and quantified using the UHPLC–HRMS/MS technique. Thus, the resulting identified compounds were 28 compounds in CE, 48 compounds in RE, 39 compounds in TE, 43 compounds in CHE, and 31 compounds in AE. These compounds belong to the class of flavonoids, isoflavones, phenolic acids and dicarboxylic acids, depsides, diterpenes, triterpenes, sesquiterpenes, proanthocyanidins, or coumarin derivatives. From the major polyphenolic compounds quantified in all the extracts analyzed by UHPLC–HRMS/MS, considerable amounts have been found for chlorogenic acid (619.8 µg/g extract for TE–2032.4 µg/g extract for AE), rutoside (105.1 µg/g extract for RE–1724.7 µg/g extract for AE), kaempferol (243 µg/g extract for CHE–2028.4 µg/g extract for CE), and for naringenin (383 µg/g extract for CHE–1375.8 µg/g extract for AE). The quantitative chemical analysis showed the highest content of total phenolic acids for AE (24.1528 ± 1.1936 g chlorogenic acid/100 g dry extract), the highest concentration of flavones for RE (6.0847 ± 0.3025 g rutoside/100 g dry extract), and the richest extract in total polyphenols with 31.7017 ± 1.2211 g tannic acid equivalent/100 g dry extract for AE. Several methods (DPPH, ABTS, and FRAP) have been used to determine the in vitro total antioxidant activity of the extracts to evaluate their free radical scavenging ability, influenced by the identified compounds. As a result, the correlation between the content of the polyphenolic compounds and the antioxidant effect of the extracts has been demonstrated. Statistically significant differences were found when comparing the antiradical capacity within the study groups. Although all the analyzed extracts showed good IC50 values, which may explain their antihepatotoxic effects, the highest antioxidant activity was obtained for Agrimoniae extractum (IC50ABTS = 0.0147 mg/mL) and the lowest antioxidant activity was obtained for Cynarae extractum (IC50ABTS = 0.1588 mg/mL). Furthermore, the hepatoprotective potential was evaluated in silico by predicting the interactions between the determined phytochemicals and key molecular targets relevant to liver disease pathophysiology. Finally, the evaluation of the pharmacognostic and phytochemical properties of the studied extracts validates their use as adjuvants in phytotherapy, as they reduce oxidative stress and toxin accumulation and thus exert a hepatoprotective effect at the cellular level.

Quantitative analysis of rare earth elements in Mg–Zn–RE(Ce, Y, Gd)–Zr alloy

The solid solution amount of rare earth elements and the mass fraction of compounds were measured by low-temperature phase separation technology, the existing forms of rare earth elements in ZK-RE(Ce, Y, Gd) alloy were quantitatively studied, and the difference of solid solution ability of rare earth elements and the factors affecting the number of rare earth compounds were analyzed. The experimental results show that the solid solution amount of rare earth elements mainly depends on their addition amount, Zn and RE inhibit each other’s solid solution amount, and the order of solid solution amount (wt%) of rare earth elements with the same addition amount is GD > Y > Ce. Rare earth elements are mostly distributed in Mg–Zn–RE compounds, and the increase of rare earth content is helpful to form more Mg–Zn–RE compounds. With the same content of elements, the order of mass fraction of Mg–Zn–RE compounds is ZK-Ce system > ZK-Y system > ZK-Gd system. The order of solid solution ability of rare earth elements is Gd > Y > Ce, and the amount of solid solution directly affects the initial element content of compound precipitation in the remaining melt. The influence of Zn/Ce ratio in the residual melt of ZK-Ce alloy is shown in the number of rare earth compounds, while the Zn/Y(Gd) ratio in the residual melt of ZK-RE(Y, Gd) alloy determines the type and number of rare earth compounds.

Organotin Compounds in Industrial Catalysis. I. (Re)esterification Processes

This is the first part of a series of reviews on the application of organotin compounds as the catalysts for some important industrial processes, such as (re)esterification and production of polyurethanes, and also as the catalysts for cold vulcanization of silicones and other practically important processes. The first review considers the application of organotin compounds in (re)esterification processes.

The Structure of the Dipolar Bond in the Rare Earth Nitrilotris(Methylene Phosphonate)s with Different Oxygen Coordination Symmetries

The electronic structure of 16 complex compounds of RE (Y, La–Tb) with the same ligand – nitrilotris(methylenephosphonic acid) [NTP, N(CH2PO3)3H6] and with different coordination symmetries of the RE atom is investigated. The structure of XP‐spectra of a valence band in this area significantly differs for structures with non‐octahedral O‐coordination of the RE atom, on the one hand, and those with pseudo‐octahedral O‐coordination of the RE atom, on the other hand. In the XP‐spectra of non‐octahedral O‐coordination complexes the O2s‐states have a maximum at EB = 24–26 eV and are poorly overlapped with Ln5p‐states. For pseudo‐octahedral O‐coordination structures a wide strip is observed in the field of EB = 20–28 eV corresponding to an overlap M5p‐ and O2s‐states with formation of internal valence molecular orbitals (IVMO). Apparently, in pseudo‐octahedral O‐coordination structures the arrangement of O atoms agrees with the octahedral symmetry of RE p‐orbitals and leads to the formation of IVMO M5p+O2s.

Development of a Validated UPLC-MS/MS Method for Analyzing Major Ginseng Saponins from Various Ginseng Species.

Ginsenosides, which contain one triterpene and one or more sugar moieties, are the major bioactive compounds of ginseng. The aim of this study was to develop and optimize a specific and reliable ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the analysis of twelve different resources of ginseng. The six marker compounds of ginsenoside Rb1, ginsenoside Rb2, ginsenoside Rc, ginsenoside Rd, ginsenoside Re, and ginsenoside Rg1, as well as an internal standard, were separated by a reversed-phase C-18 column with a gradient elution of water and methanol-acetonitrile. The multiple-reaction monitoring (MRM) mode was used to quantify and identify twelve market products. The results demonstrated that not only is the logarithm of its partition coefficient (cLog P; octanol-water partition coefficient) one of the factors, but also the number of sugars, position of sugars, and position of the hydroxyl groups are involved in the complicated separation factors for the analytes in the analytical system. If the amount of ginsenoside Rb1 was higher than 40 mg/g, then the species might be Panax quinquefolius, based on the results of the marker ginsenoside contents of various varieties. In summary, this study provides a rapid and precise analytical method for identifying the various ginsenosides from different species, geographic environments, and cultivation cultures.

Multiple Aromatic C-H Bond Activations by an Unsaturated Dirhenium Carbonyl Complex.

Reactions of Re2(CO)8(μ-C6H5)(μ-H), 1, with naphthalene and anthracene have yielded the first multiply-CH activated arene products through the reductive elimination of benzene from 1 and multiple oxidative-additions of the dirhenium octacarbonyl grouping to these polycyclic aromatic compounds under very mild conditions. In addition, compound 1 was found to react with itself to yield the bis-Re2-metalated C6H4 bridged compound Re2(CO)8(μ-H)(μ-1,μ-3-C6H4)Re2(CO)8(μ-H), 3. Reaction of 1 with naphthalene yielded two doubly CH activated isomers, Re2(CO)8(μ-H)(μ-η2-1,2-μ-η2-3,4-C10H6)Re2(CO)8(μ-H), 4, 41% yield, and Re2(CO)8(μ-H)(μ-η2-1,2-μ-η2-5,6-C10H6)Re2(CO)8(μ-H), 5, via the mono CH activated intermediate Re2(CO)8(μ-η2-C10H7)(μ-H), 2. Compound 4 contains two Re2(CO)8(μ-H) groups on one C6 ring formed by CH activations at the 2- and 4-positions. Compound 5 contains two Re2(CO)8(μ-H) groups; one formed by CH activation at the 2-position on one C6 ring and the other formed by CH activation at the 6-position (or centrosymmetrically related 2'-position) on the second C6 ring. The Re2(CO)8(μ-H) groups are coordinated to the C6 rings by binuclear σ + π coordination to two adjacent carbon atoms in the rings. Compound 1 reacts with anthracene to yield the mono-CH activated compound Re2(CO)8(μ-η2-1,2-C14H9)(μ-H), 6, and two doubly CH activated compounds, Re2(CO)8(μ-H)(μ-η2-1,2-μ-η2-3,4-C14H8)Re2(CO)8(μ-H), 7, and Re2(CO)8(μ-H)(μ-η2-1,2-μ-η2-5,6-C14H8)Re2(CO)8(μ-H), 8. Compounds 7 and 8 are isomers that are structurally similar to 4 and 5. Compounds 7 and 8 can also be obtained in good yields from the reaction of 6 with 1. In the presence of a 5/1 ratio of 1/anthracene, a small amount (5% yield) of the tetra-substituted anthracene product [Re2(CO)8(μ-H)]4(μ-η2-1,2-μ-η2-3,4-μ-η2-5,6-μ-η2-7,8-C14H6), 9, was formed. Compound 9 contains four σ + π coordinated Re2(CO)8(μ-H) groups formed by oxidative additions of the CH bonds of anthracene to the Re2(CO)8 groups at the 2, 4, 6, and 8 positions of the three ring system. Molecular orbital calculations have been performed for all new compounds in order to develop an understanding of the bonding of the ring systems to the Re2(CO)8(μ-H) groups. All new compounds were characterized by single-crystal X-ray diffraction analyses.

Carbonyl compounds of Tc, Re, and Bh: Electronic structure, bonding, and volatility

Calculations of molecular properties of M(CO)5 and MH(CO)5, where M = Tc, Re, and Bh, and of the products of their decomposition, M(CO)4 and MH(CO)4, were performed using density functional theory and coupled-cluster methods implemented in the relativistic program suits such as ADF, DIRAC, and ReSpect. The calculated first M-CO bond dissociation energies (FBDEs) of Bh(CO)5 and BhH(CO)5 turned out to be significantly weaker than those of the corresponding Re homologs. The reason for that is the relativistic destabilization and expansion of the 6d AOs, responsible for weaker σ-forth and π-back donations in the Bh compounds. The relativistic FBDEs of M(CO)5 have, therefore, a Λ-shape behavior in the row Tc-Re-Bh, while the non-relativistic values increase toward Bh. Using the results of the molecular calculations and a molecule-slab interaction model, adsorption enthalpies, ΔH ads, of group-7 carbonyl hydrides on quartz and Teflon were estimated for future gas-phase chromatography experiments. It was found that BhH(CO)5 should be almost as volatile as the homologs, although its interaction with the surfaces should be somewhat stronger than that of MH(CO)5 (M = Tc and Re), while the M(CO)4 (M = Tc, Re, and Bh) molecules should be non-volatile. It will, therefore, be difficult to distinguish between the group-7 MH(CO)5 species by measuring their ΔH ads on surfaces of Teflon and quartz with an error bar of ±4 kJ/mol. The trends in properties and ΔH ads of group-7 carbonyl hydrides are similar to those of group-8 carbonyls of Ru, Os, and Hs.

Multiple C-H Bond Activations and Ring-Opening C-S Bond Cleavage of Thiophene by Dirhenium Carbonyl Complexes.

The reaction of Re2(CO)8(μ-C6H5)(μ-H) (1) with thiophene in CH2Cl2 at 40 °C yielded the new compound Re2(CO)8(μ-η2-SC4H3)(μ-H) (2), which contains a bridging σ-π-coordinated thienyl ligand formed by the activation of the C-H bond at the 2 position of the thiophene. Compound 2 exhibits dynamical activity on the NMR time scale involving rearrangements of the bridging thienyl ligand. The reaction of compound 2 with a second 1 equiv of 1 at 45 °C yielded the doubly metalated product [Re2(CO)8(μ-H)]2(μ-η2-2,3-μ-η2-4,5-C4H2S) (3), formed by the activation of the C-H bond at the 5 position of the thienyl ligand in 2. Heating 3 in a hexane solvent to reflux transformed it into the ring-opened compound Re(CO)4[μ-η5-η2-SCC(H)C(H)C(H)][Re(CO)3][Re2(CO)8(μ-H)] (4) by the loss of one CO ligand. Compound 4 contains a doubly metalated 1-thiapentadienyl ligand formed by the cleavage of one of the C-S bonds. When heated to reflux (125 °C) in an octane solvent in the presence of H2O, the new compound Re(CO)4[η5-μ-η2-SC(H)C(H)C(H)C(H)]Re(CO)3 (5) was obtained by cleavage of the Re2(CO)8(μ-H) group from 4 with formation of the known coproduct [Re(CO)3(μ3-OH)]4. All new products were characterized by single-crystal X-ray diffraction analyses.

Synthesis and magnetism of RE(BaBO3)3 (RE=Dy,Ho,Er,Tm,Yb) series with rare earth ions on a two dimensional triangle-lattice

We report the synthesis, structure and magnetic properties of compounds in RE(BaBO3)3 (RE = Dy,Ho,Er,Tm,Yb), crystallize in a hexagonal structure with space group P63cm, where the rare earth local moments lay out on a quasi-two dimensional triangular lattice. The analysis of magnetic susceptibilities indicate these materials display dominant antiferromagnetic interactions without magnetic order or glassiness above 2 K, suggest this series of compounds as a potential model for investigating magnetic frustration and novel magnetic ground state in rare-earth based materials.

Coordination chemistry of thioether-carboranes in polynuclear metal carbonyl cluster complexes. B-H activation of thioether-carboranes by dirhenium carbonyl complexes

Two new dirhenium compounds Re2(CO)8[μ-η2-1,3-C2B10H10(1-SCH3)](μ-H), 1 (3.2 % yield) and Re2(CO)8[μ-η2-1,4-C2B10H10(1-SCH3)](μ-H), 2 (31 % yield) were obtained from the reaction of closo-o-(1-SCH3)C2B10H11 with Re2(CO)8[μ-η2-C(H)C(H)Bun](μ-H) in an octane solution heated to reflux. Both compounds contain a C2B10H10(1-SCH3) ligand that bridges the pair of rhenium atoms by the sulfur atom and one of the boron atoms of the carborane cage. The Re – B bonds were formed by oxidative addition of one of the B – H bonds of the carborane to one of the Re atoms. The isomers differ by which boron atom, B(3) for 1 and B(4) for 2, has been added to the Re atom. Compound 1 was isomerized to 2 by heating to 107 °C, but 2 does not isomerize back to 1. A mechanism for the isomerization that involves a reductive-elimination of B(3) and the hydride ligand of 1 followed by an oxidative-addition of the neighboring B(4)-H bond to form 2 is proposed. The new compound Re2(CO)7[μ-η3-C2B10H9(1,2-(SCH3)2](μ-H), 3 was obtained in 38% yield from the reaction of [o-1,2-(SCH3)2]C2B10H10 with Re2(CO)8[μ-η2-C(H)C(H)Bun](μ-H) in an octane solution heated to reflux for 2h. The bridging C2B10H9(1,2-(SCH3)2 ligand is coordinated to one of the rhenium atoms by the two sulfur atoms at one of the Re atoms and the carborane boron atom B(3) also underwent cleavage at the B(3) – H bond to form the Re – B(3) bond to the other Re atom.

Current and Alternative Routes in the Production of Rare Earth Elements

Rare Earth Elements (REE) are essential in the day to day life both in developed and developing countries worldwide. Due to their catalytic, magnetic, electrical, chemical, heat resistance, and optical properties, they are used in a wide range of high-tech, high value-added, and fast-growing sectors. The current state-of-the-art processes for REE extraction follows complicated, energy and resource intensive technologies, including a beneficiation stage for the production of a RE-rich concentrate, leaching/purification/separation into individual high purity RE solutions, precipitation as individual RE compounds, and finally production of RE metals or alloys through metallothermic reduction or fused-salt electrowinning. Currently, China is the main REE market player, dominating production, demand, and exports. Novel, cost-effective, and resource-efficient REE extraction processes are currently under development tailored specifically for European REE primary and secondary deposits and for European health, safety, and environmental standards, under the EURARE project. This paper analyses the currently used processing technologies for REE production, identifies problems and technical challenges associated with them, and examines the prospects of establishing novel technologies for an efficient and economically viable REE production from European REE deposits. The results are presented on a promising new technology for extracting REE from secondary resources using ionic liquids. REE extraction yield of 60–80% with respective Fe extraction less than 3% has been already achieved.

Synthesis and Reactivity of Electronically Unsaturated Dirhenium Carbonyl Compounds Containing Bridging Gold-Carbene Groups.

The electronically unsaturated compounds Re2(CO)8[μ-Au(NHC)](μ-Ph), 1, and Re2(CO)8[μ-Au(NHC)]2, 2, were obtained from the reaction of Re2(CO)8[μ-η2-C(H)═C(H)Bun](μ-H) with MeAu(NHC), NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene. Compound 1 was converted to the new compound Re2(CO)8[μ-Au(NHC)](μ-H), 3, by reaction with H2. Addition of CO to 3 yielded the new compound Re2(CO)9[Au(NHC)](μ-H), 4, which contains a terminally coordinated Au(NHC) group on one of the rhenium atoms, and the hydrido ligand was shifted to bridge the Re-Au bond. The mechanism of the formation of 4 was established by DFT computational analyses. Compound 3 also reacted with C2H2 by an addition with insertion into the Re-H bonds to yield the compound Re2(CO)8[μ-Au(NHC)](μ-C2H3), 5, which contains a σ-π coordinated, bridging C2H3 ligand. The stereochemistry of the insertion was found to proceed preferentially with a cis- (syn-) stereochemistry. Compound 1 reacted with HCl to yield Re2(CO)8[μ-Ph](μ-H), 6, and ClAu(NHC) by selective removal of the bridging Au(NHC) group. All new compounds were characterized by single-crystal X-ray diffraction analyses.

Thermoelectric properties of Tsai-type Au–Al–RE (RE: Yb, Tm, Gd) quasicrystals and approximants

The thermoelectric properties of Tsai-type Au–Al–RE (RE: Yb, Tm, Gd) icosahedral quasicrystals (QCs) and their approximant crystals (ACs) have been investigated from 373 K to 873 K. Comparison of their thermoelectric properties above room temperature is of great interest since resonant states are likely to be present in the electronic density of states near the Fermi level for the Au–Al–Yb QC, which should influence the thermoelectric properties and, hence, the dimensionless figure of merit. The electrical conductivity of Au–Al–Yb ACs varies significantly, i.e. from 3000 Ω−1 cm−1 to 5200 Ω−1 cm−1, with changing the Au/Al composition whereas the other compounds have conductivities of ∼3000 Ω−1 cm−1. Such an anomalous behavior of the Au–Al–Yb ACs is understood to be due to the existence of a resonant peak originating from hybridization of Yb f-states and Au/Al sp-states. A maximum power factor of 230 μW m−1 K−2 at 873 K is obtained in 1/1-Au48Al37Yb15 AC, which is significantly higher than those of Al-based icosahedral phases at the same temperature. On the other hand, the room-temperature thermal conductivities for Au–Al–RE compounds range from 3 to 4 W m−1 K−1, reflecting their complex crystal structures with a large unit cell and mixed and/or partially occupied sites. Consequently, both 1/1-Au50Al35Yb15 and Au48Al37Yb15 ACs have similar maximum figures of merit of 0.014 at 873 K.

Non-photochemical synthesis of Re(diimine)(CO)2(L)Cl (L = phosphine or phosphite) compounds

The synthesis and characterization of a series of compounds of the type Re(diimine)(CO)2(L)Cl (where L=P(OEt)3, PMe3) is reported. The non-photochemical ligand substitution (non-PLS) utilizes the trans-labilizing effect of phosphorus ligands to facilitate carbonyl replacement. The non-PLS pathway leads to good yields (>60%) of single isomer products, comparing favorably to the lower yield, mixed isomer products of analogous PLS pathways. The substitution of a carbonyl group by a phosphine/phosphite ligands shifts absorption further into the visible region without diminishing molar absorptivity. The synthesis presented provides a general facile ligand substitution pathway for related light-sensitive neutral rhenium/manganese carbonyl halide compounds.

Enthalpies of formation of rare earth niobates, RE3NbO7

High-temperature oxide melt solution calorimetry was used to investigate energetics of a series of rare earth niobates RE 3 NbO 7 . All of investigated compounds were found to be stable in enthalpy in respect to their oxides. The enthalpy of formation from oxides becomes more exothermic as the size of the RE cation increases, a trend seen previously in other RE compounds including pyrochlores, perovskites, and phosphates. For smaller RE cations the enthalpy of exchange of RE between niobates and titanates is close to zero, whereas larger RE are energetically favored in the titanate pyrochlores. Implications of the results from the geochemical and material engineering points of view are discussed.

Shengmai Suppressed Vascular Tension in Umbilical Arteries and Veins of Human and Sheep

Objective—The umbilical cord is a critical pathway between mothers and fetuses, and regulations of umbilical vessel tension are important for fetal growth. Shengmai is an herbal medicine being used in treatments of cardiovascular diseases. However, effects of Shengmai on human blood vessels and related pharmacological mechanisms are unclear. Methods—This study investigated the effects of related mechanisms of Shengmai and its key compounds on human and sheep umbilical arteries and veins using organ bath systems. Key Findings—Shengmai significantly suppressed phenylephrine-stimulated vasoconstriction in umbilical arteries and veins. NG-Nitro-L-arginine Methyl Estercould not change the Shengmai-suppressed vasoconstriction in human and sheep umbilical vessels. Among four key compounds of Shengmai, Ginsenoside Re, Ginsenoside Rb1, Ginsenoside Rg1, and Schisandrin, only Ginsenoside Re showed the significant effect similar to Shengmai’s in the umbilical vessels. In Ca2+-free solution, Ginsenoside Re did not affect vasoconstriction. In addition, caffeine- or phenylephrine-stimulated vasoconstriction were not changed by Ginsenoside Re. Either charybdotoxin or glibenclamide could inhibit Ginsenoside Re-caused inhibition of the stimulated vasoconstriction in both human and sheep umbilical vessels, where 4-aminopyridine did not show the similar inhibitory effect. Conclusion—The results provide new information on Shengmai’s effects and underlying mechanisms in umbilical vessels. Importantly, the information gained offers interesting potential for developing new drugs acting on umbilical cords for fetal medicine.

The Effect of Mixed RE Elements on Microstructure and Mechanical Properties of Die-Cast AZ91D Alloy

The effect of mixed RE elements (Y, Nd, Gd ) on the microstructure and tensile properties of die-cast AZ91D alloy were investigated. The results indicated that the content of mixed RE elements lead to the change of the formation of Al▔RE compounds and reduction of the fraction of β-Mg17Al12 phase. The grain size of the alloy added 1.0wt. % RE became smaller than die-cast AZ91D and AZ91D+2.0wt. % RE alloys. The UTS of die-cast AZ91D+xRE(x=0 wt. %, 1.0wt. %, 2.0 wt. %) alloys were 204MPa, 194MPa, 203.6MPa at room temperature, respectively. Moreover, RE addition resulted in fracture behaviors changed.