Qingbiao Zhao

Fermi arcs in a doped pseudospin-1/2 Heisenberg antiferromagnet

Identifying a cuprate look-alike Superconductivity in cuprate compounds remains poorly understood. Recreating its features in an unrelated material may provide insight. Kim et al. used a spectroscopic technique to study the electronic states of the material Sr2IrO4 at relatively high temperatures. They observed phenomenology similar to that of cuprates as they varied the surface carrier concentration. The study highlights the essential properties a material needs in order to exhibit cuprate-like features in the normal (nonsuperconducting) state. Science, this issue p. 187 Some of the phenomenology of cuprate superconductors is recreated in strontium iridate surface-doped with potassium. High-temperature superconductivity in cuprates arises from an electronic state that remains poorly understood. We report the observation of a related electronic state in a noncuprate material, strontium iridate (Sr2IrO4), in which the distinct cuprate fermiology is largely reproduced. Upon surface electron doping through in situ deposition of alkali-metal atoms, angle-resolved photoemission spectra of Sr2IrO4 display disconnected segments of zero-energy states, known as Fermi arcs, and a gap as large as 80 millielectron volts. Its evolution toward a normal metal phase with a closed Fermi surface as a function of doping and temperature parallels that in the cuprates. Our result suggests that Sr2IrO4 is a useful model system for comparison to the cuprates.

2H-PEROVSKITE RELATED OXIDES: SYNTHESIS, STRUCTURES AND PREDICTIONS

The ability to synthesize new complex oxide materials that belong to any of the large number of known oxide structural families relies typically on a general understanding of the relationship between the specific structure type and the chemical composition of its members. However, before one can create such a structure-composition relationship that enables the synthesis of new members, one needs structural information about a sizable number of existing compositions belonging to this structural family, somewhat of a “chicken or the egg” problem. In this Highlight we will use one family of oxides, specifically oxides related to the hexagonal perovskite structure, to illustrate how exploratory crystal growth methods have been used successfully to synthesize enough diverse compositions to enable the formulation of a general structural description. Furthermore, by now it appears that enough members with different compositions have been synthesized so that one can attempt to create a structure-composition relationship that has predictive powers.

Ba4KFe3O9: a novel ferrite containing discrete 6-membered rings of corner-sharing FeO4 tetrahedra.

Single crystals of a new iron-containing oxide, Ba(4)KFe(3)O(9), were grown from a hydroxide melt, and the crystal structure was determined by single-crystal X-ray diffraction. This ferrite represents the first complex oxide containing isolated 6-membered rings of corner-sharing FeO(4) tetrahedra. Mössbauer measurements are indicative of two tetrahedral high-spin Fe(3+) coordination environments. The observed magnetic moment (~3.9 μ(B)) at 400 K is significantly lower than the calculated spin-only (~5.2 μ(B)) value, indicating the presence of strong antiferromagnetic interactions in the oxide. Our density functional theory calculations confirm the strong antiferromagnetic coupling between adjacent Fe(3+) sites within each 6-membered ring and estimate the nearest-neighbor spin-exchange integral as ~200 K; next-nearest-neighbor interactions are shown to be negligible. The lower than expected effective magnetic moment for Ba(4)KFe(3)O(9) calculated from χT data is explained as resulting from the occupation of lower-lying magnetic states in which more spins are paired. X-band (9.5 GHz) electron paramagnetic resonance (EPR) spectra of a powder sample consist of a single line at g ~ 2.01 that is characteristic of Fe(3+) ions in a tetrahedral environment, thus confirming the Mössbauer results. Further analysis of the EPR line shape reveals the presence of two types of Fe(6) magnetic species with an intensity ratio of ~1:9. Both species have Lorentzian line shapes and indistinguishable g factors but differ in their peak-to-peak line widths (δB(pp)). The line-width ratio δB(pp)(major)/δB(pp)(minor) ~ 3.6 correlates well with the ratio of the Weiss constants, θ(minor)/θ(major) ~ 4.

Crystal growth of novel lanthanide-containing platinates K4[Ln6Pt2O15] (Ln = La, Pr, Nd, Sm) with a unique framework structure.

Crystals of a new family of lanthanide-containing platinum oxides with a unique framework structure were grown out of molten hydroxide fluxes. The structure consists of a crystallographically well-behaved [Ln(6)Pt(2)O(15)](4-) framework permeated by channels filled with disordered atoms along the [100] and equivalent directions. Open-channel structures are rare in oxides and apparently unknown in platinate chemistry.

Isotropic and anisotropic regimes of the field-dependent spin dynamics in Sr2IrO4: Raman scattering studies

A major focus of experimental interest in Sr2IrO4 has been to clarify how the magnetic excitations of this strongly spin-orbit coupled system differ from the predictions of an isotropic 2D spin-1/2 Heisenberg model and to explore the extent to which strong spin-orbit coupling affects the magnetic properties of iridates. Here, we present a high-resolution inelastic light (Raman) scattering study of the low energy magnetic excitation spectrum of Sr2IrO4 and doped Eu-doped Sr2IrO4 as functions of both temperature and applied magnetic field. We show that the high-field (H > 1.5 T) in-plane spin dynamics of Sr2IrO4 are isotropic and governed by the interplay between the applied field and the small in-plane ferromagnetic spin components induced by the Dzyaloshinskii-Moriya interaction. However, the spin dynamics of Sr2IrO4 at lower fields (H < 1.5 T) exhibit important effects associated with interlayer coupling and in-plane anisotropy, including a spin-flop transition at Hc in Sr2IrO4 that occurs either discontinuously or via a continuous rotation of the spins, depending upon the in-plane orientation of the applied field. Furthermore, these results show that in-plane anisotropy and interlayer coupling effects play important roles in the low-field magnetic and dynamical properties of Sr2IrO4.

Rapid and sensitive determination of formamidines and metabolites with HPLC-MS/MS using core-shell columns

A number of poisoning and suicide cases involving formamidine pesticides have been reported, thus developing a rapid and low cost determination method is crucial. In this work, a rapid, sensitive and low-cost method for the simultaneous determination of formamidine pesticides (amitraz, chlordimeform, formetanate) and their main metabolites, N-(2,4-dimethylphenyl)-N-methyl-formamidine, 2,4-dimethylformamidine, 2,4-dimethylaniline, 4-chloro-2-methylaniline and 3-hydroxyacetanilide in human blood by high-performance liquid chromatography with tandem mass spectrometry is developed. The application of columns with core-shell particles significantly reduced the analysis time. Very low LODs (0.01-0.04 μg L-1) were obtained for formamidine pesticides and their metabolites. The method was successfully applied to the analysis of human blood samples from a real forensic case. The significantly reduced analysis time, high sensitivity and low cost are the primary advantages of the developed method. This methodology provides important value for sensitive and rapid determination of residue pesticides and metabolites, study of residue pesticides behavior in human body, as well as application in real forensic cases.

A bifunctional NiCo2S4/reduced graphene oxide@polyaniline nanocomposite as a highly-efficient electrode for glucose and rutin detection

A novel NiCo2S4/reduced graphene oxide@polyaniline (NiCo2S4/rGO@PANI) composite was synthesized by a facile two-step hydrothermal treatment and calcination, which was coupled with an in situ polymerization process. A bifunctional electrochemical sensor was developed for glucose electrocatalysis and rutin oxidation based on this composite modified glassy carbon electrode (GCE). The as-prepared composite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR). Furthermore, the NiCo2S4/rGO@PANI/GCE composite displayed excellent electrocatalytic activity towards glucose in the linear range of 1–7000 μM and a detection limit of 0.14 μM (S/N = 3). And for rutin, the linear range was 0.01–200 μM with a low detection limit of 0.007 μM (S/N = 3). The sensitivity of this sensor for glucose and rutin was evaluated to be 4.924 and 75.50 μA μM−1 cm−2, respectively. In addition, this sensor delivered high selectivity, good reproducibility, and long-term stability. The modified electrode was also employed to determine glucose in human blood serum samples and rutin in orange juice, buckwheat tea, and compound rutin tablet samples.

Simultaneous determination of nine anticoagulant rodenticides by ultra-performance liquid chromatography–tandem mass spectrometry with ultrasound-assisted low–density solvent dispersive liquid–liquid microextraction

A sensitive determination method is developed for nine anticoagulant rodenticides (ARs) in urine samples by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) with ultrasound-assisted low-density solvent dispersive liquid-liquid microextraction (UA-LDS-DLLME) pretreatment. The target analytes are brodifacoum, bromadiolone, warfarin, coumachlor, coumatetralyl, difenacoum, pindone, diphacinone and chlorophacinone. The parameters that influence the extraction recovery in the UA-LDS-DLLME were systematically investigated and optimized. With the optimized extraction parameters, recoveries ranging from 64.6%-124.2% were obtained for the target analytes. The linear range for all analytes was 0.1-100 ng/mL with correlation coefficients higher than 0.99. Very low LODs ranging in 0.003-0.03 ng/mL were obtained. LOQs were in the range of 0.01-0.1 ng/mL for the nine target analytes. The accuracy that was expressed as mean relative error was within ±5.8% while the precision expressed as relative standard error was less than 5.9%. The combination of UA-LDS-DLLME with UPLC-MS/MS is a feasible, sensitive and rapid analytical approach for the determination of ARs in urine matrix, which is particularly suitable for clinical and forensic purposes.

Sensitive and simultaneous determination of nine anticoagulant rodenticides in human blood by UPLC–MS-MS with phospholipid removal pretreatment

A sensitive and rapid method for the simultaneous determination of nine anticoagulant rodenticides (ARs) in human blood is reported herein. The method involves phospholipid removal pretreatment for reduced matrix effect (ME) and detection with ultra-performance liquid chromatography coupled with tandem mass spectrometry. Satisfactory recoveries were achieved ranging from 80.6% to 113.1% for the nine analytes, with the intra-day relative standard deviations (RSDs) in the range of 3.4-7.9% and inter-day RSDs in the range of 4.1-8.3%, indicating good precision. Linear relationships with correlation coefficients above 0.998 (n = 6) were found in the range of 1-2,000 ng/mL. High sensitivity was achieved with limits of detection ranging from 0.02 to 0.3. The application of phospholipid removal step significantly optimized the ME, and the reduction of ME ranged from 6.1% to 15.5%. This method was successfully applied to the determination of ARs for blood samples from real forensic cases. These results prove that this method is reliable for rapid forensic and clinical diagnosis. The removal capabilities for five representative phospholipids that are abundant in blood were evaluated individually with Phree™ phospholipid removal plates. While significant capabilities for phospholipid removal were confirmed, the results showed that the removal capability for certain phospholipid could be improved.

Sensitive and rapid determination of glyphosate, glufosinate, bialaphos and metabolites by UPLC–MS/MS using a modified Quick Polar Pesticides Extraction method

Phosphoric acid-containing amino acid pesticides, including glyphosate, glufosinate, and bialaphos, have been frequently encountered in human poisoning and suicidal cases, thus a quick and sensitive determination method for these compounds is very important. Herein we report a sensitive and rapid method for the determination of glyphosate, glufosinate, bialaphos and their metabolites, aminomethylphosphonic acid (AMPA) and 3-methylphosphinicopropionic acid (MPPA) in human blood samples. The method involves extraction using a modified Quick Polar Pesticides Extraction (QuPPe) method, cleanup with the PRiME HLB sorbents and detection with ultra performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). The LODs were 0.02mg/L for glyphosate, glufosinate and AMPA, 0.01mg/L for bialaphos and MPPA, with the analysis time as short as ∼6min. To the best of our knowledge, the LODs are lower and the analysis time is shorter than previous reports on determination of these compounds in blood and serum samples. The method was successfully applied to the detection and quantification of glyphosate and AMPA for blood samples from real forensic cases. This extremely rapid determination method with high sensitivity is of significant importance, particularly for forensic cases where quick determination is vital.