Magnetic polyethyleneimine functionalized reduced graphene oxide as a novel magnetic solid-phase extraction adsorbent for the determination of polar acidic herbicides in rice

A novel magnetic polyethyleneimine modified reduced graphene oxide (Fe₃O₄@PEI-RGO) had been fabricated based on a self-assemble approach between positive charged magnetic polyethyleneimine (Fe₃O₄@PEI) and negative charged GO sheets via electrostatic interaction followed by chemical reduction of GO to RGO. The as-prepared Fe₃O₄@PEI-RGO was characterized by transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), thermal gravimetric analyzer (TGA), vibrating sample magnetometer (VSM) and zeta potential analysis, and then was successfully applied to determine four phenoxy acid herbicides and dicamba in rice coupled with high performance liquid chromatography (HPLC). As a surface modifier of RGO, PEI not only effectually affected the surface property of RGO (e.g. zeta potential), but also changed the polarity of RGO and offered anion exchange groups to polar acidic herbicides, which would directly influence the type of adsorbed analytes. Compared with Fe₃O₄@PEI, Fe₃O₄/RGO and Fe₃O₄@PEI-GO, the as-prepared Fe₃O₄@PEI-RGO, integrating the superiority of PEI and RGO, showed higher extraction efficiency for polar acidic herbicides. Besides, the adsorption mechanism was investigated as well. It turned out that electrostatic interaction and π-π interaction were considered to be two major driving force for the adsorption process. Response surface methodology (RSM), a multivariate experimental design technique, was used to optimize experimental parameters affecting the extraction efficiency in detail. Under the optimal conditions, a satisfactory performance was obtained. The calibration curves were linear over the concentration ranging from 2 to 300 ng g⁻¹ with correlation coefficients (r) between 0.9985 and 0.9994. The limits of detection (LODs) were in the range of 0.67–2 ng g⁻¹. The recoveries ranged from 87.41% to 102.52% with relative standard deviations (RSDs) less than 8.94%. Taken together, the proposed method was an efficient pretreatment and enrichment procedure and could be successfully applied for selective extraction and determination of polar acidic herbicides in complex matrices.     

One-pot synthesis of new 6-(alkylamine)dibenzo[c,e][1,2]oxaphosphinine-6-oxides

Several new 6-(alkylamine)-6H-dibenz[c,e][1,2]oxaphosphinine-6-oxides were prepared through a one-pot reaction, starting with 2-phenylphenol, phosphorus trichloride, and a Zn catalyst, to form 6-chloro-6H-dibenz[c,e][1,2]oxaphosphine. The alkylamine derivatives were subsequently prepared through a nucleophilic substitution reaction involving aliphatic amines and H₂O₂ oxidation under soft conditions. This method has the advantages that it is a one-pot synthesis, does not require an inert atmosphere, and involves in situ catalyst formation.     

Plasmon heating mediated Friedel-Crafts alkylation of anisole using supported AuNP@Nb2O5 catalysts

Two different hybrid materials composed of gold nanoparticles (AuNPs) supported on either commercial niobium oxide HY 340 or mesoporous niobium oxide catalyzed the Friedel-Crafts alkylation of anisole by benzyl chloride. Excitation of the surface plasmon of the supported AuNPs allowed the reaction to occur at lower temperatures by acting as an alternative heat source. The localized heating produced via plasmon excitation permitted the acid catalyzed reaction to occur - at the Lewis acid sites on the Nb₂O₅ support - at 80 °C while thermal-dark reactions using a conventional heat source, required temperatures of 120 °C or higher. The catalytic activity of the tested hybrid materials decreased with storage time. However, the deactivation showed to be reversible upon lyophilisation indicating that the nature of the deactivation could be due to water adsorption.     

Ionization Constants of DL-2-Aminobutyric Acid and DL-Norvaline Under Hydrothermal Conditions by UV–Visible Spectroscopy

The first and second ionization constants for the amino acids DL-2-aminobutyric acid (DL-2-aminobutanoic acid) and DL-norvaline (DL-2-aminopentanoic acid) were determined under hydrothermal conditions, from 175 to 275 °C at 10 MPa, using thermally-stable colorimetric pH indicators (acridine, 4-nitrophenol and 2-naphthoic acid). The measurements were carried out by UV–visible spectroscopy using a high-temperature, high-pressure platinum flow cell with sapphire windows, which minimized the effects of thermal decomposition. The results were combined with literature values from titration calorimetry at 25–130 °C to yield an extended van’t Hoff model for the temperature dependence of the ionization constants for the carboxylic acid and ammonium groups, \( K_{\text{a,COOH}} \) and \( K_{{{\text{a,NH}}_{3}^{ + } }} \), over the entire temperature range. The experimental results for the second ionization constant \( K_{{{\text{a,NH}}_{3}^{ + } }} \) at elevated temperatures are consistent with the predictions from the Yezdimer–Sedlbauer–Wood functional group additivity model, but for the first ionization constant \( K_{\text{a,COOH}} \) are not. This suggests that the group contribution parameters for the standard partial molar heat capacity of the carboxylic acid group are in error, or that nearest neighbor interactions between the –COOH and \( - {\text{NH}}_{3}^{ + } \) groups cause a breakdown in the functional group additivity relationship.     

ZSM-5分子筛催化甲醇制汽油反应中的晶粒粒径效应研究

通过调控水热合成ZSM-5凝胶液中H_2O/Si物质的量比,实现了粒径为70、200、400和650 nm四种单分散ZSM-5的可控合成。采用XRD、TEM、BET和NH_3-TPD等多种表征对其微观结构进行分析,结合催化性能评价,考察了晶粒粒径对其催化甲醇制汽油反应性能的影响机制。结果表明,整体上随着ZSM-5晶粒粒径的增加,其外比表面积减小,结晶度提高,酸量呈现出先增加后基本不变的趋势。但外表面附着小晶粒的粒径为650 nm的分子筛体现出了大的外表面积和强的酸性。ZSM-5晶粒粒径的增加整体上降低了其催化MTG反应的寿命和最高收率。晶粒粒径为70 nm时,ZSM-5体现出了96 h的催化寿命和30.8%的最高收率。晶粒粒径为650 nm样品由于其大的外比表面积和较强的表面酸性,也体现出91 h的寿命。在大晶粒ZSM-5外表面附着生长小晶粒ZSM-5,是一种制备高性能催化剂的新方法。     

On the geometric–arithmetic index by decompositions-CMMSE

The concept of geometric–arithmetic index was introduced in the chemical graph theory recently, but it has shown to be useful. There are many papers studying different kinds of indices (as Wiener, hyper–Wiener, detour, hyper–detour, Szeged, edge–Szeged, PI, vertex–PI and eccentric connectivity indices) under particular cases of decompositions. The main aim of this paper is to show that the computation of the geometric-arithmetic index of a graph G is essentially reduced to the computation of the geometric-arithmetic indices of the so-called primary subgraphs obtained by a general decomposition of G. Furthermore, using these results, we obtain formulas for the geometric-arithmetic indices of bridge graphs and other classes of graphs, like bouquet of graphs and circle graphs. These results are applied to the computation of the geometric-arithmetic index of Spiro chain of hexagons, polyphenylenes and polyethene.     

A Practical System for High-Throughput Screening of Mutants of <Emphasis Type="Italic">Bacillus fastidiosus</Emphasis> Uricase

For high-throughput screening (HTS) of Bacillus fastidiosus uricase mutants, a practical system was proposed. By error-prone PCR with final 1.5 mM MnCl₂, two focused libraries of mutants for A1-V158 and V150-D212 were generated separately. After induced expression of individual clones in 48-well microplates, Escherichia coli cells (BL21) were lyzed by 1.0 M Tris-HCl at pH 9.0 in 96-well microplates at 25 °C for 7.5 ~ 10.5 h; uricase reaction was continuously monitored with 0.15 mM uric acid in 96-well plates by absorbance at 298 nm to estimate V _m/K _m by kinetic analysis of reaction curve for comparison. V _m/K _m was resistant to initial uric acid levels with an upper limit 3-fold over that of initial rates. By receiver-operator-characteristic analysis of the recognition of the one of higher activity in uricase pair whose specific activity ratio was 1.8 or 3.3, the area-under-the-curve was comparable to that with cell lysates prepared by sonication treatment. A cutoff for the maximum Youden index was thus developed to recognize positive mutants of 1-fold higher activity. Indeed, mutant L171I/Y182F/Y187F/A193S of higher activity but lower thermostability at pH 7.4 and mutant V144A of higher activity and consistent thermostability were discovered. Therefore, the proposed system was practical for HTS of uricase mutants.     

A model with cosmological Bell inequalities

We discuss the possibility of devising cosmological observables which violate Bell's inequalities. Such observables could be used to argue that cosmic scale features were produced by quantum mechanical effects in the very early universe. As a proof of principle, we propose a somewhat elaborate inflationary model where a Bell inequality violating observable can be constructed.     

A well posed problem in singular Fickian diffusion

We prove that the problem of solving $$u_t = (u^{m - 1} u_x )_x {\text{ for }} - 1< m \leqq 0$$ with initial conditionu(x, 0)=φ(x) and flux conditions at infinity \(\mathop {\lim }\limits_{x \to \infty } u^{m - 1} u_x = - f(t),\mathop {\lim }\limits_{x \to - \infty } u^{m - 1} u_x = g(t)\) , admits a unique solution \(u \in C^\infty \{ - \infty< x< \infty ,0< t< T\} \) for every φεL¹(R), φ≧0, φ≡0 and every pair of nonnegative flux functionsf, g ε L _loc ^∞ [0, ∞) The maximal existence time is given by $$T = \sup \left\{ {t:\smallint \phi (x)dx > \int\limits_0^t {[f} (s) + g(s)]ds} \right\}$$ This mixed problem is ill posed for anym outside the above specified range.