Relative importance of hydrolyzed Al(III) species (Al(a), Al(b), and Al(c)) during coagulation with polyaluminum chloride: a case study with the typical micro-polluted source waters

The relative importance of three different Al species, Al(a) (monomeric species, instantaneous reacted species), Al(b) (medium polymer species, reacted less than 120 min), and Al(c) (colloidal or solid species, no reaction), defined by timed complexation reaction rate measured by using ferron reagent in polyaluminum chloride (PACl) was investigated in terms of DOC (dissolved organic carbon), UV(254), and turbidity removal efficiencies. Micro-polluted, typical North China, source waters were used to conduct the experiments. The results show that DOC removal is correlated well to the content of Al(b). Removal of UV(254) is determined by the content of Al(b) and Al(c), particularly Al(c). Turbidity removal is primarily related to the content of Al(c); however, Al(b) could destabilize particles efficiently, and the flocs formed by Al(b) are not as large as those formed by Al(c), which affected the settling efficiency. Unlike the preformed Al(b), the in situ formed Al(b) could remove turbidity more efficiently since Al(c) is the dominant final species formed during coagulation. Al(a) shows a strong ability to react with some unsatisfied coordinate bonds of organic matter to facilitate particle and DOC removal. The distinct coagulation feature of Al(a), Al(b), and Al(c) can be applied to develop tailor-made PACl (with the correct distribution of Al species) to match the characteristics of raw water for optimized coagulation.     

The trans effect in square-planar platinum(II) complexes--a density functional study

The mechanism of substitution water exchange reactions in square planar trans-Pt[(NH(3))(2)T(H(2)O)](n+) complexes is studied (T = H(2)O, NH(3), OH(-), F(-), Cl(-), Br(-), H(2)S, CH(3)S(-), SCN(-), CN(-), PH(3), CO, CH(3)(-), H(-), C(2)H(4)). The trans effect is explained in terms of sigma-donation and pi-back-donation whose relative strengths are quantified by the changes of electron occupations of 5d platinum atomic orbitals. The sigma-donation strength is linearly correlated with the Pt-H(2)O (leaving ligand) bond length (trans influence). The kinetic trans effect strength correlates proportionally with the sigma-donation ability of the trans-ligand except the ligands with strong pi-back-donation ability that stabilizes transition state structure. The sigma-donation ability of the ligand is dependent on the sigma-donation strength of the ligand in the trans position. Therefore the trans effect caused by sigma-donation can be understood as a competition between the trans-ligands for the opportunity to donate electron density to the central Pt(II) atom. The influence of the trans effect on the reaction mechanism is also shown. For ligands with a very strong sigma-donation (e.g. CH(3)(-) and H(-)), the substitution proceeds by a dissociative interchange (I(d)) mechanism. Ligands with strong pi-back donation ability (e.g. C(2)H(4)) stabilize the pentacoordinated intermediate and the substitution proceeds by a two step associative mechanism. For ligands with weak sigma-donation and pi-back-donation abilities, the highest activation barriers have to be overcome and substitutions can be described by an associative interchange (I(a)) mechanism. The results are supported by the energy decomposition and the natural orbital analysis.     

2-氨基-3-氰基-4-(4-氟苯基)-4H-苯并[h]苯并吡喃的合成和晶体结构

标题化合物与N,N-二甲基甲酰胺(DMF)形成的1:1混合结晶物C20H23FN2OC3H7NO由对氟苯甲醛、丙二腈、-萘酚在六氢吡啶存在下合成并经DMF与水的混合溶剂重结晶而得, 其结构通过元素分析、IR 和1H NMR对化合物进行了表征,用X-射线单晶衍射法测定了该化合物的晶体结构。结果表明,晶体属于单斜晶系,P21/n空间群,a = 6.365(1), b = 10.620(2), c = 29.122(6) ? b = 92.00(1), V = 1967.3(6) ?, Mr = 389.42, Z = 4, Dc = 1.315 g/cm3, m (MoKa) = 0.092 mm-1, F(000) = 816。晶体结构用直接法解出,经全矩阵最小二乘法修正,最终偏离因子R = 0.047, wR = 0.1053。化合物分子中,原子C(1), C(2), C(3), C(4), C(5) 和O(1)形成1个六员环,该六员环中C(1)C(2)键长为1.346(3) 牛砻魑肆被肺焦瓜蟆?     

Microdetermination of Heavy Metal Chelates by High-Performance Liquid Chromatography

Abstract

Adsorption chromatography of diethyldithiocarbamate chelates of heavy metals is described. Determination of heavy metals including Hg (II), Cd (II), Pb (II), Cr (VI), Bi (III) and Cu (II) in micro to nano gram order is successfully carried out with good accuracy and reproducibility by a deactivated silica gel column. Separative microdetermination of these chelates is accomplished within 12 min, and selective determination is also possible by choosing the detection wavelength of a UV detector.     

Quantitative estimation of constituents in fly ash by lithium tetraborate fusion

Silica is removed from fly ash sample by hydroflourination for its effective determination gravimetrically and the remaining residue is subjected to lithium tetraborate (Li₂B₄O₇) fusion followed by dissolution in dilute nitric acid to obtain a clear solution in which elements including aluminum (Al), iron (Fe), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu) and zinc (Zn), have been determined by Flame Atomic Absorption Spectrometry (FAAS). Two fly ash samples analyzed by the proposed method have been received from the National Council of Cement and Building Materials (NCCBM), India (proposed CRM in future) and fly ash CRM 1633 (b) from NIST, USA. The validity of the method has been established by analyzing fly ash CRM 1633 (b) as reference standard. The standard deviation has been calculated for each measurement.     

Kinetochromic spectrophotometry-II Determination of sulphate by catalysis of the zirconium-methylthymol blue reaction

A direct spectrophotometric method is proposed for the determination of sulphate, based on its ability to catalyse the slow reaction between Methylthymol Blue and zirconium in slightly aged solution. The procedure is operated in the same way as a normal spectrophotometric method but with stricter control of timing. The interference of 100-fold excesses of 40 other ions was studied. Of these, Ce(III), Sr, Fe(III), Th, Sn(II), U(V), Mn(II), Sb(III), Se(IV), Bi(III), Te(IV), SO(3)(2-), F(-), PO(4)(3-), AsO(4)(3-), S(2-), tartrate, oxalate and citrate interfered. Cationic interferences may be removed by cation-exchange. The interference of equimolar ratios of arsenate, fluoride and phosphate may be removed by preliminary treatment with magnesium oxide. Sulphate may be determined in the range 0.1-2.4 ppm by the recommended procedure with a net molar absorptivity of 2.0 x 10(4) at 586 nm. The colour development time is 60 min.     

Separation of trivalent rare earths plus sc(iii) from al,ga,in,tl, fe,ti, u and other elements by cation-exchange chromatography

A method is presented for the quantitative separation of the trivalent rare earths plus Sc(III) as a group from Al(III), Ga(III), In(III), Tl(III), Fc(III). Ti(IV), U(VI), Be(II). Mn(II), Co(II), Cu(II), Ni(II). Zn(II). and Cd(II). These elements can be eluted from a cation-exchange column with 1.75 N HCl, while the rare earth group elements are retained. Numerous other elements not investigated have low distribution coefficients in 1.75 N HCl and therefore should be separated by the same procedure; Th(IV) is retained by the column when the rare earths are elutcd with 3.0 N HCl. The only elements which partially accompany the rare earths plus Sc(III) are Zr(IV), Hf(IV), Sr(II), and Ba(II) ; these have to be separated by special procedures. The method is suitable for accurate reference analysis over a wide range of concentrations.     

Study on Preconcentration of Trace Copper Using Microcrystalline Triphenylmethane Loaded with Malachite Green

The paper describes a novel method for copper preconcentration using microcrystalline triphenylmethane loaded with malachite green prior to the determination by the flame atomic absorption spectrometry （FAAS）. Under the optimum conditions, Cu（Ⅱ） can be totally adsorbed on the surface of microcrystalline triphenylmethane, and completely separated from Pb（Ⅱ）, Cd（Ⅱ）, Co（Ⅱ）, Cr（Ⅲ）, Ni（Ⅱ）, Mn（Ⅱ）, Fe（Ⅲ） and Al（Ⅲ） by controlling acidity. The preconcentration factor of this proposed method is 200. The recovery is in a range of 97.5%-105%. The relative standard deviation （RSD） is not beyond 3.0%. The proposed method has been successfully applied to the determination of trace copper in various water samples with satisfactory results.     

Preparation, characterization, and application of a new thiol-functionalized ionic liquid for highly selective extraction of Cd(II)

A highly selective thiol-functionalized ionic liquid (thiol-FIL) was synthesized and characterized by FT-IR and ESI mass spectroscopy. The capability of thiol-FIL to extract Cd(II), Ni(II), Cr(III) and Pb(II) was evaluated. It is found that thiol-FIL possesses high selectivity for Cd(II), and this has led to a method for determination of Cd(II) by flame atomic absorption spectrometry that is free of interferences by up to a 1,000-fold excess of Na(I), Mg(II), Ca(II), Mn(II), Fe(III), Al(III), Cu(II), Zn(II), Ni(II), Cr(III), Co(II), As(III), Pb(II), and Hg(II). With extraction equilibrium time of 1 min, a good linearity (r = 0.9998) and a detection limit of 0.39 μg?L^?1 were obtained. The precision (RSD) for 11 replicate measurements of 10 μg?L^?1 Cd was 1.6%. The method was validated using certified reference materials. The recoveries of cadmium in spiked real samples ranged from 97% to 102%.     

Analytical possibilities of pyridine-2-acetaldehyde benzoylhydrazone as a chromogenic reagent

With a view to the use of pyridine-2-acetaldehyde benzoylhydrazone is an analytical reagent, a study of the physical properties and fundamental solution chemistry of the complexes formed by PABH with Fe(II), Fe(III), Ni(II), Pd(II), V(V), Ti(IV), Hg(II), Mn(II), Zn(II), Bi(III), Co(II), Cu(II), Pb(II), and Ga(III) metal ions has been carried out. A critical comparison of pyridine-2-carbaldehyde and pyridine-2-acetaldehyde salicyloylhydrazones and pyridine-2-acetaldehyde benzoylhydrazone as analytical reagents is given.     

Beyond NICS: estimation of the magnetotropicity of inorganic unsaturated planar rings

A simple classical model of magnetic-field induced electron flow is used to evaluate the ring current strength for a few inorganic monocyclic compounds: B(3)H(3)N(3), B(3)H(3)O(3), P(6), N(6), Si(6)H(6), N, Al and H(6). It is shown that, for these neutral and charged systems, sustaining delocalized electron currents in the presence of a magnetic field B(ext) orthogonal to the σ(h) plane, the out-of-plane component of the nuclear magnetic shielding along the central axis is connected to the out-of-plane magnetizability by a simple equation, involving the radius of an average loop of current. A novel estimate of this effective radius is provided. Reliable ring current susceptibilities (that is, current strengths) can be evaluated by a simple relationship, using the out-of-plane components of nuclear shielding and magnetizability tensors. The accuracy of the current susceptibilities calculated by the classical model is established by comparison with corresponding ab initio estimates obtained by integrating the quantum mechanical current-density vector field. The out-of-plane components of nuclear shielding and magnetizability are both strongly biased by the molecular geometry. Their combined use to estimate the ring current susceptibility offers a quantifier of magnetotropicity more reliable than (i) the ξ(∥) out-of-plane component of magnetizability, (ii) the σ(∥)(CM) out-of-plane component of the magnetic shielding at the center of mass, widely reported as NICS(∥)(0) = -σ(∥)(CM). The inadequacy of these commonly adopted magnetotropicity measures is demonstrated by comparing a set of related molecules, C(6)H(6) and Si(6)H(6), N(6) and P(6).     

用于乙炔氢氯化反应的活性炭负载铋无汞催化剂

采用浸渍法制备了活性炭负载铋无汞催化剂,并通过X射线衍射、氮气物理吸附、透射电镜、扫描电镜和X射线电子能谱等方法对催化剂进行了表征。对催化剂进行了催化乙炔氢氯化反应性能的研究,结果表明,催化剂对乙炔氢氯化反应具有良好的催化性能,活性组分主要以BiOCl的形式存在于催化剂表面。反应过程中积碳的产生使得催化剂活性有所降低。     

Stereoselective synthesis of tetrahydrofuran lignans via BF(3) x OEt(2)-promoted reductive deoxygenation/epimerization of cyclic hemiketal: synthesis of (-)-odoratisol C, (-)-futokadsurin A, (-)-veraguensin, (+)-fragransin A(2), (+)-galbelgin, and (+)-talaumidin

A versatile route to the synthesis of 2,5-diaryl-3,4-dimethyltetrahydrofuran lignans, (-)-odoratisol C (1), (-)-futokadsurin A (2), (-)-veraguensin (3), (+)-fragransin A2 (4), (+)-galbelgin (5), and (+)-talaumidin (6), is described. Central to the synthesis of the lignans is BF(3) x OEt(2)-promoted deoxygenation/epimerization of the hemiketal 9a followed by stereoselective reduction of the oxocarbenium ion intermediates 8a,b.     

Adsorption and dissociation of NH3 on clean and hydroxylated TiO2 rutile (110) surfaces: a computational study

The adsorption and dissociation of NH(3) on the clean and hydroxylated TiO(2) rutile (110) surfaces have been investigated by the first-principles calculations. The monodentate adsorbates such as H(3)N-Ti(a), H(2)N-Ti(a), N-Ti(a), H(2)N-O(a), HN-O(a), N-O(a) and H-O(a), as well as the bidentate adsorbate, Ti-N-Ti(a) can be formed on the clean surface. It is found that the hydroxyl group enhances the adsorption of certain adsorbates on the five-fold-coordinated Ti atoms (5c-Ti), namely H(2)N-Ti(a), HN-Ti(a), N-Ti(a) and Ti-N-Ti(a). In addition, the adsorption energy increases as the number of hydroxyl groups increases. On the contrary, the opposite effect is found for those on the two-fold-coordinated O atoms (2c-O). The enhanced adsorption of NH(x) (x = 1-2) on the 5c-Ti is due to the large electronegativity of the OH group, increasing the acidity of the Ti center. This also contributes to diminish the adsorption of NH(x) (x = 1-2) on the two-fold-coordinated O atoms (2c-O) decreasing its basicity. According to potential energy profile, the NH(3) dissociation on the TiO(2) surface is endothermic and the hydroxyl group is found to lower the energetics of H(2)N-Ti(a)+H-O(a) and HN-Ti(a)+2{H-O(a)}, but slightly raise the energetic of Ti-N-Ti(a)+3{H-O(a)} compare to those on the clean surface. However, the dissociation of NH(3) is found to occur on the hydroxylated surface with an overall endothermic by 31.8 kcal/mol and requires a barrier of 37.5 kcal/mol. A comparison of NH(3) on anatase surface has been discussed. The detailed electronic analysis is also carried out to gain insights into the interaction nature between adsorbate and surface.     

3-邻氯苯基-3-(5,5二甲基-3-羟基-2-环己烯-1-酮-2-基)丙酸乙酯的合成和晶体结构

标题化合物C19H23O4Cl（4）是由邻氯苯甲醛（1）与5，5-二甲基-1，3-环己二酮（2）、2，2-二甲基-1，3-二氧六环-4，6-二酮（3）在乙醇中反应而得。结构通过单晶X-射线衍射分析确定，其晶体属于单斜晶系，空间群晶体结构用直接法解出，使用全矩阵最小二乘法对原子参数进行修正，最后的偏离因子R＝0．034，Rw＝0．042。在晶体结构中存在一个共轭的烯醇结构。单晶X-射线分析表明；平面1（C（1）～C（6）、Cl）和平面2（C（8）～C（10）、C（12）、C（13））之间的两面角为97．11°，原子C（7）呈变形的四面体构型。     

Single-step versus stepwise two-electron reduction of polyarylpyridiniums: insights from the steric switching of redox potential compression

Contrary to 4,4'-dipyridinium (i.e., archetypal methyl viologen), which is reduced by two single-electron transfers (stepwise reduction), the 4,1'-dipyridinium isomer (so-called "head-to-tail" isomer) undergoes two electron transfers at apparently the same potential (single-step reduction). A combined theoretical and experimental study has been undertaken to establish that the latter electrochemical behavior, also observed for other polyarylpyridinium electrophores, is due to potential compression originating in a large structural rearrangement. Three series of branched expanded pyridiniums (EPs) were prepared: N-aryl-2,4,6-triphenylpyridiniums (Ar-TP), N-aryl-2,3,4,5,6-pentaphenylpyridiniums (Ar-XP), and N-aryl-3,5-dimethyl-2,4,6-triphenylpyridinium (Ar-DMTP). The intramolecular steric strain was tuned via N-pyridinio aryl group (Ar) phenyl (Ph), 4-pyridyl (Py), and 4-pyridylium (qPy) and their bulky 3,5-dimethyl counterparts, xylyl (Xy), lutidyl (Lu), and lutidylium (qLu), respectively. Ferrocenyl subunits as internal redox references were covalently appended to representative electrophores in order to count the electrons involved in EP-centered reduction processes. Depending on the steric constraint around the N-pyridinio site, the two-electron reduction is single-step (Ar = Ph, Py, qPy) or stepwise (Ar = Xy, Lu, qLu). This steric switching of the potential compression is accurately accounted for by ab initio modeling (Density Functional Theory, DFT) that proposes a mechanism for pyramidalization of the N(pyridinio) atom coupled with reduction. When the hybridization change of this atom is hindered (Ar = Xy, Lu, qLu), the first reduction is a one-electron process. Theory also reveals that the single-step two-electron reduction involves couples of redox isomers (electromers) displaying both the axial geometry of native EPs and the pyramidalized geometry of doubly reduced EPs. This picture is confirmed by a combined UV-vis-NIR spectroelectrochemical and time-dependent DFT study: comparison of in situ spectroelectrochemical data with the calculated electronic transitions makes it possible to both evidence the distortion and identify the predicted electromers, which play decisive roles in the electron-transfer mechanism. Last, this mechanism is further supported by in-depth analysis of the electronic structures of electrophores in their various reduction states (including electromeric forms).     

Tuning of optical band gaps: syntheses, structures, magnetic properties, and optical properties of CsLnZnSe(3) (Ln = Sm, Tb, Dy, Ho, Er, Tm, Yb, and Y)

Eight new quaternary selenides CsSmZnSe(3), CsTbZnSe(3), CsDyZnSe(3), CsHoZnSe(3,) CsErZnSe(3), CsTmZnSe(3), CsYbZnSe(3), and CsYZnSe(3) have been synthesized with the use of high-temperature solid-state experimental methods. These compounds are isostructural with KZrCuS(3), crystallizing with four formula units in the orthorhombic space group Cmcm. The structure of these CsLnZnSe(3) compounds is composed of [LnZnSe(3)(-)] layers separated by Cs atoms. The Ln atom is octahedrally coordinated by six Se atoms, the Zn atom is tetrahedrally coordinated by four Se atoms, and the Cs atom is coordinated by a bicapped trigonal prism of eight Se atoms. Because there are no Se-Se bonds in the structure, the oxidation state of Cs is 1+, that of Ln is 3+, and that of Zn is 2+. CsYbZnSe(3) exhibits an antiferromagnetic transition at 11 K, whereas CsSmZnSe(3) does not follow a Curie-Weiss law. The remaining rare-earth compounds are paramagnetic, and the calculated effective magnetic moments of the rare-earth ions agree well with their theoretical values. Optical absorption data on face-indexed single crystals of CsSmZnSe(3), CsErZnSe(3), CsYbZnSe(3), and CsYZnSe(3) demonstrate that the optical band gap changes by more than 0.75 eV with the composition and by as much as 0.20 eV with the crystal orientation. The optical band gaps range from 2.63 eV (CsSmZnSe(3), CsErZnSe(3)) to 1.93 eV (CsYbZnSe(3)) for the (010) crystal face and 2.56 eV (CsErZnSe(3)) to 1.88 eV (CsYbZnSe(3)) for the (001) crystal face. The difference in the optical band gap of the (010) face vs the (001) face varies from +0.05 eV (CsYbZnSe(3)) to +0.20 eV (CsSmZnSe(3)).     

How we are cited: Russian analytical chemistry in the mirror of the science citation index (1991–2004)

An analysis of citations of scientific papers written by Russian analysts in 1991–2004 is presented, including those by the members of the Scientific Council on Analytical Chemistry of the Russian Academy of Sciences. Publications by 55 analysts within the studied period were cited from 100 to 400 times, and publications by 31 researchers were cited more than 400 times. Russian journals publishing articles in analytical chemistry are almost wholly covered by the Science Citation Index. Works by Russian analysts are actively cited by foreign scientists. The highest citation indexes were found for B.V. L’vov (2624 citations), V.A. Davankov (1826), Yu.A. Zolotov (1670), Yu.G. Vlasov (1279), L.A. Gribov (1264), A.R. Timerbaev (1239), A.A. Karyakin (1220), Kh.Z. Brainina (1002), V.G. Berezkin (942), and S.B. Savvin (913). The high citation index of a researcher is an important criterion for his positive appraisal; however, a low citation index of a scientific worker is not indicative of his low scientific qualification.     

The induced magnetic field in cyclic molecules

The response of a molecule to an applied external magnetic field can be evaluated by a graphical representation of the induced magnetic field. We have applied this technique to four representative, cyclic organic molecules, that is, to aromatic (C(6)H(6), D(6h)), anti-aromatic (C(4)H(4), D(2h)) and non-aromatic (C(4)H(8), D(4h), and C(6)H(12), D(3d)) molecules. The results show that molecules that contain a pi system possess a long-range magnetic response, while the induced magnetic field is short-range for molecules without pi systems. The induced magnetic field of aromatic molecules shields the external field. In contrast, the anti-aromatic molecules increase the applied field inside the ring. Aromatic, anti-aromatic, and non-aromatic molecules can be characterized by the appearance of the magnetic response. We also show that the magnetic response is directly connected to nucleus-independent chemical shifts (NICS).     

Unified synthesis of quinone sesquiterpenes based on a radical decarboxylation and quinone addition reaction

A unified synthesis of several quinone sesquiterpenes is described herein. Essential to this strategy is a novel radical addition reaction that permits the attachment of a fully substituted bicyclic core 16 to a variably substituted quinone 10. The addition product 15 can be further functionalized, giving access to natural products with a high degree of oxygenation at the quinone unit. The quinone addition reaction is characterized by excellent chemoselectivity, taking place only at conjugated and unsubstituted double bonds, and regioselectivity, being strongly influenced by the resonance effect of heteroatoms located on the quinone ring. These features were successfully applied to the synthesis of avarol (1), avarone (2), methoxyavarones (4, 5), ilimaquinone (6), and smenospongidine (7), thereby demonstating the synthetic value of this new method.