bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluorine⋅⋅⋅ and π⋅⋅⋅Alkali Metal Interactions Control in the Stereoselective Amide Enolate Alkylation with Fluorinated Oxazolidines (Fox) as a Chiral Auxiliary: An Experimental and Theoretical Study
Authors: Sini Gjergji , Tessier Arnaud , Pytkowicz Julien , Brigaud Thierry 
Published: February 2008

AbstractThe α‐alkylation of amide enolates by using a pseudo‐C2 symmetry trans 4‐phenyl‐2‐trifluoromethyloxazolidine (trans‐Fox) as a chiral auxiliary occurs with an extremely high diastereoselectivity (>99 % de). The origin of this excellent stereocontrol was investigated by an experimental and theoretical (DFT) study. With this trans chiral auxiliary, both F⋅⋅⋅metal and π⋅⋅⋅metal interactions compete to give the same diastereomer through Re face alkylation of the enolate. A 5.5 kcal mol−1 energy difference found between the Re face and the Si face attack transition states is consistent with the complete diastereoselectivity that has been experimentally achieved. On the other hand, in the case of the cis chiral auxiliary (cis‐Fox) the competition between the F⋅⋅⋅metal and π⋅⋅⋅metal interactions is unfavourable to the diastereoselectivity. In this case, the Re face and the Si face attack transition states were found to be nearly isoenergetic (0.3 kcal mol−1 difference), which is in good agreement with the very low diastereoselectivity observed.
Towards the Rational Design of MRI Contrast Agents: Electron Spin Relaxation Is Largely Unaffected by the Coordination Geometry of Gadolinium(III)–DOTA‐Type Complexes
Authors: Borel Alain , Bean Jonathan F. , Clarkson Robert B. , Helm Lothar , Moriggi Loïck , Sherry A. Dean , Woods Mark 
Published: February 2008

AbstractElectron‐spin relaxation is one of the determining factors in the efficacy of MRI contrast agents. Of all the parameters involved in determining relaxivity it remains the least well understood, particularly as it relates to the structure of the complex. One of the reasons for the poor understanding of electron‐spin relaxation is that it is closely related to the ligand‐field parameters of the Gd3+ ion that forms the basis of MRI contrast agents and these complexes generally exhibit a structural isomerism that inherently complicates the study of electron spin relaxation. We have recently shown that two DOTA‐type ligands could be synthesised that, when coordinated to Gd3+, would adopt well defined coordination geometries and are not subject to the problems of intramolecular motion of other complexes. The EPR properties of these two chelates were studied and the results examined with theory to probe their electron‐spin relaxation properties.
Enantioselective Formation of tert‐Alkylamines by Desymmetrization of 2‐Substituted Serinols
Authors: Hong Mi Sook , Kim Tae Woo , Jung Byunghyuck , Kang Sung Ho 
Published: February 2008

AbstractNovel enantioselective desymmetrization of 2‐substituted 2‐amino‐1,3‐propanediols has been established to generate asymmetric quaternary carbon centers comprising an amino group. Enantioselective as well as chemical conversion proved to be greatly dependent on the protecting group of the amino group in the substrate, desymmetrizing reagent, base, solvent, and naturally, catalyst. The highly effective desymmetrization has been implemented by using N‐benzoylated substrates with benzoyl chloride and triethylamine in the presence of tetraphenylbisoxazoline (24)–CuCl2 complex in THF at ambient temperature. An extensive survey of catalysts revealed that dimethylmalonate‐bridged bisoxazoline–CuCl2 complexes were superior. Among them, the tetraphenylbisoxazoline (24)–CuCl2 complex turned out to work most efficiently with a wide array of the substrates. All the examined substrates, with the exception of 2‐phenylserinol 36, were desymmetrized in the presence of 24–CuCl2 complex to give high enantioselectivities ranging from 85 to 95 % ee. Complementary use of the diisopropylbisoxazoline (22)–CuCl2 complex has remedied the mediocre desymmetrization of 36 to give a significantly improved enantioselectivity from 63 to 83 % ee.
A Persistent Alkylaluminum Peroxide: Surprising Stability of a Molecule with Strong Reducing and Oxidizing Functions in Close Proximity
Authors: Uhl Werner , Jana Barun 
Published: February 2008

AbstractThe reaction of the β‐diketiminato coordinated aluminum dihydride, [{HC[C(Me)NC6H5]2}AlH2] (1) with bis(trimethylsilyl)methyllithium afforded the monoalkylaluminum derivative [{HC[C(Me)NC6H5]2}Al(H)CH(SiMe3)2] (2) by the precipitation of lithium hydride. Interestingly, treatment of 2 with tert‐butyl hydrogenperoxide did not result in the formation of the simple oxidation product containing a hydroxo or alkoxo group, instead, elemental hydrogen was released and the hydrido ligand attached to aluminum was replaced by an intact tert‐ butylperoxo group. The AlC bond, which normally is extremely sensitive towards an attack of oxygen, was not affected. Hence, the product exhibits quite conflicting chemical properties in a close proximity: a strongly reducing AlC bond beside an oxidizing peroxo group.
Evaluation of a decision support training effectiveness measure
Authors: Bohler Jeffrey , Hall Dianne 
Published: February 2008

AbstractResource constraints affect the US Department of Defense's ability to simultaneously sustain current operations and recapitalize for future challenges. An assumption is that decision support training may improve resource allocation decisions; however, few instruments are available to measure the effectiveness of decision support training to verify that assumption. The purpose of this research is to evaluate an instrument to measure decision support training effectiveness. Using data collected from a resource allocation simulation, we found a significant positive relationship between decision support training and outcomes in a controlled field study involving a complex problem. Thus, in the proper context, the resource allocation simulation described herein may be a reliable measure of decision support training effectiveness. Copyright © 2008 ASAC. Published by John Wiley & Sons, Ltd.
Stable Small Gas‐Phase Dianion C7H22−
Authors: ZHANG Cong‐Jie , LIANG Jin‐Xia , CAO Ze‐Xing 
Published: February 2008

AbstractThe geometries and vibrational frequencies of C7H22− and C7H32− dianions, as well as their corresponding anions were investigated theoretically using HF, MP2, CCSD and CISD methods. The lowest energy structures are C2C(H2)C42− and C2CHCHCHC22− for C7H22− and C7H32− dianions, respectively. Analysis of possible detachment channels of the two structures indicates that the two isomers are stable with respect to fragmentation into two monoanions. However, the vertical and adiabatic detachment energies of the two structures show that C2C(H2)C42− is electronically stable, while C2CHCHCHC22− is not.
Titration Calorimetry Applied to the Thermokinetics Study of Consecutive First‐order Reactions
Authors: SHI Jing‐Yan , LI Jie , WANG Zhi‐Yong , LIU Yu‐Wen , WANG Cun‐Xin 
Published: February 2008

AbstractThe thermokinetic mathematical models for consecutive first‐order reactions in titration period and the stopped‐titration reaction period were proposed for titration calorimetry, based on which, thermodynamic parameters (reaction enthalpies, ΔrHm1and ΔrHm2) and kinetic parameters (rate constants, k1 and k2) of the consecutive first‐order reactions could be obtained by directly simulating the calorimetric curve from a single experiment with the method of nonlinear least squares regression (NLLS). The reliability of the model has been verified by investigating the reaction of the saponification of diethyl succinate in an aqueous ethanol solvent.
Density Functional Theory Study of Red‐shifted Hydrogen Bonds of 4‐Pyridinemethanol with Water
Authors: LI Quan , CAI Jing , CHEN Jun‐Rong , ZHAO Ke‐Qing 
Published: February 2008

AbstractThe hydrogen bonds of 1:1 and 1:2 complexes formed between 4‐pyridinemethanol and water have been investigated using a density functional theory (DFT) method and 6‐311++G∗︁ ∗︁ basis set, and three and eight stable geometries have been obtained for 1:1 and 1:2 complexes, respectively. The interaction energy is −20.536 and −44.256 kJ/mol for the most stable 1:1 and 1:2 complexes, respectively, after the basis set superposition error and zero‐point corrections. The formation of OH···N(O) hydrogen bonds makes OH symmetric stretching modes in the complexes red‐shifted relative to those of the monomer. The natural bond orbit analysis indicates that the intermolecular charge transfer between 4‐pyridinemethanol and water is 0.02642 e and 0.03813 e for the most stable 1:1 and 1:2 complexes, respectively. In addition, TD‐B3LYP/6‐311++G∗︁ ∗︁ calculations show that formation of water‐OH···N and water‐OH···OH hydrogen bonds makes maximum absorbance wavelength λmax blue‐shifted 8–16 nm and red‐shifted 4–11 nm compared to that of 4‐pyridinemethanol monomer molecule, respectively.
C–H···Cl Hydrogen Bond and π‐ π Interaction Based Two 3D Supramolecular Architectures of Cu(II) and Co(II) Complexes with Chiral 1,2‐Bis(benzimidazol‐2‐yl) ethane Ligand Containing 2D Grids
Authors: JI Bao‐Ming , WANG Xiu‐Ge , XU Chen , MA Ning , MIAO Shao‐Bin 
Published: February 2008

AbstractTwo new complexes, CuLCl2·2EtOH (1) and CoLCl2 (2) [L= (S,S)‐1,2‐bis(1‐methylbenzimidazol‐2‐yl)‐1,2‐bis‐(methoxy)ethane], have been synthesized in ethanol solution and structurally characterized by single crystal X‐ray diffraction analysis. The crystal structure data indicated that ligand L was coordinated to copper(II) ion as a tridentate ligand using [N, N, O] atoms, while it was coordinated to cobalt(II) ion as a bidentate ligand using [N, N] atoms. The most striking common feature of the structures of both complexes is the formation of 2D grid structures, which are formed by six and three types of intermolecular hydrogen bonds for complexes 1 and 2. These 2D grids are extended by CH···Cl hydrogen bonds and π‐π stacking interactions, leading to a 3D framework.
Synthesis and Thermal Decomposition Kinetics of Uranium(VI) Complex with Unsymmetrical Schiff Base Ligand
Authors: BI Cai‐Feng , ZHANG Xia , FAN Yu‐Hua , BI Shuang‐Yu , YU Hai‐Qin 
Published: February 2008

AbstractA new unsymmetrical tetradentate Schiff base ligand N‐(5‐chloro‐2‐hydroxy‐α‐phenylbenzylidene)‐N′‐(2‐hydroxy‐3‐methoxybenzylidene)‐o‐phenylenediamine (H2L) was synthesized using 5‐chloro‐2‐hydroxybenzophenone, o‐phenylenediamine and o‐vanillin. A solid UO2(II) complex of this ligand [UO2(HL)(NO3)(H2O)]·H2O was prepared and characterized by elemental analyses, IR, UV, 1H NMR spectra and molar conductance. The thermal decomposition kinetics of the complex for the third stage was studied under a non‐isothermal condition by TG and DTG methods. The kinetic equation may be expressed as: dα/dt=A·e−E/RT·3/2[(1−α)−1/3−1]−1. The kinetic parameters (E, A), activation entropy ΔS≠ and activation free‐energy ΔG≠ were also gained: E=69.08 kJ/mol, ln A=20.63, r=0.9867, ΔS≠= −79.84 J·mol−1·K−1 and ΔG≠=120.6 kJ/mol.
Layer‐by‐layer Assembly of Noble Metal Nanoparticles on Glassy Carbon Electrode
Authors: CHEN Da , ZHENG Long‐Zhen 
Published: February 2008

AbstractSilver, gold, platinum and palladium nanoparticles were initially prepared in the AOT [sodium bis(2‐ethylhexyl)‐ sulfosuccinate] micelle and characterized by ultraviolet‐visible spectroscopy, transmission electron macroscopy, X‐ray diffraction, Fourier transform‐infrared spectroscopy, and zeta potential analysis. The negatively charged Pt nanoparticles were self‐assembled on a glassy carbon electrode by a layer‐by‐layer method and the modified electrode electrocatalytic reactivity toward methanol oxidation was studied.
A Simple and Novel Route for The Preparation of Chiral Sodium Zincophosphate
Authors: LIAO Sen , WU Wen‐Wei , SUN Ya‐Bo , SONG Bao‐Ling 
Published: February 2008

AbstractA simple and novel route for the preparation of chiral sodium zincophosphate (NaZnPO4·H2O) (CZP) was studied, and the target product was obtained with Na3PO4·12H2O and ZnSO4·7H2O as raw materials and polyethylene glycol‐400 (PEG‐400) as a surfactant via one step low heat solid state reaction. The product was characterized with TG/DTG, XRD, TEM and SEM. The experimental results showed that the NaZnPO4·H2O, which was all obtained from different P/Zn atomic ratios (0.9–1.15) of Na3PO4·12H2O to ZnSO4·7H2O and different ageing time (2.0–8.0 h) at 60 °C, had the same chiral crystal structures except slight difference in their crystallinity. The comparison experimental results suggest that the ageing temperature and anion control the enantiomorphism of NaZnPO4·H2O, that is, if ZnSO4·7H2O or Zn(NO3)2·6H2O were used as Zn source, the first chiral structure of space group P6122 was formed when the reaction mixture was aged at 60 °C, and the second chiral structure of space group P6522 was got when the reaction mixture was aged at room temperature.
Synthesis, Crystal Structure and Thermal Stability Study of [Cu2(bpe)X2]n (bpe=1,2‐trans‐bi(4‐pyridyl)ethene, X=Cl, Br, I)
Authors: CHEN San‐Ping , FAN Guang , GAO Sheng‐Li 
Published: February 2008

AbstractA series of copper(I) halide complexes bridged by bpe (bpe=1,2‐trans‐bi(4‐pyridyl)ethene), [Cu2(bpe)Cl2]n (1), [Cu2(bpe)Br2]n (2) and [Cu2(bpe)I2]n (3) were successfully synthesized and complex 1 has been structurally characterized by a single crystal X‐ray diffraction method. Crystal data for 1 are monoclinic, space group P2(1)/c, a=0.3788(8) nm, b=1.5059(3) nm, c=1.0875(2) nm, β=96.262(4) °, V=0.6165(2) nm3, Z=2, S=1.002, final R indices [I>2δ(I)] R1=0.0288, wR2=0.0579, R index (all data) R1=0.0509, wR2=0.0615. Elemental analyses and IR spectra reveal that the complexes are of isomorphic compounds. In addition, thermogravimetric analyses were also applied to research of the thermal stability of the title complexes.
High‐rate Lithium Iron(II) Phosphate as Cathode Material for Rechargeable Lithium Batteries
Authors: ZHAO Ming , JIAO Li‐Fang , YUAN Hua‐Tang , SUN Jun‐Li , FENG Yan 
Published: February 2008

AbstractHigh‐rate carbon coated LiFePO4 was synthesized by citric acid assistant aqueous chemical route employing polyethyleneoxide as the carbon source. The structural and electrochemical properties were intensively investigated by thermogravimetry, powder X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge‐discharge tests. The results of structural tests showed that the material consisted of small LiFePO4 particles of good phase purity and the particles of the material were coated and connected with approximate 5 wt% incompact porous carbon. The material performed very well in electrochemical measurements, and was suitable for high‐rate charge and discharge. The material exhibited stable discharge capacities of 120, 90 and 60 mAh·g−1 at 5 C, 10 C and 20 C rates respectively (1 C=150 mA·g−1, charge at 1 C).
A Highly Sensitive Resonance Rayleigh Scattering Method for the Determination of Penicillin Antibiotics with Potassium Ferricyanide
Authors: DUAN Hui , LIU Zhong‐Fang , LIU Shao‐Pu , KONG Ling 
Published: February 2008

AbstractHeated in a boiling water bath, penicillin antibiotics such as amoxicillin, ampicillin, sodium cloxacillin, sodium carbenicillin and sodium benzylpenicillin could react with K3[Fe(CN)6] to form combined products in a dilute HCl medium. As a result, resonance Rayleigh scattering (RRS) intensity was enhanced greatly and new RRS spectra appeared. The maximum scattering wavelengths of the five combined products are all located at 330 nm. The scattered intensity increments (ΔI) of the combined products are directly proportional to the concentrations of the antibiotics in a certain range. The methods exhibit high sensitivity, and the detection limits for the five penicillin antibiotics are between 4.61 and 5.62 ng·mL−1. The spectral characteristics of RRS and the optimum reaction conditions were investigated. The mechanism of reaction and the reasons for the enhancement of resonance light scattering were discussed. The effects of coexisting substances have been examined, and the results indicated that the method had a good selectivity. It can be applied to the determination of penicillin antibiotics in capsule, tablet, human serum and urine samples.
Platinum Nanoparticles Modified Electrode for Rapid Electrochemical Detection of Escherichia coli
Authors: CHENG Yu‐Xiao , LIU Ya‐Jun , HUANG Jing‐Jing , FENG Zhen , XIAN Yue‐Zhong , WU Zi‐Rong , Zhang Wen , JIN Li‐Tong 
Published: February 2008

AbstractA platinum nanoparticles chemically modified electrode (PtNP/GCE) was fabricated by electro‐deposition and used to detection of Escherichia coli (E. coli). The detection principle was based on determination of p‐aminophenol that was produced by an enzymatic reaction in E. coli solution. The sensitivity of the detection was improved by the platinum nanoparticle modified electrode and optimization of the detection system. The current responses were proportional to the density of E. coli ranging from 50 to 1.0×105 cfu/mL, with detection limit of 20 cfu/mL, and the detection time was less than 4 h. Compared with conventional methods, the electrochemical technology described here could be suitable for rapid detection of E. coli in the fields of food industry, environmental monitoring and clinic biomedicine.
Studies on Chromatographic Properties of Perhydroxycucurbit[6]uril as a New Type of Gas Chromatographic Column Packing Material
Authors: LI Lai‐Sheng , WANG Shang‐Wen , CHEN Xiong‐Quan , LIU Chao , XU Li‐Li 
Published: February 2008

AbstractPerhydroxycucurbit[6]uril {(HO)12CB[6]} has been used successfully as a stationary phase for packed column gas chromatography for the first time. Perhydroxycucurbit[6]uril stationary phase (PSP) exhibited wide operational temperature, outstanding thermostability and good selectivities to various organic compounds, such as alkanes, aromatic hydrocarbons, alcohols, esters, ketones, amines, etc. It was also found that some positional isomers, such as disubstituted benzenes could be well separated on this column. PSP has excel1ent separation abilities to some complicate samples, for example, commercial toilet water. Some mechanism of the new packing for GC‐separation was preliminarily discussed. It was observed that the partial inclusion complexation of PSP with analytes could improve separation selectivity and column efficiency, instead of complete inclusion. Moreover, PSP exhibited low baseline shift even at dramatically programmed temperature for complicate samples covering a wide boiling point range so as to fast assay.
Ru(bpy)32+‐doped Silica Nanoparticle Aptasensor for Detection of Thrombin Based on Electrogenerated Chemiluminescence
Authors: WANG Xiao‐Ying , YUN Wen , ZHOU Jing‐Ming , DONG Ping , HE Pin‐Gang , FANG Yu‐Zhi 
Published: February 2008

AbstractA new electrogenerated chemiluminescent (ECL) detection system for protein using the aptamers was developed. Two different aptamers, which recognize different positions of thrombin, were chosen to construct sandwich type sensing system for protein, one was immobilized onto the gold electrode for capturing thrombin onto the electrode and the other was used for detection. To obtain the signal, the aptamer for detection was labeled with tris(2,2′‐bipyridyl)ruthenium(II)‐doped silica nanoparticles (Ru(bpy)32+‐doped SNPs). The increase of the ECL signal generated by Ru(bpy)32+‐doped SNPs was observed in dependent manner on the concentration of thrombin added. Bovine serum albumin and bovine hemoglobin had almost negligible responses. The assay allows detection at levels as low as 1.0 fmol·L−1 of the thrombin due to that there are a large number of Ru(bpy)32+ molecules inside SNPs labeled on the aptamer used for detection. The ECL signal was linearly related to the concentration of the thrombin analyte in the range of 2.0 fmol·L−1 to 2.0 pmol·L−1.
A Novel Metal‐free and Highly Efficient Hydroarylation of Styrenes Catalyzed by Molecular Iodine
Authors: SUN Gao‐Jun , ZHANG Tai‐Chang , SHENG Liu‐Si , QI Fei , WANG Zhi‐Yong 
Published: February 2008

AbstractA molecular iodine catalyzed hydroarylation of styrenes by arenes has been developed. This reaction could be carried out at 25 °C under a solvent‐free condition, giving rise to the corresponding products with yields up to 93%. A series of 1,1‐diarylalkane derivatives were easily prepared without any involvement of metal catalysts.
Synthesis and Properties of Two Second‐Order Nonlinear Optical Polymers: an Attempt toward the Balance between Nonlinearity and Transparence against Intrinsic Trade‐off
Authors: LI Su‐Yue , LI Zhong‐An , ZHU Zhi‐Chao , ZHANG Wei , HUANG Ting , LI Zhen , YE Cheng , QIN Jin‐Gui 
Published: February 2008

AbstractTwo new poly(arylene ether sulfone)s (P1 and P2) with two new accepting group (TCF)‐based chromophores (1 and 2) in side chains, respectively, were designed and synthesized. The two chromophores contain the same electron donating group (dialkylamino group) and the same accepting group (TCF), but different conjugation bridges. Compound 2 contains a combined conjugation bridge (phenyl‐diazene plus styrene), but the bridge of 1 is much shorter (styrene only). A variety of optical properties were studied. Compared with P1, P2 exhibited comparable nonlinear optical coefficient (d33) and better transparency (the maximum absorption was blue‐shifted by 16 nm), though the conjugation bridge of chromophore 2 in P2 was much longer than that of 1 in P1. This result may help design nonlinear optical polymers achieving the balance between nonlinearity and transparence against the intrinsic trade‐off.
Poly(diallyldimethylammonium chloride) as an Efficient Phase Transfer Catalyst in Solvent‐Free Reduction of Carbonyl Compounds with NaBH4
Authors: MAHDAVI Hossein , HAGHANI Ekram 
Published: February 2008

AbstractPoly(diallyldimethylammonium chloride) resin was used as an efficient polymeric phase transfer catalyst, which catalyzed the chemoselective reduction of aldehydes and ketones by NaBH4 to give the corresponding alcohols in high yields under solvent‐free conditions.
Synthesis of Andrographolide Glucopyranoside and Selective Cleavage of O‐acetyl Groups in Sugar Moiety
Authors: WANG Shao‐Min , LIU Hong‐Min 
Published: February 2008

AbstractAndrographolide glucopyranosides were synthesized from andrographolide and tetra‐O‐acetyl‐β‐D‐gluco‐ pyranosyl bromide via a Koenigs‐Knorr reaction and deacetylation with a moderate deacetylation reagent dibutyltin oxide in methanol for the first time. The structures of the andrographolide derivatives were confirmed by IR, NMR, and HRMS. Deprotection of the acetylated andrographolide glucopyranoside with dibutyltin oxide in methanol selectively removed all acetyl groups of the sugar moiety, whereas the acetyl group of the andrographolide part and the base‐ or acid‐sensitive functional groups were retained.
Further Daphniphyllum Alkaloids from the Bark of Daphniphyllum macropodum Miq.
Authors: LI Zhen‐Yu , CHEN Ping , XU Hong‐Gui , PENG Shu‐Ying , YANG Yi‐Ming , ZHAO Zhong‐Zhen , Guo Yue‐Wei 
Published: February 2008

AbstractFour new Daphniphyllum alkaloids, namely dehydroxymacropodumine A (1), 4,21‐deacetyl‐23‐demethyl‐deoxyyuzurimine (2), 7‐oxo‐deoxyyuzurimine (3), and 4‐acetoxydaphmanidin B (4), together with seven known related alkaloids, were isolated from the bark of Daphniphyllum macropodum Miq. The structures of new compounds 1–4 including relative configurations were elucidated on the basis of detailed spectroscopic data analysis and by comparison with related known compounds. Dehydroxymacropodumine A (1) possesses a rare eleven‐membered macrolactone ring representing the second example of this backbone isolated from natural sources.