Diels-Alder reactions of quinol lactones: a change of regioselectivity with stannic chloride catalysis

Lewis acid-mediated Diels-Alder reactions of quinol lactone 2 gave regioselectivity opposite to that of the uncatalyzed reaction. Compound 12 is proposed as the reactive intermediate generated by the reaction of 2 with stannic chloride.     

Correlation and response functions with non-Markovian dissipation: a reduced Liouville-space theory

Based on a recently developed quantum dissipation formulation [R. X. Xu and Y. J. Yan, J. Chem. Phys. 116, 9196 (2002)], we present a reduced Liouville-space approach to evaluate the response and correlation functions of dissipative systems. The weak system-bath interaction is treated properly for its effects on the initial state, the evolution, and the correlation between coherent driving and non-Markovian dissipation. Numerical demonstration shows this correlated effect cannot be neglected even in the calculation of linear response quantities that do not explicitly depend on external fields. Highlighted in this paper is also the proper choice of theory among various formulations in the weak system-bath interaction regime.     

A highly enantioselective hetero-Diels-Alder reaction of aldehydes with Danishefsky's diene catalyzed by chiral titanium(IV) 5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol complexes

The catalytic effect of chiral Lewis acids on the hetero-Diels-Alder reaction between aldehydes and Danishefsky's diene (1) has been investigated. A variety of combinations of different ligands and Lewis acids have been examined as catalysts for the hetero-Diels-Alder reaction between benzaldehyde and 1, and it has been found that the readily accessible Ti(IV)-H(8)-BINOL (TiHBOL) complex is a very effective catalyst for the reaction, leading to products with very high enantioselectivity (up to 99% ee) and yield (92%). The hetero-Diels-Alder reaction of other aldehydes with 1 under the catalysis of TiHBOL is a general reaction which proceeds well with very high enantioselectivity and isolated yield for various aldehydes at 0 degrees C to room temperature. Based on the experimental results, the proposed mechanism of the hetero-Diels-Alder reaction and the dihedral angle effects of ligands are discussed.     

Importance of van der Waals Interactions in QM/MM Simulations

The importance of accurately treating van der Waals interactions between the quantum mechanical (QM) and molecular mechanical (MM) atoms in hybrid QM/MM simulations has been investigated systematically. First, a set of van der Waals (vdW) parameters was optimized for an approximate density functional method, the self-consistent charge-tight binding density functional (SCC-DFTB) approach, based on small hydrogen-bonding clusters. The sensitivity of condensed phase observables to the SCC-DFTB vdW parameters was then quantitatively investigated by SCC-DFTB/MM simulations of several model systems using the optimized set and two sets of extreme vdW parameters selected from the CHARMM22 forcefield. The model systems include a model FAD molecule in solution and a solvated enediolate, and the properties studied include the radial distribution functions of water molecules around the solute (model FAD and enediolate), the reduction potential of the model FAD and the potential of mean force for an intramolecular proton transfer in the enediolate. Although there are noticeable differences between parameter sets for gas-phase clusters and solvent structures around the solute, thermodynamic quantities in the condensed phase (e.g., reduction potential and potential of mean force) were found to be less sensitive to the numerical values of vdW parameters. The differences between SCC-DFTB/MM results with the three vdW parameter sets for SCC-DFTB atoms were explained in terms of the effects of the parameter set on solvation. The current study has made it clear that efforts in improving the reliability of QM/MM methods for energetical properties in the condensed phase should focus on components other than van der Waals interactions between QM and MM atoms.     

Temperature-sensitive polypeptide brushes-coated mesoporous silica nanoparticles for dual-responsive drug release

A multifunctional nanohybrid based on mesoporous silica nanoparticle and biocompatible polypeptide was fabricated for targeted and dual-responsive therapy of tumor cells.     

ICP-AES determination of trace elements after preconcentrated with p-dimethylaminobenzaldehyde-modified nanometer SiO2 from sample solution

A new method that utilizes p-dimethylaminobenzaldehyde-modified nanometer SiO₂ (SiO₂-p-DMABD) as a solid phase extractant has been developed for simultaneous preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). The preconcentration conditions of analytes were investigated, including the pH value, the shaking time, the mass of sorbent, the sample flow rate and volume, the elution condition and the interfering ions. The adsorption capacity of nanometer SiO₂-p-DMABD was found to be (mg g^− 1) Cr(III): 6.2, Cu(II): 18.6, Fe(III): 4.7 and Pb(II): 6.0 at pH 4. The adsorbed metals were quantitatively eluted with 4 mL of 1.0 mol L^− 1 HCl. According to the definition of IUPAC, the detection limits (3σ) of this method for Cr(III), Cu(II), Fe(III) and Pb(II) were 0.79, 1.27, 0.40 and 1.79 ng mL^− 1, respectively. The proposed method achieved satisfied results when it was applied to the determination of trace Cr(III), Cu(II), Fe(III) and Pb(II) in biological and water samples.     

Synthesis, structure, and fluorescence of the novel cadmium(II)-trimesate coordination polymers with different coordination architectures

Three novel complexes, Cd3tma2*13H2O (1), Cd3tma2*dabco*2H2O (2), and Cd3Htma3*8H2O (3) (tma = trimesate), of cadmium(II)-trimesate coordination polymers are obtained from hydrothermal reaction. 1 (C18H32O25Cd3) crystallizes in the monoclinic C2/c space group [a = 18.985(2) A, b = 7.3872(6) A, c = 20.432(2) A, = 97.1660(10), and Z = 4]. 2 (C24H22N2O14Cd3) crystallizes in the monoclinic P2(1)/c space group [a = 10.1323(2) A, b = 19.5669(5) A, c = 13.15880(10) A, = 108.9810(10), and Z = 4]. 3 (C27H28O26Cd3) belongs to the trigonal P31c space group [a = 15.7547(3) A, b = 15.7547(3) A, c = 7.93160(10) A, and Z = 2]. The Cd(II) centers in the three complexes are bridged by tma ligands in the coordination fashion of unidentate, bridging unidentate, bidentate, chelating bis-bidentate, chelating/bridging bis-bidentate, or chelating/bridging bidentate to form the T-shaped molecular bilayer motif for 1, chicken-wire-like motif for 2, and honeycomb-like porous structure for 3, respectively, in which the T-shaped molecular bilayer motif and chicken-wire-like motif are further interlinked in interdigitating or alternating fashion to construct the different coordination architectures. These three complexes exhibit strong fluorescent emission bands at 355 nm (lambda(ex) = 220 nm) for 1, 437 nm (lambda(ex) = 365 nm) for 2, and 353 nm (lambda(ex) = 218 nm) for 3 in the solid state at room temperature.     

Preparation of multihollow P(St-MAA) particles by sequence soap-free/soap emulsion polymerization and followed by stepwise alkali/acid posttreatment

The effects of ionic emulsifier, sodium dodecylbenzene sulfate (SDBS), on the formation of the multihollow structures in sub-micron sized polymer particles produced by alkali/acid posttreatment were investigated. The original latex particles with narrow size distribution were synthesized by a new sequence emulsifier-free/emulsifier emulsion copolymerization of styrene (St) and methacrylic acid (MAA). Results indicated that the pore size decreased and the pore number increased with the increase of SDBS amount, and the morphology of the posttreated latex particles was also significantly influenced by the introducing time of SDBS in the preparation of the original latex particles, and a suitable introducing time was 3 h of polymerization.     

Stannous oxalate as a novel catalyst for the synthesis of polytrimethylene terephthalate

Stannous oxalate was prepared efficiently and characterized by XRD and FT-IR. It exhibited higher catalytic activity and had profitable effect than tetrabutyl titanate and stannous octoate for the synthesis of polytrimethylene terephthalate (PTT) via esterification-route. Over this catalyst, the degree of esterification of pure terephthalic acid was up to 94.4% at 260°C after 1.5 h, while the intrinsic viscosity and content of terminal carboxyl groups of the corresponding PTT polyester, polymerized at 260°C, 60 Pa for 2 h, was 0.8950 dL/g and 15 mol/t, respectively. Stannous oxalate was a promising catalyst for the synthesis of PTT polyester.     

CO2选择性氧化甲烷制C2烃催化剂La2O3/ZnO的氧化还原和CO2吸附性能

Ｌａ２Ｏ３／ＺｎＯ催化剂体系在以二氧化碳作为氧化剂的甲烷氧化偶联反应中具有很高的Ｃ２烃选择性和稳定性．采用ＣＯ２－ＴＰＤ－ＭＳ和ＴＰＲ技术考察了Ｌａ２Ｏ３／ＺｎＯ对ＣＯ２的吸附性质及其氧化还原行为．结果表明：（１）Ｌａ２Ｏ３／ＺｎＯ催化剂体系存在着强、弱两种碱中心，其中弱碱中心数量随样品中Ｌａ２Ｏ３含量增加而减少，强碱中心强度随样品中Ｌａ２Ｏ３含量增加而增强．（２）由于组分相互作用，高温下，Ｌａ２Ｏ３／ＺｎＯ易产生晶格氧空位，使之对ＣＯ２的吸附增强，吸附后的ＣＯ２与晶格氧作用形成立方晶型Ｌａ２Ｏ２ＣＯ３．（３）Ｌａ２Ｏ３／ＺｎＯ表面的Ｌａ３＋和Ｚｎ２＋可以部分被还原，由于组分间的相互作用，使得二者的还原都较单一组分存在时更难．（４）Ｈ２－ＣＯ２－Ｈ２氧化还原循环实验表明，Ｌａ２Ｏ３／ＺｎＯ表面被部分还原后，ＣＯ２可以将部分被还原的表面再氧化．在此基础上对Ｌａ２Ｏ３／ＺｎＯ催化剂上甲烷与ＣＯ２转化为Ｃ２烃的机制也进行了讨论．