铜镍双金属催化剂上糠醛水相选择性偶联加氢-重排制环戊酮

生物质资源高效催化转化制备高附加值化学品具有重要的科学意义与工业应用潜力.生物质基糠醛催化加氢-重排制备环戊酮是一条具有吸引力的"非石油"制备路线,但该过程面临副产物多、环戊酮选择性难以提高等难题,除糠醛外,中间物种也很容易发生多种聚合副反应.因此,探索中间物种聚合副反应的条件和作用机制,是提高目标产物环戊酮的选择性和收率的关键.本文制备了CuNi/Al-MCM-41双金属纳米过渡金属催化剂,通过精确调控介质水的pH值和原料浓度,实现了糠醛加氢-重排耦合制备环戊酮的高选择性和高收率.在2.0 MPa H2,160oC和近中性条件下反应5 h,糠醛的转化率为99.0％,环戊酮的选择性达到97.7％;其催化性能远远高于单组份铜或镍催化剂以及其它分子筛载体(MCM-41,SBA-15,HY,ZSM-5)负载的CuNi双金属催化剂.研究结果表明,高度分散在MCM-41上的少量Al组分,有利于Cu,Ni金属组分相互均匀分散.XPS结果表明,双金属催化剂CuNi/Al-MCM-41中Cu和Ni具有明显的电子结合能偏移,表明Ni向Cu转移电子;耦合催化反应性能的提高可能与CuNi双金属协同作用及电荷转移效应有关.傅立叶变换红外光谱和质谱结果表明,聚合副反应对反应体系的pH值敏感.在酸性条件下,中间产物糠醇在反应体系中容易发生聚合,导致糠醇重排生成3-羟基环戊烯酮的选择性降低;在碱性条件下,3-羟基环戊烯酮转化为4-羟基-环戊-2-烯酮后,容易进一步发生聚合副反应.在近中性条件下可有效避免中间体的聚合,提高加氢重排生成环戊酮的选择性.此外,降低原料糠醛的初始浓度,有利于降低聚合等副反应,能够进一步提高目标产物环戊酮的收率.本文为研制双金属纳米过渡金属催化剂以及利用双金属协同作用等方面提供新的启示,为解决生物质原料转化过程中普遍存在的聚合副反应和碳平衡降低等问题提供了新思路.     

Effect of sodium dodecyl sulfate and cetyltrimethylammonium bromide catanionic surfactant on the enzymatic hydrolysis of Avicel and corn stover

Nonionic surfactants could effectively improve the enzymatic hydrolysis efficiency of lignocellulose, while small molecule anionic and cationic surfactants usually inhibited the enzymatic hydrolysis. The results showed that the anionic surfactant sodium dodecyl sulfate (SDS) could improve the enzymatic hydrolysis efficiency of Avicel at the concentration range of 0.1–1 mM, but it did inhibit enzymatic hydrolysis at higher concentration. Cationic surfactant cetyltrimethylammonium bromide (CTAB) was used to regulate the surface charge of SDS; thereby catanionic surfactant SDS-CTAB was formed. The effect of SDS-CTAB catanionic surfactant with varied molar ratios on the enzymatic hydrolysis of pure cellulose and corn stover at various enzymatic hydrolysis environments was investigated. SDS-CTAB could increase the enzymatic hydrolysis of corn stover at high solid loading from 33.3 to 42.4%. Using SDS-CTAB could reduce about 58% of the cellulase dosage to achieve 80% of the enzymatic hydrolysis of corn stover. SDS-CTAB catanionic surfactant could regulate the surface charge of cellulase in the hydrolyzate and reduce the non-productive adsorption of cellulase on the lignin, thereby improving the enzymatic hydrolysis efficiency of lignocellulose.     

Achieving Morphological Control over Lamellar Manganese Metal-Organic Framework through Modulated Bi-Phase Growth

A modulated bi-phase synthesis towards large-scale manganese 1,4-benzenedicarboxylate (MnBDC) MOFs with a precise control over their morphology (bulk vs. layered) is presented. Metal precursors and organic ligands are separated to reduce the kinetic reaction rates for better control over the crystallization process. Based on scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy studies, the continuous ligand supply along with the presence of pyridine capping agent are highly effective in promoting the layer-by-layer growth and achieving large crystal sizes. Once layered MnBDC is stabilized, topotactic intercalation chemistry was used to demonstrate the feasibility of bromine intercalation on these layered materials. Bromine intercalation is possible between the MOFs layers for the first time. Bromine intercalation causes colossal reduction in layered MnBDC band gap while it has no observable effect on bulk MOFs.     

Polyethylene glycol-functionalized benzylidene cyclopentanone dyes for two-photon excited photodynamic therapy

A series of polyethylene glycol-functionalized benzylidene cyclopentanone dyes with varying lipid/water partition coefficients were synthesized in high yields by a simple process. Detailed characterization and systematic studies of these molecules, including linear and nonlinear photophysical properties, reactive oxygen yields, and in vitro photodynamic therapy (PDT) activities, were conducted. Four of these dyes exhibited good solubility in PBS (>2 mg ml(-1), which is sufficient for clinical venous injection), high reactive oxygen yields, large two-photon absorption and low dark toxicity, under the therapy dosage. Among them, two dyes could be absorbed efficiently by human rectal cancer 1116 cells, and presented strong two-photon excited PDT activity in in vitro cell experiments.     

自然增长条件下非线性椭圆方程的全局BMO估计

本文研究自然增长条件下一类具有H?lder连续系数的椭圆方程弱解梯度的全局BMO估计.在系数矩阵A为H?lder连续并满足一致椭圆条件下,利用极大函数方法,获得非线性Calderón-Zygmund型全局BMO估计.     

Numerical study of radial temperature distribution in the AlN sublimation growth system

A large radial temperature gradient in the AlN sublimation growth system would lead to non‐uniform growth rate along the radial direction and introduce thermal stress in the as grown crystal. In this paper, we have numerically studied the radial thermal uniformity in the crucible of a AlN sublimation growth system. The temperature difference on the source top surface is insignificant while the radial temperature gradient on the lid surface is too large to be neglected. The simulation results showed that the crucible material with a large thermal conductivity is beneficial to obtain a uniform temperature distribution on the lid surface. Moreover, it was found that the temperature gradient on the lid surface decreases with increased lid thickness and decreased top window size.     

Ionic liquid-assisted synthesis of carbon nanotube/platinum nanocomposites

A novel solution-enhanced dispersion by supercritical CO₂ (SEDS) was employed to prepare silk fibroin (SF) nanoparticles. The resulting SF nanoparticles exhibited a good spherical shape, a smooth surface, and a narrow particle size distribution with a mean particle diameter of about 50?nm. The results of X-ray powder diffraction, thermo gravimetry-differential scanning calorimetry, and Fourier transform infrared spectroscopy analysis of the SF nanoparticles before and after ethanol treatment indicated conformation transition of SF nanoparticles from random coil to ??-sheet form and thus water insolubility. The MTS assay also suggested that the SF nanoparticles after ethanol treatment imposed no toxicity. A non-steroidal anti-inflammatory drug, indomethacin (IDMC), was chosen as the model drug and was encapsulated in SF nanoparticles by the SEDS process. The resulting IDMC?CSF nanoparticles, after ethanol treatment, possessed a theoretical average drug load of 20%, an actual drug load of 2.05%, and an encapsulation efficiency of 10.23%. In vitro IDMC release from the IDMC?CSF nanoparticles after ethanol treatment showed a significantly sustained release over 2?days. These studies of SF nanoparticles indicated the suitability of the SF nanoparticles prepared by the SEDS process as a biocompatible carrier to deliver drugs and also the feasibility of using the SEDS process to reach the goal of co-precipitation of drug and SF as composite nanoparticles for controlled drug delivery.     

Supercritical biharmonic elliptic problems in domains with small holes

Let D be a bounded and smooth domain in R^N, N ≥ 5, P ∈ D. We consider the following biharmonic elliptic problemin Ω = D \B_δ (P), with p supercritical, namely . We find a sequence of resonant exponents such that if is given, with p ≠ p_j for all j, then for all δ > 0 sufficiently small, this problem is solvable (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical investigation on possible mechanisms on regioselective formation of (η-siloxyallyl)tungsten complexes

Selective formation of (η³-siloxyallyl)tungsten complexes by reaction of hydrido(hydrosilylene)tungsten complexes with α,β-unsaturated carbonyl compounds was reported experimentally. The mechanisms have been investigated by employing the model reaction of [Cp(CO)₂(H)WSi(H)–{C(SiH₃)₃}] (R), derived from the original experimental complex Cp′(CO)₂(H)WSi(H)–[C(SiMe₃)₃] (1a, Cp′ = Cp*; 1b, Cp′ = η⁵-C₅Me₄Et), with methyl vinyl ketone, under the aid of the density functional calculations at the b3lyp level of theory. It is theoretically predicted that the route involving migration of the hydride to silicon to afford a 16e intermediate [Cp(CO)₂W–SiH₂–{C(SiH₃)₃}] is inaccessible (route 2), supporting the proposition by experiments. Another route, via [2 + 4] cycloaddition followed by directly Si–H reductive elimination, is theoretically predicted to be accessible (route 1). In route 1, two possible paths with different attacking directions of the oxygen of methyl vinyl ketone at Si (WSi) are put forward. The attack at the Si atom from the hydride (H1) side of the plane W–Si–H1 in R is found to be preferred kinetically. The regioselectivity for formation of (η³-siloxyallyl)tungsten complexes, where only the exo-anti isomer was obtained, is discussed based on the consideration of thermodynamics and kinetics.