Selective degradation of lignin and elimination of HO radicals in pulps by O<Subscript>3</Subscript> and UV laser flash irradiation

HO^. radical is an aggressive reagent to abstract hydrogen from diverse substitutes and lead them to degradation, however, in reaction of active oxygen species with lignins, complex phenolic polymers, in dispersed lignocellulose such as pulp for environment-benign delignification, HO^. radicals should be eliminated as more as possible to prevent cellulose from unfavorably concomitant degradation. A reaction system of O₃ is constructed under UV laser flash irradiation, and HO^. radicals are controlled efficiently by it. A new mechanism is proposed, for the first time, that O^. radicals generated from reaction of O₃ with UV laser flash irradiation might be the contributor to scavenge HO^. radicals.     

Rigid nanoscopic containers for highly dispersed, stable metal and bimetal nanoparticles with both size and site control

We demonstrate a novel strategy for the preparation of mesoporous silica-supported, highly dispersed, stable metal and bimetal nanoparticles with both size and site control. The supporting mesoporous silica, functionalized by polyaminoamine (PAMAM) dendrimers, is prepared by repeated Michael addition with methyl acrylates (MA) and amidation reaction with ethylenediamine (EDA), by using aminopropyl-functionalized mesoporous silica as the starting material. The encapsulation of metal nanoparticles within the dendrimer-propagated mesoporous silica is achieved by the chemical reduction of metal-salt-impregnated dendrimer-mesoporous silica by using aqueous hydrazine. The site control of the metal or bimetal nanoparticles is accomplished by the localization of inter- or intradendrimeric nanoparticles within the mesoporous silica tunnels. The size of the encapsulated nanoparticles is controlled by their confinement to the nanocavity of the dendrimer and the mesopore. For Cu and Pd, particles locate at the lining of mesoporous tunnels, and have diameters of less than 2.0 nm. For Pd/Pt, particles locate at the middle of mesoporous tunnels and have diameters in the range of 2.0-4.2 nm. The Pd and Pd/Pt nanoparticles are very stable in air, whereas the Cu nanoparticles are stable only in an inert atmosphere.     

REVERSE ATOM TRANSFER RADICAL POLYMERIZATION OF STYRENE WITH COPPER-BASED CATALYST

 "Living"/controlled radical polymerization of styrene was carried out with diethyl 2,3-dicyano-2,3-diphenylsuccinate (DCDPS)/CuCl₂/bipyridine (bipy) initiation system at 120℃. The molecular weights of resultant PSt increased with the monomer conversion and the polydispersities were in the range of 1.37 ～ 1.52. A linear ln([M]o/[M])versus time plot was also obtained indicating the constant concentration of growing radicals during the polymerization with this initiation system. End group analysis by ¹H-NMR spectroscopic studies showed that the end groups of the polymer obtained is cω-functionalized by a chlorine group from the catalyst and a-functionalized by a (carbethoxy-cyano-phenyl)methyl group from the fragments of the initiator. Having C1 atom at the chain end, the PSt obtained can be used as a macroinitiator to promote a chain-extension reaction with fresh St and block copolymerization reaction with a second monomer, such as methyl methacrylate, in the presence of CuC1/bipy catalyst via a conventional ATRP process.     

Synthesis and structural identification of a highly ordered mesoporous organosilica with large cagelike pores

Using 1,2-bis(trimethoxysilyl)ethane as organosiloxane precursor and a triblock copolymer surfactant, Pluronic F127, as template, a highly ordered mesoporous organosilica with large cagelike pores has been successfully synthesized. Its structure was resolved to be 3-D cubic Fmm by high-resolution transmission electron microscopy. The intergrowth of hexagonal close-packed and cubic close-packed phases was observed in this material. The effect of different siliceous precursors on the mesostructure was also investigated.     

Two new triterpene glycosides with monomethyl malonate groups from the rhizome of Cimifuga foetida L

Two new 9,19-cycloartane triterpene glycosides 1-2, together with four known compounds--26-deoxyactein (3), actein (4), 7,8-didehydro-26-deoxyactein (5) and cimiaceroside B (6)--were isolated from the rhizome of Cimicifuga foetida. The new triterpene glycosides were identified as 23-O-methyl-24-deoxy-2'-O-(3'-methylmalonyl)-cimiaceroside B (1) and 2'-O-(3'-methylmalonyl)actein (2) based on analysis of their spectral data and chemical reactions.     

Oil phase evaporation-induced self-assembly of hydrophobic nanoparticles into spherical clusters with controlled surface chemistry in an oil-in-water dispersion and comparison of behaviors of individual and clustered iron oxide nanoparticles

We report a general method for preparing nanoparticle clusters (NPCs) in an oil-in-water emulsion system mediated by cetyl trimethylammonium bromide (CTAB), where previously only individual nanoparticles were obtained. NPCs of magnetic, metallic, and semiconductor nanoparticles have been prepared to demonstrate the generality of the method. The NPCs were spherical and composed of densely packed individual nanoparticles. The number density of nanoparticles in the oil phase was found to be critical for the formation, morphology, and yield of NPCs. The method developed here is scalable and can produce NPCs in nearly 100% yield at a concentration of 5 mg/mL in water, which is approximately 5 times higher than the highest value reported in the literature. The surface chemistry of NPCs can also be controlled by replacing CTAB with polymers containing different functional groups via a similar procedure. The reproducible production of NPCs with well-defined shapes has allowed us to compare the properties of individual and clustered iron oxide nanoparticles, including magnetization, magnetic moments, and contrast enhancement in magnetic resonance imaging (MRI). We found that, due to their collective properties, NPCs are more responsive to an external magnetic field and can potentially serve as better contrast enhancement agents than individually dispersed magnetic NPs in MRI.     

SYNTHESIS OF MESOPOROUS POLY(STYRENE-co-MALEIC ANHYDRIDE)/SILICA HYBRID MATERIALS VIA A NONSURFACTANT-TEMPLATED SOL-GEL PROCESS*

Mesoporous poly (styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis wasachieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydride copolymerin the presence of 3-aminopropyl triethoxysilane (APTES) as a coupling agent and citric acid as a nonsurfactant template orpore-forming agent, followed by ethanol extraction. Characterization results from nitrogen sorption isotherms and powder X-ray diffraction indicate that polymer-modified mesoporous materials with large specific surface areas (e.g. 900 m~2/g) andpore volumes (e.g. 0.6 cm~3/g) could be prepared. As the citric acid concentration is increased, the specific surface areas, porevolumes and pore diameters of the hybrid materials increase.     

VINYL MONOMERS BEARING CHROMOPHORE MOIETIES AND THEIR POLYMERS——Ⅹ.INITIATION AND PHOTOCHEMICAL PROPERTIES OF p-(N,N-DIMETHYLAMINO)STYRENE AND ITS POLYMERS*

A vinyl monomer having an electron-donating moiety, p-(N,N-dimethylamino)styrenc (DMAS),was synthesized. It was combined with benzoyl peroxide (BPO) to form a redox initiation system to initiatethe polymerization of methyl methacrylate (MMA). UV spectra measurements show that DMAS enters thePMMA chain as well. Both DMAS and its polymer P(DMAS) display strong fluorescence, and thefluorescence can be quenched by electron-deficient compounds such as methacrylonitrile, fumaronitrile andmethyl methacrylate etc. Moreover, DMAS can also form charge transfer complex (CTC) with strongelectron acceptors such as tetracyanoethylene (TCNE). The difference between the photochemical propertiesof DMAS and P(DMAS) were explained in terms of molecular structure change and polymer conformationeffect in solution. In addition, the CTC and exciplex formation of DMAS or P(DMAS) with C_(60) were alsostudied.     

微米级PSt,P(St/MAA)磁性高分子微球的合成Ⅰ. 温度、引发剂、介质极性、稳定剂量的影响

以Fe3O4为核，采用分散聚合法，合成了粒径为0．5－2．0μm、单分散性好、磁含量可达10％的PSt、P（St/MAA)磁性高分子微球。讨论了温度、引发剂、分散介质、稳定剂等因素对反应结果的影响。对所得磁性微球的外观形态、磁响应性进行了表征。     

Synthesis and Structure of an Extremely Air‐Stable Binuclear Hafnocene Perfluorooctanesulfonate Complex and Its Use in Lewis Acid‐Catalyzed Reactions

Stable complexes : An extremely air‐stable μ²‐hydroxy‐bridged binuclear hafonocene perfluorooctanesulfoante complex shows high catalytic efficiency in Lewis acid‐catalyzed reactions, such as esterification, Friedel–Crafts acylation, the Mukaiyama aldol reation, and the allylation of aldehyde (see scheme).