Synthesis and characterization of original alternated fluorinated copolymers bearing glycidyl carbonate side groups

A vinyl ether bearing a carbonate side group (2‐oxo‐1,3‐dioxolan‐4‐yl‐methyl vinyl ether, GCVE) was synthesized and copolymerized with various commercially available fluoroolefins [chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), and perfluoromethyl vinyl ether (PMVE)] by radical copolymerization initiated by tert‐butyl peroxypivalate. Although HFP, PMVE, and vinyl ether do not homopolymerize under radical conditions, they copolymerized easily yielding alternating poly(GCVE‐alt‐F‐alkene) copolymers. These alternating structures were confirmed by elemental analysis as well as ¹H, ¹⁹F, and ¹³C NMR spectroscopy. All copolymers were obtained in good yield (73–85%), with molecular weights ranging from 3900 to 4600 g mol^?1 and polydispersities below 2.0. Their thermogravimetric analyses under air showed decomposition temperatures at 10% weight loss (T_d,10%) in the 284–330°C range. The HFP‐based copolymer exhibited a better thermal stability than those based on CTFE and PMVE. The glass transition temperatures were in the 15–65°C range. These original copolymers may find potential interest as polymer electrolytes in lithium ions batteries. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Pulse Radiolysis and Ultra‐High‐Performance Liquid Chromatography/High‐Resolution Mass Spectrometry Studies on the Reactions of the Carbonate Radical with Vitamin B12 Derivatives

The reactions of the carbonate radical anion (CO₃ ^{. ?}) with vitamin B₁₂ derivatives were studied by pulse radiolysis. The carbonate radical anion directly oxidizes the metal center of cob(II)alamin quantitively to give hydroxycobalamin, with a bimolecular rate constant of 2.0×10⁹ M ^?1 s^?1. The reaction of CO₃ ^{. ?} with hydroxycobalamin proceeds in two steps. The second‐order rate constant for the first reaction is 4.3×10⁸ M ^?1 s^?1. The rate of the second reaction is independent of the hydroxycobalamin concentration and is approximately 3.0×10³ s^?1. Evidence for formation of corrinoid complexes differing from cobalamin by the abstraction of two or four hydrogen atoms from the corrin macrocycle and lactone ring formation has been obtained by ultra‐high‐performance liquid chromatography/high‐resolution mass spectrometry (UHPLC/HRMS). A mechanism is proposed in which abstraction of a hydrogen atom by CO₃ ^{. ?} from a carbon atom not involved in the π conjugation system of the corrin occurs in the first step, resulting in formation of a Co^III C‐centered radical that undergoes rapid intramolecular electron transfer to form the corresponding Co^II carbocation complex for about 50 % of these complexes. Subsequent competing pathways lead to formation of corrinoid complexes with two fewer hydrogen atoms and lactone derivatives of B₁₂. Our results demonstrate the potential of UHPLC combined with HRMS in the separation and identification of tetrapyrrole macrocycles with minor modifications from their parent molecule.     

Anhydrous Conditions Enable the Catalyst-Free Carboxylation of Aromatic Alkynes with CO2 under Mild Conditions

The direct carboxylation of aromatic alkynes with CO₂, a cheap and widely available C1 source, is the most attractive method for the synthesis of carboxylic acids. Here we show that direct carboxylation of terminal alkynes can be simply performed in near-quantitative yield in four hours with anhydrous Cs₂CO₃ under mild conditions without need of a metal catalyst.     

Comb‐Like Amphiphilic Polycarbonates with Different Lengths of Cationic Branches for Enhanced siRNA Delivery

Owing to the biodegradability and good biocompatibility polycarbonates show the versatile class of applications in biomedical fields. While their poor functional ability seriously limited the development of functional polycarbonates. Herein, a new Br‐containing cyclic carbonate (MTC‐Br) and a polycarbonate atom transfer radical polymerization (ATRP) macro‐initiator (PEG‐PMTC‐Br) is synthesized. Then, by initiating the side‐chain ATRP of 2‐(dimethyl amino)ethyl methacrylate (DMAEMA) on PEG‐PMTC‐Br, a series of comb‐like amphiphilic cationic polycarbonates, PEG‐b‐(PMTC‐g‐PDMAEMA) (GMDMs), with different lengths of cationic branches are successfully prepared. All these poly(ethylene glycol)‐b‐(poly((5‐methyl‐2‐oxo‐1,3‐dioxane‐5‐yl) methyl 2‐bromo‐2‐methylpropanoate/1,3‐dioxane‐2‐one)‐g‐poly(2‐dimethyl aminoethyl methacrylate) (GMDMs) self‐assembled nanoparticles (NPs) (≈180 nm, +40 mV) can well bind siRNA to form GMDM/siRNA NPs. The gene silence efficiency of GMDM/siRNA high to 80%, which is even higher than the commercial transfection reagent lipo2000 (76%). But GMDM/siRNA shows lower cell uptake than lipo2000. So, the high gene silence ability of GMDM/siRNA NPs can be attributed to the strong intracellular siRNA trafficking capacity. Therefore, GMDM NPs are potential siRNA vectors and the successful preparation of comb‐like polycarbonates also provides a facile way for diverse side‐chain functional polycarbonates, expanding the application of polycarbonates.     

镁、铝与碳酸钠溶液反应的差异性研究

“镁|NaOH （aq）|铝”所形成的原电池，反应开始镁电极为负极，几秒钟后铝电极为负极，其原因是什么？从原电池形成理论以及通过对Mg和Al分别与饱和Na2CO3溶液反应的热力学和动力学分析角度，详细阐述上述原电池电极性质发生反转的理论基础，体验原电池反应与氧化还原反应在微观层面无实质性差异的事实。     

Interaction of dimethyl carbonate with anilines in the presence of potassium methylate: Kinetics and the role of the base

The kinetic patterns of the reaction between dimethyl carbonate and anilines in the presence of a potassium methylate as a catalyst were studied. The mechanism of aminolysis was clarified, which includes the detachment of the proton from the amino group of aniline and the subsequent attack of the resulting anion on the carbonyl group of dimethyl carbonate. It is shown that when the reaction occurs in the dimethyl carbonate-methanol 3:1 system, the process can be described as an irreversible first-order reaction in the aniline though the target reaction is complicated by side interaction between potassium methylate and dimethyl carbonate. The rate constants of the target reaction with substituted anilines and of the side reaction in the temperature range of 70-90°C were determined. It is shown that the influence of the substituent on the reaction rate is described by the Hammett equation, with the constant of the reaction series being positive and the best correlation being achieved for σ-scale. The results obtained are consistent with the proposed mechanism of the reaction and are explained by the facilitation of the aniline deprotonation with increasing acceptor properties of the substituent. Effective activation energies for the reaction of various anilines with dimethyl carbonate are found.     

Copper supported on phenanthroline-functionalized porous polymer as an active catalyst for the oxidative carbonylation of methanol

Porous organic polymer has recently attracted tremendous interest because of its potential to combine the best features of homogeneous and heterogeneous catalysts. In this study, copper supported on phenanthroline-functionalized porous polymer (Cu@PCP-Phen) was prepared by a co-polymerization method and used as a heterogeneous catalyst for dimethyl carbonate synthesis via the oxidative carbonylation of methanol. The catalyst was characterized by N₂ adsorption, scanning electron microscopy, transmission electron microscopy, ¹³C solid-state nuclear magnetic resonance, and X-ray photoelectron spectroscopy, which suggested that it possessed a big surface area, hierarchical porous structure, and strong electron-donating effect toward copper species. The Cu@PCP-Phen catalyst showed high catalytic activity, which was significantly higher than those achieved with Cu-based catalysts under similar reaction conditions. In addition, the catalyst can be easily separated and reused at least six times with only a slight decrease in activity. The salient features of this protocol are the simplicity in handling of the catalyst, high catalytic activity, excellent selectivity, low copper leaching, and good catalyst recyclability.     

New strategies for synthesis of amino-functionalized poly(propylene carbonate) over SalenCo(III)Cl catalyst

New strategies for synthesis of amino-functionalized poly(propylene carbonate) (PPC) were applied by terpolymerization of carbon dioxide, propylene oxide, with (a) N-(2,3-epoxypropyl)-2-phthalimide (Monomer A )/N-(2-oxiranylmethyl)-1 or (b) N-(2-oxiranylmethyl)-1,1-dimethylethyl ester (Monomer B ) over SalenCo^(III)Cl/PPNCl catalysts system, followed by the removal of the respective protecting groups. The SalenCo^(III)Cl presented high activity and yielded the terpolymer with high polycarbonate selectivity, carbonate linkage content, as well as high head-to-tail stereoregularity (>99%). In terpolymerization, the Monomer A contents in PPC-Pht were easily regulated up to 12.0 mol%. However, the protecting groups could not be completely removed because of the degradation of PPC-NH₂- A during the deprotection process. Meanwhile, when terpolymerization with Monomer B , PPC-butoxy carbonyl was obtained varied the Monomer B contents from 1.3 to 4.5 mol%, and could be transformed completely into the amino-functionalized PPC-NH₂- B without significant backbone degradation. The contact angles of the functionalized PPC-NH₂s prepared by two strategies showed the expected increase in hydrophilicity with the increasing content of amino entities.     

TEM preparation methods and influence of radiation damage on the beam sensitive CaCO3 shell of Emiliania huxleyi

The ultrastructure of biologically formed calcium carbonate crystals like the shell of Emiliania huxleyi depends on the environmental conditions such as pH value, temperature and salinity. Therefore, they can be used as indicator for climate changes. However, for this a detailed understanding of their crystal structure and chemical composition is required. High resolution methods like transmission electron microscopy can provide those information on the nanoscale, given that sufficiently thin samples can be prepared. In our study, we developed sample preparation techniques for cross-section and plan-view investigations and studied the sample stability under electron bombardment. In addition to the biological material (Emiliania huxleyi) we also prepared mineralogical samples (Iceland spar) for comparison. High resolution transmission electron microscopy imaging, electron diffraction and electron energy-loss spectroscopy studies revealed that all prepared samples are relatively stable under electron bombardment at an acceleration voltage of 300 kV when using a parallel illumination. Above an accumulated dose of ∼10⁵ e/nm² the material – independent whether its origin is biological or geological – transformed to poly-crystalline calcium oxide.     

A unified approach to simulation and upscaling of single‐phase flow through vuggy carbonates

Numerical modeling of flow through vuggy porous media, mainly vuggy carbonates, is a challenging endeavor. Firstly, because the presence of vugs can significantly alter the effective porosity and permeability of the medium. Secondly, because of the co‐existence of porous and free flow regions within the medium and the uncertainties in defining the exact boundary between them. Traditionally, such heterogeneous systems are modeled by the coupled Darcy–Stokes equations. However, numerical modeling of flow through vuggy porous media using coupled Darcy–Stokes equations poses several numerical challenges particularly with respect to specification of correct interface condition between the porous and free‐flow regions. Hence, an alternative method, a more unified approach for modeling flows through vuggy porous media, the Stokes–Brinkman model, is proposed here. It is a single equation model with variable coefficients, which can be used for both porous and free‐flow regions. This also makes the requirement for interface condition redundant. Thus, there is an obvious benefit of using the Stokes–Brinkman equation, which can be reduced to Stokes or Darcy equation by the appropriate choice of parameters. At the same time, the Stokes–Brinkman equation provides a smooth transition between porous and free‐flow region, thereby taking care of the associated uncertainties. A numerical treatment for upscaling Stokes–Brinkman model is presented as an approach to use Stokes–Brinkman model for multi‐phase flow. Numerical upscaling methodology is validated by analyzing the error norm for numerical pressure convergence. Stokes–Brinkman single equation model is tested on a series of realistic data sets, and the results are compared with traditional coupled Darcy–Stokes model. Copyright © 2011 John Wiley & Sons, Ltd.