Nanoparticulate platinum films on gold using dendrimer-based wet chemical method

There is a growing interest in devising wet chemical alternatives for physical deposition methods for applications involving thin films, e.g., catalysis. Deposition of platinum on thin gold films is often a problem leading to incomplete coverage and improper adhesion to solid surfaces. Gold substrates often need pre-activation for achieving complete coverage. We demonstrate here that dendrimers with proper functionalities and size work as well-defined nucleating agents and adhesion promoters. This feature is demonstrated using an amine-terminated dendrimer of generation 4.0. This approach allows one to obtain adherent nanoparticulate films of platinum on gold. Unlike other nucleating agents and adhesion promoting compounds, dendrimers have a well-defined ordered structure in terms of their space filling ability. The stability of the films obtained with adsorbed dendrimers is demonstrated using the electrocatalytic reactions of fuels like methanol. The films formed without dendrimers cannot sustain the electro-oxidation currents due to the instability of the films while the films formed with dendrimers can sustain currents for longer duration and for several cycles. The dendrimer-derived Pt films exhibit higher catalytic activity compared to other methods     

Synthesis and Striking Fluorescence Properties of Hyperbranched Poly(amido amine)

Hyperbranched poly(amido amine) (h‐PAMAM) was synthesized from different feed ratios of diethylene triamine and methyl acrylate by the simple one‐pot and commercial synthesis method. Reaction procedures and products were intensively studied by FTIR, inherent viscosity and fluorescence techniques. The ill‐structured h‐PAMAM shared similar chemical and physical properties with well defined poly(amido amine) (PAMAM) dendrimers in generation 2 or 3. Its strong fluorescence properties were influenced by pH values, solvents, concentrations, terminal groups and other factors.     

A Serum‐Resistant Low‐Generation Polyamidoamine with PEI 423 Outer Layer for Gene Delivery Vector

A new derivative of polyamidoamine and polyethylenimine, G2.5‐PEI 423 or G1.5‐PEI 423, is prepared by an amidation reaction of PAMAM G2.5 or PAMAM G1.5 using PEI 423. The polycations show a great ability to combine with pDNA to form complexes, which protect the pDNA from nuclease degradation. The polymers display stronger buffer capacity and lower cytotoxicity. The complexes have particle sizes of 120–180 nm and zeta potentials of 20–40 mV. The G2.5‐PEI 423 complexes display much higher transfection efficiencies than PAMAM G5 and Lipo‐2k, and the G1.5‐PEI 423 complexes display higher transfection efficiencies than PAMAM G4 and PEI‐25k. The complexes possess better serum‐resistant capacity. The G2.5‐PEI 423 has a great potential to be used as a serum‐resistant gene vector.

     

Self‐assembly of a new class of amphiphilic poly(amidoamine) dendrimers and their electrochemical properties

Amphiphilic poly(amidoamine) (PAMAM) dendrimers consisting of a hydrophilic dendrimer core and hydrophobic aromatic dansyl or 1‐(naphthalenyl)‐2‐phenyldiazene (NPD) shells have been synthesized. These amphiphilic dendrimers from the zero generation to the third generation self‐assemble into vesicular aggregates in water. The self‐assembly behavior of these dendrimers strongly depends on their generations. The generation dependence has been further investigated by an exploration of their electrochemical properties. For the PAMAM–NPD aggregates, the photoisomerization process leads to a change in the aggregate size. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5512–5519, 2005     

Structural deviations in poly(amidoamine) dendrimers: a MALDI-TOF MS analysis

A step-by-step synthesis/purification (CC, HILIC, HPLC) of poly(amidoamine) PAMAM dendrimers was performed. MALDI-TOF MS in the linear and reflectron mode was used to analyze the purified samples and byproduct samples of G0-G5 generations of the dendrimers up to the mass of 35 000 Da. DHB/fucose was found to give the best resolution, causing the least fragmentation of the samples. The precise mass number for the ideally branched dendrimers and their “structural errors” was obtained. The profile of the structural errors was established.     

聚酰胺氨类树枝形聚合物插入式自组装膜的制备与摩擦学性能：小分子链长的影响

在硅基片上制备了聚酰胺氨类树枝形聚合物与不同链长的脂肪酸小分子复合自组装单层膜,用椭圆偏振光测厚仪、DSA 100接触角测量仪、X 射线光电子能谱（XPS）和原子力显微镜（AFM）对所制备的薄膜结构进行了表征,并分别考察了薄膜的纳米摩擦学性能和宏观摩擦学性能。结果表明：C18和C12成功组装到了PAMAM单层膜上PAMAM分子间的空白处。小分子的插入减小了PAMAM自组装膜表面的摩擦力和摩擦系数,提高了PAMAM自组装膜的承载能力。小分子链长的差别对复合薄膜的结构及摩擦学性能影响的差别不明显。     

Rapid aqueous ‘click chemistry’ using Cu(I)-loaded dendrimers as macromolecular catalysts

Here, we investigate the catalytic activity of various copper (Cu)-loaded poly(amido amine) (PAMAM) dendrimers towards the Cu(I)-catalysed azide-alkyne cycloaddition (CuAAC). Reactivity is tested on a model reaction between azido propanol and propargyl alcohol in aqueous solution. We observe significantly faster conversion using PAMAM dendrimers as macromolecular Cu(I) ligands compared to traditional small molecular ligand systems, and demonstrate that the macromolecular catalyst can be removed by ultrafiltration.     

Cobalt supported on dendronized magnetic nanoparticles: A new highly efficient and recyclable catalyst for the Mizoroki–Heck cross‐coupling reaction

Polyamidoamine (PAMAM) is one of the most interesting types of hyperbranched polymers that carry a large number of amino groups on its surface. PAMAM has gained significant attention from synthetic organic chemists due to its structural characteristics, controllable structure, inner porosity, and ability to trap a wide range of ions and molecules. So, in this work, the PAMAM dendrimer was synthesized, grafted onto the surface of magnetite nanoparticles, and the resulting hybrid nanoparticles were then employed as suitable host for immobilizing cobalt nanoparticles. The newly developed catalyst was well characterized by Fourier transform‐infrared, X‐ray diffraction, thermogravimetric analysis, field emission‐scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, element mapping and energy‐dispersive X‐ray analysis. The efficiency of the as‐prepared nanocatalyst was evaluated for the Mizoroki–Heck cross‐coupling reactions. The MNP@PAMAM‐Co represented perfect catalytic efficiency and high selectivity for the Mizoroki–Heck cross‐coupling reaction compared with previously reported catalysts. The catalyst separation from the reaction mixture was easily achieved with the assistance of an external magnetic field, and its recycling was also investigated for five consecutive runs. Hot filtration confirmed no leaching of the active metal during the Heck coupling.     

壳聚糖微球负载的己二胺型聚酰胺-胺树状大分子的制备及对胆红素的吸附

通过反相悬浮反应制备了戊二醛交联的壳聚糖微球。以所制备的壳聚糖微球为载体,合成了己二胺型低代数聚酰胺-胺（Polyamidoamine,简称PAMAM）树枝状大分子（Genaration≤3）。考察了该微球在生理条件下对水溶液中胆红素的吸附行为,以及溶液的pH值,离子强度,温度,胆红素初始浓度,牛血清白蛋白等因素对吸附的影响。结果表明,吸附剂对胆红素具有良好的吸附性能,CS-G2.0,CS-G3.0,CS-G1.0,CS-G0和CS微球的平衡吸附率分别为94.61%,93.44%,92.97%,86.47%,52.38%,CS-G1.0-G3.0微球在0.5h吸附率已经超过70%,1h基本接近平衡,对胆红素的吸附量高达42.78mg/g。     

CdSe量子点/聚酰胺-胺树形分子纳米复合材料的制备与表征

以NaHSe为硒源,以聚酰胺-胺树形分子(PAMAM)为内模板,在水溶液中制备了尺寸均一、分散良好、荧光性强的CdSe量子点.分别用紫外-可见吸收光谱、荧光发射光谱和高分辨透射电镜对树形分子包裹的CdSe量子点进行表征.结果表明:在紫外光的激发下,树形分子与CdSe量子点间发生了强烈的界面电荷转移作用.质子化后整代数树形分子模板作用优于半代数树形分子.高代数树形分子的模板作用优于低代数树形分子.pH在7.5时,纳米簇粒径小而均匀,且溶液稳定性高.改变Cd2+与PAMAM物质的量比,可得到一系列尺寸不同、发光颜色不同的CdSe量子点.0℃低温时制备的量子点光致发光效率最高.