Antioxidant action by gold-PAMAM dendrimer nanocomposites

Gold-dendrimer nanocomposites were prepared in the presence of poly(amidoamine) (PAMAM) dendrimer (generation 3, 3.5, 5, and 5.5) via reduction of HAuCl4 with sodium borohydride. The average particle size of the gold nanoparticles was independent of the dendrimer concentration, ranging between 3.0 and 4.3 nm in diameter. The catalytic activities of the gold-dendrimer nanocomposites upon elimination of hydroxyl radicals formed in an H2O2/FeSO4 system were examined using a spin-trapping method. The gold-dendrimer nanocomposites exhibited high catalytic activities which were hardly affected by the concentration and the generation of the dendrimer except PAMAM dendrimer 3.5. The highest activity for the gold-PAMAM dendrimer 3.5 nanocomposites was 85 times that of ascorbic acid.     

Comparison of PAMAM-Au and PPI-Au nanocomposites and their catalytic activity for reduction of 4-nitrophenol

Dendrimer-Au nanocomposites are prepared in aqueous solutions using poly(amidoammine)dendrimers (PAMAM) (generation 2, 3, and 5) and poly(propyleneimine)dendrimers (PPI)(generation 2, 3, and 4) by wet chemical NaBH(4) method. The Au nanoparticles thus obtained are 2-4 nm in diameter for both dendrimers and no generation dependence on the particle size is observed, whereas the generations of the dendrimers are increased as stabilization of Au-nanoparticles is achieved with lower dendrimer concentrations. Studies of the reduction reaction of 4-nitrophenol using these nanocomposites show that the rate constants for the PAMAM dendrimers (generations 2 and 3) are higher than those for the PPI dendrimers (generations 2 and 3), while a distinct difference in the rate constants is not seen for the PAMAM dendrimer (generation 5) or the PPI dendrimer (generation 4). In addition, the rate constants for the reduction of 4-nitrophenol involving all the dendrimers decrease with increases in dendrimer concentrations.     

Preparation of PAMAM- and PPI-metal (silver, platinum, and palladium) nanocomposites and their catalytic activities for reduction of 4-nitrophenol

Dendrimer-metal (silver, platinum, and palladium) nanocomposites are prepared in aqueous solutions containing poly(amidoamine) (PAMAM) dendrimers with surface amino groups (generations 3, 4, and 5) or poly(propyleneimine) (PPI) dendrimers with surface amino groups (generations 2, 3, and 4). The particle sizes of the metal nanoparticles obtained are almost independent of the generation as well as the concentration of the dendrimer for both the PAMAM and the PPI dendrimers; the average sizes of silver, platinum, and palladium nanoparticles are 5.6-7.5, 1.2-1.6, and 1.6-2.0 nm, respectively. It is suggested that the dendrimer-metal nanocomposites are formed by adsorbing the dendrimers on the metal nanoparticles. Studies of the reduction reaction of 4-nitrophenol by these nanocomposites show that the rate constants are very similar between PAMAM and PPI dendrimer-silver nanocomposites, whereas the rate constants for the PPI dendrimer-platinum and -palladium nanocomposites are greater than those for the corresponding PAMAM dendrimer nanocomposites. In addition, it is found that the rate constants for the reduction of 4-nitrophenol involving all the dendrimer-metal nanocomposites decrease with an increase in the dendrimer concentrations, and the catalytic activity of dendrimer-palladium nanocomposites is highest.     

Preparation of gold-, gold/silver-dendrimer nanocomposites in the presence of benzoin in ethanol by UV irradiation

Gold- and gold/silver-dendrimer nanocomposites have been synthesized by UV irradiation of their salts dissolved in ethanol containing dendrimers. As dendrimers, poly(amidomaine) PAMAM dendrimers and poly(propyleneimine) PPI dendrimers of various generations were used. The photoreduction of their salts is greatly accelerated by using benzoin as a photoinitiator. The sizes of gold in the nanocomposites are affected by the concentration of benzoin as well as the concentration of dendrimers, but are hardly changed with the kind of dendrimers. For gold/silver-dendrimer nanocomposites, the absorption spectra of gold/silver nanoparticles in the nanocomposites are very similar to the theoretical spectra of gold/silver alloy nanoparticles, suggesting the formation of gold/silver alloy nanoparticles. From the comparison of TEM and DLS measurements, it is found that the metal-dendrimer nanocomposites consist of metal nanoparticles covering by dendrimer molecules.     

低代端酯基PAMAM树形分子存在下银纳米颗粒的制备

在低代端酯基PAMAM树形分子(G1.5-COOCH₃)存在时，用氢气还原AgNO₃制备出银纳米颗粒。用透射电子显微镜(TEM)，电子衍射(ED)，紫外-可见吸收光谱(UV-Vis)和红外光谱(FT-IR)对所制备的银纳米颗粒进行了表征。实验结果表明，当用氢气作为还原剂时，以低代树形分子为保护剂，通过优化还原条件，可成功制备尺寸稳定、均一的银纳米颗粒，其粒径为2.9±0.5 nm，且所制备的银纳米颗粒的粒径分布较窄。根据树形分子的理论尺寸与制备的银纳米颗粒的粒径关系，可推断出大多数的银纳米颗粒是由多个树形分子所包围而稳定存在。     

New insights into the structure of PAMAM dendrimer/gold nanoparticle nanocomposites

In this work, we have employed a suite of complementary analytical techniques to shed light on the nanocomposite structures formed during gold nanoparticles (AuNPs) synthesis in the presence of poly(amidoamine) (PAMAM) dendrimers. Nanocomposites of AuNPs and either fourth or eighth generation amine-terminated PAMAM dendrimers (G4 or G8) were prepared. The size distributions of AuNPs and the nanocomposites were determined by transmission electron microscopy. Atomic force microscopy phase imaging and neutral impact collision ion scattering spectroscopy (NICISS) were utilized for the first time to investigate and compare nanocomposite structures formed from G4 and G8. Our results suggest that G4 stabilized the AuNP by capping the AuNP particle surface but that a certain fraction of the gold surface was still barely covered. In contrast, the metal nanoparticle surface was completely covered by G8. In addition, NICISS results provided evidence that nanocomposites deformed when being deposited directly onto a substrate.     

磁性Fe_3O_4@PS@PAMAM-Ag复合催化粒子的制备及其可再生催化性能(英文)

采用聚苯乙烯(PS)包裹Fe3O4磁性纳米粒子,制得Fe3O4@PS复合微球,以此作为磁性载体,通过微球表面的羧基将聚酰胺-胺类树形大分子(PAMAM)连接到磁性载体上,然后使Ag纳米粒子镶嵌在树形分子层中,制得可再生的金属复合催化粒子Fe3O4@PS@PAMAM-Ag.并采用红外光谱、扫描电镜、电感耦合等离子体质谱(ICP-MS)和X射线光电子能谱等方法对复合催化粒子进行了表征,结果表明,树形分子可以较好地分散和稳定金属Ag纳米粒子,所制复合催化粒子表面Ag含量为1.64%,具有较高的催化还原对硝基苯酚的活性.同时,利用外加磁场可以方便快捷地从反应体系中分离出来,继续用于下一次反应中,复合催化粒子循环使用6次后,仍保持完全的催化性能.     

以聚酰胺-胺树形分子为模板制备AgI纳米簇

本文以聚酰胺-胺(PAMAM)树形分子为模板,原位制备AgI纳米簇.系统地研究了AgI纳米簇制备过程中各种反应条件如树形分子端基、反应时间、Ag⁺与PAMAM摩尔比等对AgI纳米簇粒径的影响,分别用紫外-可见光谱、荧光光谱、透射电镜等对所制备的纳米簇进行表征.在相同的条件下,以G4.5-COOH₃为模板较以G5.0-NH₂为模板制备的AgI纳米簇粒径小、分布均匀,这主要取决于G4.5-COOCH₃PAMAM树形分子所起的“内模板”作用.G4.5-COOH₃树形分子浓度为1×10^-5mol/L,Ag⁺与树形分子摩尔比为30:1时所制备的AgI纳米簇的粒径分布均匀、稳定性好,室温避光可稳定存在两个月以上.     

Synthesis of P(MBA-co-MAA) microsphere-grafted PAMAM dendrimers and their application as supporters for gold nanoparticles

Poly(N,N′-methylenebisacrylamide-co-acrylic acid) microsphere-supported polyamidoamine (PAMAM) dendrimers up to third generation (G) were grown onto the surface as well as the gel-layer of P(MBA-co-MAA) microspheres by a divergent method. The P(MBA-co-MAA) supported PAMAM dendrimers were used as heterogeneous stabilizers for the gold nanoparticles by an in situ reduction of HAuCl₄ via the efficient coordination interaction between the amino groups of the supported PAMAM dendrimers and the gold atoms. The effects of the generations of the P(MBA-co-MAA) supported PAMAM dendrimer on the loadings and the catalytic activity of the heterogeneous Au nanoparticles were systematically investigated with the reduction of 4-nitrophenol to 4-aminophenol as a model reaction.     

Interaction forces between poly(amidoamine) (PAMAM) dendrimers adsorbed on gold surfaces

Interaction forces between two gold surfaces with adsorbed poly(amidoamine) (PAMAM) dendrimers (generations G3.0 and G5.0) have been investigated using colloidal probe atomic force microscopy (AFM). In the absence of dendrimers or at their low concentrations, an attractive force derived from the van der Waals interaction was observed. On the other hand, this attractive interaction changed to repulsion with increasing dendrimer concentration. The origin of the repulsion can be attributed to either an electric double layer interaction or a steric effect of the adsorbed dendrimers, depending on the concentration of dendrimer. The steric hindrance was also influenced by the generation of the dendrimer; the force-detectable distance in the presence of PAMAM G5.0 dendrimer was slightly longer than that in the presence of G3.0 dendrimer. In order to estimate the occupied area of each dendrimer adsorbed on gold, quartz crystal microbalance (QCM) measurement was also carried out.     

PAMAM树形分子与Cd2＋的配位作用研究及CdS/PAMAM纳米复合材料的制备与表征

CdS半导体纳米簇具有独特的光、电性能, 如何制备均匀分散的、能够稳定存在的CdS纳米簇是目前的研究热点之一. 以聚酰胺-胺(PAMAM)树形分子为模板, 原位合成了CdS纳米簇. 首先用UV-Vis分光光度法研究了与树形分子的配位机理, 得出G4.5和G5.0的平均饱和配位数分别为16和34, 并发现在G4.5PAMAM树形分子中Cd^2＋主要与最外层叔胺基配位, 在G5.0PAMAM树形分子中Cd^2＋主要与最外层伯胺基配位. 酯端基的G4.5的模板作用要明显优于胺端基的G5.0. 通过改变Cd^2＋与G4.5树形分子的摩尔比可以得到不同粒径的CdS纳米簇. 溶液的pH值对CdS纳米簇影响很大, pH在7.0左右制备的CdS纳米簇粒径小而均匀, 且溶液稳定性高. 用UV-Vis分光光度计和TEM对CdS纳米簇的大小和形貌进行了表征. 结果表明TEM观测CdS纳米簇的粒径要大于用Brus公式的估算值.     

New Dendrimers: Synthesis and Characterization of Popam - Pamam Hybrid Dendrimers

Recently developed multifunctional cancer therapeutic nano-device production is based on poly(amidoamine) PAMAM generation 5 (G5) dendrimer as a carrier 1-5. Scale up synthesis of this nano-device is limited because of long reaction sequence (12 reaction steps) and long and not easy work up of the products after each reaction step. Combination of poly(propyle-imine) and poly(amidoamine) synthesis can improve the production of the drug carrier.In this paper we give a general overview of the synthesis and characterization of a series of novel hybrid dendrimers which we coined as novel POMAM hybrid dendrimers, constructed from poly(propylene-imine) (PPI or POPAM) core and poly(amidoamine) PAMAM shells. The synthesis was accomplished by a divergent reiterating method involving repeating subsequent Michael addition and amidation reactions. Each generation of the newly synthesized dendrimer was characterized by using HPLC, GPC, NMR and AFM.     

Investigation of thermal behaviour of hybrid nanostructures based on Fe2O3 and PAMAM dendrimers

Dendrimers or biofunctionalized dendrimers can be assembled onto magnetic iron oxide nanoparticles to stabilize or functionalize inorganic nanoparticles. Carboxylated poly(amidoamine) PAMAM dendrimers (generation 4.5) have been used for the synthesis of iron oxide nanoparticles, resulting nanocomposites with potential biomedical applications. The present paper aims to systematically investigate the thermal behaviour of nanostructured hybrids based on ferric oxide and PAMAM dendrimers, by differential scanning calorimetry (DSC) technique. The novelty consists both in synthesis procedure of hybrid nanostructures as well as in DSC approach of these nanocomposites. For the first time, we propose a new method to prepare Fe₂O₃??dendrimer nanocomposite, using soft chemical process at high pressure. Commercial PAMAM dendrimers with carboxylic groups on its surface were used. When high pressure is applied, polymeric structures suffer morphological changes leading to hybrid nanostructures' formation. In the same time, crystallinity of inorganic nanoparticles is provided. DSC results showed an increase in thermal stability of composites as compared to commercial dendrimers. This could be due to the formation of strong interactions between ferric oxide and carboxyl groups, as confirmed by Fourier transform infrared spectroscopy. Electron microscopy analysis (SEM/EDX) and size measurements were performed to demonstrate the existence of nanosized particles.     

Preparation, characterization, resistance to protein adsorption, and specific avidin-biotin binding of poly(amidoamine) dendrimers functionalized with oligo(ethylene glycol) on gold

Protein-resistant films derived from the fifth-generation poly(amidoamine) dendrimers (PAMAM G5) functionalized with oligo(ethylene glycol) (OEG) derivatives consisting of various ethylene glycol units (EG(n), n = 3, 4, and 6) were prepared on the self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid (MUA) on gold substrates. The resulting films were characterized by ellipsometry, contact angle goniometry, and X-ray photoelectron spectroscopy (XPS). About 35% of the peripheral amines of the dendrimers were reacted with N-hydroxysuccinimide-terminated EG(n) derivatives (NHS-EG(n)). The dendrimer films showed improved stability over octadecanethiolate SAMs on gold in hot solvents, attributed to the formation of multiple amide bonds per PAMAM unit with underlying NHS-activated MUA monolayer. The EG(n)-attached PAMAM surfaces with n = 3 reduced the adsorption of fibrinogen to approximately 20% monolayer, whereas 2-3% for n = 4 or 6. The dendrimer films with various densities of EG(n) molecules on PAMAM surfaces were prepared by immersion of the NHS-terminated MUA-functionalized gold substrates in ethanolic solutions containing PAMAM and NHS-EG(n) of various mole ratios. The density (r) of the EG(n) molecules on the PAMAM surfaces is consistent with the mole ratio (r') of NHS-EG(n)/free amine of PAMAM in solutions. The resistance to protein adsorption of the resulting surfaces is correlated with the surface density and the length of the EG chains. At their respective r, the EG(n)-modified dendrimer films resisted approximately 95% adsorption of fibrinogen on gold surfaces. Finally, the specific binding of avidin to the approximately 5% and approximately 40% biotinylated EG3 dendrimers (surface density of biotin with respect to the total number of terminal amino groups on PAMAM G5) gave rise to about 50% and 100% surface coverage by avidin, respectively.     

Direct force measurements between adlayers consisting of poly(amidoamine) dendrimers with primary amino groups or quaternary ammonium groups

Adsorption of poly(amidoamine) generation 3 (PAMAM G3) dendrimer with surface amino groups or PAMAM G0 dendrimer with quaternary ammonium groups (C8qbG0) onto glass has been studied by colloidal probe atomic force microscopy. The adlayer-adlayer interactions for these adsorbates are quite different despite the fact that they are almost equal in the hydrodynamic radius. In aqueous PAMAM G3 dendrimer solutions the electrostatic repulsion is predominant. The conformation of the adsorbed layer is flat and the protrusion of the individual dendrimers is negligible. On the other hand, C8qbG0 behaves as a surfactant and the layered structure of C8qbG0 is expected to be a patchy bilayer. Dispersion stability of silica suspensions with the adsorption of these dendrimers can be correlated with the force data obtained.     

CE of poly(amidoamine) succinamic acid dendrimers using a poly(vinyl alcohol)-coated capillary

Various generations (G1-G8) of negatively charged poly(amidoamine) (PAMAM) succinamic acid dendrimers (PAMAM-SAH) were analyzed by CE using a poly(vinyl alcohol)-coated capillary. Due to its excellent stability and osmotic flow-shielding effect, highly reproducible migration times were achieved for all generations of dendrimer (e.g., RSD for the migration times of G5 dendrimer was 0.6%). We also observed a reverse trend in migration times for the PAMAM-SAH dendrimers (i.e., higher generations migrated faster than lower generation dendrimers) compared to amine-terminated PAMAM dendrimers reported in the literature. This reversal in migration times was attributed to the difference in counterion binding around these negatively charged dendrimers. This reverse trend allowed a generational separation for lower generation (G1-G3) dendrimers. However, a sufficient resolution for the migration peaks of higher generations (G4-G5) in a mixture could not be achieved. This could be due to their nearly identical charge/mass ratio and dense molecular conformations. In addition, we show that dye-functionalized PAMAM-SAH dendrimers can also be analyzed with high reproducibility using this method.     

PAMAM树形分子为模板低温制备纳米硫化锌空心球

Hollow ZnS spheres have been prepared in the presence of generation 3.5 poly (amidoamine) dendrimers with surface ester groups (G3.5-COOCH3 PAMAM dendrimer) as synthetic matrix template. The products obtained were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-Vis absorption. TEM studies show that the hollow spheres with diameters ranging from 80 to 100 nm are prepared. The range of wall thickness was estimated to be about 20～30 nm. It was found that the concentration of PAMAM dendrimer had a significant influence on the formation of hollow ZnS spheres. The possible formation mechanism of the hollow spherical structure is also discussed.     

Photoresponsive nanocarriers based on PAMAM dendrimers with a o‐nitrobenzyl shell

Gn (n = 3, 4, and 5) poly(amidoamine) (PAMAM) dendrimers were synthesized and peripherally modified with photocleavable o‐nitrobenzyl (NB) groups by reacting o‐nitrobenzaldehyde with the terminal amine groups of PAMAM dendrimers, followed by reducing the imine to amine groups with NaBH₄. The NB‐modified dendrimers, Gn‐NB (n = 3, 4, and 5), were characterized by nuclear magnetic resonance and fourier transform infrared spectroscopy. The results showed that the NB groups were successfully attached on the periphery of the dendrimers with near 100% grafting efficiency. Such a photosensitive NB shell could be cut off on irradiation with 365 nm ultraviolet (UV) light. The encapsulation and release of guest molecules, that is, salicylic acid (SA) and adriamycin (ADR), by Gn‐NB were explored. The encapsulation capability of these dendrimers was found to increase as the guest molecular size was decreased and have dependence on the generation of dendrimers as well. For both of SA and ADR, the average encapsulation numbers per dendrimer decreased in the order of G4‐NB > G5‐NB > G3‐NB, indicating that the fourth generation dendrimer was a better container for the guest molecules. The rate of SA release was found to be greater with UV irradiation than that without, suggesting that the NB‐shelled PAMMAM dendrimers could function as a molecular container/box with photoresponsive characteristics. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 551–557, 2010     

Effects of various thiol molecules added on morphology of dendrimer-gold nanocomposites

Interactions between poly(amidoamine) dendrimer (PAMAM)-gold nanocomposites and alkanethiols and between the former nanocomposites and thiol-modified poly(amidoamine) dendrons in ethyl acetate were investigated by adding alkanethiols, such as 1-propanethiol and 1,3-propanedithiol, and thiol-modified poly(amidoamine) dendrons, generations 0.5 and 2.5 (G0.5-SH and G2.5-SH). The PAMAM dendrimers with surface methyl ester groups used were generations 1.5 and 5.5 (G1.5 and G5.5). The mean particle sizes of PAMAM-gold nanocomposites were about 2.1 for G1.5 and 2.4 nm for G5.5. In both nanocomposite systems where 1-propanethiol and 1,3-propanedithiol were added, the mean particle size was about 4 nm, twice that of the systems where these thiols were not added. Increasing the addition of 1,3-propanedithiol made the average particle size smaller for both nanocomposites systems. To compare with alkanethiol, thiol-modified poly(amidoamine) dendron with a highly branched structure on one side was synthesized. Using G2.5-SH as a protective agent, dendron-gold nanocomposites with mean diameters of 3 to 4 nm were obtained. The difference in particle size was seen only when the combination of PAMAM-gold nanocomposites and thiol-modified dendron was less sterically dense, modified dendron (G0.5-SH). The mechanisms for morphology changes in the dendrimer-gold nanocomposites by the addition of these thiols are discussed.     

Effect of the surface functional groups of dendrimer-entrapped gold nanoparticles on the improvement of PCR

PCR has been identified as one of the most important tools in molecular biology and clinical medicine. Improvement of the specificity and efficiency of PCR is often required, and it still remains a great challenge. Here, we introduce the use of dendrimer-entrapped gold nanoparticles (Au DENPs) with different terminal groups prepared using poly(amidoamine) (PAMAM) dendrimers of generation 5 (G5) as a novel class of enhancers to improve the specificity and efficiency of PCR amplification. We show that the optimum concentrations of all the tested Au DENPs are lower than those of the corresponding PAMAM dendrimers without gold nanoparticles (AuNPs). For amine-terminated [(Au(0) )(51.2) -G5.NH(2) ] DENPs, the optimum required concentration is slightly lower than that of G5.NH(2) dendrimers, whereas for glycidol-modified [(Au(0) )(51.2) -G5.NGlyOH] and acetylated [(Au(0) )(51.2) -G5.NHAc] DENPs, the optimum required concentrations are one and three magnitude lower than the corresponding dendrimers, respectively. Our results suggest that the entrapment of AuNPs within the dendrimer interior helps to reserve the 3D spherical morphology of dendrimers, allowing for enhanced interaction with the PCR components. Simultaneously, because of the existence of thermal conductive AuNPs, the enhanced local heat transfer rate may afford decreased chances of mispairing between primers and templates, which is beneficial for enhancing the PCR specificity and efficiency. Therefore, the use of Au DENPs as a novel class of PCR enhancers may enable both improved interaction with the PCR components and the thermal conductivity, which allow them to be used for enhancing different error-prone PCR systems.