以酯端基PAMAM树形分子为模板在N，M-二甲基甲酰胺溶剂中制备金纳米粒子

用UV-vis、FT-IR光谱研究了HAuCl4和酯端基聚酰胺胺(PAMAM)树形分子在N，N-二甲基甲酰胺(DMF)溶剂中的相互作用，提出HAuCl4与树形分子之间的络合机理：[AuCl4]^-离子与质子化叔胺基团形成离子对，Au^3 离子与PAMAM树形分子上的酯基和酰胺基团形成配位作用。在DMF溶剂中酯端基PAMAM树形分子与HAuCl4配位后用柠檬酸钠还原形成金纳米粒子，UV-vis光谱和TEM图像分析表明了随树形分子代数的增加，金纳米粒子的直径减小，并提出了树形分子-金纳米复合物的结构模型：(1)较低代数的树形分子环绕在金粒子的外围；(2)在较高代数的树形分子空腔内部封装金纳米粒子。     

Stability, antimicrobial activity, and cytotoxicity of poly(amidoamine) dendrimers on titanium substrates

In this article, we present the first report on the antibacterial activity and cytotoxicity of poly(amidoamine) (PAMAM) dendrimers immobilized on three types of titanium-based substrates with and without calcium phosphate coating. We show that the amino-terminated PAMAM dendrimers modified with various percentages (0-60%) of poly(ethylene glycol) (PEG) strongly adsorbed on the titanium-based substrates. The resultant dendrimer films effectively inhibited the colonization of the Gram-negative bacteria Pseudomonas aeruginosa (strain PAO1) and, to a lesser extent, the Gram-positive bacteria Staphylococcus aureus (SA). The antibacterial activity of the films was maintained even after storage of the samples in PBS for up to 30 days. In addition, the dendrimer films had a low cytotoxicity to human bone mesenchymal stem cells (hMSCs) and did not alter the osteoblast gene expression promoted by the calcium phosphate coating.     

纳滤膜纯化球状大分子的可行性研究

分析了球状大分子合成中的目标产物难分离难纯化的特点，采用纳滤膜分离技术纯化新型纳米材料——球状大分子；通过HPLC和元素分析测试了纯化前后的纯度，证明了纳滤膜是可以提高目标球状大分子的纯度；孔径较大的NF1膜有利于乙二胺的透过，其纯度提高较大，而孔径较小的NF2膜对乙二胺的透过能力下降，所以纯度提高较小。     

Dip-pen nanolithography on (bio)reactive monolayer and block-copolymer platforms: deposition of lines of single macromolecules

The application of atomic force microscopy (AFM) tip-mediated molecular transfer (dip-pen nanolithography or DPN) to fabricate nanopatterned (bio)reactive platforms based on dendrimers on reactive self-assembled monolayer (SAM) and polymer thin films is discussed. The transfer of high-molar-mass polyamidoamine (PAMAM) dendrimers (generation 5) and the rapid in situ covalent attachment of the deposited adsorbates onto reactive N-hydroxysuccinimide (NHS) terminated SAMs on gold and NHS-activated polystyrene-block-poly(tert-butyl acrylate) (PS(690)-b-PtBA(1210)) block copolymer thin films were investigated as strategies to suppress line broadening by surface diffusion in DPN. By exploiting carefully controlled environmental conditions (such as temperature and relative humidity), scan rates, and in particular the covalent attachment of the dendrimers to the reactive films, the observed line broadening and hence the lateral diffusion of dendrimers was substantially less pronounced compared to that observed with DPN of thiols on gold. By this method, high-definition patterns of dendrimers were conveniently fabricated down to 30-nm length scales. The presence of primary amino groups in the deposited dendrimers ultimately offers the possibility to anchor biochemically relevant molecules, such as proteins and polypeptides, to these nanostructured platforms for a wide range of possible applications in the life sciences and in particular for the investigation of controlled cell-surface interactions.     

Synthesis and characterization of quaternized carboxymethyl chitosan/poly(amidoamine) dendrimer core–shell nanoparticles

With the aim to develop a novel water-soluble modified chitosan nanoparticle with tuned size and improved antibacterial activity, quaternized carboxymethyl chitosan/poly(amidoamine) dendrimers (CM-HTCC/PAMAM) were synthesized. Firstly low-generation amino-terminated poly(amidoamine) (PAMAM) dendrimers were prepared via repetitive reactions between Michael addition and amidation, which were then employed for modifying quaternized carboxymethyl chitosan (CM-HTCC). Prior to the reaction of CM-HTCC with PAMAM, carboxylic groups in CM-HTCC were activated with EDC/NHS in order to enhance the reaction efficiency. FT-IR, ¹H NMR, elemental analysis and XRD were performed to characterize CM-HTCC/PAMAM dendrimers. Turbidity measurements showed that CM-HTCC/PAMAM dendrimers had good water-solubility. TEM images indicated that CM-HTCC/PAMAM dendrimers existed as smooth and spherical nanoparticles in aqueous solution. The results of antibacterial activity explored that CM-HTCC/PAMAM dendrimer nanoparticles displayed higher antibacterial activity against Gram-negative bacteria Escherichia coli (E. coli), whereas they showed much less efficiency against Gram-positive bacteria Staphylococcus aureus (S. aureus) compared to quaternized chitosan (HTCC).     

Synthesis of core-shell Au@polypyrrole nanocomposite using a dendrimer-template approach

Conducting polymeric nanostructures have been reported recently, which were produced from polypyrrole (PPy), including hollow nanocapsules, nanofibers, nanoporous membranes, nanowires, and nanofilms. In most cases, new synthetic routes were used aimed at controlling specific properties of these conducting nanostructures at the molecular level. In this communication we present a new chemical route to synthesize polypyrrole-based nanocomposites, in which polyamidoamine (PAMAM) dendrimers encapsulating Au nanoparticles are used as template. The two-step synthesis comprises the reduction of Au nanoparticles inside PAMAM molecules followed by PPy polymerization around the PAMAM-Au nanoparticles. The structure of the core-shell PAMAM-gold@polypyrrole nanospheres comprises a 40 nm PPy shell enclosing a core of 3 nm gold nanoparticles, as revealed by Transmission Electronic Microscopy (TEM). This new, environmentally-friendly approach may be suitable to produce hybrid nanomaterials for applications in catalysis, batteries, sensors, and micro/nanoelectronic devices.     

Stealth dendrimers for drug delivery: correlation between PEGylation,cytocompatibility, and drug payload

It is advantageous to utilize low generation polyamidoamine (PAMAM) dendrimers for drug delivery because low generations (generation 4.0 or below) have more biologically favorable properties as compared to high generations. Nevertheless, modification of low generation dendrimers with PEG to create stealth dendrimers is still necessary to avoid potential side effects by long term accumulation. However, low generation dendrimers have much fewer surface sites for drug loading as compared to higher generations. To efficiently utilize low generation dendrimer-based stealth dendrimers for drug loading, PEGylation needs to be optimized. In this study, we synthesized a series of stealth dendrimers based on low generation Starburst™ PAMAM dendrimers (i.e., G2.5, G3.0, G3.5, and G4.0) and quantitatively assessed PEGylation efficacy in modulating cytocompatibility of low generation PAMAM dendrimers. Cytocompatibility of stealth dendrimers was examined using endothelial cells. The results showed that PEGylation degree on low generation dendrimers could be dramatically reduced to leave as many unoccupied surface groups as possible for drug loading, while maintaining the drug carrier cytocompatibility. 3PEGs-G3.0 and 10PEGs-G4.0 were considered initially optimized stealth dendrimers that would be further modified to deliver drugs of interest. Correlation of PEGylation, cytocompatibility, and drug payload allowed us to optimize low generation dendrimer-based stealth dendrimers for drug delivery and advance the understanding of structure-property relationship of stealth dendrimers.     

HPLC separation of different generations of poly(amidoamine) dendrimers modified with various terminal groups

Polyamidoamine (PAMAM) dendrimers of different generations with various terminal groups were analyzed, for the first time, using a combination of high-performance liquid chromatography (HPLC), size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) techniques. Separation of amine-terminated dendrimers from generation 1 through generation 9 (G1NH(2)-G9NH(2)) was achieved using reversed-phase HPLC with elution time increasing gradually as the density of terminal amine groups increases as a function of generation. Furthermore, separation of dendrimers with terminal amino, acetamide, hydroxyl, and carboxylate groups was obtained. It has also been shown that HPLC can be used to separate dendrimers based on some structural defects inherent during the syntheses of PAMAM dendrimers. MALDI-TOF mass spectra of G1NH(2) identify the major imperfections present during typical synthesis processes. The absolute molar masses (M(n)) and molar mass distributions of the dendrimers were measured using the SEC system equipped with multiangle laser light scattering and refractive-index detectors. Findings from this study suggest HPLC can be a vital tool for characterization and preparative separation of PAMAM dendrimers.     

Binding and conformation of dendrimer-based drug delivery systems:a molecular dynamics study

All atomistic molecular dynamics simulations were performed on poly(amidoamine)(PAMAM) dendrimers that compound non-covalently with anticancer drug molecules including DOX,MTX,CE6,and SN38.The binding energies as well as their associated interaction energies and deformation energies were combined to evaluate the relative binding strength among drug,PAMAM,and PEG chains.We find that the deformation of dendrimers due to drug loading plays a crucial role in the drug binding.It is energetically favorable for the drug molecules to bind with PAMAM while the drugs bind with PEG metastable chains via kinetic confinement.Surface PEGylation helps dendrimers to accommodate more drug molecules with greater strength without inducing too much expansion.This work indicates that tuning the functionalized terminal groups of dendrimers is critical to design efficient dendrimer-based drug delivery systems.     

Controllable synthesis of hydroxyapatite nanocrystals via a dendrimer-assisted hydrothermal process

The morphology and size of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (denoted HAP) can be controlled under hydrothermal treatment assisted with different dendrimers, such as carboxylic terminated poly(amidoamine) (PAMAM) and polyhydroxy terminated PAMAM. The structure and morphology were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and transmission electron microscopy (TEM). IR spectra were also used to investigate the complexation of Ca²⁺ with PAMAM. The results revealed that the inner cores of the PAMAM dendrimers are hydrophilic and potentially open to calcium ions, since interior nitrogen moieties serve as complexation sites, especially in case of the polyhydroxy terminated PAMAM. And the reasonable mechanism of crystallization was proposed that it can be attributed to the localization of nucleation site: external or interior PAMAM. Additionally, the PAMAM dendrimer with carboxylic and polyhydroxy groups has an effective influence on the size and shape of hydroxyapatite (HAP) nanostructures. Different crystal morphology was accomplished by adsorption of different dendrimers onto specific faces of growing crystals, altering the relative growth rates of the different crystallographic faces and leading to different crystal habits.     

Modifying the adsorption behavior of polyamidoamine dendrimers at silica surfaces investigated by total internal reflection fluorescence correlation spectroscopy

Polyamidoamine (PAMAM) dendrimers were modified and tested for use as solution-phase diffusion probes in silica nanostructures. In order for the successful application of dendrimers as solution-phase probes, their interactions with silica surfaces must be understood and controlled, so that the motion of the probe is not influenced by adsorption. Adsorption/desorption kinetics of PAMAM dendrimers and their diffusion in solution near silica surfaces were investigated with total internal reflection fluorescence correlation spectroscopy (TIR-FCS). Dendrimers of generations 3, 5, and 7 were dye-labeled with carboxyrhodamine 6G. Because PAMAM dendrimers are positively charged in solution (having primary amines as end groups), significant adsorption of these molecules to the negatively charged silica surface was observed. Adsorption/desorption rates and the equilibrium constant for adsorption were determined by fitting the autocorrelation functions to a kinetic model. The desorption rate decreases and the absorption equilibrium constant increases with higher dendrimer generation. To reduce the adsorption of these probes to silica surfaces, the labeled dendrimers were reacted with succinic anhydride, converting the primary amine end groups to negatively charged carboxylic acid groups. These carboxylated dendrimers did not detectably adsorb to silica from aqueous solution. TIR-FCS was used to determine their free-solution diffusion constants near silica surfaces, and the corresponding hydrodynamic radii compare favorably with values reported from forced Rayleigh scattering measurements.     

Effect of sodium dodecylsulfate and dodecyltrimethyl ammonium bromide on the morphologies of gold nanoparticles in the presence of poly(amidoamine) dendrimers

The synthesis of gold nanoparticles has been carried out in aqueous phase in the presence of both ionic surfactants (i.e., sodium dodecylsulfate (SDS) and dodecyltrimethylammonium bromide (DTAB)) and poly(amidoamine) dendrimers (PAMAM). It has been observed that the fluoroderivative of 2G PAMAM (2D) acts as reducing agent in reducing Au(lll) to Au(0) leading to the formation of fine gold nanoparticles. This process has been further evaluated in the presence of fixed amounts of both SDS and DTAB in their respective pre and post micellar concentration regions. The presence of SDS leads to the appearance of clear ordered morphologies such as triangular, hexagonal, spherical, and rod shaped, while the presence of DTAB does not show this effect. The formation of nanoparticles in triangular morphologies is more significant in the premicellar concentration range of SDS whereas hexagonal morphologies in the post micellar concentration range. On the contrary, increase in the DTAB concentration from pre to post micellar range only reduces the size of gold nanoparticles without the appearance of any ordered morphology. The formation of ordered gold nanoparticles in the presence of SDS has been further attributed to the significant SDS-dendrimer interactions and an appropriate mechanism has been proposed to justify the results.     

笼状PAMAM模板纳米钯催化Suzuki反应

针对PAMAM模板纳米钯催化剂在循环使用中容易团聚产生钯黑的问题,文章利用4．5代PAMAM端基的酯基团与乙二胺反应形成鸟笼状大分子,以其为模版合成纳米钯催化剂,研究发现,当端基连接50％,反应条件温和,催化剂易于分离,循环使用4次,仍能保持70％的收率。     

De novo growth of poly(amidoamine) dendrimers on the surface of multi-walled carbon nanotubes

Carbon nanotubes (CNTs) are often used after modification. Poly(amidoamine) (PAMAM) dendrimers modified CNTs have attracted attentions due to their rich terminal amino groups. However, direct grafting of PAMAM dendrimers on CNTs’ surface is limited by the steric hindrance and its supply. De novo growth of PAMAM on multi-walled carbon nanotubes (MWCNTs), i.e., PAMAM@CNTs, is expected to eliminate the limits since the adopted reagents are readily available small molecular chemicals. It was realized using a divergent method and a “grafting from” technique by alternate amidization of terminal ester groups with ethylenediamine and Michael addition of methyl acrylate to the yielding amino groups. Spectral analysis, including Fourier transform infrared, Raman, hydrogen nuclear magnetic resonance, and X-ray photo-electron spectroscopy, verified that the functional groups were covalently grafted on the surface of MWCNTs, while thermogravimetric and elemental analysis showed that these groups were exponentially grown on MWCNTs, suggesting the formation of a dendritic PAMAM. Besides, high resolution transmission electron microscopy also confirmed that the spherical PAMAM was formed on the CNTs’ surface and an average particle size of 15–20 nm for G8.0-dendrimers was obtained.     

Improved adhesion of Au thin films to SiOx/Si substrates by dendrimer mediation

Quantitative evidence of significantly improved interfacial adhesion between Au films and SiO_x/Si substrates induced by an organic dendrimer monolayer was presented. For dendrimer-mediated Au films, nanoscratch tests revealed a critical load that was two times higher than that for films without dendrimer mediation. Atomic force microscopy (AFM) examination of nanoindents revealed much constrained lateral flow of metals in the dendrimer-mediated Au films during nanoindentation, indicating enhanced adhesion due to the presence of the dendrimer layer.     

Potentiometric response characteristics of polycation-sensitive membrane electrodes toward poly(amidoamine) and poly(propylenimine) dendrimers

The potentiometric response characteristics of polycation-sensitive membrane electrodes toward two classes of polycationic dendrimers are examined. Using appropriately formulated polymer membrane electrodes composed of a dinonylnaphthalenesulfonate (DNNS) salt in a plasticized polyurethane matrix, it is shown that poly(amidoamine) (PAMAM) and poly(propylenimine) (PPI) dendrimers are readily detected at submicrogram per milliliter levels via a nonequilibrium response mechanism. The relationship between the total EMF response (at equilibrium) and the specific dendrimer structure is also examined. For both the PAMAM and PPI species, it is shown that the total EMF response does not change significantly with dendrimer generation number; however, the nonequilibrium analytically useful response curves are shifted to higher mass concentrations as the generation number is increased. The relative contributions of the terminal primary amines and the interior tertiary amines of the dendrimers to the observed EMF response are investigated by synthesis of various dendrimer derivatives (acetylated, quaternized, etc.). By comparing the total EMF responses for these derivatives as a function of sample pH, it is demonstrated that the lipophilic cation exchanger (DNNS) within the membrane phase can likely interact electrostatically with both protonated forms of the terminal primary amines and interior tertiary amines of the dendrimer structures. The practical application of the nonequilibrium potentiometric detection of dendrimers for monitoring their interaction with DNA is also demonstrated.     

Preparation and in vitro characterization of pluronic-attached polyamidoamine dendrimers for drug delivery

Context: Polyamidoamine (PAMAM) dendrimers have attracted lots of interest as drug carriers. And little study about whether pluronic-attached PAMAM dendrimers could be potential drug delivery systems has been carried on.

Objective: Pluronic F127 (PF127) attached PAMAM dendrimers were designed as novel drug carriers.

Methods: Two conjugation ratios of PF127-attached PAMAM dendrimers were synthesized. ¹H nuclear magnetic resonance (¹H-NMR), Fourier transform infrared spectrum (FTIR), element analysis and ninhydrin assay were used to characterize the conjugates. Size, zeta potential and critical micelle concentrations (CMC) were also detected. And DOX was incorporated into the hydrophobic interior of the conjugates. Studies on their drug loading and drug release were carried on. Furthermore, hemolysis and cytotoxicity assay were used to evaluate the toxicity of the conjugates.

Results and discussion: PF127 was successfully conjugated to the fifth generation PAMAM dendrimer at two molar ratios of 19% and 57% (PF127 to surface amine per PAMAM dendrimer molecular). The conjugates showed an increased size and a reduced zeta potential. And higher CMC values were obtained than pure PF127. Compared with unconjugated PAMAM dendrimer, PF127 conjugation significantly reduced the hemolytic toxicity and cytotoxicity of PAMAM dendrimer in vitro. The encapsulation results showed that the ability to encapsulate DOX by the conjugate of 19% conjugation ratio was better than that of 57% conjugation ratio. And the maximum is ～12.87 DOX molecules per conjugate molecule. Moreover, the complexes showed a sustained release behavior compared to pure DOX.

Conclusion: Findings from the in vitro study show that the PF127-attached PAMAM dendrimers may be potential carriers for drug delivery.     

Reversible pH manipulation of the fluorescence emission from sectorial poly(amido amine) dendrimers

The first to fourth generation (G1-G4) of sectorial poly(amido amine) (PAMAM) dendrimers with ethanolamine core and amino terminals are synthesized by a divergent route. Blue fluorescence emission from these dendrimers is observed. It is found that there is a remarkable difference in the fluorescence behavior for these different generations of dendrimers. The emission intensity of these dendrimers is almost linearly enhanced along with the increase of their concentrations. A significant pH-dependent profile of the fluorescence intensity is also observed. As the pH value decreases from 8 to 3, the fluorescence intensity increases almost linearly. Furthermore, the fluorescence intensity of the dendrimers shows a reversible behavior depending on pH value within the pH range from 3 to 11. This property enables the reversible manipulation of the fluorescence of these dendrimers by adjusting the pH values, which contributes to a potential application of these materials in fluorescent pH sensors.     

Photolithographic patterning of dendrimer monolayers and pattern-selective adsorption of linear macromolecules

Alkyl groups of n-octadecyltrimethoxysilane (ODS) in a self-assembled monolayer on a silicon substrate were oxidized to carboxyl groups by partial irradiation of vacuum ultra-violet light under the photomask, producing a COOH/ODS line pattern. After active esterification of carboxyl groups, two kinds of amine-terminated dendrimers, poly(propyleneimine) and poly(amido amine) (PAMAM) dendrimers, were immobilized on a COOH line through amide-bond so that photolithographic dendrimer/ODS pattern was finally fabricated. Preparation was certified by atomic force microscopy (AFM) and surface-enhanced infrared absorption spectroscopy at transmission mode. Adsorption of linear macromolecules was examined on PAMAM dendrimer/ODS pattern. After adsorption of poly-L-glutamic acid (PGA) at a pH below alpha-helix--random coil transition, rod-shape texture was observed only on the dendrimer line in an AFM image. This texture is an aggregate of alpha-helical PGA. Sodium hyaluronate and DNA were also adsorbed selectively on the dendrimer line, keeping the line profile, although characteristic textures were not observed.     

Synthesis and Characterization of Dendrimer-Encapsulated Iron and Iron-Oxide Nanoparticles

In this paper, a series of iron (Fe) containing nanoparticles were prepared by employing PAMAM (Poly(amidoamine), dendrimers with different generations (G0?CG3) as templates and sodium borohydride as a reducing agent. The products have been characterized by TEM, FT-IR, XRD, VSM, TGA, and XPS. XRD analysis reveal low crystallinity of formed particles within the dendrimers, however, crystallinity of the nanoparticles was observed to increase with increasing generation of dendrimers. Dominant phases were determined as magnetite (Fe₃O₄ or maghemite, ??-Fe₂O₃). XPS analysis revealed the chemical composition of nanoparticles as iron oxide which indicated the oxidation of Fe species subsequent to the reduction process, in agreement with XRD analysis. The magnetization curves have superparamagnetic nonhysteretic characteristic at lower fields and with nonsaturation characteristic at high fields. Magnetic evaluation of samples with the 20:1?molar ratio of Fe:PAMAM showed decreasing superparamagnetic character and decreasing saturation magnetisation with increasing generation of dendrimers.