Study on Interaction Energy of PAMAM/Lanthanide（ Ⅲ ） by Molecular Dynamics Method

PAMAM/lanthanide （Ⅲ） nanocomposite was studied by molecular simulation method. Molecular simulation enabled study of the lanthanide tetrad effect at atomic level. However, PAMAM dendrimer exhibiting unique properties such as nanometer size and highly functionalized terminal surface provided a novel space for lanthanide （Ⅲ） to show their peculiar tetrad effect. The results showed that total energies of PAMAM/lanthanide（Ⅲ） nanocomposites presented obvious tetrad effect and special double-double effect. Nd, Gd, and Er fell to the lower point and Gd fell to the lowest point in the TE-Ln curve with four groups. In order to explain the tetrad effect, kinetic energy （KE） and potential energy （PE） were analyzed. The KE curve consisted of three W-type parts （La - Pm, Pm - Tb, Tb - Tm, and the latter two W-type part were axial symmetry） and an exception part （Yb - Lu）. It also showed that the KE of odd atomic number was higher than the even one＇s with exception of Yb and Lu. Furthermore, decomposed potential energies gave out the atomic-level subtle difference of lanthanide which present more regulations for Eu（Ⅲ） - Lu（Ⅲ） compared with La（Ⅲ） - Sm（Ⅲ）. And also Ho-valley and three platforms （Sm - Eu, Td - Dy, Er - Tm） were discovered that refect the regular change of nanocomposite structures. Additionally, there are distinct correlations between Ebond and EInversion, EAngle and EVDW, Eworsion and ECoul, respectively. Therefore, PAMAM could be used in separation of lanthanide by changing conditions.     

Dynamics in complex systems: Dendrimer-polymer blends in electric and mechanical fields

An investigation was carried out on the molecular dynamics of blends composed of poly(amidoamine) (PAMAM) dendrimers with ethylenediamine core and amino surface groups (generations 0 and 3) and three linear polymers: poly(propylene oxide) - PPO and two block copolymers, poly(propylene oxide)/poly(ethylene oxide) - PPO/PEO with different mole ratios: 29/6 (amorphous) and 10/31 (crystalline). The results were generated over a broad range of frequency and temperature by Dielectric Relaxation Spectroscopy (DRS) and Dynamic Mechanical Spectroscopy (DMS). Dielectric spectra of dendrimers in the PPO matrix reveal a decrease in the time scale of normal and segmental relaxation with increasing dendrimer concentration. In the amorphous blends with 29PPO/6PEO matrix, no effect of concentration on the time scale of normal and segmental processes was observed. But in the crystalline blends with 10PPO/31PEO matrix, relaxation time increases with increasing dendrimer concentration. Results acquired by DRS and DMS were contrasted and the obtained relaxation times were found to be in excellent agreement. A detailed analysis of the effect of generation and concentration of dendrimers, hydrophilicity and morphology of the polymer matrix and temperature on the molecular origin, the shape of the relaxation spectra, the dielectric relaxation strength and the frequency location for the maximum loss in dendrimer-polymer blends is provided.     

树形分子包覆硫化镉量子点的抗老化性能研究

以聚酰胺-胺树形分子为模板制备了平均粒径为2.5nm的CdS量子点, 采用HRTEM、EDS、UV-vis、PL等手段对样品进行表征, 研究了其在室温避光条件下的老化过程. 结果表明, CdS量子点在刚制备的前5d里UV-vis、PL谱峰半峰宽变窄, 发光效率迅速上升, 表明量子点以尺寸窄化生长为主; 5d后UV-vis、PL谱峰半峰宽逐渐宽化, 发光效率缓慢下降, 表明量子点以尺寸宽化(Ostwald 熟化)过程为主. 树形分子的配位作用和模板作用赋予CdS量子点良好的抗老化性能, 6个月后量子点粒径增量<0.3nm, PL强度约降低22%.     

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.     

PAMAM-stabilized Pt-Ru nanoparticles for methanol electro-oxidation

This work utilizes poly(amidoamine) dendrimers (PAMAM) as a protective ligand in solution to produce carbon-supported, Pt-Ru bimetallic nanoparticles for use as methanol electro-oxidation catalysts. UV-vis spectra show that after initial Pt²⁺ complexation with PAMAM G4OH dendrimer in water, appropriate adjustment of solution pH permits subsequent Ru³⁺ complexation without displacing Pt²⁺, demonstrating the formation of an aqueous, bimetallic solution complex. Catalysts (nominally 20 wt% metals, confirmed by AA spectroscopy) are produced by impregnating high surface area carbon black with G4OH-(Pt²⁺)_x(Ru³⁺)_y complex solution, drying, and activation in H₂ gas at elevated temperature. XPS results show that activation in H₂ at 400 °C removes virtually all of the PAMAM and reduces all of the Pt and most of the Ru to zero valence. TEM and XRD results show that the use of G4OH in the recipe is crucial for controlling metal particle size, and that the particles are crystalline with lattice parameters indicative of bimetallic Pt-Ru alloys. XRD data also suggest that G4OH promotes greater Pt-Ru alloying when Pt:Ru = 1:1. Catalytic activity for methanol oxidation increases with Ru content and is greatest for the catalyst with 1:1 Pt:Ru ratio. Per unit mass of Pt, the methanol oxidation activity of 20 wt% G4OH-PtRu/C catalyst is about 60% greater than that of E-Tek's commercially available 20 wt% PtRu catalyst.     

树状大分子聚酰胺-胺固化环氧树脂性能研究

采用发散法由乙二胺和丙烯酸甲酯合成了树状聚酰胺-胺(PAMAM).以PAMAM作为环氧树脂(EP)的固化剂,用差示扫描量热法确定其固化工艺及固化物的玻璃化转变温度(T_g),探讨了树状PAMAM用量对固化物力学性能的影响.结果表明,PAMAM与EP的质量比为0.26时,固化物的力学性能最佳,其冲击强度为166.43 kJ/m~2,拉伸强度为43.54 Mpa;明显高于低分子量聚酰胺/EP固化物的冲击强度和拉伸强度.     

Preparation and application of fluorescence dendritic macromolecular nanoparticles

Abstract

In recent years, carbon dots have shown great potential in biological imaging, drug delivery, and other fields. In this study, red fluorescent carbon dots with carboxyl functional groups on the surface were designed and prepared, and the fluorescence properties were studied. At the same time, the carbon dot was combined with dendritic macromolecules, and the aggregate particle size was about 25nm. This combination has good dispersion and stability in both water and methanol, and the DOX-loaded is about 6.72%. The small particle size makes it easy to enter the cells, so as to achieve the function of tumor treatment and cell imaging.     

包覆多层聚电解质/树状大分子的聚合物微球表面CdS纳米粒的形成

将聚酰胺-胺(PAMAM)树形大分子、聚对苯乙烯磺酸钠(PSS)和聚二烯丙基二甲基氯化铵(PDADMAC)在三聚氰胺甲醛(MF)微球上进行静电自组装,制得聚电解质壳层的核壳式微球. 通过反应沉积吸附方法生成具有稳定荧光性能的CdS/聚电解质核壳式复合微球. 用透射电镜表征复合微球形貌,用反射紫外和荧光表征了CdS/聚电解质核壳式复合微球的光学特性.     

Detection of aflatoxin B1 by aptamer-based biosensor using PAMAM dendrimers as immobilization platform

We report an aptamer-based biosensor for detection of aflatoxin B₁ (AFB₁), a mycotoxin identified as contaminant in food. The sensor is assembled in a multilayer framework that utilizes cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for acquiring the signal response by means of redox indicators: K[Fe(CN)₆]^−3/−4. Poly (amidoamine) dendrimers of fourth generation (PAMAM G4) immobilized on gold electrode covered by cystamine, were employed for attachment of single stranded amino-modified DNA aptamers specific to AFB₁. The cystamine-dendrimers (Cys-PAMAM) layers were compared with other immobilization platforms such as cystamine (Cys), 11-mercaptoundecanoic acid (MUA) and 11-mercaptoundecanoic acid-dendrimers (MUA-PAMAM), being the first approach the most appropriate for producing sensitive and reproducible signal in the range of concentrations 0.1–10 nM AFB₁. The sensor was validated in certified contaminated peanuts extract as well as in spiked samples of peanuts-corn snacks and the sensing response was evaluated and compared in terms of the matrix effect. The aptamer specificity was analyzed by testing the sensor in other mycotoxins such as aflatoxin B₂ (AFB₂) and ochratoxin A (OTA). The limit of detection achieved by this sensor was LOD = 0.40 ± 0.03 nM, it was regenerable in 0.2 M glycine-HCl and it did not lose its stability up to 60 h storing at 4 °C. Atomic Force Microscopy (AFM) studies were also performed for illustrating individual steps of biosensor assembly.