Estimation of PAMAM Dendrimers' Binding Capacity by Fluorescent Probe ANS

Dendrimers are globular, hyperbranched polymers which possess a high concentration of surface functional groups and internal cavities. These unique features make them very useful to many biomedical applications, especially as carrier molecules. This study presents results of estimation of polyamidoamine (PAMAM) dendrimers and human serum albumin (HSA) binding capacity of fluorescent probe 1-anilinonaphthalene-8-sulfonic acid (ANS). It has been shown that fluorescent probes can be used for quantitative analysis of dendrimers' binding capacity.     

(聚酰胺-胺)树状大分子对甲氨蝶呤的复合和释放研究

以甲氨蝶呤(MTX)为模型药物,研究了PAMAM与MTX的复合及体外释放.1H-,13C-NMR数据表明MTX与PAMAM树状大分子形成复合物是由于MTX羧基和PAMAM树状大分子外端氨基之间的相互作用.该复合物在pH=7.4,10 mmol/L Tris-HCl中非常稳定,表现出明显的缓释效果.当溶液中的离子强度增加时,会破坏PAMAM-MTX复合物的稳定性,缓释作用部分或全部失去,说明PAMAM树状大分子与MTX之间的相互作用属于静电作用.UV测得每个G5.0 PAMAM、G4.0 PAMAM树状大分子分别能复合271、4个MTX分子.     

Electrocatalysis of the hydrogen evolution reaction by nanocomposites of poly(amidoamine)-encapsulated platinum nanoparticles and phosphotungstic acid

Poly(amidoamine) dendrimer (Generation-4) encapsulated platinum nanoparticles (PtNP-PAMAM) were prepared and used to fabricate nanocomposites with Keggin-type phosphotungstic acid (PW₁₂O₄₀³⁻) using a layer by layer electrostatic assembly technique. Indium tin oxide (ITO) electrodes, which were first modified with a monolayer of 3-aminopropyl triethoxysilane (3-APTES), were used as substrates for assembly of the PW₁₂O₄₀³⁻ monolayer. Nanocomposites were then fabricated by depositing PtNP-PAMAM on the monolayer of PW₁₂O₄₀³⁻. The amount of PtNP-PAMAM deposited was controlled by using different concentrations of PtNP-PAMAM diluted in 0.1 M H₂SO₄ solution. The hydrogen evolution reaction (HER) was used to test electrocatalytic activities of these nanocomposite modified electrodes. Modification of ITO|3-APTES with PW₁₂O₄₀³⁻ |PtNP-PAMAM showed significantly higher electrocatalytic activities toward the HER than electrodes modified with either PW₁₂O₄₀³⁻ or PtNP-PAMAM alone. The electrocatalytic activities were found to depend on the composition of PtNP-PAMAM and PW₁₂O₄₀³⁻ on electrode surfaces, which was attributed to an interaction between these species. Heat treatment of ITO|3-APTES|PW₁₂O₄₀³⁻ |PtNP-PAMAM electrodes at 200 °C produced significantly higher electrocatalytic activities, which supported the suggestion of an interaction. Presented at the 4th Baltic conference on Electrochemistry, Griefswald, March 13.−16., 2005.     

Poly(amidoamine) dendrimers peripherally modified with 4-ethylamino-1,8-naphthalimide. Synthesis and photophysical properties

New fluorescent poly(amidoamine) (PAMAM) dendrimers, comprising 4-ethylamino-1,8-naphthalmide units on the periphery have been synthesized. Their photophysical properties in organic solvents of different polarity have been determined. The photodegradation of the dendrimers in organic solvents has been investigated. The effect of the coordination of the dendrimer with transition metal cations in N,N-dimethylformamide solution has been discussed.     

Amperometric Detection of H2O2 Using Gold Electrodes Modified with Starburst PAMAM Dendrimers and Prussian Blue

Gold‐bead electrodes were modified by covalent bonding or physical adsorption of several Starburst PAMAM dendrimers (generations 2.0, 3.0 and 4.0) followed by absorption of Prussian Blue (PB). The covalent dendrimer‐PB‐modified electrodes can be used as amperometric sensors of H₂O₂ in aqueous solution. They offer enhanced sensitivity with correspondingly lower detection and quantification limits compared to similar amperometric detectors.     

Destabilization of fatty acid-containing liposomes by polyamidoamine dendrimers

Polyamidoamine dendrimers have been shown to be very effective at transporting DNA across cell membranes in transfection experiments. To investigate the membrane interactions with dendrimers that could contribute to this efficacy, the ability of dendrimers to permeabilize lipid vesicles in suspension has been studied. Vesicles were prepared containing the self-quenching, membrane impermeant dye calcein, and were treated with dendrimers of different sizes. Increase in fluorescence was attributed to release of the dye. Membranes containing dioleoyl phosphatidylethanolamine and stearic or oleic acid, lipids with a preference for non-lamellar phases, were very susceptible to disruption by dendrimers, with larger dendrimers being more effective than smaller. However, membranes containing lipids with a preference for the lamellar phase (either pure phosphatidylcholine, or phosphatidylcholine:phosphatidylserine) were largely unaffected. The concentration dependence of the permeabilization strongly suggests an aggregation-mediated mechanism for membrane disruption. Requenching measurements using cobalt citrate showed that permeabilization did not occur uniformly among the vesicles, but rather was all-or-none, with a subpopulation of vesicles responsible for essentially all of the dye release. This is also suggestive of an aggregation-induced response. Lastly, although osmotic forces are thought to play an important role in dendrimer-mediated transfection, we observed no effect of osmotic pressure and membrane tension on the efficacy of dendrimers in solution. It is likely that, in cells, dendrimers traverse cell membranes via endosomes, and the entrapment of the dendrimer itself within the endosomal vesicle may be a key factor in its ability to cause rupture.     

PAMAM dendrimer composite membrane for CO2 separation: Formation of a chitosan gutter layer

A poly(amidoamine) (PAMAM) dendrimer composite membrane with an excellent CO₂/N₂ separation factor was developed in-situ. The In-situ Modification (IM) method was used to modify the surface of commercial porous membranes, such as ultrafiltration membranes, to produce a gas selective layer by controlling the interface precipitation of the membrane materials in the state of a received membrane module. Using the IM method, a chitosan layer was prepared on the inner surface of a commercially available ultrafiltration membrane as a gutter layer, in order to affix PAMAM dendrimer molecules on the porous substrate. After chitosan treatment, the PAMAM dendrimer was impregnated into the gutter layer to form a PAMAM/chitosan hybrid layer. The CO₂ separation performance of the resulting composite membrane was tested at a pressure difference of 100 kPa and a temperature of 40 °C, using a mixed CO₂ (5 vol%)/N₂ (95 vol%) feed gas. The PAMAM dendrimer composite membrane, with a gutter layer prepared from ethylene glycol diglycidyl ether and a 0.5 wt% chitosan solution of two different molecular weight chitosans, revealed an excellent CO₂/N₂ separation factor and a CO₂ permeance of 400 and 1.6 × 10⁻⁷ m³ (STP) m⁻² s⁻¹ kPa⁻¹, respectively. SEM observations revealed a defect-free chitosan layer (thickness 200 nm) positioned directly beneath the top surface of the UF membrane substrate. After PAMAM dendrimer treatment, the hybrid chitosan/PAMAM dendrimer layer was observed with a thickness of 300 nm. XPS analysis indicated that the hybrid layer contained about 20–40% PAMAM dendrimer.     

Synthesis of azide-functionalized PAMAM dendrons at the focal point and their application for synthesis of PAMAM-like dendrimers

For the first time, the divergent synthesis of azide-functionalized PAMAM dendrons using azidopropyl amine as an azide focal point and convergent synthesis of symmetric PAMAM-like dendrimers containing 1,2,3-triazole rings as connectors via click chemistry with a dialkyne core is described.     

Enzyme immobilisation on electroactive nanostructured membranes (ENM): optimised architectures for biosensing

Electroactive nanostructured membranes have been produced by the layer-by-layer (LbL) technique, and used to make electrochemical enzyme biosensors for glucose by modification with cobalt hexacyanoferrate redox mediator and immobilisation of glucose oxidase enzyme. Indium tin oxide (ITO) glass electrodes were modified with up to three bilayers of polyamidoamine (PAMAM) dendrimers containing gold nanoparticles and poly(vinylsulfonate) (PVS). The gold nanoparticles were covered with cobalt hexacyanoferrate that functioned as a redox mediator, allowing the modified electrode to be used to detect H₂O₂, the product of the oxidase enzymatic reaction, at 0.0 V vs. SCE. Enzyme was then immobilised by cross-linking with glutaraldehyde. Several parameters for optimisation of the glucose biosensor were investigated, including the number of deposited bilayers, the enzyme immobilisation protocol and the concentrations of immobilised enzyme and of the protein that was crosslinked with PAMAM. The latter was used to provide glucose oxidase with a friendly environment, in order to preserve its bioactivity. The optimised biosensor, with three bilayers, has high sensitivity and operational stability, with a detection limit of 6.1 μM and an apparent Michaelis–Menten constant of 0.20 mM. It showed good selectivity against interferents and is suitable for glucose measurements in natural samples.     

A NOVEL NANOFILTRATION MEMBRANE PREPARED WITH PAMAM AND TMC (Ⅰ)

A series of nanofiltration (NF) membranes were prepared with poly(amido-amine) (PAMAM) and trimesoyl chloride (TMC) via in situ interfacial polymerization.The effects of the generation number and concentration of PAMAM on the properties of NF membranes were discussed.Fourier transform infrared spectroscopy (FTIR-ATR),atomic force micrgscopy (AFM),scanning electron microscopy (SEM) and contact angle measurements were employed to characterize the resulting membranes.The nanofiltration performances were eva...