Preparation of the Cationic Dendrimer-Based Hydrogels for Controlled Heparin Release

We introduce a cationic polyamidoamine (PAMAM) dendrimers and tetronic (Te) based hydrogels in which precursor copolymers were prepared with simple methods. In the synthetic process, tyramine-conjugated tetronic (TTe) was prepared via activation of its four terminal hydroxyl groups by nitrophenyl chloroformate (NPC) and then substitution of tyramine (TA) into the activated product to obtain TTe. Cationic PAMAM dendrimers G3.0 functionalized with p-hydroxyphenyl acetic acid (HPA) by use of carbodiimide coupling agent (EDC) to obtain Den-HPA. ¹H-NMR confirmed the amount of HPA and TA conjugations. The aqueous TTe and Den-HPA copolymer solution rapidly formed the cationic hydrogels in the presence of horseradish peroxidase enzyme (HRP) and hydrogen peroxide (H₂O₂) at physiological conditions. The gelation time of the hydrogels could be modulated ranging from 7 to 73 secs, when the concentrations of HRP and H₂O₂ varied. The hydrogels exhibited minimal swelling degree and low degradation under physical condition. In vitro cytotoxicity study indicated that the hydrogels were highly cytocompatible as prepared at 0.15 mg/mL HRP and 0.063 wt% of H₂O₂ concentration. Heparin release profiles show that the cationic hydrogels can sustainably release the anionic anticoagulant drug. The obtained results demonstrated a great potential of the cationic hydrogels for coating medical devices or delivering anionic drugs.     

Interaction between PAMAM 4.5 dendrimer, cadmium and bovine serum albumin: a study using equilibrium dialysis, isothermal titration calorimetry, zeta-potential and fluorescence

Binding of Cd²⁺ by PAMAM 4.5 dendrimer was studied by equilibrium dialysis, isothermal titration calorimetry and zeta-potential measurement. The following binding parameters were obtained: n = 23.8 ± 9.5, K_b = 4.7 ± 0.9 × 10³ in water; and n = 41.3 ± 13.4, K_b = 2.1 ± 0.8 × 10³ in 0.15 mol/l phosphate-buffered saline. The location of the bound Cd²⁺ is discussed. The interactions between bovine serum albumin, PAMAM 4.5 dendrimer and cadmium were analyzed using fluorescence and equilibrium dialysis. The competition between Cd²⁺ binding to BSA and PAMAM 4.5 dendrimer was investigated. It is proposed that PAMAM 4.5 dendrimer could be successfully used for extracting Cd²⁺ from aqueous solutions (environmental protection).     

AgBr纳米簇：PAMAM树形分子模板法制备及光催化性能研究

以酯端基聚酰胺-胺(PAMAM)树形分子为模板，原位制备了AgBr纳米簇。由于酯端基的半代PAMAM树形分子起到“内模板”作用，制得的AgBr纳米簇粒径小、尺寸分布窄、稳定性好，并通过改变Ag⁺∶PAMAM树形分子的物质的量的比可以精确控制纳米簇的尺寸。AgBr纳米簇/树形分子纳米复合材料在光催化降解甲基橙方面具有很好的催化能力，且随纳米簇的尺寸减小，其催化能力增强。     

Fragmentation of poly(amidoamine) dendrimers in matrix-assisted laser desorption

Fragmentation of different generations of poly(amidoamine) dendrimers was explored in five common MALDI matrices: 2,5-dihydroxybenzoic acid (DHB), 4-hydroxy-3-methoxycinnamic acid (FER), α-cyano-4-hydroxycinnamic acid (ACH), 2,4,6-trihydroxyacetophenone (THAP), and 3-hydroxypicolinic acid (HPA). Of these, DHB was the softest matrix and ACH produced significant fragment intensity already at MALDI threshold, FER and THAP being in between. HPA was not a convenient matrix for dendrimers and produced a specific fragmentation pattern. Fragmentation analysis was mainly concentrated on generation G1, which contains already all essential structural elements. Dendrimers showed complicated fragmentation behavior with multiple fragmentation channels in our MALDI experiments. The relative intensities of these channels depended selectively on choice of the matrix and showed dissimilar dependence on the laser pulse energy. This was attributed to different fragmentation mechanisms, due to different protonation pathways, occurring in the same MALDI plume. The fragmentation pathways were proposed for all observed fragmentation channels. All fragmentation sites of protonated ions were found to be directly attached to the protonation sites and the fragmentation was surplus charge driven in this sense. No charge remote fragmentation channels were detected. Cationized dendrimers showed higher stability than the protonated ions.     

Enhancement of composite‐metal interfacial adhesion strength by dendrimer

The interface between carbon fiber reinforced polymer composites and metal plays a critical role in determining the strength of epoxy/metal laminated composites. We propose to introduce one dendrimer layer into the epoxy/metal interface, aiming to enhance the interfacial adhesion strength so that the interface could more effectively transfer the load from epoxy to metal. In this paper, the preparation and adsorption of dendrimer layer onto the alumina surface were systematically investigated. The results show that a highly stable and nanopatterned dendrimers layer was dip‐coated onto alumina substrates by adsorbing poly (amidoamine) dendrimers. It was confirmed that the dendrimers were adsorbed onto the alumina via acid‐base chemical interactions. The adsorption depends on the reaction time. The adhesion property between dendrimers and alumina was examined by sonication method. Copyright © 2010 John Wiley & Sons, Ltd.     

Fluorescence enhancement for the complex PAMAM-BSA in the presence of photonic crystal heterostructures

The paper presents the optical characterization of the multilayer film composed of styrene (ST)-poly(ethylene glycol) methyl ether methacrylate (PEGMA 1100)-gold nanoparticles (Au)-poly(amidoamine) PAMAM (G4)-bovine serum albumin (BSA). The addition of the last layer composed of BSA resulted in an unusual optical behaviour, i.e. increase of the fluorescence emission intensity, respectively the intensity of the UV-vis reflection, compared with the ST-PEGMA 1100-Au-G4 film. The explanation could be attributed to the presence of photonic crystal heterostructures. The multilayer film has been characterized by optical microscopy, AFM, UV-vis, and fluorescence.     

Catalytic Oxidation of Cyclohexene by Dendrimer-bond Metal Catalysts

Since Tomalia and Dovornic discussed the promising outlook of surface-functionalized dendrimer catalysts in 1994, [1] dendritic catalysts have been proposed to many kinds of catalysis.These well-defined macromolecular structures enable the construction of precisely controlled catalyst structures. The large number of the peripheral functionalities enhanced their activity in many processes. [2,3] We report herein a new method of using the dendritic catalysts in the oxidation of cyclohexene. The reactions give some interesting results.In short, the synthesis of the dendritic catalysts was initiated from the well-known PAMAM dendrimers by using their peripheral ammonia groups. The condensation reactions of these ammonia groups and salicyaldehyde (SA) offer the ligands PAMAMSA with different generation (G) numbers.dendrimer-bond PAMAMSA-Ni(Ⅱ) complexes.In the presence of the dendritic PAMAMSA-Ni(Ⅱ) catalysts, cyclohexene was fully oxidized under 1 atm of molecular oxygen at 70℃. All the oxidations give 7-oxabicyclo[4.1.0]heptane 1,2-cyclohexen-l-ol 2, 2-cyclohexen-1-one 3 and 7-oxabicyclo [4.1.0]heptan-2-one 4 as the major products. The results of the oxidation are shown in the table below (table 1):Table 1 Oxidation of cvclohexene bv PAMAMSA-Ni2+ catalysts** Reaction condition: cat. 2mg, cyclohexene 5mL, 1atm O2, 6hat 70℃.**Oxygen absorption (mL) per mol catalyst.It can be seen from table that the oxidations give a new product 7-oxabicyclo[4.1.0]heptan-2-one 4, which is the first reported product in this oxidation. Meanwhile, product 4possesses relatively high selectivity in the six oxidation processes. It will arise much more emphasison the optimizing of these reactions.     

Silsesquioxane Modified with PAMAM Dendrimer and a Bimetallic Complex for Electrochemical Detection of Ascorbic Acid

Octakis(3-chloropropyl)octasilsesquioxane (S) was organofunctionalized with the PAMAM Dendrimer G.0 (SPD). After functionalization, silsesquioxane interacts with copper chloride and subsequently with potassium hexacyanoferrate (III) to produce the structure CuHSPD. The silsesquioxane functionalized with the PAMAM dendrimer (SPD) and the obtained novel hybrid composite (CuHSPD) were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The CuHSP voltammogram showed two well-defined redox pairs with E^θ′= 0.27 and 0.74 V, that are assigned to the Cu^I/Cu^II and Fe^II(CN)₆/Fe^III(CN)₆ redox pairs, respectively. The graphite paste electrode containing CuHSPD allowed the electrocatalytic determination of ascorbic acid using various electrochemical techniques such as cyclic voltammetry, differential pulse voltammetry, and chronoamperometry.     

Exploring the physicochemical and morphological properties of peptide-hybridized dendrimers (DendriPeps) and their aggregates

This article presents an integrated experimental and computational study of DendriPeps, a novel class of dendrimers featuring a polyamidoamine (PAMAM) backbone hybridized with peptide segments. Hydroxyl-terminated Generation 2 (G.2) DendriPeps, comprising either four lysines (Lys) or four glutamic acids (Glu), and G.3 DendriPeps, comprising 8 Lys or 8 Glu, were first characterized in terms of hydrodynamic radius (R_h) and ζ-potential in aqueous solution. Unlike PAMAM dendrimers, DendriPeps form aggregates with R_h between 60 and 980 nm and ζ-potential between −130 and 80 mV despite their strong net charge. Upon application of shear, all aggregates disassemble into monomeric DendriPeps (R_h ~ 1–3 nm), but reform rapidly as shear is removed. Rheological characterization confirmed that DendriPep aggregates are disrupted by mild shear, but reform reversibly. Molecular dynamics simulations, informed by titrimetry, suggest that DendriPep aggregation derives from their multipolar structure and ability to rearrange the intermolecular/intramolecular pairing of titratable moieties at different pH values.