Scaling trend in diffusion coefficients of low generation G0–G3 PAMAM dendrimers in aqueous solution at high and neutral pH

Aqueous solution diffusion coefficients for G0–G3 PAMAM dendrimers were determined from DOSY-NMR spectroscopy at high and neutral pH. The study was performed in a dilute regime and diffusion coefficients at infinite dilution (D ₀) were estimated from the variation of diffusion coefficients with dendrimer concentration. Hydrodynamic radii (R _h) for each dendrimer were estimated from D ₀ using the Stoke–Einstein relationship at both pH. According to D ₀ and R _h values, the structure of G0–G1 PAMAM dendrimers is almost insensitive to pH variations, whereas G2–G3 PAMAM dendrimers undergo swelling at neutral pH, due to surface amino groups protonation. Experimental diffusion coefficients show a scaling trend with the number of dendrimer atoms (N), with scaling laws of the type D₀ μ N^a D_{0} \propto N^{\alpha } , where α takes values of −0.39 and −0.50 at pH 12 and 7, respectively. For the first time, experimental data accounts for the scaling behavior of aqueous diffusion coefficients for low generation PAMAM dendrimers, as previously reported from molecular dynamics simulations.     

Synthesis of siloxane-based PAMAM dendrimers and luminescent properties of their lanthanide complexes

The 0.5-2 generations of siloxane-based PAMAM dendrimers with 1, 3-bis(3-aminopropyl) tetramethyldisiloxane (G0) as core unit were synthesized by two different methods. Their structures were characterized by FTIR, ¹H NMR, ¹³C NMR, LC/MS, TGA, and DSC. Results show that method two is more suitable as its synthetic procedure is simple and it provides higher yield than method one. DSC analysis indicates that the introduction of the siloxane linkage into the interior of the dendrimers has significant effect on the flexibility of the dendrimer structures. Lanthanide complexes of the newly designed siloxane-based PAMAM dendrimers were obtained by complexing with Eu(III) and Tb(III), respectively. The luminescent properties of the complexes in the solution were investigated. Narrow-width red and green emissions were observed from the complexes of G0.5, G1.5, and G2.0, indicating intramolecular energy transfer process takes place between ligands and lanthanide ions.     

Self‐Host Blue‐Emitting Iridium Dendrimer with Carbazole Dendrons: Nondoped Phosphorescent Organic Light‐Emitting Diodes

A blue‐emitting iridium dendrimer, namely B‐G2 , has been successfully designed and synthesized with a second‐generation oligocarbazole as the dendron, which is covalently attached to the emissive tris[2‐(2,4‐difluorophenyl)‐pyridyl]iridium(III) core through a nonconjugated link to form an efficient self‐host system in one dendrimer. Unlike small molecular phosphors and other phosphorescent dendrimers, B‐G2 shows a continuous enhancement in the device efficiency with increasing doping concentration. When using neat B‐G2 as the emitting layer, the nondoped device is achieved without loss in efficiency, thus giving a state‐of‐art EQE as high as 15.3 % (31.3 cd A^?1, 28.9 lm W^?1) along with CIE coordinates of (0.16, 0.29).     

Novel amphiphilic linear polymer/dendrimer block copolymer: Synthesis of poly(2-methyl-2-oxazoline)-block-poly(amido amine) dendrimer

Novel linear polymer/dendrimer block copolymers, poly(2-methyl-2-oxazoline)-block-poly(amido amine) dendrimers (water-soluble full-generation type 4 (G = 4.0 and 5.0) and amphiphilic half-generation type 5 (G = 3.5, 4.5, and 5.5)), were synthesized by divergent-growth dendrimer construction with ω-ethylenediamine-terminated poly(2-methyl-2-oxazoline), which was prepared by living ring-opening polymerization of 2-methyl-2-oxazoline. Assembly of the amphiphilic dendrimer-based block copolymer (G = 5.5) was investigated by surface tension measurements (critical micelle concentration, 0.49 wt.-%) and by small-angle neutron scattering analysis (spherical particles; assembled number, ca. 10³).     

Novel carbazole dendrimers having a metal coordination site as a unique hole-transport material

We have synthesized novel carbazole dendrimers via the cyclotrimerization of aminophenylketones in the presence of titanium tetrachloride. These dendrimers have the ability to assemble metal ions such as Sn²⁺ and Eu³⁺ with no significant difference in their generation, suggesting the dendrimer with an interior with a small density up to the third generation. We show the dendrimers with higher generations have the higher HOMO values. The most electron rich molecule, the G3 dendrimer, has the highest HOMO value of −5.2 eV. However, for the HOMO energy levels of the carbazole dendrimer complex with Eu(OTf)₃, the energy levels of the carbazoles did not change based on almost the same redox potentials as those of the dendrimers, themselves. Using the carbazole dendrimers and their europium complex, a homogeneous film was produced, which enhanced the performance of the electroluminescence device in comparison with only the dendrimer as the hole-transporting layer. This approach was managed by a solution process, i.e., the spin-coating method, without using the coevaporation technique based on the large equilibrium constants of the coordination of metal ions on the imine sites (K = 10⁵ M⁻¹).     

Cellular internalization of targeted and non-targeted delivery systems for contrast agents based on polyamidoamine dendrimers

New high-molecular-weight contrast agents based on polyamidoamine (PAMAM) dendrimers for targeted imaging of malignant tumors characterized by overexpression of human epidermal growth factor receptor (EGFR) and human alpha-fetoprotein receptor (RECAF) were designed. Conjugates of second (G2) and third (G3) generation polyamidoamine dendrimers with 1,4,7,10-tetraazocyclodecane-1,4,7,10-tetraacetic acid (DOTA) were obtained. The quantitative composition of the conjugates was determined by ¹HNMR spectroscopy. It was shown that four out of the 16 terminal NH₂ groups in G2-DOTA and nine out of the 32 groups in G3-DOTA were modified with DOTA. The morphology, size, and charge of the synthesized macromolecules were characterized by dynamic light scattering and electrophoresis. Gadolinium(III) was loaded into the conjugates and the Gd content was determined by atomic emission spectroscopy. For increasing the selectivity of accumulation in the tumor cells, two recombinant proteins able to bind selectively to EGFR and RECAF, namely, human recombinant epidermal growth factor (rEGF) and human recombinant 3rd domain of alpha-fetoprotein (3dAFPpG), were conjugated with G2 and G3 dendrimers. The conjugates containing vector molecules were mainly accumulated via clathrin-dependent endocytosis, whereas G2-DOTA and G3-DOTA were absorbed via caveolin-dependent endocytosis and macropinocytosis. The dendrimer conjugates with vector molecules were intensely accumulated in A549 cells characterized by high expression of EGFR (Herl) and RECAF, whereas the accumulation of conjugates in the control K562 cells (with low expression of Her1) and in the CD14^? population of human unstimulated mononuclear white blood cells was insignificant. The 3dAFPpG-conjugated dendrimers were partly recycled. All synthesized conjugates had a rather low toxicity in the range of 350–450 µmol L^?1 (IC₅₀).

     

Synthesis of dicarboxylate oligosaccharide multilayer terminal functionality upon poly(lysine) dendrimer scaffolding

A reactive three‐layered dendrimer containing carboxyl groups was synthesized by the coupling of dicarboxylic acid and a highly reactive, two‐layered glycopeptide dendrimer. Lactose, maltose, or maltotriose was reacted with the poly(lysine) dendrimer in its third and fourth generations by reductive amination and afforded two‐layered glycolysine dendrimers. The reaction was conducted in a borate buffer (pH 9.0). ¹H NMR, ¹³C NMR, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analyses were applied for the determination of the structures of the products. When an excess amount of the oligosaccharide and a long reaction time were used, the degree of substitution increased to 1.5–2.0 against an amino group. For the preparation of highly reactive, multilayered dendrimers for an antigen carrier, C6 hydroxy groups of the oligosaccharides were selectively esterified by adipic acid and suberic acid to give 6‐O‐adipoyl oligosaccharide–poly(lysine) dendrimers and 6‐O‐suberoyl oligosaccharide–poly(lysine) dendrimers. The reactivity of these multilayered dendrimers was examined by a model reaction with phenylalanine ethyl ester. The dendrimer showed high reactivity, providing phenylalanine ethyl ester–dicarboxylate oligosaccharide–poly(lysine) dendrimers with a considerably high proportion of phenylalanine residues. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3622–3633, 2002     

溶剂对聚酰胺-胺树形分子模板法原位制备CdS量子点的影响

为了研究非配位型溶剂对聚酰胺-胺(PAMAM)树形分子的模板法制备CdS量子点的影响, 分别以水、甲醇及二者的混合物( ∶ ＝2∶1)为溶剂, 以4.5代PAMAM树形分子为模板制备了CdS量子点. 结果表明, 相同条件下, 以甲醇为溶剂时制备的CdS量子点为单晶, 平均直径2.7 nm, 尺寸分布窄, 发光强度高; 以水为溶剂制备的CdS量子点为多晶, 平均直径为5.7 nm, 尺寸分布宽, 发光强度低; 在甲醇与水的混合溶剂中制备的CdS量子点为单晶和多晶共存, 平均直径为4.1 nm, 尺寸分布及发光强度都居中. 这主要是由于树形分子的模板作用不同造成的. 树形分子在甲醇中能充分伸展, 起到内模板作用; 树形分子与水之间由双氢键作用而产生交联, 不利于Cd^2＋与树形分子内部基团的配位, 主要起到外模板作用; 在甲醇与水的混合溶剂中, 树形分子则同时起到了内模板和外模板作用.     

N‐Boc‐Protected 1,2‐Diphenylethylenediamine‐Based Dendritic Organogels with Multiple‐Stimulus‐Responsive Properties

A new class of poly(benzyl ether) dendrimers, decorated in their cores with N‐Boc‐protected 1,2‐diphenylethylenediamine groups, were synthesized and fully characterized. It was found that the gelation capability of these dendrimers was highly dependent on dendrimer generation, and the second‐generation dendrimer (R,R)‐G₂DPENBoc proved to be a highly efficient organogelator. A number of experiments (SEM, TEM, FTIR spectroscopy, ¹H NMR spectroscopy, rheological measurements, UV/Vis absorption spectroscopy, CD, and XRD) revealed that these dendritic molecules self‐assembled into elastically interpenetrating one‐dimensional nanostructures in organogels. The hydrogen bonding, π–π, and solvophobic interactions were found to be the main driving forces for formation of the gels. Most interestingly, these dendritic organogels exhibited smart multiple‐stimulus‐responsive behavior upon exposure to environmental stimuli such as temperature, anions, and mechanical stress.     

Polyelectrolyte behavior and interpolyelectrolyte matching of AstramolTM poly(propylene imine) dendrimers

Polyelectrolyte behavior of Astramol^TM poly(propylene imine) dendrimers of five generations, G1‐G5, namely DAB‐dendr‐(NH₂)_x (where x is equal to 4, 8, 16, 32 or 64) was studied by means of potentiometric titration in salt‐free water solutions and also in the presence of a shielding low molecular electrolyte (NaCI). In addition to x outer primary amine groups the dendrimer molecule contains x‐2 inner tertiary amine groups. The repeating unit, the core molecule and the fifth generation dendrimer structure are shown in the following Scheme.     

Synthesis of conjugates of β-cyclodextrin with polyamidoamine dendrimers and their molecular inclusion interaction with levofloxacin lactate

Polyamidoamine (PAMAM) dendrimers of different generations (G2 and G4) conjugated with β-cyclodextrin (β-CD), PAMAM (G2, G4)-CD, were synthesized using substitution reaction from mono-6-iodine-β-cyclodextrin and PAMAM dendrimers. The resulting molecular structures were characterized by NMR, IR. The molecular interaction between various dendrimers and levofloxacin lactate (LFL) were investigated by monitoring the fluorescence of LFL in the presence of dendrimers in buffer solution (pH 7.4) at 25?°C. It was found that the PAMAM (G2, G4)-CD possesses higher sensitizing ability than that of the corresponding parent dendrimers and natural β-CD, and increases concomitantly with the increases of generation and content of β-CD, suggesting that the PAMAM (G2, G4)-CD possesses stronger inclusion ability with LFL. The possible interaction mechanism between PAMAM-CD and LFL was proposed by ¹H NMR analysis and theoretical calculation. The results show that the LFL molecule is located at the amine end of dendrimer molecule and along the side of cyclodextrin cavities to form supramolecular complexes. Furthermore, results indicate that the main driving force of the complex could be attributed to the electrostatic interactions and hydrogen bonding between LFL and PAMAM-CD, as well as the synergistic effect of intermolecular forces.     

Determination of maximum loading capacity of polyamidoamine (PAMAM) dendrimers and evaluation of Cu55 dendrimer‐encapsulated nanoparticles for catalytic activity

Spectrophotometric titrations provide information about the interior of the polyamidoamine (PAMAM) dendrimers, and therefore how nanoparticles are encapsulated. In this work, binding studies were performed to determine maximum loading capacities (N) of hydroxyl terminated G4, G5, and G6 PAMAM dendrimers with Cu²⁺ ions. The values of N found via spectrophotometric titrations were 16.22, 31.86, and 57.36 for G4‐OH, G5‐OH, and G6‐OH, respectively. The determination of loading capacity was also done using Viva spin filtration, and the results were found to be in agreement with those found via spectrophotometric titrations. From the binding isotherm, the values of equilibrium constant (K′) were determined and found to be 0.0488 (G4‐OH), 0.0291 (G5‐OH), and 0.0158 (G6‐OH). Owing to instability of G4‐OH (Cu₁₆), G5‐OH (Cu₃₂), and G6‐OH (Cu₅₇) dendrimer‐encapsulated nanoparticles (DENs) synthesized, G6‐OH (Cu₅₅) DENs of average size 2.6 ± 0.3 nm were prepared and were found to be relatively stable. Thus G6‐OH (Cu₅₅) catalyst was evaluated for the reduction of 4‐nitrophenol and was found to be catalytically active toward reduction of 4‐nitrophenol. Reaction kinetics of 4NP reduction was thoroughly studied in light of the Langmuir‐Hinshelwood kinetic model, and surface rate k, and the adsorption rates K_4NP, and K_BH4 were determined. The reaction was performed at different temperatures, which further expanded the study into determination of thermodynamic (ΔH^‡, ΔS^‡, ΔG^‡, and E_A) parameters.     

Bipolar Heteroleptic Green Iridium Dendrimers Containing Oligocarbazole and Oxadiazole Dendrons for Bright and Efficient Nondoped Electrophosphorescent Devices

Bipolar heteroleptic green light‐emitting iridium (Ir) dendrimers G(OXD) and G(DOXD) have been designed and synthesized under mild conditions in high yields, in which the first C^N and second O^O ligands are functionalized with oligocarbazole‐ and oxadiazole‐based dendrons, respectively. To avoid affecting the optical properties of the emissive iridium core, all the functional moieties are attached to the ligands through a flexible spacer. Compared with the unipolar dendrimer G(acac ), dendrimers G(OXD) and G(DOXD) exhibit the close emission maxima of 511–512 nm and photoluminescence quantum yield of 0.39–0.40 in a solution of toluene. Moreover, on going from G(acac) to G(OXD) and G(DOXD) , we have found that the introduction of oxadiazole fragments decreases the lowest unoccupied molecular orbital (LUMO) energy levels to facilitate the electron injection and electron transporting, while their highest occupied molecular orbital (HOMO) energy levels remain unchanged. This means that, we can individually tune the HOMO and LUMO energy levels based on the heteroleptic structure to ensure the relative independence between the hole and electron in the emitting layer (EML), which is a favorable feature for bipolar optoelectronic materials. As a result, a bilayer nondoped electrophosphorescent device with G(DOXD) as the EML gives a maximum luminous efficiency of 25.5 cd A⁻¹ (η_ext: 7.4 %) and a brightness of 33 880 cd m⁻². In comparison to G(acac) (17.2 cd A⁻¹, 17 680 cd m⁻²), both the efficiency and brightness are improved by about 1.5 and 2 times, respectively. These state‐of‐the‐art performances indicate the potential of these bipolar heteroleptic iridium dendrimers as solution‐processible emitting materials for nondoped device applications.     

Cu2+对联苯甲醛修饰的树状大分子聚酰胺-胺荧光性能的影响

采用小分子联苯甲醛(BPA)分别修饰第一和第二代树状大分子聚酰胺-胺(PAMAM), 合成了2种PAMAM的修饰产物G1-BPA4和G1-BPA8. 利用IR, 1H NMR及MALDI-TOF MS等手段表征了2种产物的结构, 研究了Cu2+浓度对其荧光性能的影响. 结果表明, 在一定的浓度范围内, 作为常见荧光猝灭剂的Cu2+能使2种产物的荧光均显著增强.     

Deep‐red light‐emitting phosphorescent dendrimer encapsulated tris‐[2‐benzo[b]thiophen‐2‐yl‐pyridyl] iridium (III) core for light‐emitting device applications

New deep‐red light‐emitting phosphorescent dendrimers with hole‐transporting carbazole dendrons were synthesized by reacting tris(2‐benzo[b]thiophen‐2‐yl‐pyridyl) iridium (III) complex with carbazolyl dendrons by DCC‐catalyzed esterification. The resulting first‐, second‐, and third‐generation dendrimers were found to be highly efficient as solution‐processable emitting materials and for use in host‐free electrophosphorescent light‐emitting diodes. We fabricated a host‐free dendrimer EL device with configuration ITO/PEDOT:PSS (40 nm)/dendrimer (55 nm)/BCP (10 nm)/Alq₃ (40 nm)/LiF (1 nm)/Al (100 nm) and characterized the device performance. The multilayered devices showed luminance of 561 cd/m² at 383.4 mA/cm² (12 V) for 15 , 1302 cd/m² at 321.3 mA/cm² (14 V) for 16 , and 422 cd/m² at 94.4 mA/cm² (18 V) for 17 . The third‐generation dendrimer, 17 (η_ext = 6.12% at 7.5 V), showed the highest external quantum efficiency (EQE) with an increase in the density of the light‐harvesting carbazole dendron. Three dendrimers exhibited considerably pure deep‐red emission with CIE 1931 (Commission International de L'Eclairage) chromaticity coordinates of x = 0.70, y = 0.30. The CIE coordinates remained very stable with the current density. The integration of rigid hole‐transporting dendrons and phosphorescent complexes provides a new route to design highly efficient solution‐processable materials for dendrimer light‐emitting diode (DLED) applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7517–7533, 2008     

Silole‐core phenylacetylene dendrimers and their application in detecting picric acid

Silole‐core phenylacetylene dendrimers were designed and synthesized, among them, the model compound (n = 0) and the first generation of the dendrimer (n = 1) were obtained by the reaction of 2,5‐dibromosilole with corresponding terminal alkynes, the second generation of the dendrimers (n = 2) was synthesized from 2,5‐diiodosilole. These compounds indicated the absorptions of both phenylacetylene dendrons (250–350 nm) and silole core (400–500 nm). The first generation displayed efficient energy transfer from phenylacetylene dendrons to silole core, whose energy transfer efficiency was as high as 80%. These compounds were used as chemical sensors to probe explosive, for picric acid (PA), the Stern–Volmer constants of model compound and the first generation are 7120 and 5490M^?1, respectively. J. Heterocyclic Chem., (2012).     

激发态分子内质子转移(ESIPT)发色团修饰的树枝形聚合物合成及光物理研究

设计合成了0～4代外围修饰激发态分子内质子转移(ESIPT)发色团的聚酰胺-胺树枝形聚合物G0～G4,化合物结构经过IR,1H NMR,13C NMR和MS表征.稳态光谱研究表明,树枝形聚合物在四氢呋喃溶液中形成了聚集体,发色团酮式发光随着化合物代数增大呈先增加后减小的变化.质子化树枝形聚合物G1-H～G4-H能溶于水,并在水中形成20 nm左右的聚集体,发色团在聚集体疏水区中构象受限,仅发射酮式发光,并且发光强度受树枝形聚合物分子大小的影响.     

以尼罗红为探针对新型两亲性树枝形聚合物微环境的研究

本工作合成了一系列外围以三缩四乙二醇单甲醚修饰的烷基芳醚骨架两亲性树枝形聚合物Gn(n=0—3),化合物通过了¹H-NMR,IR和MALDI-TOF-MS的表征.利用吸收光谱,稳态和时间分辨荧光光谱研究了水溶液中Gn对尼罗红分子的增溶作用以及Gn内部微环境的极性.研究结果表明,高代数树枝形聚合物Gn对尼罗红具有更好的增溶效果.1—3代树枝形聚合物Gn内部疏水孔腔微环境极性随代数增加而逐渐降低,G1和G2树枝形聚合物具有相似的微环境极性,而由于构象的变化使G3具有更加疏水的微环境.     

The Preparation of a New Kind of Carbosilane Dendrimer with 4‐(Naphthalen‐1‐yl)phenyl Core‐An Application of Suzuki Coupling Reaction

Using the divergent method, carbosilane dendrimers with p‐bromophenyl core were synthesized by using alternating Grignard and hydrosilylation reactions. And then, α‐naphthalenyl was connected to the core by using Suzuki coupling reaction. This gave a new carbosilane dendrimer with a 4‐(naphthalen‐1‐yl)phenyl core. All the products were characterized by IR, ¹H NMR, ¹³C NMR, ²⁹Si NMR, and MS. The study shows that Suzuki Coupling reaction is an effective and powerful core‐functionalization method and a satisfactory result can be achieved through prolonging the reaction time.     

1,6‐Dinitroperylene Bisimide Dyes: Synthesis,Characterization and Photophysical Properties

1,6‐ and 1,7‐regioisomers of dinitro‐substituted perylene bisimides ( 1a — 1b and 2a — 2b ) were synthesized under mild condition in high yields. The 1,6‐ and 1,7‐regioisomers were successfully isolated from the regioisomeric mixture using conventional methods of separation and subsequently characterized by 500 MHz ¹H NMR spectroscopy. This is the first time when 1,6‐dinitroperylene bisimides ( 1a — 1b ) are obtained in pure form. Furthermore, the photophysical and electrochemical properties of 1 and 2 were found to be almost the same. The nitro functionalities provide stability of n‐type charge carriers by lowering the LUMO to resist ambient oxidation, which may offer potential applications in air‐stable n‐type organic semiconductors.