Bioapplications of poly(amidoamine) (PAMAM) dendrimers in nanomedicine

Poly(amidoamine) (PAMAM) dendrimers are a novel class of spherical, well-designed branching polymers with interior cavities and abundant terminal groups on the surface which can form stable complexes with drugs, plasmid DNA, oligonucleotides, and antibodies. Amine‐terminated PAMAM dendrimers are able to solubilize different families of hydrophobic drugs, but the cationic charges on dendrimer surface may disturb the cell membrane. Therefore, surface modification by PEGylation, acetylation, glycosylation, and amino acid functionalization is a convenient strategy to neutralize the peripheral amine groups and improve dendrimer biocompatibility. Anticancer agents can be either encapsulated in or conjugated to dendrimer and be delivered to the tumor via enhanced permeability and retention (EPR) effect of the nanoparticle and/or with the help of a targeting moiety such as antibody, peptides, vitamins, and hormones. Biodegradability, non-toxicity, non-immunogenicity, and multifunctionality of PAMAM dendrimer are the key factors which facilitate steady increase of its application in drug delivery, gene transfection, tumor therapy, and diagnostics applications with precision and selectivity. This review deals with the major topics of PAMAM dendrimers including structure, synthesis, toxicity, surface modification, and also possible new applications of these spherical polymers in biomedical fields as dendrimer-based nanomedicine.     

Effect of solvent-controlled aggregation on the intrinsic emission properties of PAMAM dendrimers

Solvent-induced aggregation and its effect on the intrinsic emission properties of amine, hydroxy and carboxylate terminated, poly(amidoamine) (PAMAM) dendrimers have been investigated in glycerol, ethylene glycol, methanol, ethylene diamine and water. Altering the solvent medium induces remarkable changes in the intrinsic emission properties of the PAMAM dendrimers at identical concentration. Upon excitation at 370 nm, amine terminated PAMAM dendrimer exhibits an intense emission at 470 nm in glycerol, ethylene glycol as well as glycerol-water mixtures. Conversely, weak luminescence is observed for hydroxy and carboxylate terminated PAMAM dendrimers in the same solvent systems. When the solvent is changed to ethylene diamine, hydroxy terminated PAMAM exhibits intense blue emission at 425 nm. While the emission intensity is varied when the solvent milieu is changed, excited state lifetime values of PAMAM dendrimers remain independent of the solvent used. UV-visible absorption and dynamic light scattering (DLS) experiments confirm the formation of solvent-controlled dendrimer aggregates in the systems. Comparison of the fluorescence and DLS data reveals that the size distribution of the dendrimer aggregates in each solvent system is distinct, which control the intrinsic emission intensity from PAMAM dendrimers. The experimental results suggest that intrinsic emission intensity from PAMAM dendrimers can be regulated by proper selection of solvents at neutral conditions and room temperature.     

Fluorescent properties of novel dendrimer dyes based on thiazole orange

In this paper, polyamidoamine (PAMAM) dendrimers with active amino group of some generations (G=0.5-2) were prepared from commercial aminoacetaldehyde diethyl acetal by the divergent method. After that, thiazole orange (TO) with -COOH was incorporated with dendrimers of G=1 and 2 to afford novel dendrimer-TO dyes. The fluorescent properties studies showed that the fluorescent intensity of the same concentration of dendrimer-TO (G=2) was higher than that of the dendrimer-TO (G=1), and both of them were much stronger than free TO with -COOH. There was a fluorescent enhancement of the dendrimer dyes compared with free dye. The dendrimer dyes were of well-defined chemical structure,with little aggregation and self-quenching as well as good fluorescence properties of good stability, high intensity and sensitivity, which could be used in labeling cancer cells and further in diagnosis and detection of early-stage tumors.     

Determination of non-traditional intrinsic fluorescence (NTIF) emission sites in 1-(4-carbomethoxypyrrolidone)-PAMAM dendrimers using CNDP-based quenching studies

A unique photoluminescent phenomenon producing inexplicable, blue emissions [λ_Ex?=?365 nm; λ_Em?=?460 nm] in the absence of traditional aromatic fluorophores has been observed in a variety of surface functionalized poly(amidoamine) (PAMAM) dendrimers over the past two decades. This emission phenomenon, referred to as non-traditional intrinsic fluorescence (NTIF), originates from the intra-molecular clustering of electron-rich sub-fluorophores (i.e., tertiary amines and/or amido groups) residing in the interior of all PAMAM dendrimers. The intra-molecular clustering of these interior sub-fluorophores is hypothesized to account for the modest but reproducible, blue emissions observed for a variety of dendrimer surface moieties (i.e., –OH, –CO₂H, and –NH₂). Unexpectedly, a simple, one-step conversion of amine-terminated PAMAM dendrimers to 1-(4-carbomethyoxy) pyrrolidone-terminated dendrimers (4-CMP) was found to produce a 50-fold increase in blue NTIF emission compared to other surface moieties. In an effort to understand this new enhanced emission property, critical nanoscale design parameter (CNDP)-directed quenching experiments were devised to probe the increased NTIF emissions. Was it originating from the interior sub-fluorophoric tertiary amine/amido moieties or from the surface-attached, sub-fluorophoric pyrrolidone amido groups or both? Four generations of 4-CMP PAMAM dendrimers were examined. Two classical quenchers, namely, potassium iodide and acrylamide were selected to probe surface versus interior domains, respectively, as a function of predictable CNDPs associated with generation levels. With increasing dendrimer generation, quencher penetration into the dendrimer interior is impeded due to CNDP-directed generational congestion. Stern-Volmer plots for each quencher, as a function of generation, exhibited appropriate linear or non-linear correlations that corroborated behavior expected for two distinct region-specific emission sites.     

Photophysical property of rhodamine-cored poly(amidoamine) dendrimers: Simultaneous effect of spirolactam ring-opening and PET process on sensing trivalent chromium ion

Two novel poly(amidoamine) (PAMAM) dendrimers, comprising rhodamine B unit in the core and 1-phenyl-3-methyl-5-pyrazolone unit at the periphery, have been synthesized and characterized. Both dendrimers displayed high selectivity and sensitivity towards Cr³⁺ ion. As considering the potential of being applied as fluorescent sensors for Cr³⁺ ion, we studied the complexes formed between the dendrimers and Cr³⁺ ion. Different PAMAM dendrimers had different recognition mechanism towards Cr³⁺ ion. For dendrimer G2, the recognition of Cr³⁺ was mainly due to the ring-opening of spirolactam. However, it significantly depended on the simultaneous effect of ring-opening of spirolactam and photoinduced electron transfer (PET) in the case of dendrimer G3.     

Development of TREN dendrimers over mesoporous SBA-15 for CO2 adsorption

Mesoporous SBA-15 was synthesized using rice husk ash (RHA) as the silica source and their defective Si-OH groups were grafted with tris(2-aminoethyl) amine (TREN) dendrimers generation through step-wise growth technique. The X-ray diffraction (XRD) and nitrogen adsorption/desorption results of parent SBA-15 obtained from RHA, suggests its resemblance with SBA-15 synthesized using conventional silica sources. Furthermore, the nitrogen adsorption/desorption results of SBA-15/TREN dendrimer generations (G1-G3) illustrates the growth of dendrimer inside the mesopores of SBA-15 and their CO₂ adsorption capacity was determined at 25 °C. The maximum CO₂ adsorption capacity of 5-6 and 7-8 wt% over second and third dendrimer generation was observed which is discernibly higher than the reported melamine and PAMAM dendrimers. The experimental CO₂ adsorption capacity was found to be less than theoretically calculated CO₂ adsorption capacity due to inter and intra molecular amidation as result of steric hindrance during the dendrimer growth. These SBA-15/TREN dendrimer generations also exhibit thermal stability up to 350 °C and CO₂ adsorption capacity remains unaltered upon seven consecutive runs.     

香豆素-3-甲酰氯修饰聚酰胺-胺大分子的荧光性能研究

用香豆素-3-甲酰氯对聚酰胺-胺树状大分子末端修饰合成了树状大分子PAMAM-CMAC,经FTIR,1H-NMR分析确证了其结构。荧光分析表明,PAMAM-CMAC树状大分子具有强的荧光发光,荧光强度比聚酰胺-胺树状大分子荧光强度增加很多。其荧光强度受pH值、溶液浓度和溶剂等各种因素的影响,在酸性条件下,荧光强度受溶液pH影响较大;但在强碱性介质中,氢键被完全破坏,荧光强度明显减弱。pH在7.00～10.00之间时,荧光发光比较稳定。溶液浓度对荧光强度也有影响,浓度太大或太小,荧光强度都相应减小,而且浓度大的溶液比浓度小的溶液荧光猝灭的快。这与理论相一致。同时,随着溶剂极性的增加,荧光发射向长波方向移动。     

Studying Complexes Between PPI Dendrimers and Mant-ATP

The aim of this study was to investigate the interactions between poly(propylene imine) (PPI) dendrimers and 2′-/3′-O-(N′-methylanthraniloyl)-ATP (Mant-ATP). Mant-ATP was used as a model molecule. Purine and pyrimidine nucleoside analogues are antimetabolites commonly used in therapy for cancer. Drug molecules can complex with dendrimers in two ways: therapeutic agents may be attached in dendrimer interior or bind to functional groups on the surface. Drugs attached to nanoparticles are characterized by improved solubility, pharmacokinetics and stability. Here, we have used poly(propylene imine) dendrimers of the 4th and 5th generations (PPI G4 and PPI G5) with primary amino surface groups partially modified with maltose (PPI-m) or without modification (PPI). We assessed the efficiency of complex formation in relation to dendrimer generation, pH of solution and the type of dendrimer used. A double fluorimetric titration method was used to estimate the binding constant (K _b ) and the number of binding centers per molecule of the binding agent (n).     

Deformability of poly(amidoamine) dendrimers

Experimental data indicates that poly(amidoamine) (PAMAM) dendrimers flatten when in contact with a substrate, i.e. they are no longer spherical, but resemble flat disks. In order to better understand the deformation behavior of these branched polymers, a series of atomistic molecular dynamics simulations is performed. The resulting flattened dendrimer conformations are compared to atomic force microscopy (AFM) images of individual dendrimers at air/mica and water/mica interfaces. The ability of the polymers to deform is investigated as a function of dendrimer generation (2-5) and the required energies are calculated. Our modeling results show good agreement with the experimental AFM images, namely that dendrimers are highly flexible and capable of forming multiple interaction sites between most of their branch ends and the substrate. The deformation energy scales with dendrimer generation and does not indicate an increase in stiffness between generations 2 and 5 due to steric effects.PACS: 81.07.Nb Molecular nanostructures - 82.20.Wt Computational modeling; simulation - 68.37.Ps Atomic force microscopy (AFM)     

A novel amperometric hydrogen peroxide biosensor based on pyrrole-PAMAM dendrimer modified gold electrode

Horseradish peroxidase (HRP) was immobilized into an electrochemically prepared copolymer of pyrrole–PAMAM (PAMAM; polyamidoamine) dendrimers for the construction of amperometric hydrogen peroxide biosensor. First, second, and third generation amidoamine–pyrrole dendrons having branched amine periphery and focal pyrrole functionality were synthesized via divergent pathway. Pyrrole dendrimers were covalently attached onto the electrode surface and polymerized by electrochemical copolymerization with pyrrole monomer. The synthesized dendrimers and copolymers have been characterized by FTIR-ATR and NMR. These copolymers have been utilized as conducting films for amperometric hydrogen peroxide sensing. The HRP retains its bioactivity after immobilization into the dendronized pyrrole-copolymers. Amperometric response was measured as a function of concentration of hydrogen peroxide, at fixed potential of +0.35 V vs. Ag/AgCl in a phosphate buffered saline (pH 7.5). The effect of pH and temperature of the medium, storage, and reusability properties were investigated. The results indicate an efficient immobilization of enzyme onto the PAMAM type dendrimer modified surface containing pyrrole monomer, which leads to high enzyme loading, and increased lifetime stability of the electrode.     

Formation of Silver and Gold Dendrimer Nanocomposites

Structural types of dendrimer nanocomposites have been studied and the respective formation mechanisms have been described, with illustration of nanocomposites formed from poly(amidoamine) PAMAM dendrimers and zerovalent metals, such as gold and silver. Structure of {(Au(0))_n–PAMAM} and {(Ag(0))_n–PAMAM} gold and silver dendrimer nanocomposites was found to be the function of the dendrimer structure and surface groups as well as the formation mechanism and the chemistry involved. Three different types of single nanocomposite architectures have been identified, such as internal (I), external (E) and mixed (M) type nanocomposites. Both the organic and inorganic phase could form nanosized pseudo-continuous phases while the other components are dispersed at the molecular or atomic level either in the interior or on the surface of the template/container. Single units of these nanocomposites may be used as building blocks in the synthesis of nanostructured materials.     

荧光光谱法研究G3.0 PAMAM树状大分子与牛血清白蛋白的相互作用

聚酰胺-胺型(PAMAM)树状大分子是一类新型的纳米级、球型、高度分支、单分散性的聚合物,并具有安全、低毒、无免疫原性等许多独特的生物学性质。正是由于这些优势使其有望成为一种新型有效的生物材料,用于作为寡核苷酸的转运因子和药物转运载体。因此,深入了解树状大分子的生物学性质对进一步研究其在治疗方面的应用是至关重要的。文章应用荧光光谱法在生理条件下研究了具有表面氨基的3.0代聚酰胺-胺型(G3.0 PAMAM)树状大分子与牛血清白蛋白(BSA)间的相互作用。结果表明,加入G3.0 PAMAM树状大分子后,BSA内源性荧光发生猝灭,其猝灭机制属于静态猝灭,符合Stern-Volmer方程。通过计算得到该树状大分子与BSA间的结合常数为(1.067±0.025)L·mmol-1。通过同步荧光、红边激发荧光位移(REES)等方法的研究发现,树状大分子的存在会改变BSA的构象。此外还考查了体系的pH值和离子强度对该树状大分子与BSA相互作用的影响,由实验结果可推断静电作用是二者结合的主要作用机制。     

Dendrimer Interactions with Hydrophobic Fluorescent Probes and Human Serum Albumin

The interactions between three types of polyamidoamine dendrimers (with anionic, cationic, and neutral charge on a surface) and fluorescent dye 1-anilinonaphthalene-8-sulfonate (ANS) were studied. Double fluorimetric titration method was employed to estimate a binding constant and the number of binding centers. As fluorescent probes can serve as models of toxin molecules, dendrimers, and human serum albumin (HSA) abilities to bind ANS were compared. In the presence of HSA and dendrimers, ANS located both in HSA and in dendrimers, but the interactions between ANS and HSA were stronger.     

The fluorescence of polyamidoamine dendrimers peripherally modified with 1,8-naphthalimide groups: Effect of the rare earth ions and protons

We report the absorption spectra, fluorescent spectra and photophysical properties of G 2.0 polyamidoamine dendrimers with peripheral 1,8-naphthalimide groups with the hydrogen ions, the rare earth ions (Er³⁺, Tb³⁺, Nb³⁺, Eu³⁺, Yb³⁺ and Gd³⁺) and the mixture of the rare earth metal and hydrogen ions. The presence of the rare earth ions and hydrogen ions was found to enhance the fluorescence owing to the coordination between the rare earth metal or hydrogen ions and internal amido groups of polyamidoamine (PAMAM) from dendrimer. The result from the 3D isogram of the fluorescence spectra for the dendrimers with peripheral 1,8-naphthalimide groups show that it was obtained for the different emission fluorescence intensity and scope by varying the excitation wavelength and the different rare earth ions as well as its concentration. The results obtained reveal that the capacities of these systems might have acted as a sensitive label agent of the rare earth cations and protons.     

Self‐Assembly of Functionalized Gold Nanoparticles with Rigid and Flexible Multifunctional Linkers

The interparticle spacing of carboxyl functionalized gold nanoparticles (Au–COOH) was mediated by rigid cross‐linkers, octa(3‐aminopropyl)octasilsesquioxane (POSS–NH₃ ⁺) and poly(amidoamine) dendrimer terminated with hydroxyl groups (PAMAM–OH), and a flexible polymeric linker, poly(hexanyl viologen) (6‐VP). Regular interparticle spacing was achieved by utilizing POSS–NH₃ ⁺ and PAMAM–OH dendrimer as cross‐linkers, whereas size growth of Au–COOH was observed featuring no interparticle spacing by utilizing 6‐VP as the cross‐linker.     

Photoluminescence study of tetra-dendron dendrimers derived from ethylenediamine cores and di-dendron dendrimers derived from mono-Boc-protected ethylenediamine cores

Strong UV absorbance spectra and fluorescence spectra from tetra-dendron dendrimers derived from ethylenediamine cores with different terminal groups (-NH₂, -COOCH₃) or di-dendron dendrimers derived from mono-Boc-protected ethylenediamine cores were studied under different conditions by varying experimental parameters such as pH value and concentration. The result shows a rapid increase of fluorescence intensity at low pH. It was reasonable that the formation of a fluorescence-emitting moiety had a close relationship to protonated tertiary amine groups in tetra-dendron dendrimers derived from ethylenediamine cores or di-dendron dendrimers derived from mono-Boc-protected ethylenediamine cores. Furthermore, it was confirmed that the concentration of two dendrimers plays an important role in fluorescence intensity. The increase in fluorescence intensity was linear with respect to concentration at low concentration regions but the intensity increases slowly at high concentration regions.     

ZnO/PAMAM G5.0的合成及其对“502”熏显处理指印的增显作用研究

为了同时解决纳米指印显现试剂的灵敏度、专属性以及安全性等方面的问题,设计出氧化锌/聚酰胺-胺树形分子纳米复合材料(ZnO/PAMAM G5.0)的构架,并探索了相关的合成条件、产物的荧光性能及其在潜指印显现方面的应用前景。实验结果表明,ZnO纳米颗粒可以在PAMAM G5.0树形分子的模板作用下控制生成;合成产物在中波紫外光的激发作用下可以发出蓝色可见光;当锌离子与树形分子的负载比介于10~100范围内时,合成产物的荧光性能呈现先增长后下降的趋势,并在负载比为60时得到最强光致发光效果;对于经"502"熏显法固定后的潜指印样本,ZnO/PAMAM G5.0纳米复合材料可以通过胺解反应途径对其进行有效的增显。ZnO/PAMAM G5.0纳米复合材料有望引领纳米指印显现试剂新的发展方向。     

Investigation the effects of nano golds on the fluorescence properties of the sectorial poly(amidoamine) (PAMAM) dendrimers

The influence of nano golds on fluorescence properties of sectorial Polyamidoamine dendrimers (G4 s-PAMAM) was investigated in this paper. It was found that gold nanoparticles (GNPs) with definite surface plasmon absorption can quench the fluorescence of G4 s-PAMAM dendrimers. With the increasing of the concentration of GNPs, the fluorescence intensity of G4 s-PAMAM decreased correspondingly, and varied linearly at low concentration of GNPs. This phenomenon was owing to the fluorescence resonance energy transfer (FRET) between the dendrimers and GNPs. In contrast, the complex with smaller gold nanodots (GNDs) encapsulated in the interior of the G4 s-PAMAM presented greatly enhanced emission. Those results show that the size of nano golds may be used to adjust the fluorescence properties of sectorial PAMAM dendrimers and may extend potential applications of PAMAM dendrimers and nano golds.     

Imaging {Au0-PAMAM} Gold-dendrimer Nanocomposites in Cells

Dendrimer nanocomposites (DNC) are hybrid nanoparticles formed by the dispersion and immobilization of guest atoms or small clusters in dendritic polymer matrices. They have a great potential in biomedical applications due to their controlled composition, predetermined size, shape and variable surface functionalities. In this work, d=5–25nm spherical nanoparticles composed of gold and poly(amidoamine) (PAMAM) dendrimers have been selected to demonstrate this nanoparticle based concept. {Au(0)_n-PAMAM} gold dendrimer nanocomposites with a well-defined size were synthesized and imaged by transmission electron microscopy both in vitro and in vivo. DNC have also the potential to be used for imaging and drug delivery vehicles either by utilizing bioactive guests or through the incorporation of radioactive isotopes, such as Au-198.     

官能团及修饰位点对金属有机骨架化合物（MOFs）CO2/CH4分离性能的影响：蒙特卡洛模拟研究

In order to explore the in uence of modification sites of functional groups on landfill gas (CO₂/CH₄) separation performance of metal-organic frameworks (MOFs), six types of organic linkers and three types of functional groups (i.e. -F, -NH₂, -CH₃) were used to construct 36 MOFs of pcu topology based on copper paddlewheel. Grand canonical Monte Carlo simulations were performed in this work to evaluate the separation performance of MOFs at low (vacuum swing adsorption) and high (pressure swing adsorption) pressures, respectively. Simulation results demonstrated that CO₂ working capacity of the unfunctionalized MOFs generally exhibits pore-size dependence at 1 bar, which increases with the decrease in pore sizes. It was also found that -NH₂ functionalized MOFs exhibit the highest CO₂ uptake due to the enhanced Coulombic interactions between the polar -NH₂ groups and the quadrupole moment of CO₂ molecules, which is followed by -CH₃ and -F functionalized ones. Moreover, positioning the functional groups -NH₂ and -CH₃ at sites far from the metal node (site b) exhibits more significant enhancement on CO₂/CH₄ separation performance compared to that adjacent to the metal node (site a).