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)     

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.     

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.     

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.     

Quantitative assessment of surface functionality effects on microglial uptake and retention of PAMAM dendrimers

Dendrimers are a promising class of polymeric nanoparticles for delivery of therapeutics and diagnostics. Polyamidoamine (PAMAM) dendrimers have shown significant efficacy in many animal models, with performance dependent on surface functionalities. Understanding the effects of end groups on biological interactions is critical for rational design of dendrimer-mediated therapies. In this study, we quantify the cellular trafficking kinetics (endocytosis and exocytosis) of generation 4 neutral (D4-OH), cationic (D4-NH₂), anionic (D3.5-COOH), and generation 6 neutral (D6-OH) PAMAM dendrimers to investigate the nanoscale effects of surface functionality and size on cellular interactions. Resting and LPS-activated microglia were studied due to their central roles in dendrimer therapies for central nervous system disorders. D4-OH exhibits greater cellular uptake and lower retention than the larger D6-OH. D4-OH and D3.5-COOH exhibit similar trafficking kinetics, while D4-NH₂ exhibits significant membrane interactions, resulting in faster cell association but lower internalization. Cationic charge may also enhance vesicular escape for greater cellular retention and preferential partitioning to nuclei. LPS activation further improves uptake of dendrimers, with smaller and cationic dendrimers experiencing the greatest increases in uptake compared to resting microglia. These studies have implications for the dependence of trafficking pathway on dendrimer properties and inform the design of dendrimer constructs tailored to specific therapeutic needs. Cationic dendrimers are ideal for delivering genetic materials to nuclei, but toxicity may be a limiting factor. Smaller, neutral dendrimers are best suited for delivering high levels of therapeutics in acute neuroinflammation, while larger or cationic dendrimers provide robust retention for sustained release of therapeutics in longer-term diseases.     

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.     

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.     

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).     

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。     

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.     

Structural response of polyelectrolyte dendrimer towards molecular protonation: the inconsistency revealed by SANS and NMR

Polyamidoamine (PAMAM) dendrimers and their charged state in deuterium oxide have been investigated with proton pulsed field gradient diffusion nuclear magnetic resonance (PFG-NMR) and small-angle neutron scattering (SANS) techniques. NMR measurements suggest that significant variation of the hydrodynamic radius, calculated by the Stokes-Einstein relation with appropriate surface conditions, is observed upon increasing the molecular protonation. However, a comparative SANS experiment indicates little dependence of the dendrimer global size, in terms of its radius of gyration, on molecular protonation. The inconsistency indicates the necessity of incorporating the effect of molecular interface modification and molecular porosity provided by dressed counterions, when dynamical measurements are used for the determination of the structural characteristics of ionic soft colloids even in dilute suspensions.     

Binding Properties of Water-Soluble Carbosilane Dendrimers

Dendrimers have been proposed as new carriers for drug delivery. They have distinctive characteristics, such as uniform and controlled size, monodispersity and modifiable surface group functionality, which make them extremely useful for biomedical applications. In this study, the binding capacity of water-soluble carbosilane dendrimers was examined. A double fluorimetric titration method with 1-anilinonaphthalene-8-sulphonic acid (ANS) was used to estimate the binding constant and the number of binding centers per dendrimer molecule. The data obtained suggest that ANS interacts non-covalently with the dendrimers. Second generation dendrimers have an open, asymmetric structure that allows them to encapsulate ANS. The ability of the polymers to interact with DNA was assessed by an ethidium bromide (EB) displacement assay. All the dendrimers studied bound to DNA in competition with EB, though the strength of binding varied. Dendrimer interactions with a protein (BSA) were tested using fluorescence quenchers. The dendrimers caused no conformation change in the protein, indicating that interactions between carbosilane dendrimers and BSA are weak and occur preferentially at the protein surface.     

Dendronization of gold and CdSe/cdS (core-shell) quantum dots with tomalia type, thiol core, functionalized poly(amidoamine) (PAMAM) dendrons

Poly(amidoamine) (PAMAM) dendrimers containing disulfide cores (i.e., cystamine) and possessing carboxylic acid or hydroxyl terminal groups were reduced with dithiothreitol (DTT) to yield single site, thiol core, functionalized PAMAM dendron reagents. These thiol functionalized dendron reagents were used to surface modify (dendronize) both gold nanoparticles, as well as CdSe/CdS (core-shell) quantum dots (QDs). Dendronization involved self-assembly of the focal point thiol functional dendrons at the metal interface of both gold and CdSe/CdS QDs by ligand exchange of protective surfactants used for their synthesis. The synthesis, characterization and preliminary luminescence studies of these new dendritic hybrids are reported.     

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.     

Phosphorylcholine functionalized dendrimers for the formation of highly stable and reactive gold nanoparticles and their glucose conjugation for biosensing

Phosphorylcholine (PC)-functionalized poly(amido amine) (PAMAM) dendrimers were prepared and used as both reducing and stabilizing agents for synthesis of highly stable and reactive gold nanoparticles (Au NPs). Biomimetic PC-functionalized PAMAM dendrimers-stabilized gold nanoparticles (Au DSNPs) were formed by simply mixing the PC modified amine-terminated fifth-generation PAMAM dendrimers (G5-PC) with AuCl₄ ⁻ ions by controlling the pH, no additional reducing agents or other stabilizers were needed. The obtained Au DSNPs were shown to be spherical, with particle diameters ranging from 5 to 12 nm, the sizes and growth kinetics of Au DSNPs could be tuned by changing the pH and the initial molar ratio of dendrimers to gold as indicated by transmission electron microscopy (TEM) and UV–Vis data. The prepared Au DSNPs showed excellent stability including: (1) stable at wide pH (7–13) values; (2) stable at high salt concentrations up to 2 M NaCl; (3) non-specific protein adsorption resistance. More importantly, surface functionalization could be performed by introducing desired functional groups onto the remained reactive amine groups. This was exemplified by the glucose conjugation. The glucose conjugated Au DSNPs showed bio-specific interaction with Concanavalin A (Con A), which induced aggregation of the Au NPs. Colorimetric detection of Con A based on the plasmon resonance of the glucose conjugated Au DSNPs was realized. A limit of detection (LOD) for Con A was 0.6 μM, based on a signal-to-noise ratio (S/N) of 3. These findings demonstrated that the PC modified Au DSNPs could potentially serve as a versatile nano-platform for the biomedical applications.     

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。     

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.     

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.     

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.     

Optical absorption in compact and extended dendrimers

Dendrimers are highly branched molecules, which are expected to be useful, for example, as efficient artificial light harvesting systems, in nano-technological or in medical applications. There are two different classes of dendrimers: compact dendrimers with constant distance between neighboring branching points throughout the macromolecule and extended dendrimers, where this distance increases from the system periphery to the center. We investigate the linear optical absorption spectra of these dendrimer types using the Frenkel exciton concept. The electron-phonon interaction is taken into account by introducing a heat bath that interacts with the exciton in a stochastic manner. We discuss compact dendrimers with equal excitation energies at all molecules, dendrimers with a functionalized core as well as with a whole branch functionalized. Furthermore the line shape of a compact dendrimer is discussed when neighboring molecules at the periphery interact and when all molecules have randomly distributed excitation energies due to disorder. Finally, we discuss two models for extended dendrimers.