Dendrimer Complexes Research Articles

Charged dendrimers in trivalent salt solutions under the action of DC electric fields.

The structural properties and electrophoretic mobility of charged dendrimers in 3:1 electrolyte solutions subjected to direct current electric fields are studied using molecular dynamics simulations. The simulated dendrimer size is studied in zero fields and found to scale as R(g) ∼ N(0.29). The dendrimers exhibit shape distortions when the applied electric field is larger than some critical value, which scales with the number of dendrimer monomers as E(z,crit) ∼ N(0.39(6)). Families of curves, such as the curves of the square of radius of gyration, the asphericity, the degree of prolateness, and the electrophoretic mobility of dendrimers, are shown to collapse to single, master curves in electric fields through appropriate scaling. This reflects the fractal characteristics of these systems. The density profile of the surface monomers and salt cations reveals two pronounced combination effects between the polarization of dendrimer complexes and stripping-off of the condensed salt cations from the dendrimer surface.

Interaction of a hydrophobic-functionalized PAMAM dendrimer with bovine serum albumin: thermodynamic and structural changes.

The interaction between a hydrophobic-functionalized PAMAM dendrimer (PAMAM-NH2-C12, 25%, G4) and bovine serum albumin (BSA) has been investigated by circular dichroism (CD), UV-vis, and fluorescence spectroscopic methods and molecular modeling. The analysis of the effects of dendrimer complexation on the stability and conformation of BSA indicated that the binding process of the hydrophobic-functionalized dendrimer with BSA induced the relatively large changes in secondary structure of protein. Thermal denaturation of BSA, when carried out in the presence of dendrimer, also indicated that this hydrophobic-functionalized dendrimer acted as a structure destabilizer for BSA. The hydrophobic, electrostatic, and hydrogen bonding forces played important roles in the complex formation. The putative binding site of PAMAM-NH2-C12 (25%) dendrimer on BSA was near to domain I and domain II. The effect of hydrophobic modification on the stability and structure of BSA would find useful information on the cytotoxicity of PAMAM dendrimer.

Polynuclear SmIIIPolyamidoamine-Based Dendrimer: A Single Probe for Combined Visible and Near-Infrared Live-Cell Imaging

We report herein the synthesis of a luminescent polynuclear dendritic structure (SmIII-G3P-2,3Nap) in which eight SmIII ions are sensitized by thirty-two 2,3-naphthalimide chromophores. Upon a single excitation wavelength, the dendrimer complex exhibits two types of emission in the visible and in the near-infrared (NIR) ranges. SmIII-G3P-2,3Nap was non-cytotoxic after 24 h of incubation and up to 2.5 μM. The ability of the SmIII-based probe to be taken up by cells was confirmed by confocal microscopy. Epifluorescence microscopy validated SmIII-G3P-2,3Nap as a versatile probe, capable of performing interchangeably in the visible or NIR for live-cell imaging. As both emissions are obtained from a single complex, the cytotoxicity and biodistribution are inherently the same. The possibility for discriminating the sharp SmIII signals from autofluorescence in two spectral ranges increases the reliability of analysis and reduces the probability of artifacts and instrumental errors.

Polynuclear SmIII Polyamidoamine‐Based Dendrimer: A Single Probe for Combined Visible and Near‐Infrared Live‐Cell Imaging

We report herein the synthesis of a luminescent polynuclear dendritic structure (Sm(III)-G3P-2,3Nap) in which eight Sm(III) ions are sensitized by thirty-two 2,3-naphthalimide chromophores. Upon a single excitation wavelength, the dendrimer complex exhibits two types of emission in the visible and in the near-infrared (NIR) ranges. Sm(III)-G3P-2,3Nap was non-cytotoxic after 24 h of incubation and up to 2.5 μM. The ability of the Sm(III)-based probe to be taken up by cells was confirmed by confocal microscopy. Epifluorescence microscopy validated Sm(III)-G3P-2,3Nap as a versatile probe, capable of performing interchangeably in the visible or NIR for live-cell imaging. As both emissions are obtained from a single complex, the cytotoxicity and biodistribution are inherently the same. The possibility for discriminating the sharp Sm(III) signals from autofluorescence in two spectral ranges increases the reliability of analysis and reduces the probability of artifacts and instrumental errors.

Preparation of Saccharide Exchange Membrane Modified by Phenylboronic Acid Azoprobe/Polyamidoamine (PAMAM) Dendrimer

Phenylboronic acid azoprobe (B-Azo-Cb) for saccharide recognition was synthesized. B-Azo-Cb/polyamidoamine (PAMAM) complex was synthesized by the condensation reaction of terminal carboxylic group of B-Azo-Cb and surface amine of PAMAM dendrimer. Thin porous cellulose acetate membrane embedded with B-Azo-Cb/PAMAM dendrimer complex was prepared from cellulose acetate, formamide, acetone, and B-Azo-Cb/PAMAM dendrimer complex by casting on the glass plate at various temperatures. The saccharide transportability was evaluated by measuring the amount of saccharide in receiving solution. The amount of saccharide transport of porous cellulose acetate membrane embedded with B-Azo-Cb/PAMAM dendrimer complex was higher at low temperature-treated membrane, and low pH of receiving solution. In contrast, the saccharide transportabilities through non-treated cellulose acetate membrane were the same at any pH of receiving solution. Saccharide transportability was in the order of galactose > glucose > fructose (B-Azo-Cb/PAMAM G4 modified membrane), and glucose > galactose > fructose (B-Azo-Cb/PAMAM G5 modified membrane). These orders were the same of the saccharide response in solution. These results indicated that the saccharide transport of B-Azo-Cb/PAMAM-embedded membrane is successfully mediated by the phenylboronic acid.

Ternary Complex of Plasmid DNA Electrostatically Assembled with Polyamidoamine Dendrimer and Chondroitin Sulfate for Effective and Secure Gene Delivery

The purpose of this study was to develop a ternary complex of plasmid DNA (pDNA) electrostatically assembled with polyamidoamine (PAMAM) dendrimer and chondroitin sulfate (CS) for effective and secure gene delivery. PAMAM dendrimers are new cationic polymers that are expected to be used as gene delivery vectors. However, cationic non-viral gene vectors showed cytotoxicity by binding to negative cellular membranes. We therefore prepared a ternary complex by adding CS, an anionic polymer, and examined its usefulness. The pDNA/PAMAM dendrimer complex (PAMAM dendriplex) and the PAMAM dendriplex coated by CS (CS complex) showed nanoparticles with positive ζ-potential and negative ζ-potential, respectively. The CS complex had no cytotoxicity against B16-F10 cells and no agglutination activity, although severe cytotoxicity and high agglutination were observed in the PAMAM dendriplex. As a result of an in vitro gene expression study of B16-F10 cells, not only the PAMAM dendriplex but also the CS complex showed high transfection efficiency. The transfection efficiency of the CS complex was significantly inhibited by clathrin-mediated endocytosis inhibitor (chlorpromazine), caveolae-mediated endocytosis inhibitor (genistein), and hypothermia. Tail-vein injection of the CS complex into mice led to significantly higher gene expression in the spleen than the PAMAM dendriplex. Thus, the ternary complex of pDNA electrostatically assembled with PAMAM denriplex and CS showed safe high gene expression in the spleen. This vector is expected to be useful for useful gene delivery.

Oligoamine-tethered low generation polyamidoamine dendrimers as potential nucleic acid carriers.

In recent years, dendrimers have emerged as the most widely explored materials for theranostics emphasizing their potential in therapeutic delivery and diagnostics as well as in pharmaceutical technology. Amongst them, PAMAM dendrimers have been extensively studied for their prospects in various biomedical applications due to their defined structures and distinctive features such as monodispersity, uniformity and amenability to functionalization. Here, low generation PAMAM dendrimers (G2-G4) have been modified via Michael addition reaction followed by amidation with an oligoamine linker, tetraethylenepentamine (TEPA). Subsequently, these modified dendrimers were characterized by physicochemical techniques and evaluated for their capability to transfer nucleic acids in vitro. The results displayed significant improvements in the transfection efficiency in both HeLa and A549 cells maintaining higher cell viability. Sequential delivery of GFP-specific siRNA resulted in ∼73% suppression of the target gene. Flow cytometry results revealed that one of the formulations, mG3-pDNA complex, exhibited the highest gene transfection (∼49-68%) outperforming pDNA complexes of native dendrimers and the standard transfection reagent, Superfect (∼32-36%). All these results ensure the potential of the modified dendrimers as effective vectors for future gene delivery applications.

Intermolecular forces between low generation PAMAM dendrimer condensed DNA helices: role of cation architecture

In recent years, dendriplexes, complexes of cationic dendrimers with DNA, have become attractive DNA delivery vehicles due to their well-defined chemistries. To better understand the nature of the forces condensing dendriplexes, we studied low generation poly(amidoamine) (PAMAM) dendrimer-DNA complexes and compared them to comparably charged linear arginine peptides. Using osmotic stress coupled with X-ray scattering, we have investigated the effect of molecular chain architecture on DNA-DNA intermolecular forces that determine the net attraction and equilibrium interhelical distance within these polycation condensed DNA arrays. In order to compact DNA, linear cations are believed to bind in DNA grooves and to interact with the phosphate backbone of apposing helices. We have previously shown a length dependent attraction resulting in higher packaging densities with increasing charge for linear cations. Hyperbranched polycations, such as polycationic dendrimers, presumably would not be able to bind to DNA and correlate their charges in the same manner as linear cations. We show that attractive and repulsive force amplitudes in PAMAM-DNA assemblies display significantly different trends than comparably charged linear arginines resulting in lower DNA packaging densities with increasing PAMAM generation. The salt and pH dependencies of packaging in PAMAM dendrimer-DNA and linear arginine-DNA complexes were also investigated. Significant differences in the force curve behaviour and salt and pH sensitivities suggest that different binding modes may be present in DNA condensed by dendrimers when compared to linear polycations.

The influence of heterocyclic compound-PAMAM dendrimer complexes on evoked electrical responses in slices of hypoxic brain tissue.

We used complexes between a fourth generation polyamidoamine (PAMAM) dendrimer and one of two heterocyclic compounds — 1-(6-hydroxyhexyl)-3-(5-phenyl-isoxazole-3-yl)-urea or 5-phenyl-isoxazole-3-carboxylic acid — to reduce oxygen consumption in transverse slices of the hippocampus taken from 4-week old male rats. In vitro electrophysiological experiments revealed that the inhibitory effect of the hypoxic state on the evoked responses was enhanced in the presence of the complexes. The data were analyzed in terms of the potential antitumor effects of these complexes.

Monte-Carlo simulations of PAMAM dendrimer-DNA interactions.

We use Monte Carlo simulations to determine the influence of poly(amido amine) (PAMAM) dendrimer size and charge on its interactions with double-stranded DNA conformation and interaction strength. To achieve a compromise between simulation speed and molecular detail, we combine the coarse-grained DNA model of de Pablo et al. which resolves each DNA base using three beads - and thereby retains the double-helix structure - with a dendrimer model with resolution similar to that of the DNA. The resulting predictions of the effects of dendrimer generation, dendrimer surface charge density, and salt concentration on dendrimer-DNA complexes are in agreement with both experiments and all-atom MD simulations. The model predicts that DNA wraps a fully charged G5 or G6 dendrimer at low salt concentration (10 mM) similarly to a histone octamer, and for the G5 dendrimer, DNA super helices with both handednesses occur. At salt concentrations above 50 mM, or when a high fraction of dendrimer surface charges are neutralized by acetylation, DNA adheres but does not compactly wrap the dendrimer, in agreement with experimental findings. We are also able to simulate pairs of dendrimers binding to the same DNA strand. Thus, our mesoscale simulation not only elucidates dendrimer-DNA interactions, but also provides a methodology for efficiently simulating chromatin formation and other cationic macroion-DNA complexes.

Abstract P1-07-08: RNA based Twist1 inhibition via dendrimer complex to reduce breast cancer cell metastasis

Abstract Breast cancer remains a leading cause of cancer related deaths for women in the United States with the principal cause of mortality being metastatic disease. Mortality rates associated with metastatic breast cancer tumors are significantly elevated compared to localized disease because the most common metastatic sites (brain, bone marrow, and lungs) are difficult to target either with chemotherapy or surgical intervention. Therefore reduction of tumor cell dispersion is a key component to a reduction in mortality rates among patients with breast cancer. Epithelial-Mesenchymal Transition (EMT) is the process by which cancer cells downregulate proteins associated with cell to cell adhesion (e.g. E-cadherin) resulting in cells that are able to detach from neighboring cells, invade adjacent tissue, and eventually enter the circulatory system or lymphatics. Many breast cancers are known to commandeer the EMT process, thus allowing the cells to metastasize beyond the primary tumor. The process of EMT is tightly regulated by the transcription factor Twist1, which is often overexpressed in breast cancer. Therefore, Twist1 serves as an excellent therapeutic target whose downregulation would result in fewer metastatic cancer cells and correspondingly reduce cancer mortality. Twist1 is also a desirable target because it is almost nonexistent in adult tissues and thus its silencing would have minimal side effects, especially compared to many of the non-specific cancer treatments used today. Our lab has elected to use an RNA-based mediated gene silencing approach to decrease the expression levels of Twist1 in a highly invasive breast cancer cell line (SUM 1315). Due to their fragile nature, siRNA molecules are often difficult to deliver at therapeutic levels either in vitro or in vivo. We have overcome these delivery and degradation limitations through the optimization and use of Poly (amidoamine) (PAMAM) dendrimers. By complexing the siRNA with the PAMAM dendrimers not only protects the RNA molecules, but also facilitates their uptake into the tumor cells. We hypothesize that suppression of the activity of Twist1 via dendrimer-delivered Twist1 siRNA will inhibit metastatic behavior of aggressive breast cancer cells. Here we demonstrate successful delivery of Alexa Fluor® 488 labeled siRNA using two different dendrimers (Generation 5 and a modified Generation 3) with transfection efficiency results exceeding those of Lipofectamine 2000 and with far less toxicity to cells. We also show up to a 90% reduction (lasting at least 7 days) in Twist1 expression using Western Blot and qPCR analysis. Along with the knock down of Twist1, here we also demonstrate a significant knockdown of EMT proteins N-Cadherin and Vimentin. Functionally, luciferase promoter assays of Twist1 targets were also reduced. Furthermore, we were able to appreciate a significant phenotypic decrease in the invasive nature of the breast cancer cells using migration/invasion assays. Taken together these results demonstrate successful knockdown of Twist1 using siRNA dendrimer complexes resulting in an altered cellular phenotype and function. These data will serve as a foundation for optimization of future in vivo experiments with both orthotopic and metastatic breast cancer models. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-07-08.

Copper(II) Complexes with 4-Carbomethoxypyrrolidone Functionalized PAMAM-Dendrimers: An EPR Study

The internal flexibility and interacting ability of PAMAM-dendrimers having 4-carbomethoxypyrrolidone-groups as surface groups (termed Gn-Pyr), which may be useful for biomedical purposes, and ion traps were investigated by analyzing the EPR spectra of their copper(II) complexes. Increasing amounts (with respect to the Pyr groups) of copper(II) gave rise to different signals constituting the EPR spectra at room and low temperature corresponding to different coordinations of Cu(2+) inside and outside the dendrimers. At low Cu(2+) concentrations, CuN4 coordination involving the DAB core is preferential for G3- and G5-Pyr, while G4-Pyr shows a CuN3O coordination. CuN2O2 coordination into the external dendrimer layer was also contributing to G3- and G4-Pyr spectra. The structures of the proposed copper-dendrimer complexes were also shown. G4-Pyr displays unusual binding ability toward Cu(II) ions. Mainly the remarkably low toxicity shown by G4-Pyr and its peculiar binding ability leads to a potential use in biomedical fields.

Chemicals-Inspired Biomaterials: Developing Biomaterials Inspired by Material Science Based on POSS

Abstract The concept of “chemicals-inspired biomaterials” and several examples are demonstrated in this review. The idea and background for the design of chemicals-inspired biomaterials which are constructed based on the chemistry and characteristics in material science are explained. As an example, we show several chemicals-inspired materials utilizing polyhedral oligomeric silsesquioxane (POSS) as a building block to apply the material functions of the POSS chemicals for fabricating a series of biomaterials having superior properties. Initially, the filler effects of POSS are explained. Because of the robust silica cube, POSS derivatives can show significant effect as a filler reinforcing the thermal and mechanical properties of conventional plastics simply by mixing. Based on these results, we designed rigid chelators for the complexation with gadolinium ions as an MRI contrast agent. It is demonstrated that the enhancement of the rigidity is a valid strategy for the improvement of the sensitivity. Next, we assembled the functional molecules into the POSS-core dendrimer. We observed from the dendrimer complexes that photon upconversion can be accomplished via an optical process which should be suppressed in electroluminescence devices. The last topic concerns the selective encapsulation by the POSS-core dendrimer for biomolecules. From the study of POSS-based ionic liquids, it was found that the strength of the hydrogen bonds with the ion pair moiety was significantly increased by tethering to POSS. Based on this enhancement, we accomplished selective encapsulation with the POSS-core dendrimer. The results and the prominent properties of the chemicals-inspired biomaterials are shown in this review.

Efficient Dendrimer–DNA Complexation and Gene Delivery Vector Properties of Nitrogen-Core Poly(propyl ether imine) Dendrimer in Mammalian Cells

Dendrimers as vectors for gene delivery were established, primarily by utilizing few prominent dendrimer types so far. We report herein studies of DNA complexation efficacies and gene delivery vector properties of a nitrogen-core poly(propyl ether imine) (PETIM) dendrimer, constituted with 22 tertiary amine internal branches and 24 primary amines at the periphery. The interaction of the dendrimer with pEGFPDNA was evaluated through UV-vis, circular dichroism (CD) spectral studies, ethidium bromide fluorescence emission quenching, thermal melting, and gel retardation assays, from which most changes to DNA structure during complexation was found to occur at a weight ratio of dendrimer:DNA ∼ 2:1. The zeta potential measurements further confirmed this stoichiometry at electroneutrality. The structure of a DNA oligomer upon dendrimer complexation was simulated through molecular modeling and the simulation showed that the dendrimer enfolded DNA oligomer along both major and minor grooves, without causing DNA deformation, in 1:1 and 2:1 dendrimer-to-DNA complexes. Atomic force microscopy (AFM) studies on dendrimer-pEGFP DNA complex showed an increase in the average z-height as a result of dendrimers decorating the DNA, without causing a distortion of the DNA structure. Cytotoxicity studies involving five different mammalian cell lines, using [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide] (MTT) assay, reveal the dendrimer toxicity profile (IC50) values of ∼400-1000 μg mL(-1), depending on the cell line tested. Quantitative estimation, using luciferase assay, showed that the gene transfection was at least 100 times higher when compared to poly(ethylene imine) branched polymer, having similar number of cationic sites as the dendrimer. The present study establishes the physicochemical behavior of new nitrogen-core PETIM dendrimer-DNA complexes, their lower toxicities, and efficient gene delivery vector properties.

Coarse grained simulations of neutral and charged dendrimers

Dendrimers are macromolecules with a regular-treelike, branched architecture of their skeleton. In terms of the branching number and the number of terminal groups they represent an extreme case among branched polymers. Dendrimers can occur in neutral and various charged states. Due to their highly branched architecture excluded volume effects are of great importance and conformational properties and monomer distribution profiles of dendrimers differ considerably from those of linear polymers. We give an overview of the state-of-the-art knowledge of physical properties of dendrimers as seen from coarse-grained computer simulations. Our main focus is on isolated dendrimers with flexible spacers both in the neutral and in the charged state, as well as complexation of dendrimers with oppositely charged linear polyelectrolytes. We briefly address problems of adsorption and concentration effects in dendrimer solutions and outline recent progress and open questions in this field.

Abstract 2692: Dendrimer delivery of RNA based Twist1 inhibitors to reduce breast cancer cell metastasis.

Abstract Breast cancer in women is a leading cause of cancer related deaths in the United States with metastatic disease being the chief cause of mortality. Metastatic breast cancer tumors are often found in their later stages making them difficult to remove or treat. Inhibition of tumor cell dispersion is therefore a key component to a reduction in mortality rates among women with breast cancer. Epithelial-Mesenchymal Transition (EMT) is the process by which cancer cells downregulate proteins associated with cell to cell adhesion (e.g. E-cadherin) resulting in cells that are able to mobilize. Breast cancer cells are known to commandeer the EMT process through overexpression of Twist1, thus allowing the cells to metastasize beyond the primary tumor. Twist1 therefore serves as an excellent therapeutic target whose disruption would result in fewer metastatic cancer cells and correspondingly reduce cancer mortality. Twist1 is also a desirable target because it is almost nonexistent in adult tissues and thus its silencing would have minimal side effects. Our lab has elected to use an siRNA mediated gene silencing approach to decrease the expression levels of Twist1 in two highly invasive breast cancer cell lines (SUM 1315 and MCF7-Tw). Due to their fragile nature, siRNA molecules are often difficult to deliver at therapeutic levels. We have overcome these delivery limitations through the optimization and use of Poly (amidoamine) (PAMAM) dendrimers. We hypothesize that suppression of the activity of Twist1 via dendrimer-delivered Twist1 siRNA will inhibit metastatic behavior of aggressive breast cancer cells. Here we demonstrate successful delivery of Cy3-labled siRNA using two different dendrimers (Generation 5 and a modified Generation 3) with transfection efficiency results exceeding those of Lipofectamine 2000 and with far less toxicity to cells. We also show up to a 90% reduction (lasting at least 4 days) in Twist1 expression using Western Blot and qPCR analysis. Phenotypically we were able to appreciate a significant decrease in the invasive nature of the breast cancer cells using migration/invasion assays. Taken together these results demonstrate successful knockdown of Twist1 using siRNA dendrimer complexes resulting in an altered cellular phenotype. These data will serve as a foundation for optimization of future in vivo experiments with both orthotopic and metastatic breast cancer models. Citation Format: James B. Finlay, Cai M. Roberts, Carlotta A. Glackin. Dendrimer delivery of RNA based Twist1 inhibitors to reduce breast cancer cell metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2692. doi:10.1158/1538-7445.AM2013-2692

Hypoxic condition-selective upconversion via triplet–triplet annihilation based on POSS-core dendrimer complexes

The influence on the efficiencies of the triplet–triplet annihilation (TTA)-supported upconversion by oxygen under biomimetic conditions was investigated. From the solution containing the dendrimer complexes based on polyhedral oligomeric silsesquioxane (POSS)-core dendrimer with the Pt complex of octaethylporphyrin (PtOEP) and anthracene in PBS, the fluorescence emission of anthracene depending on the dissolved oxygen (DO) concentrations via the TTA-supported upconversion was obtained with the excitation light at 540nm. In particular, we observed strong emission only under hypoxic conditions. In addition, it was found that the emission intensity via TTA-supported upconversion can be reversibly regulated by the DO concentrations in the solution.

Computational Modeling of Environmentally Responsive Hydrogels (ERH) for Drug Delivery System

The present work aims at computational analysis of environmentally responsive hydrogels with enormous prospective in the formulation aspect of drug delivery systems. The drug delivery potential of hydrogels to the targets is owing to the specific stimuli responsive nature of the hydrogels. The environmental factors looked upon in the study are changes in pH, alteration of temperature and glucose concentration rise originated in the body as a result of various disease conditions. Polymers, synthetic polypeptides and dendrimers have been used in the present work to study the feasibility of drug delivery. The computational methods have been used to formulate polymer properties, pharmacokinetics and toxicity studies. Diverse interactions approximating electrostatic, hydrophobic and hydrogen bond interactions acquire place during incorporation of drugs within the polymer and dendrimers. The covalent and electrostatic interactions between a drug and the surface of polymer and dendrimer have been analyzed. The docking interaction studies have been performed and the best polymer and dendrimer complex have been selected based on the docking score, binding energy and interaction energy with the drugs. G5 generation of poly amidoamine dendrimers and poly N-Ndiethyl acrylamide (PDEAAM) have been identified as most suitable stimuli-responsive effective drug carriers for anti diabetic drugs and diuretics. Favorable results have been obtained while using poly acrylic acid (PAA) for corticosteroids and polylysine for diabetic drugs. ConA protein along with poly aspartic acid also showed good results.

Lanthanide(III) dendrimer complexes based on diphenylquinoxaline derivatives for photonic amplification

A series of novel lanthanide(III) complexes (Ln=Gd, Er, Yb) based on dendritic diphenylquinoxaline (DPQ) ligands was designed and synthesized with the aim of enhancing the luminescence intensity of Er3+ and Yb3+ ions for photonic applications. The diphenyl-quinoxaline ligand was introduced as a photon antenna for efficient light harvesting and subsequent energy transfer onto the Ln(3+) ions. The dendritic complexes showed strong near-IR emission at 981 (Yb3+) and 1,530 (Er3+) nm, which was sensitized through energy transfer from the excited states of the diphenyl-quinoxaline ligands. The near-IR emission intensity of the lanthanide ions in second-generation [Ln(G2-DPQ-COO)(3)(terpy)] complexes was significantly enhanced, due to the light-harvesting effect, with respect to [Ln(G1-DPQ-COO)(3)(terpy)]. However, increasing the size of the dendron in [Ln(G3-DPQ-COO)(3)(terpy)] was found to be detrimental to the emission efficiency. This may be attributed to the twisted structure of the dendritic ligand and suggests that conformational effects should be taken into consideration when designing ligands for photonic amplification.

Analytical model study of complexation of dendrimer as an ion penetrable sphere with DNA

Poly (amidoamine) (PAMAM) dendrimers, being protonated under physiological conditions, have great potential as nonviral vectors for gene transfection. Many experimental and simulation studies have been performed to study the effect of dendrimer size, charge, and salt concentration on the structure and transfection efficiency of condensed DNA aggregates. In this study a theoretical model describing a linear polyelectrolyte (LPE) and ion-penetrable spheres has been developed and applied to investigate the interaction between linearized DNA and positively charged dendrimer of different generations. Throughout the study, we emphasized on the effect of the medium’s environments on the complexation of LPE chain with one dendrimer. It is found that the wrapping degree of the chain around the dendrimer increases by increasing dendrimer’s charge (decreasing pH), Bjerum length, salt concentration, and decreases by increasing the rigidity of the chain. Also, the effect of 1:1 salt concentration on complexation of DNA plasmids with one dendrimer of different generations has been investigated, and found that the optimal wrapping length of the LPE chain around the dendrimer depends on dendrimer generation.