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Marie-louise Ainalem - One of the best experts on this subject based on the ideXlab platform.
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complexes formed between dna and poly amido amine Dendrimers of different generations modelling dna wrapping and penetration
Physical Chemistry Chemical Physics, 2014Co-Authors: Khawla Qamhieh, Marie-louise Ainalem, Tommy Nylander, Camilla F Black, George S Attard, Rita S DiasAbstract:This study deals with the build-up of biomaterials consisting of biopolymers, namely DNA, and soft particles, poly(amido amine) (PAMAM) Dendrimers, and how to model their interactions. We adopted and applied an analytical model to provide further insight into the complexation between DNA (4331 bp) and positively charged PAMAM Dendrimers of generations 1, 2, 4, 6 and 8, previously studied experimentally. The theoretical models applied describe the DNA as a semiflexible polyelectrolyte that interacts with Dendrimers considered as either hard (impenetrable) spheres or as penetrable and soft spheres. We found that the number of DNA turns around one Dendrimer, thus forming a complex, increases with the Dendrimer size or generation. The DNA penetration required for the complex to become charge neutral depends on Dendrimer generation, where lower generation Dendrimers require little penetration to give charge neutral complexes. High generation Dendrimers display charge inversion for all considered Dendrimer sizes and degrees of penetration. Consistent with the morphologies observed experimentally for Dendrimer/DNA aggregates, where highly ordered rods and toroids are found for low generation Dendrimers, the DNA wraps less than one turn around the Dendrimer. Disordered globular structures appear for high generation Dendrimers, where the DNA wraps several turns around the Dendrimer. Particularly noteworthy is that the Dendrimer generation 4 complexes, where the DNA wraps about one turn around the Dendrimers, are borderline cases and can form all types of morphologies. The net-charges of the aggregate have been estimated using zeta potential measurements and are discussed within the theoretical framework.
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interactions between dna and poly amido amine Dendrimers on silica surfaces
Langmuir, 2010Co-Authors: Marie-louise Ainalem, Richard A. Campbell, Tommy NylanderAbstract:This study increases the understanding at a molecular level of the interactions between DNA and poly(amido amine) (PAMAM) Dendrimers on solid surfaces, which is a subject of potential interest in applications such as gene therapy. We have used in situ null ellipsometry and neutron reflectometry to study the structure of multilayer arrangements formed by PAMAM Dendrimers of generation 2 (G2), 4 (G4), and 6 (G6) and DNA on silica surfaces. Specifically, we adsorbed cationic Dendrimer layers, then we condensed DNA to form Dendrimer-DNA bilayers, and last we exposed further Dendrimer molecules to the interface to encapsulate DNA in Dendrimer-DNA-Dendrimer trilayers. The Dendrimer monolayers formed initially result in the deformation of the cationic adsorbates as a result of their strong electrostatic attraction to the hydrophilic silica surface. The highest surface excess and most pronounced deformation occurs for the G6 molecules due to their relatively large size and high surface charge density. G6-functionalized surfaces give rise to the highest surface excess of DNA during the bilayer formation process. This result is explained in terms of the high number of charged binding sites in the G6 monolayer and the low electrostatic repulsion between DNA and exposed patches of silica surface due to the relatively thick G6 monolayer. The binding strengths of the silica-Dendrimer and Dendrimer-DNA interactions are demonstrated by the high stability of the interfacial bilayers during rinsing. For the formation of trilayers of Dendrimers, DNA, and Dendrimers, G2 adsorbs as a smooth layer while G4 and G6 induce the formation of less well-defined structures due to more complex DNA layer morphologies.
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on the ability of pamam Dendrimers and Dendrimer dna aggregates to penetrate popc model biomembranes
Journal of Physical Chemistry B, 2010Co-Authors: Marie-louise Ainalem, Richard A. Campbell, Syma Khalid, Richard J. Gillams, Adrian R. Rennie, Tommy NylanderAbstract:Poly(amido amine) (PAMAM) Dendrimers have previously been shown, as cationic condensing agents of DNA, to have high potential for nonviral gene delivery. This study addresses two key issues for gene delivery: the interaction of the biomembrane with (i) the condensing agent (the cationic PAMAM Dendrimer) and (ii) the corresponding Dendrimer/DNA aggregate. Using in situ null ellipsometry and neutron reflection, parallel experiments were carried out involving Dendrimers of generations 2 (G2), 4 (G4), and 6 (G6). The study demonstrates that free Dendrimers of all three generations were able to traverse supported palmitoyloleoylphosphatidylcholine (POPC) bilayers deposited on silica surfaces. The model biomembranes were elevated from the solid surfaces upon Dendrimer penetration, which offers a promising new way to generate more realistic model biomembranes where the contact with the supporting surface is reduced and where aqueous cavities are present beneath the bilayer. The largest Dendrimer (G6) induced partial bilayer destruction directly upon penetration, whereas the smaller Dendrimers (G2 and G4) leave the bilayer intact, so we propose that lower generation Dendrimers have greater potential as transfection mediators. In addition to the experimental observations, coarse-grained simulations on the interaction between generation 3 (G3) Dendrimers and POPC bilayers were performed in the absence and presence of a bilayer-supporting negatively charged surface that emulates the support. The simulations demonstrate that G3 is transported across free-standing POPC bilayers by direct penetration and not by endocytosis. The penetrability was, however, reduced in the presence of a surface, indicating that the membrane transport observed experimentally was not driven solely by the surface. The experimental reflection techniques were also applied to Dendrimer/DNA aggregates of charge ratio = 0.5, and while G2/DNA and G4/DNA aggregates interact with POPC bilayers, G6/DNA displays no such interaction. These results indicate that, in contrast to free Dendrimer molecules, Dendrimer/DNA aggregates of low charge ratios are not able to traverse a membrane by direct penetration.
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condensing dna with poly amido amine Dendrimers of different generations means of controlling aggregate morphology
Soft Matter, 2009Co-Authors: Marie-louise Ainalem, Tommy Nylander, Anna M Carnerup, John Janiak, Viveka Alfredsson, Karin SchillenAbstract:The morphology of the aggregates formed between DNA and poly(amido amine) (PAMAM) Dendrimers depends on the Dendrimer generation as previously reported in separate studies at high Dendrimer/DNA charge ratios (>1). This has lead to substantial work on Dendrimers as possible transfection agents. Inspired by these studies, we here present novel results from a coherent and systematic study using cryo-TEM, dynamic light scattering (DLS) and fluorescence spectroscopy to reveal how the size, composition and morphology of aggregates formed between DNA (4331 base pairs) and PAMAM Dendrimers, are affected by Dendrimer size and charge at low charge ratios (<1) in dilute solutions. At such conditions the process is cooperative and kinetically controlled and well-defined structured aggregates are formed for lower Dendrimer generations. The smaller sized Dendrimers (generation 1 and 2), which have a lower total charge per molecule, allow the formation of well-structured rods and toroids. In contrast, globular and less defined aggregates, which are less stable against precipitation, are formed with higher generation Dendrimers. We were also able to directly visualise the cooperative nature of the condensation process as cryo-TEM and DLS show that Dendrimer/DNA aggregates, containing condensed DNA, coexist with free extended DNA chains. In fact, the apparent hydrodynamic radii of the Dendrimer/DNA aggregates, obtained using DLS, are found to be almost constant for charge ratios ≤1. The fluorescence study shows that the number of Dendrimers bound per DNA chain decreases with the Dendrimer generation but is independent of the charge ratio.
James R. Baker - One of the best experts on this subject based on the ideXlab platform.
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dna condensation by partially acetylated poly amido amine Dendrimers effects of Dendrimer charge density on complex formation
Molecules, 2013Co-Authors: Seokki Choi, James R. Baker, Ronald G LarsonAbstract:The ability of poly(amido amine) (or PAMAM) Dendrimers to condense semiflexible dsDNA and penetrate cell membranes gives them great potential in gene therapy and drug delivery but their high positive surface charge makes them cytotoxic. Here, we describe the effects of partial neutralization by acetylation on DNA condensation using light scattering, circular dichroism, and single molecule imaging of Dendrimer-DNA complexes combed onto surfaces and tethered to those surfaces under flow. We find that DNA can be condensed by generation-five (G5) Dendrimers even when the surface charges are more than 65% neutralized, but that such Dendrimers bind negligibly when an end-tethered DNA is stretched in flow. We also find that when fully charged Dendrimers are introduced by flow to end-tethered DNA, all DNA molecules become equally highly coated with Dendrimers at a rate that becomes very fast at high Dendrimer concentration, and that Dendrimers remain bound during subsequent flow of Dendrimer-free buffer. These results suggest that the presence of Dendrimer-free DNA coexisting with Dendrimer-bound DNA after bulk mixing of the two in solution may result from diffusion-limited irreversible Dendrimer-DNA binding, rather than, or in addition to, the previously proposed cooperative binding mechanism of Dendrimers to DNA.
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Diffusion of Alexa Fluor 488-conjugated Dendrimers in rat aortic tissue.
Annals of the New York Academy of Sciences, 2006Co-Authors: Brenda S. Cho, James R. Baker, Karen J. Roelofs, Istvan J. Majoros, James C. Stanley, Peter K. Henke, Gilbert R. UpchurchAbstract:In this study, the distribution of labeled Dendrimers in native and aneurysmal rat aortic tissue was examined. Adult male rats underwent infrarenal aorta perfusion with generation 5 (G5) acetylated Alexa Fluor 488-conjugated Dendrimers for varying lengths of time. In a second set of experiments, rats underwent aortic elastase perfusion followed by aortic Dendrimer perfusion 7 days later. Aortic diameters were measured prior to and postelastase perfusion, and again on the day of harvest. Aortas were harvested 0, 12, or 24 h postperfusion, fixed, and mounted. Native aortas were harvested and viewed as negative controls. Aortic cross-sections were viewed and imaged using confocal microscopy. Dendrimers were quantified (counts/high-powered field). Results were evaluated by repeated measures ANOVA and Student's t-test. We found that in native aortas, Dendrimers penetrated the aortic wall in all groups. For all perfusion times, fewer Dendrimers were present as time between Dendrimer perfusion and aortic harvest increased. Longer perfusion times resulted in increased diffusion of Dendrimers throughout the aortic wall. By 24 h, the majority of the Dendrimers were through the wall. Dendrimers in aneurysmal aortas, on day 0 postDendrimer perfusion, diffused farther into the aortic wall than controls. In conclusion, this study documents labeled Dendrimers delivered intra-arterially to native rat aortas in vivo, and the temporal diffusion of these molecules within the aortic wall. Increasing perfusion time and length of time prior to harvest resulted in continued Dendrimer diffusion into the aortic wall. These preliminary data provide a novel mechanism whereby local inhibitory therapy may be delivered locally to aortic tissue.
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targeted drug delivery with Dendrimers comparison of the release kinetics of covalently conjugated drug and non covalent drug inclusion complex
Advanced Drug Delivery Reviews, 2005Co-Authors: Anil K Patri, Jolanta F Kukowskalatallo, James R. BakerAbstract:Abstract Dendrimers have unique characteristics including monodispersity and modifiable surface functionality, along with highly defined size and structure. This makes these polymers attractive candidates as carriers in drug delivery applications. Drug delivery can be achieved by coupling a drug to polymer through one of two approaches. Hydrophobic drugs can be complexed within the hydrophobic Dendrimer interior to make them water-soluble or drugs can be covalently coupled onto the surface of the Dendrimer. Using both methods we compared the efficacy of generation 5 PAMAM Dendrimers in the targeted drug delivery of methotrexate coupled to the polymer. The amine-terminated Dendrimers bind to negatively charged membranes of cells in a non-specific manner and can cause toxicity in vitro and in vivo. To reduce toxicity and to increase aqueous solubility, modifications were made to the surface hydroxyl groups of the Dendrimers. For targeted drug delivery, the Dendrimer was modified to have a neutral terminal functionality for use with surface-conjugated folic acid as the targeting agent. The complexation of methotrexate within a Dendrimer changes the water insoluble drug into a stable and readily water-soluble compound. When this Dendrimer complexed drug, however, was placed in a solution of phosphate buffered saline, the methotrexate was immediately released and displayed diffusion characteristics identical to free methotrexate. Covalently coupled methotrexate Dendrimer conjugates were stable under identical conditions in water and buffered saline. Cytotoxicity tests showed that methotrexate as the Dendrimer inclusion complex had an activity identical to the free drug in vitro. In contrast, folic acid targeted Dendrimer with covalently conjugated methotrexate specifically killed receptor-expressing cells by intracellular delivery of the drug through receptor-mediated endocytosis. This study demonstrates that while drug as a Dendrimer inclusion complex is readily released and active in vitro, covalently conjugated drug to Dendrimer is better suited for specifically targeted drug delivery.
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synthesis and functional evaluation of dna assembled polyamidoamine Dendrimer clusters for cancer cell specific targeting
Chemistry & Biology, 2005Co-Authors: Youngseon Choi, Thommey P Thomas, Alina Kotlyar, Mohammad T Islam, James R. BakerAbstract:Summary We sought to produce Dendrimers conjugated to different biofunctional moieties (fluorescein [FITC] and folic acid [FA]), and then link them together using complementary DNA oligonucleotides to produce clustered molecules that target cancer cells that overexpress the high-affinity folate receptor. Amine-terminated, generation 5 polyamidoamine (G5 PAMAM) Dendrimers are first partially acetylated and then conjugated with FITC or FA, followed by the covalent attachment of complementary, 5′-phosphate-modified 34-base-long oligonucleotides. Hybridization of these oligonucleotide conjugates led to the self-assembly of the FITC- and FA-conjugated Dendrimers. In vitro studies of the DNA-linked Dendrimer clusters indicated specific binding to KB cells expressing the folate receptor. Confocal microscopy also showed the internalization of the Dendrimer cluster. These results demonstrate the ability to design and produce supramolecular arrays of Dendrimers using oligonucleotide bridges. This will also allow for further development of DNA-linked Dendrimer clusters as imaging agents and therapeutics.
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dna directed synthesis of generation 7 and 5 pamam Dendrimer nanoclusters
Nano Letters, 2004Co-Authors: Youngseon Choi, Almut Mecke, Bradford G. Orr, Mark Banaszak M Holl, James R. BakerAbstract:A novel nanostructure was constructed using two different generations of polyamidoamine (PAMAM) Dendrimers and three sets of complementary oligonucleotides (34, 50, and 66 bases in length). The oligonucleotides were covalently conjugated to partially acetylated generation 5 and 7 PAMAM Dendrimers, and these conjugates were characterized by agarose gel electrophoresis. The agarose gel electrophoresis appearance of these covalently linked oligonucleotide Dendrimers was also compared to electrostatically bound oligonucleotide-Dendrimer complexes. Equimolar amounts of the G5 and G7 conjugates were then hybridized together to allow for the DNA-directed self-assembly of supramolecular clusters. Dynamic light scattering (DLS) analysis indicated that the overall size of the DNA-linked Dendrimer clusters tended to increase according to the length of the oligonucleotide used ranging from 30 to 50 nm, which agreed with the diameter of Dendrimer nanoclusters predicted by molecular modeling. The DNA-linked novel Dendrimer nanoclusters were also examined with tapping-mode atomic force microscopy (AFM) to distinguish the DNA-linked structure from a nonlinked simple G7/G5 Dendrimer mixture. AFM image analysis suggested that the distance between the DNA-linked Dendrimers was significantly larger than what was seen after simple mixing of G7/G5 Dendrimers. The mixture showed a few Dendrimers physically in contact with an interDendrimer distance of 8-10 nm. The interDendrimer distance of the nanoclusters linked with the 50-base-long oligonucleotide pairs was measured to be 21 ± 2 nm, which is in agreement with the theoretical length of the oligonucleotides duplex. These results suggest that PAMAM Dendrimers can be self-assembled via complementary oligonucleotides to form supramolecular nanoclusters.
Yiyun Cheng - One of the best experts on this subject based on the ideXlab platform.
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disulfide cross linked low generation Dendrimers with high gene transfection efficacy low cytotoxicity and low cost
Journal of the American Chemical Society, 2012Co-Authors: Hongmei Liu, Hui Wang, Wenjun Yang, Yiyun ChengAbstract:Cationic poly(amidoamine) (PAMAM) Dendrimers were widely used as nonviral gene carriers. PAMAM Dendrimer-based products such as Superfect and Priofect were already commercially available gene transfection reagents. However, these products are based on high generation Dendrimers with high cost and serious cytotoxicity. In this study, we prepared high efficient gene carriers using disulfide cross-linked low generation (generation 2, G2) PAMAM Dendrimers. These synthesized materials can effectively condense DNA into ∼200 nm polyplexes and degrade into G2 Dendrimers after cellular uptake. Confocal laser scanning microscope studies revealed high cellular uptake behavior of disulfide cross-linked G2 PAMAM Dendrimers. Compared to G2 and G5 PAMAM Dendrimers, disulfide cross-linked G2 PAMAM Dendrimers showed much improved gene transfection efficacy (both EGFP and luciferase gene) and low cytotoxicity on both HEK293 and HeLa cell lines. The disulfide cross-linked G2 Dendrimer prepared at a linker/Dendrimer molar ra...
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disulfide cross linked low generation Dendrimers with high gene transfection efficacy low cytotoxicity and low cost
Journal of the American Chemical Society, 2012Co-Authors: Hongmei Liu, Hui Wang, Wenjun Yang, Yiyun ChengAbstract:Cationic poly(amidoamine) (PAMAM) Dendrimers were widely used as nonviral gene carriers. PAMAM Dendrimer-based products such as Superfect and Priofect were already commercially available gene transfection reagents. However, these products are based on high generation Dendrimers with high cost and serious cytotoxicity. In this study, we prepared high efficient gene carriers using disulfide cross-linked low generation (generation 2, G2) PAMAM Dendrimers. These synthesized materials can effectively condense DNA into ~200 nm polyplexes and degrade into G2 Dendrimers after cellular uptake. Confocal laser scanning microscope studies revealed high cellular uptake behavior of disulfide cross-linked G2 PAMAM Dendrimers. Compared to G2 and G5 PAMAM Dendrimers, disulfide cross-linked G2 PAMAM Dendrimers showed much improved gene transfection efficacy (both EGFP and luciferase gene) and low cytotoxicity on both HEK293 and HeLa cell lines. The disulfide cross-linked G2 Dendrimer prepared at a linker/Dendrimer molar ratio of 1:1 showed the highest gene transfection efficacy and exhibited comparable efficacy to branched PEI with a molecular weight of 25 kD, a commercially available nonviral gene vector. Our study demonstrated that disulfide cross-linked low generation PAMAM Dendrimers with high transfection efficacy, low cytotoxicity, and low cost are efficient alternatives to high generation PAMAM Dendrimers in gene delivery.
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design of biocompatible Dendrimers for cancer diagnosis and therapy current status and future perspectives
Chemical Society Reviews, 2011Co-Authors: Yiyun Cheng, Libo ZhaoAbstract:In the past decade, nanomedicine with its promise of improved therapy and diagnostics has revolutionized conventional health care and medical technology. Dendrimers and Dendrimer-based therapeutics are outstanding candidates in this exciting field as more and more biological systems have benefited from these starburst molecules. Anticancer agents can be either encapsulated in or conjugated to Dendrimer and be delivered to the tumour 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. Imaging agents including MRI contrast agents, radionuclide probes, computed tomography contrast agents, and fluorescent dyes are combined with the multifunctional nanomedicine for targeted therapy with simultaneous cancer diagnosis. However, an important question reported with Dendrimer-based therapeutics as well as other nanomedicines to date is the long-term viability and biocompatibility of the nanotherapeutics. This critical review focuses on the design of biocompatible Dendrimers for cancer diagnosis and therapy. The biocompatibility aspects of Dendrimers such as nanotoxicity, long-term circulation, and degradation are discussed. The construction of novel Dendrimers with biocompatible components, and the surface modification of commercially available Dendrimers by PEGylation, acetylation, glycosylation, and amino acid functionalization have been proposed as available strategies to solve the safety problem of Dendrimer-based nanotherapeutics. Also, exciting opportunities and challenges on the development of Dendrimer-based nanoplatforms for targeted cancer diagnosis and therapy are reviewed (404 references).
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host guest chemistry of Dendrimer drug complexes 4 an in depth look into the binding encapsulation of guanosine monophosphate by Dendrimers
Journal of Physical Chemistry B, 2010Co-Authors: Min Fang, Yiyun Cheng, Jiahai ZhangAbstract:In the present study, we investigated the host−guest chemistry of Dendrimer/guanosine monophosphate (GMP) and present an in-depth look into the binding/encapsulation of GMP by Dendrimers using NMR studies. 1H NMR spectra showed a significant downfield shift of methylene protons in the outmost layer of the G5 Dendrimer, indicating the formation of ion pairs between cationic amine groups of Dendrimer and anionic phosphate groups of GMP. Chemical shift titration results showed that the binding constant between G5 Dendrimer and GMP is 17 400 M−1 and each G5 Dendrimer has 107 binding sites. The binding of GMP to Dendrimers prevents its aggregation in aqueous solutions and thereby enhances its stability. Nuclear Overhauser effect measurements indicated that a GMP binding and encapsulation balance occurs on the surface and in the interior of Dendrimer. The binding/encapsulation transitions can be easily tailored by altering the surface and interior charge densities of the Dendrimer. All these findings provide a ...
Tommy Nylander - One of the best experts on this subject based on the ideXlab platform.
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complexes formed between dna and poly amido amine Dendrimers of different generations modelling dna wrapping and penetration
Physical Chemistry Chemical Physics, 2014Co-Authors: Khawla Qamhieh, Marie-louise Ainalem, Tommy Nylander, Camilla F Black, George S Attard, Rita S DiasAbstract:This study deals with the build-up of biomaterials consisting of biopolymers, namely DNA, and soft particles, poly(amido amine) (PAMAM) Dendrimers, and how to model their interactions. We adopted and applied an analytical model to provide further insight into the complexation between DNA (4331 bp) and positively charged PAMAM Dendrimers of generations 1, 2, 4, 6 and 8, previously studied experimentally. The theoretical models applied describe the DNA as a semiflexible polyelectrolyte that interacts with Dendrimers considered as either hard (impenetrable) spheres or as penetrable and soft spheres. We found that the number of DNA turns around one Dendrimer, thus forming a complex, increases with the Dendrimer size or generation. The DNA penetration required for the complex to become charge neutral depends on Dendrimer generation, where lower generation Dendrimers require little penetration to give charge neutral complexes. High generation Dendrimers display charge inversion for all considered Dendrimer sizes and degrees of penetration. Consistent with the morphologies observed experimentally for Dendrimer/DNA aggregates, where highly ordered rods and toroids are found for low generation Dendrimers, the DNA wraps less than one turn around the Dendrimer. Disordered globular structures appear for high generation Dendrimers, where the DNA wraps several turns around the Dendrimer. Particularly noteworthy is that the Dendrimer generation 4 complexes, where the DNA wraps about one turn around the Dendrimers, are borderline cases and can form all types of morphologies. The net-charges of the aggregate have been estimated using zeta potential measurements and are discussed within the theoretical framework.
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interactions between dna and poly amido amine Dendrimers on silica surfaces
Langmuir, 2010Co-Authors: Marie-louise Ainalem, Richard A. Campbell, Tommy NylanderAbstract:This study increases the understanding at a molecular level of the interactions between DNA and poly(amido amine) (PAMAM) Dendrimers on solid surfaces, which is a subject of potential interest in applications such as gene therapy. We have used in situ null ellipsometry and neutron reflectometry to study the structure of multilayer arrangements formed by PAMAM Dendrimers of generation 2 (G2), 4 (G4), and 6 (G6) and DNA on silica surfaces. Specifically, we adsorbed cationic Dendrimer layers, then we condensed DNA to form Dendrimer-DNA bilayers, and last we exposed further Dendrimer molecules to the interface to encapsulate DNA in Dendrimer-DNA-Dendrimer trilayers. The Dendrimer monolayers formed initially result in the deformation of the cationic adsorbates as a result of their strong electrostatic attraction to the hydrophilic silica surface. The highest surface excess and most pronounced deformation occurs for the G6 molecules due to their relatively large size and high surface charge density. G6-functionalized surfaces give rise to the highest surface excess of DNA during the bilayer formation process. This result is explained in terms of the high number of charged binding sites in the G6 monolayer and the low electrostatic repulsion between DNA and exposed patches of silica surface due to the relatively thick G6 monolayer. The binding strengths of the silica-Dendrimer and Dendrimer-DNA interactions are demonstrated by the high stability of the interfacial bilayers during rinsing. For the formation of trilayers of Dendrimers, DNA, and Dendrimers, G2 adsorbs as a smooth layer while G4 and G6 induce the formation of less well-defined structures due to more complex DNA layer morphologies.
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on the ability of pamam Dendrimers and Dendrimer dna aggregates to penetrate popc model biomembranes
Journal of Physical Chemistry B, 2010Co-Authors: Marie-louise Ainalem, Richard A. Campbell, Syma Khalid, Richard J. Gillams, Adrian R. Rennie, Tommy NylanderAbstract:Poly(amido amine) (PAMAM) Dendrimers have previously been shown, as cationic condensing agents of DNA, to have high potential for nonviral gene delivery. This study addresses two key issues for gene delivery: the interaction of the biomembrane with (i) the condensing agent (the cationic PAMAM Dendrimer) and (ii) the corresponding Dendrimer/DNA aggregate. Using in situ null ellipsometry and neutron reflection, parallel experiments were carried out involving Dendrimers of generations 2 (G2), 4 (G4), and 6 (G6). The study demonstrates that free Dendrimers of all three generations were able to traverse supported palmitoyloleoylphosphatidylcholine (POPC) bilayers deposited on silica surfaces. The model biomembranes were elevated from the solid surfaces upon Dendrimer penetration, which offers a promising new way to generate more realistic model biomembranes where the contact with the supporting surface is reduced and where aqueous cavities are present beneath the bilayer. The largest Dendrimer (G6) induced partial bilayer destruction directly upon penetration, whereas the smaller Dendrimers (G2 and G4) leave the bilayer intact, so we propose that lower generation Dendrimers have greater potential as transfection mediators. In addition to the experimental observations, coarse-grained simulations on the interaction between generation 3 (G3) Dendrimers and POPC bilayers were performed in the absence and presence of a bilayer-supporting negatively charged surface that emulates the support. The simulations demonstrate that G3 is transported across free-standing POPC bilayers by direct penetration and not by endocytosis. The penetrability was, however, reduced in the presence of a surface, indicating that the membrane transport observed experimentally was not driven solely by the surface. The experimental reflection techniques were also applied to Dendrimer/DNA aggregates of charge ratio = 0.5, and while G2/DNA and G4/DNA aggregates interact with POPC bilayers, G6/DNA displays no such interaction. These results indicate that, in contrast to free Dendrimer molecules, Dendrimer/DNA aggregates of low charge ratios are not able to traverse a membrane by direct penetration.
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condensing dna with poly amido amine Dendrimers of different generations means of controlling aggregate morphology
Soft Matter, 2009Co-Authors: Marie-louise Ainalem, Tommy Nylander, Anna M Carnerup, John Janiak, Viveka Alfredsson, Karin SchillenAbstract:The morphology of the aggregates formed between DNA and poly(amido amine) (PAMAM) Dendrimers depends on the Dendrimer generation as previously reported in separate studies at high Dendrimer/DNA charge ratios (>1). This has lead to substantial work on Dendrimers as possible transfection agents. Inspired by these studies, we here present novel results from a coherent and systematic study using cryo-TEM, dynamic light scattering (DLS) and fluorescence spectroscopy to reveal how the size, composition and morphology of aggregates formed between DNA (4331 base pairs) and PAMAM Dendrimers, are affected by Dendrimer size and charge at low charge ratios (<1) in dilute solutions. At such conditions the process is cooperative and kinetically controlled and well-defined structured aggregates are formed for lower Dendrimer generations. The smaller sized Dendrimers (generation 1 and 2), which have a lower total charge per molecule, allow the formation of well-structured rods and toroids. In contrast, globular and less defined aggregates, which are less stable against precipitation, are formed with higher generation Dendrimers. We were also able to directly visualise the cooperative nature of the condensation process as cryo-TEM and DLS show that Dendrimer/DNA aggregates, containing condensed DNA, coexist with free extended DNA chains. In fact, the apparent hydrodynamic radii of the Dendrimer/DNA aggregates, obtained using DLS, are found to be almost constant for charge ratios ≤1. The fluorescence study shows that the number of Dendrimers bound per DNA chain decreases with the Dendrimer generation but is independent of the charge ratio.
Richard M Crooks - One of the best experts on this subject based on the ideXlab platform.
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nmr characterization of fourth generation pamam Dendrimers in the presence and absence of palladium Dendrimer encapsulated nanoparticles
Journal of the American Chemical Society, 2009Co-Authors: Victoria M Gomez, Aldrik H Velders, Javier Guerra, Richard M CrooksAbstract:High-resolution solution NMR spectroscopy has been used to characterize the structure of Pd Dendrimer-encapsulated nanoparticles (DENs), consisting of approximately 55-atom nanoparticles encapsulated within fourth-generation, hydroxyl-terminated poly(amidoamine) PAMAM Dendrimers (G4-OH). Detailed analysis of 1D and 2D NMR spectra of Dendrimers with (G4-OH(Pd(55))) and without (G4-OH) nanoparticles unambiguously demonstrate that single nanoparticles are encapsulated within individual Dendrimers. This conclusion is based on the following results. First, the NMR data show that signals arising from the innermost methylenes of G4-OH(Pd(55)) are more highly influenced by the presence of the Pd nanoparticles than are the terminal functional groups. This means that DENs are encapsulated within Dendrimers rather than being adsorbed to their surface, as would be the case for aggregates consisting of multiple Dendrimers and nanoparticles. Second, extraction of DENs from within their Dendrimer hosts results in an increase in the NMR intensity associated with the interior methylenes, which corroborates the previous point. Third, NMR pulse-field gradient spin-echo experiments demonstrate that G4-OH and G4-OH(Pd(55)) have identical hydrodynamic radii, and this finding excludes the presence of Dendrimer/nanoparticle aggregates.
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synthesis characterization and stability of Dendrimer encapsulated palladium nanoparticles
Chemistry of Materials, 2003Co-Authors: Robert W J Scott, Ronald R Henriquez, Richard M CrooksAbstract:Here we report on the synthesis, physical and chemical properties, and stability of Pd nanoparticles encapsulated within poly(amidoamine) (PAMAM) Dendrimers. Specifically, amine- and hydroxyl-terminated PAMAM Dendrimers ranging in generation from 4 to 8 were studied. Under appropriate conditions, addition of K2PdCl4 results in covalent attachment of the PdCl3- hydrolysis product of this complex to tertiary amines within the Dendrimers. Reduction with NaBH4 results in conversion of Dendrimer-encapsulated PdCl3- to nearly size monodisperse, encapsulated, zerovalent Pd nanoparticles. Details regarding the Pd species present in solution and within the Dendrimer prior to reduction are reported, as is the maximum Pd2+ loading of the Dendrimers. Dendrimer-encapsulated Pd nanoparticles undergo oxidation in air, but this process is slowed significantly when coordinating ions are removed from solution. In the absence of O2, Dendrimer-encapsulated Pd nanoparticles are stable indefinitely. The oxidation product is no...
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Dendrimer encapsulated metals and semiconductors synthesis characterization and applications
2001Co-Authors: Richard M Crooks, Li Sun, Buford I Lemon, Lee K Yeung, Mingqi ZhaoAbstract:This chapter describes composite materials composed of Dendrimers and metals or semiconductors. Three types of Dendrimer/metal-ion composites are discussed: Dendrimers containing structural metal ions, nonstructural exterior metal ions, and nonstructural interior metal ions. Nonstructural interior metal ions can be reduced to yield Dendrimer-encapsulated metal and semiconductor nanoparticles. These materials are the principal focus of this chapter. Poly(amidoamine) (PAMAM) and poly(propylene imine) Dendrimers, which are the two commercially available families of Dendrimers, are in many cases monodisperse in size. Accordingly, they have a generation-dependent number of interior tertiary amines. These are able to complex a range of metal ions including Cu2+, Pd2+, and Pt2+. The maximum number of metal ions that can be sorbed within the Dendrimer interior depends on the metal ion, the Dendrimer type, and the Dendrimer generation. For example, a generation six PAMAM Dendrimer can contain up to 64 Cu2+ ions. Nonstructural interior ions can be chemically reduced to yield Dendrimer-encapsulated metal nanoparticles. Because each Dendrimer contains a specific number of ions, the resulting metal nanoparticles are in many cases of nearly monodisperse size. Nanoparticles within Dendrimers are stabilized by the Dendrimer framework; that is, the Dendrimer first acts as a molecular template to prepare the metal nanoparticles and then as a stabilizer to prevent agglomeration. These composites are useful for a range of catalytic applications including hydrogenations and Heck chemistry. The unique properties of the interior Dendrimer microenvironment can result in formation of products not observed in the absence of the Dendrimer. Moreover the exterior Dendrimer branches act as a selective gate that controls access to the interior nanoparticle, which results in selective catalysis. In addition to single-metal nanoparticles, it is also possible to prepare bimetallic nanoclusters and Dendrimer-encapsulated semiconductor nanoparticles, such as CdS, using this same general approach.
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preparation of cu nanoclusters within Dendrimer templates
Journal of the American Chemical Society, 1998Co-Authors: Mingqi Zhao, Li Sun, Richard M CrooksAbstract:Abstract : A new template synthesis strategy for preparing Cu nanoclusters within Dendrimer 'nanoreactors' is demonstrated. Hydroxyl-terminated polyamidoamine (PAMAM) Dendrimers of generation higher than 2 act as monodispersed templates as well as stabilizers for nanocluster synthesis. Cu(2+) ions are first quantitatively sorbed into the Dendrimer via a strong coordinative interaction with interior amines and then chemically reduced to yield Cu nanoclusters. The nanoclusters are composed of a well-defined number of atoms. Importantly, cluster size can be controlled by varying the size of the host Dendrimer nanoreactor (16-atom Cu cluster in G4 and 64-atom Cu cluster in G6 Dendrimers). The clusters remain trapped within the Dendrimers for extended periods of time, do not agglomerate, and do not precipitate. The clusters can also be oxidized to yield Dendrimer-encapsulated Cu(2+).
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structural distortion of Dendrimers on gold surfaces a tapping mode afm investigation
Journal of the American Chemical Society, 1998Co-Authors: Andreas Hierlemann, Richard M Crooks, Lane A. Baker, Joseph K Campbell, Antonio J RiccoAbstract:Abstract : Atomic force microscopy (AFM) investigations of polyamidoamine (PAMAM) Starburst (Trademark) Dendrimers, generations 4 and 8 (G4, G8), absorbed on Au (111) surfaces were conducted. By controlling Dendrimer concentration and exposure time during adsorption, coverages ranging from completely isolated molecules to a monolayer were prepared. The individual Dendrimer molecules forming a monolayer were clearly imaged. Upon exposure to hexadecanethiol, the shapes of individual Dendrimers change and they become taller and narrower as more stable thiol-Au bonds replace some of the amine-Au bonds. In the case of monolayers, exposure to hexadecanethiol causes the Dendrimers to gradually agglomerate, forming Dendrimer "pillars" up to 30 nm in height and freeing progressively more surface area for thiol adsorption.
