Primary Amine End Groups Research Articles

Efficient polycation non-viral gene delivery system with high buffering capacity and low molecular weight for primary cells: Branched poly(β-aminoester) containing primary, secondary and tertiary amine groups

Gene transfer studies, preferred in many biotechnology studies such as in vitro transgenic cell modeling systems, gene therapy, transgenic animal production by cloning, etc., are quite limited due to transfection difficulties on primary cell lines. The main purpose of this study is on the production of biocompatible gene carrier systems with high transfection efficiency for Primary Ovine Fibroblast cell lines (POF). To achieve this goal, the synthesis of the branched poly(β-aminoester) (PBAE) containing primary, secondary and tertiary amino groups in their molecular structures was carried out via step-growth polymerization by a typical Michael addition reaction between bisphenol A-ethoxylate diacrylate (BPAEDA) and ethylenediamine (EDA) for the first time. PBAEs were characterized using FTIR and NMR techniques. GPC-SEC system was used to determine the molecular weight of these polymers. Proton buffering capacity of the PBAE was also determined. In order to optimize the preparation of the PBAE nanoparticles (nPBAE), two different methods, which are solvent evaporation and solvent displacement techniques, were used. Their physicochemical properties such as particle size, polydispersity index (PDI), zeta potential and stability were identified. nPBAE-gene complexes (gnPBAE) were obtained according to the adsorption or encapsulation mechanisms and their properties were evaluated by comparative surface charge and gel electrophoresis. In vitro studies including gene binding capacity, cytotoxicity and the transfection efficiency for primary ovine fibroblast (POF) cell lines were also realized. Consequently, (egnPBAE)dw formulation, which is obtained from PBAEEDA with the lowest Mw by encapsulation method in this study, have very high in vitro transfection efficiency up to 78.3% in POF cells and it was also exhibited almost 1.5 times more transfection efficiency against commercial product Lipofectamine because of its low Mw and the presence of the secondary and tertiary amine structures as well as primary amine end groups in its backbone.

Poly(n-butyl methacrylate) with primary amine end groups for supporting cell adhesion and proliferation of renal epithelial cells

ABSTRACTPolymer coatings that support epithelial cell culture have been developed. Ozonolysis and subsequent workup of poly(butyl methacrylate-co-butadiene) copolymers is used to form oligomers with carboxylic acid end groups, which are then further reacted with diamines to provide poly(butyl methacrylate)s with primary amine end groups. The polymers are cast as films and used as cell culture substrates for human dermal fibroblasts and human renal epithelial cells. Fibroblast and epithelial cells adhere and proliferate on acid functional materials but on amine functional films epithelial cells show greater viability than fibroblasts.

Study of Oxovanadium Polymer Complexes Using Electron Paramagnetic Resonance

The complexes were prepared on the basis of polymer ligands with carboxylic and nitrogen-containing functionalities by complexation with VO2+ cations in aqueous solutions of VOSO4.5H2O. The degree of introduction of VO2+ ions into the polymer matrices depended on the kind of the functional groups in the polymers studied, such as polyacrylic acid, poly-4-vinylpyridine, poly(2-N,N-dimethylaminoethyl) methacrylate, poly(propylene imine) dendrimers such as D8[DAB-dendr-(NH2)8] and D32 [DAB-dendr-(NH2)32], with 8 and 32 primary amine end groups. It was found to be from 31.15 to 69.6 mg metal ions per gram of polymer carrier. An attempt was made to evaluate the structure of the VO2+-containing polymer complexes by electron paramagnetic resonance. The parameters of the electron paramagnetic resonance were determined (gII, g⊥; AII and A⊥) for the complexes studied. The anticipated coordination structure of the compounds was suggested.

The Stability of Amino-Functionalized Polyhedral Oligomeric Silsesquioxanes in Water

Octa(aminopropylsilsesquioxane) Si8O12[(CH2)3NH2]8 is a very important precursor for many other hybrid organic/inorganic polyhedral oligomeric silsesquioxanes (POSS) because of the reactivity of its primary amine groups. Unfortunately, it is unstable in water, which can lead to the cleavage of its siloxane cage. In the present work, such a degradation was confirmed using solid-state (29)Si NMR spectroscopy, and the molecular features at the basis of this instability were studied using molecular dynamics simulations (MD). It was also investigated whether replacing the primary amine end groups by secondary amines or by amides with long aliphatic chains could lead to an improvement in the water stability of the Si/O framework. In the pure bulk models, all POSS interdigitate with their pendant organic arms intertwined. Upon insertion of isolated molecules into water, the dimensions of the primary amine POSS remain close to those of the bulk, while the secondary amine and the amide POSS favor conformations that optimize the intramolecular chain-chain interactions. When there are several POSS molecules in water, they cluster with each other through both intra- and intermolecular chain-chain interactions. This tendency for the organic chains to intertwine whenever possible provides some protection to the siloxane cages from water, but also leaves some of the siloxane O exposed. As such, the latter are accessible to form transient hydrogen bonds with the water molecules, which could be a precursor step to hydrolysis and thus cage breakage. In the molecular models, a better protection was obtained in the amide POSS for two reasons: its chains tended to wrap efficiently around its cage, and its ketone O kept water from getting close to the siloxanes. The molecular modeling characterizations were found to agree very well with experimental evidence.

Characterization of cationic polymers by asymmetric flow field-flow fractionation and multi-angle light scattering—A comparison with traditional techniques

In the field of nanomedicine, cationic polymers are the subject of intensive research and represent promising carriers for genetic material. The detailed characterization of these carriers is essential since the efficiency of gene delivery strongly depends on the properties of the used polymer. Common characterization methods such as size exclusion chromatography (SEC) or mass spectrometry (MS) suffer from problems, e.g. missing standards, or even failed for cationic polymers. As an alternative, asymmetrical flow field-flow fractionation (AF4) was investigated. Additionally, analytical ultracentrifugation (AUC) and 1H NMR spectroscopy, as well-established techniques, were applied to evaluate the results obtained by AF4. In this study, different polymers of molar masses between 10 and 120kgmol−1 with varying amine functionalities in the side chain or in the polymer backbone were investigated. To this end, some of the most successful gene delivery agents, namely linear poly(ethylene imine) (LPEI) (only secondary amines in the backbone), branched poly(ethylene imine) (B-PEI) (secondary and tertiary amino groups in the backbone, primary amine end groups), and poly(l-lysine) (amide backbone and primary amine side chains), were characterized. Moreover, poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), poly(2-(amino)ethyl methacrylate) (PAEMA), and poly(2-(tert-butylamino)ethyl methacrylate) (PtBAEMA) as polymers with primary, secondary, and tertiary amines in the side chain, have been investigated. Reliable results were obtained for all investigated polymers by AF4. In addition, important factors for all methods were evaluated, e.g. the influence of different elution buffers and AF4 membranes. Besides this, the correct determination of the partial specific volume and the suppression of the polyelectrolyte effect are the most critical issues for AUC investigations.

Osmotic Pressure of Biomimetic Aggrecan from “Grafting “To Synthesis

IntroductionThe proteoglycan content of the nucleus pulposus (NP) decreases linearly with degeneration.1 This loss of proteoglycan is attributed to both a reduction of the synthesis of aggrecan by the NP cells and an increase degradation by MMP's and proteases, which attack the aggrecan protein core, resulting in aggrecan fragmentation.2-5 We envision a treatment strategy for restoration of the NP, by the addition of an enzymatically-resistant, biomimetic aggrecan (BioAGG) to the NP. This BioAGG, which “grafts” chondroitin sulfate (CS) bristles “to” a synthetic polymer core resistant to enzymatic degradation, will have osmotic pressure as a key functional property for application in the NP. We hypothesize that osmotic pressure can be impacted by both the number and density of the CS bristles incorporated, which will influence the fixed charge density and configurational entropy of this biomimetic macromolecule. Materials and MethodsTo synthesize BioAGG, linear CS molecules (bristles) with primary amine end groups were “grafted to” functional groups along poly-acrylic acid (PAA) chains. Reactions were performed with two PAA molecules at different lengths (250 kDa and 10 kDa) and varying ratios (mol/mol) of CS molecules to AA functional groups (CS; AA). Reaction kinetics was monitored using fluorescamine assay. Resulting macromolecules were purified via membrane dialysis. Polymer samples were dialyzed for 96 hours against DI water (50K MWCO) and lyophilized. Their chemical structure was confirmed with 1H NMR (300 MHz UnityInova NMR Spectrometer, 30 mg/mL samples in D2O).Using a custom membrane osmometer, osmotic pressures of the synthesized molecules were measured and compared to CS alone and an unreacted mixture of PAA and CS. All solutions were tested at the same fixed charge density based on calculations of fixed charge density. ResultsThree different molecules were fabricated using two molecular weights of the PAA core (250 kDa and 10 kDa). For PAA 250-CS samples, we varied the bristle density by controlling the molar ratio of CS to acrylic acid monomer units (CS: AA). PAA250-CS-high with “high” bristle density was synthesized with CS: AA at 1:15, and PAA250-CS-low with “low” bristle density was synthesized with CS:AA at 1:30. The molar ratio of CS: AA for PAA10-CS was kept constant at 1:10. Our theoretical estimation of the molecular weight of BioAGG samples has been done from conjugation data for CS, as determined using a fluorescamine assay, which is sensitive to the reduction in primary amines (PA) on CS. Results of these calculations are seen in Table 1.Table 1 Table 1MoleculeMolecular Wt (kDa)Number of BristlesBristle Spacing (nm)PAA250-CS-high≈2000≈854 to 8PAA250-CS-low≈1100≈4010 to 15PAA250-CS-high≈250≈93 to 5Chemical structures of the synthesized molecules were confirmed via 1H-NMR showing characteristic peaks for CS and corresponding polymer backbones for all purified compounds. No degradation of CS bristles after the synthesis and purification was observed. At the highest concentrations examined (25 mg/mL PAA250: CS) no gelation was observed. Osmotic pressure result of the PAA250-CS-high was 560 kPA about 8× higher than 70 kPA for CS alone (Fig. 1). Interestingly, when the same concentrations of PAA250 and CS are just mixed in solution (PAA250 + CS mixture), the osmotic pressure is close to that of CS alone (∼70 kPA). The same PAA250 with a lower CS bristle density, (PAA250-CS-low) is about 20% lower than the high-density version (410 kPA). A lower molecular weight with high bristle density (PAA10-CS) has an intermediate osmotic pressure between the PAA250-CS and CS alone (140 kPA). ConclusionBioAGG molecules were synthesized using a “grafting to” strategy incorporating CS bristles on PAA polymer backbones. The resultant molecules showed osmotic pressures in excess of those for the fixed charge alone. Moreover, the number and density of CS side chains influences the osmotic pressure supporting a hypothesis that the electrostatic repulsion and conformation entropy derived from the 3D macromolecular bottle-brush structure contributes to the osmotic pressure. BioAGG shows promise for mimicking physical and osmotic properties of natural aggrecan.Acknowledgment Coulter Foundation GrantI confirm having declared any potential conflict of interest for all authors listed on this abstractYesDisclosure of InterestNone declaredOlczyk K. Zeitschrift für Rheumatologie 1994;53:19Roberts S, et.al. Spine 2000;25:3005Goupille P, et.al. Spine 1998;23:1612Le Maitre C, et.al. Biochemical Society Transactions 2007;35:652Kiani C, et al. Cell Research 2002;12:19

Osmotic Pressure of Biomimetic Aggrecan from “Grafting “To Synthesis

Introduction The proteoglycan content of the nucleus pulposus (NP) decreases linearly with degeneration.1 This loss of proteoglycan is attributed to both a reduction of the synthesis of aggrecan by the NP cells and an increase degradation by MMP's and proteases, which attack the aggrecan protein core, resulting in aggrecan fragmentation.2-5 We envision a treatment strategy for restoration of the NP, by the addition of an enzymatically-resistant, biomimetic aggrecan (BioAGG) to the NP. This BioAGG, which “grafts” chondroitin sulfate (CS) bristles “to” a synthetic polymer core resistant to enzymatic degradation, will have osmotic pressure as a key functional property for application in the NP. We hypothesize that osmotic pressure can be impacted by both the number and density of the CS bristles incorporated, which will influence the fixed charge density and configurational entropy of this biomimetic macromolecule. Materials and Methods To synthesize BioAGG, linear CS molecules (bristles) with primary amine end groups were “grafted to” functional groups along poly-acrylic acid (PAA) chains. Reactions were performed with two PAA molecules at different lengths (250 kDa and 10 kDa) and varying ratios (mol/mol) of CS molecules to AA functional groups (CS; AA). Reaction kinetics was monitored using fluorescamine assay. Resulting macromolecules were purified via membrane dialysis. Polymer samples were dialyzed for 96 hours against DI water (50K MWCO) and lyophilized. Their chemical structure was confirmed with 1H NMR (300 MHz UnityInova NMR Spectrometer, 30 mg/mL samples in D2O). Using a custom membrane osmometer, osmotic pressures of the synthesized molecules were measured and compared to CS alone and an unreacted mixture of PAA and CS. All solutions were tested at the same fixed charge density based on calculations of fixed charge density. Results Three different molecules were fabricated using two molecular weights of the PAA core (250 kDa and 10 kDa). For PAA 250-CS samples, we varied the bristle density by controlling the molar ratio of CS to acrylic acid monomer units (CS: AA). PAA250-CS-high with “high” bristle density was synthesized with CS: AA at 1:15, and PAA250-CS-low with “low” bristle density was synthesized with CS:AA at 1:30. The molar ratio of CS: AA for PAA10-CS was kept constant at 1:10. Our theoretical estimation of the molecular weight of BioAGG samples has been done from conjugation data for CS, as determined using a fluorescamine assay, which is sensitive to the reduction in primary amines (PA) on CS. Results of these calculations are seen in Table 1 . [Table: see text] Chemical structures of the synthesized molecules were confirmed via 1H-NMR showing characteristic peaks for CS and corresponding polymer backbones for all purified compounds. No degradation of CS bristles after the synthesis and purification was observed. At the highest concentrations examined (25 mg/mL PAA250: CS) no gelation was observed. Osmotic pressure result of the PAA250-CS-high was 560 kPA about 8× higher than 70 kPA for CS alone (Fig. 1). Interestingly, when the same concentrations of PAA250 and CS are just mixed in solution (PAA250 + CS mixture), the osmotic pressure is close to that of CS alone (∼70 kPA). The same PAA250 with a lower CS bristle density, (PAA250-CS-low) is about 20% lower than the high-density version (410 kPA). A lower molecular weight with high bristle density (PAA10-CS) has an intermediate osmotic pressure between the PAA250-CS and CS alone (140 kPA). Conclusion BioAGG molecules were synthesized using a “grafting to” strategy incorporating CS bristles on PAA polymer backbones. The resultant molecules showed osmotic pressures in excess of those for the fixed charge alone. Moreover, the number and density of CS side chains influences the osmotic pressure supporting a hypothesis that the electrostatic repulsion and conformation entropy derived from the 3D macromolecular bottle-brush structure contributes to the osmotic pressure. BioAGG shows promise for mimicking physical and osmotic properties of natural aggrecan. Acknowledgment Coulter Foundation Grant I confirm having declared any potential conflict of interest for all authors listed on this abstract Yes Disclosure of Interest None declared Olczyk K. Zeitschrift für Rheumatologie 1994;53:19 Roberts S, et.al. Spine 2000;25:3005 Goupille P, et.al. Spine 1998;23:1612 Le Maitre C, et.al. Biochemical Society Transactions 2007;35:652 Kiani C, et al. Cell Research 2002;12:19

A study of antimicrobial property of textile fabric treated with modified dendrimers

AbstractDendrimers have been used as a vehicle to develop the antimicrobial properties of textile fabrics. We have taken advantage of the large number of functional groups present in the regular and highly branched three‐dimensional architecture of dendrimers. In this study, the poly(amidoamine) (PAMAM) G‐3 dendrimer was modified to provide antimicrobial properties. Following a procedure similar to what is suggested in the literature, PAMAM (G3) with primary amine end groups was converted into ammonium functionalities. The modification was then confirmed by FTIR and 13C‐NMR analysis. Dendrimers have unique properties owing to their globular shape and tunable cavities, this allows them to form complexes with a variety of ions and compounds; and also act as a template to fabricate metal nanoparticles. AgNO3–PAMAM (G3) complex as well as a MesoSilver–PAMAM (G3) complex were formed and these modified dendrimers were characterized by a UV–Visible spectrophotometer to study the complex formation. Modified dendrimers were applied to the Cotton/Nylon blend fabric. SEM and EDX analysis were performed to study the dispersion of silver nanoparticles onto the fabric. An antimicrobial test of the treated‐fabric against Staphylococcus aureus exhibited significant biocidal activities for each type of modified‐dendrimer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

A combinatorial polymer library approach yields insight into nonviral gene delivery.

The potential of gene therapy to benefit human health is tremendous because almost all human diseases have a genetic component, from untreatable monogenic disorders to cancer and heart disease. Unfortunately, a method for gene therapy that is both effective and safe has remained elusive. It has been said that "there are only three problems in gene therapy - delivery, delivery, and delivery." (quote from I. M. Verma in Jaroff, L. TIME, 1999; Jan 11). This Account describes an alternative strategy to viral gene delivery: the design of biodegradable polymers that are able to deliver DNA like a synthetic virus. Using high-throughput synthesis and screening techniques, we have created libraries of over 2000 structurally unique poly(β-amino esters) (PBAEs). PBAEs are formed by the conjugate addition of amines to diacrylates. These biomaterials are promising for nonviral gene delivery due to their ability to condense plasmid DNA into small and stable nanoparticles and their ability to promote cellular uptake and endosomal escape. Our laboratory has iteratively improved PBAE nanoparticles through polymer end modifications and nanoparticle coatings. Lead PBAEs have high gene delivery efficacy and low cytotoxicity both in vitro and in vivo. Certain polymer structural characteristics are important for effective gene delivery. The best PBAEs are linear polymers of ~10 kDa that contain hydroxyl side chains and primary amine end groups. These polymers bind DNA to form nanoparticles that are small (<200 nm) and stable and have near-neutral ζ potential in the presence of serum-containing media. Lead PBAEs also contain tertiary amines that can buffer the low pH environment of endosomes and facilitate escape of polymer/DNA particles into the cytoplasm. Diamine end-modified 1,4-butanediol diacrylate-co-5-amino-1-pentanol polymers (C32) bind DNA more tightly and form smaller nanoparticles than other PBAEs. These nanoparticles also have higher cellular uptake and the best gene expression of all gene delivery polymers in the library. These polymers are more effective for gene delivery than top commercially available nonviral vectors including jet-PEI and Lipofectamine 2000 and are comparable to adenovirus for in vitro gene delivery to human primary cells. In vivo, these PBAE/DNA particles are promising as cancer therapeutics. This Account summarizes the results of our laboratory in using a combinatorial polymer library approach to elucidate polymer structure/function relationships and enable the development of polymeric gene delivery nanoparticles with viral-like efficacy.

A Facile Synthesis of Azido-Terminated Heterobifunctional Poly(ethylene glycol)s for “Click” Conjugation

New azido-terminated heterobifunctional poly(ethylene glycol) (PEG) derivatives having primary amine and carboxyl end groups, (Azide-PEG-NH 2 and Azide-PEG-COOH, respectively) were synthesized with high efficiency. An alpha-allyl-omega-hydroxyl PEG was prepared as the first step to Azide-PEG-X (X = NH 2 and COOH) through the ring-opening polymerization of ethylene oxide (EO) with allyl alcohol as an initiator, followed by two-step modification of the hydroxyl end to an azido group. To introduce primary amino or carboxyl functional groups, amination and carboxylation reactions of the allyl terminal ends was then conducted by a radical addition of thiol compounds. Molecular functionalities of both ends of the PEG derivatives thus prepared were characterized by (1)H, (13)C NMR, and MALDI-TOF MS spectra, validating that the reaction proceeded quantitatively. The terminal azido functionality is available to conjugate various ligands with an alkyne group through the 1,3-dipolar cycloaddition reaction condition ("click chemistry").

Branched poly(styrene‐b‐tert‐butyl acrylate) and poly(styrene‐b‐acrylic acid) by ATRP from a dendritic poly(propylene imine)(NH2)64 core

AbstractWith the aim of creating highly branched amphiphilic block copolymers, the primary amine end groups of the poly(propylene imine) dendrimers DAB‐dendr‐(NH2)8 and DAB‐dendr‐(NH2)64 were converted to 2‐bromoisobutyramide groups. Poly (styrene‐b‐tert‐butyl methacrylate) (PS‐b‐PtBMA) was synthesized by ATRP from the eight end group initiator, and poly(styrene‐b‐tert‐butyl acrylate) (PS‐b‐PtBA) was synthesized from the 64 end group initiator. The tert‐butyl groups were removed to produce poly(styrene‐b‐methacrylic acid) (PS‐b‐PMAA) and poly(styrene‐b‐acrylic acid) (PS‐b‐PAA). Comparison of size exclusion chromatography (SEC) absolute molecular weight analyses of the polystyrenes with calculated molecular weights showed that the eight end group initiator produced a polystyrene with about eight branches, and that the 64 end group initiator produced polystyrene with many fewer than 64 branches. The PS‐b‐PtBA materials also have many fewer than 64 branches. The PS‐b‐PAA samples dissolved molecularly in DMF but formed aggregates in water even at pH 10. AFM images of the PS‐b‐PtBAs spin coated from THF and DMF onto mica showed aggregates. AFM images of the PS‐b‐PAAs spin coated from various mixtures of DMF and water at pH 10 showed flat disks and worm‐like images similar to those observed with linear PS‐b‐PAAs. Use of a PS‐b‐PAA and a PS‐b‐PMAA as templates for emulsion polymerization of styrene produced latexes 100–200 nm in diameter. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4623–4634, 2007

Synthesis of Well-Defined Polystyrene with Primary Amine End Groups through the Use of Phthalimido-Functional RAFT Agents

Phthalimidomethyl trithiocarbonates are used as reversible addition fragmentation chain transfer (RAFT) agents to provide low polydispersity α-(phthalimidomethyl)polystyrene with number-average molecular weight in the range 1000−100000 g mol-1. The activity of the phthalimidomethyl trithiocarbonates in RAFT polymerization of styrene, which appears to be similar to that of analogous benzyl trithiocarbonates, is attributed to the electrophilic character of the phthalimidomethyl group. The trithiocarbonate functionality in the products was quantitatively transformed to inert chain ends either by radical-induced reduction with tributylstannane or by thermal elimination, allowing the phthalimido end groups to be cleanly converted to primary amine end groups by hydrazinolysis. Thermolysis experiments, in which the polymers are cleaved at the trithiocarbonate linkage, also provide information on the mechanism of RAFT polymerization. In the case of the symmetrical bis(phthalimidomethyl) trithiocarbonate the two chains grow stepwise indicating that this RAFT agent has a higher transfer constant than the phthalimidomethyl polystyrene trithiocarbonate and that polystyrene propagating radical is a better homolytic leaving group than the phthalimidomethyl radical.

Core−Shell-Structured Highly Branched Poly(ethylenimine amide)s: Synthesis and Structure

The synthesis of amphiphilic macromolecules by amidation of hyperbranched polyethyl- enimine was studied. Amidation with palmitic acid or the methyl ester proceeds up to 84% degree of amidation (140 °C, vacuum). The primary amine end groups react preferentially. With carbonyldiimidazole (CDI)-activated acids nearly complete conversion of all primary amine end groups and secondary amine linear units can be achieved; with a corresponding limited amount of CDI the end groups can be amidated selectively. The products of these reactions are free of any unreacted carboxylic acid or other impurities (1H and 13C NMR) and can be optionally purified by pressure ultrafiltration washing with a toluene/ amine solution. Side-chain crystallization is observed (DSC), which can be supressed entirely employing branched alkyl moieties (2-hexyldecanoic acid as amidating agent). Solution structures were studied by SANS. In C6D6 radii of gyration of 2-5 nm (Guinier analysis) were observed for samples differing in PEI core molecular weight. These sizes and their observed independence of concentration in the range of 5- 40 gL -1 indicate the presence of nonaggregated unimolecular inverted micelles.

Polyethylene glycol–polyamidoamine dendritic micelle as solubility enhancer and the effect of the length of polyethylene glycol arms on the solubility of pyrene in water

Unimolecular dendritic micelles designed as solubility enhancers were obtained by coupling polyethylene glycol (PEG) to Starburst TM polyamidoamine (PAMAM) dendrimers. Micelles-750, -2000, and -5000 have a generation 3.0 dendrimer core (32 primary amine end groups) and PEG arms with molecular weights of 750, 2000, and 5000, respectively. The conjugate of dendrimer core and PEG was characterized by MALDI-TOF MS and 1H NMR. 1H NMR was also used to estimate the average number of PEG arms on each dendrimer molecule. A typical hydrophobic compound, pyrene, was sonicated in an excess amount together with micelles at 50 °C for 6 h to produce its saturated water solution. The change of the solubility of pyrene was monitored at 334 nm, its maximum adsorption wavelength, by UV–VIS spectra. Concentrated micelles tended to dissolve more pyrene. However, there is no obvious linear relationship between micelle type and the amount of pyrene entrapped within micelles. Micelle-2000 could solubilize more pyrene than micelle-750. It is hypothesized that micelle-5000 did not solubilize more pyrene than micelle-2000 because of the PEG shell disruption by adjacent interpenetration of individual micelles when PEG arm length increased.

Modifying the Adsorption Behavior of Polyamidoamine Dendrimers at Silica Surfaces Investigated by Total Internal Reflection Fluorescence Correlation Spectroscopy

Polyamidoamine (PAMAM) dendrimers were modified and tested for use as solution-phase diffusion probes in silica nanostructures. In order for the successful application of dendrimers as solution-phase probes, their interactions with silica surfaces must be understood and controlled, so that the motion of the probe is not influenced by adsorption. Adsorption/desorption kinetics of PAMAM dendrimers and their diffusion in solution near silica surfaces were investigated with total internal reflection fluorescence correlation spectroscopy (TIR-FCS). Dendrimers of generations 3, 5, and 7 were dye-labeled with carboxyrhodamine 6G. Because PAMAM dendrimers are positively charged in solution (having primary amines as end groups), significant adsorption of these molecules to the negatively charged silica surface was observed. Adsorption/desorption rates and the equilibrium constant for adsorption were determined by fitting the autocorrelation functions to a kinetic model. The desorption rate decreases and the absorption equilibrium constant increases with higher dendrimer generation. To reduce the adsorption of these probes to silica surfaces, the labeled dendrimers were reacted with succinic anhydride, converting the primary amine end groups to negatively charged carboxylic acid groups. These carboxylated dendrimers did not detectably adsorb to silica from aqueous solution. TIR-FCS was used to determine their free-solution diffusion constants near silica surfaces, and the corresponding hydrodynamic radii compare favorably with values reported from forced Rayleigh scattering measurements.

Polystyrene Latexes Containing Poly(propyleneimine) Dendrimers

Polymerization of styrene in aqueous dispersions of sodium dodecyl sulfate (SDS) and the poly(propyleneimine) dendrimer DAB-dendr-(NH2)64 with initiation by potassium persulfate at 80 °C produced latexes with diameters in the range of 26−64 nm and coefficients of variation of diameters of less than 10%. Stable latexes were obtained starting with 1.0 to 4.0 molar ratios of SDS to dendritic primary amine end groups, 5.5 to 11 wt % of SDS relative to styrene, and SDS concentrations below the critical micelle concentration in water at 25 °C. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) showed both individual particles and small clusters. TEM and AFM measurements of particle sizes agreed well. Dynamic light scattering measurements gave larger sizes and large polydispersities, presumably due to the presence of clusters.

Catalysis by colloidal polymers in aqueous media

Crosslinked polymer latexes were prepared by emulsion copolymerization of either styrene or one of 14 different alkyl methacrylates and vinylbenzyl chloride and converted to quaternary ammonium ion latexes by reaction with trimethylamine or tributylamine. As catalytic colloidal media the cation exchange latexes increased the rate decarboxylation of 6-nitrobenzisoxazole-3-carboxylate up to 10 000 times and the rate of basic hydrolysis of p-nitrophenyl alkanoates up to 16 times in aqueous dispersions at room temperature. Latexes containing either 2-ethylhexyl methacrylate as the inert component of the polymer or tributylammonium ion active sites were most active. Catalytic activity for the decarboxylation did not depend on particle size when the diameter was <1 μm. Polyampholyte latexes containing 29/18 and 25/23 molar ratios of styrylmethyl(trimethyl)ammonium cations and methacrylate anions were colloidally stable in 4 M NaCl. Catalytic activity decreased with increasing concentrations of NaCl in the dispersions, and all of the latexes except the polyampholytes coagulated at>0.1 M NaCl. Dendrimers having one hydrophobic octyl group and one hydrophilic tri(ethylene glycol) methyl ether group on each tertiary amine end were prepared from commercial poly(propylene imine) dendrimers having eight and 32 primary amine end groups and were converted to quaternary ammonium dendrimers by methyl iodide. After ion-exchange for chloride, the polycationic dendrimers increased the rate of the decarboxylation by 200–500 times the rate in pure water.

Highly Convergent Synthesis of Dendrimerized Chitosan−Sialic Acid Hybrid

Surface bound chitosan−sialodendrimers with a high degree of substitution were successfully prepared using a doubly convergent approach. Poly(amidoamine) (PAMAM) dendrimers (G = 1−5) having a 1,4-diaminobutane core were amidated to N-carboxyethylchitosan methyl ester under conditions that prevented cross-linking. The extent of attachment (DS) to the polysaccharide backbone decreased from 0.53 to 0.11 with increasing dendrimer generation. Peracetylated p-formylphenyl α-sialoside was then successfully attached to the primary amine end groups of the dendrimerized chitosan hybrid with degree of substitution (DS) ranging from 0.7 to 1.4 using reductive amination. Water-soluble chitosan−sialodendrimer hybrids were finally obtained after protecting group hydrolysis and chitosan N-succinylation.

Adsorption of Poly(amidoamine) Dendrimers on Gold

Adsorption of poly(amidoamine) (PAMAM) dendrimers from dilute solution onto cleaned gold has been studied in-situ by a quartz crystal microbalance technique. All experiments were carried out at 21 °C, with either anhydrous ethanol or deionized water as solvent. In ethanol, the equilibrium frequency shifts, proportional to the equilibrium surface coverages, Γ [M/L2], correspond to about a monolayer and increase weakly (roughly linearly) with generation, G. The adsorption is likely driven by the weak favorable interaction between the primary amine end groups on PAMAM and gold. In aqueous media, the results are completely different. Under the conditions employed (low ionic strength and pH 6.5−7) the PAMAM amine end groups tend to protonate in aqueous solution, so that the macromolecules bear positive charge. The equilibrium frequency shift grows exponentially with generation G up to G = 6. For G = 7 a drastic drop is observed, but the increasing trend resumes again for G = 7 through G = 9. Estimates of the adsorbed layer thickness indicate that multilayers form on the clean gold surface in the aqueous system with the number of layers increasing exponentially up to G = 6. The formation of multilayers can be explained by a favorable electrostatic image−charge interaction between the positively charged dendrimers in aqueous solution and the gold substrate. By accounting for charge renormalization and screening, this picture quantitatively accounts for the dependence of Γ on G, for G ≤ 6. The drop in frequency shift from G = 6 to G = 7 may be the result of surface crowding discussed in connection with the “dense-shell” transition of the dendrimer external surface.

Poly(propylene imine) dendrimer complexes of Cu(II), Zn(II), and Co(III) as catalysts of hydrolysis ofp-nitrophenyl diphenyl phosphate

Poly(propylene imine) dendrimers having 8, 32, and 64 primary amine end groups form diamino Cu(II), diamino Zn(II), and tetramino Co(III) complexes that are identified spectrophotometrically and titrimetrically. The dendrimer-metal ion complexes catalyze the hydrolysis of p-nitrophenyl diphenyl phosphate in zwitterionic buffer solutions at pH Zn(II) > Co(III). The rates of hydrolysis are faster with sodium perchlorate than with sodium chloride to control ionic strength. In sodium perchlorate solutions with Cu(II) the rates increase with increasing size of the dendrimer. In sodium chloride solutions with Cu(II) the rates decrease with increasing size of the dendrimer. Rate constants in buffered sodium chloride solutions of dendrimers and 1.0mM Cu(II) are 1.3-6.3 times faster than in the absence of Cu(II). The fastest hydrolyses occurred at a dendrimer primary amine to Cu(II) ratio NH 2 /Cu ≤ 2. At NH 2 /Cu = 4 and with the 1,4,7,10-tetraazacyclodecane complex of Cu(II) hydrolysis rates were much slower.