Amine Groups Of Dendrimers Research Articles

Novel platform based on polystyrene electrospun nanofibrous mats doped with PAMAM dendritic polymer for enhanced immunosensing

A novel and ideal immunosensor platform with customized tailored chemistry is suggested by combining the characteristics of nanofibers (NFs) and dendrimers. Polystyrene (PS) NFs were doped with polyamidoamine (PAMAM) dendritic polymer and utilized for covalent immobilization of FITC-labeled anti-human TNF-α antibodies by activation of the amine groups of dendrimer on the surface of NFs using a glutaraldehyde (GA) coupling agent. SEM, ATR-FTIR, contact angle, EDX, XPS, TGA, and fluorescence microscopy were performed. The findings demonstrated that (1) PS-PAMAM NFs were produced with significantly smaller diameters (295 ± 94 nm), more uniform morphology, and more hydrophilic (44 ± 5.5°) with dendrimer amine groups on the surface that can provide a better path for antibodies to be immobilized compared to pure PS NFs, (2) the PAMAM was distributed evenly throughout the NFs, (3) GA was uniformly applied to the surface of NFs via covalent bonding, (4) the PAMAM played a critical role in substantially increasing antibody immobilization at the surface of each NFs without causing agglomeration. According to the findings, the PS-PAMAM electrospun mat is suitable for immobilizing biomolecules and may be utilized as a support to boost immunosensor sensitivity.

Biotin Transport-Targeting Polysaccharide-Modified PAMAM G3 Dendrimer as System Delivering α-Mangostin into Cancer Cells and C. elegans Worms

The natural xanthone α-mangostin (αM) exhibits a wide range of pharmacological activities, including antineoplastic and anti-nematode properties, but low water solubility and poor selectivity of the drug prevent its potential clinical use. Therefore, the targeted third-generation poly(amidoamine) dendrimer (PAMAM G3) delivery system was proposed, based on hyperbranched polymer showing good solubility, high biocompatibility and low immunogenicity. A multifunctional nanocarrier was prepared by attaching αM to the surface amine groups of dendrimer via amide bond in the ratio 5 (G32B12gh5M) or 17 (G32B10gh17M) residues per one dendrimer molecule. Twelve or ten remaining amine groups were modified by conjugation with D-glucoheptono-1,4-lactone (gh) to block the amine groups, and two biotin (B) residues as targeting moieties. The biological activity of the obtained conjugates was studied in vitro on glioma U-118 MG and squamous cell carcinoma SCC-15 cancer cells compared to normal fibroblasts (BJ), and in vivo on a model organism Caenorhabditis elegans. Dendrimer vehicle G32B12gh at concentrations up to 20 µM showed no anti-proliferative effect against tested cell lines, with a feeble cytotoxicity of the highest concentration seen only with SCC-15 cells. The attachment of αM to the vehicle significantly increased cytotoxic effect of the drug, even by 4- and 25-fold for G32B12gh5M and G32B10gh17M, respectively. A stronger inhibition of cells viability and influence on other metabolic parameters (proliferation, adhesion, ATP level and Caspase-3/7 activity) was observed for G32B10gh17M than for G32B12gh5M. Both bioconjugates were internalized efficiently into the cells. Similarly, the attachment of αM to the dendrimer vehicle increased its toxicity for C. elegans. Thus, the proposed α-mangostin delivery system allowed the drug to be more effective in the dendrimer-bound as compared to free state against both cultured the cancer cells and model organism, suggesting that this treatment is promising for anticancer as well as anti-nematode chemotherapy.

Cellulose fibers functionalized by metal nanoparticles stabilized in dendrimer for formaldehyde decomposition and antimicrobial activity

Viscose rayon cellulose fiber was selectively oxidized so that carboxylate functional group was introduced on the fiber. Enough dispersed platinum nanoparticles and silver nanoparticles having average sizes of around 5nm with small size distribution were prepared with capping of amine-terminated fourth generation poly(amido amine) dendrimer and they were immobilized on oxidized fibers through amidation between terminal amine groups of dendrimer and carboxylic acids on oxidized fibers. The fiber containing dendrimer (1wt%) and platinum (2wt%) exhibited the 84 times higher adsorption capacity for formaldehyde gas on dendrimer site than on fiber site and the catalytic efficiency (65%) towards decomposition of formaldehyde gas adsorbed on the dendrimer site, and the silver (0.2wt%)-loaded fiber revealed excellent biocidal activity against E. coli. Thus, it can be noted that the immobilization of functional metal nanoparticles protected by dendrimer on cellulose fibers is effective to produce efficient textile products with smart functions like the degradation of causative agents for sick building syndromes.

Incorporating functionalized silica nanoparticles in polyethersulfone‐based anion exchange nanocomposite membranes

ABSTRACTIn order to investigate for anion exchange membranes (AEMs) with improved properties, four series of polyethersulfone‐based composite AEMs are fabricated by incorporating pristine and three functionalized silica nanoparticles containing propylamine, trimethylpropylamine, and melamine‐based dendrimer amine groups. The results show that by choosing appropriate functional agent, anion exchange membranes with improved parameters can be achieved. The polymeric matrix of the membranes is synthesized by chloromethylation of polyethersulfone using thionyl chloride followed by amination with trimethylamine (TMA). The effectiveness of chloromethylation process is confirmed by 1H NMR analysis. The effects of functional groups on characteristic and transport properties of the prepared composite membranes i.e., SEM, IEC, water uptake, porosity transport properties, and conductivity are investigated. The scanning electron microscope images illustrates that the synthesized membranes possess dense structures. Ion exchange capacity (IEC), water uptake, transport properties, and conductivity of the composite membranes are measured. In addition, the morphology and thermal stability are characterized. IECs and ion conductivities of up to 1.45 meq g−1 and 45.46 mS cm−1 and moderate transport characteristics are obtained from the modified membranes which confirm that these membranes are appropriate for applying in electro‐membrane processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44596.

Inhibiting shale hydration and dispersion with amine-terminated polyamidoamine dendrimers

Dendrimers have been paid increasing attention in the area of drilling fluid recently due to their unique structure and properties. The inhibitive properties of amine terminated polyamidoamine (PAMAM) dendrimers ranging from G0 to G5 were evaluated by relative inhibition rate, shale cuttings hot-rolling dispersion test and particle size distribution measurement respectively. Meanwhile the inhibitive capacity of the polymers under various pH value conditions was studied. The interaction between sodium bentonite and PAMAM dendrimers was characterized by zeta potential measurement and X-ray diffraction (XRD). The results indicated that, G0 and G5 are superior to polyether diamine, while G1, G2, G3 and G4 perform better than KCl. PAMAM dendrimers from G0 to G5 can decrease the zeta potential of clay particles from −39 mV to about −22.6 mV at natural pH values and reverse the charge when the pH value is adjusted to 9. When intercalated into the clay interlayer in aqueous solution, the candidate PAMAM dendrimers can form monolayer arrangement at lower concentrations and reduce the interlayer spacing of hydrated clay from 1.95 nm to 1.38–1.63 nm, which is the direct evidence of inhibiting shale hydration. With the increase of concentration, mixed phase and bilayer orientation are formed in the interlayer. The multi-terminal amine groups of dendrimers can effectively bind the adjacent layers together with electrostatic attraction and hydrogen bonding, and expel the water molecules out of the interlayer, contributing to the suppression of clay swelling and dispersion. The pH value reduction of aqueous solution improves the protonation of terminal-amine group, which can intensify the interaction between the polymers and clay, inducing the decrease of hydrated interlayer spacing and the zeta potential of clay particles, thus enhancing the inhibitive properties.

Dendrimer-Functionalized Laponite Nanodisks as a Platform for Anticancer Drug Delivery.

In this study, we synthesized dendrimer-functionalized laponite (LAP) nanodisks for loading and delivery of anticancer drug doxorubicin (DOX). Firstly, LAP was modified with silane coupling agents and succinic anhydride to render abundant carboxyl groups on the surface of LAP. Then, poly(amidoamine) (PAMAM) dendrimer of generation 2 (G2) were conjugated to form LM-G2 nanodisks. Anticancer drug DOX was then loaded on the LM-G2 with an impressively high drug loading efficiency of 98.4% and could be released in a pH-sensitive and sustained manner. Moreover, cell viability assay results indicate that LM-G2/DOX complexes could more effectively inhibit the proliferation of KB cells (a human epithelial carcinoma cell line) than free DOX at the same drug concentration. Flow cytometry analysis and confocal laser scanning microscope demonstrated that LM-G2/DOX could be uptaken by KB cells more effectively than free DOX. Considering the exceptional high drug loading efficiency and the abundant dendrimer amine groups on the surface that can be further modified, the developed LM-G2 nanodisks may hold a great promise to be used as a novel platform for anticancer drug delivery.

Self-Assembled Hybrids of Fluorescent Carbon Dots and PAMAM Dendrimers for Epirubicin Delivery and Intracellular Imaging.

Advanced nanomaterials integrating imaging and therapeutic modalities on a single platform offers a new horizon in current cancer treatment strategies. Recently, carbon dots (CQDs) have been successfully employed for bioimaging of cancer cells. In the present study, luminescent CQDs with anionic terminus and cationic acetylated G5 poly(amido amine) (G5-Ac85) dendrimers were combined via noncovalent interactions to form self-assembled fluorescent hybrids. The fluorescence of CQDs in hybrids is enhanced in the vicinity of primary amine groups of dendrimers, making them suitable as cellular imaging probes. Encapsulation of chemo-drug epirubicin (EPI) in the dendrimer interiors endowed the fluorescent hybrids with therapeutic potential. The in vitro release of an entrapped EPI drug from CQDs@EPI⊂G5-Ac85 hybrids was faster in an acidic environment than under physiological conditions. Herein, multifunctional CQDs@EPI⊂G5-Ac85 hybrids serve as a dual-emission delivery system, to track the intracellular distribution and cytotoxic effects of EPI drugs. Green emission properties of CQDs were used for fluorescence microscopic imaging and cellular uptake by flow cytometry. Cell cycle analysis, field-emission scanning electron microscopy (FE-SEM), reactive oxygen species (ROS) generation, and up-regulation of apoptotic signaling genes unanimously demonstrated the apoptosis inducing ability of CQDs@EPI⊂G5-Ac85 hybrids in breast cancer (MCF-7) cells. Therefore, we have evaluated CQDs@EPI⊂G5-Ac85 hybrids as prospective candidates to achieve simultaneous imaging and drug delivery in cancer cells.

Evaluation of poly(amidoamine) dendrimers as potential carriers of iminodiacetic derivatives using solubility studies and 2D-NOESY NMR spectroscopy

The interactions between dendrimers and different types of drugs are nowadays one of the most actively investigated areas of the pharmaceutical sciences. The interactions between dendrimers and drugs can be divided into: internal encapsulation, external electrostatic interaction, and covalent conjugation. In the present study, we investigated the potential of poly(amidoamine) (PAMAM) dendrimers for solubility of four iminodiacetic acid derivatives. We reported that PAMAM dendrimers contribute to significant solubility enhancement of iminodiacetic acid analogues. The nature of the dendrimer–drug complexes was investigated by 1H NMR and 2D-NOESY spectroscopy. The 1H NMR analysis proved that the water-soluble supramolecular structure of the complex was formed on the basis of ionic interactions between terminal amine groups of dendrimers and carboxyl groups of drug molecules, as well as internal encapsulation. The 2D-NOESY analysis revealed interactions between the primary amine groups of PAMAM dendrimers and the analogues of iminodiacetic acid. The results of solubility studies together with 1H NMR and 2D-NOESY experiments suggest that the interactions between PAMAM dendrimers of generation 1–4 and derivatives of iminodiacetic acid are based on electrostatic interactions and internal encapsulation. Electronic supplementary material The online version of this article (doi:10.1007/s10867-012-9277-5) contains supplementary material, which is available to authorized users.

Host−Guest Chemistry of Dendrimer−Drug Complexes. 6. Fully Acetylated Dendrimers as Biocompatible Drug Vehicles Using Dexamethasone 21- Phosphate as a Model Drug

Fully acetylated poly(amidoamine) (PAMAM) dendrimer was proposed as a biocompatible drug vehicle using dexamethasone 21-phosphate (Dp21) as a model drug. NMR techniques including (1)H NMR and 2D NOE NMR were used to characterize the host-guest chemistry of acetylated dendrimer/Dp21 and cationic dendrimer/Dp21 complexes. The pH-dependent micellization, complexation, and inclusion behaviors of Dp21 were observed in the presence of acetylated and cationic PAMAM dendrimers. Acetylated dendrimer only encapsulates Dp21 at acidic conditions, while cationic dendrimer can host Dp21 at both acidic and neutral conditions. The orientation of Dp21 molecules in the dendrimer cavities depends on the quaternization degree of tertiary amine groups of dendrimer and the protonation ratio of phosphate group of Dp21. A distinctive pH-dependent release behavior of Dp21 from the acetylated and nonacetylated dendritic matrix was observed: Dp21 exhibits a much slower release rate from acetylated dendrimer at lower pH conditions and a much faster release rate from nonacetylated dendrimer with decreasing pH values. Cytotoxicity studies further confirmed the biocompatibility of acetylated dendrimers, which are much safer in the delivery of therapeutics for the treatment of various diseases than nonacetylated dendrimers. The dendrimer-drug binding and release mechanisms provide a new insight for the design and optimization of biocompatible dendrimer-based drug delivery systems.

Host−Guest Chemistry of Dendrimer−Drug Complexes. 4. An In-Depth Look into the Binding/Encapsulation of Guanosine Monophosphate by Dendrimers

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. (1)H 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 new insight into the host-guest chemistry of dendrimer/guest complexes and may play important roles in the study of dendrimer/DNA aggregates by a "bottom-up" strategy.

Modification of a glassy carbon surface with amine-terminated dendrimers and its application to electrocatalytic hydrazine oxidation

Amine-terminated polyamidoamine (PAMAM) dendrimers were immobilized on glassy carbon electrodes (GCEs) via electrochemical oxidation of the terminal amine groups of dendrimers. The electrochemical immobilization of dendrimers was confirmed by cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The immobilized dendrimer films were robust and behaved as charge-selective electrochemical gates for oppositely charged redox molecules. The immobilization approach was applied to assemble Au dendrimer-encapsulated nanoparticles (Au DENs, dia. 1.5 ± 0.3 nm) on GCEs, and the resulting Au DEN films showed electrocatalytic activity to hydrazine oxidation.

Insights into the Interactions between Dendrimers and Bioactive Surfactants: 3. Size-Dependent and Hydrophobic Property-Dependent Encapsulation of Bile Salts

The supramolecular structures of dendrimer-bile salt complexes have been investigated by multidimensional and multinuclear NMR techniques, such as (1)H NMR, COSY, TOCSY, NOESY, and DOSY. 2D-NOESY analysis indicated the localization of bile salt in the interior pockets of dendrimers. The orientation of the guest in the pockets was predicted by the NOE cross-peaks based on NOESY spectrum. (1)H NMR experiments suggested that no electrostatic interactions between the amine groups of dendrimers and the negatively charged group of bile salts occur in the complexes. DOSY studies further confirmed the inclusion structures based on the diffusion coefficient information. The supramolecular structures of dendrimer-bile salt complexes were mainly formed by hydrophobic interactions/hydrogen-bond interactions in the interior pockets of dendrimers. In addition, size- and hydrophobic property-dependent encapsulation of bile salts and bile derivates in the cavities was observed. These results suggest a new interaction model of dendrimer-surfactant aggregates and provide new insight into the interactions between dendrimers and bioactive surfactants.

Boronic acid-modified thin film interface for specific binding of glycated hemoglobin (HbA 1c) and electrochemical biosensing

We studied electrochemical detection of glycated hemoglobin (HbA 1c) using boronic acid-modified electrodes. Boronic acid is known to form covalent bonds between its diol group and cis-diol group of the carbohydrate chain. Therefore, to detect HbA 1c, boronic acid was functionalized on the chemically modified electrode surface using poly(amidoamine) G4 dendrimer as an interface material. HbA 1c was biospecifically attached to the chip surface through the cis-diol interaction between peripheral glucose from HbA 1c and functionalized boronic acid. To confirm the HbA 1c binding to the boronic acid layer, periodate-treated glucose oxidase (GO x) was backfilled to the remaining amine groups of dendrimer on the electrode surface and quantified electrochemically. A sensitive decrement of the current was achieved with increasing percentile concentration from 2.5% to 15% HbA 1c per total hemoglobin. This method has potential not only to determine HbA 1c concentration but also to determine the concentrations of a variety of glycoproteins that contain peripheral sugar groups.

Columnar Mesophases of the Complexes of DNA with Low-Generation Poly(amido amine) Dendrimers

The electrostatic complexes of polyanionic DNA with dendrimers have been considered as a class of nonviral vector for gene therapy. The gene transfection efficiency has been believed to be influenced by the structure of the complex. In this study, we have systematically characterized the supramolecular structures of the complexes of DNA duplexes with poly(amido amine) (PAMAM) dendrimers with generation two (G2) and three (G3) in pure water using small-angle X-ray scattering. The structures were examined as a function of the charge density of the dendrimer expressed by its degree of protonation (dp) and the molar ratio of the amine groups of dendrimer to the phosphate groups of DNA (N/P). The DNA chains in all complexes under study were found to self-organize into two-dimensional hexagonal or square lattice. In general, hexagonal phase was the favorable structure for G2 complexes, while the DNA in G3 complexes tended to organize into a square lattice. Interesting transitions between the columnar mesophases with respect to the changes of N/P ratio and dp have been identified. The geometric features of the dendrimer molecules accommodated within the interstitial tunnels of the DNA lattices have also been revealed. The B conformation of DNA was effectively retained in the complexes in spite of the influence of the electrostatic interaction with the dendrimers.

Fabrication of disposable sensors for biomolecule detection using hydrazine electrocatalyst

We have developed electrochemical DNA and protein sensors on screen-printed electrodes based on the catalytic activity of hydrazine. The sensors use carboxylic acid-functionalized conductive polymer, poly-5,2′,5′,2′′-terthiophene-3′-carboxylic acid (polyTTCA) to make firm immobilization of dendrimer (DEN) through the covalent bond formation between the carboxylic acid groups of polymer and amine groups of dendrimer. The gold nanoparticles (AuNPs) were adsorbed on the remaining amine groups of dendrimer. The thiolated DNA probe or primary antibody was subsequently immobilized on the AuNP-covered dendrimer surfaces. Avidin-labeled hydrazine (Av–Hyd) was then immobilized on the sensor surfaces through the avidin–biotin interaction between the Av–Hyd unit and the biotinylated DNA or secondary antibody. The electrocatalytic reduction current of H 2O 2 was measured by differential pulse voltammetry. The detection signal was amplified by the polyTTCA/DEN assembly loaded with AuNPs (∼ 3.5 nm) onto which target analyte-linked Av–Hyd was adsorbed. Linear dynamic ranges for the electrocatalytic detection of DNA and human immunoglobulin G (IgG) extending from 50 fM to 7.5 nM and from 40 fg/ml to 2.5 ng/ml, respectively, were observed along with detection limits of approximately 30 fM and 25 fg/ml, respectively. The low detection limit of the disposable sensors offers good promise for practical DNA and protein detection.

Biofunctionalization of collagen for improved biological response: Scaffolds for corneal tissue engineering

Residual dendrimer amine groups were modified with incorporate COOH group containing biomolecules such as cell adhesion peptides into collagen scaffolds. YIGSR, as a model cell adhesion peptide, was incorporated into both the bulk structure of the gels and onto the gel surface. The effects of the peptide modified collagen gels on corneal epithelial cell behavior were examined with an aim of improving the potential of these materials as tissue-engineering scaffolds. YIGSR was first chemically attached to dendrimers and the YIGSR attached dendrimers were then used as collagen crosslinkers, incorporating the peptide into the bulk structure of the collagen gels. YIGSR was also attached to the surface of dendrimer crosslinked collagen gels through reaction with excess amine groups. The YIGSR modified dendrimers were characterized by H-NMR and MALDI mass spectra. The amount of YIGSR incorporated into collagen gels was determined by (125)I radiolabelling at maximum to be 3.1-3.4 x 10(-2)mg/mg collagen when reacted with the bulk and 88.9-95.6 microg/cm(2) when attached to the surface. The amount of YIGSR could be tuned by varying the amount of peptide reacted with the dendrimer or the amount of modified dendrimer used in the crosslinking reaction. It was found that YIGSR incorporation into the bulk and YIGSR modification of surface promoted the adhesion and proliferation of human corneal epithelial cells as well as neurite extension from dorsal root ganglia.

Self-organization of cationic dendrimers in polyanionic hydrogels

Protonated poly(propylene imine) dendrimers (Astramol) of five generations: DAB-dendr-(NH2)x (where x=4, 8, 16, 32 or 64) are sorbed by slightly cross-linked polyanionic hydrogels: poly(sodium acrylate) and poly(sodium 2-acrylamido-2-methylpropane sulfonate). As a result highly swollen original hydrogel transforms into compact cross-linked polyelectrolyte-dendrimer complexes. Sorption of dendrimers by the hydrogels is a chemically drawn frontal diffusion process. Driving force comes from the gain in the free energy of interpolyelectrolyte coupling reaction between the charged dendrimer molecules and the oppositely charged hydrogel network, accompanied with entropically favourable release of low molecular salt into environment. The amount of a simple salt released is equivalent to a number of intermolecular salt bonds, formed between protonated dendrimers and hydrogel networks. Apparently the mechanism of dendrimer uptake involves a "relay-race" transfer of dendrimer polycations from one fragment of polyelectrolyte network to the other via interpolyelectrolyte exchange reaction. As a result "core-shell" constructs consisting of outer weakly swollen complex shell and highly swollen hydrogel core are formed at intermediate stages of the process. The rate of sorption is determined by the rate of the interpolyelectrolyte exchange reaction that is the rate of the formation of free fragments of polyelectrolyte network (vacancies) on the inner complex-hydrogel boundary. The amount of vacancies depends on the area of this boundary. Consequently kinetics of dendrimer uptake could not be fitted in terms of Fickian diffusion (except DAB-dendr-(NH2)4), but expressed in terms of the kinetic equation derived for a frontal heterogeneous reaction. Sorbed dendrimers of all studied generations at pH values ensuring complete protonation of primary and tertiary amine groups are closely packed in hydrogel networks, so that all dendrimer cationic units form ion pairs with anionic units of hydrogels. In other words polyanionic network fragments are able to penetrate into the interior of fully protonated DAB-dendr-(NH2)x species as it was earlier shown for flexible linear polyanions. In such case the ultimate amount of sorbed dendrimer molecules is always determined by the condition n(a)/N- = 1, where n(a) is the total number of dendrimer amine groups, N- is the number of the anionic hydrogel units. The latter is also true for the complex shell composition in the heterogeneous reacting samples formed at intermediate stages of dendrimers uptake. Variation of pH and sorption extent is an effective tool to control dendrimer distribution, self-organization and the final structure of dendrimer-hydrogel constructs.

Functionalization of a poly(amidoamine) dendrimer with ferrocenyls and its application to the construction of a reagentless enzyme electrode.

Poly(amidoamine) dendrimers having various degrees of modification with the redox-active ferrocenyls were prepared by controlling the molar ratio of ferrocenecarboxaldehyde to amine groups of dendrimers. By alternate layer-by-layer depositions of partial ferrocenyl-tethered dendrimers (Fc-D) with periodate-oxidized glucose oxidase (GOx) on a Au surface, an electrochemically and enzymatically active multilayered assembly of enzyme was constructed. The resulting GOx/Fc-D multilayer-associated electrodes were electrochemically analyzed, and the surface concentration of ferrocenyl groups, active enzyme coverage, and sensitivity were estimated. A 32% dendrimer modification level of surface amines to ferrocenyls was found to be an optimum in terms of enzyme-dendrimer network formation, electrochemical interconnectivity of ferrocenyls, and electrode sensitivity. With the prepared Fc(32%)-tethered dendrimers, mono- and multilayered GOx/Fc-D electrodes were constructed, and their electrochemical and catalytic properties were characterized. The bioelectrocatalytic signals from the multilayered GOx/Fc-D electrodes were shown to be directly correlated to the number of deposited bilayers. From this result, it seems that the electrode sensitivity is directly controllable, and the multilayer-forming strategy with partial ferrocenyl-tethered dendrimers is useful for the construction of reagentless biosensors.

Interaction of Astramol Poly(propyleneimine) Dendrimers with Linear Polyanions

Interaction between Astramol poly(propylene imine) dendrimers of five generations, DAB-dendr-(NH2)x (where x is equal to 4, 8, 16, 32, or 64) and linear poly(sodium acrylate), poly(acrylic) acid, poly(sodium styrenesulfonate), or native DNA was studied in salt-free solutions by means of potentiometric, argentometric, and turbidimetric titrations. In addition to x outer primary amine groups the dendrimer molecule contains x − 2 inner tertiary amine groups. It is found that the pH-controlled interpolyelectrolyte coupling reaction resulting in formation of the corresponding interpolyelectrolyte complexes occurs on mixing of the dendrimer and the polyanion solutions. A peculiar finding was that all dendrimer amine groups being protonated can form ion pairs with carboxylate or sulfonate groups of the polyanions. In other words DAB-dendr-(NH2)x molecules are fully penetrable for rather flexible oppositely charged polyelectrolyte chains. However, this is not the case for rigid negatively charged DNA double helixes which apparently bind only to the dendrimer shell. The complexes of dendrimers, with polyanions containing equal amounts of cationic and anionic groups mostly ion-paired (stoichiometric complexes), are insoluble in water. At the same time water soluble nonstoichiometric interpolyelectrolyte complexes can be obtained if the dendrimer is a deficient component of the complex species. This behavior is similar to that of complexes formed by oppositely charged linear polyions.