Electrochemically driven transfer of carboxyl-terminated PAMAM dendrimers at the water/dichloroethane interface

The transfer of PAMAM dendrimers bearing carboxylic acid peripheral groups between two immiscible liquids was studied by means of the three phase junction system, using a gold wire vertically crossing the interface and decamethyl ferrocene as the redox probe in the organic phase. While the voltammetric behavior indicates kinetic limitations of the overall ion–electron transfer process, thermodynamic data shows that the phase transfer process is entropically controlled. Four dendrimer generations were analyzed and it was found that the kinetics as well as the thermodynamics of the phase transfer reaction are size dependent.     

Fluorescence emission from PAMAM and PPI dendrimers

A strong fluorescence emission from poly(amido amine) (PAMAM) dendrimers with different terminal groups or a poly(propylene imine) (PPI) dendrimer was studied under different conditions by varying experimental parameters such as pH value, aging time, temperature, and concentration. The increase of fluorescence intensity was fast at low pH or high temperature but linear with respect to dendrimer concentration. It was reasonable that the formation of a fluorescence-emitting moiety had a close relation to protonated tertiary amine groups in PAMAM or PPI dendrimers. Furthermore, oxidation of the tertiary amines was confirmed to play an important role, which was evidently caused by oxygen in air. The results of fluorescence decay indicated that the deactivation of luminescence was raised with increasing temperature. Dendrimers emitted blue photoluminescence along fiber chain templates on a fluorescent microscope.     

Convergent synthesis of internally branched PAMAM dendrimers

[reaction: see text] A series of aliphatic internally branched poly(amido amine) dendrons and dendrimers has been synthesized. The internal branching unit was 1,2-propanediamine and a series of PAMAM-type dendrons of the types AB2, AB4, and AB8 were built. These were anchored on a core molecule containing four carboxylic acid moieties and the 1,2-propanediamine unit resulted in PAMAM dendrimers with 4, 8, 16, and 32 end groups.     

Convergent synthesis of PAMAM dendrimers using click chemistry of azide-functionalized PAMAM dendrons

Azide-functionalized PAMAM dendrons containing an azidopropylamine focal point were synthesized by the divergent method and applied for the construction of symmetric PAMAM-like dendrimers containing 1,2,3-triazole rings as connectors via stitching with two different multi-terminal alkynes. The stitching method was based on the click chemistry protocol, i.e., the copper-catalyzed cycloaddition reaction between an alkyne and an azide.     

Incorporation of fluorescent probes into PAMAM dendrimers

Interactions of two fluorescent probes 1-(trimethylammoniumphenyl)-6-phenyl-1,3,5 hexatriene p-toluenesulfonate (TMA-DPH) and 12-(9-anthroyloxy) stearic acid (12-AS) with polyamidoamine (PAMAM) dendrimers were studied. Changes in fluorescence intensity and steady-state fluorescence anisotropy of TMA-DPH and 12-AS were monitored. It was found that 12-AS molecules incorporated into dendrimer cavities whereas TMA-DPH molecules aggregated on the surface of polymer. Dendrimer size had not significant impact on its host properties.     

DNA-templated covalent coupling of G4 PAMAM dendrimers

Generation-4 polyamidoamine (PAMAM) dendrimers were surface-functionalized with azides or alkynes and conjugated to one DNA strand. DNA-controlled self-assembly of alternating azide and alkyne dendrimers on a DNA template enabled the coupling of the dendrimers by the azide-alkyne "click" reaction to form covalently coupled dimers, trimers, and tetramers. Polymerization of the DNA-dendrimer conjugates was also demonstrated, as well as assembly in a circular structure on DNA origami and imaging by atomic force microscopy.     

EPR and affinity studies of mannose-TEMPO functionalized PAMAM dendrimers

Mannose-TEMPO functionalized G4-PAMAM dendrimers with increasing mannose loadings have been synthesized and characterized by MALDI-TOF MS and EPR spectroscopy. Analysis of linebroadening effects in the EPR spectra of these dendrimers allowed us to determine the relative presentation of mannose and TEMPO on the dendrimer surface. Hemagglutination assays and affinity chromatography/EPR experiments to assess the activity of the mannose-TEMPO dendrimers with Concanavalin A are presented.     

Supramolecular mimetic peroxidase based on hemin and PAMAM dendrimers

An acid-base interaction between hemin and PAMAM dendrimers affords supramolecular non-covalent peroxidase systems whose catalytic activity is enhanced after spontaneous electrostatic self-assembling onto a solid surface.     

Structure factor and thermodynamics of rigid dendrimers in solution

The "polymer reference interaction site model" (PRISM) integral equation theory is used to determine the structure factor of rigid dendrimers in solution. The theory is quite successful in reproducing experimental structure factors for various dendrimer concentrations. In addition, the structure factor at vanishing scattering vector is calculated via the compressibility equation using scaled particle theory and fundamental measure theory. The results as predicted by both theories are systematically smaller than the experimental and PRISM data for platelike dendrimers.     

PAMAM dendrimers for efficient siRNA delivery and potent gene silencing

Genuine, nondegraded PAMAM dendrimers self-assemble with siRNA into nanoscale particles that are efficient for siRNA delivery and induce potent endogenous gene silencing.     

Influence of PAMAM dendrimers on human red blood cells

Polyamidoamine (PAMAM) dendrimers with different concentrations (1 nM-1 mM) (generations 2, 3, and 4) impact on human red blood cell morphology, and membrane integrity is studied. Erythrocyte shape changes from biconcave to echinocytic in dendrimers. Cell aggregation occurs. Polymers cause also concentration- and generation-dependent haemolysis.     

Hydrogel of ketoconazole and PAMAM dendrimers: formulation and antifungal activity

Ketoconazole (KET), an imidazole derivative with well-known antifungal properties, is lipophilic and practically insoluble in water, therefore its clinical use has some practical disadvantages. The aim of the present study was to investigate the influence of PAMAM-NH(2) and PAMAM-OH dendrimers generation 2 and generation 3 on the solubility and antifungal activity of KET and to design and evaluate KET hydrogel with PAMAM dendrimers. It was shown that the surface charge of PAMAM dendrimers strongly affects their influence on the improvement of solubility and antifungal activity of KET. The MIC and MFC values obtained by broth dilution method indicate that PAMAM-NH(2) dendrimers significantly (up to 16-fold) increased the antifungal activity of KET against Candida strains (e.g., in culture Candida albicans 1103059/11 MIC value was 0.008 μg/mL and 0.064 μg/mL, and MFC was 2 μg/mL and 32 μg/mL for KET in 10 mg/mL solution of PAMAM-NH(2) G2 and pure KET, respectively). Antifungal activity of designed KET hydrogel with PAMAM-NH(2) dendrimers measured by the plate diffusion method was definitely higher than pure KET hydrogel and than commercial available product. It was shown that the improvement of solubility and in the consequence the higher KET release from hydrogels seems to be a very significant factor affecting antifungal activity of KET in hydrogels containing PAMAM dendrimers.     

Synthesis of azide-functionalized PAMAM dendrons at the focal point and their application for synthesis of PAMAM-like dendrimers

For the first time, the divergent synthesis of azide-functionalized PAMAM dendrons using azidopropyl amine as an azide focal point and convergent synthesis of symmetric PAMAM-like dendrimers containing 1,2,3-triazole rings as connectors via click chemistry with a dialkyne core is described.     

Synthesis of siloxane-based PAMAM dendrimers and luminescent properties of their lanthanide complexes

The 0.5-2 generations of siloxane-based PAMAM dendrimers with 1, 3-bis(3-aminopropyl) tetramethyldisiloxane (G0) as core unit were synthesized by two different methods. Their structures were characterized by FTIR, ¹H NMR, ¹³C NMR, LC/MS, TGA, and DSC. Results show that method two is more suitable as its synthetic procedure is simple and it provides higher yield than method one. DSC analysis indicates that the introduction of the siloxane linkage into the interior of the dendrimers has significant effect on the flexibility of the dendrimer structures. Lanthanide complexes of the newly designed siloxane-based PAMAM dendrimers were obtained by complexing with Eu(III) and Tb(III), respectively. The luminescent properties of the complexes in the solution were investigated. Narrow-width red and green emissions were observed from the complexes of G0.5, G1.5, and G2.0, indicating intramolecular energy transfer process takes place between ligands and lanthanide ions.     

A comparative study of amphiphilic PAMAM dendrimers at the air-water interface with different hydrophobe attachment groups

Generation 0 through 5 polyamidoamine (PAMAM) dendrimers with three different types of groups connecting to hydrophobic C12 tails and one type of group connecting to C18 tails were synthesized and studied as monolayers at the air-water interface with a Langmuir trough. The molecular areas were significantly influenced by the size and the type of connecting group. Higher-generation (e.g., G4 and G5) amphiphilic PAMAMs with amide connecting groups were more responsive to changes in compression rate and subphase temperature and less stable than the corresponding opened epoxide- or ester-connected counterparts. Intramolecular (and possibly also intermolecular) attractive hydrogen-bond interactions between the amide connectors are proposed as the reason for this behavior.     

The excited states interaction of safranine-O with PAMAM and DAB dendrimers in methanol

The quenching of the excited singlet and triplet states of the synthetic dye safranine-O by low generation PAMAM and DAB dendrimers was investigated in methanol. The rate constants for the quenching of the excited singlet state depend on the number of primary amino groups in the dendrimer. The first-order rate constant for the decay of the triplet state presents a downward curvature as a function of the quencher concentration. This behavior was interpreted in terms of the reversible formation of an intermediate complex in the excited state. From a kinetic analysis of the quenching mechanism the equilibrium constant K_exc could be extracted. The values of K_exc may be related to the proton affinity of the quencher. The results were interpreted in terms of a reversible proton transfer quenching. This was further confirmed by the transient absorption spectra obtained by laser flash photolysis. The transient absorption immediately after the triplet state quenching could be assigned to the unprotonated form of the dye. At later times the spectrum matches the semireduced form of the dye. The overall process corresponds to a one-electron reduction of the dye mediated by the deprotonated triplet state.     

Interactions between PAMAM dendrimers and gallic acid molecules studied by spectrofluorimetric methods

Interactions between gallic acid molecules and different types of polyamidoamine (PAMAM) dendrimers with modified surfaces were studied by spectrofluorimetric methods. Changes in fluorescence intensity of gallic acid and in a position of spectrum were monitored. It was found that the extent of gallic acid incorporation into dendrimers depends on a type of a dendrimer.     

Strong blue photoluminescence and ECL from OH-terminated PAMAM dendrimers in the absence of gold nanoparticles

A product showing strong blue photoluminescence was obtained by oxidation of OH-terminated PAMAM dendrimers, such as G4-OH, G2-OH, and G0-OH, with HAuCl4 or (NH4)2S2O8. The fluorescence emission spectrum peaked at 450 nm, while the excitation maximum was at 380 nm, independent of the generation of dendrimer. The product also shows two weak electrogenerated chemiluminescence (ECL) signals upon cycling the potential between about 1.2 and -1.7 V.     

Electrochemical behavior of bisphenol A at glassy carbon electrode modified with gold nanoparticles, silk fibroin, and PAMAM dendrimers

A glassy carbon electrode was modified with a composite made from gold nanoparticles and silk fibroin whose surface was further modified with amino-terminated G4 poly(amidoamine) dendrimer. This electrode shows distinct electrochemical response to bisphenol A (BPA). Electrochemical impedance spectroscopy was used to characterize the surface. The electrode displayed improved adsorption capacity and an increased response to BPA, compared to a surface without modification. Under the optimal detection conditions, the respeonse is linear in the concentration range from 1 nM to 1.3 μM, the correlation coefficient is 0.9991, and the detection limit is 0.5 nM (at an S/N of 3). The method was applied to the determination of BPA in water samples, and the recovery was in the range from 97% to 105%.