Study of Poly(amidoamine) Starburst Dendrimers by Fluorescence Probing (original) (raw)
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Incorporation of fluorescent probes into PAMAM dendrimers
Bioelectrochemistry, 2004
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. D
The physical and chemical properties of PAMAM-AT dendrimers' interior were investigated using the fluorescent, solvatochromic probe phenol blue. In aqueous solutions of each generation studied except G0, two discrete dye populations were clearly observed. PAMAM-AT dendrimers were shown to form a tight, nonpolar association with the majority of available dye within the dendrimer interior, probably near its core. In the absorption and steady-state fluorescence emission spectra, a microenvironment of decreasing polarity in increasingly larger-generation PAMAM-AT dendrimers (up to G3) is seen for the associated probe. The remaining larger-generation dendrimers (G4-8) all provide a microenvironment of essentially equal polarity. Fluorescence anisotropy values for phenol blue in the PAMAM-AT dendrimers demonstrate the dye's sensitivity to the changing molecular volumes of the dendrimer generations. Model compounds that mimic PAMAM-AT's surface groups and branching moieties were used to better define the associated dye's location. The mimics further confirm that phenol blue is associated inside the dendrimer, where it does not interact with the dendrimer surface groups.
Journal of Fluorescence, 2006
The interactions between polycationic poly-lysine dendrimers and hydrophobic fluorescent probes (anionic ANS and neutral Prodan) were studied. R121 and R131 dendrimers were not able to interact with anionic and neutral hydrophobic groups. R124 was able to interact with neutral and anionic hydrophobic fluorescent probes, however mainly through hydrophobic forces. Dendrimers R155 and R169 showed the maximal effects. The strongest interactions observed for R169 can be explained by intramolecular folding (stacking) of its two L-proline residues. Using double fluorescence titration technique for ANS probe allowed to receive such constant of binding and the number of binding centers: for R121, 1.8•10 3 (mol/l) -1 and 1.07; for R124, 12.1•10 3 (mol/l) -1 and 0.48; for R131, 4.7•10 3 (mol/l) -1 and 0.48; for R155, 9.2•10 3 (mol/l) -1 and 1.36; for R169, 39.6•10 3 (mol/l) -1 and 0.97. Thus, neutral and anionic hydrophobic probes can be used for the fast preliminary screening of binding properties of newly synthesized polycationic dendrimers.
Photophysical properties of Newkome-type dendrimers in aqueous medium
Photochemical & Photobiological Sciences, 2007
Newkome-type first, second and third generation dendrimers, having t-butyl (GB), ethyl (GE) and carboxylic (GA) end groups, were synthesized. A pyrene group, which can act as fluorescent sensor, was attached to the core of the dendrimers and their photophysical properties in aqueous solution were studied. These dendrimers were found to aggregate in aqueous solution, which manifested as an excimer peak in the pyrene emission spectra for the first and second generation dendrimers with ethyl and t-butyl end groups. The excimer peak however was not seen in case of the third generation dendrimer. Dendrimers with carboxylic end groups, did not show the excimer peak in water, which implies the hydrophobic nature of the aggregation. It is observed that the intensity of the excimer peak decreases with the increase in the size of the dendrimer. Lifetime studies carried out on the first and second generation dendrimers showed the formation of excimer species as a risetime in the decay curve. The aggregation of the third generation dendrimer was proposed from the quenching studies using silver ions and CCl 4 as quenchers.
Intrinsic Fluorescence of Carboxylate-Terminated Polyamido Amine Dendrimers
Applied Spectroscopy, 2001
The ''intrinsic'' uorescence of carboxylate-terminated polyamido amine (PAMAM-CT) dendrimers is studied by two uorescence techniques-excitation-emission matrices (EEMs) and lifetimes. The EEM s show similar spectral pro les for all dendrimer generations (a broad peak with an excitation and em ission m aximum of 380 and 440 nm, respectively) and an overall increase in relative uorescence emission with increasing generation. Three distinct, fairly discrete lifetimes are also recovered . The shortest lifetime (0.2-0.4 ns) is a background signal from the solvent. The two longer lifetimes are attributed to the dendrimer. There is a general shift to longer lifetimes in t 2 and t 3 , with increasing generation (G n). Both lifetim es nearly double in m agnitude, going from G2.5 to G7.5, which is indicative of a speci c uorescen t component being in a more protected or constrained microenvironment. These results imply that the dendrimer becomes densely packed with increasing generation. The weak, but detectable, uorescence is most likely due to an n ® p * transition from the amido groups throughout the dendritic structure. Even though the exact nature of PA-MAM -CT uorescence is not fully understood, it is clear that this property shows the unique aspects of the architecture of these dendrim ers and can be utilized in their characterization.
Langmuir, 1997
The structure of a series of poly(amidoamine) dendrimers Gn(C12) generated from a diaminododecane core have been investigated using the photophysical properties of an external dye, nile red. The modified dendrimers Gn(C12) show the ability to host the hydrophobic dye, nile red, in aqueous solution. The ability of Gn(C12) to host nile red has been compared to corresponding amino-core Gn(NH3) and diaminoethanecore Gn(C2) dendrimers of the same generation size. The emission of nile red in aqueous media is significantly enhanced in the presence of Gn(C12) and not at all for Gn(NH3) and Gn(C2). These results imply a strong tendency for the nile red probe to associate with the long methylene chain of the modified dendrimers in aqueous solutions. Moreover, the interactions of these dendrimers with anionic surfactants generate supramolecular assemblies which greatly enhance their ability to accomodate the nile red. Fluorescence polarization and emission as a function of pH were also studied in an effort to elucidate the interaction of the nile red probe with the dendrimer-surfactant assemblies.
Journal of Colloid and Interface Science, 2002
The intermolecular dendrimer interactions between poly (amidoamine) dendrimers (SBDs) of different generations (G = 2, 4, and 6) were studied in aqueous solution by EPR and fluorescence depolarization. For the EPR studies a spin probe (TEMPO) was covalently linked to the SBDs, and for the fluorescence depolarization studies a fluorophor (fluorescein) was covalentely linked to the SBDs. The mobility of the TEMPO labeled SBDs was determined by EPR over a range of the concentration of added SBDs (unlabeled SBD of the same generation) from 0.01 to 75% (w/w) in water solutions. The mobility of the TEMPO label was not influenced by added SBD below a concentration of approximately 5%, suggesting that no significant interdendrimer interactions, such as aggregation, occurred. Above a concentration of 30% SBD in water (w/w), the mobility of the TEMPO label decreased dramatically; the effect is mostly attributed to the viscosity increase at such high concentrations. Fluorescence depolarization studies, employing fluorescein-labeled dendrimers are in agreement with the EPR studies.
Analytica Chimica Acta, 1999
Alternant and nonalternant polycyclic aromatic hydrocarbons (PAHs) are employed to compare carboxylate-terminated polyamido amine (PAMAM) dendrimers to typical anionic micelles. Nitromethane is a known, selective, quenching agent of alternant PAHs. However, recent studies by Acree and co-workers have found that nitromethane will also quench the fluorescence emission intensity of nonalternant PAHs in the presence of anionic surfactants above the critical micelle concentration. The quenching of alternant and nonalternant PAHs by nitromethane is used to compare dendritic 'unimolecular micelles' to traditional micelles. Experimental results indicate that the PAHs' association with these dendrimers does not appear to occur in the 'palisade' region, as seen in traditional micelles, but rather deeper within the dendrimer structure. Solvent polarity probe studies and quenching in the absence of nitromethane also support this conclusion. Due to the fact that the PAHs do not reside near the negatively charged surface groups, the nitromethane selective quenching rule is obeyed in carboxylate-terminated PAMAM dendrimers (10 mM in surface groups).