Study of Poly(amidoamine) Starburst Dendrimers by Fluorescence Probing (original) (raw)
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).
Molecules
Poly(ethyleneimine) (PEI) is a weakly basic, synthetic, polycationic polymer, due to the presence of primary, secondary, and tertiary amino groups. The amino groups are responsible for the variety of applications of PEI (e.g., transfection, bioimaging, solar cell, etc.). Our study presents some new and reproducible methods for the quantification of molecular or mass concentration of highly branched PEI of different molecular weights (800–2000–25,000–750,000 MW PEI). In the course of the direct method, spectrophotometry and fluorometry were applied to determine the absorption and fluorescence of PEI dilution series. An increase in the MW at the same concentration produces a higher count number because of the higher number of amino groups in PEI molecules. The character of increment in fluorescence intensity is essentially different in the case of mass concentrations and molar concentrations. The increment of the fluorescence intensity related to the molar concentration is non-linear....
Journal of Polymer Science Part A: Polymer Chemistry, 2007
An inexpensive and highly efficient synthesis of first example of fluorescent aromatic dendrimers having alternative ether and urea linkages without the need for protection and deprotection steps has been developed. Dendrons and dendrimers up to third generation, with amine end-groups, were prepared by convergent growth approach in high yield. A repetitive synthetic sequence of nucleophilic addition reaction between amine and regenerated isocyanate and reduction of nitro groups into amine are adopted for the synthesis of these dendrimers. The peripheries of the dendrimers contained 6, 12, and 24 amino groups, for the first, second, and third generation, respectively. Materials were characterized by FTIR, NMR, and MALDI-TOF MS spectrometry. These dendrimers were soluble in amide solvents, THF and acetone and displayed fluorescence maxima in the 440-500 nm range with relatively narrow peak widths indicating that they had pure and intense fluorescence. These dendrimers form chargetransfer (CT) complexes with electron acceptor molecules such as 7,7,8,8,-tetracyanoquino-dimethane and 1,1,2,2 tetracyanoethane as evidenced by UV-visible absorption spectra. V
Poly(propyleneimine) Dendrimers as pH-Sensitive Controlled-Release Systems
Chemistry-a European Journal, 1999
Molecular composites were prepared by solubilizing pyrene in diaminobutane poly(propyleneimine) dendrimers having 32 or 64 primary amine end groups (DAB-32 or DAB-64). The dendrimer ± pyrene binding constants were determined as K py/DAB-32 16 725 AE 200 m À1 and K py/DAB-64 33 858 AE 663 m À1 by fluorescence spectroscopy. Fluorescence studies were also employed to probe the release of pyrene from the interior of dendrimers as a function of pH. When the pH value of the system was decreased from pH 11 by addition of HCl, the fluorescence intensity of the system was found to increase by approximately tenfold at pH 2 ± 4. In addition, at pH 2, the ratio of the first to the third vibrational peak of pyrene (I 1 /I 3 ) increased from 0.9, the value typical for pyrene solvated in dendrimer solution, to 1.60, the value characteristic of pyrene in water. Pyrene release from the interior of dendrimers was confirmed by fluorescence quenching when sodium iodide was added, since NaI does not affect the emission of dendrimer-solubilized pyrene. Finally, fluorescence quenching was used to locate the solubilization sites of pyrene within the dendrimer microcavities. These sites are close to the core of the dendrimer, near the tertiary amino groups which are also responsible for quenching the fluorescence of the dendrimer-bound pyrene.
Macromolecules, 2004
Protected Newkome-type second-generation dendrimers (based on Lin's amine) were synthesized with a pyrene moiety attached to the core. The photophysical property in aqueous solution of the protected dendrimers shows self-association behavior in water. Pyrene excimer emission at 475 nm is observed in water even at very low concentrations of protected dendrimer (ca. 5 × 10-8 M). This emission band is absent in other solvents even up to a concentration of 10-5 M. The corresponding unprotected dendrimer does not show the pyrene excimer fluorescence. The amide of pyrene butyric acid with tert-butylamine shows the formation of excimer, albeit with very low intensity. Quenching studies on the dendrimer with hydrophilic quencher iodide anion (I-) reveal that there is significant quenching of fluorescence intensity in the case of N-tert-butyl-4-pyren-1-ylbutyramide as compared to that of the pyrene-attached second-generation protected dendrimer. This shows that the pyrene moiety in the case of the protected dendrimer is significantly shielded from the surrounding.
Binding properties of polyamidoamine dendrimers
Journal of Applied Polymer Science, 2006
Dendrimers are globular, hyperbranched polymers possessing a high concentration of surface functional groups and internal cavities. These unique features make them good host molecules for small ligands. To reveal relationships between dendrimer size and its encapsulating properties, the interactions of the fourth and the sixth generations of polyamidoamine dendrimers (PAMAM G4 and PAMAM G6) with a fluorescent dye 1‐anilinonaphthalene‐8‐sulfonate (ANS) were studied. Because ANS is a fluorescent molecule and its fluorescence is very sensitive to changes in its microenvironment, it was possible to use spectrofluorometric methods to evaluate the interactions with dendrimers. A double fluorometric titration method was used to estimate a binding constant and the number of binding centers. There were two types of dendrimer binding centers characterized by different affinity towards ANS. For PAMAM G4, the values of Kb and n for low‐affinity and high‐affinity sites equaled to 2.6 × 105, 0.60...
Solvent Effect on Fluorescence Properties of Stilbene Dendrimer Surrounded by Benzyl-Ether Dendrons
Bulletin of the Chemical Society of Japan, 2015
The fluorescence maximum of the fourth generation of stilbene-cored dendrimer (trans-G4) was affected by solvent polarity. These results indicated that the core of even higher generation dendrimer was not isolated from solvent molecules and the environment of the dendrimer core is constructed by both surrounding dendron groups and penetrated solvent molecules.