The association constants obtained from fitting of the ITC-data, along with calculated enthalpy increases.

<p>The association constants obtained from fitting of the ITC-data, along with calculated enthalpy increases.</p

ITC-binding curve of 2-naphthoate, showing the best fit.

<p>The ITC raw data was treated by blank subtraction (titration of guest into water).</p

Stacked ¹H-NMR spectra of different ratios of 3-hydroxy-2-naphthoate incubated with a 1 mM G4 1-(4-carbomethoxy) pyrrolidone dendrimer in D₂O.

<p>Stacked ¹H-NMR spectra of different ratios of 3-hydroxy-2-naphthoate incubated with a 1 mM G4 1-(4-carbomethoxy) pyrrolidone dendrimer in D₂O.</p

Guest-Host Chemistry with Dendrimers—Binding of Carboxylates in Aqueous Solution

<div><p>Recognition and binding of anions in water is difficult due to the ability of water molecules to form strong hydrogen bonds and to solvate the anions. The complexation of two different carboxylates with 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers was studied in aqueous solution using NMR and ITC binding models. Sodium 2-naphthoate and sodium 3-hydroxy-2-naphthoate were chosen as carboxylate model compounds, since they carry structural similarities to many non-steroidal anti-inflammatory drugs and they possess only a limited number of functional groups, making them ideal to study the carboxylate-dendrimer interaction selectively. The binding stoichiometry for 3-hydroxy-2-naphthoate was found to be two strongly bound guest molecules per dendrimer and an additional 40 molecules with weak binding affinity. The NOESY NMR showed a clear binding correlation of sodium 3-hydroxy-2-naphthoate with the lyophilic dendrimer core, possibly with the two high affinity guest molecules. In comparison, sodium 2-naphthoate showed a weaker binding strength and had a stoichiometry of two guests per dendrimer with no additional weakly bound guests. This stronger dendrimer interaction with sodium 3-hydroxy-2-naphthoate is possibly a result of the additional interactions of the dendrimer with the extra hydroxyl group and an internal stabilization of the negative charge due to the hydroxyl group. These findings illustrate the potential of the G4 1-(4-carbomethoxy) pyrrolidone dendrimer to complex carboxylate guests in water and act as a possible carrier of such molecules.</p></div

Interactions of Functionalized PAMAM Dendrimers with Model Cell Membranes Studied via Spin-Labeling Technique

Polyamidoamine (PAMAM) dendrimers are exploited as drug carriers in various biomedical research fields, especially cancer therapy. The present study analyzes the interactions occurring between differently functionalized PAMAM dendrimers, namely, amine, acetamide, and 3-methoxy-carbonyl-5-pyrrolidonyl (“pyrrolidone”), and model membranes, namely, sodium dodecyl sulfate (SDS), sodium hexadecylsulfate (SHS) micelles, and egg-lecithin liposomes. For this purpose, the dendrimers were spin-labeled with the 3-carbamoyl-PROXYL radical. 1H-NMR spectra allowed the verification not only that labeling was successful but also that acetamide and (even more so) pyrrolidone functions shield the proton signals from the influence of the neighboring nitroxide groups. The computer-aided analysis of the electron paramagnetic resonance (EPR) spectra showed that the dendrimers with the acetamide function largely (60%) entered the SDS–micelles interface, while the amino-dendrimer electrostatically interacted with both the SDS and SHS surface forming dendrimer aggregates in solution. The pyrrolidone-dendrimers showed an intermediate behavior between those with the amino and acetamide functions. The acetamide- and pyrrolidone-dendrimers weakly interacted with the lecithin liposome surface, with a synergy between hydrophilic and hydrophobic interactions. Conversely, liposomes/amino-dendrimers interactions were quite strong and led to dendrimer aggregation at the liposome surface in solution. This information showed that acetamide- and pyrrolidone-dendrimers may be used as good alternatives to amino-dendrimers for drug delivery

The two model guests illustrated within a G4 1-(4-carbomethoxy) pyrrolidone dendrimer.

<p>The two model guests illustrated within a G4 1-(4-carbomethoxy) pyrrolidone dendrimer.</p

ITC-binding curve of 3-hydroxy-2-naphthoate, showing the best fit.

<p>The ITC raw data was treated by blank subtraction (titration of guest into water).</p

The best fit obtained for the ¹H-NMR-titration of sodium 2-naphthoate into the PyrG4 dendrimer in aqueous solution.

<p>The calculated binding constant corresponds to K_<i>a</i> = 5.35±0.7 M^-1 for <i>n</i> = 2 carboxylates.</p

2D-NOE-spectrum showing a significant correlation between sodium 3-hydroxy-2-naphthoate and the G4 1-(4-carbomethoxypyrrolidone) PAMAM-dendrimer.

<p>2D-NOE-spectrum showing a significant correlation between sodium 3-hydroxy-2-naphthoate and the G4 1-(4-carbomethoxypyrrolidone) PAMAM-dendrimer.</p

Photophysical Properties of Fluorescent Core Dendrimers Controlled by Size

A series of different generation PAMAM dendrimers with sulforhodamine B covalently attached to the dendrimer core was investigated regarding their optical properties. Steady-state and time-resolved spectroscopic techniques were used to determine the size influence of the dendrimers on the photophysical behavior of the luminescent core. New blue emissive species were formed as the generation increased from zero to four. The growth of the dendritic branches resulted in a rise of fluorescence quantum yield and fluorescence lifetime values. Rotational correlation times were used to determine the hydrodynamic diameters of the fluorescent-core dendrimers, and good accordance was found with the values previously reported for unlabeled PAMAM dendrimers, which makes them potentially suitable diagnostic tools for biomedical tracing