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

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

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

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

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

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

Toward Plasmonic Biosensors Functionalized by a Photoinduced Surface Reaction

We present a method for efficient coupling of amine nucleophilic molecules of choice to a nanostructured gold surface via photoinduced surface chemistry. The method is based on photoactive self-assembled monolayers and can be used to functionalize localized surface plasmon resonance (LSPR) based biosensors with biorecognition motifs while reducing nonspecific binding via introduction of hydrophilic units. The photoactive linker molecule, 5-bromo-7-nitroindoline, couples nucleophilic molecules such as biotin ethylenediamine to a surface when exposed to UV-light. The specific, noncovalent recognition between biotin and streptavidin is used for demonstration of a simple biorecognition assay based on the LSPR sensing principle. By doing so, one can envision that the binding of any streptavidin fusion protein, being attached to specific spots at the gold surface, is monitored by an LSPR peak shift. Since the surface functionalization is based on a photoinduced reaction, this method can be used to functionalize the surface in a local and site-specific way, and biomedical applications such as drug-screening platforms, microarrays, solid support protein synthesis, and even single molecule experiments can be envisioned

Copper(II) Complexes with 4‑Carbomethoxypyrrolidone Functionalized PAMAM-Dendrimers: An EPR Study

The internal flexibility and interacting ability of PAMAM-dendrimers having 4-carbomethoxypyrrolidone-groups as surface groups (termed Gn-Pyr), which may be useful for biomedical purposes, and ion traps were investigated by analyzing the EPR spectra of their copper­(II) complexes. Increasing amounts (with respect to the Pyr groups) of copper­(II) gave rise to different signals constituting the EPR spectra at room and low temperature corresponding to different coordinations of Cu²⁺ inside and outside the dendrimers. At low Cu²⁺ concentrations, CuN₄ coordination involving the DAB core is preferential for G3- and G5-Pyr, while G4-Pyr shows a CuN₃O coordination. CuN₂O₂ coordination into the external dendrimer layer was also contributing to G3- and G4-Pyr spectra. The structures of the proposed copper–dendrimer complexes were also shown. G4-Pyr displays unusual binding ability toward Cu­(II) ions. Mainly the remarkably low toxicity shown by G4-Pyr and its peculiar binding ability leads to a potential use in biomedical fields

Complexes of Indomethacin with 4‑Carbomethoxy-pyrrolidone PAMAM Dendrimers Show Improved Anti-inflammatory Properties and Temperature-Dependent Binding and Release Profile

COX-2 inhibitors such as nonsteroidal anti-inflammatory drugs (NSAIDs) are the most common treatment for chronic inflammatory diseases like arthritis and atherosclerosis. However, they are associated with severe side effects such as cardiovascular events or stomach bleeding, due to coinhibition of other enzymes (COX1) and off-target accumulation. PAMAM dendrimers can solubilize lipophilic drugs and increase their circulation time; furthermore, PAMAM dendrimers seem to have some accumulation in inflammatory sides. Three different generations of 4-carbomethoxypyrrolidone (Pyr) surface-modified PAMAM dendrimers were complexed with the NSAID drug indomethacin, and their in-solution thermodynamic profiles were studied by means of NMR experiments. The binding stoichiometry was found dependent on solvent system and dendrimer generation. Larger dendrimers (G3-Pyr) were found to bind indomethacin through entropy driven binding mode, while G1-Pyr and G2-Pyr expressed an enthalpy driven complex formation, which means that the binding constants have a generational temperature dependency. G1/2-Pyr showed reduced binding with increasing temperature, which could be important for drug release at inflammatory sites, which have, in general, elevated temperatures. In vitro studies elucidated that the indomethacin drug remained its activity when delivered as a dendrimer–indomethacin complex. A slight reduction in toxicity profile was noticed for G2/G3-Pyr-indomethacin dendrimers. Both free indomethacin and dendrimer–indomethacin complex inhibited a variety of pro-inflammatory cytokines in LPS treated cells. However, only the indo–dendrimer complexes showed a significant reduction of IL-1β in LPS-treated THP-1 cells, which was not present in the control with free indomethacin