The effect of TEMPO-NH₂ on the signal intensity of G4-OH and G3.5-COONa.

<p>¹H NMR spectra of the G4-OH/TEMPO-NH₂ (a) and the G3.5-COONa/TEMPO-NH₂ (b) complexes in D₂O/d6-DMSO solutions (80/20, V/V), the molar ratio of TEMPO-NH₂ and dendrimer ranges from 0 to 64.</p

Increased concentration of TEMPO-COOH decreases the signal intensity of G4-NH₂.

<p>(a) ¹H NMR spectra of the G4-NH₂/TEMPO-COOH complexes in D₂O/d6-DMSO solutions (80/20, V/V), the molar ratio of TEMPO-COOH and G4-NH₂ ranges from 0 to 64. (b) The linewidth variations of G4-NH₂ peaks in ¹H NMR spectra during the titration experiment.</p

Molecular structures and proton labeling of PAMAM dendrimers.

<p>Amine-ternimated (a), hydroxyl-terminated (b) and carboxylate-terminated (c) PAMAM dendrimers.</p

Molecular structures of the three nitroxide spin probes (a) TEMPO-NH₂ (b) TEMPO-OH (c) TEMPO-COOH and structure chart of PAMAM dendrimers with three types of surface groups.

<p>Molecular structures of the three nitroxide spin probes (a) TEMPO-NH₂ (b) TEMPO-OH (c) TEMPO-COOH and structure chart of PAMAM dendrimers with three types of surface groups.</p

¹H NMR spectra of G3.5-COONa/TEMPO-COOH complexes.

<p>The molar ratio of TEMPO-COOH and G3.5-COONa ranges from 0 to 64. The solvent is D₂O/d6-DMSO (80/20, V/V).</p

Paramagnetic NMR Investigation of Dendrimer-Based Host-Guest Interactions

<div><p>In this study, the host-guest behavior of poly(amidoamine) (PAMAM) dendrimers bearing amine, hydroxyl, or carboxylate surface functionalities were investigated by paramagnetic NMR studies. 2,2,6,6-Tetramethylpiperidinyloxy (TEMPO) derivatives were used as paramagnetic guest molecules. The results showed that TEMPO-COOH significantly broaden the ¹H NMR peaks of amine- and hydroxyl-terminated PAMAM dendrimers. In comparison, no paramagnetic relaxation enhancement (PRE) was observed between TEMPO-NH₂, TEMPO-OH and the three types of PAMAM dendrimers. The PRE phenomenon observed is correlated with the encapsulation of TEMPO-COOH within dendrimer pockets. Protonation of the tertiary amine groups within PAMAM dendrimers plays an important role during this process. Interestingly, the absence of TEMPO-COOH encapsulation within carboxylate-terminated PAMAM dendrimer is observed due to the repulsion of TEMPO-COO- anion and anionic dendrimer surface. The combination of paramagnetic probes and ¹H NMR linewidth analysis can be used as a powerful tool in the analysis of dendrimer-based host-guest systems.</p></div

The effect of TEMPO-OH on the signal intensity of G4-NH₂.

<p>(a) ¹H NMR spectra of the G4-NH₂/TEMPO-OH complexes in D₂O/d6-DMSO solutions (80/20, V/V), the molar ratio of TEMPO-OH and G4-NH₂ ranges from 0 to 64. (b) The linewidth variations of G4-NH₂ peaks in ¹H NMR spectra during the titration experiment.</p

Comparison of TEMPO-COOH and acetic acid on the signal intensity of G3.5-COONa.

<p>(a) ¹H NMR spectra of the G3.5-COONa/acetic acid complexes in D₂O/d6-DMSO solutions (80/20, V/V), the molar ratio of acetic acid and G3.5-COONa from 0 to 64. (b) The linewidth variations of G3.5-COONa peaks in ¹H NMR spectra during the titration of G3.5-COONa with TEMPO-COOH and acetic acid.</p

Host–Guest Chemistry of Dendrimer–Cyclodextrin Conjugates: Selective Encapsulations of Guests within Dendrimer or Cyclodextrin Cavities Revealed by NOE NMR Techniques

In this study, G5 PAMAM dendrimer and α-, β-, γ-cyclodextrin (CD) conjugates were synthesized. Host–guest behaviors of the conjugates toward five guest molecules including sodium methotrexate (MTX), amantadine hydrochloride (ADH), sulfamethoxazole (SMZ), sodium deoxycholate (SDC), and sodium dodecyl sulfate (SDS) were analyzed by NOE NMR techniques. Among the five guest molecules, ADH only binds with β-CD in G5−β-CD, SDC shows higher priority to localize within the cavity of γ-CD in G5−γ-CD, while MTX exhibits selective encapsulation within the cavities of G5 dendrimer in G5−α-CD. SDS has high binding affinity with α-CD in G5−α-CD but forms a precipitate in the complex solution. SMZ shows simultaneous encapsulation within CDs (α-, β-, and γ-CD) or G5 in the presence of the three conjugates. The host behavior of G5–CD conjugates depends on CD cavity size, guest size, and hydrophobicity. The results obtained in this study are helpful in the optimization of dendrimer–CD conjugate-based drug delivery systems

Fast Screening of Dendrimer-Binding Compounds by Diffusion NMR Techniques

High-throughput screening of dendrimer-binding drugs is essential for the design and optimization of dendrimer-based drug delivery systems. In this study, pulsed gradient spin echo (PGSE) NMR was used for fast screening dendrimer-binding compounds using common amino acids as a screening pool. Diffusion coefficients of the amino acids before and after the addition of poly­(propylene imine) (PPI) dendrimer were used to rank the binding affinities of the amino acids to the dendrimer. Among the common amino acids, cysteine, glutamic acid, aspartic acid, and tryptophan show strong binding affinity to PPI dendrimer. Tryptophan forms inclusion complexes with PPI dendrimer through hydrophobic interactions, while other amino acids mainly bind with PPI dendrimer via ionic and hydrogen-bond interactions. The PGSE NMR-based screening method provides new insights into high-throughput screening of dendrimer-binding compounds and should facilitate the study of dendrimer-based host–guest systems