Abstract
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.
Highlights
Dendrimers are a new class of nanoscopic containers and delivery devices [1,2,3,4]
Generation 4 (G4)-NH2, G4 EDA-cored and hydroxyl-terminated PAMAM dendrimer (G4-OH), and G3.5-COONa PAMAM dendrimers were used because these dendrimers have the same numbers of surface functionalities (64) and similar molecular size
Previous studies have demonstrated that ionic binding of anionic guests on the surface of amine-terminated PAMAM dendrimer shifts the resonance signals of dendrimer surface (Hb’ and Hd’) to higher frequencies, and hydrophobic encapsulation of guests within dendrimer interior pockets shifts the signals of dendrimer interior (Ha,d) to lower frequencies
Summary
Dendrimers are a new class of nanoscopic containers and delivery devices [1,2,3,4]. They have unique molecular architectures, spherical shapes, interior cavities, excellent monodispersity, and high density of surface functionalities [5,6,7,8,9,10,11]. Dendrimers have high solubility in various organic solvents and water, allowing miscellaneous modifications on dendrimer surface and in-depth characterization by different techniques [4] These physicochemical properties render dendrimers the applications in host-guest systems [12,13]. Meijer et al synthesized a dendritic box by modification of poly(propylene imine) (PPI) dendrimer surface with 9-fluorenylmethyloxycarbonyl (FMOC)-protected amino acids and the dendritc box was able to encapsulate guest molecules such as Rose Bengal and p-nitrobenzoic acid [15,16,17]. In a separate study by the Meijer group, palmitic acid modified PPI dendrimers were successfully used for the extraction of anionic xanthene dyes from aqueous solution [18] These pioneer studies significantly promote the interests of scientific community in dendrimer-based host-guest systems [12,19,20,21]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
