Spectroscopic Investigations of Poly(Propyleneimine)Dendrimers Using the Solvatochromic Probe Phenol Blue and Comparisons to Poly(Amidoamine) Dendrimers

Abstract

The physical and chemical properties of PPI dendrimers' interior were investigated using the fluorescent, solvatochromic probe phenol blue. In aqueous solutions of each generation studied, two discrete dye populations were clearly observed. PPI dendrimers were shown to form a tight, nonpolar association with the vast majority of available dye, within the dendrimer interior, near the core. In the steady-state fluorescence emission spectra, a microenvironment of decreasing polarity in increasingly larger-generation PPI dendrimers (up to G3) was seen for the associated probe. Each of the remaining larger-generation dendrimers provided a microenvironment of essentially equal polarity. Fluorescence anisotropy values for phenol blue in the PPI dendrimers demonstrated the dye's sensitivity to the changing molecular volumes of the dendrimer generations. Model compounds that mimicked PPI's surface groups and branching moieties were used to better define the associated dye's location. The mimics further confirmed that phenol blue was associated inside the dendrimer, where it did not interact with the dendrimer surface groups. The comparison of amine-terminated PPI and PAMAM dendrimers clearly demonstrated the effects of their structural differences and the ability of phenol blue to have sensed those differences, including the initiator core length, branching unit length, and branching unit chemical composition.

Comparison of generation 3 polyamidoamine dendrimer and generation 4 polypropylenimine dendrimer on drug loading, complex structure, release behavior, and cytotoxicity

“…With regard to interior hydrophobicity, generation 4 PPI has a much more hydrophobic interior than generation 3 PAMAM, suggesting that PPI should be able to encapsulate more drugs in its interior pockets than PAMAM, 16,28 which is opposite to the results shown in Figure 1. For pocket volume, it is known that the length of branching units for constructing PPI dendrimer is much shorter than that for PAMAM dendrimer (4-bond versus 7-bond), thereby the size of generation 4 PPI is much smaller than that of generation 3 PAMAM Further, the amido groups in the scaffold of PAMAM (60 amido groups in each generation 3 PAMAM) may facilitate the encapsulation of phenylbutazone molecules via hydrogen bond interactions (N-H in the amido group as hydrogen bond donor and oxygen atoms in phenylbutazone as receptors).…”

“…14,15 The predominant difference in the structure of PAMAM and PPI is their interior pockets, ie, PAMAM has relatively polar pockets consisting of alkyl chain, tertiary amine, and amido groups, while PPI possesses nonpolar pockets consisting of alkyl chain and tertiary amine groups. 16 In addition, the length of branching units for PAMAM (seven bonds) is different from that of PPI dendrimer (four bonds), indicating that the size of PAMAM dendrimer is much larger than that of PPI dendrimer with an equivalent number of surface amine groups. These structural differences may have interesting physicochemical implications for the host behavior of PAMAM and PPI dendrimers.…”

“…The binding constants of dendrimer and phenol blue are an order of magnitude larger for PPI versus PAMAM with the same amount of surface groups, indicating fewer polar pockets of PPI dendrimer. 16 Dendrimer with a PPI core and a PAMAM shell encapsulates hydrophobic pyrene molecules in the PPI layers rather than in the PAMAM layers. 17 Also, PAMAM and PPI dendrimers exhibited distinct behaviors in their ionic interactions with negatively charged guests, such as vitamins C, B 3 , and B 6 .…”

Unimolecular micelles: supramolecular use of dendritic constructs to create versatile molecular containers

“…Numerous modifications of the surface coatings have appeared instilling a capping property thereby enhancing the host properties, e.g., a peripheral dansyl host surface and the hosted eosin guest [23]. Comparative unimolecular micellar studies of the amino-terminated PAMAMs and PPIs have also appeared demonstrating the importance of internal structure [24][25][26].…”

“…Attachment to a divalent core and conversion to the polycarboxylate 25 (Fig. 5) yielded dendrimers, which facilitated a 200 fold increase in pyrene (26) solubility in water compared with that of pure water without the dendrimer. Notably, use of sodium dodecyl sulfate (SDS; above cmc; 9 × 10 -3 M) for pyrene encapsulation resulted in only a 100-fold enhancement.…”