Structure Tuning of Electrostatically Self‐Assembled Nanoparticles through pH: The Role of Charge Ratio

Abstract

Systems that can be controlled through external triggers are of interest for a variety of applications from medicine to energy conversion. Here, the effects of pH on the electrostatic self‐assembly of generation four poly(amidoamine) dendrimers and a divalent azo dye, keeping constant the charge ratio, are discussed. Nanoparticles stabilized by an excess of dendrimer charge form at 3.5 ≤ pH ≤ 8.5. The nanoparticle structure strongly depends on pH: at 7 ≤ pH ≤ 8.5, where only the dendrimer primary amines are protonated, spherical particles form, while at 3.5 ≤ pH < 7 where also the tertiary amines are protonated, cylinders form. Not only the nanoparticle structure but also the interaction of the molecular building blocks is controlled by pH: the dye stacking changes and the twist angle of the dye molecules increases as the pH decreases. Results are related to changes in the dye–dendrimer and dye–dye interaction, in particular spherical nanoparticles are formed when the interaction is small. Finally, the structures at different pH and constant charge ratio are compared to results at constant loading ratio to understand the overall role of the pH in electrostatic self‐assembly. A pH‐responsive shape is of great interest, for example, for drug delivery.

Dendrimer‐Based Polyion Complex Vesicles: Loops Make Loose

“…Possibly, formation of the PEO loop may hamper the full charge complexation between the PSS and PAMAM dendrimers, and this may also lead to deviation of the charge ratio at PMC. [33] The assemblies obtained at f +/− = 0.8 display a hydro-dynamic radius (R h ) of ≈55 nm with a narrow size distribution (Figure 1b), a neutralized surface (Figure S8a, Supporting Information), and spherical morphology as evidenced by the angle-independent self-diffusion coefficient D (Figure S8b, Supporting Information). TEM and Cryo-TEM images in Figure 1c confirm that the particles are well-defined vesicles with an estimated diameter around 110 nm.…”

Functional Nano-Objects by Electrostatic Self-Assembly: Structure, Switching, and Photocatalysis

“…At pH > 7 only the outer primary amine groups of the dendrimers are protonated, and the resulting particles are spherical, whereas at lower pH the ternary amines are protonated additionally and rod-like structures form. For stable particles, there has to be an excess of dendrimer charges ( Mariani et al, 2017b ). PAMAM dendrimers with the trivalent dye Ar27 form pH-switchable capsules (see section Switchable Structures) ( Gröhn et al, 2010 ).…”

One‐Pot Synthesis of Highly Fluorescent Poly(methacrylic acid)‐Capped Silver Nanoclusters for the Specific Detection of Iron(II)

“…One thing that deserves mentioning in the nanocluster synthesis is that scaffolds are used to avoid particle aggregation. Such types of stents as dendrimers, DNA, polyelectrolytes, and polymers, are used in synthesis of AgNCs . Methacrylic acid (PMAA) is an appropriate and ideal template for enhancing the high‐quality AgNCs by diverse methods.…”

“…Such types of stents as dendrimers, DNA, polyelectrolytes, and polymers, are used in synthesis of AgNCs. [9][10][11] Methacrylic acid (PMAA) is an appropriate and ideal template for enhancing the high-quality AgNCs by diverse methods. Up to now, most reports are built on the research of fluorescence emission like the UV irradiation synthesis of AgNCs.…”