Quasi-Elastic Light Scattering of Platinum Dendrimer-Encapsulated Nanoparticles

Abstract

Platinum dendrimer-encapsulated nanoparticles (DENs) containing an average 147 atoms were prepared within sixth-generation, hydroxyl-terminated poly(amidoamine) dendrimers (G6-OH). The hydrodynamic radii (R(h)) of the dendrimer/nanoparticle composites (DNCs) were determined by quasi-elastic light scattering (QLS) at high (pH ∼10) and neutral pH for various salt concentrations and identities. At high pH, the size of the DNC (R(h) ∼4 nm) is close to that of the empty dendrimer. At neutral pH, the size of the DNC approximately doubles (R(h) ∼8 nm) whereas that of the empty dendrimer remains unchanged. Changes in ionic strength also alter the size of the DNCs. The increase in size of the DNC is likely due to electrostatic interactions involving the metal nanoparticle.

Dendrimer-encapsulated nanoparticles: New synthetic and characterization methods and catalytic applications

“…We also used QLS to determine the hydrodynamic radius of G6-OH(Pd 147 ), and under similar solution conditions the result (3.3 AE 0.3 nm) was the same as determined by PFGSE NMR. 95 Similar results were obtained for G6-OH(Au 147 ) (3.2 AE 0.2) and G6-OH(Pt 147 ) (4.0 AE 0.2 nm). 95 However, under certain solution conditions, primarily around neutral pH, the hydrodynamic radius of G6-OH(A 147 ) (A ¼ Pd, Au and Pt) was found to nearly double, even though the size of the empty dendrimer (G6-OH) and the precursors (for example, G6-OH(Pt 2+ ) 147 ) maintained a normal radius of around 3.5 nm.…”

“…95 The PFGSE NMR results indicated a radius of 2.0 AE 0.2 nm for both G4-OH and G4-OH(Pd 55 ), 20 and a radius of 3.3 AE 0.3 nm for G6-OH and G6-OH(Pd x ) (x ¼ 55, 147, 200, 250).…”

“…The final evidence for encapsulation was demonstrated using two techniques that measure changes to the hydrodynamic radius of the dendrimer after nanoparticle formation: pulsedfield gradient spin-echo (PFGSE) NMR 20,94 and quasi-elastic light scattering (QLS). 95 The PFGSE NMR results indicated a radius of 2.0 AE 0.2 nm for both G4-OH and G4-OH(Pd 55 ), 20 and a radius of 3.3 AE 0.3 nm for G6-OH and G6-OH(Pd x ) (x ¼ 55, 147, 200, 250). 94 If the nanoparticle is truly encapsulated within the dendrimer, then the hydrodynamic radius of the dendrimer should not be affected by its presence.…”

“…95 However, under certain solution conditions, primarily around neutral pH, the hydrodynamic radius of G6-OH(A 147 ) (A ¼ Pd, Au and Pt) was found to nearly double, even though the size of the empty dendrimer (G6-OH) and the precursors (for example, G6-OH(Pt 2+ ) 147 ) maintained a normal radius of around 3.5 nm. Importantly, there was no indication of aggregation in the TEM analysis of G6-OH(A 147 ) (A ¼ Pd, Au and Pt).…”

In Situ Structural Characterization of Platinum Dendrimer-Encapsulated Oxygen Reduction Electrocatalysts

“…The Pt DEN system has been studied extensively, and the results obtained here are consistent with those published previously. 14,15,33,34,38,39 The Pt DENs were characterized electrochemically using a standard three-electrode cell and a polished GCE working electrode. Immobilization of the DENs onto the GCE was achieved using a previously published method.…”