Platinum Ion Uptake by Dendrimers:  An NMR and AFM Study

Abstract

The reaction of generation 2 and generation 4 poly(amidoamine) (PAMAM) dendrimers with K2PtCl2 was studied by several NMR methods. The time dependency of the Pt(II) complexation was followed with 195Pt NMR for both dendrimers and the equilibrium product was further characterized with (1)H NMR, and indirectly detected 13C NMR, in the case of the generation 2 dendrimer. After 2 days, a black precipitate of Pt(0) was observed, half the original 195Pt signal was lost, and approximately 20% of the initial Pt(II) was coordinated to the tertiary and secondary nitrogens of the generation 2 dendrimer. The uptake of Pt(II) by the generation 4 dendrimer was much slower, consistent with the steric crowding of the surface groups on the generation 4 dendrimer compared to the more open generation 2. After 10 days, 80% of the Pt(II) was deep within the generation 4 dendrimer; the remaining 20% was unreacted or bound near the surface nitrogens of a single dendrimer. The location and time course of the platinum ion uptake by the dendrimers provides valuable insight into the formation of Pt(0) nanoparticles made in the presence of dendrimers as stabilizers, visualized by atomic force microscopy.

Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt−Cu Nanoparticles

“…Our study is consistent with studies from other labs in that UVvis spectra of mixtures of PtCl 4 2-and PAMAM dendrimers cease to change after approximately 2 days. 21,28,41,42 However, detailed 195 Pt NMR studies by Murphy and co-workers indicate that as many as 10 days may be required to equilibrate the various aqueous Pt(II) species with dendrimer amine groups. 41 Our current results are also consistent with Ploehn's studies, which indicate that, during borohydride reduction, Pt species are particularly mobile and can escape dendrimer interiors.…”

“…21,28,41,42 However, detailed 195 Pt NMR studies by Murphy and co-workers indicate that as many as 10 days may be required to equilibrate the various aqueous Pt(II) species with dendrimer amine groups. 41 Our current results are also consistent with Ploehn's studies, which indicate that, during borohydride reduction, Pt species are particularly mobile and can escape dendrimer interiors. 42 Transmission electron microscopy studies of these samples are complicated by the difficulties in obtaining sufficient contrast with the support and the relatively low electron density of Cu.…”

Evaluation of anionic half generation 3.5–6.5 poly(amidoamine) dendrimers as delivery vehicles for the active component of the anticancer drug cisplatin

“…Free cisplatin is known to react with guanosine/DNA in a relatively short time period (t 1/2 = 0.5-4 h) [29][30]. For our drug-dendrimer complexes the platinum release is significantly slower and in fact never goes to theoretical completion (see Table 1 [18], and these are likely to also be formed by our aquated cisplatin.…”

“…Previously dendrimers have been examined sporadically as delivery vehicles for several different types of platinum drugs and complexes [15][16][17][18][19][20][21][22]. These dendrimers have included PAMAM, polyglycerol [22], poly(propyleneimine) [23], and thiol-yne derived [21] dendrimers with the active components of both cisplatin [17] and oxaliplatin [16] and a novel DNA intercalating platinum complex [15].…”

PAMAM Dendrimer Templated Nanoparticle Catalysts

“…c Core -shell nanoparticles where [ ] = core metal(s) and ( ) = shell metal are an important consideration for this synthetic scheme. PdCl 4 2 − complexes quickly, while PtCl 4 2 − requires several days to react [35] , so, in practice, these syntheses likely involve sequential complexation of the ions with the more reactive complex binding fi rst. This method was employed for PtCu DENs, allowing PtCl 4 2 − to bind G5 -OH for 2 days before adding Cu(NO 3 ) 2 , which binds in minutes.…”