title: Spectrophotometric titration of bimetallic metal cation binding in polyamido(amine) dendrimer templates.
abstract: Spectrophotometric titration and a binding isotherm were used to accurately assess the loading capacity of generation four polyamido(amine) (PAMAM) dendrimer templates with terminal alcohol groups (G4-OH). Preparation of bimetallic G4-OH dendrimer-encapsulated metal nanoclusters (DENs) necessitates knowledge of the precise metal-ion binding capacity. The binding of metal ions such as Pt(2+) and Pd(2+) has proven difficult to assess via UV-vis spectroscopy because the absorbance shifts associated with metal-ion binding within the dendrimer template are masked by the absorbance of the PAMAM dendrimer itself. In contrast, the binding of Cu(2+) to G4-OH PAMAM dendrimer results in a strong, distinct absorption band at 300 nm, making UV-vis spectrophotometric titration with copper straightforward. Here we use copper binding as a means to assess the number of binding sites remaining within the PAMAM G4-OH dendrimer after the complexation of a specified molar excess of Pd(2+) or Pt(2+). In addition, we use a binding isotherm to mathematically estimate the loading capacity of the dendrimer in each case. The loading capacities for M(2+) in the G4-OH dendrimer were found to be ∼16 for copper alone, ∼21 for copper combined with palladium, and ∼25 for copper combined with platinum.
authors.affiliation: Department of Chemistry, University of Central Arkansas, 201 Donaghey Avenue, Conway, Arkansas 72035, United States.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Marvin
authors.forename: Justin A
authors.initials: JA
authors.lastname: Johnson
authors.forename: Stacia E
authors.initials: SE
authors.lastname: Rodenbusch
authors.forename: Lucy
authors.initials: L
authors.lastname: Gong
authors.forename: David A
authors.initials: DA
authors.lastname: Vanden Bout
authors.forename: Keith J
authors.initials: KJ
authors.lastname: Stevenson
mesh_terms: D001665:Binding Sites; D002412:Cations; D003300:Copper / Q000737:chemistry*; D050091:Dendrimers / Q000737:chemistry*; D007700:Kinetics; D049329:Nanostructures / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods; D013499:Surface Properties; D013816:Thermodynamics; D017186:Titrimetry / Q000379:methods
chemical_list: D002412:Cations; D050091:Dendrimers; C104700:PAMAM Starburst; D010984:Platinum; D010165:Palladium; D003300:Copper