Spectroscopic characterization of polyamido amine dendrimers and their application in high-performance liquid chromatography

Carboxylate-terminated polyamido amine (PAMAM-CT) dendrimers were studied using two distinctly different methods---fluorescence spectroscopy and high performance liquid chromatography (HPLC). Dendrimers are monodisperse polymers with a regular, highly-branched, three-dimensional structure. Fluorescence spectroscopy was used in an effort to better understand how the unique dendritic architecture dictates its chemical and physical properties. Also, a "proof of concept" study looked at the ability of PAMAM-CT dendrimers as a viable alternative to micellar modified mobile phases in reversed-phase high performance liquid chromatography (HPLC) for the separation of polycyclic aromatic hydrocarbons (PAH). The PAMAM-CT dendrimers are considered "unimolecular" micelles because of their similar structural appearance, which makes them a logical substitute for micelles.; The fluorescence techniques of excitation emission matrices (EEMs) and lifetimes were employed to study the "intrinsic" fluorescence of PAMAM-CT dendrimers. The EEMs showed similar spectral profiles for all dendrimer generations (a broad peak with an excitation and emission maximum of 380 nm and 440 nm, respectively) and an overall increase in relative fluorescence emission with increasing generation. Three distinct, fairly discrete lifetimes were also recovered. These results implied that the dendrimer becomes densely packed with increasing generation. The weak, but detectable fluorescence, was most likely due to an n → pi* transition from the hydrogen bonded amido groups throughout the dendritic structure.; PAMAM-CT dendrimers were also used as mobile phase modifiers in reversed-phase HPLC to separate PAH. Two analytical columns were used in the study. PAMAM-CT dendrimer fragments modified the stationary phase of Column 1. The primary evidence for stationary phase modification was the elemental analysis of packing material exposed to dendrimer, which showed nitrogen content presumably from the dendrimer adsorbed onto the packing material. Chromatograms from Column 1 resulted in increased retention factors (k') with the addition of PAMAM-CT generation 2.5 (G2.5) to the mobile phase and decreased k' for G3.5 or G4.5 for the separation of the PAH mixture. These results agreed with reported shape changes that occur with increasing PAMAM-CT generation.; A commonality observed in both studies is that the two distinctly different techniques sensed the known dendritic shape change with increasing generation. The significance of this observation is that any application employing PAMAM-CT dendrimers will be strongly influenced by the generation used. (Abstract shortened by UMI.)...