title: Surface-immobilized PAMAM-dendrimers modified with cationic or anionic terminal functions: physicochemical surface properties and conformational changes after application of liquid interface stress.
abstract: Functionalization of surfaces with highly branched dendrimer molecules has gained attractiveness for various applications because the number of functional groups exceeds those of surfaces functionalized with self-assembled monolayers. So far, little is known about the physicochemical properties of dendrimer functionalized surfaces, especially if the flexibility of dendrimer structure remains after covalent immobilization. Therefore, the purpose of this study was to covalently immobilize polyamidoamine (PAMAM) dendrimer molecules exhibiting terminal amine and carboxyl groups to silicon model surfaces and to explore their properties and structure at the solid-air and solid-liquid interface. Our results show that the surface free energy is higher for PAMAM coatings than for analogously terminated SAMs and also higher for carboxyl than amine functionalized coatings. Furthermore, several findings suggest that conformational freedom of the dendrimers was preserved after surface immobilization. Wet compared to dry PAMAMNH(2) surfaces show reduced hydrophilicity and increased contact angle hysteresis, whereas PAMAMCOOH surfaces become more hydrophilic and showed decreased hysteresis. Streaming current measurements showed an unexpected behavior for PAMAMCOOH surfaces in that they reveal a net positive surface charge over a wide pH range in spite of the carboxylated periphery. All of these results indicate a certain degree of masking, burrowing, back-folding and unfolding of functional groups upon environmental changes.
authors: Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany.
authors: Verena
authors: V
authors: Katzur
authors: Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany; Section Medical Materials and Technology, Department of Prosthodontics, University Hospital Tübingen, Osianderstr. 2-8, 72076 Tübingen, Germany.
authors: Mirjam
authors: M
authors: Eichler
authors: Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany.
authors: Erika
authors: E
authors: Deigele
authors: Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany.
authors: Christiane
authors: C
authors: Stage
authors: Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany.
authors: Peter
authors: P
authors: Karageorgiev
authors: Section Medical Materials and Technology, Department of Prosthodontics, University Hospital Tübingen, Osianderstr. 2-8, 72076 Tübingen, Germany.
authors: Jürgen
authors: J
authors: Geis-Gerstorfer
authors: Department of Operative Dentistry and Periodontology, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany.
authors: Gottfried
authors: G
authors: Schmalz
authors: Department of Oral Biology, School of Dental Medicine, State University of New York at Buffalo, 3435 Main Street, Buffalo, NY 14214, USA.
authors: Stefan
authors: S
authors: Ruhl
authors: Section Medical Materials and Technology, Department of Prosthodontics, University Hospital Tübingen, Osianderstr. 2-8, 72076 Tübingen, Germany.
authors: Frank
authors: F
authors: Rupp
authors: Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany. Electronic address: rainer.mueller@chemie.uni-regensburg.de.
authors: Rainer
authors: R
authors: Müller
mesh_terms: D000838:Anions; D002412:Cations; D050091:Dendrimers / Q000737:chemistry*; D049449:Luminescence; D008968:Molecular Conformation; D056951:Photoelectron Spectroscopy; D013055:Spectrophotometry, Infrared; D013499:Surface Properties
chemical_list: D000838:Anions; D002412:Cations; D050091:Dendrimers; C104700:PAMAM Starburst