title: Orientation modulation of a synthetic polypeptide in self-assembled monolayers: a TOF-SIMS study.
abstract: Structure and orientation of molecules are key properties of functionalized surfaces. Using time-of-flight secondary ion mass spectrometry (TOF-SIMS), here we investigate how to modulate these parameters upon the immobilization process varying the conditions of self-assembly. The molecule of interest, a template-assembled synthetic protein (TASP), consists of a central peptide ring with orthogonally arranged residues. Thioalkane chains allow the directed self-assembly of the molecule on a gold surface; four serine residues on the opposite side of the ring can be used as anchoring sites for various functional sensing molecules. The TASP conformation and its orientation in self-assembled monolayers (SAMs) play a central role for the accessibility of these serine residues. To study the influence of the self-assembly conditions, two series of samples were prepared. Pure TASP monolayers of different surface densities are compared to mixed TASP/alkanethiol monolayers prepared by sequential adsorption varying sequence and particular incubation times as well as by coadsorption modifying incubation times and TASP/alkanethiol mass ratios. Switching the TASP orientation from a state where the molecules are lying flat on the surface to an upright orientation turned out to be possible by inserting the TASP into a preformed alkanethiol monolayer of an appropriate surface density. This study demonstrates that TOF-SIMS is an excellent tool not only to investigate the surface composition, but also the molecular structure of functionalized surfaces.
authors.affiliation: Laboratory of Physical Chemistry of Polymers and Membranes (LCPPM), Institute of Biomolecular Sciences (ISB), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Leufgen
authors.forename: Manfred
authors.initials: M
authors.lastname: Mutter
authors.forename: Horst
authors.initials: H
authors.lastname: Vogel
authors.forename: Wilfried
authors.initials: W
authors.lastname: Szymczak
mesh_terms: D013058:Mass Spectrometry / Q000379:methods; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: D010455:Peptides; D010456:Peptides, Cyclic; D013438:Sulfhydryl Compounds