Synthesis and Surface‐Spectroscopic Characterization of Photoisomerizable glyco‐SAMs on Au(111)

Abstract

Photoisomerizable glyco-SAMs (self-assembled monolayers), utilizing synthetic azobenzene glycoside derivatives were fabricated. The ultimate goal of this project is to assay the influence of the 3D arrangement of sugar ligands on cell adhesion, and eventually make cell adhesion photoswitchable. However, it is a prerequisite for any biological study on the spatial conditions of carbohydrate recognition, that photoisomerization of the surface molecules can be verified. Here, we employed IRRAS and XPS to spectroscopically characterize glyco-SAMs. In particular and unprecedented to date, we prove reversible E→Z→E isomerization of azobenzene glycoside-terminated SAMs.

Improving the Switching Capacity of Glyco‐Self‐Assembled Monolayers on Au(111)

“…The observed intensity change (Δ I exp =2 %) would thus indicate that only 3 % of the molecules switch to the cis isomer (Table ). Taking the steric demand of the TBDPS group into account, this result is consistent with previous studies on pure glyco‐SAMs.…”

“…Based on the rotationally averaged cis configuration C, this intensity change indicates that 7 % of the molecules on the surface switched to the cis isomer, corresponding to an increase of the switching capability of more than 100 % with respect to the original 7‐SAM . The performance of the self‐diluting SAM was thus superior to results for alkyl‐based glyco‐SAMs, the maximum switching capacity of which (using a diluent compound) was determined as 4 % . From Figure b, d, it is also clear that the cis / trans isomerization was fully reversible.…”

“…This, in turn, directly influences the intensity of the band in the surface IR spectrum because of the surface selection rule . The C aryl −O vibration is thus well suited for monitoring the cis / trans isomerization of the glyco‐SAMs adsorbed on Au(111) through IRRAS …”

“…Therefore, model systems, in particular so‐called glyco‐SAMs (self‐assembled monolayers), have been used to mimic the glycocalyx and to allow the investigation and interrogation of carbohydrate–protein interactions on surfaces. As a first step in this direction, we prepared glyco‐SAMs derived from molecules composed of an azobenzene moiety, an alkanethiol linker, and a mannoside head group, and investigated them by X‐ray photoelectron spectroscopy (XPS), near‐edge X‐ray absorption fine structure (NEXAFS), and infrared reflection‐absorption spectroscopy (IRRAS) . Here, photoisomerization of the azobenzene N=N double bond between two isomeric states ( trans and cis ) allows the reversible reorientation of a sugar ligand, if the molecule is properly adsorbed on a surface.…”

Schaltung bakterieller Adhäsion auf glycosylierten Oberflächen durch reversible Reorientierung der Kohlenhydratliganden

“…Um diesen Effekt zu untersuchen, haben wir vor kurzem ein System vorgestellt, welches die Kontrolle der Orientierung von Oberflächen-gebundenen Kohlenhydratliganden ermçglicht. [8] Dazu werden Azobenzolglycoside auf einer Goldoberfläche immobilisiert, um eine photoschaltbare Glyco-SAM (selbstanordnende Monoschicht) zu erzeugen. Derartige Systeme ermçglichen die Unterscheidung der Schalteffekte von anderen, mçglicherweise irreversiblen Nebeneffekten, wie beispielsweise der photolytischen Schädigung der Monoschicht.…”