Noradrenaline and a Thiol Analogue on Gold Surfaces: An Infrared Reflection-AbsorptionSpectroscopy, X-ray Photoelectron Spectroscopy, and Near-Edge X-ray Absorption FineStructure Spectroscopy Study

Self-assembled monolayers and multilayers of a noradrenaline analogue (Nor-Pt) on gold substrates as wellas multilayers of noradrenaline have been investigated by means of the molecular orientation, themolecule-surface interaction, the molecular composition and the functional group availability for furtherbiointeraction processes, using X-ray photoelectron spectroscopy (XPS), infrared reflection-absorptionspectroscopy (IRAS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. A chemicalshift (1.7 eV) of the S 2p peak to lower binding energies is observed, in the XPS spectrum, indicating thatthe Nor-Pt molecules are chemisorbed onto the gold substrate. The IR results show that Nor-Pt adsorbate hasthe CdO stretching vibration modes parallel oriented relative to the gold substrate. The average tilt angleof the aromatic ring relative to the gold surface normal is determined to be approximately 51°, based on theNEXAFS measurements on Nor-Pt monolayers. The experimental results and assignments are supported withtheoretical studies where we use the building block principle in the spectral analysis and compare with themeasurements of noradrenaline and Nor-Pt. The theoretical calculations are shown to be useful; for angledependence NEXAFS studies as resonances with fully π* or σ* character are preferred for correct analysis.