Manganese-based systems are considered as candidate electrocatalysts for the electrochemical oxygen evolution reaction (OER), because of their abundance in biochemical oxygen producing catalyst systems. In this work, the surface of metallic manganese was investigated in situ and operando in potentiodynamic cyclic voltammetry (CV) experiments and potentiostatic chronoamperometry (CA) experiments in NaOH. In both cases, the surfaces were initially reduced. At corresponding potentials, no oxide species can be detected by Raman spectroscopy, though electrochemical data and the absence of dissolution above the reversible potential for reactions of type Mn → Mn^II indicate that the material is passive. The CV shows anodic peaks at potentials in line with expectations on the basis of thermodynamic data for the oxidation to Mn₃O₄ and Mn₂O₃; the thickness of the surface layer increases by a few nm during these peaks, as evidenced by spectroscopic ellipsometry. Dissolution of Mn as evidenced by downstream electrolyte analysis by inductively coupled plasma mass spectrometry in a scanning flow cell (SFC-ICP-MS) of the electrolyte is negligible in the range of electrode potential vs. Ag|AgCl|3 M KCl, E_Ag|AgCl, up to 0.3 V. Remarkably, Raman spectra already show the occurrence of α-MnO₂ at E_Ag|AgCl > −0.25 V, which is ca. 0.5 V below the potential at which oxidation to MnO₂ is expected. This observation is attributed to disproportionation above a certain level of Mn^III. For E_Ag|AgCl > 0.4 V, dissolution sets in, at a constant layer thickness. Above the onset potential of the OER, at E_Ag|AgCl ≈ 0.6 V, SFC-ICP-MS analysis shows fast dissolution, and the oxide layer thickness is constant or increases. CA experiments during the OER show strong dissolution, and the re-formation of a strongly disordered, β-MnO₂-like oxide, which exists in a quasi-stationary state at the interface. Several CV cycles increase the dissolution per cycle and the fraction of α-MnO₂ on the surface which cannot be reduced. The high dissolution currents show that metallic Mn is hardly suitable as an OER catalyst, however, at least the Mn^IV oxides remain stationarily present in the system.

Tween (polysorbate) 20 and 80 are surfactants used for the development of parenteral protein drugs, due to their beneficial safety profile and stabilisation properties. To elucidate the mechanism by which Tween 20 and 80 stabilise proteins in aqueous solutions, either by a “direct” protein to surfactant interaction and/or by an interaction with the protein film at the air–water interface, we used spectroscopic (Infrared Reflection Absorption Spectroscopy, IRRAS) and microscopic techniques (Brewster Angle Microscopy, BAM) in combination with surface pressure measurements. To this end, the impact of both types of Tweens with regard to the displacement of the protein from the air–water interface was studied. As a model protein, human serum albumin (HSA) was used. The results for the displacement of the adsorbed HSA films by Tweens 20 and 80 can partially be understood on the basis of an orogenic displacement mechanism, which depends on the critical surface pressure of the adsorbed protein film. With increasing concentration of Tween in the sub-phase, BAM images showed the formation of different domain morphologies. IRRA-spectra supported the finding that at high protein concentration in the sub-phase, the protein film could not be completely displaced by the surfactants. Comparing the impact of both surfactants, we found that Tween 20 adsorbed faster to the protein film than Tween 80. The adsorption kinetics of both Tweens and the speed of protein displacement increased with rising surfactant concentration. Tween 80 reached significant lower surface pressures than Tween 20, which led to an incomplete displacement of the observed HSA film.

The effect of surface-attached PEG on the peptide-mediated fusion of liposomes was investigated. A complementary pair of coiled-coil forming lipidated peptides was introduced to two batches of small unilamellar liposomes separately. Upon mixing, efficient liposome membrane fusion was apparent when the liposomes were not decorated with pegylated lipids, however when the liposomes were pegylated the fusion was inhibited. A FRET-based fluorescence assay indicated that the fusion can be prevented effectively with less than two mole percent of pegylated lipid. DLS and CD spectroscopy were used to further evaluate the influence of pegylation on fusion. These data revealed that the pegylated lipids inhibit peptide complex formation and liposome docking, thereby preventing liposome fusion at the initial stage of the process. In contrast, when the PEG is not covalently attached to the liposome, no fusion inhibition was observed. Thus we conclude that the steric effect of the surface-bound PEG chains, which prevents sustained docking of liposomes, is the main cause of fusion inhibition.