Interactions of metal particles with oxide supports can radically enhance the performance of supported catalysts. At the microscopic level, the details of such metal-oxide interactions usually remain obscure. This study identifies two types of oxidative metal-oxide interaction on well-defined models of technologically important Pt-ceria catalysts: (1) electron transfer from the Pt nanoparticle to the support, and (2) oxygen transfer from ceria to Pt. The electron transfer is favourable on ceria supports, irrespective of their morphology. Remarkably, the oxygen transfer is shown to require the presence of nanostructured ceria in close contact with Pt and, thus, is inherently a nanoscale effect. Our findings enable us to detail the formation mechanism of the catalytically indispensable Pt-O species on ceria and to elucidate the extraordinary structure-activity dependence of ceria-based catalysts in general.

Human immunodeficiency virus type 1 (HIV-1) buds from the cell as an immature particle requiring subsequent proteolysis of the main structural polyprotein Gag for morphological maturation and infectivity. Visualization of the viral envelope (Env) glycoprotein distribution on the surface of individual HIV-1 particles with stimulated emission depletion (STED) superresolution fluorescence microscopy revealed maturation-induced clustering of Env proteins that depended on the Gag-interacting Env tail. Correlation of Env surface clustering with the viral entry efficiency revealed coupling between the viral interior and exterior: Rearrangements of the inner protein lattice facilitated the alteration of the virus surface in preparation for productive entry. We propose that Gag proteolysis-dependent clustering of the sparse Env trimers on the viral surface may be an essential aspect of HIV-1 maturation.

The use of high numerical aperture immersion lenses in optical microscopy is compromised by spherical aberrations induced by the refractive index mismatch between the immersion system and the embedding medium of the sample. Especially when imaging >10 micro m deep into the specimen, the refractive index mismatch results in a noticeable loss of image brightness and resolution. A solution to this problem is to adapt the index of the embedding medium to that of the immersion system. Unfortunately, not many mounting media are known that are both index tunable as well as compatible with fluorescence imaging. Here we introduce a nontoxic embedding medium, 2,2'-thiodiethanol (TDE), which, by being miscible with water at any ratio, allows fine adjustment of the average refractive index of the sample ranging from that of water (1.33) to that of immersion oil (1.52). TDE thus enables high resolution imaging deep inside fixed specimens with objective lenses of the highest available aperture angles and has the potential to render glycerol embedding redundant. The refractive index changes due to larger cellular structures, such as nuclei, are largely compensated. Additionally, as an antioxidant, TDE preserves the fluorescence quantum yield of most of the fluorophores. We present the optical and chemical properties of this new medium as well as its application to a variety of differently stained cells and cellular substructures.