The mechanism of bifunctional activation in the asymmetric aza-Baylis-Hillman (aza-BH) reaction was studied using NMR spectroscopic techniques. The reaction involves rate-limiting proton transfer in the absence of added protic species, but exhibits no autocatalysis. Brønsted acidic additives lead to substantial rate enhancements through acceleration of the elimination step. Furthermore, it was found that phosphine catalysts either alone or in combination with protic additives can cause racemization of the aza-BH product by proton exchange at the stereogenic center. This indicates that the spatial arrangement of a bifunctional chiral catalyst for the asymmetric aza-BH reaction is crucial not only for the stereodifferentiation within the catalytic cycle but also for the prevention of subsequent racemization.

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Antireflective coatings (ARCs) are applied to reduce surface reflections. We review coatings that reduce the reflection of the surface of the transparent substrates float glass, polyethylene terephthalate, poly(methyl methacrylate), and polycarbonate. Three main coating concepts exist to lower the reflection at the interface of a transparent substrate and air: multilayer interference coatings, graded index coatings, and quarter-wave coatings. We introduce and discuss these three concepts, and zoom in on porous quarter-wave coatings comprising colloidal particles. We extensively discuss the four routes for introducing porosity in quarter-wave coatings through the use of colloidal particles, which have the highest potential for application: (1) packing of dense nanospheres, (2) integration of voids through hollow nanospheres, (3) integration of voids through sacrificial particle templates, and (4) packing of nonspherical nanoparticles. Finally, we address the remaining challenges in the field of ARCs, and elaborate on potential strategies for future research in this area.