In this issue, D. A. Malyshev and F. E. Romesberg review the expanded genetic alphabet. What potentially revolutionary applications do unnatural base pairs enable? In a Minireview, M. K. Brown et al. discuss syntheses of cyclobutane and cyclobutene by means of [2+2] cycloadditions. D. Trauner looks back at the life and achievements of the 1915 Nobel laureate Richard Willstätter in an Essay. The Highlight deals with hydroaminations of alkenes (M. Villa and A. Jacobi von Wangelin).

In the Communications section, J. G. Chen et al. descibe the direct epoxidation of propylene over stabilized Cu⁺ surface sites (see picture). M. R. Wasielewski et al. succeeded in the charge and spin transport in an organic molecular square and C. M. Niemeyer et al. report on site-directed, on-surface assembly of DNA nanostructures.

• Angewandte Chemie 41/2015: Essential Reading,
  Angew. Chem. Int. Ed. 2015, 54 (41).