The self-assembly process of racemic mixtures of right (L)-and left (D)-handed α-polyalanine molecules (DL-PA) with a length of 4 nm (27 alanine units) and a helix pitch of λ = 0.54 nm on HOPG was investigated by scanning tunneling microscopy and spectroscopy under ambient conditions. While enantiopure PA molecules adsorb in a hexagonally close-packed structure, we found heterochiral dimers with a rectangular unit cell for DL-PA. Despite the steric hindrance, the packing density of the DL-PA heterophase is increased by 25% compared to the enantiopure PA structure. Apparently, this is achieved by shifting D-and L-PA along their helical axis by λ/2 to enable the formation of intermolecular hydrogen bonds. Our results support Wallach's empirical rule also for molecular 2D layers on surfaces, where intermolecular interactions are mediated by dipolar forces and Hbonds rather than dispersing forces. Moreover, the α-helix structure of the PA molecules seems to be preserved; thus, electrostatic forces indeed play an important role for the formation and stabilization of the helical structure.

A carbapenem-based fluorogenic reagent has been developed to detect the activity of carbapenemases, exhibiting high specificity to all carbapenemases, including both metallo carbapenemases and serine carbapenemases, over other β-lactamases.

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