New mechanistic insight in the thermal helix inversion of second-generation molecular motors

The introduction of dibenzocyclohepten-5-ylidene as part of a unidirectional light-driven molecular motor allows a more complete picture of the pathway of thermal helix inversion to be developed. The most stable conformation is similar to that found in related motors in that it has, overall, an anti-folded structure with the substituent at the stereogenic centre adopting an axial orientation. Photochemical cis/trans isomerisation at -40 degrees C results in the formation of an isomer in a syn-folded conformation with the methyl group in an axial orientation. This contrasts with previous studies on related molecular rotary motors. The conformation of the higher energy intermediate typically observed for this class of compound is the anti-folded conformation, in which the methyl group is in an equatorial orientation. This conformation is available through an energetically uphill upper half ring inversion of the observed photochemical product. However, this pathway competes with a second process that leads to the more stable anti-folded conformation in which the methyl group is oriented axially. It has been shown that the conformations and pathways available for second-generation molecular motors can be described by using similar overall geometries. Differences in the metastable high-energy species are attributable to the relative energy and position on the reaction coordinate of the transition states. Kinetic studies on these new molecular motors thus provide important insights into the conformational dynamics of the rotation cycle.     

Synthesis and Macrodomain Binding of Mono‐ADP‐Ribosylated Peptides

Mono‐ADP‐ribosylation is a dynamic posttranslational modification (PTM) with important roles in signaling. Mammalian proteins that recognize or hydrolyze mono‐ADP‐ribosylated proteins have been described. We report the synthesis of ADP‐ribosylated peptides from the proteins histone H2B, RhoA and, HNP‐1. An innovative procedure was applied that makes use of pre‐phosphorylated amino acid building blocks. Binding assays revealed that the macrodomains of human MacroD2 and TARG1 exhibit distinct specificities for the different ADP‐ribosylated peptides, thus showing that the sequence surrounding ADP‐ribosylated residues affects the substrate selectivity of macrodomains.     

Enantiopure Functional Molecular Motors Obtained by a Switchable Chiral‐Resolution Process

Molecular switches, rotors, and motors play an important role in the development of nano‐machines and devices, as well as responsive and adaptive functional materials. For unidirectional rotors based on chiral overcrowded alkenes, their stereochemical homogeneity is of crucial importance. Herein, a method to obtain new and functionalizable overcrowded alkenes in enantiopure form is presented. The procedure involves a short synthesis of three steps and a solvent‐switchable chiral resolution by using a readily available resolving agent. X‐ray crystallography revealed the mode of binding of the motor with the resolving agent, as well as the absolute configuration of the motor. ¹H NMR and UV/Vis spectroscopy techniques were used to determine the dynamic behavior of this molecular motor. This method provides rapid access to ample amounts of enantiopure molecular motors, which will greatly facilitate the further development of responsive molecular systems based on chiral overcrowded alkenes.     

Mass spectrometric and factor discriminant analysis of complex organic matter from the bacterial culture environment of Bacteroides gingivalis

Curie point evaporation and pyrolysis mass spectrometry were applied to the analysis of samples from cultures of Bacteroides gingivalis, an anaerobic microorganism isolated from the dental sulcus of human patients. Gaseous metabolites were sampled on ferromagnetic wires with an absorbent coating of activated carbon. Smears of bacteria and media after growth were analysed on normal ferromagnetic wires. The mass spectra from analyses at the Curie-point temperatures of 358°C and 510°C were examined with a specially adapted factor discriminant analysis program based on ARTHUR. The bacteria were characterized mainly by their volatile fractious. Mass spectra of the media after growth reflected physiological differences between the strains. The absorbent wire technique proved useful for evaluation of gaseous metabolites. Curie-point evaporation and pyrolysis mass spectrometry was found to be especially useful for preliminary screening of samples of organic matter from the various compartments of the bacterial environment.