Boryl Azides in 1,3-Dipolar Cycloadditions

The 1,3-dipolar cycloaddition reaction of boron azides with alkynes has been investigated experimentally and computationally. At room temperature pinBN₃ (pin = pinacolato) reacts with the strained triple bond of cyclooctyne with formation of an oligomeric boryl triazole. Alcoholysis of the oligomer yields the parent 4,5,6,7,8,9-hexahydro-2<i>H</i>-cyclooctatriazole, which could be characterized as a hydrate by X-ray crystallography. A computational analysis of the reaction of tri- and tetracoordinate boron azides R₂BN₃ (R = H, Me, pin, cat; cat = catecholato) and <i>I</i>Me·H₂BN₃ (<i>I</i>Me = 2,6-dimethylimidazole-2-ylidene) reveals significant differences in the reactivity depending on the coordination number: tricoordinate boron azides behave as type II 1,3-dipoles, while the tetracoordinate <i>I</i>Me·H₂BN₃ is an electron-rich 1,3-dipole (type I) that strongly prefers reactions with electron-poor alkynes

TtOmp85, a β‑Barrel Assembly Protein, Functions by Barrel Augmentation

Outer membrane proteins are vital for Gram-negative bacteria and organisms that inherited organelles from them. Proteins from the Omp85/BamA family conduct the insertion of membrane proteins into the outer membrane. We show that an eight-stranded outer membrane β-barrel protein, TtoA, is inserted and folded into liposomes by an Omp85 homologue. Furthermore, we recorded the channel conductance of this Omp85 protein in black lipid membranes, alone and in the presence of peptides comprising the sequence of the two N-terminal and the two C-terminal β-strands of TtoA. Only with the latter could a long-living compound channel that exhibits conductance levels higher than those of the Omp85 protein alone be observed. These data support a model in which unfolded outer membrane protein after docking with its C-terminus penetrates into the transmembrane β-barrel of the Omp85 protein and augments its β-sheet at the first strand. Augmentation with successive β-strands leads to a compound, dilated barrel of both proteins