Crystal Structure of 9-Dibenzylsulfide-7,8-dicarba-nido-undecaborane 9-Bn2S-7,8-C2B9H11

The crystal structure of 9-dibenzylsulfide-7,8-dicarba-nido-undecaborane 9-Bn2S-7,8-C2B9H11 was determined by a single-crystal X-ray diffraction. One of the benzyl groups is located above the open face of the carborane cage with a short H···H distance (2.29 and 2.71 Å for two symmetrically independent molecules) between the BHB-bridging hydrogen atom of the carborane fragment and the ortho-CH group of the aromatic ring. Topological analysis has revealed the existence of a critical bond point with a calculated energy of −0.8 kcal/mol in accordance with an X-ray diffraction molecular geometry. The crystal packing analysis revealed that this benzyl group is also involved in π-stacking interactions, while another benzyl group participates in numerous weak H···π, H···H and van der Waals interactions.

Head-to-Tail Complex of Dishevelled and Axin-DIX Domains: Expression, Purification, Crystallographic Studies and Packing Analysis

Background: Head-to-tail polymerising domains generating heterogeneous aggregates are generally difficult to crystallise. DIX domains, exclusively found in the Wnt signalling pathway, are polymerising factors following this head-to-tail arrangement; moreover, they are considered to play a key role in the heterotypic interaction between Dishevelled (Dvl) and Axin, which are cytoplasmic proteins also positively and negatively regulating the canonical Wnt/β- catenin signalling pathway, but this interaction mechanism is still unknown. Objective: This study mainly aimed to clarify whether the Dvl2 and Axin-DIX domains (Dvl2-DIX and Axin-DIX, respectively) form a helical polymer in a head-to-tail way during complexation. Methods: Axin-DIX (DAX) and Dvl2-DIX (DIX), carrying polymerisation-blocking mutations, were expressed as a fusion protein by using a flexible peptide linker to fuse the C-terminal of the former to the N-terminal of the latter, enforcing a defined 1:1 stoichiometry between them. Results: The crystal of the DAX–DIX fusion protein diffracted to a resolution of about 0.3 nm and a data set was collected at a 0.309 nm resolution. The structure was solved via the molecular replacement method by using the DIX and DAX structures. A packing analysis of the crystal revealed the formation of a tandem heterodimer in a head-to-tail way, as predicted by the Wntsignalosome model. Conclusion: The results demonstrated that the combination of polymerisation-blocking mutations and a fusion protein of two head-to-tail polymerising domains is effective especially for crystallising complexes among heterologous polymerising proteins or domains.

Crystal packing analysis of in situ cryocrystallized 2,2,2-trifluoroacetophenone

Crystals of the liquid compound 2,2,2-trifluoroacetophenone (TFAP, C8H5F3O) were obtained using the state-of-art in situ cryocrystallization technique. TFAP crystallizes in the monoclinic space group C2/c, and its crystal structure is mainly stabilized by a set of C—H...F, C—H...O, F...F and F...O supramolecular contacts. The overall molecular arrangement shows the formation of molecular sheets parallel to the bc plane, which are in turn stacked along the a-axis direction. The weak interactions have been studied thoroughly, performing both a Hirshfeld surface analysis and theoretical calculations, to obtain the intermolecular interaction energies. A structural comparison of this compound with the previously reported substituted analogs was also carried out, showing a qualitative difference in terms of packing behaviour.

Uniaxial negative thermal expansion induced by moiety twisting in an organic crystal

Anomalous thermal expansion of a new diyn-diol molecule was studied by means of variable-temperature single-crystal X-ray diffraction. Analysis of the unit cell axes as a function of temperature shows that the material experiences uniaxial negative thermal expansion. Packing analysis of the crystal structures reveals twisting of the cyclopentyl moiety relative to the diyne spine with increasing temperature.