The 3rd lesson in this tutorial course of SHELXL includes an overview of the instruction commands, a brief guide to their input formats, some Q&A concerning their applications, and a review of the treatments against disordered crystal solvents in recent papers.
We report the broadband light-scattering spectroscopy of a single crystal of a prototypical relaxor ferroelectric, Pb（Mg1/3Nb2/3）O3. A self-similar, “power-law central peak” has been observed, indicating the presence of a fractal in the crystal. A strong correspondence exists between the temperature dependence of the power exponent, and that of the reported behaviors of “polar nanoregions”, which consist of the fractal percolation cluster in the crystalline matrix of the material.
We report the first photoinduced single-crystal-to-single-crystal (SCSC) phase transition of a gold complex 1 that involves strengthening of intermolecular aurophilic interactions. This is also the first solid state photochromism of gold complexes. Upon UV irradiation, blue-emitting crystals 1B of aryl gold(I) isocyanide complex 1 transform into the weakly yellow-emitting crystals 1Y. X-ray diffraction analyses exhibit that the phase transition proceeds in an SCSC manner. After phase transition from 1B to 1Y, the intermolecular Au…Au separation decreases from 3.5041(14) to 3.2955(6) Å, resulting in a red-shifted emission. The photoinduced strengthening of the aurophilic interactions in the excited state initiates the change in the crystal structure from 1B to 1Y. Moreover, crystal 1B showed a photosalient effect: the 1B crystals jump upon irradiation with strong UV light owing to the phase transition into 1Y. The photoinduced strengthening of aurophilic interactions in the crystal generate the sudden mechanical movement of the crystal.
Botulinum neurotoxins (BoNTs), which are produced by Clostridium botulinum, are the most potent toxins, and cause the highly lethal food poisoning. BoNTs are produced as the assemblies with non-toxic components. Hemagglutinin (HA), one of the non-toxic components, has three biological activities: one is protecting BoNT from degradation in gastrointestinal tract, another is binding activity to carbohydrates and the other is disrupting of the epithelial barrier by direct binding to E-cadherin, which are critical for oral toxicity of BoNT. Here, we review the study on the crystal structure of type B whole HA. This structure reveals whole HA to be a huge triskelion-shaped molecule composed of 12 subcomponents, and biochemical data show that these functions of HA are employed at distinct sites.
Cycloparaphenylenes (CPPs), the shortest structural unit of armchair carbon nanotube (CNT), efficiently encapsulate various fullerenes, such as C60, C70, and La@C82, forming the supramolecular complexes, the shortest CNT-fullerene peapods. The structures of the complexes were unambiguously determined and elucidated at a molecular level by single crystal X-ray analysis combined with computational analyses. The results distinctly clarify factors determining the peapod formation, such as importance of van der Waals interaction, elastic character of CPPs, and electronic interaction between CPPs and fullerenes. These findings would increase the understandings of structures and properties of fullerene-peapods and be useful for the rational design of hierarchically ordered π-materials having concave-convex π-π interactions.
While aminoacyl-tRNAs are synthesized by aminoacyl-tRNA synthetase (aaRS), many methanogenic archaea lack Cys-tRNA synthetase, and Cys-tRNACys is synthesized through indirect pathway. It has been known that two enzymes are required in such indirect pathway. PhosphoseryltRNA synthetase (SepRS) attaches phosphoserine (Sep) to tRNACys to form Sep-tRNACys which is subsequently converted to Cys-tRNACys by Sep-tRNA : Cys-tRNA synthase (SepCysS). However, the catalytic efficiency of SepRS and SepCysS in vitro is very low, indicating the existence of unknown components. Here we present a translation factor SepCysE, essential for methanococcal Cys-tRNACys synthesis, and report a crystal structure of SepCysE in complex with SepCysS. Based on the structure, mutational analysis was carried out. Taken all results together, we propose that the CystRNACys synthesis is performed without release of the intermediate by a multienzyme complex named transsulfursome.