Entanglement of Square Nets in Covalent Organic Frameworks

Two entangled 2D square COFs have been synthesized from 4,4',4'',4'''-(9,9'-spirobi[fluorene]-2,2',7,7'-tetrayl)-tetrabenzaldehhyde (SFTB) and p-phenylenediamine (PPA) and benzidine (BZD) to form COF-38, [(SFTB)(PPA)2]imine and its isoreticular form COF-39, [(SFTB)(BZD)2]imine. We also report the single crystal electron diffraction structure of COF-39 and find that it is composed of mutually entangled 2D square nets (sql). These COFs represent the first examples of entangled 2D COF structures, which as we illustrate were made possible by our strategy of using the distorted tetrahedral SFTB building unit. SFTB overcomes the propencity of 2D COFs to stack through π-π stacking and allows for entanglements to form. This work adds significantly to the design principles of COFs.

New Phenotype and Mineralization of Biogenic Iron Oxide in Magnetotactic Bacteria

Many magnetotactic bacteria (MTB) biomineralize magnetite crystals that nucleate and grow inside intracellular membranous vesicles originating from invaginations of the cytoplasmic membrane. The crystals together with their surrounding membranes are referred to as magnetosomes. Magnetosome magnetite crystals nucleate and grow using iron transported inside the vesicle by specific proteins. Here, we tackle the question of the organization of magnetosomes, which are always described as constituted by linear chains of nanocrystals. In addition, it is commonly accepted that the iron oxide nanocrystals are in the magnetite-based phase. We show, in the case of a wild species of coccus-type bacterium, that there is a double organization of the magnetosomes, relatively perpendicular to each other, and that the nanocrystals are in fact maghemite. These findings were obtained, respectively, by using electron tomography of whole mounts of cells directly from the environment and high-resolution transmission electron microscopy and diffraction. Structure simulations were performed with the MacTempas software. This study opens new perspectives on the diversity of phenotypes within MTBs and allows to envisage other mechanisms of nucleation and formation of biogenic iron oxide crystals.

Forced laser nanostructuring of the surface of alumina-oxide ceramics

The possibility of creating quasiperiodic nanostructures on the surface of articles made of ceramic materials based on -Al2O3 under the action of a laser beam moved by a two-coordinate linear stepping motor (LSM) is shown. It is shown that the cause of the arising non-uniformity of heat release and convective instability of the molten layer are electromagnetic surface waves at the "conductor-insulator" interface, while the "conductor" is the melt layer. The discreteness of the laser beam movement due to LSD makes it possible to create a regular wave-like relief on the melt surface, which plays the role of an input diffraction structure for gen-erating a surface wave of TM polarization.

Hydrogen Bonds in Bis(1H-benzimidazole-κN3)cadmium(II) Dibenzoate: Hirshfeld Surface Analysis and AIM Perspective

The coordination complex bis(1H-benzimidazole-κN3)cadmium(II) dibenzoate has been synthesized and characterized by single crystal diffraction analysis. Cadmium center is six coordinated and formed a distorted octahedron coordinated geometry. The Hirshfeld analysis shows that in the dnorm-surface of the compound, there are dark red spots near the hydrogen-bonds acceptor and donor atoms, while intermolecular interactions result in faint-red spots. The AIM analysis was performed, there exist a BCP in each N(C)–H∙∙∙O hydrogen bond, the bond paths also can be seen, the |V(b)|/G(b) < 1 and the H(b) > 0, the interaction is indicative of being a closed shell. The TG results are consistent with the X-ray diffraction structure.

Magnetically Tunable Liquid Crystal-Based Optical Diffraction Gratings

We present a theoretical analysis of optical diffractive properties of magnetically tunable optical transmission gratings composed of periodically assembled layers of a polymer and a ferromagnetic liquid crystal (LC). The orientational structure of the LC layers as a function of an applied magnetic field is calculated by minimization of the Landau-de Gennes free energy for ferromagnetic LCs, which is performed numerically and also analytically by using the one-constant approximation and the approximations of the high and the low magnetic fields. Optical diffractive properties of the associated diffraction structure are calculated numerically in the framework of rigorous coupled-wave analysis (RCWA). The presented methodology provides a basis for designing new types of diffractive optical element based on ferromagnetic LCs and simulating their operation governed by the in-plane magnetic field.