The evolution of eukaryotic life was predicated on the development of organelles such as mitochondria and plastids. During this complex process of organellogenesis, the host cell and the engulfed prokaryote became genetically codependent, with the integration of genes from the endosymbiont into the host nuclear genome and subsequent gene loss from the endosymbiont. This process required that horizontally transferred genes become active and properly regulated despite inherent differences in genetic features between donor (endosymbiont) and recipient (host). Although this genetic reorganization is considered critical for early stages of organellogenesis, we have little knowledge about the mechanisms governing this process. The photosynthetic amoeba Paulinella micropora offers a unique opportunity to study early evolutionary events associated with organellogenesis and primary endosymbiosis. This amoeba harbors a "chromatophore," a nascent photosynthetic organelle derived from a relatively recent cyanobacterial association (similar to 120 million years ago) that is independent of the evolution of primary plastids in plants (initiated similar to 1.5 billion years ago). Analysis of the genome and transcriptome of Paulinella revealed that retrotransposition of endosymbiont-derived nuclear genes was critical for their domestication in the host. These retrocopied genes involved in photoprotection in cyanobacteria became expanded gene families and were "rewired," acquiring light-responsive regulatory elements that function in the host. The establishment of host control of endosymbiont-derived genes likely enabled the cell to withstand photo-oxidative stress generated by oxygenic photosynthesis in the nascent organelle. These results provide insights into the genetic mechanisms and evolutionary pressures that facilitated the metabolic integration of the host-endosymbiont association and sustained the evolution of a photosynthetic organelle.

Na-rich antiperovskites are recently developed solid electrolytes with enhanced sodium ionic conductivity and show promising functionality as a novel solid electrolyte in an all solid-state battery. In this work, the sodium ionic transport pathways of the parent compound Na3OBr, as well as the modified layered antiperovskite Na4OI2, were studied and compared through temperature-dependent neutron diffraction combined with the maximum entropy method. In the cubic Na30Br antiperovskite, the nuclear density distribution maps at SOO K indicate that sodium ions hop within and among oxygen octahedra, and Br- ions are not involved. In the tetragonal Na4OI2 antiperovskite, Na ions, which connect octahedra in the oh plane, have the lowest activation energy barrier. The transport of sodium ions along the c axis is assisted by I- ions.

Materials with an abrupt volume collapse of more than 20% during a pressure-induced phase transition are rarely reported. In such an intriguing phenomenon, the lattice may be coupled with dramatic changes of orbital and/or the spin-state of the transition metal. A combined in situ crystallography and electron spin-state study to probe the mechanism of the pressure-driven lattice collapse in MnS and MnSe is presented. Both materials exhibit a rocksalt-to-MnP phase transition under compression with ca. 22% unit-cell volume changes, which was found to be coupled with the Mn2+(d(5)) spin-state transition from S = 5/2 to S = 1/2 and the formation of Mn-Mn intermetallic bonds as supported by the metallic transport behavior of their high-pressure phases. Our results reveal the mutual relationship between pressure-driven lattice collapse and the orbital/spin-state of Mn2+ in manganese chalcogenides and also provide deeper insights toward the exploration of new metastable phases with exceptional functionalities.

Employing particle swarm optimization (PSO) combined with first-principles calculations, we systemically studied high-pressure behaviors of hard CrB4. Our predictions reveal a distinct structural evolution under pressure for CrB4 despite having the same initial structure as FeB4. CrB4 is found to adopt a new P2/m structure above 196 GPa, another Pm structure at a pressure range of 261-294 GPa and then a Pmma structure beyond 294 GPa. Instead of puckering boron sheets in the initial structure, the high-pressure phases have planar boron sheets with different motifs upon compression. Comparatively, FeB4 prefers an I4(1)/acd structure over 48 GPa with tetrahedron B-4 units and a P2(1)3 structure above 231 GPa having equilateral triangle B-3 units. Significantly, CrB4 exhibits persistent metallic behavior in contrast with the semiconducting features of FeB4 upon compression. The varied pressure response of hard tetraborides studied here is of importance for understanding boron-rich compounds and designing new materials with superlative properties.

First-principles calculations were performed to understand the structural stability, synthesis routes, mechanical and electronic properties of diverse ruthenium nitrides. RuN with a new I-4m2 symmetry stabilized by pressure is found to be energetically preferred over the experimental NaCl-type and ZnS-type ones. The Pnnm-RuN2 is found to be stable above 1.1 GPa, in agreement with the experimental results. Specifically, new stoichiometries like RuN3 and RuN4 are proposed firstly to be thermodynamically stable, and the dynamical and mechanical stabilities of the newly predicted structures have been verified by checking their phonon spectra and elastic constants. A phase transition from P4/mmm-RuN4 to C2/c-RuN4 is also uncovered at 23.0 GPa. Drawn from bonding and band structure analysis, P4/mmm-RuN4 exhibits semi-metal-like behavior and becomes a semiconductor for the high-pressure C2/c-RuN4 phase. Meanwhile the P2(1)/c-RuN3 shows metallic feature. Highly directional covalent N-N and Ru-N bonds are formed and dominating in N-enriched Ru nitrides, making them promising hard materials.

An organic-inorganic halide CH3NH3SnI3 perovskite with significantly improved structural stability is obtained via pressure-induced amorphization and recrystallization. In situ high-pressure resistance measurements reveal an increased electrical conductivity by 300% in the pressure-treated perovskite. Photocurrent measurements also reveal a substantial enhancement in visible-light responsiveness. The mechanism under lying the enhanced properties is shown to be associated with the pressure-induced structural modification.

Strong spin orbital interaction (SOI) can induce unique quantum phenomena such as topological insulators, the Rashba effect, or p-wave superconductivity. Combining these three quantum phenomena into a single compound has important scientific implications. Here we report experimental observations of consecutive quantum phase transitions from a Rashba type topological trivial phase to topological insulator state then further proceeding to superconductivity in a SOI compound BiTeI tuned via pressures. The electrical resistivity measurement with V shape change signals the transition from a Rashba type topological trivial to a topological insulator phase at 2 GPa, which is caused by an energy gap close then reopen with band inverse. Superconducting transition appears at 8 GPa with a critical temperature T-C of 5.3 K. Structure refinements indicate that the consecutive phase transitions are correlated to the changes in the Bi-Te bond and bond angle as function of pressures. The Hall Effect measurements reveal an intimate relationship between superconductivity and the unusual change in carrier density that points to possible unconventional superconductivity.

We utilized the pair distribution function method to characterize the pressure-induced polyamorphic transition in Ce60Al20Cu20 and Ce55Al45 metallic glass at room temperature. Using synchrotron high-energy x-ray diffraction we collected scattering information from a large Q-space coverage, which in turn gave a high resolution g(r) that provided accurate local structure information. We observed a sudden change in compressibility and the nearest neighbor distance at 3.50-6.32 GPa for Ce60Al20Cu20 and 2.20-6.89 GPa for Ce55Al45. The origin of the volume collapse seemed to be pressure-induced qualitative changes in bond shortening that corresponded to different coordination spheres. The polyamorphic transitions in these two systems from low-density glass (LDG) to high-density glass (HDG) are associated with local atomic rearrangements. (C) 2016 Elsevier B.V. All rights reserved.

Boron carbide (B4C) is one of the hardest materials known to date. The extreme hardness of B4C arises from architecturally efficient B-12 or B11C icosahedrons and strong inter-icosahedral B-C bonding. As an excellent material for use in ballistic armor, the mechanic limit of B4C and possible phase transitions under extreme stress conditions are of great interest. Here we systematically explored the post-icosahedral solid structures of B4C under high pressure, using an unbiased structure search method. A new structure composed of extended framework of B and zigzag chains of C is predicted to be stable above 96 GPa. The new structure was predicted to have a high Vickers hardness of 55 GPa and simultaneously to retain a metallic ground state. The exceptional mechanical properties found in this structure are attributed to strong sp(3) covalent network formed under extreme pressure conditions. The predicted structure represents a new type of superhard boron carbides that form under high pressure without the presence of boron icosahedrons, which encourages experimental exploration in this direction.

Controlled nanotwinning is an effective way to enhance the mechanical properties of materials. Recent discovery of nanotwinned diamond converted from carbon nano-onions with high-density defects reveals that the presence of nanotwinned structures can increase the hardness of the product to exceed that of natural diamond by a surprisingly large margin. To understand the mechanism of nanotwinning, the microscopic transformation pathway from carbon nano-onions to nanotwinned diamond was investigated in the present study. We carried out a direct high-pressure high-temperature synthesis of nanotwinned diamond from onion carbon without high-density defects. The obtained nanotwinned diamond possesses an exceptionally high Vickers hardness of 215 GPa at 4.9 N. The transformation path was analyzed using aberration-corrected transmission electron microscopy (TEM) which suggests a martensitic process strongly influenced by the pressure-temperature conditions. Specifically, the appearance of {111} nanotwinned structure and stacking faults was determined by the characteristics of the onion shells, while the accumulation of the stress due to the sliding of the shells cause the crystal to re-align along the shear direction. These findings not only clarify the direct transformation mechanism from onion-like precursors to nanotwinned diamond, but also have broad implications for further exploration of new materials with exceptional properties. (C) 2017 Elsevier Ltd. All rights reserved.