Data-driven Exploration of New Pressure-induced Superconductivity in PbBi2_2Te4_4 with Two Transition Temperatures

Candidates compounds for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were exhaustively searched by the high-throughput first-principles calculation from an inorganic materials database named AtomWork. We focused on PbBi$_2$Te$_4$ which has the similar electronic band structure and the same crystal structure with those of a pressure-induced superconductor SnBi2Se4 explored by the same data-driven approach. The PbBi$_2$Te$_4$ was successfully synthesized as single crystals using a melt and slow cooling method. The core level X-ray photoelectron spectroscopy analysis revealed Pb2+, Bi3+ and Te2- valence states in PbBi$_2$Te$_4$. The thermoelectric properties of the PbBi$_2$Te$_4$ sample were measured at ambient pressure and the electrical resistivity was also evaluated under high pressure using a diamond anvil cell with boron-doped diamond electrodes. The resistivity decreased with increase of the pressure, and two pressure-induced superconducting transitions were discovered at 3.4 K under 13.3 GPa and at 8.4 K under 21.7 GPa. The data-driven approach shows promising power to accelerate the discovery of new thermoelectric and superconducting materials

Influences of liquid fuel atomization and flow rate fluctuations on spray combustion instabilities in a backward-facing step combustor

Combustion instabilities occurring in spray combustion fields inside a backward facing step combustor have been investigated by performing large-eddy simulations (LES). In this study, the influence of fluctuations in the incoming oxidizer air velocity (caused by drastic pressure oscillations in the combustor during combustion instability) on the droplet diameter distribution (due to atomization) of the injected liquid fuel spray, as well as the influence of pressure oscillations on the fuel flow rate have been taken into consideration using appropriate models. For the temporal fluctuations in fuel droplet diameter distribution, a model for the Sauter Mean Diamter (SMD) of atomized droplets, obtained as a function of spray injection parameters and gas/liquid properties, is incorporated in the LES. Additionally, to consider the temporal fluctuations in fuel flow rate along with its phase difference with the pressure oscillations, a model derived from Bernoullis principle is proposed and employed in the LES. The objective is to examine in detail, the impacts of the fluctuations in fuel droplet diameter distribution and the fluctuations in fuel injection rate individually, as well as the impact of the mutual interaction of these two fluctuations, on the spray combustion instability characteristics. Results of the LES reveal that the temporal fluctuations in fuel droplet diameter distribution resulting from combustion instability, lead to a reduction in the intensity of pressure oscillations and hence the combustion instability’s strength. Additionally, the temporal fluctuations in liquid fuel flow rate strongly influence the intensity of spray combustion instability, and it is observed that the combustion instability intensity increases with the increase in phase difference between the fuel flow rate fluctuations and pressure oscillations. Furthermore, the effect of the temporal fluctuations in fuel droplet diameter distribution resulting in the reduction of combustion instability intensity, becomes more pronounced as the phase shift between the fuel flow rate fluctuations and pressure oscillations becomes larger. It is clarified that the above-mentioned behavior of spray combustion instability, results from the change in the correlation between heat release rate fluctuations and pressure oscillations near the combustor’s dump plane, which is caused by the change in the local residence time of fuel droplets and the local fuel droplet evaporation rate

Alterations in photosynthetic pigments and amino acid composition of D1 protein change energy distribution in photosystem II

AbstractThe marine cyanobacterium Prochlorococcus marinus accumulates divinyl chlorophylls instead of monovinyl chlorophylls to harvest light energy. As well as this difference in its chromophore composition, some amino acid residues in its photosystem II D1 protein were different from the conserved amino acid residues in other photosynthetic organisms. We examined PSII complexes isolated from mutants of Synechocystis sp. PCC 6803, in which chromophore and D1 protein were altered (Hisashi Ito and Ayumi Tanaka, 2011) to clarify the effects of chromophores/D1 protein composition on the excitation energy distribution. We prepared the mutants accumulating divinyl chlorophyll (DV mutant). The amino acid residues of V205 and G282 in the D1 protein were substituted with M205 and C282 in the DV mutant to mimic Prochlorococcus D1 protein (DV-V205M/G282C mutant). Isolated PSII complexes were analyzed by time-resolved fluorescence spectroscopy. Energy transfer in CP47 was interrupted in PSII containing divinyl chlorophylls. The V205M/G282C mutation did not recover the energy transfer pathway in CP47, instead, the mutation allowed the excitation energy transfer from CP43 to CP47, which neighbors in the PSII dimer. Mutual orientation of the subcomplexes of PSII might be affected by the substitution. The changes of the energy transfer pathways would reduce energy transfer from antennae to the PSII reaction center, and allow Prochlorococcus to acquire light tolerance

Identification of the basic amino acid residues on the PsbP protein involved in the electrostatic interaction with photosystem II

AbstractThe PsbP protein is an extrinsic subunit of photosystem II (PSII) that is essential for photoautotrophic growth in higher plants. Several crystal structures of PsbP have been reported, but the binding topology of PsbP in PSII has not yet been clarified. In this study, we report that the basic pocket of PsbP, which consists of conserved Arg48, Lys143, and Lys160, is important for the electrostatic interaction with the PSII complex. Our release-reconstitution experiment showed that the binding affinities of PsbP-R48A, -K143A, and -K160A mutated proteins to PSII were lower than that of PsbP-WT, and triple mutations of these residues greatly diminished the binding affinity to PSII. Even when maximum possible binding had occurred, the R48A, K143A, and K160A proteins showed a reduced ability to restore the rate of oxygen evolution at low chloride concentrations. Fourier transform infrared resonance (FTIR) difference spectroscopy results were consistent with the above finding, and suggested that these mutated proteins were not able to induce the normal conformational change around the Mn cluster during S1 to S2 transition. Finally, chemical cross-linking experiments suggested that the interaction between the N-terminus of PsbP with PsbE was inhibited by these mutations. These data suggest that the basic pocket of PsbP is important for proper association and interaction with PSII. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy

D139N mutation of PsbP enhances the oxygen-evolving activity of photosystem II through stabilized binding of a chloride ion

植物の光合成初期過程の酸素発生活性を向上させるアミノ酸変異を発見 --光合成・人工光合成の光エネルギー変換効率の向上へ期待--. 京都大学プレスリリース. 2022-08-18.Photosystem II (PSII) is a multi-subunit membrane protein complex that catalyzes light-driven oxidation of water to molecular oxygen. The chloride ion (Cl−) has long been known as an essential cofactor for oxygen evolution by PSII, and two Cl− ions (Cl-1 and Cl-2) have been found to specifically bind near the Mn4CaO5 cluster within the oxygen-evolving center (OEC). However, despite intensive studies on these Cl− ions, little is known about the function of Cl-2, the Cl− ion that is associated with the backbone nitrogens of D1-Asn338, D1-Phe339, and CP43-Glu354. In green plant PSII, the membrane extrinsic subunits—PsbP and PsbQ—are responsible for Cl− retention within the OEC. The Loop 4 region of PsbP, consisting of highly conserved residues Thr135–Gly142, is inserted close to Cl-2, but its importance has not been examined to date. Here, we investigated the importance of PsbP-Loop 4 using spinach PSII membranes reconstituted with spinach PsbP proteins harboring mutations in this region. Mutations in PsbP-Loop 4 had remarkable effects on the rate of oxygen evolution by PSII. Moreover, we found that a specific mutation, PsbP-D139N, significantly enhanced the oxygen-evolving activity in the absence of PsbQ, but not significantly in its presence. The D139N mutation increased the Cl− retention ability of PsbP and induced a unique structural change in the OEC, as indicated by light-induced Fourier transform infrared (FTIR) difference spectroscopy and theoretical calculations. Our findings provide insight into the functional significance of Cl-2 in the water-oxidizing reaction of PSII