Highly selective CO2 electrolysis in aqueous media by a water-soluble cobalt dimethyl-bipyridine complex.

A water-soluble Co complex with dimethyl-bipyridine ligands reduced CO2 to CO electrochemically with almost 100% selectivity at -0.80 V vs. NHE in an aqueous medium (pH 6.8) without an organic solvent. The reaction overpotential was 270 mV. A possible CO formation mechanism was discussed based on experiments and calculations.

Reversible CO2 Fixation and Release by a Trinuclear Zn(II) Cryptate Complex and Operando Analysis of the Complex Structure.

Metal complexes inspired by carbonic anhydrase (CA), which is a metalloenzyme containing Zn(II), have been investigated as alternatives for CO2 fixation systems operating under ambient temperature and pressure conditions. In this study, we designed a trinuclear Zn(II) cryptate complex (Zn3 L) and demonstrated rapid CO2 fixation with carbonation of CO2 using Zn3 L. The CO2 fixation performance of Zn3 L surpassed that of a standard CO2 absorbent, KOH(aq) solution, under conditions of the same solute concentration. In addition, the reaction achieved operation without support addition of base, which has been often required in systems of CA-inspired complexes. Fixed CO2 was released by protonating polyazacryptate ligand (L) and breaking the complex structure, and deprotonation of L induced the reconstruction of Zn3 L, allowing it to refix CO2 . This reaction mechanism was proposed based on the analysis of operando extended X-ray absorption fine structure spectroscopy. Zn3 L also demonstrated the ability to capture dilute CO2 from air, and the volume of CO2 captured by Zn3 L was approximately 2.6 times that captured by the KOH(aq) solution. Our Zn3 L exhibited three valuable properties: rapid CO2 fixation without a base, reversibility, and ability to capture dilute CO2 ; thus Zn3 L is a promising candidate as CO2 fixatives.

Toward Improving the Thermal Stability of Negative Electrode Materials: Differential Scanning Calorimetry and In Situ High-Temperature X-ray Diffraction/X-ray Absorption Spectroscopy Studies of Li2ZnTi3O8 and Related Compounds.

Negative electrode materials with high thermal stability are a key strategy for improving the safety of lithium-ion batteries for electric vehicles without requiring built-in safety devices. To search for crucial clues into increasing the thermal stability of these materials, we performed differential scanning calorimetry (DSC) and in situ high-temperature (HT)-X-ray diffraction (XRD)/X-ray absorption (XAS) up to 450 °C with respect to a solid-solution compound of Li4/3-2x/3ZnxTi5/3-x/3O4 with 0 ≤ x ≤ 0.5. The DSC profile of fully discharged x = 0.5 (Li2ZnTi3O8) with a LiPF6-based electrolyte could be divided into three temperature (T) regions: (i) T ≤ 250 °C for ΔHaccumi, (ii) 250 °C < T ≤ 350 °C for ΔHaccumii, and (iii) T > 350 °C for ΔHaccumiii, where ΔHaccumn is the accumulated change in enthalpy in region n. The HT-XRD/XAS analyses clarified that ΔHaccumi and ΔHaccumii originated from the decomposition of solid electrolyte interphase (SEI) films and the formation of a LiF phase, respectively. Comparison of the DSC profiles with x = 0 (Li[Li1/3Ti5/3]O4) and graphite revealed the operating voltage, i.e., amount of SEI films, and stability of the crystal lattice play significant roles in the thermal stability of negative electrode materials. Indeed, the highest thermal stability was attained at x = 0.25 using this approach.

Dynamic Structural Transformations in a Series of Zero-Strain Lithium-Ion Battery Materials: Almost Simultaneous Operando X-ray Diffraction and X-ray Absorption Spectroscopy on Li2ZnTi3O8 and Related Compounds.

A series of Li4/3-2x/3ZnxTi5/3-x/3O4 (LZTO) with 0 ≤ x ≤ 0.5 have received considerable interest as a negative electrode material for long-cycle-life lithium-ion batteries. However, their dynamic structural transformations under operating conditions have remained unknown, making an in-depth understanding essential for further improving the electrochemical performance. We, thus, performed almost simultaneous operando X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) studies on x = 0.125, 0.375, and 0.5. The x = 0.5 sample, Li2ZnTi3O8, indicated differences in the cubic lattice parameter between the discharge and charge reactions (δacs), corresponding to the reversible movement of Zn2+ ions between the tetrahedral and octahedral sites. δac was also observed for x = 0.125 and 0.375, although the capacity region exhibiting δac decreased with a decrease in x. For all of the samples, there is no significant difference in the nearest-neighbor distance of the Ti-O bond (dTi-O) between the discharge and charge reactions. We also demonstrated different structural transformations between the micro- (XRD) and atomic (XAS) scales. In the case for x = 0.5, for instance, the maximum microscale change in ac was within +0.29(3)%, whereas at the atomic scale, dTi-O changed by up to +4.8(3)%. Combined with our previous results for ex situ XRD and operando XRD/XAS measurements on other x compositions, the whole structural nature of LZTO, such as correspondence between ac and dTi-O, origins for voltage hysteresis, and zero-strain reaction mechanisms, has been unveiled.

How Fluorine Introduction Solves the Spinel Transition, a Fundamental Problem of Mn-Based Positive Electrodes.

In pursuit of high-capacity Mn-based oxides as positive electrode materials for lithium-ion batteries, the changes in the charge-discharge curve due to the spinel transition still stand in the way of the cycling stability. We found in this study that Li1.12Mn0.74O1.60F0.40 (LMOF05) positive electrodes with a loose-crystalline rock salt structure (LCRS), in which F is placed near Mn, show a stable and high capacity (300 mA h g-1, 952 W h kg-1) with little change in the charge-discharge curve. We demonstrated by F K-edge soft X-ray absorption spectroscopy and X-ray diffraction (XRD) that a part of F in the LCRS positive electrode forms F-Mn bonds. Operando XRD/X-ray absorption fine structure measurements revealed the lattice size and Mn surrounding environment during charge/discharge of F-containing LCRS positive electrodes (LMOF05), LCRS-LiMnO2 (LMO), and a spinel-like Li1.1Al0.1Mn1.8O4 positive electrode (SPINEL). Micro- and macroscopic structural changes indicate how the introduction of F suppresses the local spinel transition in Mn-based positive electrodes. These findings should be an effective tool for applying Co-free positive electrode materials for lithium-ion batteries.

Comprehensive Approach of 19F Nuclear Magnetic Resonance, Enzymatic, and In Silico Methods for Site-Specific Hit Selection and Validation of Fragment Molecules that Inhibit Methionine γ-Lyase Activity.

Fragment-based screening using 19F NMR (19F-FS) is an efficient method for exploring seed and lead compounds for drug discovery. Here, we demonstrate the utility and merits of using 19F-FS for methionine γ-lyase-binding fragments, together with a 19F NMR-based competition and mutation assay, as well as enzymatic and in silico methods. 19F NMR-based assays provided useful information on binding between 19F-FS hit fragments and target proteins. Although the 19F-FS and enzymatic assay were weakly correlated, they show that the 19F-FS hit fragments contained compounds with inhibitory activity. Furthermore, we found that in silico calculations partially account for the differences in activity levels between the 19F-FS hits as per NMR analysis. A comprehensive approach combining the 19F-FS and other methods not only identified fragment hits but also distinguished structural differences in chemical groups with diverse activity levels.

Development of an in situ high-temperature X-ray diffraction technique for lithium-ion battery materials.

The development of an in situ high-temperature X-ray diffraction technique for lithium-ion battery materials is crucial for understanding the detailed mechanism of thermal runaway. We realized such a technique and employed it on a C6Lix electrode with an LiPF6-based electrolyte, thereby revealing multiple transformations through several intermediate stages, i.e., C6Li → C12Li → C18Li/C24Li → C36Li → C6, which could be helpful to improve the thermal stability.

Thermal Behavior of Li1+x[Li1/3Ti5/3]O4 and a Proof of Concept for Sustainable Batteries.

An in-depth understanding of the thermal behavior of lithium-ion battery materials is valuable for two reasons: one is to devise strategies for inhibiting the risk of catastrophic thermal runaway and the other is to respond to the increasing demand for sustainable batteries using a direct regeneration method. Li1+x[Li1/3Ti5/3]O4 (LTO) is regarded as a suitable negative electrode under the type of severe conditions that cause this thermal runaway, such as in ignition systems for automobiles. Thus, in this study, we used differential scanning calorimetry to systematically analyze lithiated LTO combined with ex situ and in situ high-temperature X-ray diffraction measurements. The observed thermal reactions with a LiPF6-based electrolyte were divided into three processes: (i) the decomposition of the initially formed solid electrolyte interphase below 200 °C, (ii) the formation of a LiF phase at 200 °C ≤ T ≤ 340 °C, and (iii) the formation of a TiO2 phase at T > 340 °C. Because the enthalpy change in process (ii) mainly contributed to the total heat generation, fluorine-free Li salts and/or stabilization of the LTO lattice may be effective in coping with the thermal runaway. Even in various lithiated states, a direct regeneration method returned the discharge capacity of LTO to ∼90% of its initial value, if we ignore the contributions from the electrochemically inactive LiF and TiO2 rutile phases. Hence, it can be concluded that the recycling performance of LTO is far superior to those of lithium transition metal oxides for a positive electrode, whose delithiated states easily convert into electrochemical-inactive phases at high temperatures.

Structural basis for an exceptionally strong preference for asparagine residue at the S2 subsite of Stenotrophomonas maltophilia dipeptidyl peptidase 7.

The emergence of drug-resistant bacteria has become a major problem worldwide. Bacterial dipeptidyl peptidases 7 and 11 (DPP7s and DPP11s), belonging to the family-S46 peptidases, are important enzymes for bacterial growth and are not present in mammals. Therefore, specific inhibitors for these peptidases are promising as potential antibiotics. While the molecular mechanisms underlining strict specificity at the S1 subsite of S46 peptidases have been well studied, those of relatively broad preference at the S2 subsite of these peptidases are unknown. In this study, we performed structural and biochemical analyses on DPP7 from Stenotrophomonas maltophilia (SmDPP7). SmDPP7 showed preference for the accommodation of hydrophobic amino acids at the S2 subsite in general, but as an exception, also for asparagine, a hydrophilic amino acid. Structural analyses of SmDPP7 revealed that this exceptional preference to asparagine is caused by a hydrogen bonding network at the bottom of the S2 subsite. The residues in the S2 subsite are well conserved among S46 peptidases as compared with those in the S1 subsite. We expect that our findings will contribute toward the development of a universal inhibitor of S46 peptidases.

Identification and Analysis of a Novel NR0B1 Mutation in Late-Onset Adrenal Hypoplasia Congenita and Hypogonadism.

OBJECTIVE: X-linked adrenal hypoplasia congenita (AHC) is a rare disorder characterized by primary adrenal insufficiency and hypogonadotropic hypogonadism (HHG) caused by mutations of the NR0B1/DAX1 gene. We aimed to search for the presence of any NR0B1/DAX1 gene mutations in a referred patient and to further characterize the phenotypes of the identified mutation. CASE PRESENTATION: Herein, we report a Japanese patient with a novel missense mutation of the NR0B1/DAX1 gene resulting in adult-onset AHC and HHG. The patient was referred with diffuse skin pigmentation at 28 years of age, presented partial adrenal insufficiency and had undiagnosed incomplete HHG. Urological examination revealed severe oligospermia and testicular microlithiasis. RESULTS: The NR0B1/DAX1 gene mutation was identified by exome sequencing as a novel missense mutation (c.884A>T, p.Leu295His). We conducted in silico modeling of this mutant NR0B1/DAX1 protein (p.Leu295His) which affected the conserved hydrophobic core of the putative ligand-binding domain (LBD). In addition, functional analysis revealed that this mutant showed a decreased ability as a transcriptional repressor to suppress target genes, such as STAR and LHB. Furthermore, this mutant showed functionally impaired repression of steroidogenesis in human adrenocortical H295R cells. CONCLUSIONS: We identified a novel missense mutation of the NR0B1/DAX1 gene in a patient suffering from late-onset AHC and HHG, who presented with oligospermia and testicular microlithiasis. This mutant NR0B1/DAX1 protein was found to have reduced repressor activity, according to in vitro studies, clinically consistent with the patient's phenotypic features.

Operando X-ray Diffraction and Double-Edge X-ray Absorption Spectroscopy Studies on a Perfect Zero-Strain Material.

"Zero-strain" insertion materials are essential for high-performance Li-ion batteries, but the experimental determination of changes in their local structures remains challenging. In this study, we successfully visualized the reaction scheme of a perfect zero-strain material, (Li0.75Zn0.25)[Li0.417Ti1.583]O4 with a spinel framework, using operando X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). The operando XRD/XAS technique, which provided a series of XRD, Ti K-edge XAS, and Zn K-edge XAS data, can be employed owing to a recently developed tapered undulator and monochromator system. Although previous ex situ XRD measurements indicated the immutable cubic lattice parameter (ac) during the discharge process, these studies unveiled drastic structural variations occurring on the atomic scale between the charge and discharge reactions, such as differences in the ac, bond distances, and occupancies of the Zn2+ ions. This dynamic information obtained under operating conditions could be useful not only for understanding the zero-strain reaction scheme but also for designing advanced zero-strain insertion materials with enhanced energy density.

Revisiting LiCoO2 Using a State-of-the-Art In Operando Technique.

Lithium overstoichiometric cobalt oxide, Li(LiδCo1-δ)O2-δ, still occupies a privileged position as a positive electrode material for lithium-ion batteries. However, despite its widespread applications in commercial lithium-ion batteries, little is known about its reaction mechanisms and the effects of δ on cyclability at deep charge. We herein revisited this material through a recently developed in operando technique, i.e., rapid, alternating measurements of X-ray diffraction and X-ray absorption spectroscopy. The cyclability degraded when the charge cutoff voltage was >4.4 V versus Li+/Li, which corresponds to the Li composition exhibiting a minimum (maximum) lattice parameter along the ah (ch) axis. Differences in the structural parameters such as lattice parameters and bond distances clearly appeared between the charge and discharge reactions at a capacity below ∼220 mAh g-1. These changes occurred because deep charge and/or increasing the amount of δ induced a local distortion in the CoO6 octahedra. We found a critical Li extraction content that satisfied the need for both high capacity and cyclability for Li(LiδCo1-δ)O2-δ, which can be applied to other layered materials.

Charge Trapping Process in Photoexcited Nitrogen-Doped Titanium Oxides.

We present a first-principles study on the structural changes induced by charge trapping that occurs after photoexcitation in nitrogen-doped titanium oxide (N-TiO2). The charge trapping site and the corresponding K edge EXAFS spectra of Ti atoms were predicted and compared with those obtained by an experiment under ultraviolet (UV) light excitation. The results indicate that charge trapping occurs in the neighborhood of the oxygen vacancy (O-vac) sites. Furthermore, our calculations show that the O-vac site significantly affects the EXAFS spectra, while substitutional nitrogen doping for an oxygen site in the vicinity of the O-vac site is insensitive in the EXAFS spectra. Based on this observation combined with the knowledge from previous experiments, we propose a charge trapping process where the UV light-excited electron migrates at the O-vac site in bulk (∼300 ps) while the visible light-excited electron (N 2p → Ti 3d) is immediately trapped at the O-vac site neighboring the N site (∼1 ps).

Fe2+ Ions Alleviate the Symptom of Citrus Greening Disease.

Citrus greening (CG) is among the most devastating citrus diseases worldwide. CG-infected trees exhibit interveinal chlorotic leaves due to iron (Fe) deficiency derived from CG; thus, Fe content is lower in infected leaves than in healthy leaves. In this study, we demonstrated that the foliar application of Fe2+ relieves the symptom of CG infection in citrus trees. We applied Fe2+ and citrate to the leaves of infected rough lemon plants. Following this treatment, a reduction in the number of yellow symptomatic leaves was observed, and their growth was restored. Using chlorophyll content as an index, we screened for effective Fe complexes and found that a high ratio of citrate to Fe2+ in the applied solution led to effects against CG in Shikuwasa trees. A high proportion of Fe2+ to total Fe was another key factor explaining the effectiveness of the solution in CG infection, indicating the importance of Fe2+ absorption into plant cells. We confirmed the proportion of Fe2+ to total Fe through the high correlation of reflectometry data via a triazine reaction and X-ray absorption fine structure analysis. These results demonstrate that the foliar application of a high-Fe2+ citrate solution can restore the growth of CG diseased trees.

In situ X-ray Raman spectroscopy and magnetic susceptibility study on the Li[Li0.15Mn1.85]O4 oxygen anion redox reaction.

Li-rich compounds have received significant attention as electrode materials for lithium-ion batteries (LIBs) because of their large rechargeable capacities (qrecha). We have demonstrated a novel reaction scheme of one of the Li-rich compounds, Li[Li0.15Mn1.85]O4, where Mn4+ ions are reduced to lower valence states such as Mn3+ and Mn2+ ions during charging at voltages above 5.0 V.

High-pressure synthesis of ε-FeOOH from ß-FeOOH and its application to the water oxidation catalyst.

Research on materials under extreme conditions such as high pressures provides new insights into the evolution and dynamics of the earth and space sciences, but recently, this research has focused on applications as functional materials. In this contribution, we examined high-pressure/high-temperature phases of ß-FeO1-x (OH)1+x Cl x with x = 0.12 (ß-FeOOH) and their catalytic activities of water oxidation, i.e., oxygen evolution reaction (OER). Under pressures above 6 GPa and temperatures of 100-700 °C, ß-FeOOH transformed into ε-FeOOH, as in the case of α-FeOOH. However, the established pressure-temperature phase diagram of ß-FeOOH differs from that of α-FeOOH, probably owing to its open framework structure and partial occupation of Cl- ions. The OER activities of ε-FeOOH strongly depended on the FeOOH sources, synthesis conditions, and composite electrodes. Nevertheless, one of the ε-FeOOH samples exhibited a low OER overpotential compared with α-FeOOH and its parent ß-FeOOH, which are widely used as OER catalysts. Hence, ε-FeOOH is a potential candidate as a next-generation earth-abundant OER catalyst.

Fragment-based discovery of the first nonpeptidyl inhibitor of an S46 family peptidase.

Antimicrobial resistance is a global public threat and raises the need for development of new antibiotics with a novel mode of action. The dipeptidyl peptidase 11 from Porphyromonas gingivalis (PgDPP11) belongs to a new class of serine peptidases, family S46. Because S46 peptidases are not found in mammals, these enzymes are attractive targets for novel antibiotics. However, potent and selective inhibitors of these peptidases have not been developed to date. In this study, a high-resolution crystal structure analysis of PgDPP11 using a space-grown crystal enabled us to identify the binding of citrate ion, which could be regarded as a lead fragment mimicking the binding of a substrate peptide with acidic amino acids, in the S1 subsite. The citrate-based pharmacophore was utilized for in silico inhibitor screening. The screening resulted in an active compound SH-5, the first nonpeptidyl inhibitor of S46 peptidases. SH-5 and a lipophilic analog of SH-5 showed a dose-dependent inhibitory effect against the growth of P. gingivalis. The binding mode of SH-5 was confirmed by crystal structure analysis. Thus, these compounds could be lead structures for the development of selective inhibitors of PgDPP11.

Characterization of the phosphotransacetylase-acetate kinase pathway for ATP production in Porphyromonas gingivalis.

Acetyl phosphate (AcP) is generally produced from acetyl coenzyme A by phosphotransacetylase (Pta), and subsequent reaction with ADP, catalyzed by acetate kinase (Ack), produces ATP. The mechanism of ATP production in Porphyromonas gingivalis is poorly understood. The aim of this study was to explore the molecular basis of the Pta-Ack pathway in this microorganism. Pta and Ack from P. gingivalis ATCC 33277 were enzymatically and structurally characterized. Structural and mutational analyses suggest that Pta is a dimer with two substrate-binding sites in each subunit. Ack is also dimeric, with a catalytic cleft in each subunit, and structural analysis indicates a dramatic domain motion that opens and closes the cleft during catalysis. ATP formation by Ack proceeds via a sequential mechanism. Reverse transcription-PCR analysis demonstrated that the pta (PGN_1179) and ack (PGN_1178) genes, tandemly located in the genome, are cotranscribed as an operon. Inactivation of pta or ack in P. gingivalis by homologous recombination was successful only when the inactivated gene was expressed in trans. Therefore, both pta and ack genes are essential for this microorganism. Insights into the Pta-Ack pathway reported herein would be helpful to understand the energy acquisition in P. gingivalis.

Crystal structures of a bacterial dipeptidyl peptidase IV reveal a novel substrate recognition mechanism distinct from that of mammalian orthologues.

Dipeptidyl peptidase IV (DPP IV, DPP4, or DAP IV) preferentially cleaves substrate peptides with Pro or Ala at the P1 position. The substrate recognition mechanism has been fully elucidated for mammalian DPP IV by crystal structure analyses but not for bacterial orthologues. Here, we report the crystal structures of a bacterial DPP IV (PmDAP IV) in its free form and in complexes with two kinds of dipeptides as well as with a non-peptidyl inhibitor at 1.90 to 2.47 Å resolution. Acyl-enzyme intermediates were observed for the dipeptide complexes of PmDAP IV, whereas tetrahedral intermediates were reported for the oligopeptide complexes of mammalian DPP IVs. This variation reflects the different structural environments of the active site Arg residues, which are involved in the recognition of a substrate carbonyl group, of mammalian and bacterial enzymes. A phylogenetic analysis revealed that PmDAP IV is a closer relative of dipeptidyl peptidases 8 and 9 (DPP8 and DPP9, DPP IV-family enzymes) than DPP IV. These results provide new insights into the substrate recognition mechanism of bacterial DAP IVs and may assist in the development of selective inhibitors for DAP IVs from pathogenic asaccharolytic bacteria, which utilise proteins or peptides as an energy source.

Structural insights into the catalytic mechanism of cysteine (hydroxyl) lyase from the hydrogen sulfide-producing oral pathogen, Fusobacterium nucleatum.

Hydrogen sulfide (H2S) plays important roles in the pathogenesis of periodontitis. Oral pathogens typically produce H2S from l-cysteine in addition to pyruvate and [Formula: see text] However, fn1055 from Fusobacterium nucleatum subsp. nucleatum ATCC 25586 encodes a pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes the production of H2S and l-serine from l-cysteine and H2O, an unusual cysteine (hydroxyl) lyase reaction (ß-replacement reaction). To reveal the reaction mechanism, the crystal structure of substrate-free Fn1055 was determined. Based on this structure, a model of the l-cysteine-PLP Schiff base suggested that the thiol group forms hydrogen bonds with Asp232 and Ser74, and the substrate α-carboxylate interacts with Thr73 and Gln147 Asp232 is a unique residue to Fn1055 and its substitution to asparagine (D232N) resulted in almost complete loss of ß-replacement activity. The D232N structure obtained in the presence of l-cysteine contained the α-aminoacrylate-PLP Schiff base in the active site, indicating that Asp232 is essential for the addition of water to the α-aminoacrylate to produce the l-serine-PLP Schiff base. Rapid-scan stopped-flow kinetic analyses showed an accumulation of the α-aminoacrylate intermediate during the reaction cycle, suggesting that water addition mediated by Asp232 is the rate-limiting step. In contrast, mutants containing substitutions of other active-site residues (Ser74, Thr73, and Gln147) exhibited reduced ß-replacement activity by more than 100-fold. Finally, based on the structural and biochemical analyses, we propose a mechanism of the cysteine (hydroxyl) lyase reaction by Fn1055. The present study leads to elucidation of the H2S-producing mechanism in F. nucleatum.