Development of immobilized Sn4+ affinity chromatography material for highly selective enrichment of phosphopeptides

In this work, we first immobilized tin(IV) ion on polydopamine‐coated magnetic graphene (magG@PDA) to synthesize Sn⁴⁺‐immobilized magG@PDA (magG@PDA‐Sn⁴⁺) and successfully applied the material to highly selective enrichment of phosphopeptides. The material gathered the advantages of large surface area of graphene, superparamagnetism of Fe₃O₄, good hydrophilicity and biocompatibility of polydopamine, and strong interaction between Sn⁴⁺ and phosphopeptides. The enrichment performance of magG@PDA‐Sn⁴⁺ toward phosphopeptides from digested β‐casein at different concentrations, with and without added digested BSA was investigated and compared with magG@PDA‐Ti⁴⁺. The results showed high selectivity and sensitivity of the Sn⁴⁺‐IMAC material toward phosphopeptides, as good as the Ti⁴⁺‐IMAC material. Finally, magG@PDA‐Sn⁴⁺ was applied to the analysis of endogenous phosphopeptides from a real sample, human saliva, with both MALDI‐TOF MS and nano‐LC‐ESI‐MS/MS. The results indicated that the as‐synthesized Sn⁴⁺‐IMAC material not only has good enrichment performance, but also could serve as a supplement to the Ti⁴⁺‐IMAC material and expand the phosphopeptide coverage enriched by the single Ti⁴⁺‐IMAC material, demonstrating the broad application prospects of magG@PDA‐Sn⁴⁺ in phosphoproteome research.     

基于Ti4+-IMAC富集的分枝菌酸小杆菌深度覆盖磷酸化蛋白质组研究

【目的】本研究以分枝菌酸小杆菌(Mycolicibacterium smegmatis)为研究对象,探索适于原核微生物理想的磷酸化富集方法。【方法】我们比较了二氧化钛(TiO₂)、Fe³⁺-NTA和Ti⁴⁺螯合在磷酸酯修饰的固相微球(Ti⁴⁺-IMAC) 3种不同富集方法磷酸化肽段的富集效率,并用不同分辨率的质谱仪评估富集稳定性。【结果】Ti⁴⁺-IMAC富集效率最高,磷酸化位点数是TiO₂或Fe³⁺-NTA方法的7倍以上;TiO₂和Fe³⁺-NTA方法富集到的磷酸化位点数相差不大,与已报道的用TiO₂方法富集的磷酸化位点数目接近。Ti⁴⁺-IMAC富集结果稳定性很好,高分辨率Lumos质谱仪鉴定到的磷酸化位点数是Velos的2.6倍。【结论】本研究较高效地实现了分枝菌酸小杆菌磷酸化事件的鉴定,共鉴定到2 280个磷酸化蛋白、10 880个磷酸化肽段及4 433个可信磷酸化位点,有望用于其他微生物的磷酸化蛋白质组学研究。     

Luminescence properties of barium – gadolinium–titanate ceramics doped with rare‐earth ions (Eu3+ and Tb3+)

Barium‐gadolinium‐titanate (BaGd₂Ti₄O₁₂) powder ceramics doped with rare‐earth ions (Eu³⁺ and Tb³⁺) were synthesized by a solid‐state reaction method. From the X‐ray diffraction spectrum, it was observed that Eu³⁺ and Tb³⁺:BaGd₂Ti₄O₁₂ powder ceramics are crystallized in the form of an orthorhombic structure. Scanning electron microscopy image shows that the particles are agglomerated and the particle size is about 200 nm. Eu³⁺‐ and Tb³⁺‐doped BaGd₂Ti₄O₁₂ powder ceramics were examined by energy dispersive X‐ray analysis, Fourier transform infrared spectroscopy, photoluminescence and thermoluminescence (TL) spectra. Emission spectra of Eu³⁺‐doped BaGd₂Ti₄O₁₂ powder ceramics showed bright red emission at 613 nm (⁵D₀ → ⁷F₂) with an excitation wavelength λ_exci = 408 nm (⁷F₀ → ⁵D₃) and Tb³⁺:BaGd₂Ti₄O₁₂ ceramic powder has shown green emission at 534 nm (⁵D₄ → ⁷F₅) with an excitation wavelength λ_exci = 331 nm ((⁷F₆ → ⁵D₁). TL spectra show that Eu³⁺ and Tb³⁺ ions affect TL sensitivity. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and blood compatibility of rutile-type titanium oxide coated LTI-carbon

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DFT model cluster studies of O2 adsorption on hydrogenated titania sub-nanoparticles

In the present paper, we examine the general applicability of different TiO₂ model clusters to study of local chemical events on TiO₂ sub-nanoparticles. Our previous DFT study of TiO₂ activation through H adsorption and following deactivation by O₂ adsorption using small amorphous Ti₈O₁₆ cluster were complemented by examination of rutile-type and spherical Ti₁₅O₃₀ nanoclusters. The obtained results were thoroughly compared with experimental data and results of related computational studies using other TiO₂ models including periodic structures. It turned out that all considered model TiO₂ model systems provide qualitatively similar results. It was shown that atomic hydrogen is adsorbed with negligible activation energy on surface O atoms, which is accompanied by the appearance of reduced Ti³⁺ species and corresponding localized band gap 3d-Ti states. Oxygen molecule is adsorbed on Ti³⁺ sites spontaneously forming molecular O₂ ^– species by capturing an extra electron of Ti³⁺ ion, which results in disappearance of Ti³⁺ species and corresponding band gap states. Calculated g-tensor values of Ti³⁺ and O₂ ^– species agree well with the results of EPR studies and do not depend on the used TiO₂ model cluster. Additionally, it was shown that the various cluster calculations provide results comparable with the calculations of periodic structures with respect to the modeling of chemical processes under study. As a whole, the present study approves the validity of molecular cluster approach to study of local chemical events on TiO₂ sub-nanoparticles.

Rapid synthesis of titanium(IV)‐immobilized magnetic mesoporous silica nanoparticles for endogenous phosphopeptides enrichment

The MALDI‐TOF MS has already been a main platform for phosphoproteome analysis. However, there are some weaknesses in direct analysis of endogenous phosphopeptides by MALDI‐TOF MS because of the serious suppression effect and poor ionization efficiency, which is brought by the excess of nonphosphopeptides and protein. It is essential to enrich endogenous phosphopeptides from complex biosamples efficiently prior to MALDI‐TOF MS analysis. Herein, we present a time‐saving and detailed protocol for the synthesis of titanium(iv)‐immobilized magnetic mesoporous silica nanoparticles (denoted as Fe₃O₄@mSiO₂‐Ti⁴⁺), the subsequent enrichment process, and MALDI‐TOF MS analysis. We tested the LOD, size‐exclusive effect, reproducibility, and stability of Fe₃O₄@mSiO₂‐Ti⁴⁺ nanoparticles. Furthermore, the ability of this protocol for identifying endogenous phosphopeptides in healthy human serum and saliva was investigated.     

Enhanced photoluminescence of the Ca0.8Zn0.2TiO3:0.05% Pr3+ phosphor by optimized hydrothermal conditions

The red‐emitting phosphor Ca_0.8Zn_0.2TiO₃:Pr³⁺ was synthesized using an ethylene glycol (EG)‐assisted hydrothermal method. The effects of additional amounts of and order of adding EG, plus hydrothermal temperature, time, and pH on the composition, morphology and optical properties of the titanate phosphors were studied. The crystalline phases of the titanate phosphors were confirmed to be constituted of a series of co‐existing CaTiO₃, Zn₂TiO₄ and Ca₂Zn₄Ti₁₆O₃₈ compounds in various proportions that were visualized using an X‐ray diffractometer (XRD). The optical properties of the phosphors were studied using photoluminescence spectra and UV–visible spectroscopy. The results show that the impurities Zn₂TiO₄:Pr³⁺ and Ca₂Zn₄Ti₁₆O₃₈:Pr³⁺ significantly contributed to the enhancement of an absorption band around 380 nm. The optimum Ca_0.8Zn_0.2TiO₃:Pr³⁺ phosphor consisting of appropriate amounts of CaTiO₃, Ca₂Zn₄Ti₁₆O₃₈ and Zn₂TiO₄ in three phases was achieved by controlling the hydrothermal conditions, and the obtained red phosphor exhibited the highest red emission (¹D₂ → ³H₄ transition of Pr³⁺) with an ideal chromaticity coordinate located at (x = 0.667, y = 0.332) under 380 nm excitation.     

Study on the preparation and luminescence properties of SrGe4O9:Mn4+ red phosphors for plant illumination

In this study, SrGe₄O₉:Mn⁴⁺ red phosphors for plant illumination were prepared using a high-temperature solid-phase method. The samples were characterized and analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), fluorescence spectroscopy, and other techniques. The phase structure, apparent morphology, and luminescence properties of the SrGe₄O₉:Mn⁴⁺ red phosphors were investigated. The results indicated that the dopant Mn⁴⁺ was incorporated into the matrix structure by substituting some Ge⁴⁺ ions without any changes in the crystal structure of the SrGe₄O₉ matrix. The samples comprised micron-scale particles and exhibited high purity and uniform distribution of elements. The SrGe₄O₉:Mn⁴⁺ phosphors exhibited relatively strong red light emission at 660 nm under the excitation of a 430-nm blue light, and the luminescence intensity was the highest when the Mn⁴⁺ doping amount was 1%. Proper doping of Ti⁴⁺ or Sn⁴⁺ could effectively improve the luminescence intensity of the SrGe₄O₉:Mn⁴⁺ phosphors. The light-emitting diode (LED) device packaging showed that the SrGe₄O₉:Mn⁴⁺ red phosphors could be used for plant growth illumination.     

Amorphous Carbon Coated High Grain Boundary Density Dual Phase Li4Ti5O12‐TiO2: A Nanocomposite Anode Material for Li‐Ion Batteries

This work introduces an effective, inexpensive, and large‐scale production approach to the synthesis of a carbon coated, high grain boundary density, dual phase Li₄Ti₅O₁₂‐TiO₂ nanocomposite anode material for use in rechargeable lithium‐ion batteries. The microstructure and morphology of the Li₄Ti₅O₁₂‐TiO₂‐C product were characterized systematically. The Li₄Ti₅O₁₂‐TiO₂‐C nanocomposite electrode yielded good electrochemical performance in terms of high capacity (166 mAh g^?1 at a current density of 0.5 C), good cycling stability, and excellent rate capability (110 mAh g^?1 at a current density of 10 C up to 100 cycles). The likely contributing factors to the excellent electrochemical performance of the Li₄Ti₅O₁₂‐TiO₂‐C nanocomposite could be related to the improved morphology, including the presence of high grain boundary density among the nanoparticles, carbon layering on each nanocrystal, and grain boundary interface areas embedded in a carbon matrix, where electronic transport properties were tuned by interfacial design and by varying the spacing of interfaces down to the nanoscale regime, in which the grain boundary interface embedded carbon matrix can store electrolyte and allows more channels for the Li+ ion insertion/extraction reaction. This research suggests that carbon‐coated dual phase Li₄Ti₅O₁₂‐TiO₂ nanocomposites could be suitable for use as a high rate performance anode material for lithium‐ion batteries.     

Survey of the Proteolytic Activities Degrading the Kunitz Trypsin Inhibitor and Glycinin in Germinating Soybeans (Glycine max)

The cotyledons of the soybean (Glycine max [L.] Merrill cv Amsoy 71) were examined for proteolytic activities capable of degrading soybean seed proteins. Three distinct activities were identified that attack the native Kunitz soybean trypsin inhibitor of Amsoy 71, Ti^a. Protease K1 cleaves Ti^a to Ti^a_m, the inhibitor form lacking the five carboxyl-terminal amino acid residues relative to Ti^a. Protease K1 is a cysteine protease that peaks in activity on day 4 after the beginning of imbibition, with maximal activity toward Ti^a at pH 4. The characteristics of protease K1 are consistent with the involvement of this protease in the initial proteolysis of the Kunitz inhibitor during germination. Protease K2 also degrades Ti^a at pH 4 but produces no electrophoretically recognizable products. It peaks later in seedling growth, at day 8. Protease K3 degrades Ti^a to products other than Ti^a_m. However, it is active at pH 8. Two proteolytic activities were identified that attack the major storage protein, glycinin. Protease G1 (which appears by 4 days after imbibition) specifically cleaves the acidic polypeptides of glycinin at pH 4, yielding a product approximately 1.5 kilodaltons smaller. Protease G1 is inhibited by metal chelators as well as by reagents reactive toward thiols. Protease G2 also degrades the glycinin acidic chains at pH 4, but without the appearance of electrophoretically recognizable products. Protease G2, while present at low levels in the dry seed, is found primarily in the cotyledons after 8 days of growth.     

A simple method for the rapid and economical immobilization of glucose isomerase

The immobilization of glucose isomerase by adsorption on a macroreticular polystyrene sulphonate cation exchanger equilibrated with Ti⁴⁺, Zr⁴⁺, V⁵⁺ ions, followed by alkaline glutaraldehyde-induced crosslinking, is described. Experimental conditions are fixed for a selective and optimal retention of glucose isomerase and for its minimal leaching during subsequent use as a continuous compact glucose isomerase bed reactor, the performance of which is assessed on a laboratory scale for glucose isomerization. Factors influencing the glucose isomerase activity on solid supports, such as ratios of enzyme load - carrier - metal ion concentration, substrate feed concentration, residence period, loss of enzymic activity during storage and use, etc. are studied. The merits and drawbacks of the newly developed glucose isomerase reactor are discussed.     

Ultrathin Li4Ti5O12 Nanosheet Based Hierarchical Microspheres for High‐Rate and Long‐Cycle Life Li‐Ion Batteries

Ultrathin Li₄Ti₅O₁₂ nanosheet based hierarchical microspheres are synthesized through a three‐step hydrothermal procedure. The average thickness of the Li₄Ti₅O₁₂ sheets is only ≈(6.6 ± 0.25) nm and the specific surface area of the sample is 178 m² g^?1. When applied into lithium ion batteries as anode materials, the hierarchical Li₄Ti₅O₁₂ microspheres exhibit high specific capacities at high rates (156 mA h g^?1 at 20 C, 150 mA h g^?1 at 50 C) and maintain a capacity of 126 mA h g^?1 after 3000 cycles at 20 C. The results clearly suggest that the utility of hierarchical structures based on ultrathin nanosheets can promote the lithium insertion/extraction reactions in Li₄Ti₅O₁₂. The obtained hierarchical Li₄Ti₅O₁₂ with ultrathin nanosheets and large specific surface area can be perfect anode materials for the lithium ion batteries applied in high power facilities, such as electric vehicles and hybrid electric vehicles.     

Demethylation and degradation of phenylmethylethers by the sulfide-methylating homoacetogenic bacterium strain TMBS 4

Biochemical studies on anaerobic phenylme-thylether cleavage by homoacetogenic bacteria have been hampered so far by the complexity of the reaction chain involving methyl transfer to acetyl-CoA synthase and subsequent methyl group carbonylation to acetyl-CoA. Strain TMBS 4 differs from other demethylating homoacetogenic bacteria in using sulfide as a methyl acceptor, thereby forming methanethiol and dimethylsulfide. Growing and resting cells of strain TMBS 4 used alternatitively CO₂ as a precursor of the methyl acceptor CO for homoacetogenic acetate formation. Demethylation was inhibited by propyl iodide and reactivated by light, indicating involvement of a corrinoid-dependent methyltransferase. Strain TMBS 4 contained ca. 750 nmol g dry mass^-1 of a corrinoid tentatively identified as 5-hydroxybenzimidazolyl cobamide. A photometric assay for measuring the demethylation activity in cell extracts was developed based on the formation of a yellow complex of Ti³⁺ with 5-hydroxyvanillate produced from syringate by demethylation. In cell extracts, the methyltransfer reaction from methoxylated aromatic compounds to sulfide or methanethiol depended on reductive activation by Ti³⁺. ATP and Mg²⁺ together greatly stimulated this reductive activation without being necessary for the demethylation reaction itself. The specific activity of the transmethylating enzyme system increased proportionally with protein concentration up to 3 mg ml^-1 reaching a constant level of 20 nmol min^-1 mg^-1 at protein concentrations 10 mg ml^-1. The specific rate of activation increased in a non-linear manner with protein concentration. Strain TMBS 4 degraded gallate, the product of sequential demethylations, to 3 acetate through the phloroglucinol pathway as found earlier with Pelobacter acidigallici.Abbreviations BV benzyl viologen - CTAB cetyltrimethylammonium bromide - H₄folate tetrahydrofolate - MOPS 3-[N-morpholino]propanesulfonic acid - MV methyl viologen - NTA nitrilotriacetate - t_d doubling time - TMB 3,4,5-trimethoxybenzoate     

Realizing Three‐Electron Redox Reactions in NASICON‐Structured Na3MnTi(PO4)3 for Sodium‐Ion Batteries

Developing multielectron reaction electrode materials is essential for achieving high specific capacity and high energy density in secondary batteries; however, it remains a great challenge. Herein, Na₃MnTi(PO₄)₃/C hollow microspheres with an open and stable NASICON framework are synthesized by a spray‐drying‐assisted process. When applied as a cathode material for sodium‐ion batteries, the resultant Na₃MnTi(PO₄)₃/C microspheres demonstrate fully reversible three‐electron redox reactions, corresponding to the Ti^3+/4+ (≈2.1 V), Mn^2+/3+ (≈3.5 V), and Mn^3+/4+ (≈4.0 V vs Na⁺/Na) redox couples. In situ X‐ray diffraction results reveals that both solid‐solution and two‐phase electrochemical reactions are involved in the sodiation/desodiation processes. The high specific capacity (160 mAh g^?1 at 0.2 C), outstanding cyclability (≈92% capacity retention after 500 cycles at 2 C), and the facile synthesis make the Na₃MnTi(PO₄)₃/C a prospective cathode material for sodium‐ion batteries.     

A Strategy for Synthesis of Carbon Nitride Induced Chemically Doped 2D MXene for High‐Performance Supercapacitor Electrodes

A step‐by‐step strategy is reported for improving capacitance of supercapacitor electrodes by synthesizing nitrogen‐doped 2D Ti₂CT_x induced by polymeric carbon nitride (p‐C₃N₄), which simultaneously acts as a nitrogen source and intercalant. The NH₂CN (cyanamide) can form p‐C₃N₄ on the surface of Ti₂CT_x nanosheets by a condensation reaction at 500–700 °C. The p‐C₃N₄ and Ti₂CT_x complexes are then heat‐treated to obtain nitrogen‐doped Ti₂CT_x nanosheets. The triazine‐based p‐C₃N₄ decomposes above 700 °C; thus, the nitrogen species can be surely doped into the internal carbon layer and/or defect site of Ti₂CT_x nanosheets at 900 °C. The extended interlayer distance and c‐lattice parameters (c‐LPs of 28.66 Å) of Ti₂CT_x prove that the p‐C₃N₄ grown between layers delaminate the nanosheets of Ti₂CT_x during the doping process. Moreover, 15.48% nitrogen doping in Ti₂CT_x improves the electrochemical performance and energy storage ability. Due to the synergetic effect of delaminated structures and heteroatom compositions, N‐doped Ti₂CT_x shows excellent characteristics as an electrochemical capacitor electrode, such as perfectly rectangular cyclic voltammetry results (CVs, R² = 0.9999), high capacitance (327 F g^?1 at 1 A g^?1, increased by ≈140% over pristine‐Ti₂CT_x), and stable long cyclic performance (96.2% capacitance retention after 5000 cycles) at high current density (5 A g^?1).     

Dinuclear Ti and Ti complexes supported by calix[4]arene ligands. Binding alkali-metal cations inside and outside the cavity of calix[4]arenes

New dinuclear Ti^IV and Ti^III complexes with the calix[4]arene ligand C₂₈H₂₀O₄H₄ (H₄L) have been isolated from the reaction of Ti(NMe₂)₄, H₄L, and Na (or KC₈) in THF. X-ray analyses revealed a similar core structure for the two complexes Na₄(THF)₈[Ti^IV ₂(μ-O)₂L₂] (1) and K₄(THF)₈[Ti^III ₂(μ-NMe₂)₂L₂] (2). Two titanium atoms are bridged by two oxygen atoms in 1 and by two dimethylamido groups in 2 and are also supported by two deprotonated calix[4]arene ligands in a cone conformation. This resulted in a similar Ti?Ti separation of about 3.29 Å in 1 and 3.28 Å in 2 and in a distorted octahedral environment for each Ti center in both complexes. In contrast, in a novel complex 3, Na₂(THF)₆[Ti^III ₂L₂], two Ti^III atoms are supported only by two deprotonated ligands. This results in a five-coordinate environment for both titanium(III) centers with the separation between them being 3.133(1) Å.     

Chemical Bonding and Physical Trapping of Sulfur in Mesoporous Magnéli Ti4O7 Microspheres for High‐Performance Li–S Battery

Various host materials have been investigated to address the intrinsic drawbacks of lithium sulfur batteries, such as the low electronic conductivity of sulfur and inevitable decay in capacity during cycling. Besides the widely investigated carbonaceous materials, metal oxides have drawn much attention because they form strong chemical bonds with the soluble lithium polysulfides. Here, mesoporous Magnéli Ti₄O₇ microspheres are prepared via an in situ carbothermal reduction that exhibit interconnected mesopores (20.4 nm), large pore volume (0.39 cm³ g^?1), and high surface area (197.2 m² g^?1). When the sulfur cathode is embedded in a matrix of mesoporous Magnéli Ti₄O₇ microspheres, it exhibits a superior reversible capacity of 1317.6 mA h g^?1 at moderate current (C/10) and a low decay in capacity of 12% after 400 cycles at C/5. Strong chemical bonding of the lithium polysulfides to Ti₄O₇, as well as effective physical trapping in the mesopores and voids in the matrix are considered responsible for the improved electrochemical performance. A mechanism of the physical and chemical interactions between mesoporous Magnéli Ti₄O₇ microspheres and sulfur is proposed based on systematic investigations.     

Capacity Fade Mechanism of Li4Ti5O12 Nanosheet Anode

Zero‐strain and long‐term stability of nanoscale lithium titanate (LTO) anode materials make possible the fabrication of exceptionally stable lithium ion batteries. But one issue must be considered that of nanostructure‐induced relaxation in 2D LTO nanosheets which profoundly modifies their Li storage properties and structural stability. Excessively intercalated Li ions at both 8a and 16c sites trigger nucleation of the relaxed LTO structure in the near‐surface region, which impedes Li‐ion diffusion and causes the increasing polarization of LTO nanosheet electrodes. Nuclei of relaxed LTO then undergo isotropic growth along the 3D Li‐ion pathways in LTO to completely convert near‐surface regions into relaxed LTO. With increasing population of trapped Li ions, the enhanced conductivity due to Ti⁴⁺/Ti³⁺ reduction gradually eliminates the raised polarization. In the meantime, spontaneous electrolyte/LTO reduction to form the solid electrolyte interphase starts playing a major role in capacity loss once the transformation of near‐surface region into relaxed LTO becomes saturated. Elucidation of these fundamental intercalation‐induced surface structure transformations contribute greatly into the design of highly performing 2D nanoscaled LTO and other electrode materials.     

Breathable Carbon‐Free Electrode: Black TiO2 with Hierarchically Ordered Porous Structure for Stable Li–O2 Battery

This paper introduces oxygen‐deficient black TiO₂ with hierarchically ordered porous structure fabricated by a simple hydrogen reduction as a carbon‐ and binder‐free cathode, demonstrating superior energy density and stability. With the high electrical conductivity derived from oxygen vacancies or Ti³⁺ ions, this unique electrode features micrometer‐sized voids with mesoporous walls for the effective accommodation of Li₂O₂ toroid and for the rapid transport of reaction molecules without the electrode being clogged. In the highly ordered architecture, toroidal Li₂O₂ particles are guided to form with a regular size and separation, which induces the most of Li₂O₂ external surface to be directly exposed to the electrolyte. Therefore, large Li₂O₂ toroids (≈300 nm) grown from solution can be effectively charged by incorporating a soluble catalyst, resulting in a very small polarization (≈0.37 V). Furthermore, disordered nanoshell in black TiO₂ is suggested to protect the oxygen‐deficient crystalline core, by which oxidation of Ti³⁺ is kinetically impeded during battery operation, leading to the enhanced electrode stability even in a highly oxidizing environment under high voltage (≈4 V).     

Microscopic and Thermal Characterization of Hydrogen Peroxide Killing and Lysis of Spores and Protection by Transition Metal Ions, Chelators, and Antioxidants

Killing of bacterial spores by H₂O₂ at elevated but sublethal temperatures and neutral pH occurred without lysis. However, with prolonged exposure or higher concentrations of the agent, secondary lytic processes caused major damage successively to the coat, cortex, and protoplast, as evidenced by electron and phase contrast microscopy. These processes were also reflected in changes in differential scanning calorimetric profiles for H₂O₂-treated spores. Endothermic transitions in the profiles occurred at lower temperatures than usual as a result of H₂O₂ damage. Thus, H₂O₂ sensitized the cells to heat damage. Longer exposure to H₂O₂ resulted in total disappearance of the transitions, indicative of major disruptions of cell structure. Spores but not vegetative cells were protected against the lethal action of H₂O₂ by the transition metal cations Cu⁺, Cu²⁺, Co²⁺, Co³⁺, Fe²⁺, Fe³⁺, Mn²⁺, Ti³⁺, and Ti⁴⁺. The metal chelator EDTA was also somewhat protective, while o-phenanthroline, citrate, deferoxamine, and ethanehydroxydiphosphonate were only marginally so. Superoxide dismutase and a variety of other free-radical scavengers were not protective. In contrast, reducing agents such as sulfhydryl compounds and ascorbate at concentrations of 20 to 50 mM were highly protective. Decoating or demineralization of the spores had only minor effects. The marked dependence of H₂O₂ sporicidal activity on moderately elevated temperature and the known low reactivity of H₂O₂ itself suggest that radicals are involved in its killing action. However, the protective effects of a variety of oxidized or reduced transition metal ions indicate that H₂O₂ killing of spores is markedly different from that of vegetative cells.