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Graphite as a competitive anode material of potassium-ion batteries (KIBs) is currently frustrated by the poor cycling stability and rate performance. In this study, high-performance activated graphite that derives from low-grade microcrystalline graphite ore is fabricated through a facile KOH activation method and the following HF leaching. The effect of activation temperature (from 450 to 650 °C) on the physical parameters and K-storage performance of the activated graphite materials (AMGs) is systematically investigated. The material characterization results demonstrate the activation temperature imposes distinct influence on the morphology, interlayer distance (d002), crystalline size (Lc), specific surface area and surface functional groups of the AMGs. At the optimized activation temperature of 550 °C, the activated graphite (AMG-55) presents enlarged d002 of 0.3451 nm, small Lc of 14.61 nm and lowest surface oxygen content (1.79%). Moreover, the moderate etching reactions of KOH at 550 °C results in the highest specific surface area (11.91 m2 g−1) and the creation of abundant of nanosheets which construct rich mesopores for convenient K+ diffusion. Benefitted from the high purity, increased activated sites for K+ association as well as the accelerated charge transfer/ion diffusion kinetics, the AMG-55 electrode exhibits high reversible capacity (262.3 mAh g−1), superior cycling ability and best rate performance among the activated samples. A stable charge capacity of 171.9 mAh g−1 still can be maintained after 200 discharge/charge cycles at 0.1 A g−1 with a favorable capacity retention of 65.5%. Moreover, the electrode releases a high reversible capacity of 162.1 mAh g−1 at the large current density of 0.6 A g−1, suggesting the promising application potential of activated graphite for high-performance KIBs.

Seven synthesized G-lignin oligomer model compounds (ranging in size from dimers to an octamer) with 5-5 and/or β-O-4 linkages, and three synthesized S-lignin model compounds (a dimer, trimer, and tetramer) with β-O-4 linkages, were evaporated and deprotonated using negative-ion mode ESI in a linear quadrupole ion trap/Fourier transform ion cyclotron resonance mass spectrometer. The collision-activated dissociation (CAD) fragmentation patterns (obtained in MS2 and MS3 experiments, respectively) for the negative ions were studied to develop a procedure for sequencing unknown lignin oligomers. On the basis of the observed fragmentation patterns, the measured elemental compositions of the most abundant fragment ions, and quantum chemical calculations, the most important reaction pathways and likely mechanisms were delineated. Many of these reactions occur via charge-remote fragmentation mechanisms. Deprotonated compounds with only β-O-4 linkages, or both 5-5 and β-O-4 linkages, showed major 1,2-eliminations ...

As a promising cathode for sodium ion batteries, polyanion-type phosphate compounds are considered as a potential candidate of the next-generation sodium storage materials for the three-dimensional (3D) structure and open pathways. However, several intrinsic faults, such as low electrical conductivity seriously prevent their practical application in broader fields. Herein, the nitrogen and sulfur co-doped carbon layer coated Na2VTi(PO4)3 nanocomposites have been synthesized by a facile sol-gel method. The crystal structure, surface morphology and charge-discharge performance were investigated to confirm the successful preparation of target particles and the substitution of nitrogen and sulfur elements. Among these prepared materials, the optimal sample can display a satisfactory discharge capacity of 164.85 mAh g−1 and high capacity retention of 96.5% after thirty cycles. Meanwhile, the superior rate properties and rapid reaction kinetics are achieved as a result of high electrical conductivity and fast ion diffusion coefficient, resulting in an enhanced electrochemical performance. The route in this paper may provide guidance to a large-scale commercial production of energy storage devices.

Cellulose, a major component of renewable biomass, is a polymer of glucose. Abundant and cheap iron salts promote the conversion of glucose to 5-hydroxymethylfurfural (HMF) and levulinic acid (LA). In this study, glucose transformations catalyzed by iron(III) chloride (FeCl3) in aqueous and in biphasic media (water and 2-methyltetrahydrofuran (MeTHF)) were investigated. Speciation via mass spectrometry (MS), UV-Vis, and X-ray absorption spectroscopy (XAS) show that FeIII is reduced to FeII (over 95%) readily in the early stage of carbohydrate conversion. The reaction time profiles of reactants (glucose and fructose) as well as products (HMF and LA) were modeled using MATLAB to obtain reaction rate constants. The contributions of iron and the intrinsic Bronsted acidity of iron salts in the sugar conversion are discussed. The kinetic study of sugar conversion indicated that the water–MeTHF biphasic system hinders the conversion of sugars to humins and unknown byproducts and increases the yields of HMF and LA. By adjusting concentrations of FeII and Bronsted acidity, yields of 88% LA (FeCl3, pH = 1) or 56% HMF (FeSO4, pH = 2) from glucose in a water–MeTHF biphasic system are achieved. The optimized reaction conditions proved effective in the conversion of milled poplar biomass to LA (53% yield based on glucose content) and furfural (64% yield based on xylan content) using iron salt, outperforming aluminum and chromium salts.

A negatively charged biradical intermediate was successfully generated in the gas phase via cyclization of the deprotonated bicyclo[8.3.0]trideca-12-ene-2,7-diyn-1-one precursor. The inherent negative charge of this biradical allows its characterization via collision-activated dissociation and reactions with a variety of neutral substrates in an FT-ICR mass spectrometer. Although the biradical is unreactive toward reagents that usually react rapidly with positively charged biradicals, such as dimethyl disulfide, it reacts with the halogen-containing substrates carbon tetrachloride, carbon tetrabromide, and bromotrichloromethane via bromine or chlorine atom abstraction, which supports its biradical structure. The results presented in this study indicate that cyclizations commonly used in solution to form biradical intermediates from enediyne compounds may also occur in the gas phase.

Klf4 is a transcription factor of the family of Kruppel-like factors and plays important roles in stem cell biology; however, its function during embryogenesis is unknown. Here, we report the characterization of a Klf4 homologue in Xenopus laevis during embryogenesis. Klf4 is transcribed both maternally and zygotically and the transcript is ubiquitous in embryos during germ-layer formation. Klf4 promotes endoderm differentiation in both Nodal/Activin-dependent and -independent manners. Moreover, Klf4 regulates anteroposterior body axis patterning via activation of a subset of genes in the Spemann organizer, such as Noggin, Dkk1 and Cerberus, which encode Nodal, Wnt and BMP antagonists. Loss of Klf4 function leads to the failure of germ-layer differentiation, the loss of responsiveness of early embryonic cells to inducing signals, e.g. Nodal/Activin, and the loss of transcription of genes involved in axis patterning. We conclude that Klf4 is required for germ-layer differentiation and body axis patterning by means of rendering early embryonic cells competent to differentiation signals.

The reactivity of carbon-centered distonic radical ions has been of interest for decades. The existence of distonic radical ions was first postulated by Gross and McLafferty in the early 1970’s.1,2 In 1978, Bouma, MacLeod and Radom reported experimental results that supported theoretical predictions of the existence of a stable ring-opened ethylene oxide distonic radical cation.3 Ions with spatially separated charge and radical sites were coined as “distonic ions” by Yates, Bouma, and Radom4 in 1984. They later refined this definition5 to correspond to radical ions generated by ionization of a zwitterion, ylide, or diradical. Eberlin and co-workers later introduced the term “distonoid”, meaning distonic like, to encompass any radical ion that displays distonic “character” (i.e., ions with a high degree of discrete (non-mandatory) charge-spin separation) and is over-looked as a result of the strict distonic ion definition.6 However, the “distonoid” classification is not commonly used by the scientific community. Currently, the term “distonic” is widely accepted and used to denote ions with formally separated charge and radical sites even if they do not fall into the formal definition.7 According to the conventional valence bond description, the charge and radical sites are on adjacent atoms in α-distonic ions while they are separated by one and two atoms in β- and γ-distonic ions, respectively. A vast amount of experimental and theoretical studies were dedicated to distonic ions from the 1980’s to 1990’s, which have been previously reviewed separately by Hammerum and Kenttamaa.8,9,10 The focus of this review is on gaseous ions with one or more aryl radical sites, a subgroup of distonic radical cations. The interest in these distonic ions was initially sparked by the limited knowledge on the reactivity of neutral phenyl radicals and their diradical counterparts in spite of the vast amount of research dedicated to these reactive intermediates.11–70 Many such mono- and diradicals have been investigated as they are thought to play a vital role in numerous fields, including combustion,11–13 polymerization,14–16 atmospheric chemistry,17–19 interstellar chemistry,20 organic synthesis8 and the biological activity of certain drugs.21–33 In the 1990’s, the formation of such aromatic diradicals in naturally occurring anti-tumor antibiotics was associated with their DNA-cleaving ability.21–33 The two radical sites are thought to abstract a hydrogen atom from each strand of double stranded DNA, thus causing irreversible DNA cleavage. Since then, theoretical and experimental research on aryl mono- and diradicals has boomed. An area of special interest has been the mechanistic understanding of hydrogen atom abstraction by these radicals from small organic and biological molecules both in solution34–45 and in the gas phase.46–70 However, the ability to predict the rates of such seemingly simple reactions has proven challenging due to a poor understanding of the nature of the transition states for these reactions. Further, the examination of the chemical properties of neutral radicals is a challenge due to the difficulty to cleanly generate them both in solution and in the gas phase. In order to address the above difficulties, studies were carried out in the early 1990’s on distonic radical cations’ ion-molecule reactions inside mass spectrometers as ions can be easily manipulated in this environment.46–70 Distonic radical cations that have a phenyl radical site spatially separated from a chemically inert charge site were found to almost exclusively undergo radical reactions at the radical site(s) in the gas phase46–70 and lately also in solution.45 Hence, examination of these distonic ions will provide information on the properties of phenyl mono- and diradicals. A special benefit of using mass spectrometry to study above species is that the desired charged radical can be isolated before examining its reactivity. Hence, the precursors to any products formed in these gas-phase experiments are known, which is not always true for solution experiments wherein highly reactive molecules cannot be isolated. The chemical properties of many aryl mono-, di- and triradicals have been successfully examined in mass spectrometers by using this ‘distonic ion approach’.49,50,52 The results obtained in these studies provide valuable information on the relative reactivities of mono- and polyradicals, which would otherwise not be available. This paper reviews the current knowledge of the properties and reactivity of distonic radical ions with aryl radical sites and the mechanisms of these reactions. Distonic phenyl radical ions generated within peptides are not included due to space limitations and also since these radicals are usually generated as precursors to less reactive nonaromatic peptide radicals that are the true interest of the researchers. However, this is an important and exciting new field of distonic ion research that should be reviewed separately.

Catalytic deoxydehydration (DODH) of vicinal diols is carried out employing methyltrioxorhenium (MTO) as the catalyst and a sacrificial alcohol as the reducing agent. The reaction kinetics feature an induction period when MTO is added last and show zero-order in [diol] and half-order dependence on [catalyst]. The rate-determining step involves reaction with alcohol, as evidenced by a KIE of 1.4 and a large negative entropy of activation (Delta S-double dagger = -154 +/- 33 J mol(-1) K-1). The active form of the catalyst is methyldioxorhenium(V) (MDO), which is formed by reduction of MTO by alcohol or via a novel C-C bond cleavage of an MTO-diolate complex. The majority of the MDO-diolate complex is present in dinuclear form, giving rise to the [Re](1/2) dependence. The MDO-diolate complex undergoes further reduction by alcohol in the rate-determining step to give rise to a putative rhenium(III) diolate. The latter is the active species in DODH extruding stereoselectively trans-stilbene from (R,R)-(+)-hydrobenzoin to regenerate MDO and complete the catalytic cycle.

The gas-phase reactions of sugars with aromatic, carbon-centered sigma,sigma-biradicals with varying polarities [as reflected by their calculated electron affinities (EA)] and extent of spin-spin coupling [as reflected by their calculated singlet-triplet (S-T) gaps] have been studied. The biradicals are positively charged, which allows them to be manipulated and their reactions to be studied in a Fourier-transform ion cyclotron resonance mass spectrometer. Hydrogen atom abstraction from sugars was found to be the dominant reaction for the biradicals with large EA values, while the biradicals with large S-T gaps tend to form addition/elimination products instead. Hence, not all sigma, sigma-biradicals may be able to damage DNA by hydrogen atom abstraction. The overall reaction efficiencies of the biradicals towards a given substrate were found to be directly related to the magnitude of their EA values, and inversely related to their S-T gaps. The EA of a biradical appears to be a very important rate-controlling factor, and it may even counterbalance the reduced radical reactivity characteristic of singlet biradicals that have large S-T gaps.

After publication of the paper, the authors realized that the affiliation of the fourth author (Tiberiu Esanu) was given incorrectly. Its correct version appears above. Moreover, a second funding grant was missed in the acknowledgements. We give their complete correct version below.

The gas-phase reactions of sugars with aromatic, carbon-centered σ,σ-biradicals with varying polarities [as reflected by their calculated electron affinities (EA)] and extent of spin-spin coupling [as reflected by their calculated singlet-triplet (S-T) gaps] have been studied. The biradicals are positively charged, which allows them to be manipulated and their reactions to be studied in a Fourier-transform ion cyclotron resonance mass spectrometer. Hydrogen atom abstraction from sugars was found to be the dominant reaction for the biradicals with large EA values, while the biradicals with large S-T gaps tend to form addition/elimination products instead. Hence, not all σ,σ-biradicals may be able to damage DNA by hydrogen atom abstraction. The overall reaction efficiencies of the biradicals towards a given substrate were found to be directly related to the magnitude of their EA values, and inversely related to their S-T gaps. The EA of a biradical appears to be a very important rate-controlling factor, and it may even counterbalance the reduced radical reactivity characteristic of singlet biradicals that have large S-T gaps.