Nanoporous graphitic-C3N4@carbon metal-free electrocatalysts for highly efficient oxygen reduction

Based on theoretical prediction, a g-C(3)N(4)@carbon metal-free oxygen reduction reaction (ORR) electrocatalyst was designed and synthesized by uniform incorporation of g-C(3)N(4) into a mesoporous carbon to enhance the electron transfer efficiency of g-C(3)N(4). The resulting g-C(3)N(4)@carbon composite exhibited competitive catalytic activity (11.3 mA cm(-2) kinetic-limiting current density at -0.6 V) and superior methanol tolerance compared to a commercial Pt/C catalyst. Furthermore, it demonstrated significantly higher catalytic efficiency (nearly 100% of four-electron ORR process selectivity) than a Pt/C catalyst. The proposed synthesis route is facile and low-cost, providing a feasible method for the development of highly efficient electrocatalysts.     

Chemical sensing in two dimensional porous covalent organic nanosheets

Two new imide-based crystalline, porous, and chemically stable covalent organic frameworks (COFs) (TpBDH and TfpBDH) have been successfully synthesized employing solvothermal crystallization route. Furthermore, thin layered covalent organic nanosheets (CONs) were derived from these bulk COFs by the simple liquid phase exfoliation method. These 2D CONs showcase increased luminescence intensity compared to their bulk counterparts (COFs). Notably, TfpBDH-CONs showcase good selectivity and prominent, direct visual detection towards different nitroaromatic analytes over TpBDH-CONs. Quite interestingly, TfpBDH-CONs exhibit a superior “turn-on” detection capability for 2,4,6-trinitrophenol (TNP) in the solid state, but conversely, they also show a “turn-off” detection in the dispersion state. These findings describe a new approach towards developing an efficient, promising fluorescence chemosensor material for both visual and spectroscopic detection of nitroaromatic compounds with very low [10^–5 (M)] analyte concentrations.     

A two-dimensional molecular beacon for mRNA-activated intelligent cancer theranostics

Ideal theranostics should possess directly correlated imaging and therapy modalities that could be simultaneously activated in the disease site to generate high imaging contrast and therapeutic efficacy with minimal side effects. However, so far it still remains challenging to engineer all these characteristics into a single theranostic probe. Herein, we report a new type of photosensitizer (PS)-derived “two-dimensional” molecular beacon (TMB) that could be specifically activated within tumor cells to exhibit both high imaging contrast and therapeutic efficacy that outperforms conventional photosensitizers for cancer theranostics. The TMB is constructed by integrating a photosensitizer (chlorin e6 (Ce6)), a quantum dot (QD), and a dark quencher (BHQ3) into a hairpin DNA molecule to generate multiple synergistic FRET modes. The imaging modality and therapy modality, which are mediated by FRET between the QD and BHQ3 and FRET between the QD and Ce6 respectively, are interconnected within the TMB and could be simultaneously activated by tumor mRNA molecules. We show that highly effective cancer imaging and therapy could be achieved for cancer cell lines and xenografted tumor models. The reported TMB represents an unprecedented theranostic platform for intelligent cancer theranostics.     

The approach to 4d/4f-polyphosphides

The first 4d/4f polyphosphides were obtained by reaction of the divalent metallocenes [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] or [Cp*Mo(CO)₂(η³-P₃)]. Treatment of [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] gave the 16-membered bicyclic compounds [(Cp₂*Ln)₂P₂(CpMo(CO)₂)₄] (Ln = Sm, Yb) as the major products. From the reaction involving samarocene, the cyclic P₄ complex [(Cp*₂Sm)₂P₄(CpMo(CO)₂)₂] and the cyclic P₅ complex [(Cp*₂Sm)₃P₅(CpMo(CO)₂)₃] were also obtained as minor products. In each reaction, the P₂ unit is reduced and a rearrangement occurred. In dedicated cases, a P–P bond formation takes place, which results in a new aggregation of the central phosphorus scaffold. In the reactions of [Cp*₂Ln(thf)₂] (Ln = Sm, Yb) with [Cp*Mo(CO)₂P₃] a new P–P bond is formed by reductive dimerization and the 4d/4f hexaphosphides [(Cp*₂Ln)₂P₆(Cp*Mo(CO)₂)₂] (Ln = Sm, Yb) were obtained.     

Hydrogen bonds in 4-dihydroxymethylpyridinium 2,6-dichloro-4-nitrophenolate

The ionic adduct of 2,6-dichloro-4-nitrophenol with 4-formylpyridine (which transforms into 4-dihydroxymethylpyridine), crystallizes in the space group P2₁/c with a = 12.264(2), b = 6.730(1), c = 16.731(3) Å, β = 99.46(3)° and Z = 4. Relatively long N⁺---HO⁻ hydrogen bonds (R_N = 2.683(3) Å are formed with strongly asymmetric location of the H-atom. This is well reflected both in IR and UV-VIS spectra. One of the gem diol OH group is attached to the phenolate oxygen atom and the second is engaged in the formation of infinite polyanionic chains via O---HO hydrogen bonds between OH groups.     

Taming the beast: fluoromesityl groups induce a dramatic stability enhancement in boroles

The electron-deficient pentaarylborole 1-(2′,4′,6′-tris(trifluoromethyl)phenyl)-2,3,4,5-tetraphenylborole (1) has been synthesised with the long-term aim of developing borole-based optoelectronic materials. The bulky 2,4,6-tris(trifluoromethyl)phenyl (FMes) group on the boron atom of 1 significantly improves (>600 times) its air stability relative to its mesityl analogue. Moreover, 1 shows good thermal stability without undergoing the dimerisation or isomerisation reactions reported for some other boroles. A triarylborole analogue (2), belonging to a new class of borole with the 3- and 4-positions of the BC₄ ring linked by a –(CH₂)₃– group, has also been synthesised to elucidate the influence of carbon-bonded substituents on the stability of boroles. Both boroles were prepared through the reaction of Li[FMesBF₃] and divinyldilithium reagents, a new and general method for borole syntheses. Compound 2 was found to isomerise through a [1,3]-H shift and double-bond rearrangement to an s-trans-butadienylborane species under highly basic (NaOH) conditions. The increased steric crowding at the boron centre through incorporation of the FMes group does not preclude binding of Lewis bases to either 1 or 2, as demonstrated by their fully reversible binding of pyridine. Interestingly, 1 exhibits a blue-shifted absorption spectrum, as compared with its mesityl analogue, a result contrary to previous understanding of the influence of substituent electronics on the absorption spectra of boroles. Most importantly, these boroles exhibit much greater air-stability than previously reported analogues without sacrificing the strong electron-accepting ability that makes boroles so attractive; indeed, 1 and 2 have very low reduction potentials of –1.52 and –1.69 eV vs. Fc/Fc⁺, respectively.     

One-pot synthesis of VO x /Al 2 O 3 as efficient catalysts for propane dehydrogenation

Vanadium oxides, as highly efficiently catalysts, are widely applied in various catalytic reactions, such as the dehydrogenation of light alkanes and epoxidation of alkenes. In this paper, a series of VO _x /Al ₂ O ₃ catalysts were fabricated by the 1-pot method for catalytic propane dehydrogenation. The results indicated that the VO _x /Al ₂ O ₃ catalysts with loading of 10 wt.% vanadium exhibited optimized catalytic performance. The as-prepared catalysts were characterized by N ₂ adsorption-desorption, XRD, TEM, H ₂ -TPR, and XPS to explore the texture properties, morphology, and electronic environment of vanadium. In addition, several vanadium catalysts were also prepared by the incipient wetness impregnation (IWI) method to compare their catalytic performance with the 1-pot synthesized catalysts. The catalysts synthesized by the 1-pot method exhibited higher selectivity of propylene and longer catalyst lifetime at high propane conversion when compared to the counterpart synthesized by the IWI method.     

N 6-Hydroperoxymethyladenosine: a new intermediate of chemical oxidation of N6-methyladenosine mediated by bicarbonate-activated hydrogen peroxide

N ⁶-Methyladenosine (m⁶A) represents a relatively abundant modification in eukaryotic RNA. Because m⁶A has similar properties to adenosine and a low reactivity, limited research has been focused on this nucleoside. In this study, we revealed an important intermediate in the oxidation of m⁶A through the bicarbonate-activated peroxide system. Over the course of oxidation, we found a new mechanism in which N⁶-hydroxymethyladenosine (hm⁶A), N⁶-formyladenosine (f⁶A) and N⁶-hydroperoxymethyladenosine (oxm⁶A) were intermediate products, and adenosine was the final product. In this study, oxm⁶A was isolated using HPLC and characterized by mass spectrometry, NMR and diphenyl-1-pyrenylphosphine (DPPP) fluorescence detection. This study provides a new modified nucleoside and demonstrates oxidative demethylation of m⁶A by reactive oxygen species at the nucleobase level and in RNA strands.     

Hydrogen bonds in dimers of 3-hydroxy-2-methyl-4-pyrone. AIM analysis

According to quantum topological analysis performed at the MP2/6-311++G** level the intramolecular hydrogen bond OH⋯O=C in 3-hydroxy-2-methyl-4-pyrone (maltol) is weak and has ionic nature. This bond is broken upon formation of H-complex of maltol with phosgene and with increase the polarity of medium. The chain dimer of maltol is stabilized by weak intermolecular bonds OH⋯O=C and CH⋯O=C of ionic character, whereas the cyclic dimer by two medium in strength intermolecular hydrogen bonds OH⋯O=C. Original Russian Text ? E.P. Doronina, T.N. Aksamentova, N.N. Chipanina, S.A. Mukha, S.A. Medvedeva, 2009, published in Zhurnal Obshchei Khimii, 2009, vol. 79, No. 2, pp. 308–313.     

Synthesis and characterization of piperazine-substituted dihydrofuran derivatives viaMn(OAc) 3 mediated radical cyclizations

The aim of this study is to synthesize novel piperazine-containing dihydrofuran compounds (3a-n)from radical additions and cyclizations of diacyl and alkyl-acyl piperazine derivatives (1a-h) with 1,3-dicarbonyl compounds (2a-c) mediated by Mn(OAc) ₃ for the first time. From the reactions of 1a-c with dimedone (2a);1a, 1c, and 1d with acetylacetone (2b); and 1a with ethylacetoacetate(2c) ,the dihydrofuran-piperazine compounds 3a-c, 3d-f, and 3g were obtained in medium to high yields (31%–81%), respectively. In addition, dihydrofuran-piperazine compounds 3h-j and 3k-n were prepared at low to medium yields (20%–40%) from the reactions of 1e-g with 2a and 1e-h with 2c , respectively.     

Direct in vivo imaging of ferrous iron dyshomeostasis in ageing Caenorhabditis elegans

Iron is essential for eukaryotic biochemistry. Systematic trafficking and storage is required to maintain supply of iron while preventing it from catalysing unwanted reactions, particularly the generation of oxidising reactive species. Iron dyshomeostasis has been implicated in major age-associated diseases including cancers, neurodegeneration and heart disease. Here, we employ population-level X-ray fluorescence imaging and native-metalloproteomic analysis to determine that altered iron coordination and distribution is a pathological imperative of ageing in the nematode, Caenorhabditis elegans. Our approach provides a method to simultaneously study iron metabolism across different scales of biological organisation, from populations to cells. Here we report how and where iron homeostasis is lost during C. elegans ageing, and its relationship to the age-related elevation of damaging reactive oxygen species. We find that wild types utilise ferritin to sustain longevity, buffering against exogenous iron and showing rapid ageing if ferritin is ablated. After reproduction, escape of iron from safe-storage in ferritin raised cellular Fe²⁺ load in the ageing C. elegans, and increased generation of reactive species. These findings support the hypothesis that iron-mediated processes drive senescence. We propose that loss of iron homeostasis may be a fundamental and inescapable consequence of ageing that could represent a critical target for therapeutic strategies to improve health outcomes in ageing.     

Doping-induced memory effect in Li-ion batteries: the case of Al-doped Li4Ti5O12

In Li-ion batteries (LIBs), a memory effect has been revealed in two-phase electrode materials such as olivine LiFePO₄ and anatase TiO₂, which complicates the two-phase transition and influences the estimation of the state of charge. Practical electrode materials are usually optimized by the element doping strategy, however, its impact on the memory effect has not been reported yet. Here we firstly present the doping-induced memory effect in LIBs. Pristine Li₄Ti₅O₁₂ is free from the memory effect, while a distinct memory effect could be induced by Al-doping. After being discharged to a lower cutoff potential, Al-doped Li₄Ti₅O₁₂ exhibits poorer electrochemical kinetics, delivering a larger overpotential during the charging process. This dependence of the overpotential on the discharging cutoff leads to the memory effect in Al-doped Li₄Ti₅O₁₂. Our discovery emphasizes the impact of element doping on the memory effect of electrode materials, and thus has implications for battery design.     

Carbonyl‐Grafted g‐C3N4 Porous Nanosheets for Efficient Photocatalytic Hydrogen Evolution

Carbonyl‐grafted g‐C₃N₄ porous nanosheets (COCNPNS) were fabricated by means of a two‐step thermal process using melamine and oxalic acid as starting reagents. The combination of melamine with oxalic acid to form a melamine–oxalic acid supramolecule as a precursor is key to synthesizing carbonyl‐grafted g‐C₃N₄. The bulk carbonyl‐grafted g‐C₃N₄ (COCN) was further thermally etched onto porous nanosheets by O₂ under air. In such a process, the carbonyl groups were partly removed and the obtained sample showed remarkably enhanced visible‐light harvesting and promoted the separation and transfer of photogenerated electrons and holes. With its unique porous structure and enhanced light‐harvesting capability, under visible‐light illumination (λ >420 nm) the prepared COCNPNS exhibited a superior photocatalytic hydrogen evolution rate of 83.6 μmol h⁻¹, which is 26 times that of the p‐CN obtained directly from thermal polycondensation of melamine.     

N- and O-arylation of pyridin-2-ones with diaryliodonium salts: base-dependent orthogonal selectivity under metal-free conditions

Metal-free N- and O-arylation reactions of pyridin-2-ones as ambident nucleophiles have been achieved with diaryliodonium salts on the basis of base-dependent chemoselectivity. In the presence of N,N-diethylaniline in fluorobenzene, pyridin-2-ones were very selectively converted to N-arylated products in high yields. On the other hand, the O-arylation reactions smoothly proceeded with the use of quinoline in chlorobenzene, leading to high yields and selectivities. In these methods, a variety of pyridin-2-ones in addition to pyridin-4-one and a set of diaryliodonium salts were accepted as suitable reaction partners.

The metal-free N- and O-arylation reactions of pyridin-2-ones with diaryliodonium salts were achieved on the basis of base-dependent chemoselectivity.     

Increased carrier mobility in end-functionalized oligosilanes

We show that a class of oligosilane–arene σ, π-hybrid materials exhibits distinct and enhanced solid-state electronic properties relative to its parent components. In the single crystal structure, the σ-conjugation axis of one molecule points towards the π-face of a neighboring molecule due to an unusual gauche conformation. This organization is hypothesized to be beneficial for charge transport. We show that solution-deposited crystalline films of the hybrid materials show up to a 100-fold increase in space-charge limited current (SCLC) mobility relative to literature reports of photoinduced hole transport in oligosilane films. The discovery that σ, π-hybrids are more than the sum of their parts offers a design opportunity for new materials.     

Potent and selective inhibition of SH3 domains with dirhodium metalloinhibitors

Src-family kinases (SFKs) play important roles in human biology and are key drug targets as well. However, achieving selective inhibition of individual Src-family kinases is challenging due to the high similarity within the protein family. We describe rhodium(ii) conjugates that deliver both potent and selective inhibition of Src-family SH3 domains. Rhodium(ii) conjugates offer dramatic affinity enhancements due to interactions with specific and unique Lewis-basic histidine residues near the SH3 binding interface, allowing predictable, structure-guided inhibition of SH3 targets that are recalcitrant to traditional inhibitors. In one example, a simple metallopeptide binds the Lyn SH3 domain with 6 nM affinity and exhibits functional activation of Lyn kinase under biologically relevant concentrations (EC₅₀ ∼ 200 nM).     

Exploiting parameter space in MOFs: a 20-fold enhancement of phosphate-ester hydrolysis with UiO-66-NH2

The hydrolysis of nerve agents is of primary concern due to the severe toxicity of these agents. Using a MOF-based catalyst (UiO-66), we have previously demonstrated that the hydrolysis can occur with relatively fast half-lives of 50 minutes. However, these rates are still prohibitively slow to be efficiently utilized for some practical applications (e.g., decontamination wipes used to clean exposed clothing/skin/vehicles). We thus turned our attention to derivatives of UiO-66 in order to probe the importance of functional groups on the hydrolysis rate. Three UiO-66 derivatives were explored; UiO-66-NO₂ and UiO-66-(OH)₂ showed little to no change in hydrolysis rate. However, UiO-66-NH₂ showed a 20 fold increase in hydrolysis rate over the parent UiO-66 MOF. Half-lives of 1 minute were observed with this MOF. In order to probe the role of the amino moiety, we turned our attention to UiO-67, UiO-67-NMe₂ and UiO-67-NH₂. In these MOFs, the amino moiety is in close proximity to the zirconium node. We observed that UiO-67-NH₂ is a faster catalyst than UiO-67 and UiO-67-NMe₂. We conclude that the role of the amino moiety is to act as a proton-transfer agent during the catalytic cycle and not to hydrogen bond or to form a phosphorane intermediate.     

LiLa5Si4N10O and LiPr5Si4N10O – Chain‐Type Oxonitridosilicates

The isotypic lithium rare‐earth oxonitridosilicates LiLn₅Si₄N₁₀O (Ln = La, Pr) were synthesized at temperatures of 1200 °C in weld shut tantalum ampoules employing liquid lithium as flux. Thereby, a silicate substructure with a low degree of condensation was obtained. LiLa₅Si₄N₁₀O crystallizes in space group P$\bar{1}$ [Z = 1, LiLa₅Si₄N₁₀O: a = 5.7462(11), b = 6.5620(13), c = 8.3732(17) Å, α = 103.54(3), β = 107.77(3), γ = 94.30(3), wR₂ = 0.0405, 1315 data, 96 parameters]. The nitridosilicate substructure consists of loop branched dreier single‐chains of vertex sharing SiN₄ tetrahedra. Lattice energy calculations (MAPLE) and EDX measurements confirmed the electrostatic bonding interactions and the chemical compositions. The ⁷Li solid‐state MAS NMR investigation is reported.     

Oxygen diffusion pathways in a cofactor-independent dioxygenase

Molecular oxygen plays an important role in a wide variety of enzymatic reactions. Through recent research efforts combining computational and experimental methods a new view of O₂ diffusion is emerging, where specific channels guide O₂ to the active site. The focus of this work is DpgC, a cofactor-independent oxygenase. Molecular dynamics simulations, together with mutagenesis experiments and xenon-binding data, reveal that O₂ reaches the active site of this enzyme using three main pathways and four different access points. These pathways connect a series of dynamic hydrophobic pockets, concentrating O₂ at a specific face of the enzyme substrate. Extensive molecular dynamics simulations provide information about which pathways are more frequently used. This data is consistent with the results of kinetic measurements on mutants and is difficult to obtain using computational cavity-location methods. Taken together, our results reveal that although DpgC is rare in its ability of activating O₂ in the absence of cofactors or metals, the way O₂ reaches the active site is similar to that reported for other O₂-using proteins: multiple access channels are available, and the architecture of the pathway network can provide regio- and stereoselectivity. Our results point to the existence of common themes in O₂ access that are conserved among very different types of proteins.