Discovery and Manipulation of van der Waals Polarons in Sb2O3 Ultrathin Molecular Crystal.

Manipulating single electrons at the atomic scale is vital for mastering complex surface processes governed by the transfer of individual electrons. Polarons, composed of electrons stabilized by electron-phonon coupling, offer a pivotal medium for such manipulation. Here, using scanning tunneling microscopy and spectroscopy (STM/STS) and density functional theory (DFT) calculations, we report the identification and manipulation of a new type of polaron, dubbed van der Waals (vdW) polaron, within mono- to trilayer ultrathin films composed of Sb2O3 molecules that are bonded via vdW attractions. The Sb2O3 films were grown on a graphene-covered SiC(0001) substrate via molecular beam epitaxy. Unlike prior molecular polarons, STM imaging observed polarons at the interstitial sites of the molecular film, presenting unique electronic states and localized band bending. DFT calculations revealed the lowest conduction band as an intermolecular bonding state, capable of ensnaring an extra electron through locally diminished intermolecular distances, thereby forming an intermolecular vdW polaron. We also demonstrated the ability to generate, move, and erase such vdW polarons using an STM tip. Our work uncovers a new type of polaron stabilized by coupling with intermolecular vibrations where vdW interactions dominate, paving the way for designing atomic-scale electron transfer processes and enabling precise tailoring of electron-related properties and functionalities.

Manipulating single excess electrons in monolayer transition metal dihalide.

Polarons are entities of excess electrons dressed with local response of lattices, whose atomic-scale characterization is essential for understanding the many body physics arising from the electron-lattice entanglement, yet difficult to achieve. Here, using scanning tunneling microscopy and spectroscopy (STM/STS), we show the visualization and manipulation of single polarons in monolayer CoCl2, that are grown on HOPG substrate via molecular beam epitaxy. Two types of polarons are identified, both inducing upward local band bending, but exhibiting distinct appearances, lattice occupations and polaronic states. First principles calculations unveil origin of polarons that are stabilized by cooperative electron-electron and electron-phonon interactions. Both types of polarons can be created, moved, erased, and moreover interconverted individually by the STM tip, as driven by tip electric field and inelastic electron tunneling effect. This finding identifies the rich category of polarons in CoCl2 and their feasibility of precise control unprecedently, which can be generalized to other transition metal halides.

A novel all-nitrogen molecular crystal N16 as a promising high-energy-density material.

All-nitrogen solids, if successfully synthesized, are ideal high-energy-density materials because they store a great amount of energy and produce only harmless N2 gas upon decomposition. Currently, the only method to obtain all-nitrogen solids is to apply high pressure to N2 crystals. However, products such as cg-N tend to decompose upon releasing the pressure. Compared to covalent solids, molecular crystals are more likely to remain stable during decompression because they can relax the strain by increasing the intermolecular distances. The challenge of such a route is to find a molecular crystal that can attain a favorable phase under elevated pressure. In this work, we show, by designing a novel N16 molecule (tripentazolylamine) and examining its crystal structures under a series of pressures, that the aromatic units and high molecular symmetry are the key factors to achieving an all-nitrogen molecular crystal. Density functional calculations and structural studies reveal that this new all-nitrogen molecular crystal exhibits a particularly slow enthalpy increase with pressure due to the highly efficient crystal packing of its highly symmetric molecules. Vibration mode calculations and molecular dynamics (MD) simulations show that N16 crystals are metastable at ambient pressure and could remain inactive up to 400 K. The initial reaction steps of the decomposition are calculated by following the pathway of the concerted excision of N2 from the N5 group as revealed by the MD simulations.

Planar Heterojunction of Ultrathin CrTe3 and CrTe2 van der Waals Magnet.

The fabrication of planar heterojunctions with magnetic van der Waals ultrathin crystals is essential for constructing miniaturized spintronic devices but is yet to be realized. Here, we report the growth of CrTe3 and CrTe2 ultrathin films with molecular beam epitaxy and characterize their morphological and electronic structure through low-temperature scanning tunneling microscopy/spectroscopy. The former is identified as a Mott insulator, and the latter has shown a robust magnetic order previously. Through vacuum annealing, CrTe3 can be transformed into CrTe2, whose relative ratio is controlled via the annealing time. This renders the feasibility of constructing CrTe3-CrTe2 planar heterojunctions, which express atomically sharp interfaces and smooth band bending. We also identified a superstructure conceivably formed via hybrid units of CrTe3 and CrTe2, whose electronic structure exhibits stunning tunability with the length of the superstructure. Our study sets a foundation for the development of magnetic tunneling junctions for building spintronic circuits and engineering electronic states in artificial superlattice structures.

Spin mapping of intralayer antiferromagnetism and field-induced spin reorientation in monolayer CrTe2.

Intrinsic antiferromagnetism in van der Waals (vdW) monolayer (ML) crystals enriches our understanding of two-dimensional (2D) magnetic orders and presents several advantages over ferromagnetism in spintronic applications. However, studies of 2D intrinsic antiferromagnetism are sparse, owing to the lack of net magnetisation. Here, by combining spin-polarised scanning tunnelling microscopy and first-principles calculations, we investigate the magnetism of vdW ML CrTe2, which has been successfully grown through molecular-beam epitaxy. We observe a stable antiferromagnetic (AFM) order at the atomic scale in the ML crystal, whose bulk is ferromagnetic, and correlate its imaged zigzag spin texture with the atomic lattice structure. The AFM order exhibits an intriguing noncollinear spin reorientation under magnetic fields, consistent with its calculated moderate magnetic anisotropy. The findings of this study demonstrate the intricacy of 2D vdW magnetic materials and pave the way for their in-depth analysis.

Tetrahedral DNA nanostructures synergize with MnO2 to enhance antitumor immunity via promoting STING activation and M1 polarization

Stimulator of interferon genes (STING) is a cytosolic DNA sensor which is regarded as a potential target for antitumor immunotherapy. However, clinical trials of STING agonists display limited anti-tumor effects and dose-dependent side-effects like inflammatory damage and cell toxicity. Here, we showed that tetrahedral DNA nanostructures (TDNs) actively enter macrophages to promote STING activation and M1 polarization in a size-dependent manner, and synergized with Mn2+ to enhance the expressions of IFN-β and iNOS, as well as the co-stimulatory molecules for antigen presentation. Moreover, to reduce the cytotoxicity of Mn2+, we constructed a TDN-MnO2 complex and found that it displayed a much higher efficacy than TDN plus Mn2+ to initiate macrophage activation and anti-tumor response both in vitro and in vivo. Together, our studies explored a novel immune activation effect of TDN in cancer therapy and its synergistic therapeutic outcomes with MnO2. These findings provide new therapeutic opportunities for cancer therapy.

Pharmaceutical applications of framework nucleic acids

DNA is a biological polymer that encodes and stores genetic information in all living organism. Particularly, the precise nucleobase pairing inside DNA is exploited for the self-assembling of nanostructures with defined size, shape and functionality. These DNA nanostructures are known as framework nucleic acids (FNAs) for their skeleton-like features. Recently, FNAs have been explored in various fields ranging from physics, chemistry to biology. In this review, we mainly focus on the recent progress of FNAs in a pharmaceutical perspective. We summarize the advantages and applications of FNAs for drug discovery, drug delivery and drug analysis. We further discuss the drawbacks of FNAs and provide an outlook on the pharmaceutical research direction of FNAs in the future.

Bubble-wrap carbon: an integration of graphene and fullerenes.

Graphene and fullerene, two types of C allotropes with very different structures and properties, have attracted considerable attention from the scientific community as new forms of carbon for several decades. It will be a great advantage to combine the geometrical features of the two. Herein, we report a series of novel two-dimensional carbon allotropes that possess fullerene-like hollow structures (bubbles) embedded in a graphene sheet. These carbon allotropes are both thermally and dynamically stable. Calculations using hybrid functionals show that these two-dimensional carbon allotropes could be metals or semiconductors depending on the size and the pattern of the bubbles. The band gap can be as large as 1.66 eV. Due to the unique atomic configuration, some bubble-wrap carbons have unusual negative Poisson's ratios. The combination of graphene and fullerenes provides an appealing approach to design carbon-based materials with dexterous properties. For example, the insertion of the metal atoms inside the bubbles may greatly enhance the functions of such materials in photovoltaics and catalysis.

Reactivity of He with ionic compounds under high pressure.

Until very recently, helium had remained the last naturally occurring element that was known not to form stable solid compounds. Here we propose and demonstrate that there is a general driving force for helium to react with ionic compounds that contain an unequal number of cations and anions. The corresponding reaction products are stabilized not by local chemical bonds but by long-range Coulomb interactions that are significantly modified by the insertion of helium atoms, especially under high pressure. This mechanism also explains the recently discovered reactivity of He and Na under pressure. Our work reveals that helium has the propensity to react with a broad range of ionic compounds at pressures as low as 30 GPa. Since most of the Earth's minerals contain unequal numbers of positively and negatively charged atoms, our work suggests that large quantities of He might be stored in the Earth's lower mantle.

Quasi-Emulsion Confined Synthesis of Edge-Rich Ultrathin MoS2 Nanosheets/Graphene Hybrid for Enhanced Hydrogen Evolution.

High-purity hydrogen produced by water splitting is considered as one of the most promising fuels to replace traditional fossil fuels. Developing highly efficient electrocatalysts toward hydrogen evolution is vital for the realization of large-scale H2 generation. Glycerol is used herein in a facile solvothermal process to synthesize edge-rich ultrathin MoS2 /reduced graphene oxide (RGO) composites. The introduction of glycerol plays an important role in the formation of such interesting structures. The MoS2 /RGO electrocatalyst exhibits excellent hydrogen evolution reaction (HER) activity and remarkable stability, owing to the rich active edges and improved electrical conductivity of the catalyst composites. This work provides new insights to engineer the structures of MoSx -based composites and thus achieves more active and efficient electrocatalysts.

Risk of autism spectrum disorder in offspring following paternal use of selective serotonin reuptake inhibitors before conception: a population-based cohort study.

OBJECTIVE: The present study aimed to examine the association between paternal selective serotonin reuptake inhibitor (SSRI) use before conception and the risk of autism spectrum disorder (ASD) in offspring. DESIGN: A population-based cohort study. METHODS: We conducted a cohort study of 669 922 children born from 1998 to 2008, with follow-up throughout 2013. Based on Danish national registers, we linked information on paternal use of SSRIs, ASD diagnosed in children and a range of potential confounders. The children whose fathers used SSRIs during the last 3 months prior to conception were identified as the exposed. Cox regression model was used to estimate the HR for ASD in children. RESULTS: Compared with unexposed children, the exposed had a 1.62-fold higher risk of ASD (95% CI 1.33 to 1.96) and the risk attenuated after adjusting for potential confounders, especially fathers' psychiatric conditions (HR=1.43, 95% CI 1.18 to 1.74). When extending the exposure window to 1 year before conception, the increased risk persisted in children of fathers using SSRIs only from the last year until the last 3 months prior to conception (HR=1.54, 95% CI 1.21 to 1.94) but not in children of fathers using SSRIs only during the last 3 months prior to conception (HR=1.17, 95% CI 0.75 to 1.82). We also performed stratified analyses according to paternal history of affective disorders and observed no increased ASD risk among children whose father had affective disorders. Besides, the sibling analysis showed that the ASD risk did not increase among exposed children compared with their unexposed siblings. CONCLUSIONS: The mildly increased risk of ASD in the offspring associated with paternal SSRI use before conception may be attributable to paternal underlying psychiatric indications related to SSRI use or other unmeasured confounding factors.

Honeycomb Boron Allotropes with Dirac Cones: A True Analogue to Graphene.

We propose a series of planar boron allotropes with honeycomb topology and demonstrate that their band structures exhibit Dirac cones at the K point, the same as graphene. In particular, the Dirac point of one honeycomb boron sheet locates precisely on the Fermi level, rendering it as a topologically equivalent material to graphene. Its Fermi velocity (vf) is 6.05 × 105 m/s, close to that of graphene. Although the freestanding honeycomb B allotropes are higher in energy than α-sheet, our calculations show that a metal substrate can greatly stabilize these new allotropes. They are actually more stable than α-sheet sheet on the Ag(111) surface. Furthermore, we find that the honeycomb borons form low-energy nanoribbons that may open gaps or exhibit strong ferromagnetism at the two edges in contrast to the antiferromagnetic coupling of the graphene nanoribbon edges.

Molybdenum Carbide-Based Electrocatalysts for Hydrogen Evolution Reaction.

Electrocatalytic water splitting is a promising approach for clean and sustainable hydrogen production. Its large-scale application relies on the availability of low cost and efficient electrocatalysts. Earth-abundant transition-metal carbides, especially molybdenum carbides (Mox C), are regarded as potential candidates to replace state-of-art but expensive platinum-group electrocatalysts. In this Review, we summarize recent progress in Mox C electrocatalysts for hydrogen evolution reaction (HER). Nanostructure engineering on the design and preparation of highly efficient electrocatalysts based on Mox C is presented, followed by the comparison and discussion of HER performance on Mox C-based electrocatalysts. Finally, we offer a perspective on the future development of Mox C-based electrocatalysts towards HER.

Couple's infertility in relation to male smoking in a Chinese rural area.

Smoking is a well-known risk factor of reproductive health. However, the effect of paternal smoking on fertility has been less extensively examined. We conducted a cross-sectional study in a mountainous area of South-West China to assess the effect of male smoking on couples' fertility. A total of 8200 couples aged 18-49 years in the study area were invited to participate in the study. An in-person interview was performed to collect demographic characteristics of the couples, and husbands' life style factors including smoking and drinking habits. Information on time to pregnancy (TTP) was collected retrospectively. Infertility was defined as failure to achieve clinical pregnancy after regular unprotected intercourse for ≥12 months. Logistic regression model was used to estimate the association between male smoking and infertility. A total of 7025 couples were included in the final analysis. After adjusting for potential confounders, the couples were more likely to suffer from infertility if the husbands smoked (adjusted odds ratio [aOR] =1.28, 95% CI: 1.08-1.52) before the first pregnancy. After the analyses were performed according to husbands' smoking duration, an increased risk started at a relatively longer smoking duration of 5-10 years (aOR = 1.58, 95% CI: 1.26-1.99) and a stronger association (aOR = 3.34, 95% CI: 2.45-4.56) was observed in the group of ≥10 years. Similar patterns were found for the number of cigarettes smoked per day and the total amount of cigarettes smoked. From our findings, we conclude that male smoking may have an adverse impact on couples' infertility.

Quasimolecules in Compressed Lithium.

Under high pressure, some materials form electrides, with valence electrons separated from all atoms and occupying interstitial regions. This is often accompanied by semiconducting or insulating behavior. The interstitial quasiatoms (ISQ) that characterize some high pressure electrides have been postulated to show some of the chemical features of atoms, including the potential of forming covalent bonds. It is argued that in the observed high-pressure semiconducting Li phase (oC40, Aba2), an example of such quasimolecules is realized. The theoretical evaluation of electron density, electron localization function, Wannier orbitals, and bond indices forms the evidence for covalently bonded ISQ pairs in this material. The quasimolecule concept thus provides a simple chemical perspective on the unusual insulating behavior of such materials, complementing the physical picture previously presented where the global crystal symmetry of the system plays the major role.

Macrocycles inserted in graphene: from coordination chemistry on graphene to graphitic carbon oxide.

Tuning electronic structures and properties through chemical modifications has become the focus of recent research on graphene. The adsorption of metal atoms on graphene showed strong potential but is limited due to weak binding. On the other hand, macrocyclic molecules are well known for their strong and selective binding with metal atoms in solutions through coordination bonds. The alliance of the two substances will largely benefit the two parallel fields: it will provide a scaffold for coordination chemistry as well as a controllable method for tuning the electronic structure of graphene through strong binding with metals. Here, using crown ether as an example, we demonstrate that the embedment of macrocyclic molecules into the graphene honeycomb lattice can be very thermochemically favored. The combination also leads to a family of new materials that has potential in many areas including photolysis and two-dimensional superconductivity.

Facile Probe Design: Fluorescent Amphiphilic Nucleic Acid Probes without Quencher Providing Telomerase Activity Imaging Inside Living Cells.

Nowadays, the probe with fluorophore but no quencher is promising for its simple preparation, environmental friendliness, and wide application scope. This study designs a new amphiphilic nucleic acid probe (ANAP) based on aggregation-caused quenching (ACQ) effect without any quencher. Upon binding with targets, the dispersion of hydrophobic part (conjugated fluorene, CF) in ANAP is enhanced as a signal-on model for proteins, nucleic acids, and small molecules detection or the aggregation of CF is enhanced as a signal-off model for ion detection. Meanwhile, because of the high specificity of ANAP, a one-step method is developed powerfully for monitoring the telomerase activity not only from the cell extracts but also from 50 clinic urine samples (positive results from 45 patients with bladder cancer and negative results from 5 healthy people). ANAPs can also readily enter into cells and exhibit a good performance for distinguishing natural tumor cells from the tumor cells pretreated by telomerase-related drugs or normal cells. In contrast to our previous results ( Anal. Chem. 2015 , 87 , 3890 - 3894 ), the present CF is a monomer which is just the structure unit of the previous fluorescent polymer. Since the accurate molecular structure and high DNA/CF ratio of the present CF, these advanced experiments obtain an easier preparation of probes, an improved sensitivity and specificity, and broader detectable targets.

Association between polymorphisms of prokineticin receptor (PKR1 rs4627609 and PKR2 rs6053283) and recurrent pregnancy loss.

Recurrent pregnancy loss (RPL) is a condition with complex etiologies, to which both genetic and environmental factors may contribute. During the last decade, studies indicated that the expression patterns of the prokineticin receptor (PKR1 and PKR2) are closely related to early pregnancy. However, there are few studies on the role of PKR1 and PKR2 in RPL. In this study, we purpose to investigate the association between polymorphisms of the prokineticin receptor (PKR1 rs4627609 and PKR2 rs6053283) and RPL on a group of 93 RPL cases and 169 healthy controls. Genotyping of the single nucleotide polymorphisms (SNPs) was performed using a Sequenom MassARRAY iPLEX system. The results revealed a significant association between PKR2 rs6053283 polymorphism and RPL (P=0.003), whereas no association was observed between PKR1 rs4627609 polymorphism and RPL (P=0.929) in the Chinese Han population.

Highly Robust Nanopore-Based Dual-Signal-Output Ion Detection System for Achieving Three Successive Calibration Curves.

In recent years, artificial stimuli-responsive bioinspired nanopores have attracted a lot of attention due to their unique property of confined spaces and flexibility in terms of shapes and sizes. Most of the nanopore systems demonstrated their transmembrane properties and applications in target detections. However, almost all of the nanopores can be used only once due to either the irreversible reactions between targets and probes or the plugged nanopores not easily being unplugged again. In this work, we propose a dual-signal-output nanopore system that could detect the cations (Hg(2+)) inducing the plugged nanopores. The detection system is highly recoverable by the anions (S(2-)) inducing the unplugged nanopores. More importantly, as far as we know, it is seldom reported for the same nanopores to achieve successive calibration curves for three times by subsequent reversible plug-unplug processes, which strongly demonstrates the high robustness of this novel nanopore-detection system. In addition, unlike monitoring the plug-unplug phenomena by only one type of signal, we combined the ionic current signal with the fluorescence output and could directly observe that the change of ionic current does in fact correspond to the plug-unplug of the nanopores by the target stimuli.

[Correlation of propagated sensation along meridian and TCM constitution].

OBJECTIVE: To explore the correlation between propagated sensation along meridian (PSM) and TCM constitution at different age stages. METHODS: According to age, 840 participants were divided into a youth group (326 cases), a middle aged group (243 cases) and an elderly group (271 cases). The TCM constitution of all the participants was evaluated, and the PSM test was performed. The distribution of TCM constitution, the occurring rate and transmission of PSM in each group were observed and compared; the correlation between PSM and the TCM constitution was preliminary investigated by Logistic regression analysis. RESULTS: The distribution of nine types of TCM constitution in three groups:the proportion of normal constitution and partial constitution were significantly different (all P<0.05); the occurring rate and transmission of PSM in three groups were not significantly different (all P>0.05); the proportion of occurring rate for nine types of TCM constitutions in the whole population, from high to low, presented special intrinsic quality, neutral quality, yin-deficiency quality, qi-deficiency quality, yang-deficiency quality, damp-heat quality, phlegm-dampness quality, qi-stagnation quality and blood-stasis quality; besides, the proportion of occurring rate for different TCM constitutions in the youth group, middle aged group and elderly group was similar to that of whole population. The Logistic regression analysis results indicated the neutral quality (P=0.025) and special intrinsic quality (P=0.018) were positively while blood-stasis quality (P=0.043) was negatively related with PSM in all subjects; the qi-deficiency quality (P=0.025), phlegm-dampness quality (P=0.019), blood-stasis quality (P=0.012) and qi-stagnation quality (P=0.035) were negatively related with PSM in youth group; the neutral quality (P=0.001) was positively related with PSM inthe middle aged group; the neutral quality (P=0.006) and yin deficiency quality (P=0.004) were positively related with PSM in the elderly group. CONCLUSIONS: The occurrence of PSM in different age stages is related with TCM constitution, which could be increased in clinical treatment to improve acupuncture efficacy.