Biodistribution of Vanadium Dioxide Particles in Mice by Consecutive Gavage Administration: Effects of Particle Size, Dosage, and Health Condition of Mice.

The newly developed vanadium dioxide (VO2), a material with excellent reversible and multi-stimuli responsible phase transition property, has been widely used in high-performance and energy-saving smart devices. The rapid growth of the VO2-based emerging technologies and the complex biological effect of vanadium to organisms urge a better understanding of the behavior of VO2 in vivo for safety purpose. Herein, we study the absorption, distribution, and excretion of two commercial VO2 (nanoscale SVO2 and bulk MVO2) in mice after consecutive gavage administration for up to 28 days. The absorption of both types of VO2 is as low as less than 1.5% of the injected dose within 28 days, while MVO2 is several times more difficult to be absorbed than SVO2. Almost all unabsorbed VO2 is excreted through feces. For the absorbed vanadium, bone is the organ with the largest accumulation, followed by liver, kidney, and spleen. The vanadium content in organs shows a size-, dosage-, and animal health condition-dependent manner, and increases gradually to a saturation value along with the consecutive administration. Generally, smaller particle size and higher dosage lead to higher vanadium contents in organs, and more vanadium accumulates in bone and liver in diabetic mice than in normal mice. After the treatment is stopped, the accumulated vanadium in organs decreases a lot within 14 days, even reaches to the background level in some organs, but the content of vanadium in the bone remains high after 14 days post-exposure. These findings provide basic information for the safety assessment and safe applications of VO2-based materials.

Applications of Titanium Dioxide Nanostructure in Stomatology.

Breakthroughs in the field of nanotechnology, especially in nanochemistry and nanofabrication technologies, have been attracting much attention, and various nanomaterials have recently been developed for biomedical applications. Among these nanomaterials, nanoscale titanium dioxide (nano-TiO2) has been widely valued in stomatology due to the fact of its excellent biocompatibility, antibacterial activity, and photocatalytic activity as well as its potential use for applications such as dental implant surface modification, tissue engineering and regenerative medicine, drug delivery carrier, dental material additives, and oral tumor diagnosis and treatment. However, the biosafety of nano-TiO2 is controversial and has become a key constraint in the development of nano-TiO2 applications in stomatology. Therefore, in this review, we summarize recent research regarding the applications of nano-TiO2 in stomatology, with an emphasis on its performance characteristics in different fields, and evaluations of the biological security of nano-TiO2 applications. In addition, we discuss the challenges, prospects, and future research directions regarding applications of nano-TiO2 in stomatology that are significant and worthy of further exploration.

A novel sustained release fluoride strip based Poly(propylene carbonate) for preventing caries.

Low-level fluoride in the oral environment for a long sustained period is more effective for preventing caries. However, the current fluoride delivery methods have a short fluoride retention time and high-dose fluoride administration may increase the risk of dental fluorosis. This study developed a novel fluoride strip based poly(propylene carbonate) (PPC), which can improve oral fluoride retention for desirable anticaries effect with minimal side effects. The fluoride strips based PPC (NaF-PPC strips) with different fluoride contents (0, 1.25, 2.5 and 5 wt.%) were developed by melt-blending method. The physico-chemical characteristics, drug loading, drug release properties, remineralization and antibacterial efficacy and biocompatibility of NaF-PPC strips were investigated. The in vitro drug release studies indicated that fluoride release in a sustained manner with no initial burst release and approximately 100% of fluoride ions were released from PPC strips over 24 days. NaF-PPC strips exhibited excellent remineralization and antibacterial potential when fluoride content up to 5%. Combination with biocompatibility, 2.5% NaF-PPC strips could be a promising fluoride application for preventing caries. This work provides an effective and novel topical fluoride delivery for general use.

Modulation of Structure and Optical Property of Nitrogen-Incorporated VO2 (M1) Thin Films by Polyvinyl Pyrrolidone.

VO2, as a promising material for smart windows, has attracted much attention, and researchers have been continuously striving to optimize the performance of VO2-based materials. Herein, nitrogen-incorporated VO2 (M1) thin films, using a polyvinylpyrrolidone (PVP)-assisted sol-gel method followed by heat treatment in NH3 atmosphere, were synthesized, which exhibited a good solar modulation efficiency (ΔTsol) of 4.99% and modulation efficiency of 37.6% at 2000 nm (ΔT2000 nm), while their visible integrated transmittance (Tlum) ranged from 52.19% to 56.79% after the phase transition. The crystallization, microstructure, and thickness of the film could be regulated by varying PVP concentrations. XPS results showed that, in addition to the NH3 atmosphere-N doped into VO2 lattice, the pyrrolidone-N introduced N-containing groups with N-N, N-O, or N-H bonds into the vicinity of the surface or void of the film in the form of molecular adsorption or atom (N, O, and H) filling. According to the Tauc plot, the estimated bandgap of N-incorporated VO2 thin films related to metal-to-insulator transition (Eg1) was 0.16-0.26 eV, while that associated with the visible transparency (Eg2) was 1.31-1.45 eV. The calculated Eg1 and Eg2 from the first-principles theory were 0.1-0.5 eV and 1.4-1.6 eV, respectively. The Tauc plot estimation and theoretical calculations suggested that the combined effect of N-doping and N-adsorption with the extra atom (H, N, and O) decreased the critical temperature (τc) due to the reduction in Eg1.

Double Transition Metal Carbides MXenes (D-MXenes) as Promising Electrocatalysts for Hydrogen Reduction Reaction: Ab Initio Calculations.

Double-transition-metal MXenes (D-MXenes) have been widely pursued in the advancement of the renewable energy storage technology in recent years. In this work, the hydrogen evolution reaction (HER) catalytic mechanism of several oxygen-terminated D-MXenes with the chemical formula of M'2M″C2O2 (M' = Mo, Cr; M″ = Ti, V, Nb, Ta) is theoretically studied. For comparison, the corresponding monometallic MXenes (M-MXenes, M'3C2O2) are fairly compared by means of the density functional theory calculations. Based on our theoretical results, the HER performance of M-MXenes can be improved by constructing a "sandwich-like" ordered D-MXene configuration. Moreover, the HER performance of Mo-based D-MXenes (Mo2M″C2O2) is superior to that of Cr-based D-MXenes (Cr2M″C2O2), which highlights that the HER activity of Mo2VC2O2 and Mo2NbC2O2 is better than that of Pt(111). This work not only unravels the HER mechanism of D-MXenes (M'2M″C2O2) but also paves the way in designing emergent MXene-based HER electrocatalysts with high efficiency.

Improving the Catalytic CO2 Reduction on Cs2AgBiBr6 by Halide Defect Engineering: A DFT Study.

Pb-free double halide perovskites have drawn immense attention in the potential photocatalytic application, due to the regulatable bandgap energy and nontoxicity. Herein, we first present a study for CO2 conversion on Pb-free halide perovskite Cs2AgBiBr6 under state-of-the-art first-principles calculation with dispersion correction. Compared with the previous CsPbBr3, the cell parameter of Cs2AgBiBr6 underwent only a small decrease of 3.69%. By investigating the adsorption of CO, CO2, NO, NO2, and catalytic reduction of CO2, we found Cs2AgBiBr6 exhibits modest adsorption ability and unsatisfied potential determining step energy of 2.68 eV in catalysis. We adopted defect engineering (Cl doping, I doping and Br-vacancy) to regulate the adsorption and CO2 reduction behavior. It is found that CO2 molecule can be chemically and preferably adsorbed on Br-vacancy doped Cs2AgBiBr6 with a negative adsorption energy of -1.16 eV. Studying the CO2 reduction paths on pure and defect modified Cs2AgBiBr6, Br-vacancy is proved to play a critical role in decreasing the potential determining step energy to 1.25 eV. Finally, we probe into the electronic properties and demonstrate Br-vacancy will not obviously promote the process of catalysis deactivation, as there is no formation of deep-level electronic states acting as carrier recombination center. Our findings reveal the process of gas adsorption and CO2 reduction on novel Pb-free Cs2AgBiBr6, and propose a potential strategy to improve the efficiency of catalytic CO2 conversion towards practical implementation.

Atomic-Scale Superlubricity in Ti2CO2@MoS2 Layered Heterojunctions Interface: A First Principles Calculation Study.

The two dimensional (2D)-layered transition-metal carbides and nitrides (MXene) have been proved to be an excellent solid lubricant owing to their high mechanical strength, low shearing strength, and self-lubricating properties. However, the interfacial friction behavior between Ti n+1C n (n = 1, 2) MXene and its heterogeneous system is not thoroughly exploited yet. Here, four types of van der Waals structures (Ti2CO2@Ti2CO2, Ti3C2O2@Ti3C2O2 MoS2@MoS2, and Ti2CO2@MoS2) have been investigated by density functional theory (DFT) calculations. The results exhibit that Ti2CO2@MoS2 possesses the lowest sliding energy barrier around 0.015 eV/oxygen(O) atom compared with the other three constructed models. Therefore, this work mainly focuses on the inner relation of Ti2CO2@MoS2 interlayer friction behaviors and its attributing factors, including normal force and charge density. The DFT analysis shows that the roughness of the potential energy corrugated plane is positively correlated with normal force and predicted the ultralow friction coefficient (µ) at 0.09 when sliding along the minimum energy potential route. Moreover, friction coefficient fluctuates at the normal force less than 10 nN determined by the combined effect of interfacial charge interlock and redistribution. This work reveals the intrinsic connection between the friction and charge interaction at heterogeneous interfaces.

Single-Metal Atoms Supported on MBenes for Robust Electrochemical Hydrogen Evolution.

Two-dimensional (2D) photo- and electrocatalysts play a key role in hydrogen production through water splitting, and much efforts have been undertaken to seek a low-cost and efficient alternative candidate to noble-metal Pt. Herein, the method of introducing several different transition-metal atoms to tune the catalytic properties of 2D MBene is proposed. Density functional theory calculations reveal that the H-O bonding strength can be weakened by charge transfer between the oxygen atom and the introduced single-metal atom. The weakening of the bond greatly improves the MBene catalytic activity of hydrogen evolution reaction. Interestingly, the Gibbs free energy (|ΔGH|) of W2B2O2 decreases from |-0.67| to 0.013 eV by embedding a V adatom. This work should initiate 2D material MBene applications in green catalysis and energy sectors.

Probing the active sites of site-specific nitrogen doping in metal-free graphdiyne for electrochemical oxygen reduction reactions.

The development of highly active and low-cost catalysts for electrochemical reactions is one of the most attractive topics in the renewable energy technology. Herein, the site-specific nitrogen doping of graphdiyne (GDY) including grap-N, sp-N(I) and sp-N(II) GDY is systematically investigated as metal-free oxygen reduction electrocatalysts via density functional theory (DFT). Our results indicate that the doped nitrogen atom can significantly improve the oxygen (O2) adsorption activity of GDY through activating its neighboring carbon atoms. The free-energy landscape is employed to describe the electrochemical oxygen reduction reaction (ORR) in both O2 dissociation and association mechanisms. It is revealed that the association mechanism can provide higher ORR onset potential than dissociation mechanism on most of the substrates. Especially, sp-N(II) GDY exhibits the highest ORR electrocatalytic activity through increasing the theoretical onset potential to 0.76 V. This work provides an atomic-level insight for the electrochemical ORR mechanism on metal-free N-doped GDY.

Insights into the Electrocatalytic Hydrogen Evolution Reaction Mechanism on Two-Dimensional Transition-Metal Carbonitrides (MXene).

Developing highly active, non-noble-metal H2 -evolution catalysts is appealing yet still remains a great challenge in the field of electrocatalytic and photocatalytic H2 production. In this work, high quality transition-metal carbonitrides M3 CN (MXene) are investigated using well-defined density functional theory (DFT) calculations. The structural configurations, H-adsorption free energy (ΔGH ) and charge transfer for bare, surface-terminated and transition-metal (TM)-modified M3 CNO2 are systematically studied. The calculated results indicate that all bare transition metal carbonitrides exhibit strong binding between H atom and catalysts. In addition, only Ti3 CNO2 and Nb3 CNO2 have the potential to be HER active catalysts based on the ΔGH results. In an attempt to overcome poor HER activity limitations, we apply O as well as OH mixed groups and TMs modification on the Ti3 CNO2 surface for tuning HER activity, and a significant improvement of HER activity is observed. Overall, this work presents in-depth investigations for transition-metal carbonitrides (MXene) and opens up new designs for robust metal carbonitrides as noble-metal-free cocatalysts for highly efficient and low-cost MXene-based nanocomposites for water splitting applications.

Generating plasmonic heterostructures by cation exchange and redox reactions of covellite CuS nanocrystals with Au3+ ions.

We demonstrate the fabrication of various types of heterostructures, including core-shells and dimers. This is achieved by reacting platelet-shaped covellite (CuS) nanocrystals (NCs) with Au3+ ions under various reaction conditions: the exposure of CuS NCs to Au3+ ions, in the presence or in the absence of ascorbic acid (AA), leads to the formation of CuS@Au core-shell nanostructures; the reaction of CuS NCs with Au3+ ions in the presence of oleylamine (OM) leads to the formation of CuS@Au2S; the presence of both OM and AA leads to the formation of Au/CuS dimers. Depending on which condition is chosen, either cation exchange (CE) between gold and copper ions is predominant (leading to amorphous Au2S) or the reduction of Au3+ leads to the nucleation of metallic Au domains (which are operated by the AA). In the heterostructures achieved by CE, the Au2S shell is almost entirely amorphous, and can be converted to polycrystalline upon electron beam irradiation. Finally, when both oleylamine and AA are present in the reaction environment, Au/CuS dimers are formed due to the reduction of Au3+ to metallic Au domains which nucleate on top of the CuS seeds. The experimental dual plasmonic bands of the CuS@Au core-shells and Au/CuS dimers are in agreement with the theoretical optical simulations. The procedures described here enable the synthesis of core-shell nanostructures with tunable localized surface plasmon resonances (LSPRs) in the near-infrared (NIR) region, and of plasmonic metal/semiconductor heterostructures with LSPRs in both the NIR and the visible regions.

Understanding of Electrochemical Mechanisms for CO2 Capture and Conversion into Hydrocarbon Fuels in Transition-Metal Carbides (MXenes).

Two-dimensional (2D) transition-metal (groups IV, V, VI) carbides (MXenes) with formulas M3C2 have been investigated as CO2 conversion catalysts with well-resolved density functional theory calculations. While MXenes from the group IV to VI series have demonstrated an active behavior for the capture of CO2, the Cr3C2 and Mo3C2 MXenes exhibit the most promising CO2 to CH4 selective conversion capabilities. Our results predicted the formation of OCHO• and HOCO• radical species in the early hydrogenation steps through spontaneous reactions. This provides atomic level insights into the computer-aided screening for high-performance catalysts and the understanding of electrochemical mechanisms for CO2 reduction to energy-rich hydrocarbon fuels, which is of fundamental significance to elucidate the elementary steps for CO2 fixation.

Proposing the prospects of Ti3CN transition metal carbides (MXenes) as anodes of Li-ion batteries: a DFT study.

A two-dimensional (2D) transition metal carbonitride (MXenes) with a formula of Ti3CN as an anode of a lithium-ion battery (LIB) has been proposed in this work. The mechanism of Li+ adsorption and diffusion on the surface of Ti3CN and Ti3CNT2 (T = F, O, and OH functional groups) was studied to estimate the potential application of Ti3CN as an anode material by density functional theory (DFT) and DFT+U computations. For Ti3CNT2 (T = O, F, OH), the value of Li diffusion barriers is from 0.2 eV to 0.3 eV. On the basis of our results, we can know that Li prefers adsorption on the nitrogen side for Ti3CN in the absence of functional groups and tends to adsorb on the carbon side for Ti3CNT2 (T = O, F, OH). This phenomenon can be explained by Bader charge population analysis. For Ti3CNF2, Li-F formed a six-membered ring with increasing Li concentration, thereby making the system more stable. This work contributes to offering perspectives for carbonitride systems (MXenes) as LIB anodes.

Verbascoside promotes apoptosis by regulating HIPK2-p53 signaling in human colorectal cancer.

BACKGROUND: We investigated the role of the HIPK2-p53 signaling pathway in tumorigenesis and resistance to the drug Verbascoside (VB) in colorectal cancer (CRC), using in vivo and in vitro experiments. METHODS: Primary human CRC samples and normal intestinal tissues from patients were analyzed for HIPK2 expression by immunohistochemistry (IHC) and its expression was correlated against patients' clinicopathological characteristics. Human CRC HCT-116 cells were implanted in BALB/c nude mice; mice with xenografted tumors were randomly administrated vehicle (control), 20, 40, or 80 mg/mL VB, or 1 mg/mL fluorouracil (5-FU). HIPK2, p53, Bax, and Bcl-2 expression in these tumors were determined by IHC. In vitro effects of VB on CRC cell proliferation and apoptosis were measured by CCK-8 assay and flow cytometry; HIPK2, p53, p-p53, Bax, and Bcl-2 were measured by western blot. RESULTS: IHC analysis for 100 human CRC tumor samples and 20 normal intestinal tissues, showed HIPK2 expression to inversely correlate with Dukes stage and depth of invasion in CRC (P<0.05). In vivo, the inhibition rates of 20, 40, and 80 mg/mL VB on CRC xenograft tumor weight were 42.79%, 53.90%, and 60.99%, respectively, and were accompanied by increased expression of HIPK2, p53, and Bax, and decreased Bcl-2 expression in treated tumors. In vitro, VB significantly inhibited proliferation of CRC cell lines HCT-116, HT-29, LoVo, and SW620, in a time- and dose-dependent manner. The apoptosis rates of 25, 50, and 100 µM VB on HCT-116 cells were 10.83±1.28, 11.25±1.54, and 20.19±2.87%, and on HT-29 cells were 18.92±6.12, 21.57±4.05, and 25.14±6.73%, respectively. In summary, VB treatment significantly enhanced the protein expression of pro-apoptotic HIPK2, p53, p-p53, Bax, and decreased anti-apoptotic Bcl-2 expression in CRC cells. CONCLUSIONS: HIPK2 protein modulates the phosphorylation status of p53, and levels of Bax and Bcl-2 in CRC. We also found that VB effectively activated the HIPK2-p53 signaling pathway, resulting in increased CRC cell apoptosis.

Norcantharidin inhibits tumor angiogenesis via blocking VEGFR2/MEK/ERK signaling pathways.

Norcantharidin (NCTD), the demethylated form of Cantharidin, a reagent isolated from blister beetles, has been shown to be an anti-tumor agent capable of inhibiting proliferation as well as inducing apoptosis in many cancer cell lines. However, little is known about the effect of NCTD in tumor angiogenesis. In this study, we demonstrated that NCTD inhibited vascular endothelial growth factor (VEGF)-induced cell proliferation, migration, invasion, and capillary tube formation of primary human umbilical vein endothelial cells (HUVECs) in a dose-dependent manner. Furthermore, we showed NCTD inhibited tumor growth and angiogenesis of colon cancer cells (LOVO) in vivo. We then mechanistically described that NCTD specifically abrogated the phosphorylation/activation of vascular endothelial growth factor receptor-2 (VEGFR2)/MEK/ERK pathway kinases, with little effect on the phosphorylation of p38 MAPK and Akt, and on Cox-2 expression. In summary, our results indicate that NCTD is a potential inhibitor of tumor angiogenesis by blocking VEGFR2/MEK/ERK signaling.