Amelogenin is the main component of the organic matrix necessary to the formation of tooth enamel by directing the hydroxyapatite (HAP) growth. However, the detailed mechanism of adsorption between amelogenin and HAP is still not clear. In this report, simulations of the dynamic behavior of six different orientations of leucine-rich amelogenin protein (LRAP), the amelogenin splice variant, on a fixed hydrophilic HAP surface (001) were performed. Energy minimization, molecular dynamics (MD), and steered molecular dynamics (SMD) simulations were integrated in carrying this study. The results are highly consistent with the previous experimental findings. It was confirmed that the carboxyl groups contributed mainly to the adsorption of LRAP on the HAP (001) surface. Moreover, it was found that the −COO- claw of LRAP grasps the calcium ion with its two oxygen atoms in a special triangle form. This interaction form can resist external forces and is the key factor of the adsorption between LRAP and HAP.

Summary Water blocking can be a serious problem, causing a low gas production rate after hydraulic fracturing, a result of the strong capillarity in the tight sandstone reservoir aggravating the spontaneous imbibition. Fortunately, chemicals added to the fracturing fluids can alter the surface properties and thus prevent or reduce the water-blocking issue. We designed a spontaneous imbibition experiment to explore the possibility of using novel chemicals to both mitigate the spontaneous imbibition of water into the tight gas cores and measure the surface tensions (STs) between the air and chemical solutions. A diverse group of chemical species has been experimentally examined in this study, including two anionic surfactants (O242 and O342), a cationic surfactant (C12TAB), an alkaline solution of sodium metaborate (NaBO2), an ionic liquid (BMMIM BF4), two nanofluids with aluminum oxide and silicon oxide (Al2O3 and SiO2, respectively), and a series of deep eutectic solvents (DES3-7, 9, 11, and 14). Experimental results indicate that the anionic surfactants (O242 and O342) contribute to low STs but cannot ease the water-blocking issue because they yield a more water-wet surface. The high pH solution (NaBO2), ionic liquid (BMMIM BF-4), and sodium chloride brine (NaCl) significantly decrease the volume of water imbibed to the tight sandstone core through wettability alteration, and C12TAB leads to both ST reduction and an air-wet rock surface, helping to prevent water blocking. The different types of DESs and nanofluids exhibit distinctly different effects on expelling gas from the tight sandstone cores through water imbibition. This preliminary research will be useful in both selecting and using proper chemicals in fracturing fluids to mitigate water-blocking problems in tight gas sandstones.

The tuning of structural, optical, and electrical properties of Al-doped ZnO films deposited by atomic layer deposition technique is reported in this work. With the increasing Al doping level, the evolution from (002) to (100) diffraction peaks indicates the change in growth mode of ZnO films. Spectroscopic ellipsometry has been applied to study the thickness, optical constants, and band gap of AZO films. Due to the increasing carrier concentration after Al doping, a blue shift of band gap and absorption edge can be observed, which can be interpreted by Burstein-Moss effect. The carrier concentration and resistivity are found to vary significantly among different doping concentration, and the optimum value is also discussed. The modulations and improvements of properties are important for Al-doped ZnO films to apply as transparent conductor in various applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1625-0) contains supplementary material, which is available to authorized users.

Materials combining the hardness and strength of diamond with the higher thermal stability of cubic boron nitride (cBN) have broad potential value in science and engineering. Reacting nanodiamond with cBN at moderate pressures and high temperatures provides a pathway to such materials. Here we report the fabrication of Cx-BN nanocomposites, measuring up to 10 mm in longest dimension, by reacting nanodiamond with pre-synthesized cBN in a large-volume press. The nanocomposites consist of randomly-oriented diamond and cBN domains stitched together by sp3-hybridized C-B and C-N bonds, leading to p-type semiconductivity. Dislocations near the sutures accommodate lattice mismatch between diamond and cBN. Nanotwinning within both diamond and cBN domains further contributes to a bulk hardness ~50% higher than sintered cBN. The nanocomposite of C2-BN exhibits p-type semiconductivity with low activation energy and high thermal stability, making it a functional, ultrahard substance.

The biologically important isothiocyanate sulforaphane (4-isothiocyanatobutyl methyl sulfoxide) was synthesized in six simple steps from commercially available 4-aminobutan-1-ol with an overall yield of 64%. The new synthetic method is suitable for multigram-scale preparation of sulforaphane and does not require expensive or toxic reagents. A novel one-pot procedure was also developed for preparing isothiocyanates through reaction of amines with O-phenyl chlorothioformate under mild conditions. Additionally, methyl pyrrolidine-1-carbodithioate was obtained as an unexpected byproduct, and this protocol was shown to be useful for the synthesis of S-aryl or S-heterocyclic thiocarbamates with cyclic side chains.

Synthesis of large‐scale single‐crystalline graphene monolayers without multilayers involves the fabrication of proper single‐crystalline substrates and the ubiquitous formation of multilayered graphene islands during chemical vapor deposition. Here, a method of cyclic electrochemical polishing combined with thermal annealing, which allows the conversion of commercial polycrystalline Cu foils to single‐crystal Cu(111) with an almost 100% yield, is presented. A global “bottom‐up‐etching” method that is capable of fabricating large‐area pure single‐crystalline graphene monolayers without multilayers through selectively etching bottom multilayered graphene underneath large area as‐grown graphene monolayer on Cu(111) surface is demonstrated. Terahertz time‐domain spectroscopy (THz‐TDS) measurement of the pure monolayer graphene film shows a high average sheet conductivity of 2.8 mS and mean carrier mobility of 6903 cm2 V−1 s−1 over a large area. Density functional theory (DFT) calculations show that the selective etching is induced by the much easier diffusion of hydrogen atoms than hydrocarbon radicals across the edges of the top graphene layer, and the simulated selective etching processes based on phase field modeling are well consistent with experimental observations. This work provides new ways toward the production of single‐crystal Cu(111) and the synthesis of pure monolayer graphene with high electronic quality.

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A novel Daphniphyllum alkaloid, oldhamiphylline A (1), together with five known alkaloids, deoxycalyciphylline B, deoxyisocalyciphylline B, calyciphylline, secodaphniphylline, and calycicine A, was isolated from the leaves of Daphniphyllum oldhami. The structure of 1 was established by spectroscopic methods, especially 2D NMR techniques (1H,1H-COSY, HMQC, HMBC, and NOESY).