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D G Sangiovanni, G K Gueorguiev, A Kakanakova-Georgieva
Metal organic chemical vapor deposition (MOCVD) of group III nitrides on graphene heterostructures offers new opportunities for the development of flexible optoelectronic devices and for the stabilization of conceptually-new two-dimensional materials. However, the MOCVD of group III nitrides is regulated by an intricate interplay of gas-phase and surface reactions that are beyond the resolution of experimental techniques. We use density-functional ab initio molecular dynamics (AIMD) with van der Waals corrections to identify atomistic pathways and associated electronic mechanisms driving precursor/surface reactions during metal organic vapor phase epitaxy at elevated temperatures of aluminum nitride on graphene, considered here as model case study...
June 19, 2018: Physical Chemistry Chemical Physics: PCCP
Xiaoming Wang, Mona Zebarjadi, Keivan Esfarjani
Two-dimensional (2D) van der Waals heterostructures (vdWHs) have shown multiple functionalities with great potential in electronics and photovoltaics. Here, we show their potential for solid-state thermionic energy conversion and demonstrate a designing strategy towards high-performance devices. We propose two promising thermionic devices, namely, the p-type Pt-G-WSe2 -G-Pt and n-type Sc-WSe2 -MoSe2 -WSe2 -Sc. We characterize the thermionic energy conversion performance of the latter using first-principles GW calculations combined with real space Green's function (GF) formalism...
June 18, 2018: Scientific Reports
Wei Yao, Eryin Wang, Changhua Bao, Yiou Zhang, Kenan Zhang, Kejie Bao, Chun Kai Chan, Chaoyu Chen, Jose Avila, Maria C Asensio, Junyi Zhu, Shuyun Zhou
The interlayer coupling can be used to engineer the electronic structure of van der Waals heterostructures (superlattices) to obtain properties that are not possible in a single material. So far research in heterostructures has been focused on commensurate superlattices with a long-ranged Moiré period. Incommensurate heterostructures with rotational symmetry but not translational symmetry (in analogy to quasicrystals) are not only rare in nature, but also the interlayer interaction has often been assumed to be negligible due to the lack of phase coherence...
June 18, 2018: Proceedings of the National Academy of Sciences of the United States of America
Nihong Guo, Cailian Wang, Chao Shang, Xue You, Liuyang Zhang, Wenbin Liu
Controlling the activity of tyrosinase, which plays an important role in melanin synthesis, is essential endeavor in the field of medicine, food, cosmetics, and agriculture. Baicalein is a widely available inhibitor of tyrosinase. The mechanism of this inhibition was studied through an integrated approach coupling enzyme kinetics, multiple types of spectroscopy and computational simulation. Baicalein conspicuously inhibited the diphenolase activity with an IC50 value of 0.11 mM. The inhibtion kinetics indicated that baicalein was a mix-type tight binding inhibitor with a Ki of 0...
June 13, 2018: International Journal of Biological Macromolecules
Himanshu Goel, Sanliang Ling, Breanna Nicole Ellis, Anna Taconi, Ben Slater, Neeraj Rai
Predicting vapor liquid equilibria (VLE) of molecules governed by weak van der Waals (vdW) interactions using the first principles approach is a significant challenge. Due to the poor scaling of the post Hartree-Fock wave function theory with system size/basis functions, the Kohn-Sham density functional theory (DFT) is preferred for systems with a large number of molecules. However, traditional DFT cannot adequately account for medium to long range correlations which are necessary for modeling vdW interactions...
June 14, 2018: Journal of Chemical Physics
Dheeraj S Tomar, Niral Ramesh, D Asthagiri
We study the solvation free energy of two different conformations (helix and extended) of two different peptides (deca-alanine and deca-glycine) in two different solvents (water and aqueous guanidinium chloride, GdmCl). The free energies are obtained using the quasichemical organization of the potential distribution theorem, an approach that naturally provides the repulsive (solvophobic or cavity) and attractive (solvophilic) contributions to solvation. The solvophilic contribution is further parsed into a chemistry contribution arising from solute interaction with the solvent in the first solvation shell and a long-range contribution arising from non-specific interactions between the solute and the solvent beyond the first solvation shell...
June 14, 2018: Journal of Chemical Physics
A Muralidharan, L R Pratt, M I Chaudhari, S B Rempe
Laying a basis for molecularly specific theory for the mobilities of ions in solutions of practical interest, we report a broad survey of velocity autocorrelation functions (VACFs) of Li+ and PF6 - ions in water, ethylene carbonate, propylene carbonate, and acetonitrile solutions. We extract the memory function, γ(t), which characterizes the random forces governing the mobilities of ions. We provide comparisons controlling for the effects of electrolyte concentration and ion-pairing, van der Waals attractive interactions, and solvent molecular characteristics...
June 14, 2018: Journal of Chemical Physics
Yoshiaki Kumagai, Zoltan Jurek, Weiqing Xu, Hironobu Fukuzawa, Koji Motomura, Denys Iablonskyi, Kiyonobu Nagaya, Shin-Ichi Wada, Subhendu Mondal, Tetsuya Tachibana, Yuta Ito, Tsukasa Sakai, Kenji Matsunami, Toshiyuki Nishiyama, Takayuki Umemoto, Christophe Nicolas, Catalin Miron, Tadashi Togashi, Kanade Ogawa, Shigeki Owada, Kensuke Tono, Makina Yabashi, Sang-Kil Son, Beata Ziaja, Robin Santra, Kiyoshi Ueda
We show that electron and ion spectroscopy reveals the details of the oligomer formation in Ar clusters exposed to an x-ray free electron laser (XFEL) pulse, i.e., chemical dynamics triggered by x rays. With guidance from a dedicated molecular dynamics simulation tool, we find that van der Waals bonding, the oligomer formation mechanism, and charge transfer among the cluster constituents significantly affect ionization dynamics induced by an XFEL pulse of moderate fluence. Our results clearly demonstrate that XFEL pulses can be used not only to "damage and destroy" molecular assemblies but also to modify and transform their molecular structure...
June 1, 2018: Physical Review Letters
Jaeho Shin, Kyungyeol Gu, Seunghoon Yang, Chul-Ho Lee, Takhee Lee, Yun Hee Jang, Gunuk Wang
Molecular conformation, intermolecular interaction, and electrode-molecule contacts greatly affect charge transport in molecular junctions and interfacial properties of organic devices by controlling the molecular orbital alignment. Here, we statistically investigated the charge transport in molecular junctions containing self-assembled oligophenylene molecules sandwiched between an Au probe tip and graphene according to various tip-loading forces (FL) that can control the molecular-tilt configuration and the vdW interactions...
June 15, 2018: Nano Letters
Rui Gusmão, Zdeněk Sofer, Martin Pumera
Few and monolayer black phosphorus (phosphorene) is currently an intensively researched material. Shear exfoliated black phosphorus (BPSE ) nanosheets were functionalized with the redox active antraquinone (AQ) that can provide additional charge storage capacity. The noncovalent interaction of BP with AQ occurs due to van der Waals interactions. X-ray photoelectron spectroscopy results show that AQ coverage of BPSE nanosheets led to a stabilization against BPSE degradation. Electrochemistry of the BPSE -AQ shows that AQ is stably anchored onto BPSE and exhibits redox peaks stable for more than 100 cycles...
June 15, 2018: ACS Nano
Yi Hu, Shaogang Xu, Kai Miao, Xinrui Miao, Wenli Deng
Fabricating complex nano-networks on solid substrates is a research area that has attracted much attention in the field of molecular self-assembly. By designing a fluorenone derivative of 2-heptyloxy-7-pentadecyloxy-9-fluorenone (HPF), we obtained a surface-confined system that presented diverse nanostructures. The assembled networks for HPF were highly dependent on the solvent and concentration. At the liquid/solid interface, chiral tetramer-S, hexamer-S, and tetramer-linear structures as well as achiral irregular-linear and random structures were recorded...
June 15, 2018: Physical Chemistry Chemical Physics: PCCP
Ce Huang, Awadhesh Narayan, Enze Zhang, Yanwen Liu, Xiao Yan, Jiaxiang Wang, Cheng Zhang, Weiyi Wang, Tong Zhou, Changjiang Yi, Shanshan Liu, Jiwei Ling, Huiqin Zhang, Ran Liu, Raman Sankar, Fang-Cheng Chou, Yihua Wang, Youguo Shi, Kam Tuen Law, Stefano Sanvito, Peng Zhou, Zheng Han, Faxian Xiu
The search for proximity-induced superconductivity in topological materials has generated widespread interest in the condensed matter physics community. The superconducting states inheriting nontrivial topology at interfaces are expected to exhibit exotic phenomena such as topological superconductivity and Majorana zero modes, which hold promise for applications in quantum computation. However, a practical realization of such hybrid structures based on topological semimetals and superconductors has hitherto been limited...
June 14, 2018: ACS Nano
Q H Tan, Qianjin Wang, Yingkai Liu, Chunsheng Liu, Xiaobo Feng, Dapeng Yu
Graphene is one of the most promising spintronic materials due to its high carrier mobility. However, the absence of a band gap and ferromagnetic order in graphene seriously limit its applications in spintronics. How to utilize its high carrier mobility as well as mediate its electronic structure remains a challenge. Herein, we design a novel composite, which is composed of graphene and Mn-doped monolayer MoS2. The magnetic properties and electronic structures of graphene/Mn-doped monolayer MoS2 heterostructures were studied by using density functional theory (DFT) with the van der Waals (vdW) correlations (DFT-D)...
June 14, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Priyanka Lahiri, Hitesh Verma, Ashraya Ravikumar, Jayanta Chatterjee
Reverse turns are solvent-exposed motifs in proteins that are crucial in nucleating β-sheets and drive the protein folding. The solvent-exposed nature makes reverse turns more amenable to chemical modifications than α-helices or β-sheets towards modulating the stability of re-engineered proteins. Here, we utilize van der Waals repulsive forces in tuning the steric restraint at the reverse turn. The steric restraint induced upon N -methylation of the i +1- i +2 amide bond at the reverse turn results in well-folded and stable β-sheets in aqueous solution at room temperature...
May 28, 2018: Chemical Science
Mehrdad Asgari, Sudi Jawahery, Eric D Bloch, Matthew R Hudson, Roxana Flacau, Bess Vlaisavljevich, Jeffrey R Long, Craig M Brown, Wendy L Queen
We present a comprehensive investigation of the CO2 adsorption properties of an isostructural series of metal-organic frameworks, M-BTT (M = Cr, Mn, Fe, Cu; BTT3- = 1,3,5-benzenetristetrazolate), which exhibit a high density of open metal sites capable of polarizing and binding guest molecules. Coupling gas adsorption measurements with in situ neutron and X-ray diffraction experiments provides molecular-level insight into the adsorption process and enables rationalization of the observed adsorption isotherms...
May 28, 2018: Chemical Science
Yanyong Kang, Oleg Kuybeda, Parker W de Waal, Somnath Mukherjee, Ned Van Eps, Przemyslaw Dutka, X Edward Zhou, Alberto Bartesaghi, Satchal Erramilli, Takefumi Morizumi, Xin Gu, Yanting Yin, Ping Liu, Yi Jiang, Xing Meng, Gongpu Zhao, Karsten Melcher, Oliver P Ernst, Anthony A Kossiakoff, Sriram Subramaniam, H Eric Xu
G-protein-coupled receptors comprise the largest family of mammalian transmembrane receptors. They mediate numerous cellular pathways by coupling with downstream signalling transducers, including the hetrotrimeric G proteins Gs (stimulatory) and Gi (inhibitory) and several arrestin proteins. The structural mechanisms that define how G-protein-coupled receptors selectively couple to a specific type of G protein or arrestin remain unknown. Here, using cryo-electron microscopy, we show that the major interactions between activated rhodopsin and Gi are mediated by the C-terminal helix of the Gi α-subunit, which is wedged into the cytoplasmic cavity of the transmembrane helix bundle and directly contacts the amino terminus of helix 8 of rhodopsin...
June 13, 2018: Nature
Luojia Liu, Licheng Miao, Lin Li, Fujun Li, Yong Lu, Zhenfeng Shang, Jun Chen
This work is pioneering to introduce molecular electrostatic potential (MESP) to investigate the interaction between lithium ions and organic electrode molecules. The electrostatic potential on the van der Waals surface of the electrode molecule is calculated, and then the coordinates and relative values of the local minima of MESP can be correlated to the Li binding sites and sequence on an organic small molecule, respectively, suggesting a gradual lithiation process. Similar calculations are extended to polymers and even organic crystals...
June 13, 2018: Journal of Physical Chemistry Letters
Xing Liu, Xiangxian Ying, Yanli Li, Hua Yang, Wanshan Hao, Meilan Yu
The interaction between Gd@C82 (OH)22 and serum albumin (HSA and BSA) were investigated by spectroscopic analysis. From the characteristic feature of fluorescence quenching spectra at different temperatures, the inherent binding information including quenching mechanism, association constants, number of binding site, fraction of initial fluorescence and basic thermodynamic parameters were calculated. The binding of Gd@C82 (OH)22 to serum albumin caused strong quenching of protein intrinsic fluorescence and the structural changes of serum albumin...
June 2, 2018: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Meshal Alzaid, Abu M N Taufique, Salim A Thomas, Clay Carufel, John M Harris, Alex J B Waters, Amal Altayyar, Sylvio May, Erik K Hobbie
Macroscopic single-wall carbon nanotube (SWCNT) films of nanoscale thickness have significant potential for an array of applications that demand thin, transparent, conductive coatings. Using macroscopic micrometer-thick polystyrene sheets as a reference, we characterize the elastic response of freestanding multifunctional SWCNT nanosheets possessing both exceptionally high Young's modulus and good durability. Thin SWCNT films (20 nm to 200 nm thick) asymmetrically 'doped' with dilute concentrations of super-paramagnetic colloids were suspended in ethanol as freestanding nanosheets...
June 11, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
Baile Xu, Fei Liu, Philip C Brookes, Jianming Xu
Microplastics and sulfamethoxazole coexist ubiquitously in the marine environment, and microplastics tend to sorb organic pollutants from the surrounding environment. Here, the sorption kinetics and isotherms of sulfamethoxazole on polyethylene (PE) microplastics closely fitted a pseudo-second-order model (R2  = 0.98) and linear model (R2  = 0.99), respectively, indicating that the sorption process was partition-dominant interaction. The main binding mechanism was possibly the van der Waals interaction for hydrophilic sulfamethoxazole onto hydrophobic PE microplastics...
June 2018: Marine Pollution Bulletin
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