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Physical Chemistry Chemical Physics: PCCP

Naeem Ullah, Shunwei Chen, Ruiqin Zhang
The exciton formation dynamics of several model silicon nanosheets (SiNSs) are investigated using a time-dependent density functional tight binding method. The first excited-state (S1) self-trapped exciton formation in the SiNSs is obtained by observing the frontier orbital localization related to the characteristic size of the electronic excitations. The frontier molecular orbitals are highly localized in the S1 state on the stretched Si-Si bond due to the photo-excited structural relaxation, leading to a significant Stokes shift...
November 15, 2018: Physical Chemistry Chemical Physics: PCCP
Lei Tian, Jens Föhlinger, Palas Baran Pati, Zhibin Zhang, Junzhong Lin, Wenxing Yang, Malin Johansson, Tomas Kubart, Junliang Sun, Gerrit Boschloo, Leif Hammarström, Haining Tian
Correction for 'Ultrafast dye regeneration in a core-shell NiO-dye-TiO2 mesoporous film' by Lei Tian et al., Phys. Chem. Chem. Phys., 2018, 20, 36-40.
November 15, 2018: Physical Chemistry Chemical Physics: PCCP
Vitaly G Kiselev, Nikita V Muravyev, Konstantin A Monogarov, Pavel S Gribanov, Andrey F Asachenko, Igor V Fomenkov, C Franklin Goldsmith, Alla N Pivkina, Nina P Gritsan
The thermal stability of energetic materials, being of the utmost importance for safety issues, is often considered in terms of kinetics, e.g., the Arrhenius parameters of the decomposition rate constant. The latter, in turn, are commonly determined using conventional thermoanalytical procedures with the use of simple Kissinger or Ozawa methods for kinetic data processing. However, thermal decomposition of energetic materials typically occurs via numerous exo- and endothermal processes including fast parallel reactions, phase transitions, autocatalysis, etc...
November 15, 2018: Physical Chemistry Chemical Physics: PCCP
Adam A L Michalchuk, Svemir Rudić, Colin R Pulham, Carole A Morrison
As initiation of an energetic material requires rupture of a covalent bond, and therefore population of antibonding electronic states, consideration of the electronic band gap has dominated initiation mechanisms for solid state materials. Most prominent are models based on metallisation, where static mechanical perturbation leads to closing of the electronic band gap. This work explores an alternative mechanism for the dynamic metallisation of a model energetic material, where vibrational excitation resulting from mechanical impact is found to induce transient metallisation of α-NaN3...
November 15, 2018: Physical Chemistry Chemical Physics: PCCP
Wandong Xing, Yang Zhang, Fanyan Meng, Changchun Wang, Qiang Tao, Pinwen Zhu, Jing Zhu, Rong Yu
The microscopic structure of cubic WN has been studied combining scanning transmission electron microscopy and first-principles calculations. Because of the contribution of configurational entropy, NaCl-type WN with disordered vacancies becomes more stable at high temperatures than NbO-type WN. Moreover, electron beam irradiation can induce an order-disorder transition in cubic WN. It is suggested that the ordered NbO-type WN can be obtained after annealing below the transition temperature. The results shed light on the stability of materials synthesized at high pressures and high temperatures...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
A N Starukhin, D K Nelson, D A Kurdyukov, D A Eurov, V G Golubev
The nonlinear fluorescence properties of colloidal carbon dot solutions in glycerol were investigated at T = 298 K and 77 K. It was first found that the fluorescence intensity depended sublinearly on optical excitation intensity even at moderate excitation levels. With increasing excitation, the fluorescence signal shows a trend toward saturation, the latter being most pronounced at liquid nitrogen temperature. The relation between the fluorescence intensity and the excitation density was shown to be well approximated by the hyperbola equation...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Beibei Huang, Zhi Tan, Klemen Bohinc, Shuxing Zhang
Charged lipids in cell membranes and subcellular organelles are arranged in the form of a bilayer with the hydrocarbon tails sequestered away from the water and the polar head groups exposed to the aqueous environment. Most of them bear net negative charges leading to the negatively charged cell membranes. Charged lipid-lipid and lipid-protein interactions are generally dynamic and heavily depend on their local molecular concentrations. To examine the electrostatic properties of charged lipid layers in contact with an electrolyte solution, we incorporate the single chain mean field theory with Poisson-Boltzmann theory to explore the equilibrium structure of charged phospholipid membranes...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Zhequan Yan, Satish Kumar
β-Ga2O3 is emerging as a promising semiconductor for high-power high-frequency electronics. The low thermal conductivity of pristine β-Ga2O3 and the presence of defects, which can further suppress the thermal conductivity, will result in critical challenges for the performance and reliability of β-Ga2O3-based devices. We use first-principles density functional theory (DFT) along with the Boltzmann transport equation (BTE) to predict the phonon transport properties of pristine and defective β-Ga2O3. Our predictions of anisotropic thermal conductivity are in good agreement with the experimental results...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Ren-Zhong Li, Shihu H M Deng, Gao-Lei Hou, Marat Valiev, Xue-Bin Wang
We present results of combined experimental photoelectron spectroscopy and theoretical modeling studies of solvated dicarboxylate species (-O2C(CH2)2CO2-) in complex with Na+ and K+ metal cations. These ternary clusters serve as simple models for the investigation of aqueous ion/solute specific effects that play an important role in biological systems. The experimental characterization of these systems was performed in the presence of up to six solvating waters. In both Na+ and K+ cases, we observe the presence of one major broad band that gradually shifts to higher electron binding energy (EBE) with an increasing number of waters...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Amit R Sharma, David E Weeks
The excited state interatomic potential energy surfaces for Rb + He are computed at the spin-orbit multi-reference configuration interaction level of theory using all-electron basis sets of triple and quadruple-zeta quality that have been contracted for Douglas-Kroll-Hess (DKH) Hamiltonian and includes core-valence correlation. Davidson-Silver corrections (MRCI+Q) are employed to ameliorate size consistency error. An extrapolation of CASSCF energies is performed using the procedure of Karton and Martin whereas extrapolation of correlation energy is performed using an expression involving the inverse powers of (lmax + 1/2), the highest angular momentum value present in the basis set...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Alan M Szalai, Natalia G Armando, Federico M Barabas, Fernando D Stefani, Luciana Giordano, Sara E Bari, Claudio N Cavasotto, Susana Silberstein, Pedro F Aramendía
Class B G protein-coupled receptors (GPCRs) are involved in a variety of human pathophysiological states. These groups of membrane receptors are less studied than class A GPCRs due to the lack of structural information, delayed small molecule drug discovery, and scarce fluorescence detection tools available. The class B corticotropin-releasing hormone type 1 receptor (CRHR1) is a key player in the stress response whose dysregulation is critically involved in stress-related disorders: psychiatric conditions (i...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Rachel Martin, Minkyu Kim, Austin Franklin, Yingxue Bian, Aravind Asthagiri, Jason F Weaver
We investigated the adsorption and oxidation of n-propane and cyclopropane (C3H8 and c-C3H6) on the IrO2(110) surface using temperature programmed reaction spectroscopy (TPRS) and density functional theory (DFT) calculations. We find that the activation of both C3H8 and c-C3H6 is facile on IrO2(110) at low temperature, and that the dissociated alkanes oxidize during TPRS to produce CO, CO2 and H2O above ∼400 K. Propane conversion to propylene is negligible during TPRS for the conditions studied. Our results show that the maximum yield of alkane that oxidizes during TPRS is higher for c-C3H6 compared with C3H8 (∼0...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Vuk Uskoković, Smilja Marković, Ljiljana Veselinović, Srečo Škapin, Nenad Ignjatović, Dragan P Uskoković
Transformations between amorphous and crystalline apatite mechanistically govern some of the most essential processes in bone metabolism, including biomineralization and bone remodeling. Fundamental understanding of this phase transition can help us gain control over the formation and dissolution of boney tissues in vivo and utilize that knowledge for various therapeutic ends. Crystallization of hydroxyapatite (HAp) and two tricalcium phosphate (TCP) polymorphs from the metastable precursor, amorphous calcium phosphate (ACP) was here studied kinetically and mechanistically using thermal analyses, X-ray diffraction and Fourier-transform infrared spectroscopy...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Alhadji Malloum, Jean Jules Fifen, Jeanet Conradie
We report in this work the absolute solvation enthalpies and the absolute solvation free energies of the proton in methanol at temperatures ranging from 20 to 340 K and an extrapolation to a desired temperature. To achieve this, we thoroughly investigated the structures of neutral methanol clusters (MeOH)n=2-10 and those of the protonated methanol decamer H+(MeOH)n=10 at the M06-2X/6-31++g(d,p) level of theory. As a result, we noted that up to the octamer, the population of the neutral methanol clusters is constituted by cyclic isomers...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Nirod Kumar Sarangi, Jaydeep Kumar Basu
Raft-like functional domains with putative sizes of 20-200 nm and which are evolving dynamically are believed to be the most crucial regions in cellular membranes which determine cell signaling and various functions of cells. While the actual sizes of these domains are believed to vary from cell to cell no direct determination of their sizes and their evolution when cells interact with external agents like toxins and relevant biomolecules exists. Here, we report the first direct determination of the size of these nanoscale regions in model raft-forming biomembranes using the method of super-resolution stimulated emission depletion nanoscopy coupled with fluorescence correlation spectroscopy (STED-FCS)...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Gregory Hartmann, Peter L G Ventzek, Toshihiko Iwao, Kiyotaka Ishibashi, Gyeong S Hwang
Silicon nitride (SiN) thin films have been widely employed for various applications including microelectronics, but their deposition presents a challenge especially when highly conformal layers are necessary on nanoscale features with high aspect ratios. Plasma-enhanced atomic layer deposition (PEALD) has been demonstrated to be a promising technique for controlled growth of SiN thin films at relatively low temperatures (<400 °C), in which thermal decomposition of Si-containing precursors on a N-rich surface is a critical step...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Bingyun Ao, Haiyan Lu, Zhenfei Yang, Ruizhi Qiu, Shu-Xian Hu
The nature and extent of the highest oxidation state (HOS) in solid-state actinide compounds are still unexplored compared with those of small molecules, and there is burgeoning interest in studying the actinide-ligand bonding nature in the condensed state. A comprehensive understanding of the electronic structure and unraveling the possibility of a HOS are of paramount importance in solid-state actinide chemistry. Here, we report the physical OS of the early to middle actinides (Th → Cm) in solid-state compounds via a more rigorous quantum mechanical definition of OS under the DFT+U theoretical frameworks for the first time...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Nicolas A Leclaire, Musen Li, Anna C Véron, Antonia Neels, Jakob Heier, Jeffrey R Reimers, Frank A Nüesch
Crystalline organic semiconducting materials are much in demand for multiple electronic and optoelectronic device applications. Here, solution grown ultrathin rhombic crystals of a trimethine carbocyanine anionic dye are used to establish relationships between structural and optical properties. The dye crystallized in the monoclinic space group P21/c featuring alternating layers of molecules in two different herringbone type patterns, with perchlorate counterions located mostly within one of the two layers...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
Dengpan Dong, Fabian Sälzer, Bernhard Roling, Dmitry Bedrov
An experimental analysis based on very-low-frequency (VLF) impedance spectra and the Onsager reciprocal relations is combined with advanced analysis of dynamic correlations in atomistic molecular simulations in order to investigate Li+ transport in solvate ionic liquids (SILs). SILs comprised of an equimolar mixture of a lithium salt with glyme molecules are considered as a promising class of highly concentrated electrolytes for future Li-ion batteries. Both simulations and experiments on a prototypical Li-bis(trifluoromethanesulfonyl)imide (TFSI) salt/tetraglyme mixture show that while the ionic conductivity and the Li+ transport number are quite high, the Li+ transference number under 'anion-blocking conditions' is extremely low, making these electrolytes rather inefficient for battery applications...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
E M Neeman, I León, E R Alonso, L Kolesniková, S Mata, J L Alonso
The non-proteinogenic amino acid N-methyl-l-alanine has been brought into the gas phase using laser ablation techniques and studied by high resolution chirped pulse and molecular-beam Fourier transform microwave spectroscopies coupled to supersonic expansion. Four conformers showing the three types of hydrogen bond interactions I (NHO[double bond, length as m-dash]C), II (OHN) and III (N-HO-H) have been unambiguously identified, based on the comparison of the experimental rotational and 14N nuclear quadrupole constants with the calculated ab initio values...
November 14, 2018: Physical Chemistry Chemical Physics: PCCP
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