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Physical Chemistry Chemical Physics: PCCP

Marie-Christine Bacchus-Montabonel
One of the major concerns in prebiotic chemistry is the formation and destruction routes of prebiotic compounds in space. As detected for a long time, hydrogen cyanide (HCN) has been suggested to be a feedstock molecule at the origin of life driving easy oligomerization, in particular to form adenine. This may focus on its first oligomers because its dimer cyanomethanimine was recently observed in star-forming regions, or its trimer aminomalononitrile. With regard to the assumption of an extra-terrestrial origin of life, the stability of such species under ultraviolet radiation or in ion-collisions is an open question...
March 24, 2017: Physical Chemistry Chemical Physics: PCCP
César González, Blanca Biel, Yannick J Dappe
We present a theoretical study of molecular adsorption on defects on a MoS2 monolayer. Based on Density Functional Theory, our calculations confirm that small inorganic molecules, such as CO2, CO, H2O, NO, NO2, H2 and N2, remain bonded to the pristine monolayer through weak van der Waals interactions, suggesting that the molecules may easily diffuse over the clean monolayer. On the other hand, the introduction of defects can lead to three different situations, depending on the defect and the molecule considered: physisorption, chemical (strong) bonding to the metallic defects, namely the Mo substitutional atoms on the S vacancies, and dissociation, that can take place spontaneously at 0 K in some specific cases or by the effect of thermal agitation in molecules such as CO2 or NO2 on the S vacancy...
March 24, 2017: Physical Chemistry Chemical Physics: PCCP
Milena Vujović, Matija Zlatar, Miloš Milčić, Maja Gruden
A detailed theoretical investigation of cyclophanes with a divergent set of methods ranging from molecular mechanics through semiempirical to ab initio is presented. Cyclophanes have attracted interest over the years due to their unusual chemistry and increasing applications. There has been previous debate over the effects contributing to the greater stability of more-crowded in isomers of certain cyclophanes, and a higher strain in the out isomer was the prevailing explanation. Application of EDA-NOCV and SAPT analysis has enabled us to distinguish between different effects controlling isomer stability and determine the significance of all effects involved...
March 24, 2017: Physical Chemistry Chemical Physics: PCCP
Jing Wen, Xitian Zhang, Hong Gao
Although many studies have been focused on the characterization of MXenes, surface structures and formation mechanisms in terms of their experimental processes still remain controversial. Herein, we systematically investigated the structures formed from MX intercalated with different atoms from group IA to VIIA (A = H, Li, Na, K, Mg, Al, Si, P, O, S, F, and Cl) at different sites. An effective procedure based on first-principles calculations was developed to reveal the formation mechanisms of MAX, MXA2, MXTx, and MXTxAx' structures...
March 24, 2017: Physical Chemistry Chemical Physics: PCCP
Ricardo Franklin-Mergarejo, Tammie Nelson, Sergei Tretiak, Sebastian Fernandez-Alberti
In the last decade, recent synthetic advances have launched carbon-based π-conjugated hoops to the forefront of theoretical and experimental investigation not only for their potential use as bottom-up templates for carbon nanotube (CNT) growth, but also for the interesting excitonic effects arising from the cyclic geometry, unique π-system orientation, and unusual electronic interactions and couplings. In particular, cyclic materials based on pyrene, a common component in organic electronics, are popular candidates for the future design of π-conjugated nanorings for optoelectronic applications...
March 24, 2017: Physical Chemistry Chemical Physics: PCCP
Alexander Kulesza, Steven Daly, Philippe Dugourd
We have investigated the free energy landscape of Aβ-peptide dimer models in connection to gas-phase FRET experiments. We use a FRET-related distance coordinate and one conformation-related coordinate per monomer for accelerated structural exploration with well-tempered metadynamics in solvent and in vacuo. The free energy profiles indicate that FRET under equilibrium conditions should be significantly affected by the de-solvation upon the transfer of ions to the gas-phase. In contrast, a change in the protonation state is found to be less impacting once de-solvated...
March 24, 2017: Physical Chemistry Chemical Physics: PCCP
Bolong Huang, Mingzi Sun
An energy conversion model has been established for the intrinsic persistent luminescence in solids related to the native point defect levels, formations, and transitions. In this study, we showed how the recombination of charge carriers between different defect levels along the zero phonon line (ZPL) can lead to energy conversions supporting the intrinsic persistent phosphorescence in solids. This suggests that the key driving force for this optical phenomenon is the pair of electrons hopping between different charged defects with negative-Ueff...
March 23, 2017: Physical Chemistry Chemical Physics: PCCP
Xingxing Xiao, Marc Widenmeyer, Wenjie Xie, Tianhua Zou, Songhak Yoon, Marco Scavini, Stefano Checchia, Zhicheng Zhong, Philipp Hansmann, Stefan Kilper, Andrei Kovalevsky, Anke Weidenkaff
A series of Ba1-xEuxTiO3-δ (0.1 ≤ x ≤ 0.9) phases with ∼40 nm particle size were synthesized via a Pechini method followed by annealing and sintering under a reducing atmosphere. The effects of Eu(2+) substitution on the BaTiO3 crystal structure and the thermoelectric transport properties were systematically investigated. According to synchrotron X-ray diffraction data only cubic perovskite structures were observed. On the local scale below about 20 Å (equal to ∼5 unit cells) deviations from the cubic structure model (Pm3[combining macron]m) were detected by evaluation of the pair distribution function (PDF)...
March 23, 2017: Physical Chemistry Chemical Physics: PCCP
Danielle Klawinski, Christian Weinberger, Dominik Klaus, Jan-Henrik Smått, Michael Tiemann, Thorsten Wagner
The performance of many chemical gas-phase reactions is strongly influenced by the interaction of reactants with interfaces. Nanoporous materials, which exhibit pore diameters up to 100 nm and high specific surface areas, can be utilized to reduce the amount of cost-intensive materials (e.g. noble metals). However, due to limitations in material transport and reaction kinetics detailed knowledge of the diffusion and the kinetics of a chemical reaction is necessary to improve the performance of chemical processes in industry and research...
March 23, 2017: Physical Chemistry Chemical Physics: PCCP
Marianna Ambrico, Paolo F Ambrico, Teresa Ligonzo, Antonio Cardone, Maria Grazia Bridelli, Giuseppe Casamassima, Paola Manini, Marco d'Ischia
Although it has long been known that the peculiar electronic-ionic conductor behavior of eumelanin is critically dependent on hydration, the detailed mechanisms by which water-polymer interactions control and affect the conduction properties have remained largely obscure. In this paper, we report a remarkable anisotropy and giant polarization effect in a synthetic eumelanin (TEGMe) chemically functionalized with hydrophilic TEG residues. FT-IR analyses of water sorption isotherms and AC measurements were consistent with a microporous structure binding or hosting mainly isolated water molecules...
March 23, 2017: Physical Chemistry Chemical Physics: PCCP
Vivek Shukla, Ashish Bhatnagar, Pawan K Soni, Alok K Vishwakarma, M A Shaz, T P Yadav, O N Srivastava
The present investigation describes the synergistic role of Li4(BH4)(NH2)3 and ZrFe2 in the hydrogen storage behaviour of a Li-Mg-N-H hydride system. The onset desorption temperature of ZrFe2-catalysed Mg(NH2)2-LiH-Li4(BH4)(NH2)3 is ∼122 °C, which is 83 °C, 63 °C, and 28 °C lower than that of thermally treated 2LiNH2-1MgH2, 2LiNH2-1MgH2-4 wt%ZrFe2, and 2LiNH2-1MgH2-0.1LiBH4 composites, respectively. Native Mg(NH2)2-LiH-Li4(BH4)(NH2)3 absorbed only 2.78 wt% of H2 within 30 min. On the other hand, the ZrFe2-catalysed Mg(NH2)2-LiH-Li4(BH4)(NH2)3 sample absorbed 3...
March 23, 2017: Physical Chemistry Chemical Physics: PCCP
Jing Zeng, Ke-Qiu Chen
In experimental studies, magnetoresistance (MR) values of 10(3) are hard to reach for conventional single-molecule spin-valves. Motivated by a recent experiment [Nano Lett., 2016, 16, 577-582], where tailored Co-salophene-based all-spin molecular devices are successfully realized, we demonstrate the functionality of a Co-salophene-based spin chain without magnetic electrodes. By using nonequilibrium Green's functions in combination with density functional theory, we find that the maximum MR ratio of this spin chain can reach 10(6) by manipulating its spins in a controlled way, which is several orders of magnitude higher than previously reported experimental values...
March 22, 2017: Physical Chemistry Chemical Physics: PCCP
Parisa Akhshi, Gang Wu
We have applied the umbrella sampling (US) method in all-atom molecular dynamics (MD) simulations to obtain potential of mean force (PMF) profiles for ion transport through three representative G-quadruplex DNA channels: [d(TG4T)]4, [d(G3T4G4)]2, and d[G4(T4G4)3]. The US MD results are in excellent agreement with those obtained previously with the adaptive biasing force (ABF) method. We then utilized the unique features in the US MD method to investigate multi-ion effects in [d(G3T4G4)]2 and discovered that the concerted ion movement is crucial for fully explaining the unusual experimental results on ion movement in this particular G-quadruplex system...
March 22, 2017: Physical Chemistry Chemical Physics: PCCP
Martin Schnedlitz, Maximilian Lasserus, Daniel Knez, Andreas W Hauser, Ferdinand Hofer, Wolfgang E Ernst
We present time-resolved transmission electron microscopy studies of the degradation of Au, Ag, Cu and Ni nanowires deposited on a heated support. The wires are grown under fully inert conditions in superfluid helium droplets and deposited onto amorphous carbon. The inherent stability of these pristine metal nanowires with diameters below 10 nm is investigated in the absence of any stabilizers, templates or solvents. The phenomenon of Rayleigh-breakup, a consequence of diffusion processes along the wire surfaces, is analysed in situ via scans over time and support temperature...
March 22, 2017: Physical Chemistry Chemical Physics: PCCP
Yury Minenkov, Giovanni Bistoni, Christoph Riplinger, Alexander A Auer, Frank Neese, Luigi Cavallo
In this work, we tested canonical and domain based pair natural orbital coupled cluster methods (CCSD(T) and DLPNO-CCSD(T), respectively) for a set of 32 ligand exchange and association/dissociation reaction enthalpies involving ionic complexes of Li, Be, Na, Mg, Ca, Sr, Ba and Pb(ii). Two strategies were investigated: in the former, only valence electrons were included in the correlation treatment, giving rise to the computationally very efficient FC (frozen core) approach; in the latter, all non-ECP electrons were included in the correlation treatment, giving rise to the AE (all electron) approach...
March 22, 2017: Physical Chemistry Chemical Physics: PCCP
Dominic A Esan, Michael Trenary
Adsorption and thermal chemistry of propanal, 2-propenol, and 1-propanol on Ru(001) were studied using temperature programmed reaction spectroscopy (TPRS) and reflection absorption infrared spectroscopy (RAIRS). The results show that each molecule adsorbs molecularly at 90 K and displays the same spectral features as observed for the corresponding liquids after 1.0 L exposures. 2-Propenol was found to molecularly desorb at 200 K, dehydrate to yield propene around 130 K, isomerize to propanal at 180 K, and hydrogenate to 1-propanol at 220 K...
March 22, 2017: Physical Chemistry Chemical Physics: PCCP
Thomas J Salez, Bo Tao Huang, Maud Rietjens, Marco Bonetti, Cécile Wiertel-Gasquet, Michel Roger, Cleber Lopes Filomeno, Emmanuelle Dubois, Régine Perzynski, Sawako Nakamae
Currently, liquid thermocells are receiving increasing attention as an inexpensive alternative to conventional solid-state thermoelectrics for low-grade waste heat recovery applications. Here we present a novel path to increase the Seebeck coefficient of liquid thermoelectric materials using charged colloidal suspensions; namely, ionically stabilized magnetic nanoparticles (ferrofluids) dispersed in aqueous potassium ferro-/ferri-cyanide electrolytes. The dependency of thermoelectric potential on experimental parameters such as nanoparticle concentration and types of solute ions (lithium citrate and tetrabutylammonium citrate) is examined to reveal the relative contributions from the thermogalvanic potential of redox couples and the entropy of transfer of nanoparticles and ions...
March 22, 2017: Physical Chemistry Chemical Physics: PCCP
Hui-Ying Mu, Fa-Tang Li, Xing-Tao An, Rui-Hong Liu, Yi-Lei Li, Xin Qian, Yong-Qi Hu
The development of inexpensive visible-light-driven photocatalysts is an important prerequisite for realizing the industrial application of photocatalysis technology. In this paper, an earth-abundant FeAl2O4 photocatalyst is prepared via facile solution combustion synthesis. Density functional theory and the scanning Kelvin probe technique are employed to ascertain the positions of the energy bands and the Fermi level. Phenol is taken as a model pollutant to evaluate the photocatalytic activity of FeAl2O4. The scavenger experiment results, ˙OH-trapping fluorescence technique, and electron spin resonance measurements confirm that the superoxide anion radical is the main active species generated in the photocatalytic process, which also further corroborates the proposed electronic structure of FeAl2O4...
March 22, 2017: Physical Chemistry Chemical Physics: PCCP
Junxiang Zuo, Bin Zhao, Hua Guo, Daiqian Xie
A new and more accurate full-dimensional global potential energy surface (PES) for the ground electronic state of the ClH2O system is developed by fitting 15 777 points obtained using an explicitly correlated unrestricted coupled-cluster method with single, double, and perturbative triple excitations (UCCSD(T)-F12b). The fitting is carried out using the permutation invariant polynomial-neural network (PIP-NN) method and has an error of 6.9 meV. The new PES has a slightly lower barrier for the atmospherically important HCl + OH → Cl + H2O reaction than the previous PES based on multi-reference configuration interaction (MRCI) calculations...
March 22, 2017: Physical Chemistry Chemical Physics: PCCP
Stig Koust, Logi Arnarson, Poul G Moses, Zheshen Li, Igor Beinik, Jeppe V Lauritsen, Stefan Wendt
To understand the structure-reactivity relationships for mixed-metal oxide catalysts, well-defined systems are required. Mixtures of vanadia and titania (TiO2) are of particular interest for application in heterogeneous catalysis, with TiO2 often acting as the support. By utilizing high-resolution scanning tunneling microscopy, we studied the interaction of vanadium (V) with the anatase TiO2(101) surface in the sub-monolayer regime. At 80 K, metallic V nucleates into homogeneously distributed clusters onto the terraces with no preference for nucleation at the step edges...
March 22, 2017: Physical Chemistry Chemical Physics: PCCP
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