Chemical Physics Letters (v.605-606, #C)

Contents (iii-xi).

Display OmittedWe have performed structure analysis of the blue-emitting aluminum complex Alq3 using 27Al NMR and gauge-including projector-augmented wave calculations. The results clearly show that 27Al NMR spectra are insensitive to intermolecular interactions, thus providing a means of carrying out precise intramolecular structure determination. The key determinant of the blue-shifted emission of Alq3 is the facial isomerization.

Display OmittedThe surface alloys that form between Ce and Pd(1 1 1), Pd(1 0 0) and both unreconstructed and missing-row type Pd(1 1 0) at low Ce coverage ( θ Ce = 1 9 ML ) have shown permanent magnetism that is mediated in part by an RKKY-like delocalized Ce 6s–Pd 5s interaction. The Pd 4d states are significantly affected by alloying and their behavior cannot be explained by a purely spin-dependent Hamiltonian. Experimental observations of changes to the Pd 4d states are explained and the implications of Ce/Pd magnetism in reforming catalysis are discussed.

Display OmittedIn this Letter, we report the structural, elastic, and quasiparticle band structure of cynauric triazide. The structural properties using a dispersion corrected method to treat van der Waals (vdW) forces offers a significant improvement in the description of the ground state properties. The predicted bulk modulus from the equation of state and the elastic constants are consistent and the magnitude lies in the order of secondary explosives. Then, the G0W0 approximation is used to study the band structure and an indirect band gap of 6.33 eV is obtained. Finally, we have calculated the optical and detonation characteristics at ambient pressure.

Display OmittedWe perform approximate calculations of the rovibrational energy levels of HO2, using various theory-based J-shifting (JS) schemes, applied to a representative set of J values (total angular momentum). Results are compared both to exact energy levels previously reported by the authors (Chen and Poirier, 2010) [19], as well as to experimentally derived vibrational-state-dependent JS results (Zhang and Smith, 2006) [7]. This study serves both to evaluate and improve upon specific existing JS schemes, as well as to assess the general validity of the JS approach.

Self-organization of amphiphilic block copolymers in the presence of water: A mesoscale simulation by Pavel V. Komarov; Igor N. Veselov; Pavel G. Khalatur (22-27).
Display OmittedUsing dissipative particle dynamics, we analyze the suitability of amphiphilic diblock copolymers as a material for high-performance proton conducting membranes of fuel cells. It is shown that the topology of water channel network within hydrated block copolymer-based membranes can be controlled by varying the copolymer blocks length. In particular, our simulations predict the formation of bicontinuous cubic phases for hydrophilic, hydrophobic blocks, and water. The interfaces between microphase-separated subphases form triply periodic minimal surfaces.

The mechanism of hydrogen abstraction reactions between sevoflurane (CH(CF3)2OCH2F) and Cl atom was investigated using quantum chemistry methods. The geometries of all the species were optimized with wB97XD/6-311++G(d,p). Reaction pathways were confirmed with the intrinsic reaction coordinates. Thermochemistry properties were calculated with the accurate model chemistry method G3MP2 combined with the standard statistical thermodynamics. Gibbs free energies were used for analyzing reaction pathways. Three pathways were found and it corresponds to the H9, H11 and H10 abstraction reactions of –CH–, –CH2– and –CH2– groups with the barriers of 55.01, 32.50 and 32.50 kJ·mol−1, respectively. The rate constants for all the pathways over a wide temperature range of 200–2000 K were calculated. The obtained result is in good agreement with the experimental values.Display OmittedThe H abstraction reaction mechanisms between sevoflurane and Cl atom were investigated with DFT method. The geometries of all the species were optimized at wB97XD/6-311++G(d,p) level. Thermochemistry properties were calculated with the accurate model chemistry method G3MP2 combined with the standard statistical thermodynamics. Gibbs free energies were used for analyzing reaction pathways. Three pathways correspond to the H9, H11 and H10 reactions with the barriers of 55.01, 32.50 and 32.50 kJ·mol−1, respectively. The rate constants for all the pathways over a wide temperature range of 200–2000 K were calculated, and the result is in good agreement with the experimental values.

Facile coating carbon nanotubes with metal oxide nanoparticles of controlled size by Ning Wang; Tao Jiang; Yanqiu Yang; Chuxin Wu; Lunhui Guan (35-37).
Here, we present a facile one-pot method based on colloid chemistry to successfully synthesise nanocomposites of carbon nanotubes decorated with nanoparticles of different metal oxides. The as-synthesised nanocomposites were characterised by transmission electron microscopy and X-ray diffraction. The results revealed that different kinds of metal oxide nanoparticles were homogenously deposited on the carbon nanotubes. The size of the metal oxide nanoparticles could be tuned by adjusting the experimental temperature and duration of the synthesis steps.

The effect of noble metals in Si nanocrystals by Cedric L. Mayfield; Muhammad N. Huda (38-43).
Display OmittedIn this Letter, silicon nanocrystals doped with noble metal (Cu, Ag and Au) atoms have been studied by hybrid density functional theory. It is known that these metals play a significant role in Si nanowire growth, whereby Au is especially more favorable for this purpose. Our results show that the formation energies of noble metal impurities in Si nanocrystals are energetically high and hence less likely to be thermodynamically stable. In addition, our results show that Au atoms on the surfaces help promote the Si–Si covalent bonds in the nanostructures, whereas Cu and Ag induce some ionicity.

Display OmittedA formulation of the master equation for reversible association/dissociation reactions where one of the reactants is not in thermal equilibrium is presented and its detailed balance properties are discussed. This formulation incorporates the distribution of states immediately following a dissociation reaction and generalizes some earlier specific results.

Display OmittedA linear fractional transformation is proposed, which establishes the relationship between the liquid–gas coexistence curve of real substances and binodal of lattice models. Herewith the substance critical point with some density ρ c and some temperature T c is mapped in the critical point of a lattice model with density x  = 0.5 and temperature t  = 1. We found the ‘lattice analogues’ for binodals of mercury, cesium argon, ammonia and binodals of two model systems (van der Waals and Lennard-Jones). They are compared with analytical and numerical binodals known in the theory of lattice systems.

Interface chemistry of H2O on GaAs nanowires probed by near ambient pressure X-ray photoelectron spectroscopy by Xueqiang Zhang; Edward Lamere; Xinyu Liu; Jacek K. Furdyna; Sylwia Ptasinska (51-55).
Display OmittedInterface chemistry of H2O on GaAs nanowires is investigated by in situ X-ray photoelectron spectroscopy (XPS) at elevated water vapor pressures (from UHV to 5 mbar) and temperatures (from room temperature to 400 °C). Surface-assisted water dissociation leads to oxidation and hydroxylation of surface Ga atoms. In comparison with the simple planar GaAs(1 0 0) crystal, the H2O dissociation process on GaAs nanowires is greatly enhanced at elevated pressures and temperatures.

The mechanisms of impurity–impurity and impurity–matrix interactions in B/N-doped graphene by Peng Lai Gong; Liang Feng Huang; Xiao Hong Zheng; Teng Fei Cao; Ling Ling Song; Zhi Zeng (56-61).
The impurities in B-, N-, and BN-doped graphene interact with each other through the long-range screened Coulomb interaction. Display OmittedUsing DFT calculations, we investigate mechanisms of the impurity–impurity and impurity–matrix interactions in B/N-doped graphene. Our results have revealed that the impurities interact with each other through the long-range screened Coulomb interaction, and the impurity–matrix interaction is understood from the orbital hybridization. The impurity-induced inter-valley interference only shows a minor modification on the Coulombic impurity–impurity interaction. The B impurity binds more strongly with the matrix than the N impurity. The variation of the Fermi-level energy relative to Dirac point with the itinerant carrier concentration, along with the delocalized distribution of the carriers, indicates the nonlocal doping effect of the impurities.

Odd–even dependence of rectifying behavior in carbon chains modified diphenyl–dimethyl molecule by Qiu-Hua Wu; Peng Zhao; Hai-Ying Liu; De-Sheng Liu; Gang Chen (62-66).
We present a systematic study of the effects of asymmetric nonequi-length carbon chains on the electron transport properties of diphenyl–dimethyl molecule. Significant odd–even dependence is observed: the rectification appears only in the hybrid nanostructure with odd carbon chain on one side and even carbon chain on the other side, while it is negligible in those with odd/even carbon chain on both sides.Display OmittedUsing density functional theory and non-equilibrium Green’s function formalism, we investigate the effects of asymmetric nonequi-length carbon chains on the electron transport properties of diphenyl–dimethyl molecule. The results show significant odd–even dependence: the rectification appears only in the hybrid nanostructure with odd carbon chain on one side and even carbon chain on the other side, while it is negligible in those with odd/even carbon chain on both sides. The mechanism for the odd–even dependence of rectification is analyzed by the bias-dependent transmission spectra, evolution of molecular orbital levels, their spatial distributions, and projected density of states with the applied bias.

Fourier-transform microwave spectroscopy of the H2–H2O complex by Kensuke Harada; Keiichi Tanaka; Hirofumi Kubota; Toshiaki Okabayashi (67-70).
Display OmittedFourier-transform microwave spectroscopy was applied to observe the J  = 1–0 rotational transition of the ortho-H2–H2O complex and isotopologues in the ground Σ0 state (H2 in the j H2  = 1 state and H2O in the ground 000 state) to obtain precise molecular constants. Observed spectra were split into three hyperfine components, confirming the complexes are the ortho-H2/para-D2 species. The determined nuclear spin–spin coupling constant indicates H2 is rotating almost freely in the complex; the Σ0 state is nearly of j H2  = 1 and k H2  = 0. For the ortho-H2 species, the nuclear spin–rotation coupling constant was also determined.

Low-energy electron interactions with dimethyl disulphide by C. Matias; A. Mauracher; P. Scheier; P. Limão-Vieira; S. Denifl (71-76).
Electron attachment experiments have been performed with dimethyl disulphide, C2H6S2, in the gas phase by means of a crossed electron-molecular beam experiment. Ion yields for 8 anions have been measured in the energy range from ∼0 to 15 eV. Many of the dissociative electron attachment products observed at low energy arise from surprisingly complex reactions associated with multiple bond cleavages as well as structural and electronic rearrangement. Quantum chemical calculations on the electronic properties of C2H6S2 have been performed in order to complement the experimental investigations.

A hybrid Mg–Al layered double hydroxide/graphene nanostructure obtained via hydrothermal synthesis by Xiaodong Zhao; Jian-Ping Cao; Jun Zhao; Guo-Hua Hu; Zhi-Min Dang (77-80).
Display OmittedA hybrid Mg–Al layered double hydroxide/graphene (LDH–GR) material nanostructure has been fabricated by employing the hydrothermal treatment at 140 °C for 10 h. Graphene oxide is simultaneously reduced to graphene during the hydrothermal treatment. The LDH and LDH–GR have high degree of crystallinity and assembled layer structure, which is attributed to electrostatic interaction mechanism. The obtained hybrid nanostructure materials can be used as flame retardant or conductor of electricity and heat due to the combination of different properties arising from graphene and LDH.

Radicals generated from 2-chloro-5-fluorotoluene by corona discharge by Eun Hye Yi; Young Wook Yoon; Sang Kuk Lee (81-84).
Display OmittedThe generation of molecular radicals in corona discharge was investigated spectroscopically by varying the experimental conditions applied to a substituted toluene precursor. Vibronic emission spectra were observed from the corona discharge of 2-chloro-5-fluorotoluene seeded in a large amount of carrier gas helium. From an analysis of emission spectra observed, it was confirmed that bond dissociation energy plays a key role in radical formation. The possible pathway for the formation of benzyl-type radicals is proposed to explain the observation.

Preparation of Ag/Au/Pt nanoparticles and their catalytic properties by Arisa Ongartkit; Supon Ananta; Laongnuan Srisombat (85-88).
Display OmittedThe Pt deposited on hollow Ag/Au nanoparticles (Ag/Au/Pt) was successfully prepared by a successive reduction method. In general, no absorption peak at UV–visible region similar to that of Pt nanoparticles was observed for these Ag/Au/Pt nanoparticles. Almost spherical nanoparticles with average size around 20 nm were revealed by TEM. The presence of constituent metal of Ag/Au/Pt was confirmed by EDS. The catalytic properties of Ag/Au/Pt for methanol oxidation were investigated by cyclic voltammetry. The peak current density of the Ag/Au/Pt nanoparticles is higher than that of Pt nanoparticles, indicating their better potential of an electrocatalytic activity for methanol oxidation.

Display OmittedHigh room temperature ferromagnetic moment with high Curie temperature ( > 700 K) for graphene oxide (GO) is obtained by a simple chemical activation using phosphoric acid followed by heat treatment at 800 °C. The field and temperature variations of the magnetization data indicate ferromagnetic, paramagnetic and diamagnetic contributions in the acid/heat treated sample. IR spectroscopic studies suggest hydrogenation (reduction) of GO after the acid and heat treatments. The results point to the role of defects, extent of hydrogenation, changes in the bonding characteristics and the nature of the functional groups in determining the different magnetic contributions.

A metal endohedral dopant modifies the relative stability of C70O3 ozonide isomer series.Light metal atoms such as Li, K (electronic state 2S1/2) or Ca (1S0) encapsulated in a C70 cage considerably modifies the chemical properties of the fullerene surface due to metal-to-cage electron transfer. H-doped and anion ozonide systems were also considered to validate the electron transfer hypothesis. The relative stabilities of the eight isomers of the C70O3 molozonide series at room temperature depend on the identity of the endohedral guest, as was the preferred channel for thermal decomposition. No electron transfer was observed for the complex N@C70 where the fullerene acts as an inert container for the 4S3/2 radical.

An ESR study on superoxide radical anion generation and its involvement in the photooxidative degradation of poly-3-hexylthiophene in chlorobenzene solution by Liang Chen; Junji Mizukado; Yasumasa Suzuki; Shuzo Kutsuna; Yoshinori Aoyama; Yuji Yoshida; Hiroyuki Suda (98-102).
Display OmittedThe photooxidative degradation of poly-3-hexylthiophene (P3HT) in chlorobenzene solution containing dissolved oxygen was performed at room temperature. The generation of superoxide radical anion (O2 •−) during the photooxidation of P3HT was verified by ESR measurements using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin trap. The changes in mass spectra determined by MALDI-TOF MS showed that P3HT photodegradation was prevented in the presence of DMPO. Kinetics analysis shows that the prevention of P3HT photodegradation is due to the scavenging of O2 •− by DMPO. Therefore, the involvement of O2 •− in the initial step of P3HT photodegradation could be concluded.

Quantum chemical studies on the role of residues in calcium ion binding to Calmodulin by Samapan Sikdar; Mahua Ghosh; Molly De Raychaudhury; J. Chakrabarti (103-107).
We perform density functional theory (DFT) based quantum chemical calculations on calcium ion coordination to an isolated loop of Calmodulin. We show that the coordination molecular orbitals in the ground state, having contributions from the valence orbitals of the metal ion and the loop atoms, bring out the roles of the coordinating and the non-coordinating residues to stabilize the coordination geometry in agreement to the mutational studies. The coordinating molecular orbitals are observed to be robust under various truncations of the binding loop and capping at the terminal residues.

Theoretical and experimental study of the fragmentation of protonated uracil by Leila Sadr-Arani; Pierre Mignon; Henry Chermette; Thierry Douki (108-114).
Different fragmentation channels of protonated uracil (UH+) have been studied in a combined experimental and theoretical study. Various ESI mass spectrometry fragmentation spectra have been obtained by using collision induced fragmentation at increasing energy. The fragment at 85 Th was observed for a 10 eV collision energy while those at 96 and 70 Th were observed for larger collision energy, (20 eV). From the theoretical point of view, the anti and syn tautomers of uracil protonated at the O8 position have been considered. DFT calculations allowed us to describe the main dissociation channels of UH+ observed from the mass spectra.

Square-centimeter-scale 2D-arrays of Au@Ag core–shell nanoparticles towards practical SERS substrates with enhancement factor of 107 by Francesca Pincella; Yeji Song; Takao Ochiai; Katsuhiro Isozaki; Kenji Sakamoto; Kazushi Miki (115-120).
Display OmittedA series of two-dimensional (2D) arrays of Au-core/Ag-shell nanoparticles with fixed sub-3 nm gap distance was obtained on 1 cm2 substrates. All 2D arrays resulted in homogeneous and dense monolayers of nanoparticles thanks to our original hybrid deposition method based on self-assembly. Midnanosized gold nanoparticles were used as the core and Ag-shell with different thicknesses were grown to tune the LSPR to around 633 nm. The resulting SERS substrates enhanced Raman signal by up to about 107 with remarkable spatial uniformity. Our SERS substrate is highly promising as a practical SERS-based sensor substrate.

The possible phase diagrams for the transverse Ising model with temperature-dependent parameters by Bayor Jude Simons; Baohua Teng; Shanyu Zhou; Liming Zhou; Xiangyu Chen; Minghe Wu; Hao Fu (121-125).
In this Letter the transition properties of the transverse Ising model with temperature-dependent parameters are investigated. By supposing the simple dependent relations of the interaction parameters on temperature, the phase diagrams are straightforwardly obtained, which may be used to describe the closed-loop behavior for the phase transition of the systems. In fact, the reentrant phase behavior of the system obtained by this Letter is to some extent coincident with the phenomena exhibited in some colloids and complex fluid mixtures as well as proteins.

Photophysical properties of new bis-perylene dyads for potential upconversion use by Marcos R. Ribas; Ronald P. Steer; Ricardo Rüther (126-130).
Display OmittedTwo new bis-perylenes, BPC with a meta-disubstituted benzene linker, and BPD with a p,p′-disubstituted biphenyl linker, have been synthesized and their photophysical parameters measured. Their singlet and triplet energies decrease incrementally in the order perylene, BPC, BPD, making them ideally matched with C60 for triplet–triplet energy transfer in sensitized photon upconversion schemes. Following photosensitization by triplet C60, BPC exhibits strong fluorescence upconversion by triplet–triplet annihilation, indicating that these bis-perylene dyads (and the multimers that can be constructed from them) will be interesting candidates for use in organic devices such as bulk-heterojunction and dye-sensitized solar cells employing non-coherent photon upconversion.

The halogen bonds with the trivalent and pentavalent bromine centers acting as the Lewis acid are analyzed. These interactions may be classified as the σ-hole bonds. Display OmittedThe halogen bond in complexes of BrF3 and BrF5 is analyzed where the trivalent and pentavalent bromine centers interact as the Lewis acid with the nitrogen Lewis base centers of HCN and N2 molecules as well as with the F, Cl and Br anions. The halogen bonds analyzed here possess characteristics typical for other interactions as for example for the hydrogen bond or the halogen bond with the monovalent halogen center. However there are differences; the whole sphere of the multivalent Br-center is characterized by the positive electrostatic potential thus it acts as the Lewis acid, while the halogen monovalent atoms are usually characterized by the dual character since they may act simultaneously as the Lewis acid and as the Lewis base. The Quantum Theory of Atoms in Molecules and the Natural Bond Orbital method are applied here.

Generalized interatomic pair-potential function by Jianing Colin Xie; Sudhanshu K. Mishra; Tapas Kar; Rui-Hua Xie (137-146).
Meta-stable diatomic dication He 2 + + : comparison of potential energies between five-parameter potential (this Letter), full CI calculation (AH 1992), multi-reference double excitation CI calculation (MNB 1987), James-Coolidge-method based calculation (YSW 1977), and accurate data.Display OmittedBased on a three-parameter molecular orbital-type pair-potential function, we have proposed a generalized interatomic pair-potential function. This new function has been demonstrated to be able to describe accurately and adequately the potentials of the metastable diatomic dications (e.g., He 2 + + , BeH++, AlH++), and the ground states of covalent bonding systems (e.g., H2, Si2, HCl, NO, LiH, HeH+, and He 2 + ), ionic bonding systems (e.g., NaCl), and van der Waals weakly binding systems (e.g., rare-gas, alkaline-earth, group 12, rare-gas metal dimers, and rare-gas halides).

Counter ion effects on the energy transfer processes in PPV by Paulo Alliprandini Filho; Alexandre Marletta; Leni Akcelrud; Osvaldo N. Oliveira (147-151).
The emission was partially linearly polarized for PTHT-DBS and PPV-DBS cast films excited with linearly polarized excitation, but showed no polarization when excitation was performed with circularly polarized excitation. The spectral mass center (λ SMC), the degree of polarization (P) and the relative emission efficiency (η rel) depend on DBS concentration. Also worth noting is that the effects are much less significant for the PPV-DBS film converted at 200 °C.Display OmittedWe report an enhanced luminescence of cast films of poly(p-phenylenevinylene) (PPV), where the energy transfer among adjacent polymer chains was controlled by varying the concentration of counterions in the synthesis. Using as precursor poly(xylylidenetetrahydrothiophenium) with dodecylbenzenesulfonate as counter ions (PTHT-DBS) in 1:3 M basis led not only to the strongest but also the most polarized emission. Both the intensity and degree of polarization could be controlled, provided that the conversion temperature was considerably lower than the T g of PPV. These results may be exploited in optimizing organic electronic devices, for which annealing is needed.

Relative rate study of the kinetic isotope effect in the 13CH3D + Cl reaction by L.M.T. Joelsson; R. Forecast; J.A. Schmidt; C. Meusinger; E.J.K. Nilsson; S. Ono; M.S. Johnson (152-157).
Display OmittedThe 13CH3D/12CH4 kinetic isotope effect, α 13 CH 3 D , of CH4  + Cl is determined for the first time, using the relative rate technique and Fourier transform infrared (FTIR) spectroscopy. α 13 CH 3 D is found to be 1.60 ± 0.04. In addition, a quantum chemistry/transition state theory model with tunneling correction is constructed and the primary cause for α 13 CH 3 D is found to be the substantially reduced reactivity of the D atom, which, in turn, can be explained by a significant increase in the reaction barrier due to changes in the vibrational zero point energy and to a lesser extent tunneling.

Real-time molecular uptake and membrane-specific transport in living cells by optical microscopy and nonlinear light scattering by Michael J. Wilhelm; Joel B. Sheffield; Grazia Gonella; Yajing Wu; Christian Spahr; Jia Zeng; Bolei Xu; Hai-Lung Dai (158-163).
Display OmittedWe show that the comparably simple and widely available technique, optical transmission microscopy (TM), can be used in a time-resolved way to independently measure uptake of any molecule (that absorbs visible light) into living cells. This technique complements second-harmonic light scattering (SHS), which can be used for time-resolved observation of adsorption and transport of small molecules, with non-zero first-order hyper-polarizability, through membranes in living cells. While either technique can be used alone, a combination of the pair allows a fully complementary and quantitative characterization of molecular uptake with membrane specificity in living cells. Specifically, TM permits detection of the changing bulk molecular concentrations within the cell, and SHS, with its inherent interface sensitivity, provides sequential differentiation of molecular density at membrane surfaces. Simultaneous global analysis of the TM and SHS observations yield molecular diffusion rate constants for all traversed cellular barriers.