Chemical Physics Letters (v.604, #C)

Contents (iii-ix).

Display OmittedNucleation of carbon nanotubes is considered to start with the supersaturation of carbon atoms dissolved in a catalyst. In chemical vapor deposition synthesis, it is believed that condensation of the source gas terminates the growth. However, some experimental studies have suggested that termination is primarily affected by catalyst behavior. We modified the potential functions and observed the behavior of carbon–iron mixed nanoparticles by a molecular dynamics method and found that the iron fraction melted at the equivalent temperature of growth termination. Thus, we concluded that the catalyst fusion prevented nucleation that would normally occur as a consequence of solution supersaturation.

Display OmittedThe quartz crystal microbalance (QCM) was exploited for cardiac markers detection and kinetic studies of immunochemical reaction of cardiac troponin I (cTnI) and human heart fatty acid binding protein (H-FABP) with the corresponding monoclonal antibodies in undiluted plasma (serum) and standard solutions. The QCM technique allowed to dynamically monitor the kinetic differences in specific interactions and nonspecific sorption, without multiple labeling procedures and separation steps. The affinity binding process was characterized by the association (k a) and the dissociation (k d) kinetic constants and the equilibrium association (K) constant, all of which were obtained from experimental data.

Display OmittedElectronic and photophysical properties of [Ru(bpy)2(OSO)]+ (bpy = 2,2′-bipyridine; OSO = methylsulfinylbenzoate) were examined theoretically to better understand the differences between S- and O-linked ruthenium sulfoxide complexes. It is found that the strength of Ru–O1 linkage is significantly larger than that of Ru–S linkage, which makes the charge transfer amount from surrounding ligands to central Ru decreased. The energy gap is closed due to the highest occupied molecular orbital energy increases to a larger extent than the lowest unoccupied molecular orbital energy. Thereby, red shifted absorption and emission maxima in such photochromic ruthenium sulfoxide complexes can be explained.

Raman spectra of CFTSe nanoparticles synthesized at 220 °C with different amounts of En (a: 8 mL, b: 12 mL, c: 16 mL, d: 20 mL).Display OmittedCu2FeSnSe4 (CFTSe) nanoparticles including nanoflowers and nanosheets were synthesized by a simple solvothermal method. The structures, morphologies, chemical compositions and optical properties of as-synthesized CFTSe nanoparticles were studied. CFTSe nanoflowers mainly formed in the early stage of the reaction. By prolonging the reaction times, most CFTSe nanoflowers turned into CFTSe nanosheets. And the thicknesses of CFTSe nanosheets increased with increasing the reaction temperatures or decreasing the amount of the solvent. The bandgaps of CFTSe nanoparticles were about 1.19–1.25 eV determined by the UV–Vis absorption spectra, which indicated their possible photovoltaic applications.

Interface architecture determined the performance of ZnO nanorods-based photodetectors by N.K. Hassan; M.R. Hashim; K. Al-Heuseen; Nageh K. Allam (22-26).
Display OmittedHigh density ZnO nanorods grown on silicon oxide-coated Si (1 1 1) substrates were used to fabricate an MSM UV photodetector. The maximum sensitivity of the detector was about 1150, which was maintained over the wide range of applied bias. The photodetector responsivity increased slightly until reaching a maximum value at 374 nm and exhibited a sharp cutoff at 378 nm. The obtained photodetector responsivity was as high as 1.1 A/W. The detector shows fast photoresponse with a rise time of 0.008 s and a decay time of 0.021 s.

Hydrogen migration in methanol studied under asymmetric fs laser irradiation by N. Kotsina; S. Kaziannis; C. Kosmidis (27-32).
Display OmittedHydrogen migration processes in deuterated methanol (CH3OD) under the irradiation of ultrashort (30 fs) two color (400/800 nm) laser field have been investigated by means of time-of-flight mass spectrometry. The utilization of an asymmetric ω/2ω laser field contributes to a better understanding of hydrogen migration processes. Based on the comparative study of the asymmetry dependence and the angular distributions of the H2D+, HOD+ and H2OD+ fragment ions, whose formation requires hydrogen migration, it was feasible to distinguish the most probable site of the molecular skeleton where the hydrogen migrates from.

Effect of chemical environment on K shell binding energy of Ag and Sn by K.M. Niranjana; Krishnananda; N.M. Badiger (33-37).
Display OmittedThe effect of chemical environment on K shell binding energy of Ag and Sn has been studied by using external bremsstrahlung (EB). The spectrum of transmitted EB, recorded with high resolution HPGe detector spectrometer, shows a sudden drop in intensity at K edge along with unwanted K β 1 ′ and K β 2 ′ characteristic X-ray photons of the target. A modified sigmoidal function has been used to determine the K edge of Ag, Sn and their compounds to understand the effect of crystal structure on K shell binding energy.

Display OmittedCalculations of adsorption energies of bromobenzene and aniline on Cu2O(1 1 0):CuO and (1 1 1):CuO surfaces are of importance in investigations of e.g. C–N cross-coupling reactions. The present study, based on the density functional theory (DFT), proves that the van der Waals forces are important components of the total adsorption energies for these systems. On (1 1 0):CuO the dispersion forces are the dominant interactions, while on (1 1 1):CuO surface, the molecules chemisorb stronger and the dispersion forces contribute less to the total adsorption energy. In comparison with (1 1 0), the (1 1 1):CuO surface strongly distort after adsorption, which contributes as well to the total adsorption energy.

Display OmittedWe calculate potential curves for transition metal dimers using Monte Carlo configuration interaction (MCCI). These results, and their associated spectroscopic values, are compared with experimental and computational studies. The multireference nature of the MCCI wavefunction is quantified and we estimate the important orbitals. We initially consider the ground state of the chromium dimer. Next we calculate potential curves for Sc2 where we contrast the lowest triplet and quintet states. We look at the molybdenum dimer where we compare non-relativistic results with the partial inclusion of relativistic effects via effective core potentials, and report results for scandium nickel.

Effect of ionic additives on critical exponents of 2,6-dimethylpyridine–water by Dorota Truszkowska; Marzena Dzida; Udo Kaatze (53-59).
The diffusion coefficients and the shear viscosities of critical mixtures of water and 2,6-dimethylpyridine have been measured without and with small amounts of an ionic liquid or sodium bromide added. The experimental data reveal significant deviations from universal power law behaviour and also a dependence of the critical exponents on the concentration and properties of the added ions. A coupling of the critical fluctuations in the local concentrations to the formation of mesoscopic molecular aggregates is suggested. Likely the formation involves stacking of the cyclic amine molecules promoted by hydrophobic interactions and hydrogen bonding with water.

Display OmittedThree dimensional calculations of electronic dynamics of CH4 in a strong laser field are presented with time-dependent density-functional theory. Time evolution of dipole moment and electron localization function is presented. The dependence of dissociation rate on the laser characters is shown and optimal effective parameters are evaluated. The optimum field leads to 76% dissociation probability for Gaussian envelope and 40 fs (FWHM) at 1016  W cm−2. The dissociation probability is calculated by optimum convolution of dual short pulses. By combining of field assisted dissociation process and Ehrenfest molecular dynamics, time variation of bond length, velocity and orientation effect are investigated.

Display OmittedThe near-IR and the mid-IR spectrum of enflurane dissolved in liquid Xe was studied at T  ∼ 170 K. Inversion nature of the two CH stretching vibrations were analyzed by comparison of relative intensities of corresponding bands in a range of a first overtone and fundamental transition. The effect was explained by including features of the dipole moment function of enflurane. The analysis of the electro-optic parameters of the stable conformers was done with the help of MP2/6-311++G(df,pd) anharmonic calculations.

Stability analysis of lithio-silicon Si10Li8 clusters: Planar bicyclic ring vs. three-dimensional structures by Oscar Donoso-Tauda; Diana Yepes; Pablo Jaque; Juan C. Santos (72-76).
Display OmittedAfter exploration of the potential energy surface for the stoichiometry of Si10Li8 a three-dimensional motif was found as the most stable in comparison with planar and quasi-planar structures. The new minimum can be seen as the resulting of the interaction of three fragments: Si2⋯Li4⋯Si8Li4 stabilized by strong electrostatic interactions. In order to understand the stability both polarizability and aromaticity were studied. In general, the structural transition from planar or quasi-planar to three-dimensional structures increases the stability while decreases the polarizability of the system, in agreement with the minimum polarizability principle.

Co2+ acireductone dioxygenase: Fe2+ mechanism, Ni2+ mechanism, or something else? by Crystal E. Valdez; Nathan M. Gallup; Anastassia N. Alexandrova (77-82).
Display OmittedAcireductone dioxygenase (ARD) oxidizes 1,2-dihydroxy-3-keto-5-(methylthio)pentene to either formate and an α-keto acid, or formate, methylthiopropionate and CO, depending on the nature of the catalytic metal, Fe2+ or Ni2+. We recently showed that, contrary to established hypotheses, the mechanistic preference is driven solely by the RedOx behavior of the metal. Here, we address the functionality of Co2+-ARD. Using mixed quantum–classical dynamics simulations and density functional theory calculations, we show that both Fe2+-like and Ni2+-like routes are accessible to Co2+-ARD, but the mechanism involves a bifurcating transition state, and so the exact product distribution would be determined by the reaction dynamics.

Display OmittedExperimental investigation of functionalization of oxidized single-walled carbon nanotubes (OSWCNTs) with three nucleic acid bases such as uracil, guanine, thymine and one amino acid, l-alanine is carried out. Initially, the SWCNTs are oxidized by acid treatment. Further, the oxidized SWCNTs are effectively functionalized with aforementioned biological compounds by ultrasonication. The diameter of OSWCNTs has increased after the adsorption of biological compounds. The cumulative Π–Π stacking, hydrogen bond and polar interaction are the key factors to realize the adsorption. The amount of adsorption of each biological compound is estimated. The adsorption of guanine is more among all the four biological compounds.

Display OmittedWe present a study of a dilute solution (1 M) of NaCl in water, carried out using ab initio molecular dynamics with semilocal and hybrid functionals. We showed that the structural and electronic properties of the solute and the solvent are the same as those obtained in the infinite dilution limit, i.e. for aqueous ions in the presence of a uniform compensating background. Compared to semilocal functionals, simulations with hybrid functionals yield a less structured solution with a smaller number of hydrogen bonds and a larger coordination number for the Cl anion. In addition, hybrid functionals predict qualitatively correct positions of the energy levels of the ions with respect to the valence band of water.

Display OmittedCuBO2 nanocubes were synthesized for the first time through hydrothermal route. Beside compositional, morphological, structural and optical studies of the materials, IV characteristics of the fabricated p-CuBO2/n-ZnO was measured using conducting atomic force microscopy which showed excellent diode behavior with an ideality factor 1.03 and very small leakage current 0.04 nA.

Sc2S@C80 has been detected but not been isolated and characterized. DFT calculations demonstrate that Sc2S prefers to be encapsulated inside D5h-C80 and C2v-C80, and the two lowest-energy isomers of Sc2S@C80 may coexist in the soot. The calculations reveal that Sc2S@C80 may have different properties from those usual C80-based metallofullerenes.Sc2S@C80 has been detected but not been isolated and characterized. To investigate the structures and properties of Sc2S@C80, a density functional theory study on fullerene C80 and metallofullerene Sc2S@C80 was carried out. The calculations demonstrate that Sc2S prefers to be encapsulated inside D5h-C80 and C2v-C80, instead of the well-known Ih-C80. The two lowest-energy isomers of Sc2S@C80 may coexist in the soot. The calculations reveal that there exists strong covalent interaction between the cage and Sc2S cluster, suggesting Sc2S@C80 may have different properties from those usual C80-based metallofullerenes. Raman spectra are provided to help future experimental identification of Sc2S@C80.

Photoswitching of the spin crossover polymeric material [Fe(Htrz)2(trz)](BF4) under continuous laser irradiation in a Raman scattering experiment by François Guillaume; Yeny A. Tobon; Sébastien Bonhommeau; Jean-François Létard; Lucie Moulet; Eric Freysz (105-109).
Display OmittedPhotoswitching of the [Fe(Htrz)2(trz)](BF4) spin crossover polymeric material has been investigated by means of confocal Raman spectroscopy upon continuous laser irradiation outside and inside its thermal hysteresis loop. In both cases, the evolution of HS and LS Raman marker bands show that light excitation can trigger the LS to HS transition, but the long-lived HS state can be populated only within the hysteresis loop. Local sample heating can explain this light-induced effect leading to a narrowing of the thermal hysteresis loop for laser intensities higher than 0.02 mW/μm2, in strong accordance with previous time-resolved pump–probe experiments on similar materials.

Display OmittedAssembling mechanism of platinum nanoparticles into a {1 0 1} sectors of a tetragonal lysozyme crystal was examined for two different types of the platinum nanoparticles which have either positive or negative ζ potential at pH 3–7. The distribution coefficient of the positive ones inside the crystal is much higher than that of the negative ones in the whole pH range investigated. Dispersivity of the platinum nanoparticles before interaction with the lysozyme crystal surface, which is controlled by electrostatic interactions between nanoparticles, lysozyme and NaCl, causes a profound difference on the assembly of the nanoparticles into the crystal.

The ionization cross section of hexamethyldisiloxane (HMDSO) molecules (m/z  = 162), pentamethyldisiloxane radicals (m/z  = 147) and tetramethyl hydro disiloxane radicals (m/z  = 133) have been measured versus electron energy up to 30 eV. The radicals are produced selectively by two different mechanisms which are the energy transfer by collision with metastable argon species and the VUV photolysis. The absolute ionization cross section values are determined and analytical functions derived from the Binary-Encounter-Bethe theory (BEB) are given to calculate the direct ionization of molecules or radicals versus electron energy lower than 30 eV.

Display OmittedThe accuracy of both hypernetted chain (HNC) and Kovalenko–Hirata (KH) approximations assumed in an Ornstein–Zernike integral equation theory has been studied in terms of the solvation free energy (SFE) by comparing with molecular dynamics simulation for Lennard-Jones liquid. The Lennard-Jones parameters for the solute, ɛ u and σ u, were systematically varied. ɛ u-dependence of the relative SFE is found to be hardly dependent on the approximations. However, σ u-dependences of the SFE obtained both from HNC and KH approximations considerably differ from those by molecular dynamics simulation. The source of the error in the SFE from both approximations is also discussed.

We demonstrate nanoscale memristive devices based on FeWO4 nanowires array, the device shows superior bipolar resisitive switching behaviors.Display OmittedThe resistive switching behaviors of metal–oxide–metal nanoscale devices are a fascinating phenomenon for next generation nonvolatile memories. Herein for the first time we demonstrate nanoscale memristive devices made from a FeWO4 nanowires array. The device shows superior bipolar resistive switching behaviors. This study is useful for exploring the multifunctional materials and their applications in nonvolatile multistate memory devices.