Chemical Physics Letters (v.509, #4-6)

Contents (iii-viii).

Tuning the intermolecular proton bond in the H5 O 2 + ‘Zundel ion’ scaffold by S.G. Olesen; T.L. Guasco; J.R. Roscioli; M.A. Johnson (89-95).
Display Omitted► Vibrational spectra reveal quantum levels of proton trapped between oxygen atoms. ► Asymmetry in intermolecular proton bond correlated with shifts in proton frequency. ► Solvent molecules attached to the H2O·H+·H2O scaffold similar to methyl substitution. ► Ar and H2O surprisingly similar solvents despite 10× difference in bond strength.The Zundel ion, H2O·H+·H2O, provides a versatile scaffold with which to explore the quantum structure of the intermolecular proton bond (IPB). This information is encoded in the vibrational frequencies adopted by the shared proton, ν sp, which are observed to follow a remarkably similar trend as the exterior OH groups are sequentially solvated or are replaced by methyl substituents. In effect, solvents H-bonding to exterior OH groups act to increase the proton affinity of the water to which they are bound in a roughly additive fashion. We discuss this behavior in the context of the extreme sensitivity of IPBs to their solvation environments.

Display Omitted► High resolution electronic spectra of the chiral naproxen molecule are described. ► The two observed conformers of naproxen have different rotational constants. ► However, the two enantiomers of each conformer have the same rotational constants. ► Chiral discrimination of the two enantiomers is not possible at 0.1 MHz resolution.Two chiral conformers of the optically active molecule naproxen have been identified in its high resolution electronic spectrum, differing only in the orientation of the attached isopropionic acid group relative to the naphthalene ring. Both conformers exhibit b-type spectra, indicating that the S 1 states of the isolated molecules are similar to those of other 2-substituted naphthalenes. The measured rotational constants of the left- and right-handed forms of both conformers are identical to within the experimental error, ±0.1 MHz (∼1:109), indicating that they are enantiomers of each other, not diastereomers. The naphthyl ring with its attached methoxy group is insufficient to provide chiral discrimination.

Structure, bonding and reactions within protonated acetone–methanol cluster ions by Chi-Tung Chiang; Marek Freindorf; Thomas R. Furlani; Robert L. DeLeon; James F. Garvey (102-107).
Display Omitted► Structure and bonding change as a function of the number of acetones. ► Proton affinity is not a sufficient factor to determine the reactivity. ► Acetone molecules form a strong interaction with the proton bound methanol.We have studied the structure and reactivity of the acetone–methanol cluster series {(C3H6O) m (CH3OH) n }H+ as a function of cluster size. Conventional mass spectra are mainly dominated by the three series of protonated acetone–methanol cluster ions, (C3H6O) m  = 1–3(CH3OH) n H+. In the CID spectra of the (C3H6O)1(CH3OH) n H+ series, we observed two different reaction channels: the loss of CH3OH and the loss of C3H6O. The former dominates regardless of the cluster size. For the (C3H6O)2(CH3OH) n H+ series, the CID result reveals a change in the preferred reaction pathway as a function of cluster size. For the (C3H6O)3(CH3OH) n H+ series, the loss of C3H6O dominates.

The 193 nm photodissociation of borazine by Dachun Huang; Arturo Hidalgo; Vladimir I. Makarov; Gerardo Morell; Brad R. Weiner (108-113).
Display Omitted► Photodissociation of B3N3H6, following 193 nm excitation was studied by TOFMS. ► Main channel of 193 nm borazine photodissociation produces B3N3H5+H. ► H atom elimination occurs via a single photon process. ► Cannot differentiate between B-borazinyl and N-borazinyl in this study. ► Formation of HBNH via a two-photon three-body process was observed.The photodissociation of borazine, B3N3H6, following 193 nm excitation was studied by Time of Flight Mass Spectrometry (TOFMS). For one-laser experiments, the TOF mass spectrum following borazine excitation consists of m/e peaks that can be attributed exclusively to borazine ion species, i.e., no photofragments are observed. In the two-laser experiments, the TOF mass spectrum can be assigned to peaks corresponding to B3N3H6 +, B3N3H5 +, and a small amount of BHNH+ ions. We conclude that a significant channel of borazine photodissociation at 193 nm is the production of the B3N3H5 radical and H atom. The photodissociation process related to production of BHNH species is most likely due to a two-photon process.

Kinetic study of the reaction of chlorine atoms with bromoethane and D-bromoethane in the gas phase by Dariusz Sarzyński; Agnieszka A. Gola; Andrzej Dryś; Katarzyna Brudnik; Jerzy T. Jodkowski (114-118).
Display Omitted► Kinetic study of the H/D-abstraction from C2H5Br and C2D5Br by Cl atoms. ► The rate constants and their temperature dependence are found in 298–527 K. ► Values of the kinetic isotope effect were derived for the first time.The kinetics of the gas-phase reactions of chlorine atoms with bromoethane (C2H5Br) and D-bromoethane (C2D5Br) was studied experimentally. The relative rate method was applied using Cl + C2H6 as the reference reaction. The rate constants for H-abstraction from C2H5Br (k H) and D-abstraction from C2D5Br (k D) were measured in the temperature range of 298–527 K and at a total pressure of 100 Torr using N2 as a diluent. The temperature dependencies of the rate constants are described by the expressions: k H  = (2.6 ± 0.3) × 10−11  × exp(−390 ± 35/T) and k D  = (2.8 ± 0.2) × 10−11  × exp(−750 ± 30/T) cm3  molecule−1  s−1. The kinetic isotope effect, described by the ratio k H/k D, was found to be 3.2 at room temperature.

Display Omitted►In this work, we study femtosecond-pulse induced photodissociation. ► Electronic degrees of freedom modify nuclear momentum distributions. ► Diffraction patterns appear in electron momentum distributions. ► The importance of electron-nuclear correlation in photofragmentation is proved.We study fragmentation processes induced by femtosecond laser pulses. Within an adiabatic treatment of the nuclear motion, the interaction with two identical but time-delayed pulses leads to interference structures in the momentum distribution which are related to the pulse delay. These structures are modified if an electronic degree of freedom is included in the wave-packet propagation. Additional time-dependent patterns are found in the electron momentum distributions which are also present for a single-pulse excitation. They are related to the delocalization of the electron density over the different charge centers.

Size and hydrogen saturation effects on third-order polarizabilities of Si clusters by Chensheng Lin; Wendan Cheng; Jinyun Wang; Ruiqing Zhang (124-128).
Size and hydrogen saturate dependant of third-order polarizabilities γ(−3ω;ω,ω,ω) for the Si-ncs, Si17H36, Si26H32 and Si123H100 clusters in the energy range 0–4.5 eV. Larger cluster size causes the first resonant peak red-shift and higher hydrogen saturate may lead γ to be negative.Display Omitted► Third-order polarizability of hydrogenated silicon clusters up to 18Å diameter. ► TDDFT combined with SOS method. ► The sign of γ at low input photon energy changes from positive to negative when the ratio of hydrogen saturation increases. ► The magnitude of γ increases with a decrease in silicon cluster size. ► The solvent effect does not change the relative magnitude of γ for the Si-nc.We report the frequency-dependent third-order polarizabilities (γ) of a series of hydrogen-capped silicon clusters obtained using time-dependent density functional theory. We find that the magnitude of γ increases with a decrease in silicon cluster size, while the sign of γ at low input photon energy changes from positive to negative when the ratio of hydrogen saturation increases. At higher input photon energy, the sign of γ is determined mainly by cluster size. Our results rationalize several recent experiments on the optical properties of silicon nanostructures and are helpful for designing opto-electronic devices based on them.

Nature of the excited states in large photochromic dimers: A TD-DFT examination by Aurélie Perrier; François Maurel; Denis Jacquemin (129-133).
Display Omitted► TD-DFT is used to investigate the properties of diarylethene dimers. ► Very good agreement with experiment is reached for absorption. ► Orbital analysis helps understanding the observed photochromism. ► The fluorescence wavelength of a key compound is computed.Using a combination of Time-Dependent Density Functional Theory calculations and molecular orbital analysis, the electronic properties of two diarylethene dimers have been investigated in all their possible forms (doubly closed, closed-open and doubly open). The selected ab initio method allows to systematically reproduce the measured spectral features with a remarkable accuracy, and to gain insights into the observed full or partial photochromism. Indeed, in the first dimer, the two DA are mostly independent, whereas in the second, the photochromism is lost due to the π-conjugation. In this second case, the fluorescence spectrum has been simulated with TD-DFT as well.

Display Omitted►A Schottky-type model of the polymer electrolyte near Pt nanoparticles. ► Dependence of the transfer coefficients on the cathode potetial. ► The effect of the electrolyte dielectric constant and particle size.We present a Schottky-type model describing Pt 2 + dissolution and redeposition on Pt nanoparticles in polymer electrolyte fuel cells. The charge transfer is considered to occur near the surface of nanoparticles so that the potential barrier for the reaction is formed by the double-layer potential and the image interaction. With increasing electrode potential, the transfer coefficient for dissolution is found to decrease from 0.6–0.7 down to 0.3–0.4. Its dependence on the effective dielectric constant of the double layer is appreciable while the dependence on the particle size is weak.

Molecular dynamics in aluminum layered double hydroxides as studied by 1H T NMR measurements by Anastasia Vyalikh; De-Yi Wang; Udo Wagenknecht; Gert Heinrich; Ulrich Scheler (138-142).
Display Omitted► Combination of proton relaxation time measurements with chemical shift resolution permits assignment to structural motifs. ► Inverse Laplace transform is applied for data analysis. ► A significant difference of the mobility between water and OH groups is found. ► Mobility varies with the cation distribution.Proton dynamics in pristine and organically-modified layered double hydroxide has been studied by 1H T . Inverse Laplace transform with spectral resolution results in a correlation of T and chemical shift.In LDH two contributions are resolved. They are assigned to the metal hydroxides, forming the LDH sheets (4–8 ms), and mobile interlayer water (2 ms). Apparent T values of OH-protons in surfactant-modified LDH are different in dodecylbenzenesulfonate- (SDBS) and sodium octasulfonate- (C8) modified LDH. This difference is explained by the presence of water in LDH–SDBS. The effects of spin diffusion have been studied by performing 2D 1H RFDR in the LDH–SDBS.

Display Omitted► Six various allotropes of graphene-like BN (so-called white graphene) are examined. ► Using DFTB method, their stability, structural and electronic properties are predicted. ► These BN allotropes will be of interest as new semiconducting materials.Using the density-functional-based tight-binding (DFTB) method a systematic study of comparative stability, structural and electronic properties for six various monolayered allotropes of graphene-like BN (so-called white graphene), which are composed of alternant B-N bonds and include the atoms of different hybridization types (sp2, sp2  + sp1, and sp2  + sp3) was performed. All these allotropes are found to be less stable, than white BN graphene, though, preserving their integrity during molecular-dynamics simulations. Independing on the hybridization type the BN structures considered here are semiconducting with smaller band gaps, than white BN graphene.

Spectroscopic evidence of a bidentate-binding of meso-2,3-dimercaptosuccinic acid on silver nanoclusters by Oksana Zaluzhna; Lyndsey Brightful; Thomas C. Allison; YuYe J. Tong (148-151).
Display Omitted► Synthesized Ag7DMSA4 nanoclusters were studied by TEM/EDS, NMR, IR, Raman, and DFT. ► A model of sulfur bidentate-binding was proposed. ► DFT calculations suggest a deprotonation of DMSA in Ag7DMSA4 nanoclusters.New insight into the metal–ligand binding interaction in meso-2,3-dimercaptosuccinic acid (DMSA) protected silver nanoclusters (NCs) is presented in this work. IR, Raman and 13C NMR spectroscopic characterizations and DFT calculations suggest that DMSA forms a bidentate binding, rather than the originally-proposed monodentate binding, via two sulfur atoms with the underlying Ag7 NC, which is in agreement with recent ab initio calculations.

Electronic properties of individual and assembled homotype SWCNT bundles by Maria Letizia Terranova; S. Orlanducci; Antonio Serra; Daniela Manno; Emanuela Filippo; Marco Rossi (152-157).
Display Omitted► Study of homotype bundles formed by single-walled carbon nanotubes. ► Multiscale characterization at different hierarchical level (individual SWCNT → bundle → ribbon). ► Study of structure and electron transport properties at different hierarchical level. ► The conductance dependence on temperature has been attributed to tunneling phenomena.We have performed a detailed investigation of the basic electronic transport properties of single walled carbon nanotubes (SWCNT) organized in macroscopic ribbons (some millimeters long with a transversal size of tens of microns), and formed predominantly by identical nanotubes.High resolution TEM and Electron diffraction techniques have been applied in order to determine the peculiar aggregation of SWCNTs in homotype bundles.The electronic properties of individual SWCNT bundles have been investigated by scanning tunneling microscopy and spectroscopy (STM/STS). The electrical features of the ribbons have been investigated in the 100–500 K temperature range using a multifinger device.Overall, the results indicate the possibility to control the local density of state energy by tailoring different architectures.

Computational thermochemistry of iron–platinum carbonyl clusters by Michael Bühl; Herbert Früchtl; Pascal André (158-161).
Structures and energies of mixed iron–platinum carbonyl complexes, models for potential intermediates in the early stages of FePt nanoparticle formation, are studied with density functional theory.Display Omitted► A DFT protocol is validated for structures and energetics of mixed Fe–Pt complexes. ► A low barrier is found for the initial reaction between Fe(CO)5 and Pt(COD)2. ► Mixed Fe–Pt carbonyl clusters may be involved in FePt nanoparticle formation.Structures of Fe3Pt3(CO)15 (1), Fe2Pt5(CO)12(COD)2 (2), Fe2Pt(CO)8(COD) (3) and Fe2Pt2(CO)10 (4), as well as the driving forces for their formation from Fe(CO)5 and Pt(COD)2 (COD = 1,5-cyclooctadiene) have been computed at the PBE0-D3 level of density functional theory. Judged from a comparison of computation vs. experiment, this level should be well suited to study structures and thermochemistry of mixed Fe–Pt clusters, which may occur at the early stages of FePt nanoparticle synthesis.

Iridium(III) complexes in discs for two-photon excitation applications by Mei-Lin Ho; Min-Hsiu Lin; Yi-Ting Chen; Hwo-Shuenn Sheu (162-168).
Display Omitted► The 2PA cross section and two-photon assisted ESA cross section of IrHP are reported. ► The average 2PA cross section of ZnIrHP for different input irradiances was deduced. ► Results help to understand the nonlinear optical properties of IrHP and ZnIrHP.Ir(ppy)2(H2dcbpy)PF6 (IrHP, ppy = 2-phenylpyridine, H2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) as the bridging ligand mixed with Zn(NO3)2·6H2O in a ratio of 1:2 (ZnIrHP) in PMMA discs has been synthesized. The two-photon excitation emission of IrHP and ZnIrHP is ascribed to a 3MLCT transition. The two-photon absorption (2PA) cross section and two-photon induced excited state absorption (ESA) cross section of IrHP were deduced as 1.37 × 104  ± 6.87 × 102  GM and 6.63 × 10−22  ± 3.31 × 10−23  cm2, respectively, at 800 nm (1 GM = 10−50  cm4  s/photon). In contrast, the 2PA of ZnIrHP exhibits higher-order nonlinearity and the cross section was 5.68 × 105  ± 2.84 × 104  GM.

Display Omitted► Hybrid QM/MM MD simulations have been carried out for PM IV complexed with KNI-764. ► The PMF shows that the protonation of Asp214 is more favorable. ► The results reveal that there is a strong interaction between the Asp34, Gly78, Ser79, Asp214 and Thr217 residues and the KNI-764 inhibitor.Plasmepsin IV (PM IV) is a potential target for developing drugs against malaria. This Letter presents results of QM/MM dynamic simulations applied to the study of the protonation state of two aspartates (Asp34 and Asp214) catalytic residues of PM IV in complex with KNI-764 inhibitor. The potential of mean force profile was used to assign the protonation state of the two catalytic aspartates in PM IV–KNI-764 complex. The results indicate that protonation of the 214 residue is more favorable. In addition, energy terms decomposition was used to explore key interactions between the main residues and KNI-764 inhibitor.

Evaluation of nucleotide C–Br⋯O–P contacts from ONIOM calculations: Theoretical insight into halogen bonding in nucleic acids by Lin Xu; Peng Sang; Jian-Wei Zou; Ming-Biao Xu; Xue-Ming Li; Qing-Sen Yu (175-180).
Using a two-layer ONIOM method, halogen bonds buried in nucleic acid environments were exploited through modeling the nucleotide C–Br⋯O–P contact. Unconventional reduced density gradient (RDG) and electron localization function (ELF) analyses have been performed on halogen bonds within halogenated nucleic acid systems.Display Omitted► Halogen bonds buried in nucleic acids were explored by the ONIOM method. ► Analysis of reduced density gradient was carried out on halogen bonds. ► Halogen bonds were visualized by the ELF approach. ► Flexibility of nucleic acid chains is sensitive to the presence of halogen bonds.Halogen bonding can direct the local stereochemical properties of nucleic acids by unique geometric preferences but has been inaccessible to most theoretical studies. Using a two-layer ONIOM method, halogen bonds buried in nucleic acid environments were studied by modeling the nucleotide C–Br⋯O–P contacts in 1P54 and 1RLG (PDB code). Several unconventional methods, associated with the electron density distributions of the interacting atoms, showed the formation of halogen bonds through visualization of such non-covalent interactions in real space. The contributions of halogen bonds to the local conformation of the backbones were also demonstrated through comparison with parallel binding of non-brominated nucleotides.

Vibrational spectrum of water confined in and around cyclodextrins by Madhurima Jana; Sanjoy Bandyopadhyay (181-185).
Display Omitted►We study the effects of cyclodextrins on low-frequency vibrational modes of water. ► These bands are blue-shifted due to the presence of the cyclodextrins. ► The extents of the shifts depend on the degree of confinement and hydrogen bonding.The effects of α-, β-, and γ-cyclodextrins (ACD, BCD, and GCD) on the low-frequency vibrational spectrum of water present around them and those confined inside their cavities have been investigated from molecular dynamics simulations. Attempts have been made to understand the effects of variation of the number of glucose rings and the ability of these macromolecules to form hydrogen bonds with water on the distribution of the vibrational density of states of water. It is observed that these bands for water in and around the cyclodextrins suffer blue shifts, the extent of the shifts are sensitive to the degree of confinement within the cavities and their hydrogen bonding status.

EASY-GOING DUMBO on-spectrometer optimisation of phase modulated homonuclear decoupling sequences in solid-state NMR by Dennis L.A.G. Grimminck; Suresh K. Vasa; W. Leo Meerts; Arno P.M. Kentgens; Andreas Brinkmann (186-191).
Display Omitted► On-spectrometer optimisation of homonuclear decoupling for 1H solid-state NMR. ► Genetic algorithms ensure simple one-step optimisation of decoupling efficiency. ► At very high rf fields very narrow proton lines are obtained showing a very high level of suppression of the dipolar interaction. ► Competitively resolved spectra are obtained at moderate external magnetic field (400 MHz) and spinning speed (12.5 kHz).A one-step many-parameter optimisation scheme for phase modulated proton homonuclear decoupling sequences in solid-state NMR is presented. Phase modulations, parameterised by DUMBO Fourier coefficients, were optimised using a Covariance Matrix Adaptation Evolution Strategies algorithm. Our method, denoted EASY-GOING DUMBO, starts with featureless spectra and optimises proton–proton decoupling, during either proton or carbon signal detection. Optimisations at moderate sample magic angle spinning (MAS) frequencies and medium radio-frequency (rf) field strengths resulted in solutions closely resembling (e)DUMBO. Application of EASY-GOING DUMBO for optimisation at very high 680 kHz rf field strength, 12.5 kHz MAS on a 400 MHz NMR spectrometer resulted in a new solution, with competitively resolved proton spectra.

Experimental and density functional studies on the corrosion behavior of the copper-nickel-tin alloy by Bing Yin; Yansheng Yin; Yanhua Lei; Lihua Dong; Yijun Zhang (192-197).
Display Omitted► This copper-nickel-tin alloy showed excellent corrosion resistance in seawater without SRB, but SRB accelerated the corrosion process. ► Ni and Sn atoms affected clusters’ equilibrium geometries, lowered the energy, and bimetallic clusters were more stable than monometallic ones. ► Combining the theoretical and experimental results, this alloy exhibited excellent corrosion resistance.The corrosion behavior of copper-nickel-tin alloy in seawater with and without SRB has been tested by electrochemical techniques, SEM micrographs and EDX spectra. The geometric and electronic structure and active sites of Cu n , Cu n −1Ni and Cu n −1Sn (n  ⩽ 9) clusters have been studied using DFT. The results indicated nickel and tin preferred to be the surface or outer layer in copper alloy, formed an oxide film on surface, then alloy would be corroded to Cu2O mostly after immersion. The corrosion process was accelerated in the presence of SRB, the mainly corrosion product was Cu2S, which was less protective for alloy.

Author Index (198-201).