Chemical Physics Letters (v.438, #4-6)
Editorial Board (IFC).
Large scale vibrational Hamiltonian calculations on thiophosgene by Svetoslav Rashev; Isak Bivas; David C. Moule (153-156).
The Letter deals with the theoretical description and analysis of highly excited vibrational states and IVR in S0 thiophosgene.The vibrational spectrum and ground electronic state potential energy surface (PES) of thiophosgene (CSCl2) have been studied quantum mechanically using a completely symmetrized Hamiltonian formalism and vibrational basis set, including all six molecular vibrational modes in the calculations. The calculated vibrational frequencies have been compared to the experimentally measured data by other authors. From a good fit achieved between the theoretical and experimental frequencies up to considerably high excess vibrational energies, the harmonic and some anharmonic (cubic and quartic) force constants of the molecular PES have been reliably determined.
Computational research of the electronic structure of benzene trimer cation by ab initio method by M. Mine; H. Mori; M. Ogata; S. Tanaka; T. Tsutsui; E. Miyoshi (157-161).
Several stable structures of the benzene trimer cation were systematically obtained using ab initio calculations.The most stable structure of the benzene trimer cation was systematically searched using CCSD(T)/6-31G(d)//MP2/6-31G calculations, and several stable structures were obtained. A sandwich structure (SW) is found to be the most stable, though a few other structures have similar energies. Calculated differential spin densities indicate that the positive charge of SW is localized around a dimer core in SW, as suggested from experiments. A calculated infrared spectrum and the low-lying excited states of the obtained stable structures are compared with the experimental results. It is also shown that the core switching of a dimer cation can occur in SW.
Electronic states and stability of GeC2N radical by Guang-hui Chen; Krishnan Balasubramanian (162-168).
Electronic states of the GeC2N radical are explored at various theoretical levels which revealed ten minimal energy isomers and 10 interconversion transition states. The thermodynamically most stable isomer is a linear form GeCCN 1 which is qualitatively described as a resonance hybrid of •∣Ge＝C＝C＝N∣, ∣Ge＝C•-CN∣, and ∣Ge＝C＝C＝N∣•.Electronic states of the GeC2N radical are explored at various theoretical levels including complete active space multi-configuration self-consistent field followed by complete active space perturbation computations. Ten minimal energy isomers and 10 interconversion transition states are found. The thermodynamically most stable isomer is a linear form GeCCN 1 which is qualitatively described as a resonance hybrid of •∣Ge＝C＝C＝N∣, ∣Ge＝C•-CN∣, and ∣Ge＝C＝C＝N∣• forms, with the second one contributing to a greater extent suggestive of a radical adduct between Ge＝C and CN. The second low-lying linear isomer GeCNC 2 (21.9 kcal/mol) has resonating structures ∣Ge＝C•-NC∣, •∣Ge＝C＝NC∣, and ∣Ge＝C＝N–C∣•.
How energy constraints on orbital angular momentum limit product j-distributions: The case of BaI from Ba + HI by Anthony J. McCaffery (169-172).
When reactants of heavy reduced mass yield products having light reduced mass, constraints arise on accessible product rotational states from the energy conservation requirements of product (recoil) orbital angular momentum. For Ba + HI → BaI + H this effect is particularly marked and leads to a narrow distribution of j BaI states in crossed beam experiments.In elementary reactions, constraints on product rotation may occur when the reactants have large reduced mass while that of the products is very low. In these circumstances the energy conservation on recoil orbital angular momentum may severely restrict access to product rotation states. This is illustrated for Ba + HI → BaI + H demonstrating that the constraint is highly (product) rotational state specific and ultimately determines which product states may be populated. When this energy conservation condition is properly included, predicted peak j-values and distribution widths agree very well with experiment.
Theoretical studies on structure, energetic and intramolecular proton transfer of alkannin by Yong H. Liang; Ping G. Yi (173-177).
The B3LYP/6-31+G(d, p) and TD B3LYP/6-31+G(d, p) calculations were applied to predict ground- and excited-state intramolecular proton transfer (GSIPT and ESIPT) of alkannin.The structure and energetic of four tautomers (‘normal’ tautomer NT, ‘double’ tautomer DT, M1 and M2) and four rotamers (NT-R1, NT-R2, NT-R3 and DT-R1) of alkannin had been studied theoretically at the B3LYP/6-31+G(d, p) level. In the ground-state, the calculated results predicted that NT is dominant, and DT is less stable with 1.31 kcal/mol than NT. However, NT and M2 are two most stable tautomers in the excited-state, and NT is more stable with 0.59 kcal/mol than M2. Furthermore, ground- and excited-state intramolecular proton transfer occurring in the four tautomers (the processes NT ↔ M1, NT ↔ M2, DT ↔ M1 and DT ↔ M2) was investigated by DFT.
Complex resonance energy transfer in the LiH–Li system by Marin Pichler; Davorka Azinović; Slobodan Milošević; Goran Pichler (178-183).
The resonant energy transfer in a LiH–Li system was established and investigated. The specific collisional energy transfer was studied by measuring the excitation spectra of the 3s, 3d, 4s, 4d → 2p Li atomic transitions.The resonant energy transfer in the LiH–Li system was established and investigated. The specific collisional energy transfers LiH(A 1Σ+ v ′, J′) + Li(2p) → LiH(X1Σ+ v″, J″) + Li(3s, 3d, 4s, 4d) + ΔE were studied by measuring the excitation spectra of the 3s, 3d, 4s, 4d → 2p Li atomic transitions. The energy defect, ΔE, was taken as the energy difference between the Li atomic transition and the nearest LiH Stokes line. The intensities of Li atomic lines exhibit rather complex dependence on the energy defect diagrams. This is a consequence of five collisional energy transfer processes which occur simultaneously and are in competition with each other.
An experimental and theoretical study of the reaction of ethanethiol with Cl atoms by Andrés Garzón; Alberto Notario; José Albaladejo; Tomás Peña-Ruiz; Manuel Fernández-Gómez (184-189).
Gas-phase reaction of atmospheric chlorine atoms with ethanethiol was investigated as a function of temperature and pressure by laser photolysis-resonance fluorescence, for the first time. Theoretical calculations on the mechanism of this reaction predict two nearly energy-equivalent channels for H-abstraction by Cl.Laser photolysis-resonance fluorescence was used for the first time to investigate the reaction of ethanethiol with atmospheric relevant Cl atoms as a function of temperature and pressure. Kinetic data obtained were used to derive an Arrhenius expression. Moreover, a mechanism is proposed on the base of ab initio MP2/6-311G** calculations. Activation energies have been estimated through QCISD(T) molecular energies. Accordingly, our results predict, for the first time, two nearly energy-equivalent channels for H-abstraction from CH3CH2SH under attack by Cl, one showing attack along H–S bond whereas the other exhibits attack along H–C α bond.
Ionic dissociation of methanesulfonic acid in small water clusters by Shujin Li; Wei Qian; Fu-Ming Tao (190-195).
Ionic dissociation of methanesulfonic acid (MSA) in water is studies by theoretical calculations of the clusters MSA–(H2O) n , n = 1–5. MSA is dissociated by at least four water molecules. Hydrations of MSA by small numbers of water molecules are thermodynamically either favorable or reversible in the gas phase.Ionic dissociation of methanesulfonic acid (MSA) in the aqueous environment is studied by density functional theory and ab initio calculations of the water clusters MSA–(H2O) n , n = 1–5. Molecular structures and stabilities are discussed based on the calculated stable conformers and relative energies. The clusters with up to three water molecules (n = 1–3) are dominated by strong hydrogen bond interactions. With a minimum of n = 4, MSA is dissociated as a result of proton transfer from MSA to H2O. All of the clusters are shown thermodynamically stable in the gas phase with respect to separate monomers.
Electrical property and microstructure analysis of poly(vinylidene fluoride)-based composites with different conducting fillers by Hai-Ping Xu; Zhi-Min Dang (196-202).
PTC intensity of the PVDF-based composites with different fillers and at their percolation thresholds, herein the ratio of maximum resistivity to room temperature resistivity is defined as the PTC intensityFour systems of conductive filler/polyvinylidene fluoride (PVDF) composites were prepared. Abnormal electrical behaviors as functions of temperature and microstructure were analyzed. Results show the carbon black (CB)/PVDF composites present a lower percolation threshold than other metallic filler/PVDF composites. The crystallinity of PVDF is diminished in the order of fillers, CB, Ni, Zn and W. The Ni/PVDF composites exhibit the maximum positive temperature coefficient intensity, whereas the transition temperature is independent of the kind of fillers. The non-uniform distribution of fillers is observed since they aggregate in amorphous regions of PVDF and form a network of conductive chains.
Charge control of the water monolayer/Pd interface by J.-S. Filhol; M.-L. Bocquet (203-207).
Spontaneous disproportionation of Pd surface covered by a water monolayer: 2 H-down ice/Pd → H-down ice/Pd−q + H-up ice/Pd+q′ with q + q′ = 0.5∣e∣Using an ab initio electrochemical approach, we show that the water monolayer on Pd(1 1 1) undergoes a first order transition as the surface charge is tuned, with a phase equilibrium between two modified ice structures on opposite charged substrates. These findings refine the classical H-down and H-up configurations by invoking a permanent charged surface. We explore the experimental consequences of this phase behaviour on scanning tunneling microscopy (STM) with STM simulations. A strong dependence of the topographic contrast with surface charge (or equivalently STM potential) is exhibited allowing to reinterprete recent experimental observations.
The geometries, absorption and fluorescence wavelengths of solvated fluorescent coumarins: A CIS and TD-DFT comparative study by Denis Jacquemin; Eric A. Perpète; Xavier Assfeld; Giovanni Scalmani; Michael J. Frisch; Carlo Adamo (208-212).
CIS and TD-DFT excited-state structures in gas-phase and water have been determined for several hydroxy coumarin dyes. Though the CIS transition energies are strongly overestimated, this scheme reproduces the major chemical features. However, the solvatochromic effects are not consistently reproduced by CIS, especially for the emission properties.We compare the CIS and TD-DFT excited-state structures of several hydroxy coumarin dyes. These calculations have been performed in both gas-phase and water. In addition, the transition energies corresponding to absorption and fluorescence phenomena have been determined within several theoretical approximations. Though the CIS transition energies are strongly overestimated, this scheme reproduces the major chemical features. However, the symmetry of the excited-state geometries and the solvatochromic effects are not always consistently reproduced by CIS.
First-principles calculations of N2O adsorption and decomposition on GaN (0 0 0 1) surface by Chun-Li Hu; Yong Chen; Jun-Qian Li; Yong-Fan Zhang (213-217).
We use DFT-GGA method to study N2O adsorption and decomposition on GaN (0 0 0 1) surface. The figure describes the structure of N2O decomposition on the surface.The adsorption and decomposition of N2O on GaN (0 0 0 1) surface has been explored employing density functional theory. Our calculations indicate the parallel adsorbed N2O prefers to be dissociated on the surface, and the dissociated O atom is combined at fcc site, the N–N piece is adsorbed on top site of the surface or desorbed from the surface. From the potential curve of the reaction process of N2O dissociation on the surface, an energy barrier of 0.11 eV is derived, which is smaller than that of many widely studied adsorbents for N2O decomposition.
2-(2′-Pyridyl)benzimidazole as a fluorescent probe for monitoring protein–surfactant interaction by Tushar Kanti Mukherjee; Priyanka Lahiri; Anindya Datta (218-223).
Suppression of ESPT in 2PBI is a good marker of macromolecular interaction.The effectiveness of 2-(2′-pyridyl)benzimidazole (2PBI) as a fluorescent probe of macromolecular interactions is investigated, with the well-known human serum albumin–sodium dodecyl sulfate aggregates as the test system. The second fluorescence band of 2PBI, arising from a proton-transferred state at the surface of negatively charged sodium dodecyl sulfate micelles, is suppressed in the aggregates. The temporal features reflect the change in the relative population of the cationic and normal forms of the fluorophore. Thus, 2PBI is found to be a potentially good fluorophore for the study of complex systems like protein–surfactant aggregates.
Reaction of 2-hydroxy-2-propyl radical with maleic and fumaric acids in aqueous solution: pH dependence by László Wojnárovits; Erzsébet Takács; Salvatore S. Emmi (224-228).
The rate coefficient of 2-hydroxy-2-propyl radical addition to maleic and fumaric acids strongly depends on the protonation state. For fumaric acid it decreases in the order: protonated > monoanion > dianion. For maleic acid the monoanion form has the highest rate coefficient.2-Hydroxy-2-propyl radical reacts with highly different rate coefficients (k) with the three protonation forms of maleic and fumaric acids. With protonated fumaric acid k is high, (2.1 ± 0.4) × 109 mol−1 dm3 s−1 due to the nucleophilic character of IP reaction and the electron withdrawing –COOH groups. With mono- and dianion molecules the k′s are smaller, (6.6 ± 0.7) × 108 and (3.1 ± 3.0) × 107 mol−1 dm3 s−1. In maleic acid k for the monoanion is higher ((1.34 ± 0.03) × 109 mol−1 dm3 s−1) than for protonated and dianion species, (5.6 ± 0.6) × 108 and (3.5 ± 3.1) × 107 mol−1 dm3 s−1. The high k is interpreted in terms of cyclic structure and charge localization between carboxylic groups.
C–Si bond dissociation in highly excited triplet states of phenybenzylphenylsilanes studied by stepwise two-color laser photolysis in solution by Minoru Yamaji; Takaaki Mikoshiba; Shinji Masuda (229-233).
C–Si Bond dissociation in highly excited triplet states (T n ) of p-phenylbenzylphenylsilanes (PBPS) was found using stepwise two-color laser photolysis techniques.C–Si Bond dissociation in highly excited triplet (T n ) states of p-phenylbenzylphenylsilanes (PBPS) was found using stepwise two-color laser photolysis techniques. PBPS undergo the C–Si bond cleavage in excited singlet states with quantum yields of 0.02–0.03, whereas they did not decompose in the lowest triplet (T1) states. Upon the second laser excitation of the T1 states, the C–Si bonds were found to cleave with quantum yields of 0.04–0.06. From the viewpoint of the bond dissociation energies of the C–Si bonds, the dissociation profile in the T n state of PBPS was discussed.
Solvated electron spectrum in supercooled water and ice by Yikui Du; Erica Price; David M. Bartels (234-237).
Comparison of electrons solvated in supercooled water and ice at several temperatures.The spectrum of the solvated electron was recorded between 310 and 830 nm in water supercooled down to −18 °C, and in ice-I h between −5 °C and −34 °C. The absorption maximum in liquid water continues to blue shift by 0.0022 eV/degree from high temperatures down to −18 °C, regardless of water bulk density. We suggest that the increasing free volume of the water below 4 °C due to formation of tetrahedral bonding structures is unavailable to the electron. The spectrum of electrons trapped in a vacancy site in ice-I h is very similar to the liquid on the blue-side, but much narrower on the red side.
Modeling solution of flexible polyelectrolyte in explicit solvent by Yu.V. Kalyuzhnyi; V. Vlachy; P.T. Cummings (238-243).
Mixture of flexible polyions with 120 monomer units, equivalent number of oppositely charged counterions and solvent molecules, represented by hard spheres with four square-well off-center sites, was studied by an extension of the product-reactant Ornstein–Zernike theory. Polyions were represented as freely jointed chains of charged hard spheres, and all the species were embedded in continuous dielectric. The calculations were performed varying the concentration of monomer units and strength of interaction between various species. The model is able to mimic rich experimental behavior of polyelectrolyte solutions.Mixture of flexible polyions with 120 monomer units, equivalent number of oppositely charged counterions and solvent molecules, represented by hard spheres with four square-well off-center sites, was studied by an extension of the product-reactant Ornstein–Zernike theory. Polyions were represented as freely jointed chains of charged hard spheres, and all the species were embedded in continuous dielectric. The calculations were performed varying the concentration of monomer units and strength of interaction between various species. The model is able to mimic rich experimental behavior of polyelectrolyte solutions.
Effective anchoring energy in dipolar organic film on metals surfaces by Mitsumasa Iwamoto; A.V. Zakharov (244-248).
The dimensionless distance x = z ¯ / d dependence of the anchoring strength w 1(x)/α 1(a) and w 2(x)/β 2(b) of 5CB dipolar film on Al electrode.The influence of electron injection from the metal electrode into organic liquid crystal dipolar film on the effective anchoring energy (EAE) of the polar organic film is discussed from the energy point of view. It is shown that the accounting for the injected carrier in organic film results in a polynomial function for the EAE expanded up to the fourth order in cos θ s, where θ s is the polar angle of the director n ˆ at the film/metal interface. It is also shown that in a certain range of the location of centroid of the injected carrier z ¯ the destabilizing surface polarization mechanism may lead to destruction of the linear anchoring strength coefficient w 1. The strong influence of z ¯ on the quadratic term w 2 also has been demonstrated.
Molecular orbital shift of perylenetetracarboxylic-dianhydride on gold by J. Kröger; H. Jensen; R. Berndt; R. Rurali; N. Lorente (249-253).
Scanning tunneling microscopy and spectroscopy reveals that the energy of orbitals of individual PTCDA molecules depends on their adsorption geometry.Scanning tunneling microscopy and spectroscopy reveal that the energy of orbitals of individual perylenetetracarboxylic-dianhydride molecules depends on their adsorption geometry. Internal molecular structure appears at characteristic energies for each of the coexisting adsorption domains on Au(7 8 8) and Au(1 1 1). Tunneling spectroscopy on single molecules belonging to different adsorption domains exhibits an energy shift of the lowest and second-to-lowest unoccupied molecular orbital of ≈0.35 eV. On the basis of density functional theory calculations a possible contribution to this shift can be traced back to hydrogen bond-mediated intermolecular interaction. Hence, tunneling spectroscopy can be used as an efficient tool to discriminate between phases of organic molecular layers.
An investigation of the EPR zero-field splitting of Fe3+ ions at tetragonal sites in Tl2MgF4 and Tl2ZnF4 crystals by Zhao-Yong Jiao; Xiao-Yu Kuang; Shu-Hong Ma; Jin-Hong Li; Mei-Ling Duan (254-258).
By analyzing the EPR zero-field splitting parameters of Fe3+ located at tetrahedral site in Tl2MgF4 and Tl2ZnF4 crystals, the local lattice structure for Fe3+ doped in Tl2MgF4 and Tl2ZnF4 crystals is theoretically studied by diagonalizing the complete energy matrices for a d5 configuration ion in a tetragonal ligand-field. From the calculation, the local lattice structure parameters R ⊥ = 1.8914 Å, R ∥ = 1.84699 Å and R ⊥ = 1.88229 Å, R ∥ = 1.84490 Å for tetragonal Fe3+ center in Tl2MgF4 and Tl2ZnF4 crystals are determined, respectively. This result suggests that the ligand-fluorines on the C 4 axis deviate easily in both two crystals, which is consistent with the conclusion drawn by earlier workers.By analyzing the EPR zero-field splitting parameters of Fe3+ located at tetrahedral site in Tl2MgF4 and Tl2ZnF4 crystals, the local lattice structure for Fe3+ doped in Tl2MgF4 and Tl2ZnF4 crystals is theoretically studied by diagonalizing the complete energy matrices for a d5 configuration ion in a tetragonal ligand-field. From the calculation, the local lattice structure parameters R ⊥ = 1.8914 Å, R ∥ = 1.84699 Å and R ⊥ = 1.88229 Å, R ∥ = 1.84490 Å for tetragonal Fe3+ center in Tl2MgF4 and Tl2ZnF4 crystals are determined, respectively. This result suggests that the ligand-fluorines on the C 4 axis deviate easily in both two crystals, which is consistent with the conclusion drawn by earlier workers.
Fermi level pinning at interfaces with tetrafluorotetracyanoquinodimethane (F4-TCNQ): The role of integer charge transfer states by Slawomir Braun; William R. Salaneck (259-262).
We have shown that the energy level alignment at the interfaces of tetrafluorotetracyanoquinodimethane (F4-TCNQ) and the substrates that span work function range from 3.45 to 5.8 eV corresponds to the Fermi level pinning regime. The Fermi level is pinned at 5.55 ± 0.1 eV as measured versus vacuum level. Within the range of ϕ s studied, the magnitude of the observed interfacial dipole Δ scales linearly with substrate work function.The energy level alignment of vacuum deposited molecular films of tetrafluorotetracyanoquinodimethane (F4-TCNQ) on various substrates has been studied by photoelectron spectroscopy. The interfaces studied span the work function range from 3.45 to 5.8 eV. In this range, the Fermi level of the substrate is pinned in proximity to LUMO level. This indicates that a charge transfer mechanism is responsible for the observed alignment scheme. The photoelectron emission study of sub-monolayer of F4-TCNQ revealed presence of electrons in the charge transfer states at the interface. In this context the electronic structure of neutral and negatively charged F4-TCNQ has been studied theoretically and by photoelectron spectroscopy.
Dynamics of O2 photodesorption from metal clusters: A significant difference from bulk behaviour by Marco Niemietz; Kiichirou Koyasu; Gerd Ganteför; Young Dok Kim (263-267).
Photodesorption of O2 from Ag n O 2 - (n = 2, 3, 4 and 8) was studied using TR-PES. Direct O2 photodesorption for n = even and a long-lived excited state for Ag 3 O 2 - was observed. Both, direct desorption and long-lived excited states, have not been observed from adsorbate covered metal surfaces, suggesting unique photochemical properties of such small clusters.Photodesorption of O2 from size-selected Ag n O 2 - cluster anions with n = 2, 3, 4 and 8 was studied using time-resolved photoelectron spectroscopy (TR-PES). The spectra indicate that relaxations of photo-excited Ag n O 2 - clusters with n = even numbers accompany ultrafast direct O2 photodesorption. For the odd-numbered cluster Ag 3 O 2 - , in contrast, a long-lived excited state is observed, since O2 might be dissociatively chemisorbed, suppressing direct photodesorption of oxygen. Both, direct desorption and long-lived excited states, have not been observed from adsorbate covered metal surfaces, suggesting unique photochemical properties of such small clusters.
Effect of pH on absorption spectra of photogenerated holes in nanocrystalline TiO2 films by Toshitada Yoshihara; Yoshiaki Tamaki; Akihiro Furube; Miki Murai; Kohjiro Hara; Ryuzi Katoh (268-273).
Transient absorption spectra of nanocrystalline TiO2 films recorded at different pH values (2.0 and 7.2).We have measured transient absorption spectra of TiO2 under several pH conditions. We successfully extracted the spectral contribution of two different trapped holes from the transient absorption spectra. Based on the results, we discuss the origin of absorption spectra of holes in TiO2.
Formation of titanium-carbide in a nanospace of C78 fullerenes by Minoru Otani; Susumu Okada; Atsushi Oshiyama (274-278).
First-principles calculation for electronic and geometric structures of Ti2C2@C78.Geometric and electronic structures of C78 fullerenes encapsulating two Ti atoms and a C2 molecule are studied by the first-principle total energy calculations. We find that the substantial hybridization between the 3d state of Ti atoms and the 2p state of C atoms results in the formation of weak covalent bonds between them and that the Ti atoms and the C2 molecule form a zigzag chain inside the cage under the optimized geometry. Encapsulated C2 molecule decreases the Coulomb repulsion energy between positively charged Ti atoms and rotates inside the cage. A plausible candidate for the structure of Ti2C2@C78 extracted in a recent experiment is assigned by the density of states for the occupied electronic states.
pH-Dependent formation of boehmite (γ-AlOOH) nanorods and nanoflakes by Xiang Ying Chen; Soon W. Lee (279-284).
Under hydrothermal conditions, we prepared γ-AlOOH 1D nanorods and 2D nanoflakes by pH control. One possible mechanism for the formation of these materials was proposed.Under hydrothermal conditions, we prepared γ-AlOOH 1D nanorods and 2D nanoflakes by manipulating the amount of a base in the reaction mixture (i.e., pH control). The acidic conditions turned out to be favored toward the formation of the nanorods, and the basic conditions toward the formation of the nanoflakes. One possible mechanism for the formation of these materials was proposed. The nanorods exhibited a blue shift in the emission spectrum, but the nanoflakes did not. Our simple and straightforward method might be applied to prepare other nanocrystals with controllable sizes and shapes.
Multi-frequency high-field EPR study of (H+)(e−) pairs localized at the surface of polycrystalline MgO by M. Chiesa; E. Giamello; G. Annino; C.A. Massa; D.M. Murphy (285-289).
The g-tensor anisotropy of excess electron centres (H+)(e−) generated at the surface of polycrystalline MgO was determined by multi-frequency, high-field electron-paramagnetic resonance (EPR) performed at 9.5, 34, 190 and 285 GHz.The g-tensor of excess electron centres (H+)(e−) generated at the surface of polycrystalline MgO has been determined by multi-frequency, high-field electron-paramagnetic resonance (EPR) performed at 9.5, 34, 190 and 285 GHz. The A tensor for the interacting 1H was also determined by complementary Q-band electron-nuclear double resonance (ENDOR). Due to the high spectral resolution the anisotropy of the g-tensor could be fully resolved in the powder continuous-wave EPR spectrum. Computer simulation of the experimental data revealed small g-tensor anisotropies: Δg x = −0.00294, Δg y = −0.00286, Δg z = −0.00101, with Δg i = g i − 2.0023.
Catalytic activity of Ag/Pd bimetallic nanoparticles immobilized on quartz surfaces by Barbara Pergolese; Maurizio Muniz-Miranda; Adriano Bigotto (290-293).
The catalytic activity of new SERS substrates, composed of Ag/Pd colloidal nanoparticles immobilized on quartz surfaces, was tested for 4-nitrobenzonitrile and 4-nitro-3-pyrazole carboxylic acid.New surface enhanced Raman scattering (SERS) substrates, composed of silver colloidal nanoparticles doped with palladium, immobilized on quartz surfaces, were prepared. The Pd clusters deposited on the Ag core acted as catalyst, while Ag ensured the SERS enhancement. These novel substrates were stable and maintained a satisfactory SERS efficiency even after a long time from the preparation. The catalytic activity of these bimetallic substrates was tested for 4-nitrobenzonitrile (NBN) and 4-nitro-3-pyrazole carboxylic acid (NPC), by means of SERS, scanning electron microscopy and surface plasmon resonance measurements. The SERS spectra showed that the nitrogroup was reduced to azogroup and aminogroup for NBN and NPC, respectively.
A possible mechanism for pressure reversal of general anaesthetics from molecular simulations by P.-L. Chau; Paul N.M. Hoang; Sylvain Picaud; Pál Jedlovszky (294-297).
The effect of general anaesthetics is pressure-dependent. We have simulated a fully hydrated dimyristoylphosphatidylcholine bilayer with halothane (a general anaesthetic) embedded, at pressures of 1, 200 and 400 atm, respectively. We find that at higher pressures, halothane molecules tend to cluster together. Based on these results, we propose a possible mechanisms for pressure reversal of anaesthesia.The effect of general anaesthetics is pressure-dependent. We have simulated a fully hydrated dimyristoylphosphatidylcholine bilayer with halothane (a general anaesthetic) embedded, at pressures of 1, 200 and 400 atm, respectively. We find that at higher pressures, halothane molecules tend to cluster together. Based on these results, we propose a possible mechanisms for pressure reversal of anaesthesia.
Atomic level description of the protecting effect of osmolytes against thermal denaturation of proteins by Stefano Pieraccini; Luigi Burgi; Alessandro Genoni; Anna Benedusi; Maurizio Sironi (298-303).
Comparative behaviour of the CI2 protein in absence (upper panel) or presence (lower panel) of the osmolyte molecule taurine.The protecting effect of the osmolyte molecule taurine against thermal denaturation of the protein Chimotripsin Inhibitor 2 was modelled using Molecular Dynamics simulations. The protein was simulated in denaturing conditions at different taurine concentrations. Analysis of the molecular details of its behaviour shows that the protective effect of the osmolyte is concentration dependent. Moreover, the influence of taurine on the solvent structure was studied. A concentration dependent ordering effect of taurine on water molecules emerges from solvent structure analysis and is well correlated to the protecting effect observed. Based on these observations an interpretation of the osmoprotective effect is proposed.
Study of hydrogen bonds in 1-methyluracil by DFT calculations of oxygen, nitrogen, and hydrogen quadrupole coupling constants and isotropic chemical shifts by Mahmoud Mirzaei; Nasser L. Hadipour (304-307).
Hydrogen bonds (HB) properties were studied in 1-methyluracil (1MU) by DFT calculations of solid-state NMR parameters including quadrupole coupling constants and isotropic chemical shifts at oxygen, nitrogen, and hydrogen nuclei. To perform the calculations, the neutron diffraction crystalline structures of 1MU at 15 and 123 K were obtained from literature and heptameric clusters including the most HB interacting molecules with the target one were created and considered. The calculated results reveal different contributions of various nuclei to HB in the cluster where O4 and N3 have the major contributions.Hydrogen bonds (HB) properties were studied in 1-methyluracil (1MU) by DFT calculations of solid-state NMR parameters including quadrupole coupling constants and isotropic chemical shifts at oxygen, nitrogen, and hydrogen nuclei. To perform the calculations, the neutron diffraction crystalline structures of 1MU at 15 and 123 K were obtained from literature and heptameric clusters including the most HB interacting molecules with the target one were created and considered. The calculated results reveal different contributions of various nuclei to HB in the cluster where O4 and N3 have the major contributions.
Simultaneous acquisition and effective separation of intermolecular multiple-quantum signals of different orders by Xiaoqin Zhu; Song Chen; Zhong Chen; Shuhui Cai; Jianhui Zhong (308-314).
Five pure intermolecular multiple-coherence signals of coherence order n = 2, 1, 0, −1, and −2 were simultaneously acquired. Signal of a specific order was obtained by optimal combinations of different acquisition data, which allows about 2/3 time saving compared to the phase cycling designs targeted for individual coherence orders.A three-pulse sequence was designed to simultaneously acquire intermolecular multiple-quantum coherence (iMQC) signals of coherence order n = 2, 1, 0, −1, −2. Analytical expressions were derived from modified Bloch equations. Signal of a specific order was obtained by optimal combinations of data from different acquisition steps. This allows a time saving of 5/7 compared to the phase cycling designs targeted for individual coherence orders. The method also results in pure iMQC signal of all the above five orders which are insensitive to radio-frequency flip angle errors, in contrast to some previous methods. Theoretical predictions are supported by the experimental observations and numerically simulated results.
QTPIE: Charge transfer with polarization current equalization. A fluctuating charge model with correct asymptotics by Jiahao Chen; Todd J. Martínez (315-320).
Traditional charge equilibration methods use atomic charges as the fundamental variables. The new QTPIE method uses charge transfer as the fundamental variables and penalizes long-range charge transfer. This leads to an improved description of polarizabilities and partial charges when bonds are broken.Polarization and charge transfer are important effects which are difficult to describe using conventional force fields. Charge equilibration models can include both of these effects in large-scale molecular simulations. However, these models behave incorrectly when bonds are broken, making it difficult to use them in the context of reactive force fields. We develop a new method for describing charge flow in molecules – QTPIE. The QTPIE method is based on charge transfer variables (as opposed to atomic charges) and correctly treats asymptotic behavior near dissociation. It is also able to provide a realistic description of in-plane polarizabilities.
Dipole moments and polarizabilities of some small radicals using constrained variational response to Fock-space multi-reference coupled-cluster theory by Prashant Uday Manohar; Sourav Pal (321-325).
Analytical polarizabilities and dipole moments of doublet radicals using CVA-FSMRCCSD method are presented.In this Letter, we present dipole moments and polarizabilities of some open-shell doublet radicals, obtained analytically using constrained variational response to Fock-space (FS) multi-reference (MR) coupled cluster (CC) theory. These radicals can be treated as electron attached (EA) states of the corresponding closed-shell cations. Additionally, we also report analytical polarizabilities of some doublet radicals, which can be considered as ionized (IP) states of the corresponding anions. We compare our results with finite field FSMRCC response and the available benchmark results.
Simulation of micelle of zwitterionic DSB in NaCl aqueous solution by Xu Jun; Sun Wenqi; Li Ganzuo; Zhang Gaoyong (326-329).
The simulation of the spontaneous formation of zwitterionic micelle in NaCl solution has been performed based on a CG model. We can observe the aggregation process undergoes two steps of fast flocking and slow coalescence. The calculated results indicate the zwitterionic polar groups are unfolding on surface of micelle, and some ions of sodium chloride have been restricted in the dipolar layer of micelle.The molecular dynamics simulation of the spontaneous formation of zwitterionic micelle of 3-(N,N-dimethyldodecylammonio)-2-hydroxy-propanesulfonate (abbreviated as DSB) in sodium chloride (NaCl) solution has been performed based on a coarse grained model. By evaluating the properties of DSB micellar structure, we can obtain the results that the polar groups in the DSB monomers are unfolding on the surface of the micelle forming a dipolar layer, some ions of NaCl have been restricted inside the dipolar layer and the concentration of NaCl ions in the dipolar region is greater than that in the bulk.
Local correlation measures and atomic shell structure by Robin P. Sagar; Nicolais L. Guevara (330-335).
Figure illustrating the differences in behavior between the local correlation coefficient and local mutual information in the Rn atom.The correlation coefficient and mutual information, used to measure the interdependence between two variables, are generalized to the local level and employed to examine the radial distribution of electron correlation. We compare the behavior of the two local measures with regard to their emphasis on core and valence correlation and show that while there are differences, both are able to correctly reproduce the shell structure in atomic systems.
A fluctuating environment as a source of periodic modulation by Simone Bianco; Paolo Grigolini; Paolo Paradisi (336-340).
We discuss a physical condition where the intermittent fluorescence of a single molecule is a modulated Poisson process, with a rate changing in time due to the influence of a fluctuating environment. Aging analysis of the time series is also performed to settle ambiguities.We study the intermittent fluorescence of a single molecule, jumping from the “light on” to the “light off” state, as a Poisson process modulated by a fluctuating environment. We show that the quasi-periodic and quasi-deterministic environmental fluctuations make the distribution of the times of sojourn in the “light off” state depart from the exponential form, and that their succession in time mirrors environmental dynamics. As an illustration, we discuss some recent experimental results, where the environmental fluctuations depend on enzymatic activity.
A comparative analysis of the electrophilicity of organic molecules between the computed IPs and EAs and the HOMO and LUMO energies by Luis R. Domingo; José A. Sáez; Patricia Pérez (341-345).
The electrophilicity index, ω, of a series of substituted ethylenes has been evaluated from the IP and the EA values computed at the B3LYP/aug-cc-PVTZ level. The electrophilicities are well correlated with those obtained from the HOMO and LUMO energies through the standard B3LYP/6-31G∗ basis set.The electrophilicity index, ω, of a series of substituted ethylenes used in some relevant organic reactions has been evaluated from the ionization potential (IP) and the electron affinity (EA) computed by vertical ionization at the B3LYP/aug-cc-PVTZ level. The corresponding electrophilicity values are well correlated with those obtained from the HOMO and LUMO energies of the neutral molecules. The good linear correlation found between ω(I,A) and ω(H,L)LBS, and between ω(H,L)LBS and ω(H,L)SBS allows to confirm the use of the easily available B3LYP/6-31G∗ HOMO and LUMO energies to obtain reasonable values of the global electrophilicity index of organic molecules.
Comparative reactivity of aminyl and aminoalkyl radicals by J. Lalevée; D. Gigmes; D. Bertin; B. Graff; X. Allonas; J.P. Fouassier (346-350).
Generation and reactivity of aminoalkyl and aminyl radicals form primary and secondary amines.The reactions of aminyl and aminoalkyl radicals, derived from primary or secondary amines toward two reactants – a double bond (methylacrylate MA) and a phenol (hydroquinone methylether HQME) – were investigated for the first time through Laser Flash Photolysis (LFP). The aminoalkyl radicals were directly observed and studied by LFP; their structure was confirmed by ESR spin trapping experiments. The reactivity of the aminyl radical was also monitored by LFP using an indirect method. Compared to aminyl radicals, the addition of aminoalkyl radicals to MA is very efficient (rate constant: 0.7–1.7 × 107 M−1s−1 vs. <105 M−1s−1) whereas the interaction with HQME is rather low (<5 × 105 M−1s−1 vs. 1.1 × 108 M−1s−1). Quantum mechanical calculations allow a discussion of the aminyl vs. aminoalkyl radical reactivity.
Quantum oscillations in photo-excited triplet states in an external magnetic field by Tomoaki Yago; Jörg-Ulrich Weidner; Gerhard Link; Tien-Sung Lin; Gerd Kothe (351-357).
Quantum oscillations are induced in the electron spin magnetization of photo-excited triplet states in an external magnetic field.Using the density operator formalism, an analytical model is developed to study the time evolution of the electron spin magnetization of photo-excited triplet states in an external magnetic field. Analysis reveals that pulsed light excitation initiates an oscillatory electron spin magnetization in the direction of the external field. The frequency of the quantum oscillations is determined by the electron Zeeman and dipolar interactions. The oscillation amplitude reaches a maximum when the electron Zeeman splitting matches the energy of a zero-field transition of the triplet state. This suggests that the predicted quantum oscillations can be detected only at low magnetic fields.
‘Comment on ‘A novel experimental method: Electrochemical detection of phase transition in ferroelectric single crystals’, Chem. Phys. Lett. 384 (2004) 262 by K. Gatner and R. Jakubas’ by K. Ćwikiel; M. Matlak (358-359).
The electrochemical method presented by us has been used for the first time to study the phase transition in ionic, nonmetallic ferroelectric single crystals. Our experimental results were obtained for the crystals grown in the Faculty of Chemistry, University of Wrocław.
Author Index (360-366).