Chemical Physics Letters (v.467, #1-3)
Editorial Board (IFC).
Quantifying accumulation or exclusion of H+, HO−, and Hofmeister salt ions near interfaces by L.M. Pegram; M.T. Record (1-8).
The salt-ion partitioning model superimposed over an idealized representation of simulation results showing exclusion of Na2SO4 from the air–water interfaceRecently, surface spectroscopies and simulations have begun to characterize the non-uniform distributions of salt ions near macroscopic and molecular surfaces. The thermodynamic consequences of these non-uniform distributions determine the often-large ion-specific effects of Hofmeister salts on a very wide range of processes in water. For uncharged surfaces, where these non-uniform ion distributions are confined to the first few layers of water at the surface, a two-state approximation to the distributions of water and ions, called the salt ion partitioning model (SPM) has both molecular and thermodynamic significance. Here, we summarize SPM results quantifying the local accumulation of H+, exclusion of HO−, and range of partitioning behavior of Hofmeister anions and cations near macroscopic and molecular interfaces. These results provide a database to interpret or predict Hofmeister salt effects on aqueous processes in terms of structural information regarding amount and composition of the surface exposed or buried in these processes.
A new approach to detecting biologically active substances with evanescent-wave cavity ring-down spectroscopy by Xiaofeng Wang; Michael Hinz; Markus Vogelsang; Thomas Welsch; Dieter Kaufmann; Harold Jones (9-13).
Detecting femtomole quantities of biologically active substances with evanescent-wave cavity ring-down spectroscopy.We have shown that an amino-propyl coating, frequently used in bioanalysis to produce activated surfaces, is sufficiently transparent to allow it to be employed in evanescent-wave cavity ring-down spectroscopy (EWCRDS). Using a quartz prism with an activated surface, it was possible to detect femtomole quantities of labeled biomolecules. The target molecules were immobilized, and thus concentrated, on the total internal reflecting surface of a simple 90° prism. Initial measurements were carried out on a dye typically used for labeling biomolecules. An antigen (fibronectin) labeled with this dye, was also detected in the femtomole-range by first immobilizing the specific antibody on the activated surface.
Thermal effects on the electric deflection of toluene molecules by Álvaro Carrera; Marcos Mobbili; Gustavo Moriena; Ernesto Marceca (14-17).
Thermal effects on the electric deflection of toluene molecules evidenced by profile analysis: from non-broadened to broad/asymmetric profiles.A series of precise electric deflection experiments were done on a supersonic beam of toluene molecules in several expansion conditions and field strengths. We analyzed the effect of a gradual rotational cooling on the evolution of the beam profile by use of the available theories of asymmetric-top dipoles in electric fields. We have recorded from non-broadened (warm) to very broad and asymmetric (cold) profiles, and discussed this effect in terms of the Stark perturbation on the rotational motion.
Predicted NMR properties of noble gas hydride cations RgH+ by Janusz Cukras; Joanna Sadlej (18-22).
The dependence of the relativistic shielding constant of the noble gas atoms σ Rg on atomic number Z. The plot also shows relativistic effect on the shielding constant Δσ = σ DHF − σ HF as a function of atomic number Z.The NMR shielding constants and, for the first time, the spin–spin coupling constants of Rg and H in RgH+ compounds for Rg = Ne, Ar, Kr, Xe have been investigated by non-relativistic Hartree–Fock (HF) and relativistic Dirac–Hartree–Fock (DHF) methods. Electron-correlation effects have been furthermore calculated using SOPPA and CCSD at the non-relativistic level. The correlation effects are large on both parameters and opposite to the relativistic effects. The results indicate that both the relativistic and correlation effects need to be taken into account in a quantitative computations, especially in the case of the spin–spin coupling constants.
Structures and electron detachment energies of Ga 2 S 3 - and Ga 3 S 2 - by Neelum Seeburrun; Edet F. Archibong; Ponnadurai Ramasami (23-27).
Neutral Ga2S3 and Ga3S2 have similar C2 ν ‘V’ gas phase equilibrium geometry. Ga2S3-adopts the C2 ν kite geometry while Ga3S2-prefers the three dimensional geometry having D3 h symmetry. The predicted adiabatic electron affinities of Ga 2 S 3 - and Ga 3 S 2 - are 3.30 eV and 2.76 eV at the CCSD(T)//B3LYP/6-311+G(2df) level.The ground and low-lying excited states of Ga 2 S 3 - , Ga2S3, Ga 3 S 2 - and Ga3S2 are studied using B3LYP, MP2 and CCSD(T) methods with flexible one-particle basis sets. Neutral Ga2S3 and Ga3S2 have similar C2 ν ‘V’ gas phase equilibrium geometry. On the other hand, Ga 2 S 3 - adopts the C2 ν kite geometry while Ga 3 S 2 - prefers the three dimensional geometry (D3 h symmetry). Electron detachment energies from the ground electronic states of the anions to several neutral states are presented and discussed. The predicted adiabatic electron affinities of Ga2S3 and Ga3S2 are 3.30 eV and 2.76 eV at the CCSD(T)//B3LYP level and 6-311+G(2df) as the basis set.
Ab initio treatment of charge transfer in CS+ molecular system by Marie-Christine Bacchus-Montabonel; Dahbia Talbi (28-31).
The charge transfer process C+(2s22p)2P + S(3s23p4)3P → C(2s22p2)3P + S+(3s23p3)4S and its reverse reaction, are important for the modellisation of the chemistry of the interstellar medium. The rate constant generally used in the astrochemical models for the C+ + S → C + S+ reaction is 1.5 × 10−9 cm3 s−1 between 10 K and 41 000 K, but it remains uncertain for such a large domain of temperature. Since no precise calculation has been ever performed for this process and for the reverse one, we have undertaken the first complete ab initio molecular treatment of this collision, followed by a semi-classical dynamical calculation. The results suggest that the rate constant adopted in astrochemical models might be overestimated.The charge transfer process C+(2s22p)2P + S(3s23p4)3P → C(2s22p2)3P + S+(3s23p3)4S is important in the modellisation of the interstellar medium chemistry. The rate constant generally used in the astrochemical models for the C+ + S → C + S+ reaction is 1.5 × 10−9 cm3 s−1  between 10 K and 41 000 K, but it remains uncertain for such a large domain of temperature. Since no precise calculation has been ever performed for this process, we have undertaken the first complete ab initio molecular treatment of this collision, followed by a semi-classical dynamics. The results suggest that the rate constant adopted in astrochemical models might be overestimated.
Photoelectron imaging study of vibrationally mediated electron autodetachment in the type I isomer of the water hexamer anion by Ben M. Elliott; Laura R. McCunn; Mark A. Johnson (32-36).
Electron energy-resolved vibrational autodetachment from OH stretching fundamentals in the water hexamer anion.We exploit the high collection efficiency of negative ion photoelectron imaging for low energy electrons to monitor the energy and angular distributions of the photoelectrons arising from vibrational excitation of the water hexamer anion in the vicinity of the OH stretching fundamentals. Photoelectrons from the low electron binding energy isomer (type II) appear as a smoothly varying outer ring with the anisotropic angular distribution expected for direct photodetachment. The higher binding isomer (type I) yields very slow electrons that are strongly modulated through the OH stretching resonances, which are discussed in the context of a statistical (IVR-based) ejection mechanism.
Hydrogen bonding with a hydrogen bond: The methane–water complex and the penta-coordinate carbon by B. Raghavendra; E. Arunan (37-40).
There is a bond path connecting C to H of H2O in the methane–water dimer that could be characterized as an O–H⋯C hydrogen bond that could be the precursor of the CH 5 + . Ab initio and atoms in molecules (AIM) theoretical studies have been used to show that in a 1:1 complex formed between CH4 and H2O, CH4 acting as a hydrogen bond acceptor leads to the global minimum structure. There is a bond path connecting C to the H of H2O revealing a penta-coordinate carbon that could be the precursor to the CH 5 + . It appears to be a general feature in CH4⋯HX complexes (X = F, Cl, and SH). It is in agreement with the experimental structure for analogous complexes and also the C2H6⋯HF/HCN complexes, suggesting that it is also a general feature for hydrocarbon–HX interaction.
Symmetry-adapted perturbation theory study of dimers and water complexes of hypohalous acids HOF, HOCl and HOBr by Jarosław J. Panek; Sławomir Berski (41-45).
Dimeric complexes of hypohalous acids of (HOX)2, HOX–HOY and HOX–H2O (X, Y = F, Cl and Br) are investigated computationally. Interaction energy partitioning is carried out on the basis of symmetry-adapted perturbation theory. Detected interactions belong to the classes of hydrogen bridges and halogen bonds. Additionally, DFT interaction energy values are discussed, indicating that DFT is able to provide reasonably good description of the potential energy surface of complexes of hypohalous acids.Hypohalous acids (HOF, HOCl and HOBr), known for their oxidative abilities, are involved in stratospheric reaction chains. The current computational study concentrates on their ability to form dimeric complexes. Interaction energy partitioning for selected dimers (also with participation of water) was carried out on the basis of symmetry-adapted perturbation theory (SAPT). Hydrogen and halogen bonds formed in these complexes are discussed. Additionally, DFT calculations on the studied dimers are presented. DFT predicts energy trends generally well, even if the actual interaction energy values can be underestimated. Thus, DFT is expected to provide good description of the ice surface reactivity of hypohalous acids.
H-atom product channel and mode specificity in the near-UV photodissociation of thiomethoxy radical via the Ã 2 A 1 state by Xianfeng Zheng; Yu Song; Jingze Wu; Jingsong Zhang (46-51).
H-atom photofragment yield spectrum in the near-UV photodissociation of CH3S via the A ˜ 2 A 1 state, showing mode specificity in the H-atom product channel.Photodissociation of jet-cooled thiomethoxy radical (CH3S) via the A ˜ 2 A 1 ← X ˜ 2 E 3 / 2 transition is studied in the region of 344–362 nm. The H-atom product channel is directly observed by H-atom photofragment yield spectrum and photofragment translational spectroscopy. Two vibronic levels of A ˜ 2 A 1 , 2131 and 2132, dissociate to H + H2CS, while the others in the vicinity (2133 and 3 n , n = 3–6) dissociate to CH3 + S(3PJ) (based on a previous study by Neumark and co-workers). The H + H2CS product translational energy release is not repulsive and peaks at ∼9 kcal/mol; the H-atom angular distribution is isotropic. The dissociation mechanism is consistent with internal conversion of the excited A ˜ 2 A 1 to the ground state X ˜ 2 E followed by unimolecular dissociation of X ˜ 2 E .
Computational studies on the mechanisms for the gas-phase reaction between thiophene and NO3 by Weichao Zhang; Tao Wang; Changjun Feng; Benni Du; Lailong Mu (52-57).
The reaction is shown to start with an exothermic barrierless addition of NO3 to the double bond of thiophene ring to give thiophene-ON(O)O intermediate (IM1). IM1 can generate the predominant products including P5 + NO2 and P6.G3MP2B3 calculations have been performed to investigate the potential energy surface for the reaction of thiophene with NO3 radical. Both direct hydrogen abstraction pathways and addition–elimination pathways have been found. The reaction is shown to start with an exothermic barrierless addition of NO3 to the double bond of thiophene ring to give thiophene-ON(O)O intermediate (IM1), possibly, IM1A and IM2. Intermediate IM1 can generate various products including P5 + NO2, P4 (C(S)HCH＝CHC(O)H) + NO2, P6 (C(S)HCH＝CHC(H)ONO2), and P3 + H. The most energetically favorable channel is found to be the formation of P5 by loss of NO2 from intermediate IM1. The calculations are inconsistent with the available experimental results.
Dual fluorescence of 4-dialkylaminopyridines under supersonic jet conditions by Izabela Franssen Szydłowska; Yevgeniy Nosenko; Bernhard Brutschy; Jerzy Herbich (58-65).
4-Diisopropylaminopyridine, which is pretwisted already in the ground state, shows the long-wave fluorescence upon higher energy excitation to the CT state.The results of the spectral and photophysical investigations of 4-dimethylaminopyridine (DMAP), 4-diethylaminopyridine (DEAP), 4-diisopropylaminopyridine (DIAP) and their 1:1 complexes with alcohols under supersonic jet conditions by LIF, R2PI and IR/R2PI techniques are presented. The dispersed emission spectra of jet-cooled DMAP, DEAP and DIAP, recorded upon selective excitation in the 0 0 0 region, are attributed mostly to the radiative transition from the primary excited state. In the case of DIAP the higher energy excitation results in an appearance of the long-wave fluorescence. The low-energy luminescence band is observed also for the complexes of DEAP and DIAP with alcohols of relatively strong acidity.
Interaction potential of Al3+–Ne and the mobility of Al3+ in He and Ne by Timothy G. Wright; Edmond P.F. Lee; Larry A. Viehland (66-69).
CASSCF + MRCI + Q potential energy curves for Al3+–Ne and Al2+–Ne+. There is an avoided crossing between the two 1Σ+ states.The complex between the triply-charged cation Al3+ and a neon atom is investigated using high-level ab initio calculations. Vibrational and rotational spectroscopic parameters are calculated. It is concluded that the Al3+. Ne complex is kinetically stable and should be observable. We also report calculated mobilities of Al3+ ions moving through He and Ne, the first report of the mobility of a trication.
Pulsed laser photolysis vacuum UV laser-induced fluorescence kinetic study of the reactions of Cl(2P3/2) atoms with ethyl formate, n-propyl formate, and n-butyl formate by Tomoyuki Ide; Erika Iwasaki; Yutaka Matsumi; Jia-Hua Xing; Kenshi Takahashi; Timothy J. Wallington (70-73).
Vacuum UV laser-induced fluorescence spectroscopy probes the rate coefficients of the Cl-atom reactions with formates.Cl(2P3/2) atoms were produced by photolysis of Cl2 at 351 nm in the presence of alkyl formates and monitored by LIF spectroscopy at 134.72 nm. Rate coefficients of k(Cl + C2H5OC(O)H) = (9.5 ± 0.3)×10−12, k(Cl + n-C3H7OC(O)H) = (4.5 ± 0.3) × 10−11 and k(Cl + n-C4H9OC(O)H) = (1.2 ± 0.1) × 10−10 cm3 molecule−1 s−1 were determined at 295 ± 2 K in 6–7 Torr of Ar diluent. These values are 15–30% lower than reported in a previous pulsed laser photolysis resonance fluorescence study. The discrepancy may reflect complications arising from the fact that the time scales for chlorine atom loss and regeneration were not sufficiently decoupled in the previous study.
The rotational spectrum of a C4 anhydrosugar, 1,4-anhydrothreitol by B.M. Giuliano; S. Blanco; S. Melandri; W. Caminati (74-76).
The jet cooled rotational spectrum of the C4 anhydrosugar 1,4-anhydrothreitol has been analyzed for its most stable conformer, which exhibits a ‘pseudo rotation’ disposition of the ring and an O–H (alcoholic)⋯O (ring) hydrogen bond.The rotational spectrum of 1,4-anhydrothreitol (a C4 anhydrosugar) has been assigned by free jet millimeter wave spectroscopy. The structure, characterized by a distorted ring and one O–H⋯O hydrogen bond involving an alcoholic group and the ring oxygen, corresponds to the B3LYP/6-31G∗∗ global conformational minimum. Since C2 sugars have already been observed, and C3 sugars have been extensively searched in the interstellar medium (with controversial results) we propose 1,4-anhydrothreitol to be of interest for astrochemical observation.
Effect of ultrasound treatment on the optical properties of C60 fullerene films by U. Ritter; P. Scharff; V.V. Kozachenko; S.V. Kondratenko; O.I. Dacenko; Yu.I. Prylutskyy; V.N. Uvarov (77-79).
Photoluminescence spectra of initial C60 film and the sample after ultrasound treatment are studied. The ultrasonic treatment decreases the integral intensity and modifies the photoluminescence spectrum shape.C60 fullerene films on silicon substrates are investigated by luminescence and multi-angle-of-incidence (MAI) ellipsometry. The ultrasonic treatment decreases the integral intensity and modifies the photoluminescence spectrum shape. The optical properties of C60 fullerene films are shown to be well described within a two-layer model, a bulk fullerene layer and a surface film. It is found that the ultrasonic treatment mainly affect the optical constants of the surface layer. The change of the film optical properties is caused by the decrease of the defect concentration due to the ultrasonic treatment.
Length-dependent nucleation mechanisms rule the vaporization of n-alkanes by Dirk Zahn (80-83).
Direct comparison of the methane (left), pentane (middle) and decane (right) simulation models at a fixed intermediate stage of the vaporization process (1/25 of the systems density in the liquid state): While the methane model displays largely homogeneous characteristics, the pentane and decane models show an increasing importance of liquid droplets as intermediates during the vaporization process.The liquid → vapor transition of a series of n-alkanes is explored by means of molecular dynamics simulations. From the comparison of the vaporization of methane, pentane and decane we elaborate the dependence of the nucleation mechanisms on the chain length. While the boiling of methane may be characterized as ‘ideal’ vapor bubble nucleation and growth, our studies related to pentane and decane reveal an increasing importance of liquid droplets acting as intermediates of the vaporization process. With increasing chain length the investigated n-alkanes were found to avoid the formation of large liquid-vapor interfaces by following a different nucleation mechanism.
Pump–probe polarized transient hole burning (PTHB) dynamics of hydrated electron revisited by Ilya A. Shkrob (84-87).
In observation of PTHB signal for hydrated electron is due to rapid reorientation of s–p transition dipole moments.Femtosecond PTHB spectroscopy was expected to demonstrate the existence of distinct s–p absorption subbands originating from the three nondegenerate p-like excited states of hydrated electron in anisotropic solvation cavity. Yet no conclusive experimental evidence either for this subband structure or the reorientation of the cavity on the picosecond time scale has been obtained. It is shown here that rapid reorientation of s–p transition dipole moments in response to small scale motion of water molecules is the likely culprit. The polarized bleach is shown to be too low in amplitude and too short lived to be observed reliably on the sub-picosecond time scale.
Hydrogen bonding properties of DMSO in ground-state formation and optical spectra of 3-hydroxyflavone anion by Stefano Protti; Alberto Mezzetti; Jean-Paul Cornard; Christine Lapouge; Maurizio Fagnoni (88-93).
3-Hydroxyflavone anion formation in DMSO: hydrogen bonds play a key role in the mechanism and in modulating the spectral properties.We report ground-state formation of 3-hydroxyflavone (3HF) anion in DMSO. According to the literature this process is possible only in hydrogen bonding donor (HBD) solvents. Our results show that a solvent with zero HBD acidity but sufficiently high hydrogen bonding acceptor basicity can also give anion formation. A possible new mechanism is proposed. Furthermore, theoretical calculations show evidence for the formation of a 3HF−···DMSOH+ complex. As 3HF anion is a promising biophysical fluorescent probe, our results can help to understand the factors governing its ground-state formation and how its spectral properties are related to its microenvironment in biological systems.
Spin–orbit effects on the aromaticity of the Re3Cl9 and Re3Br9 clusters by Leonor Alvarado-Soto; Rodrigo Ramírez-Tagle; Ramiro Arratia-Pérez (94-96).
Here, we report density functional calculations of the electronic structure and nuclear independent chemical shift (NICS) values of the Re3Cl9 and Re3Br9 clusters including scalar and spin–orbit relativistic effects (ADF + ZORA + SO). Our calculations have shown that both the clusters exhibit aromaticity and that spin–orbit effects decreases aromaticity due to the fact that the 5d3/2 spinors are mostly occupied and are more contracted than the scalar 5d orbitals.Here, we report density functional calculations of the electronic structure and nuclear independent chemical shift (NICS) values of the Re3Cl9 and Re3Br9 clusters including scalar and spin–orbit relativistic effects (ADF + ZORA + SO). Our calculations have shown that both the clusters exhibit aromaticity and that spin–orbit effects decreases aromaticity due to the fact that the 5d3/2 spinors are mostly occupied and are more contracted than the scalar 5d orbitals.
Photoinduced oxidation of triphenylphosphine isolated in a low-temperature oxygen matrix by Igor Reva; Leszek Lapinski; Maciej J. Nowak (97-100).
UV (λ > 280 nm) irradiation of Ph3P monomers isolated in solid O2 (at 10 K) results in formation of Ph3P＝O and Ph2(Ph−O−)P＝O.Photooxidation reactions of triphenylphosphine (Ph3P) monomers isolated in matrices of solid oxygen at 10 K were characterized by means of infrared spectroscopy. Upon UV (λ > 280 nm) irradiation of O2 matrices, ca. 90% of Ph3P was converted to triphenylphosphine oxide (Ph3P＝O), with concomitant formation of ozone. In the competing photoreaction, ca. 10% of Ph3P was converted to diphenyl-phenyl-phosphinate, Ph2(Ph−O−)P＝O. The interpretation was assisted by theoretical [DFT(B3LYP)/6-31G(d, p)] calculations of vibrational spectra, as well as by comparison with the experimental vibrational data from separate experiments in which monomeric Ph3P and Ph3P＝O were isolated in argon and oxygen matrices at 10 K.
Surface enhanced Raman scattering of trans-3-hydroxycinnamic acid adsorbed on silver nanoparticles by Mariana Sardo; Cristina Ruano; José Luis Castro; Isabel López-Tocón; Paulo J.A. Ribeiro-Claro; Juan C. Otero (101-104).
The selective enhancement of mode 8a in the SERS of trans-3-hydroxycinnamic is due to electron transfer processes from the metal to the molecule yielding the formation of the radical dianion in the transient excited state.SERS of trans-3-hydroxycinnamic acid adsorbed on silver colloids have been analyzed in order to detect resonant charge transfer processes similar to a resonance Raman mechanism, involving the photoinduced transfer of an electron from the metal to the adsorbate (SERS-CT). Theoretical SERS-CT intensities for the neutral, anionic and dianionic forms have been calculated and it was found that the active SERS species corresponds to cinnamate ion linked to the metal through its carboxylate group. Moreover, it has been shown that the SERS-CT mechanism is operating in the SERS, explaining the strong enhancement of the band at ca. 1600 cm−1, assigned to the 8a mode.
Dye fluorescence enhancement and quenching by gold nanoparticles: Direct near-field microscopic observation of shape dependence by Noriko Nishizawa Horimoto; Kohei Imura; Hiromi Okamoto (105-109).
Strong dye fluorescence enhancement by gold nanoplates.We investigated the enhancement and quenching of dye fluorescence by single gold nanoparticles using an aperture-type scanning near-field optical microscope to evaluate the shape dependence. Enhancement or reduction of fluorescence was found to be strongly dependent on the shape of the particle. Gold nanoplates showed significant fluorescence enhancement, as did aggregated nanoparticles for the most part. On the other hand, gold nanorods with high aspect ratios showed quenching effects. The results suggest that the electromagnetic near-field in the vicinity of the surface of nanoparticles, not just near the apex or the tip but the whole surface, is important for understanding fluorescence enhancement and quenching.
Molecular simulation of thermal transport across hydrophilic interfaces by Sohail Murad; Ishwar K. Puri (110-113).
Molecular simulations of heat transfer across the solid–fluid interface formed by a silica wafer in contact with water vapor.Using molecular simulations, we have investigated heat transfer across the solid–fluid interface of a silica wafer in contact with water vapor. Our results show that the thermal or Kapitza resistance decreases significantly, as the surface becomes more hydrophilic. This is primarily due to increases in adsorption and absorption at the surface, which enhances the intermolecular collision frequency at the interface. Increasing this frequency also reduces the dependence of thermal transport on variations in the interfacial temperature and pressure. Decreasing the density diminishes the intermolecular collision frequency thus increasing the thermal resistance.
Ab initio study of magnetic properties of bimetallic Co n− 1Mn and Co n− 1V clusters by Naifeng Shen; Jinlan Wang; Liyan Zhu (114-119).
The magnetic moments of bimetallic clusters are enhanced (reduced) by 2 (6μ B) with a Mn (V) atom substituting a Co atom of Co n .Spin-polarized density functional theory calculations on bimetallic Co n− 1Mn and Co n− 1V (n = 2–9) clusters are reported. The clusters exhibit high stability at n = 6. With the exception of CoV, the magnetic moments of Co n , Co n− 1Mn and Co n− 1V increase with size by 3μ B for n = 2–5 and by 1μ B afterwards. The magnetic enhancement (reduction) is identified upon Mn (V) substitution, compared to Co n , consistent with recent experimental observation in large-sized clusters. Their different magnetic behavior of Mn and V-substituted clusters results from both differences in magnetic alignment (ferromagnetic in Co n− 1Mn and ferrimagnetic in Co n− 1V) and reduced local moments on Co in Co n− 1V.
Theoretical study of third-order nonlinear optical properties in square nanographenes with open-shell singlet ground states by Masayoshi Nakano; Hiroshi Nagai; Hitoshi Fukui; Kyohei Yoneda; Ryohei Kishi; Hideaki Takahashi; Akihiro Shimizu; Takashi Kubo; Kenji Kamada; Koji Ohta; Benoît Champagne; Edith Botek (120-125).
Nanographene with intermediate diradical character exhibits a large enhancement (about four times) of the γ component along the armchair edges as compared to that along the zigzag edges, as well as a strong spin state dependence, a large γ reduction by going from the singlet to the triplet state.Using spin-unrestricted density functional theory methods, the second hyperpolarizabilities, γ, of square nanographenes presenting different diradical characters are investigated from the viewpoint of open-shell singlet nonlinear optical systems. For nanographenes with intermediate diradical character, the γ component along the armchair edges is enhanced and amounts to about four times the γ component along the zigzag edges, whereas these γ components are of similar amplitudes when the system displays nearly pure diradical character. These observations are in conformity with the diradical character dependence of γ predicted in our previous studies.
Modelling the interaction of molecular hydrogen with lithium-doped hydrogen storage materials by Stephen J. Kolmann; Bun Chan; Meredith J.T. Jordan (126-130).
The M05-2X density functional accurately describes H2 interactions with Li+–benzene, a model for Li-doped hydrogen storage materials.Density functional theory (DFT) and ab initio methods are used to investigate the interaction of one, two and three hydrogen molecules with Li+-doped benzene, a model for lithium-doped carbon-based and metal organic framework materials. M05-2X is found to be the best DFT method considered, reproducing MP2 and CCSD(T) H2 binding energies to Li+-doped benzene. The M05-2X results also agree with H2 binding energies previously obtained in an extended model of Li atom-doped MOF-5. These calculations suggest H2 binding in Li-doped materials is, primarily, a local interaction, implying that model compounds can be used to describe these systems.
Adsorption of formaldehyde molecule on the pristine and silicon-doped boron nitride nanotubes by Ruoxi Wang; Rongxiu Zhu; Dongju Zhang (131-135).
The Si-doped BNNT presents high sensitivity to HCOH and expected to be a potential novel sensor for detecting HCOH.The adsorption of formaldehyde (HCOH) molecule on the pristine and silicon-doped (Si-doped) single-walled (8, 0) boron nitride nanotubes (BNNTs) is investigated using density functional theory (DFT) calculations. Compared with the weak physisorption on the pristine BNNT, the HCOH molecule presents strong chemisorption on both silicon-substituted boron defect site and silicon-substituted nitrogen defect site of the BNNT, as indicated by the calculated geometrical structures and electronic properties for these systems. It is suggested that the Si-doped BNNT presents high sensitivity to toxic HCOH. Based on calculated results, the Si-doped BNNT is expected to be a potential novel sensor for detecting the presence of HCOH.
Adsorption of (S)–(+)–O-acetylmandelic acid on gold nanoparticle surfaces investigated by surface-enhanced Raman scattering by Jang Suk Kwon; Heung Bae Jeon; Sung Ik Yang; Jung Jin Oh; Sang-Woo Joo (136-139).
Our observations suggest scission of the carboxyl group of an aromatic acid into a benzyl radical intermediate on gold nanoparticle surfaces.Adsorption of (S)–(+)–O-acetylmandelic acid on gold nanoparticle surfaces was examined by means of surface-enhanced Raman scattering. The adsorbate was presumed to bind to the surface via the carboxylate functional group due to the presence of symmetric stretching bands at ∼1350 cm−1. Nearly identical spectral features to those of phenylacetic acid in conjunction with the disappearance of the C＝O stretching band at ∼1700 cm−1 were exhibited in the SERS spectra. These observations suggest scission of the carboxyl group into a benzyl radical intermediate on gold nanoparticle surfaces.
Long distance chiral transfer in a gel: Experimental and ab initio analyses of vibrational circular dichroism spectra of R- and S-12-hydroxyoctadecanoic acid gels by Hisako Sato; Kayako Hori; Takara Sakurai; Akihiko Yamagishi (140-143).
From the vibrational circular dichroism (VCD) spectra recorded on a benzene-d6 gel sample of R- or S-12-hydroxyoctadecanoic acid (R- or S-12-HOA, respectively), it was concluded that 12-HOA molecules formed a curved dimer with no hopping of carboxylic protons allowed in a gel.Vibrational circular dichroism (VCD) spectra were recorded on a benzene-d6 gel sample of R- or S-12-hydroxyoctadecanoic acid (denoted by R- or S-12-HOA, respectively). The observed peaks were well reproduced by the theoretical calculation carried out for the optimized conformation of a 12-HOA molecule. The strong bisignate peaks assigned to the stretching vibrations of C＝O bond in a carboxylic group were rationalized in terms of the model that two 12-HOA molecules formed a dimer through hydrogen bonding in a bent conformation.
Mechanical aspects of nitrile hydratase enzymatic activity. Steered molecular dynamics simulations of Pseudonocardia thermophila JCM 3095 by L. Peplowski; K. Kubiak; W. Nowak (144-149).
An external force applied in silico to substrates and products of biotechnological enzyme nitrile hydratase reveals its nanomechanical properties.Nitrile hydratase (NHase), an important biotechnological enzyme, has been investigated using a steered molecular dynamics computer modelling for the first time. An external force applied to the docked ligands was used to determine transport paths for acrylonitrile (substrate) and acrylamide (product). The average drag force of 120 pN within the enzyme channel is 50% higher than that in model water. The major hindrance of 500 pN is generated by βPhe37 residue. This region may be responsible for the stereoselectivity of NHases.
On the cold denaturation of globular proteins by Eduardo Ascolese; Giuseppe Graziano (150-153).
The two endothermic peaks, corresponding to the cold renaturation and hot denaturation of globular proteins, are calculated by means of the present version of the Ikegami’s model, on changing the size of the lattice.The recent finding that yeast frataxin shows, at pH 7.0, cold denaturation at 274 K and hot denaturation at 303 K [A. Pastore, S.R. Martin, A. Politou, K.C. Kondapalli, T. Stemmler, P.A. Temussi, J. Am. Chem. Soc. 129 (2007) 5374] calls for a deeper rationalization of the molecular mechanisms stabilizing–destabilizing the native state of globular proteins. It is shown that the statistical thermodynamic model originally developed by Ikegami can reproduce in a more-than-qualitative manner the two conformational transitions of yeast frataxin, providing important clues on their molecular origin.
Resonant neutral-particle emission correlated with base–base interactions in collisions of electrons with protonated and sodiated dinucleotide monocations by Tetsumi Tanabe; Evgeni B. Starikov; Koji Noda (154-158).
Neutral-particle production rates in collisions of electrons with protonated and sodiated dinucleotide monocations correlate with various base–base interactions.Electron–monocation collisions for protonated and sodiated single-stranded dinucleotides with various base compositions and sequences have been studied using an electrostatic storage ring equipped with a merging-electron-beam device. Resonant neutral-particle emissions have been observed at a collision energy of 4–5 eV. The strength of the resonant bumps changes depending on the number of sodium, as well as the DNA base composition and sequence, which mostly increases with an increase in number of sodium. The results were compared with theoretical structures generated and studied by molecular mechanics and semiempirical quantum-chemistry calculations. It is deduced that the rate correlates with various base–base interactions.
Sum-frequency generation spectroscopy of self-assembled structures of Guanosine 5′-monophosphate on mica by Klemen Kunstelj; Lea Spindler; Francesco Federiconi; Mischa Bonn; Irena Drevenšek-Olenik; Martin Čopič (159-163).
The structure and ordering of Guanosine 5′-monophosphate on the mica monitored by sum-frequency generation spectroscopy and atomic force microscopy.The structure and ordering of Guanosine 5′-monophosphate (GMP) films self-assembled on mica from GMP salt solutions were studied by infrared-visible sum-frequency generation spectroscopy (IR-VIS SFG) and atomic force microscopy (AFM). We find that the surface self-assembly of GMP can be tuned through the concentration of the GMP solution as well as the nature of the counter ion. At low concentrations of the ammonium and the sodium GMP salt solutions, the self-assembled films are very similar, while at higher concentrations the SFG signal of ammonium GMP samples is dominated by a contribution not originating from azimuthally symmetric layers, which signifies that a helical bulk structure might be present.
Topological and spectroscopic study of three-electron bonded compounds as models of radical cations of methionine-containing dipeptides by Isabelle Fourré; Jacqueline Bergès; Benoît Braïda; Chantal Houée-Levin (164-169).
Interaction of a model of the radical cation of methionine with a peptidic bond leading to a S∴X+ complex (X = N and O).Small models of radical cations of methionine-containing dipeptides, which are stabilized by formation of two-centre three-electron (2c–3e) S∴X bonds (X = S, N and O), were investigated at the BH&HLYP/6-31G(d) level and by means of topological tools. The SX distance is not so important for stability but the relative orientation of both fragments is. The AIM and ELF topological analyses shows that the nature of the S∴X bond varies with X, from purely 2c–3e in S∴S+ entities to electrostatic in S∴O+ ones. The σ SX → σ SX ∗ wavelengths, obtained at the TD-BH&HLYP/cc-pVTZ level, strongly depend on X and on conformation.
Effect of temperature on the local angular thermal expansion and local structure for nickel-doped zinc fluosilicate by Ai-Ping Zhai; Xiao-Yu Kuang; Mei-Ling Duan; Cai-Xia Zhang; Rui-Peng Chai (170-175).
A theoretical method for studying the local properties about Ni2+ ion in a trigonal ligand-field has been proposed by diagonalizing the complete energy matrix and considering the electron paramagnetic resonance (EPR) parameters D and g. For nickel-doped ZnSiF6 · 6H2O and ZnSiF6 · 6D2O systems, the local lattice distortion and local angular thermal expansion coefficient have been investigated at various temperatures. The calculated results indicate that the local structure around octahedral Ni2+ centre has a compression distortion in the two systems. Moreover, the temperature dependence of the local angular thermal expansion coefficient has also been analysed.A theoretical method for studying the local properties about Ni2+ ion in a trigonal ligand-field has been proposed by diagonalizing the complete energy matrix and considering the electron paramagnetic resonance (EPR) parameters D and g. For nickel-doped ZnSiF6 · 6H2O and ZnSiF6 · 6D2O systems, the local lattice distortion and local angular thermal expansion coefficient have been investigated at various temperatures. The calculated results indicate that the local structure around octahedral Ni2+ centre has a compression distortion in the two systems. Moreover, the temperature dependence of the local angular thermal expansion coefficient has also been analysed.
Optimal operators for Hartree–Fock exchange from long-range corrected hybrid density functionals by Jeng-Da Chai; Martin Head-Gordon (176-178).
A conserved property is found in the middle-range region of the operator from a long-range corrected hybrid functional.The long-range operators for Hartree–Fock exchange from two recently proposed long-range corrected hybrid functionals, ωB97 and ωB97X [J.-D. Chai, M. Head-Gordon, J. Chem. Phys. 128 (2008) 084106], are discussed. A conserved property is found in the middle-range region of the operator from ωB97X. We argue that the fine details of the Hartree–Fock exchange mixing in this region are responsible for the accuracy of the long-range corrected hybrid functionals in thermochemistry and barrier heights.
Effects of meso-substituents and core-modification on photophysical and electrochemical properties of porphyrin–ferrocene conjugates by Smita Rai; G. Gayatri; G. Narahari Sastry; M. Ravikanth (179-185).
The effects of meso-substituents and porphyrin core-modification on photophysical and electrochemical properties of porphyrin–ferrocene conjugates are described.The effects of meso-substituents and porphyrin core-modification on electronic communication between ferrocene and porphyrin in covalently linked porphyrin–ferrocene conjugates are described. The electrochemical and photophysical studies indicated that the electronic communication between porphyrin and ferrocene is strong when meso-substituents are five membered aryl groups than six membered aryl groups. This may be traced to the near orthogonal arrangement of porphyrin ring with six membered meso-aryl groups leading to weaker interaction between the porphyrin and ferrocenyl groups in conjugates, while the five membered furyl and thienyl groups are closer to the porphyrin plane than being orthogonal. Molecular orbital studies are performed at semiempirical PM3 and BLYP levels to rationalize the results.
On the inversion of geometric parameters from absorption and circular dichroism spectroscopy of molecular dimers by Alexander Eisfeld; Joachim Seibt; Volker Engel (186-190).
Vibrationally broadened band-shapes of absorption and circular dichroism spectra of molecular dimers.Absorption spectra of molecular dimers usually exhibit complex line-shapes. In an approximate treatment the excited dimer states are described as a two-level system, leading to two bands separated by twice the electronic coupling element which is responsible for the splitting. The band intensities are related to the relative orientation of the monomer transition dipole-moments. We show, considering absorption and circular dichroism spectra, that extracting geometric parameters using the two-level description can lead to substantial errors when internal monomer vibrations become relevant. The application of sum-rules offers a more accurate approach to invert the data.
Effect of H2 gas as a reductant on photoreduction of CO2 over a Ga2O3 photocatalyst by Kentaro Teramura; Hideo Tsuneoka; Tetsuya Shishido; Tsunehiro Tanaka (191-194).
The photoreduction of CO2 in the presence of H2 as the reductant on irradiated β-Ga2O3 involves two chemisorbed species—H2 and CO2.Ga2O3 was used as a photocatalyst for the photoreduction of CO2 in the presence of H2 as a reductant; in this process CO gas was selectively produced at room temperature and ambient pressure. The optimum conversion of CO2 was approximately 3% using β-Ga2O3 calcined at 1073 K for 6 h. The formation of CO depended on the amounts of H2 and CO2 introduced into the system. The photoreduction of CO2 on Ga2O3 involves two chemisorbed species—H2 and CO2. This implies that the photocatalytic reaction would proceed on the basis of the typical Langmuir–Hinshelwood mechanism.
Effects of vibrational motion on core-level spectra of prototype organic molecules by Janel S. Uejio; Craig P. Schwartz; Richard J. Saykally; David Prendergast (195-199).
Particular core-level transitions are forbidden in the absence of vibrations, but become allowed in the presence of structural perturbations.A computational approach is presented for prediction and interpretation of core-level spectra of complex molecules. Applications are presented for several isolated organic molecules, sampling a range of chemical bonding and structural motifs. Comparison with gas phase measurements indicates that spectral lineshapes are accurately reproduced both above and below the ionization potential, without resort to ad hoc broadening. Agreement with experiment is significantly improved upon inclusion of vibrations via molecular dynamics sampling. We isolate and characterize spectral features due to particular electronic transitions enabled by vibrations, noting that even zero-point motion is sufficient in some cases.
Resonance-theoretic calculation of the ground state spin density of the pπ-system of edge atoms on graphene nanodots and nanoribbons by Jerry Ray Dias (200-203).
Resonance-theoretic calculations of Mulliken spin polarization of Clar’s goblet.By the resonance-theoretic method zigzag graphene nanoribbons are predicted to have an antiferromagnetic ground state with a Mulliken spin density of 0.33 on the edge atoms and the armchair graphene nanoribbons are predicted to have a nonmagnetic ground state. Similar calculations predict that sawtooth graphene nanoribbons have a weakly antiferromagnetic ground state with edge atoms having a Mulliken spin density of 0.16 on the edge atoms.
An integrated approach for the interpretation of emission fluorescence of DMABN-Crown derivatives in polar environments by Silvia Carlotto; Raffaele Riccò; Camilla Ferrante; Michele Maggini; Antonino Polimeno; Caterina Benzi; Vincenzo Barone (204-209).
Fluorescence of metal sensor DMABN-Crown5 is described by a diffusion equation and compared to measured emission.We analyze the behavior in several solvents of a perspective metal sensor, namely benzonitrile (DMABN-Crown5), a derivative of 4-(N,N-dimethylamino) benzonitrile (DMABN) that exhibits a dual fluorescence due to a twisted intra-molecular charge transfer process. To this end, we extend a stochastic modeling previously employed for DMABN, in which internal degrees of freedom are coupled with an effective solvent relaxation variable. Evaluation of potential energy surfaces using advanced QM approach and estimates of dissipative parameters based on hydrodynamic arguments are discussed. Emission fluorescence is calculated by solving a diffusion/sink/source equation for the stationary population of excited state, and compared to experimentally measured emission fluorescence of DMABN-Crown5.
Model of traveling wave formed by autonomous motion of contact line with oil/water interface by Akihisa Shioi; Takahiko Ban; Sho Suzuki (210-215).
A model for the spontaneous traveling wave in oil/water system is proposed, which reproduces many characteristics of the traveling wave.A model for the spontaneous traveling wave in oil/water system is proposed. The present model is to explain the traveling wave generated by chemical reactions between a cationic surfactant and oil-soluble anions. This is an extension of the previous model which describes the oscillatory motion of the contact line formed by the oil/water interface and a glass surface. The oscillations at different places are coupled to each other by an effect that diminishes the interfacial energy. The numerical calculations reveal that the traveling wave with a specified direction is reproduced under several assumptions for the noise term.
Erratum to ‘The atomic and electronic structure of CdZnTe (1 1 1) A surface’ [Chem. Phys. Lett. 427 (2006) 197] by Gangqiang Zha; Wanqi Jie; Tingting Tan; Peisen Li; Wenhua Zhang; Faqiang Xu (216).