Chemical Physics Letters (v.425, #4-6)

Contents (iii-xii).

Formation of HO2 and OH in photolytically initiated oxidation of dimethyl ether by Kotaro Suzaki; Nozomu Kanno; Kenichi Tonokura; Mitsuo Koshi; Kentaro Tsuchiya; Atsumu Tezaki (179-184).
Time-resolved measurements of HO2 and OH have been conducted in 355 nm photolysis of dimethyl ether/Cl2/O2 mixture at elevated temperature, using near-infrared frequency modulation spectroscopy. It was rationalized that HO2 is not a direct product of the O2 adduct decomposition, but a secondary product through HCHO + OH reaction.Time-resolved measurements of HO2 and OH have been conducted in 355 nm photolysis of dimethyl ether/Cl2/O2 mixture at elevated temperature, using near-infrared frequency modulation spectroscopy. A part of OH was found to be produced at a timescale of several microseconds by the methoxymethyl with O2 reaction, while HO2 is formed mainly in milliseconds with the yield increasing up to 60% between 500 and 600 K. It was rationalized that HO2 is not a direct product of the O2 adduct decomposition, but a secondary product through HCHO + OH reaction. Another pathway through HCO formation from the adduct is also discussed.

A study on a new 2Δ Rydberg state of SF by resonance-enhanced multiphoton ionization spectroscopy by Tingting Wang; Xianfeng Zheng; ChunYan Li; Yang Chen (185-190).
The mass spectra averaged over 512 laser-shots under the conditions: (a) the resonant wavelength of SF 279.788 nm with the discharge turned on; (b) the non-resonant wavelength of SF 278.976 nm with the discharge turned on and (c) the resonant wavelength of SF 279.788 nm with the discharge turned off.The (2 + 1) resonance-enhanced multiphoton ionization (REMPI) spectra of SF radicals have been recorded in the single-photon wavelength region of 271–286 nm for the first time. Four regular vibrational bands were observed and assigned as the transition by two-photon from the ground state to a 2Δ Rydberg state. The 2Δ Rydberg state arises from one-electron excitation from the 3π orbital of SF ground state to a 4pσ Rydberg orbital, which converging to the first excited ionic state (1Δ). The term value T e, spin–orbit coupling constant A, vibrational frequency and rotational constants for the 2Δ Rydberg state are determined.

Theoretical studies on the electronic states of BrOOCl by Yumin Li; Christopher K. Vo (191-195).
The optimized geometrical parameters of BrOOCl cis-form (A), trans-form (B) and twist-form (C) at CCSD(T)/cc-pVTZ level of theory.The electronic states of BrOOCl were investigated using computational approaches. The three forms (trans-, cis-, and twist-forms) of BrOOCl were optimized at the couple-cluster CCSD(T) level of theory with cc-pVTZ basis set. The vertical excitation energies were calculated for the six singlet and two triplet excited states of BrOOCl at the complete active space self-consistent field level of theory and the multi-reference internally contracted configuration interaction level of theory. The scalar relativistic effect on the electronic states of BrOOCl was estimated. The comparison was made for the electronic states of BrOOCl and BrOOBr.

The ground and low-lying excited states of the 5-dehydro-meta-xylylene and 2-dehydro-meta-xylylene triradicals, as well as their derivatives are characterized by the equation-of-motion spin-flip coupled-cluster method with single and double substitutions.The ground and low-lying excited states of the 5-dehydro-meta-xylylene and 2-dehydro-meta-xylylene triradicals, as well as their derivatives are characterized by the equation-of-motion spin-flip coupled-cluster method with single and double substitutions. The effect of substituents in the C2, C4, and C6 positions on electronic states ordering is investigated. In the 5-dehydro-meta-xylylene triradical, which has the 12B2 ground state, charged substituents at C2 stabilize the closed-shell 12A1 state, whereas the NO substituent lowers the 12A2 and 12B1 states. In the 2-dehydro-meta-xylylene triradical with the 14B2 ground state charged substituents also significantly stabilize the 12A1 state and 12B1 state. The observed effects are explained by the nodal structure of the π orbitals and charge localization in the σ radical center.

The potential energy surface for the addition of radical to ethylene using BHandHLYP/6-31G(d) is in excellent agreement with UQCISD(T)/aug-cc-pVTZ.The thermochemistry and kinetics of the H3Si  + C2H4  → H3Si-CH2CH2 reaction were studied using UQCISD(T)/aug-cc-pVTZ//UQCISD/aug-cc-pVDZ. Our results show that the Arrhenius activation energy, E a, for the reaction is 3.3 kcal/mol, substantially lower than the 6 kcal/mol value determined experimentally by Loh et al. [S.K. Loh, D.B. Beach, J.M. Jasinski, Chem. Phys. Lett. 169 (1990) 55]. Loh et al.’s high E a was the result of an estimate of the experimental A-factor that was two orders of magnitude too high. Our calculated rate constant of 1.41 × 106  M−1  s−1 is in very good agreement with the upper bound of 1.81 × 106  M−1  s−1 determined by Loh et al. A study of the thermochemistry and kinetics of the addition reaction using 15 density functional theory methods with 6-31G(d) basis sets indicates that BHandHLYP predicts results in best agreement with high-level theory.

Potential energy surfaces for the lowest excited state of small mercury clusters indicate that excitation energy gap depends sensitively on the nearest-neighbor interatomic distance r. The bottom of the excited energy level is lowered rapidly as the cluster size increases.Cohesive properties of small mercury clusters are analyzed for electronic ground and excited states on the basis of the diatomics-in-molecules method. The theory takes into account ab initio diatomic potential energy curves and configuration mixing of the ground and excited 1Σg states. Increment of binding energies due to s–p mixing is thus predicted in the ground state. Optimized structures of the clusters in the lowest excited state exhibit peculiar D4h and C4v symmetries with significantly small nearest-neighbor distance. As the cluster size increases, the bottom of the excited energy level is lowered rapidly. The calculated potential energy surfaces exhibit strong dependence of excitation energy gap on interatomic separation.

A conformational study of gaseous benzenepropanenitrile by resonant 2-photon ionisation spectroscopy by Danielle E. Martin; Evan G. Robertson; Richard J.S. Morrison (210-215).
Anti and gauche conformers have been identified for gas-phase benzenepropanenitrile (BPN) using one-colour resonant two-photon ionisation (R2PI) spectroscopy. Conformational assignments were based on rotational band contour analysis supported by ab initio calculations. Anti and gauche conformers have been identified for gas-phase benzenepropanenitrile (BPN) using one-colour resonant two-photon ionisation (R2PI) spectroscopy. Conformational assignments were based on rotational band contour analysis supported by ab initio calculations. The anti conformer origin shows a pure b-type rotational contour, whilst the gauche conformer origin exhibits a hybrid band with largely a-type character, resulting from significant rotation in the transition dipole moment. A slight energetic preference for the gauche conformer is observed. The spectrum of the BPN(H2O)1 water complex has also been measured, and a structure in which water acts as a proton donor inferred.

Rates of vibrational quenching of NO (v  = 1–16) in collisions with O2 have been measured at 295 K and rate constants were found to peak close to resonance for the single quantum exchange process between NO and O2.Rates of vibrational quenching of NO (v  = 1–16) in collisions with O2 have been measured at 295 K. NO(v) was formed both by the O(1D) + N2O reaction and the 193 nm photolysis of NO2, and time resolved FT-IR emission was used to follow the behaviour of the vibrationally excited species. Rate constants were found to peak close to resonance for the single quantum exchange process between NO and O2.

The bond dissociation energies (BDEs) in n-alkanes from C1 to C10 have been calculated at the G3B3 level. The BDEs asymptotically reach a constant value.All the C–C fragmentations of the linear n-alkanes, C n H2n+2, for n  = 2 to n  = 10 and the final C–H bond breaking have been calculated with the composite methods G2, G2MP2, G3, G3MP2B3 and G3B3. The results have been compared with the available experimental data.

An ab initio study of the excited states of the vinoxy radical by Katarzyna Piechowska-Strumik; Marie-Christine Bacchus-Montabonel; Yvette Suzanne Tergiman; Jozef E. Sienkiewicz (225-228).
Ab initio potential energy surfaces of the X ∼ , A ∼ and B ∼ states and radial couplings of the vinoxy radical have been calculated in a subspace of two active angles. A quasidiabatic scheme has been developed in the vicinity of the conical intersection and implications on the photodissociation mechanism are discussed.Ab initio potential energy surfaces and radial coupling matrix elements of the vinoxy radical have been calculated in a subspace of two active angles involved in the photodissociation process. A quasidiabatic scheme has been developed in the vicinity of the conical intersection and some implications on the possible photodissociation mechanism of vinoxy from different formation path have been discussed.

Kinetics of OH chemiluminescence in the presence of silicon by Joel M. Hall; Shatra Reehal; Eric L. Petersen (229-233).
Ultraviolet emission from the OH(A–X) transition has been measured in a shock-tube for temperatures from 1050 to 1400 K using mixtures of H2/SiH4/O2 highly diluted in argon. The primary Si-containing reaction found to form OH is SiH + O2  = OH  + SiO, and a rate coefficient for this reaction was estimated.Ultraviolet emission from the OH(A–X) transition near 307 nm has been measured in a shock-tube for T  = 1050–1400 K and P  ≈ 1.2 atm. Experimental mixtures of H2/SiH4/O2/Ar and kinetics calculations were used to identify the elementary reaction forming electronically excited OH (OH) in a Si-containing environment and directly measure its absolute rate coefficient. The primary Si-containing reaction found to form OH is (R0) SiH + O2  = OH  + SiO with a rate expression of k 0 = 1.5 × 10 7 exp ( + 16.4 kcal/RT ) ± 2.3 × 10 10 cm3  mol−1  s−1 This work provides insights into the mechanisms of combustion processes involving silicon.

Different excitation charge transfer and dissociation reactions are studied by crossed molecular beams experiments in the CdI 2 ( 1 Σ g + ) + Li + ( 1 S g ) collisional system and the corresponding absolute cross-sections measured at different collision energies.Charge transfer processes leading to different excited states of lithium atoms in the collision system CdI 2 ( 1 Σ g + ) + Li + ( 1 S g ) have been studied by crossed molecular beams techniques. Absolute emission cross-sections for the different exit channels have been measured as a function of the collision energy in the 0.10–4.00 keV energy range. Also the excitation function for the collision induced dissociation process leading to Cd (5 3P1) has been obtained. Ab initio structure calculations performed at the second order Möller–Plesset level furnish a picture of the non-adiabatic effects for some of the electron transfers experimentally observed.

CILS spectrum of gaseous tetramethyltin.We studied the collision-induced light scattering spectrum of tetramethyltin, Sn(CH3)4, in the gas phase. The spectra are analyzed in view of the dipole–quadrupole (A) and dipole–octopole polarizability (E) giving ∣A∣ = 149(5) au and ∣E∣ = 780(200) au. We show that these experimental results are in reasonable agreement with bond-polarizability considerations.

Proton ordering energetics in ice phases by Gareth A. Tribello; Ben Slater (246-250).
The formation of proton ordered phases such as ice XI shown here, is driven purely by electrostatic forces.Results from first-principles calculations on the subtle energetics of proton ordering in ice phases are shown only to depend on the electrostatic components of the total energy. Proton ordered ice phases can therefore be predicted using electronic structure methods or a tailored potential model. However, analysis of the electron density reveals that high order multipole components, up to hexadecapole, are needed to adequately capture total energy differences between proton ordered and disordered phases. This suggests that current potential models may be unable to reproduce the position of proton ordered ice phases in the phase diagram without extensions to describe high order electrostatics.

Synthesis, X-ray, spectroelectrochemical, and theoretical studies of a tricyanovinyl-capped quaterthiophene: A correlation of semiconductor performance with physical properties by Michael W. Burand; Kari A. McGee; Xiuyu Cai; Demetrio A. da Silva Filho; Jean-Luc Brédas; C. Daniel Frisbie; Kent R. Mann (251-256).
A new tricyanovinyl-substituted quaterthiophene compound has been synthesized and characterized by X-ray crystallography, cyclic voltammetry, spectroelectrochemistry, and theoretical analysis. The molecule forms a semiconducting layer in an n-type thin-film transistor; μ  = 3.7 × 10−6  cm2/Vs. The device properties correlate with the solid-state packing, spectroelectrochemical results, and theoretical modeling.A new tricyanovinyl-substituted quaterthiophene compound has been synthesized and characterized by X-ray crystallography, cyclic voltammetry, spectroelectrochemistry, and theoretical analysis. The tricyanovinyl group provides a dramatic change in the physical properties of the quaterthiophene. The molecule has been tested as the semiconducting layer in an n-type thin-film transistor. The device properties correlate well with the solid-state packing, spectroelectrochemical results, and theoretical modeling.

The effect of temperature on absorption and fluorescence spectra of 4-aminobenzonitrile (ABN) in 1,2-dichloroethane is studied for temperature ranging from 296 K to 343 K.The effect of temperature on absorption and fluorescence spectra of 4-aminobenzonitrile (ABN) in 1,2-dichloroethane is studied for temperature ranging from 296 K to 343 K. The analysis of absorption and fluorescence band shift on the basis of Bilot and Kawski theory [L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621], for the known dipole moment in the ground state μ g  = 5.92 D, and α/a 3  = 0.5 (α is the polarizability and a is the Onsager interaction radius of the solute) yields for ABN: (1) the empirical Onsager interaction radius a  = 3.3 Å, (2) the dipole moment in the excited S1 state μ e  = 7.14 D which agrees very well with the value of μ e  = 7.20 D obtained by Borst et al. [D.R. Borst, T.M. Korter, D.W. Pratt, Chem. Phys. Lett. 350 (2001) 485] from Stark effect studies. Both values of μ e concern free ABN molecule and differ significantly from the values of μ g (8.0 D, 8.5 D and 8.3 D in cyclohexane, benzene and 1,4-dioxane, respectively) obtained by Schuddeboom et al. [W. Schuddeboom, S.A. Jonker, J.M. Warman, U. Leinhos, W. Kühnle, K.A. Zachariasse, J. Phys. Chem. 96 (1992) 10809] from the time-resolved microwave conductivity measurements which are solvent-dependent.The group moment additivity law in the case of ABN molecule is approximately applicable, both in the ground and in the excited electronic state.

Broadening of vibrational levels in X-ray absorption spectroscopy of molecular nitrogen in compound semiconductors by M. Petravic; Q. Gao; D. Llewellyn; P.N.K. Deenapanray; D. Macdonald; C. Crotti (262-266).
Broadening of vibrational levels of molecular nitrogen buried in hexagonal matrices of different lattice constant is consistent with the finite probability of the electron to escape from the π orbital into the matrix. A spectrum from gaseous N2 is shown for comparison.We have used high-resolution near-edge X-ray absorption fine structure spectroscopy to study the N 1s → 1π resonance of N2 trapped below the surface of several compound semiconductors. The vibrational fine structure, observed from all samples under consideration, exhibits substantially larger lifetime linewidth Γ than in isolated N2. A clear correlation between Γ and the lattice constant of the host matrix has been found, indicating that the broadening of vibrational levels is governed by a finite probability of the electron to escape from the π orbital into the matrix.

Density-functional-theory study of the electric-field-induced second harmonic generation (EFISHG) of push–pull phenylpolyenes in solution by Lara Ferrighi; Luca Frediani; Chiara Cappelli; Paweł Sałek; Hans Ågren; Trygve Helgaker; Kenneth Ruud (267-272).
Comparison of experimental data from SHG experiments for a set of push–pull chromophores with their theoretical counterparts obtained at the DFT level of theory by means of response theory. The importance of solvent effects and of the right choice of functional is clearly shown. The solvent effect has been included with the polarizable continuum model.Density-functional theory and the polarizable continuum model have been used to calculate the electric-field-induced second harmonic generation of a series of push–pull phenylpolyenes in chloroform solution. The calculations have been performed using both the Becke 3-parameter Lee–Yang–Parr functional and the recently developed Coulomb-attenuated method functional. Solvation has been investigated by examining the effects of the reaction field, non-equilibrium solvation, geometry relaxation, and cavity field. The inclusion of solvent effects leads to significantly better agreement with experimental observations.

Self-catalyzed hydrogenation and dihydrogen adsorption on titanium carbide nanoparticles by Yufeng Zhao; Anne C. Dillon; Yong-Hyun Kim; Michael J. Heben; S.B. Zhang (273-277).
Totally 17 H2 molecules are adsorbed on a metallocarbohedrene Ti8C12. Ti atoms on the surface of the nanocarbides are capable of coordinating with multiple dihydrogen ligands. The Ti atoms serve as catalyst to mediate the dissociation of H2 to form carbon hydrides.The adsorptions of H2 on metallocarbohedrene Ti8C12, and nanocrystal Ti14C13 are studied using first-principles calculations. The Ti atoms serve as catalyst to mediate the dissociation of H2 to form carbon hydrides, which otherwise would not form. Ti atoms on the surface of the nanocarbides are capable of coordinating with multiple dihydrogen ligands. High hydrogen capacities, 6.1 wt% for Ti8C12 and 7.7 wt% for Ti14C13, were obtained with more than 80% of the H bound in the energy range between 0.17 and 0.89 eV/H2. Once the nanoparticles form a macroscopic material, the amount of chemisorbed hydrogen decreases, but additional hydrogen molecules is then up-taken through physisorption. Our study suggests that TiC nanoparticles have potential for H storage at near ambient conditions.

A new configuration model consisting of bulky CdS with high crystallinity decorated with nanosized TiO2 particles. The possible role of TiO2 nanoparticles is to provide sites for collecting the photoelectrons generated from CdS, enabling thereby an efficient electron–hole separation as depicted.CdS/TiO2 nano-bulk composite (NBC) photocatalyst of a new configuration consisting of bulky CdS with high crystallinity decorated with nanosized TiO2 particles exhibited an unprecedented high rate of hydrogen production under visible light irradiation (λ  ⩾ 420 nm) from water containing sulfide and sulfite ions as hole scavengers. The fabrication method of the composite photocatalysts was critical for their performance. It was demonstrated that this active composite photocatalyst could be applied for practical processes of simultaneous hydrogen production and H2S removal in the treatment of Claus plant tail gas streams or vents of hydrodesulfurization plants.

Stability and structure of cationic sodium hydroxide clusters by P. Feiden; H.-P. Cheng; J. Leygnier; Ph. Cahuzac; C. Bréchignac (283-288).
We present combined experimental and theoretical studies of Na+(NaOH) n clusters. Their stabilities are investigated observing the unimolecular dissociation channels. Ground electronic state geometries and binding energies are obtained using Born–Oppenheimer LSD molecular dynamics calculations. Experimental results are discussed in the light of the calculated data.We present combined experimental and theoretical studies of cationic sodium hydroxide clusters. The stability of Na+(NaOH) n , n  = 4–26, is investigated observing the unimolecular dissociation channels and measuring the unimolecular decays. Ground electronic state geometries and binding energies are obtained using Born–Oppenheimer local spin density molecular dynamics calculations for n  = 1–7. The observed dissociation channels are discussed in the light of the calculated dissociation energies, showing that dynamics effects should play a role in the fragmentation process.

Photo-bleaching of single terrylene molecules in frozen n-hexadecane and n-dodecane at elevated temperatures was explained in terms of enlargement of the cavity occupied by the dopant molecules, deduced from ensemble experiment.Single terrylene molecules were detected in frozen matrices of n-hexadecane and n-dodecane in the broad temperature range, above 50 K. The characteristic feature was fast photo-bleaching of terrylene molecules, accelerated with the temperature increase. The process was related to an increase of the cavity occupied by the dopant molecules at higher temperatures. The cavity enlargement was estimated from the shift of fluorescence and fluorescence excitation spectra of an ensemble of terrylene molecules in the investigated matrices.

The conductivity and viscosity of ionic liquids with acidic counteranion (DMRImH2PO4) depends upon the chainlength of the alkyl(R) group in the imidazolium cation. Polymer electrolytes containing DMEtImH2PO4 show maximum conductivity and are thermally stable up to 225 °C.Ionic liquids with acidic counteranion and having composition: 2,3-dimethyl-1-alkylimidazolium dihydrogenphosphate (DMRImH2PO4, R =  ethyl, butyl, octyl) have been prepared and the effect of alkyl (R) sidechain length on the conductivity and viscosity behavior has been studied. DMEtImH2PO4 with highest conductivity (0.07 S/cm at 120 °C) has been incorporated in polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) to obtain polymer electrolytes in the membrane form. The conductivity of membranes has been found to depend upon the concentration of ionic liquid, phosphoric acid and temperature. Polymer electrolytes containing different ionic liquids are thermally stable up to 225 °C and can be used as high temperature membranes for fuel cells.

Eutectic limit for the growth of carbon nanotubes from a thin iron film by chemical vapor deposition of cyclohexane by A. Grüneis; C. Kramberger; D. Grimm; T. Gemming; M.H. Rümmeli; A. Barreiro; P. Ayala; T. Pichler; Ch. Schaman; H. Kuzmany; J. Schumann; B. Büchner (301-305).
Carbon nanotubes are grown from a 0.6 nm thin iron film as catalyst and cyclohexane as a carbon source. The growth was performed at 720 °C, just above the iron–carbon eutectic point.Carbon nanotubes are grown from a nanometer thin iron film as catalyst by chemical vapor deposition of cyclohexane. We observe growth of carbon nanotubes in a temperature window between 720 and 845 °C. The low synthesis temperature of 720 °C results from the catalyst thickness which lowers the iron–carbon eutectic temperature as compared to bulk iron. At this temperature very little amorphous carbon is deposited on the substrate due to the absence of self pyrolysis of cyclohexane. This points out the importance of the interplay between catalyst thickness and carbon source. The synthesized nanotubes are investigated by resonance Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy.

The Dubinin–Astakhov equation can perfectly describe the CO2 adsorption on single-walled carbon nanotubes.CO2 adsorption on single-walled carbon nanotubes (SWCNTs) was carried out at 273 and 298 K, and the BET, Langmuir, and Dubinin–Astakhov equations were employed to represent the isotherms. Only Dubinin–Astakhov equation could describe the CO2 adsorption on SWCNTs. The Astakhov exponent is less than 2 for CO2 adsorption, indicating the presence of heterogeneous porosities. Furthermore, the SWCNTs’ surface area calculated using the CO2 Dubinin–Astakhov approach at 273 (or 298 K) is fairly consistent with the surface area obtained from N2 BET approach at 77 K, indicating that the CO2 molecules are adsorbed on both internal and external surfaces of the tubes.

Osmium diboride has an unusually large bulk modulus combined with high hardness. The electronic and structural properties of OsB2 and RuB2 have been calculated within LDA. It is shown that the high hardness is the result of covalent bonding between transition metal d states and boron p states.Recently it has been reported that osmium diboride has an unusually large bulk modulus combined with high hardness, and consequently is a most interesting candidate as an ultra-incompressible and hard material. The electronic and structural properties of the transition metal diborides OsB2 and RuB2 have been calculated within the local density approximation (LDA). It is shown that the high hardness is the result of covalent bonding between transition metal d states and boron p states in the orthorhombic structure.

Purification of boron nitride nanotubes by Hua Chen; Ying Chen; Jun Yu; James S. Williams (315-319).
High purity boron nitride nanotubes were synthesized using the ball milling and annealing method and purified by first selective oxidation of boron nitride nanoparticles into boron oxides and subsequent hot water washing dissolving oxide particles and layers.A purification process was developed for the first time for boron nitride (BN) nanotubes. BN nanotubes, prepared using a ball milling and annealing method, contain a high yield of nanotubes and a small amount of BN and metal catalyst particles. The metal particles can be dissolved in an HCl solution. Fine BN nanoparticles and thin layers were first converted to water soluble B2O3 via a partial oxidation treatment at 800 °C. The oxide particles and layers can then be dissolved in hot water. Thermogravimetric analysis has been used to determine an adequate oxidation temperature at which fine BN particles were oxidized.

Finite system and periodicity effects in free energy simulations of membrane proteins by Turgut Baştuğ; Swarna M. Patra; Serdar Kuyucak (320-323).
The model system: gA dimer (blue helix) embedded in a DMPC bilayer and solvated with water and KCl ions. Only the phosphate head groups of lipids (purple balls) are shown for clarity.Periodic boundary conditions are routinely used in molecular dynamics simulations of biological systems, although they are inherently nonperiodic. Simulation artifacts that may arise from such artificial periodicity have not been well studied for membrane proteins. Here we investigate the finite size and periodicity effects in the gramicidin A peptide embedded in lipid bilayer, which offers a simple and well established test system. Comparison of free energies of translocating a potassium ion from bulk to the gramicidin A center in systems with different sizes indicate that there is no discernible effect on the free energy calculations due to finite system size and periodicity.

The asymmetry in word use in coding sequences written in DNA language, motivates a quantification of the differences in the use of mutually direct-complementary triplets, by which, we characterize DNA sequences and compare the coding sequences of exon 1 of β-globin gene of 11 different species.The asymmetry in word use in coding sequences written in DNA language, motivates a quantification of the differences in the use of mutually direct-complementary triplets, by which, we characterize DNA sequences and compare the coding sequences of exon 1 of β-globin gene of 11 different species.

Hydrogen-bonding patterns of cholesterol in lipid membranes by Jérôme Hénin; Christophe Chipot (329-335).
Correlation between the rotation of the cholesterol hydroxyl group and the formation of hydrogen bonds with its lipid environment is examined through molecular dynamics (MD) simulations and compared with recently reported NMR experiments. All atom MD simulations of a fully hydrated 1:2 cholesterol–dimyristoylphosphatidylcholine bilayer have been performed.Correlation between the rotation of the cholesterol hydroxyl group and the formation of hydrogen bonds with its lipid environment is examined through molecular dynamics (MD) simulations and compared with recently reported NMR experiments. All atom MD simulations of a fully hydrated 1:2 cholesterol–dimyristoylphosphatidylcholine bilayer have been performed. Precise reproduction of the cholesterol cell parameters via simulation of its P1-group crystal validates the force field utilized. The lipid–cholesterol hydrogen-bonding pattern reflects the coexistence of alternative dimer motifs with comparable conformer populations, in line with the estimated free energy differences for the rotamers of the cholesterol C―O bond.

Water confined by lipid bilayers: A multiplex CARS study by George W.H. Wurpel; Michiel Müller (336-341).
Multiplex CARS spectra of multilamellar vesicles of DPPC in water. Spectral analysis of the data reveals that the confined interstitial water shows reduced hydrogen bonding (relative to bulk water) and absence of orientational order.The orientational and hydrogen-bonding properties of water confined between lipid bilayers of a multilamellar vesicle of DPPC (dipalmitoyl-sn-glycero-3-phosphocholine) in D2O have been investigated using multiplex coherent anti-Stokes Raman (CARS) microscopy. Spatially resolved analysis of the complete OD- and CH-stretch vibrational spectral region (2200–3200 cm−1) reveals that part of the (confined) interlamellar water has a weaker hydrogen-bond network than bulk water. Polarization dependent studies show negligible orientational order of the interstitial water molecules, in contrast to earlier CARS studies. Possible reasons for this discrepancy are explained in terms of interference between lipid and water resonances.

Theoretical support for using the Δf(r) descriptor by Christophe Morell; André Grand; Alejandro Toro-Labbé (342-346).
When the external potential applied on a molecule changes, its chemical hardness is modified. The dual descriptor characterizes locally the variation of the chemical hardness. According to the sign of the dual descriptor the electro/nucleo philicity of a molecular site can be defined. Thus, the selectivity principle in chemistry could be a manifestation of the Principle of Maximum Hardness.The Δf(r) descriptor characterizes the variations of the absolute hardness when the external potential changes. In this work, the Δf(r) descriptor is regarded through three different theoretical points of view: its relations with the Fukui functions; its links with the covalent interaction energy; and finally its compliance with the Principle of Maximum Hardness. It appears from the three studies that the sign of the descriptor is able to characterize the electrophilic/nucleophilic behavior of a molecular site.

Substituent constants for predicting aromatic molecular quadrupole moments by Dianne Tran; Shana Beg; Aimee Clements; Michael Lewis (347-352).
We present substituent constants for the accurate prediction of quadrupole moments, Θ zz , for mono-, di-, tri- and tetra-substituted aromatics. The aromatic Θ zz value is a good predictor of arene–cation binding enthalpies. The Θ zz values predicted using the developed substituent constants perform well in predicting relative arene–cation binding enthalpies.Work in our group has shown a direct relationship between arene–cation binding enthalpies and the aromatic quadrupole moment (Θ zz ); the more negative the Θ zz value, the greater the arene–cation binding enthalpy. The ability to predict aromatic Θ zz values from the aromatic substitution pattern would therefore allow for the simultaneous prediction of the arene–cation binding enthalpy. Substituent constants were developed for the accurate prediction of Θ zz values for mono-, di-, tri- and tetra-substituted aromatics. The Θ zz values predicted from the developed substituent constants perform very well in determining relative arene–cation binding enthalpies.

Enhancement of carrier mobility in MEH-PPV film prepared under presence of electric field by Quanmin Shi; Yanbing Hou; Jing Lu; Hui Jin; Yunbai Li; Yan Li; Xin Sun; Jun Liu (353-355).
Room temperature time-of-flight hole transients plot for MEH-PPV films prepared under electric field of 0 V/cm, 3 × 103  V/cm and 6 × 103  V/cm, respectively. Electric induced polarization of MEH-PPV can significantly enhance the mobility of hole. The samples were measured under electric field of 105  V/cm and excitation wavelength of 500 nm.Using the time-of-flight photocurrent measurements, the hole transport properties of polarized 2-methoxy, 5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene (MEH-PPV) were investigated. Electric induced polarization of MEH-PPV can significantly enhance the mobility of hole. The hole mobility of the MEH-PPV film fabricated under the presence of vertical electric field is about three times larger than that prepared without field.

A 3-terminal single molecule nanoscale amperometer by M. Hliwa; S. Ami; C. Joachim (356-360).
Schematic representation of a mono-molecular amperometer for intramolecular electronic using a phenyl–pyrene molecule interacting with three nanoscale gold atomic wires.A 3-terminal single molecule transducer is presented which is able to measure tunnel current intensities. The conformation of a pyrene–phenyl molecule is changed under an intramolecular inelastic current effect. This conformation change is detected by a third lateral electrode interacting also with the molecule. The full multi-channel electronic scattering matrix of the device is calculated taking into account the chemisorption of the molecule at one end and the details mechanics of the conformation change of this molecule. A semi-classical model is used to describe the intramolecular transduction effect between the electrons transferred through the molecule and its conformation change. It results a linear transduction curve between the input and the detection currents of the device for a range of tunnel current of interest for mono-molecular electronics.

The luminescence of bridging pyrazine (pyz) and pyridazine (pydz) ligands and their silver(I)–saccharinate (sac) complexes have been studied. Under UV radiation, the pyz and pydz molecules and their silver(I) complexes were shown to be luminescent in solution at room temperature. The experimental emission energies were compared by the HOMO–LUMO energy gaps calculated by density functional theory (DFT).The structures of pyrazine (pyz) and pyridazine (pydz) molecules and their silver(I) complexes with saccharinate (sac), [Ag2(sac)2(pydz)2] and [Ag(sac)(pyz)] n , have been optimized by density functional theory (DFT) to study their luminescence properties. The pyz, pydz and their silver(I) complexes luminesce in solution at room temperature. The luminescence behavior of the ligands and silver(I) complexes was mainly originated from ligand-centered transitions. A very good agreement was found between the HOMO–LUMO energy gap and the experimental emission energy for the silver(I) complexes, but in the case of pyz and pydz, the calculated energies were much higher.

Electronic circular dichroism spectrum of uridine studied by the SAC–CI method by Sareeya Bureekaew; Jun-ya Hasegawa; Hiroshi Nakatsuji (367-371).
SAC-CI method was applied to calculate electronic CD spectrum of a nucleoside, uridine. The experimentally observed CD spectrum was assigned for the first time by comparing with the SAC-CI theoretical spectrum. The origin of CD rotational strength was analyzed and rationalized for the low-lying ππ∗ and nπ∗ excited states.Symmetry-adapted cluster–configuration interaction (SAC–CI) method was applied to calculate electronic CD spectrum of a nucleoside, uridine. Based on the theoretical CD and absorption spectra, the observed peaks in the experimental spectra were assigned. The excited states of uracil, the base part of uridine, were also calculated for comparison. The origin of CD rotational strength for the low-lying π–π∗ and n–π∗ excited states was analyzed. Rotational strength of the π–π∗ transition depends on the magnitude of the electric and magnetic transition dipole moments, while that of the n–π∗ originates from the angle between the two transition moments.

The behaviour of steady-state NQR signals after applying additional RF pulses to the 14N spin-system was experimentally observed. It was found that the additional RF pulse refocuses the steady-state magnetisation and spin-echo signal can be detected. This signal can be refocused again and a train of the signals can be observed.The behaviour of nuclear quadrupole resonance (NQR) signal was studied after applying additional RF pulses to the spin-system which was previously prepared to be in the equilibrium or steady-state. The experiments revealed some peculiarities in the behaviour of the signals which are important for the understanding of the dynamic properties of the quadrupolar spin-system. The experimental results are presented for 4-cyanoperidine and sodium nitrite.

Author Index (377-383).