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The elucidation of the factors determining liquid structures and transport properties of ionic liquids is important for the design and development of ionic liquid electrolytes. This personal account introduces the importance of computational methods for studying ionic liquids. Molecular dynamics simulations provide detailed information on liquid structures of ionic liquid such as the structures of solvated cation complexes in equimolar mixtures of glymes and Li[TFSA] and the effects of the charges of electrode on liquid structure near the electrode. Ab initio calculations reveal that the magnitude of the attraction between ions and conformational flexibility ions play important roles in determining transport properties of ionic liquids. First principle molecular dynamics simulations elucidate why solvated cation complex is stable in the equimolar mixtures, although the Li+‐[TFSA]− interaction is greater than Li+‐glyme interaction. [ABSTRACT FROM AUTHOR]

The performance of 24 vdW‐DF functionals were evaluated. The calculated intermolecular interaction potentials for 11 complexes, which conatain O, S, Se, N, P, F, Cl and Br atoms, were compared with CCSD(T)/CBS level potentials to evaluate their accuracy. The performance depends on the choice of vdW‐functional significantly. The vdW‐DF3‐opt1 functional shows the best performance. The deviation ratios of calculated interaction energies of the complexes using the vdW‐DF3‐opt1 functional to CCSD(T) level interaction energies at the potential minima are −6 to 14 %. As a general tendency, the accuracy is improved in the order of vdW‐DF, vdW‐DF2, and vdW‐DF3, but even if they belong to the same group, the accuracy greatly differs depending on each functional. The calculations of hydrocarbon molecules show better performance compared with heteroatom containing molecules in most cases. The calculations using the vdW‐DF3‐opt1 functional and the best dispersion corrected DFT calculations show nearly identical performance. [ABSTRACT FROM AUTHOR]

A chiral anthranilic pyrrolidine catalyst as a custom-made amine-catalyst was developed for the enantio- and diastereo selective Michael reaction of nitroalkenes with carbonyl compounds. In particular, a peptide-like catalyst in which an α-amino acid is attached to the anthranilic acid skeleton induced the high stereoselectivity of the reaction with aldehydes. Studies of the reaction mechanism indicated that the catalyst exhibits a divergent stereocontrol in the reaction, namely, steric control by a 2-substituted group on the catalyst and hydrogen-bonding control by a carboxylic acid group on the catalyst. [ABSTRACT FROM AUTHOR]

Room temperature ionic liquids (ILs) are stable liquids composed of anions and cations. 1-ethyl-3-methyl-imidazolium (EMIm, EMI) is a popular and important cation that produces thermally stable ILs with various anions. In this study two amide-type anions, bis(trifluoro-methanesulfonyl)amide [N(SO2CF3)2, TFSA, TFSI, NTf2, or Tf2N] and bis(fluorosulfonyl)amide [(N(SO2F)2, FSA, or FSI] were investigated by multinuclear NMR spectroscopy. In addition to EMIm-TFSA and EMIm-FSA, lithium-salt-doped binary systems were prepared (EMIm-TFSA-Li and EMIm-FSA-Li). The spin-lattice relaxation times (T1) were measured by 1H, 19F, and 7Li NMR spectroscopy and the correlation times of 1H NMR, τc(EMIm) (8 × 10-10 to 3 × 10-11 s) for the librational molecular motion of EMIm and those of 7Li NMR, τc(Li) (5 × 10-9 to 2 × 10-10 s) for a lithium jump were evaluated in the temperature range between 253 and 353 K. We found that the bulk viscosity (η) versus τc(EMIm) and cation diffusion coefficient DEMIm versus the rate 1/τc(EMIm) have good relationships. Similarly, linear relations were obtained for the η versus τc(Li) and the lithium diffusion coefficient DLi versus the rate 1/τc(Li). The mean one-jump distances of Li were calculated from τc(Li) and DLi. The experimental values for the diffusion coefficients, ionic conductivity, viscosity, and density in our previous paper were analyzed by the Stokes-Einstein, Nernst-Einstein, and Stokes-Einstein-Debye equations for the neat and binary ILs to clarify the physicochemical properties and mobility of individual ions. The deviations from the classical equations are discussed. [ABSTRACT FROM AUTHOR]

Room-temperature ionic liquids (RTIL, IL) are stable liquids composed of anions and cations. N-methyl-N-propyl-pyrrolidinium (P13, Py13, PYR13, or mppy) is an important cation and produces stable ILs with various anions. In this study two amide-type anions, bis(trifluoromethanesulfonyl)amide [N(SO2CF3)2, TFSA, TFSI, NTf2, or Tf2N] and bis(fluorosulfonyl)amide [N(SO2F)2, FSA, or FSI], were investigated. In addition to P13-TFSA and P13-FSA, lithium salt doped samples were prepared (P13-TFSA-Li and P13-FSA-Li). The individual ion diffusion coefficients (D) and spin-lattice relaxation times (T1) were measured by 1H, 19F, and 7Li NMR. At the same time, the ionic conductivity (σ), viscosity (η), and density (ρ) were measured over a wide temperature range. The van der Waals volumes of P13, TFSA, FSA, Li(TFSA)2, and Li(FSA)3 were estimated by molecular orbital calculations. The experimental values obtained in this study were analyzed by the classical Stokes-Einstein, Nernst-Einstein (NE), and Stokes-Einstein-Debye equations and Walden plots were also made for the neat and binary ILs to clarify physical and mobile properties of individual ions. From the temperature-dependent velocity correlation coefficients for neat P13-TFSA and P13-FSA, the NE parameter 1-ξ was evaluated. The ionicity (electrochemical molar conductivity divided by the NE conductivity from NMR) and the 1-ξ had exactly the same values. The rotational and translational motions of P13 and jump of a lithium ion are also discussed. [ABSTRACT FROM AUTHOR]

The CCSD(T) level interaction energies of eight orientations of nitrobenzene-benzene complexes and nine orientations of nitrobenzene dimers at the basis set limit have been estimated. The calculated interaction energy of the most stable slipped-parallel (Cs) nitrobenzene-benzene complex was -4.51 kcal/mol. That of the most stable slipped-parallel (antiparallel) (C2h) nitrobenzene dimer was -6.81 kcal/mol. The interaction energies of these complexes are significantly larger than that of the benzene dimer. The T-shaped complexes are substantially less stable. Although nitrobenzene has a polar nitro group, electrostatic interaction is always considerably weaker than the dispersion interaction. The dispersion interaction in these complexes is larger than that in the benzene dimer, which is the cause of the preference of the slipped-parallel orientation in these complexes. [ABSTRACT FROM AUTHOR]

The MP2 (the second-order Mo\ller-Plesset calculation) and CCSD(T) (coupled cluster calculation with single and double substitutions with noniterative triple excitations) interaction energies of all-trans n-alkane dimers were calculated using Dunning's [J. Chem. Phys. 90, 1007 (1989)] correlation consistent basis sets. The estimated MP2 interaction energies of methane, ethane, and propane dimers at the basis set limit [EMP2(limit)] by the method of Helgaker et al. [J. Chem. Phys. 106, 9639 (1997)] from the MP2/aug-cc-pVXZ (X=D and T) level interaction energies are very close to those estimated from the MP2/aug-cc-pVXZ (X=T and Q) level interaction energies. The estimated EMP2(limit) values of n-butane to n-heptane dimers from the MP2/cc-pVXZ (X=D and T) level interaction energies are very close to those from the MP2/aug-cc-pVXZ (X=D and T) ones. The EMP2(limit) values estimated by Feller's [J. Chem. Phys. 96, 6104 (1992)] method from the MP2/cc-pVXZ (X=D, T, and Q) level interaction energies are close to those estimated by the method of Helgaker et al. from the MP2/cc-pVXZ (X=T and Q) ones. The estimated EMP2(limit) values by the method of Helgaker et al. using the aug-cc-pVXZ (X=D and T) are close to these values. The estimated EMP2(limit) of the methane, ethane, propane, n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane dimers by the method of Helgaker et al. are -0.48, -1.35, -2.08, -2.97, -3.92, -4.91, -5.96, -6.68, -7.75, and -8.75 kcal/mol, respectively. Effects of electron correlation beyond MP2 are not large. The estimated CCSD(T) interaction energies of the methane, ethane, propane, and n-butane dimers at the basis set limit by the method of Helgaker et al. (-0.41, -1.22, -1.87, and -2.74 kcal/mol, respectively) from the CCSD(T)/cc-pVXZ (X=D and T) level interaction energies are close to the EMP2(limit) obtained using the same basis sets. The estimated EMP2(limit) values of the ten dimers were fitted to the form m0+m1X (X is 1 for methane, 2 for ethane, etc.). The obtained m0 and m1 (0.595 and -0.926 kcal/mol) show that the interactions between long n-alkane chains are significant. Analysis of basis set effects shows that cc-pVXZ (X=T, Q, or 5), aug-cc-pVXZ (X=D, T, Q, or 5) basis set, or 6-311G** basis set augmented with diffuse polarization function is necessary for quantitative evaluation of the interaction energies between n-alkane chains. [ABSTRACT FROM AUTHOR]

The intermolecular interaction energy of the toluene dimer has been calculated with the ARS-F model (a model chemistry for the evaluation of intermolecular interaction energy between ARomatic Systems using Feller’s method), which was formerly called as the AIMI model III. The CCSD(T) (coupled cluster calculations with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the second-order Mo\ller–Plesset perturbation interaction energy at the basis set limit obtained by Feller’s method and the CCSD(T) correction term obtained using a medium-size basis set. The cross (C2) dimer has the largest (most negative) interaction energy (-4.08 kcal/mol). The antiparallel (C2h) and parallel (CS) dimers (-3.77 and -3.41 kcal/mol, respectively) are slightly less stable. The dispersion interaction is found to be the major source of attraction in the toluene dimer. The dispersion interaction mainly determines the relative stability of the stacked three dimers. The electrostatic interaction of the stacked three dimers is repulsive. Although the T-shaped and slipped-parallel benzene dimers are nearly isoenergetic, the stacked toluene dimers are substantially more stable than the T-shaped toluene dimer (-2.62 kcal/mol). The large dispersion interaction in the stacked toluene dimers is the cause of their enhanced stability. [ABSTRACT FROM AUTHOR]

Intermolecular interaction energies of 12 orientations of C3F8 dimers were calculated with electron correlation correction by the second-order Møller-Plesset perturbation method. The antiparallel C2h dimer has the largest interaction energy (-1.45 kcal/mol). Electron correlation correction increases the attraction considerably. Electrostatic energy is not large. Dispersion is mainly responsible for the attraction. Orientation dependence of the interaction energy of the C3F8 dimer is substantially smaller than that of the C3H8 dimer. The calculated interaction energy of the C3F8 dimer at the potential minimum is 78% of that of the C3H8 dimer (-1.85 kcal/mol), whereas the interaction energies of the CF4 and C2F6 dimers are larger than those of the CH4 and C2H6 dimers. The intermolecular separation in the C3F8 dimer at the potential minimum is substantially larger than that in the C3H8 dimer. The larger intermolecular separation due to the steric repulsion between fluorine atoms is the cause of the smaller interaction energy of the C3F8 dimer at the potential minimum. The calculated intermolecular interaction energy potentials of the C3F8 dimers using an all atom model OPLS-AA (OPLS all atom model) force field and a united atom model force field were compared with the ab initio calculations. Although the two force fields well reproduces the experimental vapor and liquid properties of perfluoroalkenes, the comparison shows that the united atom model underestimates the potential depth and orientation dependence of the interaction energy. The potentials obtained by the OPLS-AA force field are close to those obtained by the ab initio calculations. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The intermolecular interaction energies of naphthalene dimers have been calculated by using an aromatic intermolecular interaction model (a model chemistry for the evaluation of intermolecular interactions between aromatic molecules). The CCSD(T) (coupled cluster calculations with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the second-order Møller–Plesset perturbation interaction energy near saturation and the CCSD(T) correction term obtained using a medium-size basis set. The estimated interaction energies of the set of geometries explored in this work show that two structures emerge as being the lowest energy, and may effectively be considered as isoenergetic on the basis of the errors inherent in out extrapolation procedure. These structures are the slipped-parallel (C[sub i]) structure (-5.73 kcal/mol) and the cross (D[sub 2d]) structure (-5.28 kcal/mol). The T-shaped (C[sub 2v]) and sandwich (D[sub 2h]) dimers are substantially less stable (-4.34 and -3.78 kcal/mol, respectively). The dispersion interaction is found to be the major source of attraction in the naphthalene dimer. The electrostatic interaction is substantially smaller than the dispersion interaction. The large dispersion interaction is the cause of the large binding energies of the cross and slipped-parallel dimers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The π/π interaction (stacking) and N(B)–H/π interaction of the borazine (B[sub 3]N[sub 3]H[sub 6]) dimer were theoretically studied. In contrast to the benzene dimer, the gauche parallel-stacked dimer of borazine was energetically minimum, and total interaction energy was about 1 kcal/mol more negative than that of the parallel-stacked dimer of benzene. The gauche parallel-stacked dimer of borazine was more stable than slipped parallel-stacked dimers and T-shape dimers. The syn parallel-stacked dimer of borazine was energetically unstable and it was less stable than the slipped syn parallel-stacked structures. The electron correlation effect at higher than the second-order Møller–Plesset (MP2) level on the molecular interaction energy was quite small. The dispersion term and the charge transfer term had large contribution in almost all the borazine dimer formations, except the syn parallel-stacked dimer. In the case of syn parallel-stacked dimer, contribution of the dispersion term was dominant. The electrostatic term had only small contribution for all the dimer formations. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The energy profile of the interconversion path between the T-shape and slipped-parallel dimers has been studied by high level ab initio calculations. The CCSD(T) (coupled cluster calculation with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the MP2 (the second-order Møller-Plesset calculation) interaction energy near the basis set limit and the CCSD(T) correction term using the 6-311G[sup *] basis set. The calculated CCSD(T) level energy profile has shown that the potential is very flat and the interconversion barrier height is very small (around 0.2 kcal/mol). The MP2 calculations using large basis sets near the basis set limit considerably overestimate the attraction of the slipped-parallel dimer, which indicates the importance of higher level electron correlation correction for studying the potential energy surface of the benzene dimer. [ABSTRACT FROM AUTHOR]

Intermolecular interaction energies of eight orientation CF[sub 4] dimers and seven orientation C[sub 2]F[sub 6] dimers were calculated with electron correlation correction by the second-order Moller-Plesset perturbation (MP2) method. The D[sub 3d] CF[sub 4] dimer and C[sub 2h] C[sub 2]F[sub 6] dimer have the largest binding energies. Electron correlation correction increases the attraction considerably, while the effects of electron correlation beyond MP2 are small. Electrostatic and induction energies are not large in all cases. This indicates that dispersion interaction is mainly responsible for the attraction. The calculated binding energy of the CF[sub 4] dimer (0.69 kcal/mol) is about 60% larger than that of the CH[sub 4] dimer (0.44 kcal/mol), while the binding energy of the C[sub 2]F[sub 6] dimer (1.02 kcal/mol) is close to that of the C[sub 2]H[sub 6] dimer (0.90 kcal/mol). The intermolecular separations (C···C distance) in the CF[sub 4] and CH[sub 4] dimers at the potential minima are close (4.0 and 3.8 Å, respectively), while the separation in the C[sub 2]F[sub 6] dimer (4.8 Å) is appreciably larger than that in the C[sub 2]H[sub 6] dimer (4.0 Å). The larger intermolecular separation in the C[sub 2]F[sub 6] dimer reduces dispersion energy. Therefore the binding energies of the C[sub 2]F[sub 6] and C[sub 2]F[sub 6] dimers are not largely different. The molar volume of C[sub 2]F[sub 6] is substantially larger than that of C[sub 2]F[sub 6] due to bulky fluorine atoms. The small difference of the binding energies suggests that the large molecular volume of perfluoroalkanes is the cause of their small heats of vaporization per volume. [ABSTRACT FROM AUTHOR]

Studies the effects of basis set and electron correlation on the calculated interaction energies of hydrogen bonding complexes. Use of the Dunning's correlation consistent basis sets in the study; Effects of electron correlation; Effects of basis set; Interaction energies at the basis-set limit.

Calculates the internal rotational barrier heights of biphenyl with the Dunning correlation consisted basis sets and the electron correlation correction by the second order Moller-Plesset method. Calculations of benzene dimers suggesting that the dispersion interaction increased the relative stability of the coplanar conformer.

We investigated the hydration states of cholinium phosphate-type ionic liquids (ILs) in relation to ion structure, focusing on the influence of the hydroxyl group of the cation and the alkyl chain length of the anion. Water activity measurements provided information on the macroscopic hydration states of the hydrated ILs, while NMR measurements and molecular dynamics simulations clearly showed the microscopic interactions and coordination of the water molecules. The hydrogen bonding networks in these ILs were influenced by the anion structure and water content, and the mobility of water molecules was influenced by the number of hydroxyl groups in the cation and anion. The hydrogen-bonding networks in cholinium phosphate-type ILs were influenced by both anion structure and water content. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • In crossover alkyl chain length of cation (n = 6), anion size effects of RTIL were obviously observed. • Asymmetric molecular anions with asymmetric surface charge distributions promote crystallization upon cooling. • Calculated stabilization energy explains the observed data. Abstract Anion effects on phase behaviors of 1-butyl-3-methylimidazolium ([C 4 mim]+) and 1-hyexyll-3-methylimidazolium ([C 6 mim]+) based room-temperature ionic liquids (RTILs) were examined at low temperature (LT). By simultaneous X-ray diffraction and differential scanning calorimetry measurements, solid phases were determined at LT. Depending on the molecular interactions, amorphization, crystallization, and cold crystallization were clearly distinguished. In the solid phases, the anion effect differs significantly from the alkyl chain length effect of the 1-alkyl-3-methylimidazolium cations, [C n mim]+. [ABSTRACT FROM AUTHOR]

Investigates the intermolecular interaction potential of the carbon dioxide dimer. Absence of an inversion barrier; Calculation of the energy difference of the dimer; Use of diffuse polarization in evaluating the essential attractive interactions.

The 2D patterns of structural isomers in isobutenyl compounds possessing long alkyl tails were systematically investigated by using scanning tunneling microscopy at solid/liquid interface. The alkyl chains with carbon numbers of 18 and 19 were linked with either amide or ester bonds at different positions of naphthalene unit. In addition to the 2,3-substituted isobutenyl compounds of our previous studies, the 2,6- and heterogeneously substituted 2,3–2,6-isobutenyl compounds were investigated in the present study. In the 2,6-substituted amide compounds ( 2,6-NC n ), the intermolecular hydrogen bonds lead to the columnar structure without the interdigitation of alkyl chains, whereas 2,6-substituted ester compounds ( 2,6-OC n ) showed the 2D structure with interdigitated alkyl chains. In the 2,3–2,6-substituted compounds containing amide linked alkyl chains ( 2,3-2,6-NC n ), the alkyl chain unit exhibited a herring bone-like arrangement possibly due to the defined structural framework based on a intramolecular hydrogen bond. In contrast, flexibility of 2,3-2,6-OC n allowed to form the 2D structure with parallel alignment of the naphthalene unit and interdigitation of alkyl chains. The rearranged structural isomers of isobutenyl compounds could be obtained by the thermal reaction of tandem Claisen rearrangement (TCR). The different orientations of naphthalene units in the 2,6-NC n TCR were found depending on the alkyl chain length in order to avoide the steric repulsion between alkyl chains, namely odd-even effect of alkyl chains was emerged. In the case of 2,6-OC n TCR , odd-even effect was projected as presence or absence of alkyl chain interdigitation. The alkyl chain length had no influence on the 2D structures of 2,3-2,6-NC n TCR , whereas 2D structures of 2,3-2,6-OC n TCR showed slight difference in the orientation of naphthalene units depending on the alkyl chain length. These results suggest that a wide variety of 2D structures can be formed by structural isomers with different alkyl chain length, and that the TCR can be used for tuning the emergence of odd-even effect. [ABSTRACT FROM AUTHOR]

The strengths of π-bonds in a series of fluorinated ethylenes have been computationally investigated, and the potential energy surfaces for thermal C C bond rotation in fluorinated ethylenes, as well as in ethylene, have been explored. The computed thermal rotational barrier values and the π-bond strengths obtained using Benson’s procedure show parallel trends. Our calculations indicate that the π-bond in CH 2 = CHF is slightly stronger, and the one in CF 2 = CF 2 is noticeably weaker than that in CH 2 = CH 2 . In addition, the stabilization effects of fluorine substitution have been evaluated for fluorinated ethylene molecules and for singlet biradical thermal rotation transition states. Considering these fluorine substituent effects, the change in the π-bond strength of a series of fluorinated ethylenes can be qualitatively interpreted. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon materials (NDCs) play an important role in various fields. A great deal of effort has been devoted to obtaining carbon materials with a high nitrogen content; however, much is still unknown about the structure of the nitrogen-doped materials and the maximum nitrogen content possible for such compounds. Here, we demonstrate an interesting relationship between the N/C molar ratio and the N content of NDCs. The upper limit for the nitrogen content of NDCs that might be achieved was estimated and found to strongly depend on the carbonization temperature (14.32 wt % at 1000 °C and 21.66 wt % at 900 °C), irrespective of the precursor or preparation conditions. Simulations suggest that, especially in the carbon architectures obtained at high temperatures, nitrogen atoms are always located on separate hexagon moieties in a graphitic configuration, thereby yielding a critical N/C molar ratio very close to the value estimated from the experimental results. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon materials (NDCs) play an important role in various fields. A great deal of effort has been devoted to obtaining carbon materials with a high nitrogen content; however, much is still unknown about the structure of the nitrogen-doped materials and the maximum nitrogen content possible for such compounds. Here, we demonstrate an interesting relationship between the N/C molar ratio and the N content of NDCs. The upper limit for the nitrogen content of NDCs that might be achieved was estimated and found to strongly depend on the carbonization temperature (14.32 wt % at 1000 °C and 21.66 wt % at 900 °C), irrespective of the precursor or preparation conditions. Simulations suggest that, especially in the carbon architectures obtained at high temperatures, nitrogen atoms are always located on separate hexagon moieties in a graphitic configuration, thereby yielding a critical N/C molar ratio very close to the value estimated from the experimental results. [ABSTRACT FROM AUTHOR]

Ionicliquids (IL) composed of a quaternary ammonium cation havingan ether chain, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium (DEME)are electrochemically stable and used in electric double layer capacitorsand also one of important candidates to use lithium secondary batteries.In this study, three DEME-based ILs with anions BF4, CF3BF3, and N(SO2CF3)2were studied by measuring temperature dependences of ionic conductivityσ, viscosity η and density ρ. Also ion diffusioncoefficients Danionand Dcationwere obtained by NMR spectroscopy in the wide temperaturerange. Using the classical Stokes–Einstein (SE) and Nernst–Einstein(NE) equations, the relationships between η and D, and σ and Dwere evaluated. The lithiumsalt doping effects were studied by 7Li NMR spectroscopy.The lithium ion diffusion was slower than other ion diffusion at everytemperature. Arrhenius-type plots of 7Li T1showed minima in the three doped samples. Then one-jumpdistance of lithium ion was estimated in the temperature range between273 and 373 K. [ABSTRACT FROM AUTHOR]

We have measured physicochemicalproperties of five alkyltrimethylammonium cation-based room-temperatureionic liquids and compared them with those obtained from computationalmethods. We have found that static properties (density and refractiveindex) and transport properties (ionic conductivity, self-diffusioncoefficient, and viscosity) of these ionic liquids show close relationswith the length of the alkyl chain. In particular, static propertiesobtained by experimental methods exhibit a trend complementary tothat by computational methods (refractive index ∝ [polarizability/molarvolume]). Moreover, the self-diffusion coefficient obtained by moleculardynamics (MD) simulation was consistent with the data obtained bythe pulsed-gradient spin–echo nuclear magnetic resonance technique,which suggests that computational methods can be supplemental toolsto predict physicochemical properties of room-temperature ionic liquids. [ABSTRACT FROM AUTHOR]

Stable geometries and stabilizationenergies (Eform) of the alkali metal complexeswith bis(fluorosulfonyl)amide,(fluorosulfonyl)(trifluoromethylslufonyl)amide and bis(trifluoromethylsulfonyl)amide(FSA–, FTA–and TFSA–) were studied by ab initiomolecular orbital calculations.The FSA–complexes prefer the bidentate structuresin which two oxygen atoms of two SO2groups have contactwith the metal cation. The FTA–and TFSA–complexes with Li+and Na+prefer the bidentatestructures, while the FTA–and TFSA–complexes with Cs+prefer tridentate structures in whichthe metal cation has contact with two oxygen atoms of an SO2group and one oxygen atom of another SO2group. The twostructures are nearly isoenergetic in the FTA–andTFSA–complexes with K+and Rb+. The magnitude of Eformdepends on thealkali metal cation significantly. The Eformcalculated for the most stable TFSA–complexeswith Li+, Na+, K+, Rb+and Cs+cations at the MP2/6-311G** level are −137.2,−110.5, −101.1, −89.6, and −84.1 kcal/mol,respectively. The viscosity and ionic conductivity of the alkali TFSAmolten salts have strong correlation with the magnitude of the attraction.The viscosity increases and the ionic conductivity decreases withthe increase of the attraction. The melting points of the alkali TFSAand alkali BETA molten salts also have correlation with the magnitudeof the Eform, which strongly suggeststhat the magnitude of the attraction play important roles in determiningthe melting points of these molten salts. The anion dependence ofthe Eformcalculated for the complexesis small (less than 2.9 kcal/mol). This shows that the magnitude ofthe attraction is not the cause of the low melting points of alkaliFTA molten salts compared with those of corresponding alkali TFSAmolten salts. The electrostatic interactions are the major sourceof the attraction in the complexes. The electrostatic energies forthe most stable TFSA–complexes with the five alkalimetal cations are −140.3, −119.4, −104.1, −96.9,and −91.1 kcal/mol, respectively. The induction interactionsalso contribute to the attraction. In particular, the induction interactionsare large in the Li+complexes. The induction energiesfor the five complexes are −46.6, −25.2, −17.5,−13.3, and −10.4 kcal/mol, respectively. [ABSTRACT FROM AUTHOR]

Intermolecularinteraction in the 1,2,5-chalcogenadiazole dimerswas studied by ab initio molecular orbital calculations. EstimatedCCSD(T) interaction energies for the thia-, selena- and tellura-diazoledimers are −3.14, −5.29, and −12.42 kcal/mol,respectively. The electrostatic and dispersion interactions are themajor sources of the attraction in the dimers, although it was claimedthat the orbital mixing (charge-transfer interaction) was the mostprominent contribution to the stabilization. The induction (inducedpolarization) interaction also contributes largely to the attractionin the telluradiazole dimer. The large electrostatic and inductioninteractions are responsible for the strong attraction in the telluradiazoledimer. The short-range (orbital–orbital) interaction (sum ofthe exchange-repulsion and charge-transfer interactions) is repulsive.The directionality of the interactions increases in order of S

Two ionic liquids (ILs) based on the BF4–anion are studied by 1H, 11B,and 19F NMR spectroscopy by measuring self-diffusion coefficients(D) and spin–lattice relaxation times (T1). The cations are 1-ethyl-3-methylimidazolium(EMIm)and 1-butyl-3-methylimidazolium (BMIm). Since two NMR nuclei (11B and 19F) of BF4–exhibit narrow lines and high sensitivity, the 11B and 19F NMR measurements of DBF4and T1(BF4) were performed in a wide temperaturerange. The temperature-dependent behaviors of T1(19F) and T1(11B) were remarkably different, although the values of DBF4(19F) and DBF4(11B) almost agreed. Since the Arrhenius plots of T1’s for 1H, 19F,and 11B exhibited T1minima,the correlation times τc(1H), τc(19F), and τc(11B)were evaluated. The D(cation) and D(BF4) were plotted against 1/τc(1H) and 1/τc(19F), respectively,and the relationships between translational and rotational motionare discussed. The translational diffusion of the cations is relatedto molecular librational motion and that of BF4is coupledwith reorientational motion. The τc(11B) derived from 11B T1canbe attributed to a local jump. From the plots of the classical Stokes–Einstein(SE) equation, the empirical cvalues, which wereoriginally derived by theoretical boundary conditions, were estimatedfor each ion. The empirical c(BF4) wasabout 4.45, while the cvalues of thecations were smaller than 4. [ABSTRACT FROM AUTHOR]

Abstract: Growth-blocking peptide (GBP) is a member of an insect cytokine family with diverse functions including growth and immunity controls. Members of this cytokine family have been reported in 15 species of Lepidoptera, and we have recently identified GBP-like peptides in Diptera such as Lucilia cuprina and Drosophila melanogaster, indicating that this peptide family is not specific to Lepidoptera. In order to extend our knowledge of this peptide family, we purified the same family peptide from one of the tenebrionids, Zophobas atratus, 1 [1] Zophobas atratus Zmc mRNA for cytokine, AB243070. isolated its cDNA, and sequenced it. The Z. atratus GBP sequence together with reported sequence data of peptides from the same family enabled us to perform BLAST searches against EST and genome databases of several insect species including Coleoptera, Diptera, Hymenoptera, and Hemiptera and identify homologous peptide genes. Here we report conserved structural features in these sequence data. They consist of 19–30 amino acid residues encoded at the C terminus of a 73-152 amino acid precursor and contain the motif C-x(2)-G-x(4,6)-G-x(1,2)-C-[KR], which shares a certain similarity with the motif in the mammalian EGF peptide family. These data indicate that these small cytokines belonging to one family are present in at least five insect orders. [Copyright &y& Elsevier]

The interaction energy potentials for six orientations of the fucose-water complex were calculated for evaluating the magnitude of the CH/O interactions in the complex. The calculations show that the C-H bonds of the nonpolar surface of fucose prefer to have contact with the oxygen atom of the water. The substantial attraction exists between the C-H bonds of fucose and water. The interaction energy calculated for the fucose-water complex at the MP2/aug-cc-pVTZ level is −2.55 kcal/mol. The CH/O interactions in the fucose-water complex are significantly larger than those in the cyclohexane-water complex (−1.13 kcal/mol), which shows that the oxygen atoms of fucose enhance the CH/O interactions. The electrostatic and dispersion interactions are responsible for the attraction in the CH/O interactions in the fucose-water complex, while the electrostatic contributions to the attraction in the CH/O interactions in the cyclohexane-water complex is small. The DFT-SAPT calculations also show that the electrostatic interactions are responsible for the larger attraction in the fucose-water complex. These results suggest that the nature of the CH/O interactions between carbohydrate and water is significantly different from that of the CH/O interactions between saturated hydrocarbon and water. [ABSTRACT FROM AUTHOR]

Feeding activities of animals, including insects, are influenced by various signals from the external environment, internal energy status, and physiological conditions. Full understanding of how such signals are integrated to regulate feeding activities has, however, been hampered by a lack of knowledge about the genes involved. Here, we identified an anorexic Drosophila melanogaster mutant (GS1189) in which the expression of a newly identified gene, Anorexia (Anox), is mutated. In Drosophila larvae, Anox encodes an acyl-CoA binding protein with an ankyrin repeat domain that is expressed in the cephalic chemosensory organs and various neurons in the central nervous system (CNS). Loss of its expression or disturbance of neural transmission in Anox-expressing cells decreased feeding activity. Conversely, overexpression of Anox in the CNS increased food intake. We further found that Anox regulates expression of the insulin receptor gene (dInR); overexpression and knockdown of Anox in the CNS, respectively, elevated and repressed dInR expression, which altered larval feeding activity in parallel with Anox expression levels. Anox mutant adults also showed significant repression of sugar-induced nerve responses and feeding potencies. Although Anox expression levels did not depend on the fasting and feeding states cycle, stressors such as high temperature and desiccation significantly repressed its expression levels. These results strongly suggest that Anox is essential for gustatory sensation and food intake of Drosophila through regulation of the insulin signaling activity that is directly regulated by internal nutrition status. Therefore, the mutant strain lacking Anox expression cannot enhance feeding potencies even under starvation. [ABSTRACT FROM AUTHOR]

The CH/π contact structures of the fucose--phenol and fucose--indole complexes and the stabilization energies by formation of the complexes (Eform) were studied by ab initio molecular orbital calculations. The three types of interactions (CH/π and OH/π interactions and OH/O hydrogen bonds) were compared and evaluated in a single molecular system and at the same level of theory. The Eform calculated for the most stable CH/π contact structure of the fucose--phenol complex at the CCSD(T) level (-4.9 kcal/mol) is close to that for the most stable CH/π contact structure of the fucose--benzene complex (-4.5 kcal/mol). On the other hand the most stable CH/π contact structure of the fucose--indole complex has substantially larger Eform (-6.5 kcal/mol). The dispersion interaction is the major source of the attraction in the CH/π contact structures of the fucose--phenol and fucose--indole complexes as in the case of the fucose--benzene complex. The electrostatic interactions in the CH/π contact structures are small (less than 1.5 kcal/mol). The nature of the interactions between the nonpolar surface of the carbohydrate and aromatic rings is completely different from that of the conventional hydrogen bonds where the electrostatic interaction is the major source of the attraction. The distributed multipole analysis and DFT-SATP analysis show that the dispersion interactions in the CH/π contact structure of fucose--indole complex are substantially larger than those in the CH/π contact structures of fucose--benzene and fucose--phenol complexes. The large dispersion interactions are responsible for the large Eform for the fucose--indole complex. [ABSTRACT FROM AUTHOR]

This article proposes a new method for the accurate evaluation of the lattice energies (stabilization energies associated with the formation of crystals from isolated molecules) of molecular crystals by a combination of DFT and MP2 calculations. The interactions of well-separated molecules were evaluated by periodic DFT calculations. The interactions with neighboring molecules were evaluated by MP2-level two-body interaction energy calculations with the neighboring molecules. The sublimation energies calculated for crystals of urea and hexamine using the proposed method (21.2 and 20.0 kcal/mol, respectively) were close to the experimental values (20.9−23.6 and 17.7−18.8 kcal/mol, respectively). The lattice energies calculated for the two crystals by the proposed method are significantly different from those obtained by DFT calculations, suggesting that the dispersion contribution to the lattice energy is significant even in the crystal, where molecules are bound by hydrogen bonds. Lattice energies calculated by changing the range of the neighboring molecules show that the nearest-neighboring molecules are mainly responsible for the dispersion interactions in the crystals. [ABSTRACT FROM AUTHOR]

Abstract: The lattice energies for the enantiopure and racemic crystals of α-(trifluoromethyl)lactic acid were calculated by a combination of the DFT calculations with the periodic boundary condition and the MP2 calculations of the interactions with neighboring molecules. The lattice energies calculated for the two crystals (−16.56 and −17.35kcal/mol, respectively) show that the racemic crystals are thermodynamically more stable, although the racemic crystals sublime faster than the enantiopure crystals. The calculations suggest that the relative thermodynamic stability is not the cause of the faster sublimation rate of the racemic crystals compared with the enantiopure crystals. Although the crystals have hydrogen-bonding networks, the dispersion interactions contribute to the lattice energies significantly. The MP2 calculations for the evaluation of the dispersion interactions with the neighboring molecules are important for an accurate evaluation of the lattice energies. The relative thermodynamic stability of the two crystals is not determined solely by the hydrogen bonds. The interactions with other neighboring molecules also play important roles in determining the relative stability. We demonstrate that the geometry optimization is essential for an accurate evaluation of the lattice energy by the first principle calculation. The interaction energies calculated using the structure by X-ray diffraction often have large errors. [Copyright &y& Elsevier]

Abstract: To examine the mechanism by which insects change their food preferences, a simple method was developed to measure their preferences. By using this method, we demonstrated preference of Drosophila melanogaster larvae of the y control strain for a food based on soybeans over one based on cornmeal. We then screened for mutant strains with food preferences clearly different from the control y strain, using the Gene Search collection of P-element insertions (GS strains). Among 380 GS strains screened using an assay plate-containing soybean and corn tastants, we identified one mutant, GS1189 that did not show any preference for either of the foods. Further behavioral assays indicated that the GS1189 larvae could have impaired olfactory and gustatory systems. The fact that the CG33071 gene expression was inactivated by the P-element insertion in the GS1189 strain, and that reversion of this gene completely recovered the normal food preference, indicates that this gene contributes to the control of food preferences in Drosophila larvae. [Copyright &y& Elsevier]

The intermolecular interaction energies for the 1-butyl-3-methylimidazolium (bmim) and 1,3-dimethylimidazolium (dmim) complexes with halide anions were studied using the MP2/6-311G** level ab initio calculations. The DGDZVP basis set was used for iodide. Calculated formation energies for the bmim complexes with Cl, Br and I anions from isolated ions were -88.4, -86.4 and -79.0 kcal/mol, respectively. Distributed multipole analysis shows that the electrostatic interaction is the major source of the attraction. The induction energy is 13-21% of the total interaction energy. The electrostatic interaction mainly determines the magnitude of the attraction and the stable geometries of the complexes. In the most stable geometries for the [bmim]Cl and [bmim]Br complexes, the anion locates within the imidazolium plane and have close contacts with the C2-H of bmim. On the other hand the [bmim]I complex has another nearly isoenergetic geometry, in which the I anion locates above the imidazolium plane. The preferential location of anions agrees well with those observed in the crystals. The small Cl and Br anions prefer to locate within the plane due to the stabilization by the electrostatic interaction. The geometries, in which the Cl and Br anions locate above or below the imidazolium plane, are less stable due to the anisotropy of the electrostatic interaction. The anisotropy of electrostatic interaction decreases rapidly with distance. Therefore the large I anion prefers both locations. [ABSTRACT FROM AUTHOR]

Geometries and interaction energies of benzene complexes with pyridine, pyridinium, N- methylpyridinium were studied by ab initio molecular orbital calculations. Estimated CCSD(T) interaction energies of the complexes at the basis set limit were -3.04, -14.77, and -9.36 kcal/mol, respectively. The interactions in the pyridinium and N-methylpyridinium complexes should be categorized into a cationhr interaction, because the electrostatic and induction interactions greatly contribute to the attraction. On the other hand, the interaction in the pyridine complex is a π/π interaction. The dispersion interaction is mainly responsible for the attraction in the benzene-pyridine complex. Short-range interactions including charge-transfer interactions are not important for the attraction in the three complexes. The most stable pyridinium complex has a T-shaped structure, in which the NH bond points toward the benzene, while the N-methylpyridinium complex prefers a slipped-parallel structure. The benzene-pyridine complex has two nearly isoenergetic (Slipped-parallel and T-shaped) structures. [ABSTRACT FROM AUTHOR]

The CCSD(T) level interaction energies of CH/π complexes at the basis set limit were estimated. The estimated interaction energies of the benzene complexes with CH4, CH3CH3, CH2CH2, CHCH, CH3NH2, CH3OH, CH3OCH3, CH3F, CH3Cl, CH3ClNH2, CH3ClOH, CH2Cl2, CH2FCl, CH2F2, CHCl3, and CH3F3 are −1.45, −1.82, −2.06, −2.83, −1.94, −1.98, −2.06, −2.31, −2.99, −3.57, −3.71, −4.54, −3.88, −3.22, −5.64, and −4.18 kcal/mol, respectively. Dispersion is the major source of attraction, even if substituents are attached to the carbon atom of the C−H bond. The dispersion interaction between benzene and chlorine atoms, which is not the CH/π interaction, is the cause of the very large interaction energy of the CHCl3 complex. Activated CH/π interaction (acetylene and substituted methanes with two or three electron-withdrawing groups) is not very weak. The nature of the activated CH/π interaction may be similar to the hydrogen bond. On the other hand, the nature of other typical (nonactivated) CH/π interactions is completely different from that of the hydrogen bond. The typical CH/π interaction is significantly weaker than the hydrogen bond. Dispersion interaction is mainly responsible for the attraction in the CH/π interaction, whereas electrostatic interaction is the major source of attraction in the hydrogen bond. The orientation dependence of the interaction energy of the typical CH/π interaction energy is very small, whereas the hydrogen bond has strong directionality. The weak directionality suggests that the hydrogen atom of the interacting C−H bond is not essential for the attraction and that the typical CH/π interaction does not play critical roles in determining the molecular orientation in molecular assemblies. [ABSTRACT FROM AUTHOR]

Abstract: It is widely known that addition of a radical species to the sulfur atom of a reduced sulfur molecule results in formation of a two-center three-electron (2c-3e) bond, but relatively few investigations have been reported for the 2c-3e bond between the NO3 radical and a sulfur molecule. This article presents results of gas-phase DFT and ab initio investigations on the 2c-3e type adducts of the NO3 radical with reduced sulfur molecules. By using correlation consistent basis sets, geometry optimizations at the MP2 and BH&HLYP levels and single-point energy evaluations at the CCSD(T) level were carried out. Our estimates for the dissociation enthalpies (ΔH (298K)) of the 2c-3e S–O bonds in the NO3 radical adducts of the CH3SH, CH3SCH3, and CH3SSCH3 molecules are 7∼10, 15∼16, and 10∼12kcal/mol, respectively, but our calculations suggest that the H2S molecule will not actually form a 2c-3e adduct with the NO3 radical. [Copyright &y& Elsevier]

Abstract: Growth-blocking peptide (GBP) is an insect cytokine with diverse biological functions. Northern blot analysis revealed high heterogeneity in the size distribution of GBP mRNAs as well as in the tissues where they are detected. The spatio-temporal transcription pattern is dynamic, especially during embryogenesis. Gel shift assays demonstrated that the cabbage armyworm embryo nuclear extract specifically binds to a 178-bp element, at position +234 to +411 from the transcription start site of the 1.3kb GBP transcript, in which two Drosophila Deformed (Dfd) binding sites are repeated in tandem. The specific binding between this element and Dfd was demonstrated using recombinant cabbage armyworm Dfd protein. Silencing the Dfd expression in embryos by treating with Dfd double-stranded RNA did not reduce the expression level of GBP, but ectopic GBP expression was observed in the lateral region of the embryo, suggesting that Dfd could serve as a transcriptional repressor for the GBP gene. [Copyright &y& Elsevier]

Abstract: Ab initio and DFT investigations on H2S–OH and (CH3)2S–OH adducts have shown that electron correlation is essential for an accurate description of the two-center three-electron S–O bonds in the adducts. Calculations at the BH&HLYP, B3LYP, MP2, and CCSD(T) levels indicate that the S–O bond in the (CH3)2S–OH adduct is considerably stronger and shorter than that in the H2S–OH adduct. Our best estimate for the dissociation enthalpy at 298K for the S–O bond in the (CH3)2S–OH adduct is 9.0kcal/mol, which is in satisfactory agreement with experimentally derived values. [Copyright &y& Elsevier]

Abstract: The suboesophageal body of insects was identified over a century ago in the silkworm embryo, but its biological function is still unknown. We discovered that this tissue is differentiated in the earliest embryonic stages of the cabbage armyworm and secretes the insect cytokine, growth-blocking peptide (GBP), transiently from 24 to 60h after oviposition when gastrulation is in progress. Over-expression of GBP, achieved by microinjection of the GBP gene driven by a cytomegalovirus (CMV) constitutive promoter, resulted in complex deformities of the procephalon (embryonic head). Severe abnormal phenotypes of the head structure were produced by silencing the GBP expression in the embryo by treating with GBP double-stranded RNA: the procephalon-containing optic lobes diminished and completely separated into bilateral halves. This indicates that GBP secreted from the suboesophageal body plays an essential role in the formation of the procephalic domain during early embryogenesis. The cytokine-induced fusion of bilateral procephalic lobes is thought to be evolutionarily conserved at least in insects, because of the widespread occurrence of the suboesophageal body in insect embryos. [Copyright &y& Elsevier]

Abstract: The performance of a molecular sensor for detecting nucleic acid base was studied by molecular orbital calculations of model compounds. The model compounds consist of a detecting unit (pyridine derivative), a conducting unit (benzene) and a connection between them. The changes of the HOMO, LUMO energy levels and charge distributions of the conducting unit by the hydrogen bonds formation between the detecting unit and thymine were studied. The calculations show that the choice of the connection and its position are significantly important to efficiently transmit the electronic effects to the conducting unit. The comparison with aminopyridine, where the pyridine ring plays both detecting and conducting units, shows that the electronic effects are transmitted quite efficiently, if the connection is properly selected. The size of the electronic effects by the formation of the hydrogen bonds were also compared with those induced by the change of the torsional angle between the pyridine and benzene rings and by substitution of the benzene ring. [Copyright &y& Elsevier]

Ab initio investigations on the gas-phase reaction pathways for the hydrolytic decomposition of CF2O molecule have indicated that the energy barriers for the reaction channels of CF2O with a single H2O molecule are significantly reduced when an additional H2O molecule is brought into the reaction system. The additional H2O molecule serves as a proton relay acting simultaneously as a proton donor and acceptor in the transition states. These findings may imply that reaction channels in which multiple, at least two, H2O molecules participate will be important for the homogeneous gas-phase hydrolysis of CF2O. [Copyright &y& Elsevier]

Abstract: Ab initio magnetic shielding calculations (GIAO, HF/6-311G**) were performed for five compounds that contain 2-methylenepropane-1,3-diyl (so-called isobutenylene) group. By comparison among methyl-, phenyl-, and naphthyl-bearing compounds, the roles of each substituent in the stability of conformation and in the magnetic shielding were elucidated. The shielding constant of the olefinic protons showed an obvious dependence on the conformation of CC–C moiety. The conformational dependence was analyzed in terms of the shielding and deshielding effects of the ring current of aromatic substituents, leading to a general formulation for conformation-dependent shielding of olefinic protons. The results were utilised to interpret the chemical shifts observed for several macrocyclic compounds. [Copyright &y& Elsevier]

We employed ab initio quantum mechanical techniques, such as HF, MP2, and QCISD methods, to explore the conformational spaces of fluoromethyl formate and difluoromethyl formate, HC(O)OCH3 − nFn (n=1,2). Three potential energy minima, two with the syn and one with the anti configuration, were located for fluoromethyl formate, while four potential energy minima, two with the syn and the other two with the anti configuration, were located for difluoromethyl formate. In addition, we characterized several rotational transition states for the rotation of the C–O single bond adjacent to the carbonyl group or that adjacent to the fluoro-substituted methyl group. The results of the energy evaluations of the rotational stationary points suggest that the syn/anti energy difference, as well as the barrier height to the syn/anti interconversion, tends to decrease monotonously on going from methyl formate to trifluoromethyl formate, via fluoromethyl formate and difluoromethyl formate. [Copyright &y& Elsevier]

Ab initio energy evaluations on the Z and E rotamers, as well as on the rotational transition states connecting them, were carried out for methyl formate and trifluoromethyl formate. The estimates for the energy differences at the basis set limit suggested that the Z/E energy difference and the rotational barrier height are both significantly smaller for trifluoromethyl formate than for methyl formate. Our best estimate for the enthalpy difference at 298 K between the Z and E rotamers for methyl formate is 5.21 kcal/mol, which is slightly larger than the upper edge of uncertainty of previously reported experimental value. [Copyright &y& Elsevier]

The intermolecular interaction energies of thiophene dimers have been calculated by using an aromatic intermolecular interaction (AIMI) model (a model chemistry for the evaluation of intermolecular interactions between aromatic molecules). The CCSD(T) interaction energy at the basis set limit has been estimated from the MP2 interaction energy near the basis set limit and the CCSD(T) correction term obtained by using a medium-size basis set. The calculated interaction energies of the parallel and perpendicular thiophene dimers are -1.71 and -3.12 kcal/mol, respectively. The substantial attractive interaction in the thiophene dimer, even where the molecules are well separated, shows that the major source of attraction is not short-range interactions such as charge transfer but rather long-range interactions such as electrostatic and dispersion. The inclusion of electron correlation increases the attraction significantly. The dispersion interaction is found to be the major source of attraction in the thiophene dimer. The calculated total interaction energy of the thiophene dimer is highly orientation dependent. Although electrostatic interaction is substantially weaker than dispersion interaction, it is highly orientation dependent, and therefore electrostatic interaction play an important rote in the orientation dependence of the total interaction energy. The large attractive interaction in the perpendicular dimer is the cause of the preference for the herringbone structure in the crystals of nonsubstituted oligothiophenes (α-terthienyls), and the steric repulsion between the β-substituents is the cause of the π-stacked structure in the crystals of some β-substituted oligothiophenes. [ABSTRACT FROM AUTHOR]

The intermolecular interaction energies of thiophene dimers have been calculated by using an aromatic intermolecular interaction (AIMI) model (a model chemistry for the evaluation of intermolecular interactions between aromatic molecules). The CCSD(T) interaction energy at the basis set limit has been estimated from the MP2 interaction energy near the basis set limit and the CCSD(T) correction term obtained by using a medium-size basis set. The calculated interaction energies of the parallel and perpendicular thiophene dimers are 1.71 and -3.12 kcal/mol, respectively. The substantial attractive interaction in the thiophene dimer, even where the molecules are well separated, shows that the major source of attraction is not short-range interactions such as charge transfer but rather long-range interactions such as electrostatic and dispersion. The inclusion of electron correlation increases the attraction significantly. The dispersion interaction is found to be the major source of attraction in the thiophene dimer. The calculated total interaction energy of the thiophene dimer is highly orientation dependent. Although electrostatic interaction is substantially weaker than dispersion interaction, it is highly orientation dependent, and therefore electrostatic interaction play an important role in the orientation dependence of the total interaction energy. The large attractive interaction in the perpendicular dimer is the cause of the preference for the herringbone structure in the crystals of nonsubstituted oligothiophenes (α-terthienyls), and the steric repulsion between the β-substituents is the cause of the π-stacked structure in the crystals of some β-substituted oligothiophenes. [ABSTRACT FROM AUTHOR]

Focuses on the model chemistry developed for the evaluation of intermolecular interaction between aromatic molecules. Effects of electron correlation inclusion on the attraction level; Consideration of dispersion interaction as the major source of benzene dimer attraction; Difference between electrostatic and dispersion interaction.