Nobuo Tajima

Approaches to bifurcating reaction path

The intrinsic reaction path (IRP) often becomes unstable relative to some nontotally symmetric direction orthogonal to the path through a valley–ridge inflection point. We investigate geometric characters of the potential energy surface around the valley–ridge inflection boundary, and propose some ideas to determine a bifurcating reaction path, or to give a two‐dimensional potential energy surface which connects bifurcating point and product regions. As a demonstration, bifurcating reaction paths are calculated for the isomerization reaction of methoxy radical (H3CO→H2COH) by the unrestricted Hartree–Fock (UHF) method.

A Solid-State Fluorescent Host System with a 21-Helical Column Consisting of Chiral (1R,2S)-2-Amino-1,2-diphenylethanol and Fluorescent 1-Pyrenecarboxylic Acid

A solid-state fluorescent host system was created by self-assembly of a 2(1)-helical columnar organic fluorophore composed of (1R,2S)-2-amino-1,2-diphenylethanol and fluorescent 1-pyrenecarboxylic acid. This host system has a characteristic 2(1)-helical columnar hydrogen- and ionic-bonded network. Channel-like cavities are formed by self-assembly of this column, and various guest molecules can be included by tuning the packing of this column. Moreover, the solid-state fluorescence of this host system can change according to the included guest molecules. This occurs because of the change in the relative arrangement of the pyrene rings as they adjust to the tuning of the packing of the shared 2(1)-helical column, according to the size of the included guest molecules. Therefore, this host system can recognize slight differences in molecular size and shape.

Do Cu2+NH3 and Cu2+OH2 exist?: theory confirms `yes!'

Abstract CCSD(T) and MRMP calculations with TZP+ quality basis sets are used to study the interaction of Cu 2+ with up to two ligand molecules L (L=H 2 O, H 2 S, NH 3 , and PH 3 ). The dissociation to Cu + and L + is much more stable than the formation of Cu 2+ L adducts (by 76–100 kcal/mol). Nevertheless, it might be possible to obtain a one-ligand complex for H 2 O and NH 3 ; barrier heights of 7 and 9 kcal/mol, respectively, are assigned for the dissociation process. Two ligands from H 2 O and NH 3 can give more stable complexes with Cu 2+ as the barrier heights reach 40 kcal/mol. In order to obtain stable complexes of PH 3 or H 2 S with Cu 2+ , at least two ligands are required.

Carbon-Doped Silicon Oxide Films with Hydrocarbon Network Bonds for Low-k Dielectrics: Theoretical Investigations

We have computationally explored the chemical structures of carbon-doped silicon oxide (SiOCH) films that give the smallest dielectric constant (k) under the required mechanical strength for low-k dielectrics. The focus of this study is on the SiOCH structures that have hydrocarbon components in the polymer network as cross-links. It has been found that SiOCH films of small dielectric constants can have improved mechanical strengths if the hydrocarbon components form cross-links, instead of the terminal methyl groups in the conventional structure. The calculated results suggest that SiOCH films of ideal structures can have substantially smaller dielectric constants than films of current interconnect technology with the same mechanical strengths.

A theoretical study on the catalysis of Cu-exchanged zeolite for the decomposition of nitric oxide

The catalysis of Cu-exchanged zeolite for the direct decomposition of nitric oxide was investigated by hybrid density functional theory (B3LYP) using a molecular model of the active site. For reactions of two NO molecules over a Cu ion bound to the zeolite model (ZCu), the structures and energies of adsorption complexes and transition states were examined and compared with those of the corresponding reactions over an isolated Cu+ and Cu atom and also reactions of free NO. The ZCu shows an enhanced catalytic activity compared with the isolated Cu+. The ZCu and adsorbed molecules interact strongly in the transition state structures through π(d–p) bonding. Theory also suggests that the Cu atom has the potential to be a highly active catalyst for the NO decomposition reaction.

A coincident spontaneous resolution system for racemic1,1′-binaphthyl-2,2′-dicarboxylic acid and 1,2-diphenylethylenediamine induced by water

Spontaneously resolvable conglomerate crystals are obtained by combining racemic (rac)-1,1-binaphthyl-2,2-dicarboxylic acid and rac-1,2-diphenylethylenediamine, and this spontaneous resolution system is induced by water which is present in the crystallization solvent.

A possible crystal structure of 1,2-dimethoxyethane: prediction based on a lattice variable molecular dynamics

Using a newly developed method based on a lattice-constant variable molecular dynamics, the crystal structure of 1,2-dimethoxyethane (DME) has been predicted to consist of TGT conformers packed in Pnaa spatial symmetry. The prediction was carried out using our MDCP (Molecular Dynamics for Crystal Packing) program with van der Waals potentials of the MM3 force field and partial charges fitted to ab initio molecular orbital electrostatic potential. The predicted TGT conformation in the crystal agrees with the results of infrared absorption spectroscopy on solid DME. The packing analysis shows that the preference of TGT over TTT (in the gas phase TTT is the most stable) is mainly due to the Coulombic attractions between intermolecular O…CH2 pairs as well as the Coulombic repulsions between intermolecular O…O pairs.

Influence of isomorphous substitution on acidity of zeolites: ab initio and density functional studies

Abstract The influence of chemical composition on acidity of zeolite clusters and their interaction with CO molecules were investigated by quantum chemical methods. We used both Hartree–Fock and density functional theory to study the acidity of zeolite cluster models of the form (H3Si–OH–TH2(OSiH3)), where T=Al, Ga, or B. The acidity is found to decrease in the order Al(OH)Si>Ga(OH)Si>B(OH)Si in agreement with existing experimental and theoretical results. The present quantification is based on the calculated charge on hydrogen atom, bond length of bridging hydroxyl groups and their vibrational frequencies. We also studied the change in the vibrational frequencies of the CO molecule upon adsorption on the acidic sites. The CO molecule bound to the acidic hydrogen via the oxygen center is found to exhibit an adsorption-induced red shift of the stretching frequency, in contrast to the blue shift of the carbon bound species.

Theoretical study on adsorption and proton exchange reaction of H2O on H-form zeolite

Abstract The mechanism of water adsorptions onto the H-form zeolite, as well as the following proton exchange reaction, has been studied by ab initio molecular orbital calculations at the Hartree-Fock and the 2nd-order Moller Plesset levels with basis sets of double-zeta plus polarization quality. The H-form zeolite is represented by clusters consisting of 3 ∼ 8 SiO 4 (AlO 4 ) units. Some adsorption structures are located, and the normal mode analyses are performed for the respective structures to verify their geometric character and to determine the vibrational frequencies. The adsorption energies indicate that two types of complexes, i.e., a protonated form and a H-bonded form, are evenly probable as surface species, whereas the comparison of the calculated harmonic frequencies with the experimentally observed ones suggests that the adsorbed water forms the H-bonded complex. The potential energy surface related to the water adsorption and proton exchange processes is extensively investigated in terms of energy profiles along some energetically optimum paths.

Complexation behaviour of a CT complex composed of 9,10-bis(3,5-dihydroxyphenyl)anthracene and viologen derivatives

A chiral charge-transfer (CT) complex was formed using achiral 9,10-bis(3,5-dihydroxyphenyl)anthracene (BDHA) as an electron donor and achiral 1,1′-dimethyl-4,4′-bipyridinium dichloride (MVCl2) as an electron acceptor. This chiral CT complex can include n-alkyl alcohol molecules as guests. On the other hand, when 1,1′-diphenyl-4,4′-bipyridinium dichloride and 1,1′-dibenzyl-4,4′-bipyridinium dichloride were used as electron acceptors, achiral CT complexes without guests were formed. It was found that the chiral crystallisation of the BDHA/MVCl2–CT host system was caused by steric and electric intermolecular interactions between host component molecules BDHA and MVCl2 during crystallisation.