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Carbon nitride (CN x ) coatings have been found to exhibit an ultra-low friction coefficient (less than 0.01) after repeated sliding against a silicon nitride (Si 3 N 4 ) ball in a dry nitrogen gas (N 2 ) atmosphere. However, the mechanism for this has not yet been fully elucidated with respect to analyzing changes in the space structure of CN x . In the present study, we examined the microscopic structural changes in the near-surface structural transition layers of the wear track in the CN x coating and the transfer layer of the Si 3 N 4 ball, using scanning transmission electron microscopy and electron energy-loss spectroscopy. We investigated the nitrogen concentration, density, and curvature of fragmented graphitic planes in the structural transition layers of both the CN x coating and the transfer layer of the Si 3 N 4 ball by analyzing the plasmon peak and carbon K-edge. In addition, we theoretically examined the chemical bonding states of nitrogen doping in various model clusters using an ab initio molecular orbital method to clarify the role of nitrogen in the ultra-low friction behavior. The mechanism behind the ultra-low friction behavior is explained by nano-graphitization of the fragmented carbon structure with optimal nitrogen concentration passivating the contacting counter surfaces of the coating and ball formed during sliding.

A unique 1,7-S- and Se-shift reaction under Pummerer reaction conditions of 4-alkenyl-3-sulfinyl- and seleninylpyrroles was described. The usual Pummerer reaction of 4-(alkenylaminomethyl)-3-phenylsulfinylpyrroles and a successive reaction with tetrabutylammonium hydroxide (TBAH) yielded either pyrrolo[3,2-c]azepines or N-pyrrol-3-ylmethyl-N-(4-hydroxy-3-sulfanylpropyl)-p-toluenesulfonamides (diols). Seleno-Pummerer reactions of 3-selanylmethylpyrroles also proceeded via in situ generation of selenoxides, followed by a treatment with TBAH.

Five dinitrogen-molybdenum complexes bearing bis(diphenylphosphino)amine derivative ligands (L(R)) that form a unique 4-membered P-N-P chelate ring, trans-[Mo(N(2))(2)(L(R))(2)] (2(R): R = Ph, Xy, p-MeOPh, 3,5-iPr(2)Ph, iPr), were prepared for the purpose of binding a dinitrogen molecule. The corresponding two dichloride-molybdenum complexes, trans-[MoCl(2)(L(R))(2)] (1(R): R = Ph, Xy), were also prepared as comparisons. FT-IR spectra of 2(R) were measured and compared the ν(N≡N) values. Moreover, X-ray crystal structure determination of 1(R) (R = Ph, Xy) and 2(R) (R = Xy, 3,5-iPr(2)Ph) is performed. These experimental results indicated that the coordinated dinitrogen molecule gets easily influenced by the N-substitutent of diphosphinoamine ligand. In addition, to investigate the effect of the properties of the diphosphinoamine ligand for the dinitrogen molybdenum complexes, we performed DFT calculations that focused on the difference of N-substituent, the dihedral angle between P-N-P plane and N-substituent aryl group, and the P-N-P bite angle. This calculation revealed that the competition between the back-donation from metal to dinitrogen and that from metal to ligand was affected by P-N-P bite angle and the dihedral angle of N-substituent of ligand. In order to examine the reactivity with respect to conversion of dinitrogen to ammonia, protonation and trimethylsilylation reactions of the coordinated dinitrogens were carried out for 2(R).

Cyclization of N-tethered alkyne nitriles with bromoacetates gives dihydroazepinecarboxylates with excellent functional group tolerance.

Quantum Chemistry Literature Data Base (QCLDB, http://qcldb2.ims.ac.jp) is a database of those papers published after 1978 which treat only ab initio calculations of atomic and molecular electronic...

Penta-, hexa-, and heptaacetonitrile complexes of divalent cations of the first transition series are studied by ab initio molecular orbital calculations. The factors that determine the structural stability and the reaction mechanism of solvent-exchange reactions are discussed. All the penta- and hexaacetonitrile species are at local minima, whereas the geometrical stability of the heptacoordinated species depends on the 3d electron configurations. The structural stability of heptaacetonitrile species is intermediate between those of hydrogen cyanide complexes and hydrates. Acetonitrile exchange reactions have more dissociative character than hydrogen cyanide exchange reactions because the inductive effect of the methyl group in CH3CN destabilizes the heptacoordinated structures. The successive binding energies show that associative mechanisms are favorable for acetonitrile exchange with earlier members of the first transition series, whereas dissociative mechanisms become favorable for later members. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

A protocol for the direct synthesis of azepines using a hafnium(III)-catalyzed [6 + 1] annulation of N-tethered ynenitriles with Reformatsky reagents is reported. A broad range of 3-amino-2,7-dihydro-1H-azepine-4-carboxylates 4aa-4he were obtained in high yields and with excellent functional group tolerance. The copper-mediated reactions of isolable Blaise intermediates (enamino esters 3), uniquely underwent 5-endo cyclization to afford the β-2,5-dihydropyrrolyl α,β-unsaturated esters 5aa-5fc, which exhibit anticancer activity.

The stability of divalent cations (M(II)) of the first transition series, penta-, hexa-, and heptasolvated by hydrogen cyanide was studied in order to clarify the reaction mechanisms of nitrile-exchange reactions. The structural stabilities of the [M(NCH)7]2+s depend on the d-electron configurations, though all of the [M(NCH)5]2+s and [M(NCH)6]2+s are located at the local minima. The [M(NCH)7]2+s are structurally more stable than the heptahydrated analogues. Successive binding energies show that it is difficult for an incoming ligand to penetrate the first solvation shells of cations in the later members. Thus, the associative mechanism of solvent-exchange reactions is favorable for cations in the earlier members resulting from energetics as well as structural stability. The symmetry of the imaginary vibrational mode along the reaction path corresponds to that of the transition density induced by one-electron excitation from the antibonding orbital occupied in the d3 ion to the 4s orbital. The stable [M(N...

4-Hydroxy-2-nonenal (HNE), a major racemic product of lipid peroxidation, reacts with histidine to form a stable HNE-histidine Michael addition-type adduct possessing three chiral centers in the cyclic hemiacetal structure. In the present study, we characterized configurational isomers of a HNE-N α-acetylhistidine adduct by NMR spectroscopy and by molecular orbital calculations. In addition, we raised monoclonal antibodies against (R)-HNE-histidine and (S)-HNE-histidine adducts, characterized their specificities, and examined in vivo localizations of each adduct under oxidative stress. To facilitate structural characterization of the configurational isomers of an HNE-histidine adduct, we prepared the (R)-HNE-histidine and (S)-HNE-histidine adducts by incubatingN α-acetylhistidine with each HNE enantiomer, both of which provided two peaks (Ra and Rb from (R)-HNE-histidine and Sa and Sb from (S)-HNE-histidine adducts) in reversed-phase high-performance liquid chromatography. The NMR analysis showed that each peak was a mixture of two diastereomers. In addition, the analysis of the nuclear Overhauser effect enabled the determination of configurations of the eight isomers. The relative amounts of these isomers in the NMR analysis correlated with the relative energies calculated by molecular orbital methods. On the other hand, using (R)-HNE-modified and (S)-HNE-modified keyhole limpet hemocyanins as the antigens, we raised the monoclonal antibodies, mAbR310 and mAbS412, which enantioselectively recognized the (R)-HNE-histidine and (S)-HNE-histidine adducts, respectively. Among the mixtures (Ra, Rb, Sa, and Sb) of diastereomers, mAbR310 showed the highest immunoreactivity to Rb (the mixture of 2R,4S,5R and 2S,4S,5R isomers), whereas mAbS412 preferentially recognized Sa (the mixture of 2R,4S,5S and 2S,4S,5S isomers). The presence of (R)-HNE and (S)-HNE epitopes in vivo was immunohistochemically examined in the kidney of rats exposed to the renal carcinogen, ferric nitrilotriacetate, by which nuclear and cytosolic stainings with mAbR310 and mAbS412, respectively, were detected.

The thermochemical stabilities of gas phase cluster ions C 2 H 5 +(Sol) n , s-C 3 H 7 +(Sol) n , and t-C 4 H 9 +(Sol) n (Sol = CO 2 and N 2 O) were determined using a pulsed electron beam high-pressure mass spectrometer. The stabilities and structures of those cluster ions were studied theoretically by density functional theory calculations. For the free C 2 H 5 + ion, not the classical but the nonclassical bridged form is likely to be the major component. B3LYP/6-311+G(2d,p) calculations showed that the classical structure is absent. In the clustering reaction of C 2 H 5 + with Sol, a hydrogen bond type loose complex of the nonclassical C 2 H 5 + with Sol is initially formed, which is followed by the intramolecular isomerization of C 2 H 5 + to the classical structure forming the stronger bond with Sol. Surprisingly small bond energies of 4-5 kcal/mol for s-C 3 H 7 +Sol and t-C 4 H 9 +Sol arise from the hyperconjugation effect of methyl groups.

We have calculated the potential energy surfaces for the twisting around the C15 N bond of protonated Schiff base of retinal (PSBR) with and without a negative point charge or a water molecule in the vicinity of the Schiff base by means of the state-average complete active space self-consistent field (sa-CASSCF) method. We have found that the S1 potential energy surface has a large energy barrier for twisting from −180 to −90° for PSBR in vacuum and for PSBR with a water molecule. These results are quite different from the S1 potential energy surface for the twisting around the C11 C12 and C13 C14 bonds where very small energy barriers exist in the above molecular systems.

We studied the structural stability of heptahydrated trivalent cations of the first transition series from scandium to cobalt as model intermediary species in associative reaction pathways for the water exchange of the hexahydrated cations by ab initio molecular orbital methods. All the structures of heptacoordination are pentagonal bipyramidal with a distorted equatorial plane. The heptahydrated di- and trivalent cations with the same d-electron configuration are similar to each other for the structure and the structural stability which are strongly dependent on their d electron configurations. The associative mechanism is possible for the water-exchange reactions of the hexahydrated trivalent cations from scandium to cobalt, because the seven-coordinate species are located at the local minima or at the saddle points on the potential energy surface. The intrinsic reaction coordinates of the water-exchange reactions on the hexahydrated vanadium(II) and chromium(II) ions support the cis and trans attack of the associative mechanisms. The hexahydrated trivalent cations with d3 and d6 configurations [chromium(III) and cobalt(III)] prefer a cis attack, while manganese(III) with a d4 configuration prefers trans attack during the operative associative process of the water-exchange reaction.

The structure parameters around the Cu(I) ion in pyridine (PY), 4-methylpyridine (4MPY), 2-methylpyridine (2MPY), 2,6-dimethylpyridine (26DMPY), and acetonitrile (AN) were determined by the extended X-ray absorption fine structure (EXAFS) method. The solvation structures of the Cu(I) ion in PY, 4MPY, and AN are 4-coordinate tetrahedral with Cu-N bond lengths of 205, 205, and 200 pm, respectively. In the case of 2MPY and 26DMPY, the Cu(I) ion has a 3-coordinate triangular structure with a Cu-N bond length of 201 pm. Such a decrease in the coordination number was interpreted in terms of the bulkiness of the solvent molecules. In order to clarify the most stable solvation structure of the Cu(I) ion, we carried out ab initio molecular orbital calculations for the solvation system of [Cu(NCH)n]+ (n = 1 - 6 ) where the steric effect is negligible. The Gibbs free energy of solvation was the smallest in the case of n = 4 and the 4-coordinate tetrahedral solvation of the Cu(I) ion was theoretically evaluated as most stable. The enthalpy of solvation monotonously decreases with increasing n, while the entropy of solvation proportionally increases. Although a larger gain of enthalpy is observed for the octahedral structure rather than the tetrahedral one, the entropic loss for the former overcomes the enthalpic gain.

The potential energy surface of the protonated Schiff base of retinal has been calculated at the state-average complete active space self-consistent field (sa-CASSCF) level of theory to elucidate the mechanism of the trans – cis photoisomerization of the chromophore in bacteriorhodopsin. We treated two molecular systems, i.e., protonated N -methyl Schiff base retinal (C 21 H 32 N + ) and its simplified model compound, C 12 H 16 N + . We used the 6-31g split-valence basis set. To clarify the effect of the protein and hydrogen bonding with water, the same molecular system with a negative point charge or with a water molecule in the vicinity of the Schiff base was also calculated. The results show that the electrostatic environment of the protein works to produce a favorable potential energy surface for the lowest excited state of the chromophore, leading to efficient trans – cis photoisomerization.

We studied the structural stability of heptahydrated divalent cations in the first transition series as model intermediary species in associative reaction pathways for the water exchange of hexahydrated cations by ab initio molecular-orbital methods. All of the structures of heptacoordination are pentagonal bipyramidal with a distorted equatorial plane. The structural stabilities are strongly dependent on their d-electron configurations. An associative mechanism is possible for the water-exchange reactions of hexahydrated divalent cations having less than seven d electrons, because the seven-coordinate species are located at the local minima or at the saddle points on the potential-energy surface. The occupation of the antibonding b orbital induces a transition density corresponding to an antisymmetric distortion through an interaction with a low-lying 4s orbital. The large bonding interaction makes the heptahydrated manganese(II) ion to become located at a local minimum. The occupancy of antibonding a or...

Thermochemical stabilities of the cluster ions composed of mixed rare gases were measured using a pulsed-electron beam high pressure mass spectrometer. The formation of trimer ion cores, i.e., A+(B)2 and A2+(B)1, was found when A and B are next to each other in the Periodic Table. This trend is similar to that for the pure rare gas cluster ions, i.e., the formation of ion core Rg3+ for Rg=He, Ne, Ar, Kr, and Xe. Although Ar and Xe are not next to each other in the Periodic Table, the formation of the trimer ion core is found for Xe+(Ar)2. This may be due to the fact that the ionization potentials of Ar and Xe are close to each other. The bond energies of larger cluster ions A+(B)2(B)n−2 and A2+(B)1(B)n−1 were found to be similar to those of homogeneous cluster ions (B)3+(B)n−3. The experimental bond energies were confirmed by ab initio calculations with a modified G2(MP2) method [e.g., 0.2 kcal/mol (expt) and 0.3 kcal/mol (theory) for Ar2+⋅He].

The structure and stability of heptahydrated divalent cations of earlier members in the first transition series ([M(H2O)7]2+: M = Ti, V, Cr, and Mn) have been studied by ab initio molecular-orbital methods, because the heptahydrated cations are relevant to intermediates and transition states in their water-exchange reactions. The structure is pentagonal bipyramidal with a distorted equatorial plane. The heptahydrated divalent cations with d0, d1, d2, and d5 configurations are at the local minima, and those with d3 and d4 are at the saddle points, though there is an increase in hydration energy across the row of the periodic table from calcium to zinc. The trend of stability in a series of heptahydrated divalent cations strongly depends on the d-electron configuration, and differs significantly in the case of the penta- or hexahydrated cations that are at the local minima. It is concluded that an associative mechanism is possible for the water-exchange reaction on hexahydrated divalent cations of the earli...

We studied the characteristics of model intermediary species on reaction pathways using the ab initio molecular orbital method in order to explain a change in the mechanistic behavior of the water-exchange reaction of hexahydrated divalent cations when the central elements were changed in the first transition series. Calculations show that the hexacoordinated species binding to the entering water in the second shell, the dissociative pentacoordinated species of scandium(II) and copper(II) ions, and the associative heptacoordinated species of scandium(II) ion are at local minima, whereas the heptacoordinated species of copper(II) ion is at a second-order saddle point. We also considered calcium(II) and zinc(II) ions in order to examine the correlation between the intermediary species and the reaction mechanisms. All of the intermediary species for calcium(II) and zinc(II) ions resemble those of scandium(II) and copper(II) ions, respectively. The dissociative mechanism can operate for both the calcium(II) a...

Structure parameters of solvated silver(I) ions in eight neat solvents were determined by extended X-ray absorption fine structure spectroscopy. The coordination geometry of the solvated silver(I) ion is four-coordinate tetrahedral at the Ag−O bond distances of 239 pm in trimethylphosphate, 239 pm in N,N-dimethylformamide, 238 pm in 1,1,3,3-tetramethylurea, and 238 pm in dimethyl sulfoxide as oxygen-donating solvents, and at the Ag−N bond distances of 229 pm in acetonitrile, 230 pm in 2-methylpyridine, 229 pm in n-propylamine, and 231 pm in ethylenediamine as nitrogen-donating solvents. According to our present ab initio molecular orbital calculations concerning the structure of the silver(I) ion bound by n molecules of hydrogen cyanide (n = 1−6) and acetonitrile (n = 1−5) in the gas phase, the maximal stabilization for the solvation is observed at n = 4. The results of the theoretical calculations in the gas phase are consistent with the experimental observations in solution.

Ab initio calculations of 12-crown-4, 15-crown-5, and 18-crown-6 and their protonated species have been performed. As a reference molecule, 1-(2‘-methoxy)ethoxy-2-methoxyethane (glyme-2) is also examined. Three protonated crown ethers are found to have quite similar moieties to that of glyme-2H+. The ring strain due to formation of intramolecular hydrogen bonds is a measure of proton affinity (PA) values. The present computational result supports Meot-Ner's and Kebarle's PA values of 12-crown-4. Those of 15-crown-5 and 18-crown-6 reported by Kebarle were very close to the present theoretical values.

The origin of the inverted tetrahedral configurations of the bridgehead carbons in bicyclo[1.1.0]butane has been investigated in a theoretical manner. The delocalization of σ-electrons between the central C1−C3 bond and the side C1−C2 bonds was found to be bonding to relax the angle strains, while the delocalization between the geminal C−C bonds is antibonding in propane and cyclopropane, etc. The bonding property of the geminal delocalization was shown to be related to the inversion of the configurations. Inverted and normal tetrahedral bridgehead configurations in the bicyclo[1.1.0]butane frameworks were designed by controlling the geminal delocalization and confirmed by ab initio molecular orbital calculations.

Condensation of 2,4,5-triamino-6-butoxypyrimidine with various 2-formyloxiranes followed by oxidation with iodine affords 2-amino-4-butoxy-6-(1-hydroxyalkyl)pteridines regioselectively. Naturally occurring L-erythro-biopterin is synthesized from (1S,2S,3S)-2-formyl-3-(1-hydroxyethyl)oxirane. The reaction proceeds via 5,6-dihydropteridine, and the mechanism is discussed with the help of molecular orbital calculations

The geometries of diethers, diketones, and diamines and their protonated species are determined with the ab initio calculations of RHF/3-21G. The theoretical proton affinites (PA's) of MP2/6-31(+)G( ** )//RHF/3-21G reproduce well experimental PA's. A good correlation between PA's and hydrogen-bond angles is found. As the alkyl size increases, the angles and ring strains at the sp 3 carbons become larger, which leads to a saturation of PA values

The exclusive anti-π-facial selectivity in the Diels-Alder reaction of 5-formylpentamethylcyclopentadine, Cp*-CHO, was proposed to come from the π-HOMO distortion of the diene due to the perturbation by low-lying π*orbital on the substituent. The role of the π* orbital was experimentally substantiated by a considerable amount of syn-attack products in the reactions of Cp*-CH=NOH and Cp*-CH=CH2 having high-lying substituent π* orbitals.

The geometries of diethers, diketones, and diamines and their protonated species are determined with the ab initio calculations of RHF/3-21G. The theoretical proton affinites (PA's) of MP2/6-31(+)G( ** )//RHF/3-21G reproduce well experimental PA's. A good correlation between PA's and hydrogen-bond angles is found. As the alkyl size increases, the angles and ring strains at the sp 3 carbons become larger, which leads to a saturation of PA values

Condensation of 2,4,5-triamino-6-butoxypyrimidine with various 2-formyloxiranes followed by oxidation with iodine affords 2-amino-4-butoxy-6-(1-hydroxyalkyl)pteridines regioselectively. Naturally occurring L-erythro-biopterin is synthesized from (1S,2S,3S)-2-formyl-3-(1-hydroxyethyl)oxirane. The reaction proceeds via 5,6-dihydropteridine, and the mechanism is discussed with the help of molecular orbital calculations

4-Hydroxy-2-nonenal (HNE), a major racemic product of lipid peroxidation, reacts with histidine to form a stable HNE-histidine Michael addition-type adduct possessing three chiral centers in the cyclic hemiacetal structure. In the present study, we characterized configurational isomers of a HNE-N(alpha)-acetylhistidine adduct by NMR spectroscopy and by molecular orbital calculations. In addition, we raised monoclonal antibodies against (R)-HNE-histidine and (S)-HNE-histidine adducts, characterized their specificities, and examined in vivo localizations of each adduct under oxidative stress. To facilitate structural characterization of the configurational isomers of an HNE-histidine adduct, we prepared the (R)-HNE-histidine and (S)-HNE-histidine adducts by incubating N(alpha)-acetylhistidine with each HNE enantiomer, both of which provided two peaks (Ra and Rb from (R)-HNE-histidine and Sa and Sb from (S)-HNE-histidine adducts) in reversed-phase high-performance liquid chromatography. The NMR analysis showed that each peak was a mixture of two diastereomers. In addition, the analysis of the nuclear Overhauser effect enabled the determination of configurations of the eight isomers. The relative amounts of these isomers in the NMR analysis correlated with the relative energies calculated by molecular orbital methods. On the other hand, using (R)-HNE-modified and (S)-HNE-modified keyhole limpet hemocyanins as the antigens, we raised the monoclonal antibodies, mAbR310 and mAbS412, which enantioselectively recognized the (R)-HNE-histidine and (S)-HNE-histidine adducts, respectively. Among the mixtures (Ra, Rb, Sa, and Sb) of diastereomers, mAbR310 showed the highest immunoreactivity to Rb (the mixture of 2R,4S,5R and 2S,4S,5R isomers), whereas mAbS412 preferentially recognized Sa (the mixture of 2R,4S,5S and 2S,4S,5S isomers). The presence of (R)-HNE and (S)-HNE epitopes in vivo was immunohistochemically examined in the kidney of rats exposed to the renal carcinogen, ferric nitrilotriacetate, by which nuclear and cytosolic stainings with mAbR310 and mAbS412, respectively, were detected.

Hydrogenated nanostructured graphite has been reported to exhibit a characteristic peak at around 600–800 K in thermal desorption spectroscopy (TDS). The origin of this peak is still controversial. We have reexamined it based on a combination Fourier transform infrared (FT-IR), electron diffraction, and electron energy-loss spectroscopy (EELS) study. The FT-IR spectrum of HNG exhibited an unknown broad absorption band at very low frequencies around 660 cm^{−1}, which almost disappeared by annealing up to 800 K. Electron diffraction as well as plasmon peaks in EELS detected unusual shrinkage and subsequent expansion of the graphene interlayer distance by hydrogen incorporation and desorption with annealing, which were well correlated with the change in intensity of the 660 cm^{−1} IR band. An energetically stable configuration was found by theoretical model calculations based on GAUSSIAN03. All the present results are consistent with our previous studies, which suggested that hydrogen is loosely trapped between graphene layers.

The exclusive anti-π-facial selectivity in the Diels-Alder reaction of 5-formylpentamethylcyclopentadine, Cp*-CHO, was proposed to come from the π-HOMO distortion of the diene due to the perturbation by low-lying π*orbital on the substituent. The role of the π* orbital was experimentally substantiated by a considerable amount of syn-attack products in the reactions of Cp*-CH=NOH and Cp*-CH=CH2 having high-lying substituent π* orbitals.

We studied ligand effects to the pseudorotation of cyclic penta-coordinated phosphorous compounds [PX3C4H8] , X = CH3, NH2, OH, F, Cl and H using ab initio molecular orbital methods. The most stable structures and transition states are characterized. These are fundamental data for the control of reaction occurring in this type of compounds.

We developed a computer program MOLCAT to visualize results of vibrational analysis calculation. This program can treat Z-matrix used in ab initio molecular orbital calculation, and shows the vibrational mode as arrows with the molecular structure. We applied this program to show transition vectors of the intramolecular inversion of ammonia and the water exchange reaction of hexaaquacalcium(II). We are preparing to distribute MOLCAT as a free software.