Ultrafast vibrational dynamics of SCN(-) and N3(-) in polar solvents studied by nonlinear infrared spectroscopy

In this paper, we report on our investigation into the vibrational dynamics of the antisymmetric stretching modes of SCN(-) and N(3)(-) in several polar solvents. We used an infrared (IR) pump-probe method to study orientational relaxation processes. In two aprotic solvents (N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO)), the anisotropy decay shows a bimodal feature, whereas in other solvents the anisotropy decay can be fitted well by a single exponential function. We consider that the relative contribution of fast-decaying components is smaller in the other solvents than in DMF and DMSO. We discuss the possible origins of the different anisotropy decay behavior in different solvents. From the three-pulse IR photon echo measurements for SCN(-) and N(3)(-), we found that the time-correlation functions (TCFs) of vibrational frequency fluctuations decay on two different time scales, one of which is less than 100 fs and the other is approximately 3-6 ps. In aprotic solvents, the fast-decaying components of the TCFs on a <100 fs time scale play an important role in the vibrational frequency fluctuation, although the contribution of collective solvent reorganization in aprotic solvents was clearly observed to have small amplitudes. On the other hand, we found that the amplitude of components that decay in a few picoseconds and/or the constant offset of the TCF in protic solvents is relatively large compared with that in aprotic solvents. With the formation and dissociation of hydrogen bonds between ion solute and solvent molecules, the spectra of different solvated species are exchanged with each other and merged into one band. We considered that this exchange may be an origin of slow-decaying components of the TCFs and that the decay of the TCFs corresponds to the time scales of the exchange for protic solvents such as formamide. The mechanism of vibrational frequency fluctuations for the antisymmetric stretching modes of SCN(-) and N(3)(-) is discussed in terms of the difference between protic and aprotic solvents.     

Surface structures of equimolar mixtures of imidazolium-based ionic liquids using high-resolution Rutherford backscattering spectroscopy

Surface structures of equimolar mixtures of imidazolium-based ionic liquids (ILs) having a common cation (1-butyl-3-methylimidazolium ([C₄MIM]) or 1-hexyl-3-methylimidazolium ([C₆MIM])) and different anions (bis(trifluoromethanesulfonyl)imide ([TFSI]), hexafluorophosphate ([PF₆]) or chlorine) are studied using high-resolution Rutherford backscattering spectroscopy (HRBS). Both cations and anions have the same preferential orientations at the surface as in the pure ILs. In the mixture, the larger anion is located shallower than the smaller anion. The [TFSI] anion is slightly enriched at the surface relative to [PF₆] with coverage of ~ 60% for the equimolar mixtures of [C₄₍₆₎MIM] [TFSI] and [C₄₍₆₎MIM] [PF₆]. No surface segregation is observed for [C₆MIM] [TFSI]_0.5[Cl]_0.5 and [C₆MIM] [PF₆]_0.5[Cl]_0.5. These results are different from the recent TOF-SIMS measurement where very strong surface segregation of [TFSI] was concluded for the mixture of [C₄MIM] [TFSI] and [C₄MIM] [PF₆].     

Association Model and Its Representation of Phase Equilibria and Excess Enthalpies of Alcohol, Aniline, and Acetonitrile Mixtures

An association model is presented to describe vapor–liquid equilibria,liquid–liquid equilibria, and excess enthalpies of binary and ternary liquid solutionscontaining alcohols, aniline, and/or acetonitrile using the concepts of linearself-association of associated components and of solvation between unlike molecules.Calculated results also show that the model works well in representing thethermodynamic properties for alcohol + aniline, alcohol + acetonitrile, andalcohol + alcohol mixtures.     

Anisotropic special transition of semi-infinite systems in the 1/n expansion

The effect of the surface magnetic anisotropy on the critical behavior at surfaces is studied by using the 1/n expansion technique. Several surface critical exponents are obtained for the anisotropic special transition at arbitrary spatial dimensions.     

Stereochemical control of microbial reduction. 2. Reduction of β-keto esters by immobilized bakers' yeast

Ketones in β-keto esters are reduced asymmetrically by immobilized bakers' yeast. The configuration and the enantiomer excess of the products are dramatically changed by the entrapment of yeast cells in dense polyurethane matrices.     

Oxidation reaction of aliphatic amines and aminoalcohols in aqueous solution induced by argon arc plasma

Argon arc plasma induced a powerful and stepwise oxidation reaction including conversion of methyl group to carboxyl group, oxidative cleavage of carbon-carbon bond, and oxidative deamination. Main active species were considered to be hydroxyl radicals by decomposition of water molecules.     

Visual enantiomeric recognition of amino acid derivatives in protic solvents

Various types of chiral host molecules 2-7 based on a phenolphthalein skeleton and two crown ethers were prepared for use in visual enantiomeric recognition, and we examined their enantioselective coloration in complexation with chiral amino acid derivatives 9-22 in methanol solution. Methyl-substituted host (S,S,S,S)-3 showed particularly prominent enantiomer selectivity for the alanine amide derivatives 11 and 12. A combination of methyl-substituted host (S,S,S,S)-3 with guest (R)-11 or (R)-12 developed a purple color, whereas no color development was observed with (S)-11 or (S)-12. On the other hand, phenyl-substituted host (S,S,S,S)-6 showed deeper coloration with a wide range of (S)-beta-amino alcohols compared to that seen with host (S,S,S,S)-6 and the corresponding (R)-beta-amino alcohols at 0 degrees C. Furthermore, absorbance inversion temperatures (AIT) were observed within the range of 0-50 degrees C in many cases.     

The Hamiltonian systems on the Poisson structure of the quasi-classical limit of GL q (∞)

We consider the Hamiltonian systems on the Poisson structure of GL() which is introduced from the quantum group GL _q () by the so-called quasi-classical limit of GL _q (). Furthermore, we show that the Toda lattice hierarchy is a Hamiltonian system of this structure.     

Selective synthesis of 1,4,5-trisubstituted imidazoles from α-imino ketones prepared by N-heterocyclic-carbene-catalyzed aroylation

An alternative synthetic route to 1,4,5-trisubstituted imidazoles from α-imino ketone, which can be prepared from imidoyl chlorides and aromatic aldehydes via N-heterocycle carbene-catalyzed aroylation was developed. This methodology consists of simple transformations, allowing a rapid access to imidazole derivatives with various aryl substituents at the desired positions.