DFT studies of ESR parameters for N?O centered radicals,N‐alkoxyaminyl and aminoxyl radicals

Theoretical calculations of ESR parameters for aminoxyl radicals have been widely studied using the density functional theory (DFT) calculations. However, the isomer N‐alkoxyaminyl radicals have been limitedly studied. With the use of experimental data for 46 N‐alkoxyaminyl and 38 aminoxyl radicals, the isotropic ¹⁴N hyperfine coupling constants (a_N) and g‐factors have been theoretically estimated by several DFT calculations. The best calculation scheme of a_N for N‐alkoxyaminyl radicals was PCM/B3LYP/6‐31 + + G(d,p) (R² = 0.9519, MAE = 0.034 mT), and that for aminoxyl radicals was PCM/BHandHLYP/6‐31 + + G(3df,3pd) (R² = 0.9336, MAE = 0.057 mT). For aminoxyl radicals, the solvation models in calculations enhanced the accuracy of reproducibility. In contrast, for N‐alkoxyaminyl radicals the calculations with solvation models provided no improvement. The differences in the best functionals between two types of radicals were thought to come from the contribution ratios of neutral and dipolar canonical structures in resonance forms. The a_N for N‐alkoxyaminyl radicals that were stabilized by small contribution of dipolar canonical structures could be precisely reproduced by B3LYP with only 20% HF exact exchange. In contrast, the a_N for aminoxyl radicals stabilized by large contribution of dipolar canonical structures was well reproduced by BHandHLYP with 50% HF exchange. The best calculation scheme of g‐factors was IEFPCM/B3LYP/6‐31 + G(d,p) (R² = 0.9767, MAE = 0.0001) for not only aminoxyl but also N‐alkoxyaminyl radicals. Copyright © 2011 John Wiley & Sons, Ltd.     

Spin-freezing processes around the tricritical point in Mn1−xTixSb

Transitions related to the spin-glass phase in Mn_1−xTi_xSb are revisited from the nonlinear ac susceptibility. Near the tricritical point (x≈0.8), the transition between ferromagnetic and reentrant spin-glass states is sharp. At x0.8, an anomally is found slightly above the temperature of usual spin-glass freezing.     

Formation of polyelectrolyte complexes

Interactions between polyelectrolytes carrying opposite charges in aqueous media may lead to either complex coacervation or the formation of interpolymer complexes, depending on the charge density and concentration of polymer components, ionic strength, temperature, and pH. The liquid-liquid phase separation referred to as complex coacervation was thought by Oparin to be an origin of prebiological systems. This article summarizes our recent results on the intermolecular interactions between charged polymer molecules, from the point of view of biological interests.     

Sorption and partial molar volumes of C2 and C3 hydrocarbons in polypropylene copolymers

The sorption of C₂ and C₃ hydrocarbons in two ethylene–propylene copolymers and a propylene homopolymer and the simultaneous dilation of the polymers were measured at temperatures of 287–363 K and pressures up to 4 MPa. The sorption isotherms were well described by the Flory–Huggins theory of dissolution. Dilation isotherms in the form of elongation versus pressure were similar in shape to the corresponding sorption isotherms. Solubility coefficients, partial molar volumes, and Flory–Huggins interaction parameters were determined from these isotherms. The thermal expansivities of the hydrocarbons dissolved in the polymers were 0.002–0.005 K^?1, and the Flory–Huggins interaction parameters depended not only on temperature but also on concentration. At 323 K, the calculated solubilities of propylene in the ethylene–propylene‐rubber regions of the copolymers were 1.8 times higher than in the amorphous regions of the propylene homopolymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1255–1262, 2001     

Binary 1,4-asymmetric induction from a single allyltin reagent with a chiral nitrogen functional group toward aldehydes

Using a single allyltin reagent with a chiral nitrogen functionality, binary and remote asymmetric induction was realized toward various aldehydes. Either syn- or anti-1,4-amino-alcohols were selectively obtained with the use of Yb(OTf)₃ or SnCl₄, respectively. The structures of both diastereomers were identified by means of X-ray analysis.     

An efficient and selective conversion of sorbitol in ionic liquids: Use of ion exchange resin as a solid acid catalyst

Sorbitol was readily converted by heating in hydrophobic ionic liquids by the presence of ion exchange resins. Chemoseletivity of the dehydration depended on the choice of ion exchange resin; Nafion selectively produced isosorbide while Amberlite gave 1,5-anhydrosorbitol along with unreacted sorbitol. Ionic liquids used in the reaction were readily recovered by simple extraction procedure. With these procedures, we succeeded to prepare isosorbide in pure form, not contaminated with either ionic liquids or acid catalyst, by simple experimental procedure.     

PIDA-mediated synthesis of oxazoles through oxidative cycloisomerization of propargylamides

PIDA [phenyliodine(III) diacetate] in AcOH or AcOH-HFIP (hexafluoroisopropanol) efficiently promotes the formation of 2,5-disubstituted oxazoles via the oxidative cycloisomerization of propargylamide derivatives.     

Detecting coupled collective motions in protein by independent subspace analysis

Protein dynamics evolves in a high-dimensional space, comprising aharmonic, strongly correlated motional modes. Such correlation often plays an important role in analyzing protein function. In order to identify significantly correlated collective motions, here we employ independent subspace analysis based on the subspace joint approximate diagonalization of eigenmatrices algorithm for the analysis of molecular dynamics (MD) simulation trajectories. From the 100 ns MD simulation of T4 lysozyme, we extract several independent subspaces in each of which collective modes are significantly correlated, and identify the other modes as independent. This method successfully detects the modes along which long-tailed non-Gaussian probability distributions are obtained. Based on the time cross-correlation analysis, we identified a series of events among domain motions and more localized motions in the protein, indicating the connection between the functionally relevant phenomena which have been independently revealed by experiments.     

Ion-pair structure of vaporized ionic liquid studied by matrix-isolation FTIR spectroscopy with DFT calculations: a case of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate

The matrix-isolation infrared spectrum of a thermally evaporated ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([Emim][OTf]), was measured by FTIR spectroscopy and analyzed with the aid of DFT calculations. The main chemical species in the observed IR spectrum was mainly identified as the 1:1 cation-anion pair, which corresponds to the second stable ion-pair structure bonded through five hydrogen bonds between three O atoms of the anion side and four H atoms of the cation.