Ab initio and DFT calculations of three-body interactions in chiral mixtures

In order to elucidate the enthalpic stabilization of a 2-methyl-1,4-butanediol system (2M14BD) and a 3-chloro-1,2-propanediol (3C12PDO) system by mixing of each (R)- and (S)-enantiomers, three-body interaction energies are obtained by PW91/6-311G** and MP2/6-311G** level calculations. The differences between homochiral interactions and heterochiral interactions in a 3C12PDO system are found. On the other hand, in 2M14BD systems, very slight differences can be observed between the three-body interaction energies of the three ternary systems. Further, the relationship between excess enthalpies and chiral interactions is discussed.     

Excess enthalpies of binary mixtures of <Emphasis Type="Italic">ortho</Emphasis>-, <Emphasis Type="Italic">meta</Emphasis>-, <Emphasis Type="Italic">para</Emphasis>-structural isomers containing aliphatic group

To obtain further systematic information for the isomer systems, the excess molar enthalpies for binary (o + m), (o + p), (m + p)-isomers of methoxymethylbenzene, ethylmethylbenzene, diethylbenzene, chloromethylbenzene, tolunitrile and fluorobenzonitrile, tolylacetonitrile were measured at 298.15 K. In this article, the results are discussed and compared with those of previous works. The excess enthalpies of binary systems in different solid and liquid states were measured when the pure component of o-/m-tolunitrile, fluorobenzonitrile was titrated into the prior (o + p) or (m + p) mixtures. A series calculation for the interaction energies (IE) between the isomers was carried out for the pair molecules by ab initio MO of Gaussian 09. Correlations between the excess enthalpies at a molar fraction of x = 0.5 and the intermolecular energy are discussed.     

A Diels-Alder approach to the enantioselective construction of fluoromethylated stereogenic carbon centers

Highly enantioselective Diels-Alder reactions of β-fluoromethylacrylates were carried out in the presence of a Lewis acid activated chiral oxazaborolidine catalyst. These reactions yielded fluoromethylated cyclohexenes, including trifluoromethyl-, difluoromethyl-, and monofluoromethyl cyclohexenes, as nearly pure enantiomers. The resulting fluoromethyl cyclohexenes were converted into potential synthetic intermediates for bioactive compounds.     

Thermodynamic properties of inclusion complexes of α-cyclodextrin + aliphatic nitriles (H(CH2) n CN: n = 1–8) in aqueous solution

In order to investigate the contribution of the hydrophilic parts of guest molecules of aliphatic complexes to the inclusion reaction, the thermodynamic properties of inclusion complexes of cyclodextrin (α-CD) with aliphatic nitriles [H(CH₂) _n CN: n = 1–8] into the α-CD cavity in dilute aqueous solutions were measured by a micro-calorimeter at 298.15 K. The thermodynamic properties of inclusion for the octane nitrile system were different from those of others. The inclusion process of aliphatic nitriles to α-CD has two kinds of major driving force of enthalpy and entropy driven inclusion. The interaction energies of inclusion complexes of α-CD and aliphatic nitriles were determined by DFT calculation (B3LYP/6-31++G (d,p)) in water and compared with the experimental results. DFT calculations were performed on the inclusion complexes of α-CD with seven nitriles of each conformer. Both the gas phase interaction and solvent effect were taken into consideration. Also non-polar interactions between aliphatic nitriles + α-CD in aqueous solution were calculated and herein the inclusion energy is discussed.     

A mechanically controlled indicator displacement assay

Push a host: Mechanical compression was applied to a host monolayer at an interface, which facilitated an indicator displacement assay. The fluorescence resonance energy transfer (FRET) between the host and indicator was switched on by this compression. Addition of D-glucose caused the indicator to be displaced, effectively quenching the FRET process.     

Raman spectroscopic study on solvation of diphenylcyclopropenone and phenol blue in room temperature ionic liquids

We investigated the solvation of several room temperature ionic liquids by Raman spectroscopy using diphenylcyclopropenone (DPCP) and phenol blue (PB) as probe molecules. We estimated acceptor numbers (AN) of room temperature ionic liquids by an empirical equation associated with the Raman band of DPCP assigned as a C=C stretching mode involving a significant C=O stretching character. According to the dependence of AN on cation and anion species, the Lewis acidity of ionic liquids is considered to come mainly from the cation charge. The frequencies and bandwidths of the C=O and C=N stretching modes of phenol blue are found to be close to those in conventional polar solvents such as methanol and dimethyl sulfoxide. The frequencies of these vibrational modes show similar dependence upon the electronic absorption band center as is observed in conventional liquid solvents. However, peculiar behavior was found in the Raman bandwidths and the excitation wavelength dependence of the C=N stretching mode in room temperature ionic liquids. Both the bandwidth of the C=N stretching mode and the extent of the excitation wavelength dependence of the Raman shift of the C=N stretching mode tend to decrease as the absorption band center decreases, in contrast to the case of conventional solvents. This anomaly is discussed in terms of the properties of room temperature ionic liquids.     

Fluorescence spectroscopic properties and crystal structure of a series of donor-acceptor diphenylpolyenes

A series of p-nitro-p'-alkoxy(OR)-substituted (E,E,E)-1,6-diphenyl-1,3,5-hexatrienes (1a, R = Me; 1b, R = Et; 1c, R = n-Pr; 1d, R = n-Bu) were prepared. The absorption and fluorescence spectra in solution were almost independent of the alkoxy chain length. The absorption maximum showed only a small dependence on the solvent polarity, whereas the fluorescence maximum red-shifted largely as the polarity increased. The solid-state absorption and fluorescence spectra were red-shifted relative to those in low polar solvents and were clearly dependent on the alkoxy chain length. The fluorescence maxima for the crystals of 1b and 1d were observed at 635-650 nm, which were red-shifted by 40-50 nm relative to those for 1a and 1c. The Stokes shifts were all relatively small (3000-3500 cm-1). For all four compounds, the fluorescence decay curves in the solid state were able to be analyzed by single-exponential fitting to give the lifetimes of 1.1-1.3 ns. This indicates that the emission of 1a-d is not originated from an excimer or molecular aggregates, but from only one emitting monomeric species. The fluorescence quantum yields of 1a-d were considerably high compared with the values for organic solids, which is consistent with their monomeric origin of emission. Single-crystal X-ray structure analyses of 1a, 1c, and 1d showed that the crystal packing was dependent on the alkoxy chain length. The crystals of 1a and 1c had herringbone structure, whereas that of 1d had pi-stacked structure. Strong pi-pi interaction in the crystal of 1d would be the cause of the spectral red shifts relative to those for 1a and 1c. No observation of excimer fluorescence from crystal 1d can be attributed to the limited overlap between the pi-planes of the molecules due to its "slipped-parallel" structure.     

anti-Bis(μ-2-ammonio­ethane­thiol­ato-κ2S:S)­bis­[di­chloro­palladium(II)] dihydrate

Each of two square-planar Pd^II ions in the title compound, [Pd₂Cl₄(μ-Haet-S)₂]·2H₂O (Haet = 2-ammonio­ethane­thiol­ate, C₂H₇NS), which was obtained by rearrangement of [Pd₂{Pd(aet-N,S)₂}₄]⁴⁺ in acidic solution, is coordinated by two bridging S atoms from two Haet ligands and by two terminal Cl atoms, forming the dinuclear structure. Since the complex is situated on a center of symmetry, the two monodentate Haet arms are located on opposite sides of the central Pd₂S₂ square plane, i.e. the present complex is the anti isomer. The S—C—C—N torsion angle is 177.3 (6)° and some intermolecular hydrogen bonds are observed.