Magnetoresistance effects evidencing the pi-d interaction in metallic organic conductors, (EDT-DSDTFVO)2*MX4 (M = Fe, Ga; X = Cl, Br)

The 2:1 salts of a new donor molecule, EDT-DSDTFVO with MX4- (M = Fe, Ga; X = Cl, Br) ions, were prepared. The crystal structures of the donor molecules had a beta-type packing motif. All the salts essentially exhibited metallic behaviors despite the small upturns in the resistances below 30-70 K. A large negative magnetoresistance (MR) effect [-14.7% (rho(perpendicular)) at 4.0 K and 5 T] was observed in the FeCl4- salt, while a positive MR effect [+4.0% (rho(perpendicular)) at 4.0 K and 5 T] was observed in the GaCl4- salt, suggesting that there is a pi-d interaction in the FeCl4- salt. The pressure application suppressed the resistivity upturns, increased the negative MR effect (-17.7% at 9.5 kbar) in the FeCl4- salt, and decreased the positive MR effect (+3.3% at 15 kbar) in the GaCl4- salt.     

Structural basis for the phase switching of bisaminecopper(II) cations at the thermal limits of lattice stability

The structural grounds of the decrease of point and lattice symmetries coupled with switching of the exchange interaction in single crystals of a highly strained, coordinationally unsaturated bisdiaminecopper(II) cation are described. The combined magnetic susceptibility and X-ray diffraction results indicate that the interplay between the inherent vibronic instability and ligand-field strain imposed by moderately flexible, coordinationally shielding ligands enables effective switching of the pseudo-Jahn-Teller d9 centers between states with different exchange interaction in the low-temperature regime and valence orbital orientation and coordination geometry in the high-temperature regime. Within the low-temperature hysteresis region, the phase transition can also be induced by excitation of the ligand-to-metal charge-transfer bands, resulting in overall shrinkage of the lattice. The compound is a prototype of weakly electronically coupled one-dimensional Jahn-Teller systems, which can undergo phase transitions induced by light, in addition to heating, cooling, and change of pressure, and it represents a prospective basis for the design of switching materials capable of multimode external control.     

Radical hydroxyalkylation of C-H bond adjacent to nitrogen of tertiary amides, ureas, and amines

Tertiary amides, ureas, and amines undergo direct intermolecular addition to aldehydes under the Et3B/air conditions, thereby providing a unique and simple means for the radical sp3 C-H transformation of nitrogen-containing molecules.     

Practical synthesis of wybutosine, the hypermodified nucleoside of yeast phenylalanine transfer ribonucleic acid

An improved synthesis of 3-beta-D-ribofuranosylwybutine (2) has been achieved by the Wittig reaction between 4,6-dimethyl-9-oxo-3-[2,3,5-tris-O-(tert-butyldimethylsilyl)-beta-D-ribofuranosyl]-4,9-dihydro-3H-imidazo[1,2-a]-purine-7-carbaldehyde (8) and the phosphorane derived from (R)-2-[(methoxycarbonyl)amino]-3-(triphenylphosphonio)propanoate (9), followed successively by methylation, hydrogenation, and deprotection. On the other hand, the minor nucleoside wybutosine of yeast tRNA(Phe) was isolated on a scale of 80 microg by partial digestion of unfractionated tRNA (1 g) with nuclease P1, followed successively by reversed-phase column chromatography, complete digestion with nuclease P1/alkaline phosphatase, and reversed-phase HPLC. Comparison of this nucleoside with 2 has unambiguously established that the structure of wybutosine is (alphaS)-alpha-[(methoxycarbonyl)-amino]-4,6-dimethyl-9-oxo-3-beta-D-ribofuranosyl-4,9-dihydro-3H-imidazo[1,2-a]purine-7-butanoic acid methyl ester (2).     

13C NMR spectral assignments for nematic liquid crystals by 2D chemical shift gamma-encoding NMR

A novel method to accomplish 13C NMR spectral assignments for nematic liquid crystals is proposed. The two-dimensional (2D) isotropic/anisotropic chemical shift correlation spectrum is observed in which the anisotropic shift parameters are represented as sharp lines by gamma-encoding. The 13C spectral assignments can be made from the 2D spectrum with the aid of the 13C isotropic shift assignments for the same compound in the isotropic liquid state. The experiments were performed on p-methoxybenzilidene-p-n-butylaniline.     

Pile-up glass microreactor

We made a 'pile-up' microreactor in which ten levels of microchannel circuits were integrated to form a single glass entity. Solutions were distributed to each layer via cylindrical holes with a diameter much larger than that of the microchannel. Fabrication of the pile-up reactor was completed using only conventional photolithography, wet etching and thermal bonding techniques, and no special facilities or instruments were required. An amide formation reaction between amine in aqueous solution and acid chloride in organic solution was carried out using the pile-up reactor. The yield of the amide formation reaction is dependent on the size of the specific surface area between the two solutions, and the small space inside the microchannels is good for acquiring a large specific surface area without any stirring processes. The maximum throughput for the ten-layered pile-up reactor was ten times larger than that of a single-layered one, yet the reaction yield was still high. Productivity of the pile-up reactor for the reaction was as high as on a gram per hour scale. This value suggests that many conventional plants producing fine chemicals can be replaced by microreactors through the numbering-up technology.     

Novel molecular recognition via fluorescent resonance energy transfer using a biotin-PEG/polyamine stabilized CdS quantum dot

A novel functionally PEGylated quantum dot (QD) was prepared by a coprecipitation method in the presence of the biotin-PEG/polyamine block copolymer. When CdCl2 and Na2S were mixed in aqueous media in the presence of the biotin-PEG-b-poly(2-(N,N-dimethylamino)ethyl methacrylate) [biotin-PEG/PAMA], a CdS QD with a size of ca. 5 nm was prepared. The polyamine segment was anchored on the surface of the formed CdS nanoparticle, whereas the PEG segment was tethered on the surface to form a hydrophilic palisade, thus improving the dispersion stability in aqueous media even under a high salt concentration condition. An effective fluorescent resonance energy transfer (FRET) was observed by the specific interaction of the biotin-PEG/PAMA stabilized CdS QD with TexasRed-labeled streptavidin of the physiological ionic strength of 0.15 M. The extent of the energy transfer was in proportion to the concentration of the TexasRed-streptavidin. This FRET system using the PEGylated CdS QD coupled with fluorescent-labeled protein can be utilized as a highly sensitive bioanalytical system.     

Enhanced diastereoselectivity via confinement: diastereoselective photoisomerization of 2,3-diphenyl-1-benzoylcyclopropane derivatives within zeolites

Photochemistry of optically pure trans-2,3-diphenyl-1-benzoylcyclopropane has been examined in isotropic solution and within zeolites. Results suggest that it isomerizes by cleavage of either the C1-C2 or C1-C3 bond. From the perspective of chiral induction, photoisomerization of cis-2,3-diphenyl-1-benzoylcyclopropane derivatives with chiral auxiliaries placed at the meta and para positions of the benzoyl group have been examined both in isotropic solution and within zeolites. Whereas in isotropic solution the chiral auxiliaries placed at the meta position exhibit very little influence during the conversion of triplet cis-2,3-diphenyl-1-benzoylcyclopropane derivatives, they have significant influence within zeolites. For example, alpha-methyl benzylamine placed at the meta position of the benzoyl group (via an amide bond) yields the trans isomer with a diastereoselectivity (de) of 71% within NaY zeolite, whereas in solution no de is obtained. The chiral induction process within zeolites depends on the nature of the alkali ion and on the presence of water. Results suggest that the chiral auxiliary is able to control the bond being cleaved (C1-C2 vs. C1-C3 bond) within a zeolite, but it is unable to do so in an isotropic solution.     

Sequential arrangement of gamma-valerolactone enantiomers enclathrated in cholic acid channels as studied by 13C solid-state NMR: elucidation of the optical resolution mechanism

The mechanism of the optical resolution of gamma-valerolactone (VAL) enantiomers by enclathration in cholic acid (CA) channels was investigated. 13C cross-polarization magic-angle spinning spectra of CA/VAL inclusion compounds show four methyl 13C peaks of VAL with different intensities depending on the enantiomeric ratios. The four peaks were assigned to the inner and end (S)-(-)-enantiomers (S) in the S domain and the inner and end (R)-(+)-enantiomers (R). The relative intensities of the four methyl 13C peaks cannot be explained by the random process model for inclusion but are successfully reproduced by assuming the first-order Markov process, in which the inclusion probabilities of S and R depend on which enantiomer has precedingly entered the CA channel. The probability p(S/S) that two S enantiomers successively enter a channel is thus found to be 83%, and p(R/R) is 50%. The large probability of p(S/S) indicates that once an S enantiomer enters a channel, it become easy for other S enantiomers to successively enter the channel, and thus the large enantiomeric excess of S is obtained. The inclusion probabilities of S and R were confirmed by 1D 13C-13C polarization-transfer experiments among the four methyl carbons of VAL in the CA channel. Further, we found that the 13C line widths and peak positions of the CA tail group change depending on the enantiomeric ratio. We concluded that once S is included, it changes the conformation of the CA tail group so that other S enantiomers become easy to successively enter the channel.     

Diastereoselective [2 + 2] photocycloaddition of stilbene to chiral fumarate. Direct versus charge-transfer excitation

The selective excitation of the charge-transfer (CT) complex and the direct excitation of the substrate gave distinctly different product ratios and diastereomeric excesses (de's), as well as their temperature dependencies, in [2 + 2] photocycloaddition of (E)-stilbene to bis((R)-1-methylpropyl) fumarate, clearly demonstrating that the excited CT complex and the conventional exciplex differ in structure and reactivity. This conclusion is supported by the contrasting fluorescence behavior exhibited by the relevant excited species, particularly at low temperatures.