Multielement analysis of groundwater samples by neutron activation with comparison between direct and evaporation methods

This report is the results of the studies on NAA of groundwater samples with comparison between direct and evaporation methods, and of the applications for the samples of alluvium plain composed with granitiform soils and of Neogene strata composed with clay minerals.     

Photo-induced chirality switching in a cobaloxime complex crystal

Switching of molecular chirality under photo-irradiation was studied in a cobaloxime complex crystal. Excitation of the d-d transition of the Co(III) ion appeared to be much more effective in inducing the chirality change than excitation of the ligand-metal charge transfer band although the latter is more effective in breaking the Co-C bond that initiates the chirality switching. The chirality change versus irradiation time showed a steplike behavior suggesting that chirality switching of molecules occurred in correlation with their nearest neighbors.     

Rheological and related study of gelation of xyloglucan in the presence of small molecules and other polysaccharides

Interaction between tamarind seed xyloglucan and the other polysaccharides, gellan gum or xanthan investigated by rheology, differential scanning calorimetry, and related methods was discussed. All these three polysaccharides do not form a gel at lower concentrations by itself at the experimental conditions studied but the gelation of xyloglucan occurs in the presence of gellan or xanthan. Gelation of xyloglucan in the presence of a polyphenol, epigallocatechin gallate, is also discussed. Hence the gelation of these mixtures is caused by the synergistic interaction, and the models for the synergistic interaction were discussed. The gelation of polysaccharides by the synergistic interaction is of great value for food and related industries.     

New diarylheptanoids from Alpinia pinnanensis

Three new diarylheptanoids, called alpinnanins A-C (1-3), together with two known chalcones, 2',4'-dihydroxy-6'-methoxychalcone and 4',6'-dimethylchalconaringenin, two known flavanones, alpinetin and naringenin 5-O-methyl ether, a known diarylheptanoid, (3S,5S)-trans-3,5-dihydroxy-1,7-diphenyl-1-heptene, stigmasterol and beta-sitosterol as a mixture, and beta-sitosterol 3-O-beta-D-glucopyranoside were isolated from the rhizomes of Alpinia pinnanensis T. L. WU et SENJEN (Zingiberaceae). Their structures were elucidated by spectroscopic analyses.     

The use of trifluoroacetaldehyde ethyl hemiacetal or hydrate in a simple and practical regioselective synthesis of beta-hydroxy-beta-trifluoromethyl ketones from enamines and imines

The reaction of trifluoroacetaldehyde ethyl hemiacetal or hydrate with an equimolar amount of enamines, derived from various methyl ketones, smoothly proceeded to give the corresponding beta-hydroxy-beta-trifluoromethyl ketones in high yields. An equimolar amount of imines derived from various methyl ketones with aliphatic, aromatic, and heteroaromatic substituents also readily reacted with trifluoroacetaldehyde ethyl hemiacetal or hydrate to afford the corresponding beta-hydroxy-beta-trifluoromethyl ketones in good to excellent yields. Difluoroacetaldehyde ethyl hemiacetal as well as pentafluoropropionaldehyde also participated in the reaction, affording good yields of the corresponding beta-hydroxy-beta-difluoromethyl or beta-pentafluoropropyl ketones.     

Origin of the π‐Facial Stereoselectivity in the Addition of Nucleophilic Reagents to Chiral Aliphatic Ketones as Evidenced by High‐Level Ab Initio Molecular‐Orbital Calculations

Ab initio molecular‐orbital (MO) calculations were carried out, at the MP2/6‐311++G(d,p)//MP2/6‐31G(d) level, to investigate the conformational Gibbs energy of alkyl 1‐cyclohexylethyl ketones, cyclo‐C₆H₁₁CHCH₃? CO? R (R=Me, Et, iPr, and tBu). In each case, one of the equatorial conformations was shown to be the most stable. Conformers with the axial CHCH₃COR group were also shown to be present in an appreciable concentration. Short C? H???C?O and C? H???O?C distances were found in each stable conformation. The result was interpreted on the grounds of C? H???π(C?O) and C? H???O hydrogen bonds, which stabilize the geometry of the molecule. The ratio of the diastereomeric secondary alcohols produced in the nucleophilic addition to cyclo‐C₆H₁₁CHCH₃? CO? R was estimated on the basis of the conformer distribution. The calculated result was consistent with the experimental data previously reported: the gradual increase in the product ratio (major/minor) along the series was followed by a drop at R=tBu. The energy of the diastereomeric transition states in the addition of LiH to cyclo‐C₆H₁₁CHCH₃? CO? R was also calculated for R=Me and tBu. The product ratio did not differ significantly in going from R=Me to tBu in the case of the aliphatic ketones. This is compatible with the above result calculated on the basis of the conformer distribution. Thus, the mechanism of the π‐facial selection can be explained in terms of the simple premise that the geometry of the transition state resembles the ground‐state conformation of the substrates and that the nucleophilic reagent approaches from the less‐hindered side of the carbonyl π face.     

Structural investigation of the antibiotic sporaviridin: 11—Molecular secondary ion mass spectral studies on the constituent pentasaccharides viridopentaoses

Molecular secondary ion mass spectra of three pentasaccharides, viridopentaoses A, B and C, using various matrices, are discussed. The appearance of the molecular ion species is dependent upon the relative proton affinities between the sample and the organic matrix material. However, the presence of sodium ion, rather than proton, also greatly influences the appearance of the molecular ion species. The glycosidic linkages are mainly cleaved between the glycosidic oxygen atom and the anomeric carbon atom to give informative sugar sequence ions. These fragmentations have been confirmed by the linked scanning technique (B/E).     

Analysis of neutral oligosaccharides for structural characterization by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry

We have acquired multi-stage mass spectra (MSn) of four branched N-glycans derived from human serum IgG by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry (MALDI-QIT-TOF-MS) in order to demonstrate high sensitivity structural analysis. [M+H]+ and [M+Na]+ ions were detected in the positive mode. The detection limit of [M+Na]+ in MS/MS and MS3 measurements for structural analysis was found to be 100 fmol, better than that for [M+H]+. The [M+H]+ ions subsequently fragmented to produce predominantly a Y series of fragments, whereas [M+Na]+ ions fragmented to give a complex mixture of B and Y ions together with some cross-ring fragments. Three features of MALDI-QIT-CID fragmentation of [M+Na]+ were cleared by the analysis of MS/MS, MS3 and MS4 spectra: (1) the fragment ions resulting from the breaking of a bond are more easily generated than that from multi-bond dissociation; (2) the trimannosyl-chitobiose core is either hardly dissociated, easily ionized or it is easy to break a bond between N-acetylglucosamine and mannose; (3) the fragmentation by loss of only galactose from the non-reducing terminus is not observed. We could determine the existence ratios of candidates for each fragment ion in the MS/MS spectrum of [M+Na]+ by considering these features. These results indicate that MSn analysis of [M+Na]+ ions is more useful for the analysis of complicated oligosaccharide structures than MS/MS analysis of [M+H]+, owing to the higher sensitivity and enhanced structural information. Furthermore, two kinds of glycans, with differing branch structures, could be distinguished by comparing the relative fragment ion abundances in the MS3 spectrum of [M+Na]+. These analyses demonstrate that the MSn technology incorporated in MALDI-QIT-TOF-MS can facilitate the elucidation of structure of complex branched oligosaccharides.     

Model study for large deformation of physical polymeric gels

A model for large deformation of polymer gels with physical cross-linking is developed and shown to be in good agreement with experimental stress-strain curves which show strain hardening in intermediate strains followed by strain softening in large deformations near the yield strain. The model takes into account the coil-helix transition equilibrium and allows for the distribution of the end-to-end distance. The gel is considered to be formed by long flexible chains and crystalline zones acting as junctions of the chains. The number of segments contained in a flexible chain is variable due to the equilibrium between the two regions. As the end-to-end distance increases due to the deformation, more and more segments are reeled out from the junction zone. Finally, one end of the chain is librated from the junction and the chain becomes dangling. The appearance of dangling chains causes the strain softening because they cease to contribute to the elasticity. From the parameter dependence of the stress-strain relations, it was found that the yield behavior depends strongly on the distribution of end-to-end distance. The yield strain is approximately given by the ratio of the upper limit of the number of segments and the average end-to-end distance. The standard deviation of the end-to-end distance affects significantly the width of the peak in the stress-strain curve, thus determining the degree of strain softening.     

Enhanced Hydrogen Generation from Formic Acid by Half‐Sandwich Iridium(III) Complexes with Metal/NH Bifunctionality: A Pronounced Switch from Transfer Hydrogenation

By switching the catalytic function from transfer hydrogenation based on the metal/NH bifunctionality, facile dehydrogenation of formic acid was achieved by amido‐ and hydrido(amine)–Ir complexes derived from N‐triflyl‐1,2‐diphenylethylenediamine (TfDPEN) at ambient temperature even in the absence of base additives. Further acceleration was observed by the addition of water, leading to a maximum turnover frequency above 6000 h^?1. A proton‐relay mechanism guided by the protic amine ligand and water is postulated for effective protonation of metal hydrides.