Physics opportunities with the RI Beam Factory at RIKEN

The RI Beam Factory (RIBF) is presently the top world-class radioactive-isotope (RI) beam facility in the world. Construction of the factory is now in the process of being completed. This facility is based on the in-flight method to produce fast RI beams. High-energy and intense primary beams accelerated by a superconducting ring cyclotron (SRC) are converted, via the projectile fragmentation or fission reaction channels, to RI beams at a new fragment separator called BigRIPS. Construction of major experimental installations is expected to commence in 2007. Physics opportunities with the RIBF are discussed herein.     

The ASACUSA CUSP: an antihydrogen experiment

In order to test CPT symmetry between antihydrogen and its counterpart hydrogen, the ASACUSA collaboration plans to perform high precision microwave spectroscopy of ground-state hyperfine splitting of antihydrogen atom in-flight. We have developed an apparatus (“cusp trap”) which consists of a superconducting anti-Helmholtz coil and multiple ring electrodes. For the preparation of slow antiprotons and positrons, Penning-Malmberg type traps were utilized. The spectrometer line was positioned downstream of the cusp trap. At the end of the beamline, an antihydrogen beam detector was located, which comprises an inorganic Bismuth Germanium Oxide (BGO) single-crystal scintillator housed in a vacuum duct and surrounding plastic scintillators. A significant fraction of antihydrogen atoms flowing out the cusp trap were detected.     

Highly Chemoselective Aerobic Oxidation of Amino Alcohols into Amino Carbonyl Compounds

The direct oxidation of unprotected amino alcohols to their corresponding amino carbonyl compounds has often posed serious challenges in organic synthesis and has constrained chemists to adopting an indirect route, such as a protection/deprotection strategy, to attain their goal. Described herein is a highly chemoselective aerobic oxidation of unprotected amino alcohols to their amino carbonyl compounds in which 2‐azaadamantane N‐oxyl (AZADO)/copper catalysis is used. The catalytic system developed leads to the alcohol‐selective oxidation of various unprotected amino alcohols, carrying a primary, secondary, or tertiary amino group, in good to high yield at ambient temperature with exposure to air, thus offering flexibility in the synthesis of nitrogen‐containing compounds.     

Synergistic Spin Transition between Spin Crossover and Spin‐Peierls‐like Singlet Formation in the Halogen‐Bonded Molecular Hybrid System: [Fe(Iqsal)2][Ni(dmit)2]⋅CH3CN⋅H2O

To introduce halogen‐bond interactions between a cation and an anion, a novel Fe^III complex from iodine‐substituted ligands involving a paramagnetic nickel dithiolene anion was prepared and characterized. The compound exhibited the synergy between a spin‐crossover transition and a spin‐Peierls‐like singlet formation. The halogen‐bond interactions between the iodine and the sulfur atoms stabilized the paramagnetic state of π‐spins and played a crucial role in the synergistic magnetic transition between d‐ and π‐spins. In addition, the compound showed the light‐induced excited spin state trapping effect.     

Morphological changes in the cellulose and lignin components of biomass occur at different stages during steam pretreatment

Morphological changes to the different components of lignocellulosic biomass were observed as they occurred during steam pretreatment by placing a pressure reaction cell in a neutron beam and collecting time-resolved neutron scattering data. Changes to cellulose morphology occurred mainly in the heating phase, whereas changes in lignin morphology occurred mainly in the holding and cooling phases. During the heating stage, water is irreversibly expelled from cellulose microfibrils as the elementary fibrils coalesce. During the holding phase lignin aggregates begin to appear and they increase in size most noticeably during the cooling phase. This experiment demonstrates the unique information that in situ small angle neutron scattering studies of pretreatment can provide. This approach could be useful in optimizing the heating, holding and cooling stages of pretreatments to allow the exact size and nature of lignin aggregates to be controlled in order to enhance enzyme accessibility to cellulose and therefore the efficiency of biomass conversion.     

Diversity of potential hydrogen bonds in cellulose I revealed by molecular dynamics simulation

We have performed molecular dynamics calculations using a revised version of the Gromos56A_carbo force field to understand the consequences of the different potential hydrogen bonding patterns on the structural stability and thermal behavior of the I_α and I_β forms of native cellulose. For each allomorph, we considered three patterns of hydrogen bonds: two patterns obtained from neutron diffraction data refinement and a regular mixture of the two. Upon annealing, the hydrogen bonding schemes of cellulose I_β, irrespective of the starting structure, re-arranged into the main hydrogen bond pattern experimentally observed (pattern A). On the other hand, the I_α structures, irrespective of the starting hydrogen bonding pattern, converged to a non-experimental structure where the adjacent chains are shifted along the chain direction by 0.12 nm in the hydrogen-bonded plane, and the hydroxymethyl group conformation alternates between gt and tg along the chain. The exotic structure in I_α might be a consequence of a deficiency in force field parameters and/or potential molecular arrangement in less crystalline cellulose.     

Reductive coupling of N-methoxycarbonyl lactams with benzophenone and 9-fluorenone by low-valent titanium

The reductive coupling of N-methoxycarbonyl lactams with benzophenone by Zn-TiCl₄ in THF gave cross-coupled products as cyclic α-diphenylidene-N-methoxycarbonylamines and ring-opening α,α-diphenyl-α-hydroxy-ω-(N-methoxycarbonyl)amino ketones selectively depending on the reduction conditions. The reductive coupling of N-methoxycarbonyl lactams with 9-fluorenone by Zn-TiCl₄ gave cyclic α-(9H-fluoren-9-ylidene)-N-methoxycarbonylamines preferentially irrespective to the conditions.     

Ultrasonic irradiation effect in the quenched benzene

On slow cooling, a precursor phenomenon in supercooled benzene was probed by longitudinal absorption. On quenching, in-situ observation of ultrasonic measurements was carried out at the fixed temperature. Sequence of the transmitted waves was multiple scattered in quenched benzene. The dynamic ultrasound scattering is sensitive to the local strain and dynamic inhomogeneous fluctuations. The quenched benzene shows the maximum value of longitudinal absorption at incubation time, t_inc. Crystal domain growth/coarsening is promoted by the ultrasonic irradiation at t_inc < t. In addition, t_inc depends on the quenching temperature. Ultrasonic irradiation and quenching effects dominate the extraordinal nucleation and growth process of benzene in spite of simple and non-polar molecular liquid.