Frustrations in Molecular System under High Pressure

Even at ambient pressure, liquid and solid states of room temperature ionic liquids (RTILs) are quite complicated because of a variety of charge network (scalar), molecular orientational order (vector) and coordination number (topology) based on degrees of freedom of molecular conformations. The RTILs possess a unique property such as nano-heterogeneity in spite of simple molecular system. Recently, 1-butyl-3-methylimidazolium hexafluorophosphate, [C4mim][PF6], reveals crystal polymorphs at low temperature. Furthermore, the intrinsic nature of the RTILs is enhanced under high pressure [1-3]. In [C4mim][PF6], a sequence of high pressure states is liquid-crystals-glass on compression process. A significant finding is that pressure induced "conformational glass" of [C4mim][PF6] was observed consistently by X-ray diffraction and Raman spectroscopy, where the maximum pressure was 8 GPa [3]. After decompression from the maximum pressure, the sample has completely recovered without dissociation or polymerization. A balancing between molecular packing efficiency and various cation conformers causes multistep frustrations only in one system.

Enzymatic hydrolysis of the β–β amide linkage in poly-β-aspartate

Polyaspartate is a biodegradable and water-soluble polymer, and an important material as an alternative to polyacrylate. Polyacrylate is widely used as a builder of detergents, pigment dispersant, cosmetic moisturizer, water treatment agents (scale preventive, metal corrosion preventive), water absorptive polymer of disposable diaper, and so on, and are likely accumulated in the environment. Replacement of the polymer by biodegradable polyaspartate should reduce the accumulation and therefore environmental pollution. Thermally synthesized polyaspartate contains both α- and β-amide linkages. Recently, three bacterial enzymes that degrade polyaspartate have been isolated and characterized. An enzyme from Pedobacter sp. KP-2 specifically catalyzes the hydrolysis of the β–β-amide linkage in the polymer. The enzyme is a monomeric periplasmic protein, and the mature form contains 265 amino acid residues with a molecular weight of about 30,000. To understand the mechanisms underlying the interactions with the polymer substrate and hydrolysis of the β–β amide linkage, we set out the crystallographic study of the enzyme. We succeeded in crystallization of the enzyme by vapor-diffusion using polyethylene glycol 4,000. Crystals belonged to orthorhombic space group C222. Addition of cobalt salt in the mother liquor altered the space group of crystals to P6422 and greatly improved the diffraction quality. Data sets for native and mutant enzymes were collected to a resolution of 1.9 Å at SPring-8, Japan. Phases were calculated by cobalt-SAD. The obtained structure represented an α/β hydrolase fold which is often observed for a large number of serine esterases such as lipase and PHB depolymerase. Residues Ser125, Asp193, and His248 were within hydrogen bonding interactions, forming a catalytic triad. Structures of subsites 1 and 2 for binding of monomer units of the polymer were determined for the mutant enzyme complexed with an oligomer substrate. The monomer unit bound to subsite 1 was in extensive hydrogen bond interactions with residues including arginine. Though overall structural similar between the enzyme and PHB depolymerase from Penicillium funiculosum, residues that may interact with polymer substrates were totally different.

PF BL-15A for semi-microbeam XAFS/XRF and high-brilliance SAXS/GI-SAXS

New beamline, BL-15A, was completed at the BL-15 section of the PF-ring in 2014. This new beamline has a short gap undulator which produces high brilliance X-rays ranging from 2.1 keV to 15 keV. The beamline will be dedicated to both activities, XAFS/XRF/XRD studies using semi-micro focus beams (A1 station) and SAXS experiments using collimated softer and hard X-rays (A2 station). In the XAFS/XRF studies, the semi-micro beam available in a wide range of photon energies allows analyzing the local structures of the elements and valence on inhomogeneous samples in the fields of environmental science and new energy source science. The softer X-rays up to 2.1 keV will provide access to absorption edges of phosphor and sulfur, which are very important targets for those fields. The SAXS scientific programs include structural studies of functional membranes, time-resolved X-ray scattering and large hierarchical structure analysis. All of these three programs require a high-brilliance light source. In particular, grazing incidence SAXS (GI-SAXS) using vertically small-size softer beam ranging between 2.1-3.0 keV will help to control the depth of the membrane structure analysis and reduce the roughness defects of an imperfect membrane. The combination of XAFS/XRF and SAXS experiments gives wide structural information from fine atomic structure to low and medium resolution. It can be beneficial to build these instruments as two stations on the same beamline. BL-15A is oriented toward joint advanced studies by the two techniques. Old BL-15 beamlines were scrapped and new construction work started in 2013. The construction was completed in the summer shutdown of 2013 and the first beams was delivered on Oct 17, 2013. We are pursuing the beamline commissioning and the A1 and A2 stations will be opened to users in May, 2014. Here, the beamline design and performance, and the preliminary results will be reported.