2020同步年報

Facility Status 109 B iological small-angle X-ray scattering (BioSAXS) beam- line 13A of Taiwan Photon Source (TPS), open to users since September 2020, provides a high flux (4 × 10 14 photons/s) for time-resolved and synchronized small- and wide-angle X-ray scattering (SAXS-WAXS) of biomacromo- lecular solution structures over wide length and time scales. This advanced BioSAXS beamline also offers new oppor- tunities for ultra-SAXS (USAXS) to resolve the hierarchical structures of bio-machinery assemblies in solution, gel or condensed forms and anomalous SAXS/WAXS for metal or mineral distributions and compositions in an organelle or drug carrier. The beamline application extends to microbe- am SAXS/WAXS for correlated crystal and nanostructural mappings in natural fibril tissues and synthetic biomaterials under tailored environmental controls. Sensitive to the mean distribution of electron density seg- regated from a homogenous matrix, SAXS probes global conformations of scattering objects in flexible sample envi- ronments, which is particularly advantageous to reveal the solution structures of biomacromolecules of functioning in- termediates, even for multiple-domain proteins and protein complexes. In this sense, SAXS complements X-ray crystal- lography, NMR and other optical spectroscopic methods to investigate structural changes of biological macromole- cules in function. In the recent development of worldwide Biological Small-Angle X-ray Scattering at Taiwan Photon Source synchrotron facilities, a dedicated SAXS beamline to study biological solution structures has become essential. Frontier biological SAXS (BioSAXS) beamline TPS 13A reported here has been jointly developed by NSRRC and Academia Sinica (led by Ming-Daw Tsai and Meng-Chiao Ho). This large col- laborative team is a successive collaboration of a previous joint effort to upgrade SAXS beamline TLS 23A for immedi- ate BioSAXS applications. Equipped with a 4-m undulator IU24 for X-rays of energy 4 to 23 keV, biological small- and wide-angle X-ray (BioSAXS/ WAXS) scattering beamline TPS 13A is dedicated to ob- servations of biomacromolecular solution structures and kinetics, covering wide length and time scales. The MoB4C double-multilayer and Si(111) double-crystal monochro- mators (DMM/DCM), integrated on the same rotating platform, optionally provide a high flux, up to 4 × 10 14 photons/s, and a beam of great energy resolution, ∆ E / E ~ 2 × 10 −4 . The monochromatic beam is selectively focused at the sample position at 40 m from the radiation source for microbeam SAXS/WAXS, or the farthest detector position at 52 m for ultra-SAXS (USAXS), based on two parallel sets of Kirkpatrick-Baez (KB) focusing mirrors placed on a same granite platform. For USAXS, a horizontally collimated four-bounce crystal collimator (4BCC) located downstream further tailors the vertically oriented DCM monochromatic Fig. 1 : Layout of BioSAXS beamline TPS 13A , with featured operational modes indicated. Starting from undulator IU24, the beamline comprises microslits in the front-end zone. The DCM/ DMM monochromators, two sets of vertical/horizontal KB focusing mirrors (VFM/HFM), a vertical deflecting mirror (VDM) and horizontally collimating four-bounce double-crystal collimator (4BCC) are in the optical zone. The collimation, sample stage and detecting (Eiger X 1M for WAXS and Eiger X 9M for SAXS) systems are in the experimental area. beam for a minimum scattering vector q ~0.0003 Å −1 , corresponding to d -spacing resolving power ~2 µm. The 4BCC consists of two sets of horizon- tally oriented double-crystal collima- tors of Si(111), two sets of Si(311) for further improved resolution, arranged in a dispersive configuration for a sig- nificantly decreased beam divergence of 30 µrad. A set of delicate microslits (closely shielded by a set of heat-load slits) located in the beamline front- end at 15.5 m provides tunable, stable slit opening of 1–50 µm as a steady control of microbeam beam size. The slit position is critical for a set of microbeam KB mirrors to focus the mi- crobeam size to the sample position at 40 m from the IU24 source, with small demagnification ratios, near 1.5, in both vertical and horizontal direc- tions. All these operational modes of