Biomedical subjects

CK Chen

Publications and source records attributed to CK Chen.

4 recordsLinked to original sources

PubMed2000

The phenomenon of polarization suppression of X-ray Umweg multiple waves in crystals

The phenomenon of the polarization suppression of X-ray Umweg multiple waves in Renninger scans [Renninger (1937). Z. Kristallogr. 97, 107-121] of crystals, showing intensity decrease due to properly chosen wavelength and polarization of incident radiation, is observed. That is, one of the participating wave components in the multiple-wave interference is reduced considerably so that the intensity of multiple diffraction is decreased. The condition for total suppression of the multiple-wave interaction in crystals is derived theoretically from the Born approximation and verified with exact dynamical calculation and experiments. Partial suppression of the strong Umweg interfered component is demonstrated using elliptically or linearly polarized synchrotron radiation. The suppressed multiple-wave intensity distribution reveals high sensitivity to X-ray reflection phase. This multiple-diffraction technique under partial polarization suppression provides an alternative way of enhancing the visibility of multiple-wave interference in crystals for direct phase determination.

Journal Article↗

PubMed1999

Quantitative phase determination for macromolecular crystals using stereoscopic multibeam imaging.

Without invoking anomalous dispersion and heavy-atom derivatives, it is demonstrated that it is possible to directly determine the phases of a large number of reflections collected in a short time from macromolecular crystals using a stereoscopic oscillation-crystal imaging technique, in a multibeam diffraction geometry, where two crystallographic axes in opposite directions are employed as the rotation axes. The intensity profiles (distributions) of the diffraction spots versus the varying tilt Bragg angle of the rotation axis in the two stereoscopically related images yield quantitative phase information. Many multiple diffraction profiles of tetragonal lysozyme and an unknown protein structure are obtained at the rate of 100 profiles per 30 min of X-ray exposure.

Journal Article↗

PubMed1999

Acetate enhances solvent production and prevents degeneration in Clostridium beijerinckii BA101

Addition of sodium acetate to chemically defined MP2 medium was found to increase and stabilize solvent production by Clostridium beijerinckii BA101, a solvent-hyperproducing mutant derived from C. beijerinckii NCIMB 8052. C. beijerinckii BA101 demonstrated a greater increase in solvent production than C. beijerinckii NCIMB 8052 when sodium acetate was added to MP2 medium. In 1-l batch fermentations, C. beijerinckii BA101 produced 32.6 g/l total solvents, with butanol at 20.9 g/l, when grown in MP2 medium containing 60 mM sodium acetate and 8% glucose. To our knowledge, these values represent the highest solvent and butanol concentrations produced by a solventogenic Clostridium strain when grown in batch culture.

Journal Article↗

PubMed1999

Examination of physiological and molecular factors involved in enhanced solvent production by clostridium beijerinckii BA101

The specific activities and the mRNA expression levels associated with coenzyme A transferase, acetoacetate decarboxylase, and butyraldehyde dehydrogenase were elevated in hyper-solvent-producing Clostridium beijerinckii BA101 during the exponential growth phase. The increase in expression of the sol operon and associated enzyme activities may be responsible for enhanced solvent production by C. beijerinckii BA101.

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