Biomedical subjects

J Davaasambuu

Publications and source records attributed to J Davaasambuu.

3 recordsLinked to original sources

PubMed2006

Aspects of the photodimerization mechanism of 2,4-dichlorocinnamic acid studied by kinetic photocrystallography.

Photoinduced structural variations in single crystals of 2,4-dichloro-trans-cinnamic acid (C9H6Cl2O2, DiClCA) have been investigated using X-ray diffraction (photocrystallography) and optical spectroscopic methods. During UV irradiation, which initiates the irreversible dimerization reaction, a loss of the long-range order of the reactant single crystal was found, i.e., that the dimerization is a heterogeneous one. This unexpected result emphasizes the still-existing problem of predicting changes or of remaining periodicity during chemical reactions in the solid state. On the basis of the experimental results, we propose a qualitative kinetic reaction scheme for DiClCA heterogeneous dimerization reaction.

Cinnamates↗

PubMed2005

Femtosecond time-resolved powder diffraction experiments using hard X-ray free-electron lasers.

In the next decade the scientific community expects a strong impact in physics, chemistry, biology, material research and life sciences by the availability of high-brilliance X-ray radiation from free-electron laser (FEL) sources. In particular, in the field of ultrafast science these new sources will allow new types of experiments, enabling new phenomena to be discovered. Whereas today ultrafast X-ray diffraction experiments are strongly restricted by the limited X-ray flux of current sources of sub-picosecond X-ray pulses, FELs will provide short pulses of typically 10(12) photons with a duration of the order of 100 fs and monochromaticity of 10(-3). Here, the feasibility of time-resolved single-shot powder diffraction experiments using these intense pulses, and the requirements of these experiments, are discussed. The detector count rates are estimated for diffraction from a model compound in a wide q-regime under the special consideration of high resolving power. In the case of LCLS radiation parameters, single-shot experiments will be feasible although high-resolution powder diffraction will require a reduction of the intrinsic FEL radiation bandwidth.

Journal Article↗

PubMed2004

Experimental requirements for light-induced reactions in powders investigated by time-resolved X-ray diffraction.

A general outline of how to perform a light-excited time-resolved diffraction experiment by applying the optical pump/X-ray probe technique is given. Owing to the difference in penetration depths between the optical light (laser) pump and the X-ray probe, only specific or specially designed crystalline systems can be investigated, so special requirements have to be fulfilled concerning the sample and its compartments. A summary of the experimental conditions of optical pump/X-ray probe experiments is presented, emphasizing why the use of powder diffraction is a useful and necessary X-ray technique for this kind of experiment. The possibilities and bottlenecks of time-resolved X-ray diffraction on the picosecond time scale will be demonstrated in the powder diffraction studies of N,N-dimethylaminobenzonitrile and N,N-diisopropylaminobenzonitrile, where the photo-induced structural changes of these molecular organic systems have been studied as a function of time.

Artifacts↗