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- Horváth, E., et al.
(author)
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Investigation of mandelic acid bonding on Pirkle type chromatographic stationary phases by Raman spectroscopy
- 2000
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In: Journal of Chromatography A. - 0021-9673 .- 1873-3778. ; 893:1, s. 37-46
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Journal article (peer-reviewed)abstract
- The bonding of mandelic acid enantiomers has been studied on benzene-leucine, dinitrobenzene-leucine and dinitrobenzene-phenylalanine type chiral stationary phases connected to zeolite A supports. The π-donor, π-acceptor and H-bonding interactions responsible for diastereomer pair formations can be studied under quasi in situ chromatographic conditions by Fourier transform Raman and surface enhanced Raman spectroscopic techniques. Structural differences between diastereomer pairs result in observable spectral differences at a phase load of approx. 50%. It was shown that the decreasing π-acceptor character of the phase is associated with its increasing capability of H-bond formation. Correlating spectral data to chromatographic results it can be concluded that, in addition to H-bonding as well as to π-donor-π-acceptor interactions, steric hindrances due to bulky moieties of either the stationary phase or the analyte molecules are of importance in successful separations.
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| 2. |
- Fischler, H., et al.
(author)
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Concept mapping as a tool for research in science education
- 2001
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In: Research in Science Education - Past, Present, and Future. - 0792367553
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Book chapter (pop. science, debate, etc.)abstract
- In recent years concept mapping has become a powerful tool that is frequently applied in different contexts in science education. There are still, however, questions and problems that arise when researchers in science education begin to design concept map formats and search for appropriate methods of analysis. In a symposium, five research groups from different countries shared experiences of using concept maps and hence provided some answers to the questions and some illumination of the problems.
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| 5. |
- Jiang, J. Z., et al.
(author)
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Compressibility and thermal expansion of cubic silicon nitride
- 2002
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In: Physical Review B (Condensed Matter). - 0163-1829. ; 65:16, s. 1612021-1612024
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Journal article (peer-reviewed)abstract
- The compressibility and thermal expansion of the cubic silicon nitride (c-Si3N4) phase have been investigated by performing in situ x-ray powder-diffraction measurements using synchrotron radiation, complemented with computer simulations by means of first-principles calculations. The bulk compressibility of the c-Si3N4 phase originates from the average of both Si-N tetrahedral and octahedral compressibilities where the octahedral polyhedra are less compressible than the tetrahedral ones. The origin of the unit cell expansion is revealed to be due to the increase of the octahedral Si-N and N-N bond lengths with temperature, while the lengths for the tetrahedral Si-N and N-N bonds remain almost unchanged in the temperature range 295-1075 K.
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