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2 2006

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Damped Quantum Rotation of the Methyl Group in Liquid-Phase NMR Spectra of 9-Methyltriptycene Derivatives

Czerski I., Szymański S.

Polish Journal of Chemistry

2006

Vol. 80, nr 7

1233-1257

Hindered rotation of the methyl group evidenced in NMR line shapes is normally viewed as a sequence of classical random jumps between the three equivalent orientations of the group. In solids at low temperatures, possible effects of the quantum tunneling, manifested as apparent spin-spin couplings between the methyl protons, are incorporated by force into this essentially classical picture. In the damped quantum rotation (DQR) theory formulated recently, the hindered rotation is entirely a non-classical phenomenon. It is described in terms of a consistent combination of the quantum tunneling and two quantum rate (coherence-damping) processes; the phenomenological behaviour of themethyl group becomes classical only when the two quantum rate processes occur with equal rates. Occurrences of the DQR effect, i.e., differences between the two quantum rate constants, were earlier detected in solids at temperatures below 110 K and, surprisingly, also in liquids above 170 K. In this study, further examples of the DQR effects in liquid-phase NMR are reported. Like the previous observations for liquids, the present ones involve the strongly hindered methyl groups in 9-methyltriptycene derivatives. A particularly clear manifestation of theDQR effect is found for 1,4-dibromo-9-methyltriptycene.With the ratio of the two quantum rate constants exceeding 1.25, this system shows the farthest departure from the classical behaviour, ever reported for liquids.Our earlier observations of the quantum tunneling of the methyl group in liquid phase, reflected in strong dependence on temperature of the J-couplings between the methyl protons, are now augmented by further evidence.

Testing Textiles Using the LA-ICP-MS-TOF Method

Szynkowska M. I., Czerski I., Paryjczak T., Rybicki E., Włochowicz A.

Fibres & Textiles in Eastern Europe

2006

Vol. 14, no. 4 (58)

87--90

The LA-ICP-TOF-MS method (Laser Ablation Inductively Coupled Plasma Time of Flight Mass Spectrometry) is an analytical technique for determining trace elements and their isotopes in solid samples. The action of a high-energy laser beam on a solid results in the evaporation and removal of material in the form of neutral atoms and molecules, as well as, positive and negative ions from the solid surface exposed to this radiation. In chemical analysis, the pulse laser based on a solid such as neodym (Nd:YAG) has proved to be very useful as it makes it possible to incorporate solid samples directly into plasma. It has been utilised as a source of very high energy with specific properties, and can be used to analyse various solids (conductive and non-conductive) with various sizes and shapes, where the laser beam can be focused on a very small surface with exceptionally precise location, while the evaporated material can be immediately analysed. This technique has been successfully used to analyse the elemental composition of the Wawel Castle's arras pieces, where the maximum amount of information was obtained with negligible damage to the samples. The following elements have been discovered: Ag and Au (derived from strip) and Li, Al, Cr, Cu, Zn, Rb, Sr, Sn, Ba, Ce, Hg, Pb, Bi, U (mainly in fabrics). The LA-ICP-MS-TOF method is finding growing application in the analysis of geological, environmental and forensic samples. An attempt was made to apply this technique for testing textiles, especially historical ones.

W pracy podjęto próbę zastosowania unikalnej metody LA-ICP-TOF-MS (spektrometr masowy z plazmą indukcyjnie wzbudzoną z analizatorem czasu przelotu połączony z ablacją laserową) do półilościowej analizy porównawczej zawartości metali w tekstyliach. Jako obiekt badań wybrano oryginalne próbki arrasów wawelskich pochodzące z Muzeum Narodowego w Krakowie. Wykonano analizę składu pierwiastkowego i izotopowego, stwierdzono obecność następujących pierwiastków: Ag, Au (pochodzące z nici złotych i srebrnych) oraz Li, Al, Cr, Cu, Zn, Rb, Sr, Sn, Ba, Ce, Hg, Pb, Bi,U obecne głównie w tkaninie. W badaniach arrasów wykorzystano spektrometr GBC Optimass 8000 ICP-TOF-MS z przystawką do ablacji laserowej, CETAC LSX-500 Laser Ablation System.