Reorientierungsdynamik von Glycerin aus temperaturabhängigen Multi-Kern-NMR-Messungen

Nuclear magnetic resonance is a powerful tool for the investigation of the dynamic of liquids. By determining the longitudinal or spin-lattice-relaxation rates of proton-, deuteron-, and carbon-13-nuclei together with the 13C-nuclear Overhauser enhancement factors (NOE factors) it was possible to separate the mobility of parts of the molecule from the overall movement. In this work the relaxation rates were determined at different temperatures: between 270 and 330 K for 1H- and 13C-nuclei, and between 293 K (or 313 K for oxygen-bound deuterons) and 335 K for 2H-nuclei. In addition NOE-factors for 13C-nuclei were measured for the first time. They are of essential meaning for the interpretation because they are related to the dynamics only and so the separation between dynamical and structural effects can be achieved much better than with relaxation rates alone. For the evaluation the well-known model of the Cole-Davidson-spectral density and a Vogel-Fulcher-Tammann temperature dependence were combined with the model-free Lipari-Szabo-approach. This introduces the parameter S^2, which can be understood as a measure for the inner dynamics. So it was possible to determine parameters, which describe the 13C- as well as the 2H-data for the CH2-groups, for all these data depend on the dynamics of the CH-bonding vector. The proton relaxation depends on the dynamics of the H-H-bonding vector and gives a smaler value for S^2. Fitting the relaxation rates and NOE-factors of the 13C-nuclei of the CH-group a Lipari-Szabo-factor in the order of one within the margin of error was found. So we find a picture showing glycerol as highly networked liquid, were the outer CH2-groups are quite strongly bound but still can do fast librational motions. The inner CH-group shows no motion of this kind. Comparison with data from the literature was not always successful, although some good agreements were found. The reason for this can be, that for different studies different deuteration rates were used and the isotopic effects could not be taken into account during the evaluation. Additionally the preparation must not be neglected: Due to being very hydrophilic and the high viscosity, the handling of glycerol is not easy and the probes were prepared differently for the different studies. This must lead to variations in the water content and the viscosity, which highly affects the dynamics of the probe.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2003

Author dc:creator

• Friedrich, Anke

Contributors dc:contributor

• Dölle, Andreas

• info:eu-repo/classification/ddc/540
• Glycerin
• NMR-Spektroskopie
• Relaxationszeit
• Temperaturabhängigkeit
• Kern-Overhauser-Effekt
• Chemie
• 1H-NMR
• 2H-NMR
• 13C-NMR
• longitudinale Relaxation
• Spektraldichten

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-120880%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:59064