High-pressure NMR studies of model membranes and Kramers turnover on solution
Peng, Xiangdong
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https://hdl.handle.net/2142/19538
Description
Title
High-pressure NMR studies of model membranes and Kramers turnover on solution
Author(s)
Peng, Xiangdong
Issue Date
1991
Doctoral Committee Chair(s)
Jonas, Jiri
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Biochemistry
Chemistry, Physical
Language
eng
Abstract
The pressure and anesthetic effects on lineshapes and various relaxation times of phospholipid model membranes DPPC in multilamellar dispersions and in unilamellar vesicles have been investigated by using $\sp{31}$P NMR, $\sp2$H NMR, as well as one and two dimensional $\sp1$H NMR techniques in both the liquid crystalline and various gel phases. The results clearly show that the pressure has an ordering effect on both the headgroup and acyl chain regions. Pressure also induces an interdigitated GelX phase which is formed between the GelI and GelII phases. In the pressure-induced GelX phase, the chain region is packed more closely than in the GelI and GelII phases, while the opposite is found for the headgroup region. The addition of positively charged local anesthetic tetracaine molecules alters the conformation of DPPC headgroup, raises the critical pressure of main phase transition, and induces the formation of the GelX phase. The location of TTC molecules in the bilayer vesicles has been determined by 2D NOESY experiments. In particular, $\sp{31}$P NMR experiments on multilamellar dispersions suggest that the TTC molecules are gradually expelled from the bilayers and completely excluded around 3 kbar, while $\sp1$H NMR experiments on sonicated vesicles indicate that the TTC molecules are not excluded from the bilayers up to 5 kbar. $\sp2$H NMR experiments on selectively chain-deuterated DPPC samples indicate a tighter packing in the central parts of the acyl chains and a conformational change at the C-2 segment of the sn-2 chain. The $\sp2$H spin-lattice and spin-spin relaxation times for various sites of the chains indicate differential mobility along the chains.
The second main project of this thesis dealt with the temperature, pressure, and solvent effects on the internal rotation rate of the coordinated ethylene in rhodium complex as studied by $\sp1$H NMR technique. The experimental data, as interpreted in terms of stochastic models of isomerization reactions, indicate both the Kramers turnover and heavy metal bottleneck effect. The solvent viscosity and Enskog collision frequency dependences of the rate demonstrate that solvent shear viscosity represents only an approximate measure of the coupling of the reaction coordinate to the medium.
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