Dissertation/Thesis Abstract

Dynamics of bio-membranes investigated by neutron spin echo: Effects of phospholipid conformations and presence of lidocaine
by Yi, Zheng, Ph.D., Indiana University, 2009, 154; 3380145
Abstract (Summary)

Bio-membranes of the natural living cells are made of bilayers of phospholipids molecules embedded with other constituents, such as cholesterol and membrane proteins, which help to accomplish a broad range of functions. Vesicles made of lipid bilayers can serve as good model systems for bio-membranes. Therefore these systems have been extensively characterized and much is known about their shape, size, porosity and functionality. In this dissertation we report the studies of the effects of the phosoholipid conformation, such as hydrocarbon number and presence of double bond in hydrophobic tails on dynamics of phospholipids bilayers studied by neutron spin echo (NSE) technique. We have investigated how lidocaine, the most medically used local anesthetics (LA), influence the structural and dynamical properties of model bio-membranes by small angle neutron scattering (SANS), NSE and differential scanning calorimetry (DSC).

To investigate the influence of phospholipid conformation on bio-membranes, the bending elasticities κc of seven saturated and monounsaturated phospholipid bilayers were investigated by NSE spectroscopy. κ c of phosphatidylcholines (PCS) in liquid crystalline (L α) phase ranges from 0.38×10-19 J for 1,2-Dimyristoyl- sn-Glycero-3-Phosphocholine (14:0 PC) to 0.64×10-19 J for 1,2-Dieicosenoyl-sn-Glycero-3-Phosphocholine (20:1 PC). It was confirmed that when the area modulus KA varies little with chain unsaturation or length, the elastic ratios (κc/ KA)1/2 of bilayers varies linearly with lipid hydrophobic thickness d.

For the study of the influence of LA on bio-membranes, SANS measurements have been performed on 14:0 PC bilayers with different concentrations of lidocaine to determine the bilayer thickness dL as a function of the lidocaine concentration. NSE has been used to study the influence of lidocaine on the bending elasticity of 14:0 PC bilayers in Lα and ripple gel (Pβ') phases. Our results confirmed that the molecules of lidocaine loosen the packing of the membrane constituent lipids and induce lateral membrane expansion. The intercalation of lodocaine molecules provides more inter-molecular space for the lipid hydrophobic chains and results in a decrease of the bilayer thickness, a decrease of the main transition temperature from Lα to Pβ' phase and a doubling of the bending elasticity in Lα phase.

Indexing (document details)
Advisor: Bossev, Dobrin P.
Commitee: Baxter, David V., Setayeshgar, Sima, Snow, Michael W.
School: Indiana University
Department: Physics
School Location: United States -- Indiana
Source: DAI-B 70/12, Dissertation Abstracts International
Subjects: Condensed matter physics
Keywords: Bending elasticity, Biomembranes, Lidocaine, Local anesthetics, Neutron spin echo, Phospholipid bilayers
Publication Number: 3380145
ISBN: 978-1-109-50453-8
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