1 research outputs found
Conformational Distributions and Hydrogen Bonding in Gel and Frozen Lipid Bilayers: A High Frequency Spin-Label ESR Study
The ESR parameters of PC spin labels in frozen membranes
do not
simply represent the membrane polarity or water penetration profile.
Instead, they show a distribution between hydrogen-bonded (HB) and
non-hydrogen-bonded (non-HB) states, which is affected by a number
of factors in the membrane composition. Similar to the exclusion of
solutes from crystallizing solvents, the pure bulk gel phase excludes
nitroxides, forcing acyl chains to take bent conformations. In these
conformations, the nitroxide is hydrogen-bonded. Furthermore, upon
gradual cooling in the supercooled gel, PC labels undergo slow lateral
aggregation, resulting in a broad background signal. However, if the
sample is instantly frozen, this background is replaced by the HB
component. In membranes with cholesterol, the observed HB/non-HB ratio
can best be described by a partition-like equilibrium between nitroxides
located in defects of lipid structure within the hydrophobic core
and those close to the membrane surface