from c ¼ 0.01 to c ¼ 0.27) at temperature range from 18
C to 55
C in model
membranes of dipalmitoylphosphatidylcholine (DPPC). Exchange frequency of
spin-spin exchange interaction between androstane spin probes, W ex is shown as
W ex ¼
J
h . And ν encounter ¼
ν exchange
2p
is calculated using ν encounter obtained from ESR
spectrum. Consequently, diffusion constant, D diffusion is obtained from following
A
C
D
B
-parameter
CD
AB
 2
1
1
2
3
4
10
15
20
EggPC PC*
PC*
EggPC PC*
PC*
Fig. 3.12 Relation between
spin probe concentration
and ESR spectrum
Liposomes with various
ratios of
phosphatidylcholine spin
probe to egg yolk
phosphatidylcholine was
prepared, and α-parameter
in each ratio was obtained
from ESR spectrum
measured at 25
C
Fig. 3.13 Distribution of spin probes and ESR spectrum
ESR spectrum is broadened by spin-spin exchange interaction when local concentration of spin
probe is high, and α-parameter shows smaller value. Therefore, α-parameter becomes good
indication of phase separation and molecular diffusion
3.6 Magnetic Resonance
41