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peptide. This (comparing with other peptides) keeps chains in trans conformation
of dihedral angles (order parameters) and stabilizes them (amount of transitions).
Chains with less gauche dihedral angles needs less space (lower area per lipid).
V 24 has shorter side chains (only C
γ
), which causes lower area per lipid than L 24 .
8.5.5 Membrane Thickness
We have calculated thickness of membrane for 1
st
and 2
nd
shell of lipids around
peptide (see Table 8.1). The change of membrane thickness is alternate way (to
peptide tilt) to compensate the hydrophobic mismatch. In most of simulations the
thickness of 1
st
shell is lower than 2
nd
shell. The exceptions are simulations of a gel
phase (A 24 /DMPC, I 24 /DMPC, P 24 /DMPC, V 24 /DMPC, V 24 /DPPC) and I 24 /DPPC
in LC state. In these 6 cases the peptide did not tilt to compensate the hydrophobic
mismatch as mentioned bellow. Above mentioned simulations in a gel state have 1
st
shell appox. 0.1 nm thicker than 2
nd
shell and in case of I 24 /DPPC/LC the difference
is 0.15 nm. In the rest of peptides the 1st shell is up to 0.2 nm thinner than 2
nd
one.
In some cases (e.g. A 24 /DPPC/LC or V24/DMPC/LC) the thickness is virtually the
same (the changes are less than 0.01 nm). We did not find any significant influence
of amino acid side chains on this parameter.
Fig. 8.9  Amount of transitions between trans and gauche conformations (per lipid and ns)