Gh. Peters et al., MODELING OF COMPLEX BIOLOGICAL-SYSTEMS .2. EFFECT OF CHAIN-LENGTH ON THE PHASE-TRANSITIONS OBSERVED IN DIGLYCERIDE MONOLAYERS, Langmuir, 11(10), 1995, pp. 4072-4081
We have performed molecular dynamics computer simulations to examine t
he effect of chain length on the phase transitions observed in 1,2-sn-
diglyceride monolayers. Simulations were performed for three different
diglycerides of chain length 10, 16, and 22. The monolayers composed
of molecules of chain lengths 16 and 22 exhibit complex phase transiti
ons as a function of surface pressure. These two Langmuir films underg
o two phase transitions, where the transition at low surface density i
s associated with tilt. The high surface pressure transition is unique
for the diglyceride molecules and is driven by a competition of hydro
phobic/hydrophilic and intra-/intermolecular forces involving the two
head groups. Increasing the chain length, on one hand, stabilizes the
chains in the layer resulting in a lower percentage of gauche defects
but, on the other hand, the low-pressure phase transition is shifted t
o higher surface density. No tilt transition is observed in the 1,2-sn
-didecanoylglycerol film due to the short length of the alkyl chains.
This film is more mobile than the C16 and C22 layers, and the melting
of the layer proceeds by creating gauche defects in the alkyl chains.