Sphingolipids

Sphingolipids are an essential part to many cell membranes. They are all derived from a base lipid named sphingosine, which is composed of an 18 carbon chain molecule with hydroxyl and amine groups:

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Sphingolipids are present in skin, milk, egg, brain, and are believed to be present in every living cell. Not only are they functional parts of the membrane, but they also act as messengers for cell apoptosis, proliferation, and differentiation. We have been studying a variety of sphingolipids. Below we show some results concerning ceramides.

Ceramides

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Ceramide is a relatively simple sphingolipid. It is composed of a sphingosine with an amine linked hydrocarbon chain.

[Image] Surface pressure versus molecular area for ceramide. The isotherm is typical of some monolayers that bypass the liquid phase.  Our reflectivity studies indicate that at large molecular areas (70 Å2) the monolayer consists of crystalline domains surrounded by moats of water as depicted in the figure above.
[Image] Reflectivity of ceramide monolayer at the air-water interface.
The best fit models show that the amine linked tail terminates above the sphingosine tail, thus dividing the hydrophobic tail into two layers. Detailed model structure and parameters are listed below.
Reflectivity
Surface roughness.....3.12 Ang
Head group length.....5.77 Ang
Tail 1 length.....11.6 Ang
Tail 2 length.....6.69 Ang
Area/molecule.....42.5 sq Ang
Head group electrons.....98
Water molecules/head group.....0.5
Tail 1 electrons.....146
Tail 2 electrons.....72
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[Image] GID of ceramide at 35 mN/m indicating a highly ordered monolayer. The central peak corresponds to the ordering of the hydrocarbon chains as shown below. No evidence for the ordering of the head groups was observed. The nature of the other peaks is unknown yet. The rod scans across these reflections indicate that they originate from different parts of the molecule.
The area of the unit cell is calculated from the d spacing as shown below.
GID Peak (inv Ang).....1.45.....1.51.....1.59
d Spacing (inv Ang).....4.35.....4.18.....3.96
Width (inv Ang).....0.016.....0.025.....0.049
Area (sq Ang).....21.8.....20.1.....18.1
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