Collapsed bipolar glycolipids at the air/water interface: Effect of the stereochemistry on the stretched/bent conformations

• We studied the behaviors of Langmuir films based on bipolar and monopolar lipids.
• Comparative studies of lipids were done using tensiometry, ellipsometry and AFM.
• Polar head group and Stereochemistry were responsible for different behaviors.
• One configuration (cis) induced a preference for a bent conformation.
• The other configuration (trans) induced a preference for a stretched conformation.

This article describes a comparative study of several bipolar lipids derived from tetraether structures. The sole structural difference between the main two glycolipids is a unique stereochemical variation on a cyclopentyl ring placed in the middle of the lipids. We discuss the comparative results obtained at the air/water interface on the basis of tensiometry and ellipsometry. Langmuir–Blodgett depositions during lipid film compressions and decompressions were also analyzed by AFM. The lactosylated tetraether (bipolar) lipid structures involved the formation of highly stable multilayers, which are still present at 10 mN m−1 during decompression. This study suggests also that the stereochemistry of a central cyclopentyl ring dramatically drives the conformation of the corresponding bipolar lipids. Both isomers (trans and cis) adopt a U-shaped (bent) conformation at the air/water interface but the trans cyclopentyl ring induces a much more frustration within this type of conformation. Consequently, this bipolar lipid (trans-tetraether) undergoes a flip of one polar head-group (lactosyl) leading to a stretched conformation during collapse.

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