Chain-substituted lipids in monomolecular films. The effect of polar substituents on molecular packing

Abstract

A series of highly purified fatty acids and phospholipids each possessing a polar chain-substituent (hydroxy or keto) at varying locations (carbons 8,10,12, and 16 for the fatty acids and carbons 4, 6, 8,10, and 12 for the phospholipids) on an 18-carbon chain were synthesized. Pressure-area isotherms revealed how these molecules pack in monomolecular films. Most of the fatty acids and phospholipids exhibited pressure-area curves indicative of "looping" conformations where both the polar substituent and polar head group contact the aqueous subphase. As the pressure was increased, the polar substituents were forced out of the aqueous interface, and the chains assumed more vertical conformations. Pressure-area isotherms for the hydroxylated fatty acids showed unusually small molecular areas in the condensed state owing to the presence of hydrogen bonding. A phospholipid disubstituted at the 12 position with a keto group gave a molecular area of only 21.6 A2/molecule at 35 dyn/cm; this is consistent with two vertical chains, one in the water and one in the air. Isotherms reflected a strong dependence on the position of the polar substituent along the chain.

NMR-based molecular ruler for determining the depth of intercalants within the lipid bilayer

“…General procedure for preparation of keto esters 7 Keto esters 7 were prepared via the cadmium mediated coupling of acyl chlorides 6 with alkyl bromides 9, according to the procedure of Menger et al (1989). The procedure was carried out in toluene (rather than benzene) and the compounds were purified by recrystallization from hexane.…”

NMR-based molecular ruler for determining the depth of intercalants within the lipid bilayer. Part IV: Studies on ketophospholipids

“…1, ketophospholipids 4 were prepared by coupling ketoacids 2 with lysoPC 3 according to the procedure of Menger et al (1989). Ketoacids 2 were prepared, in turn, from ketoesters 1 as described in the companion paper (Afri et al, 2014).…”

“…Ketoesters 1 and ketoacids 2 were prepared as described in the companion paper (Afri et al, 2014). Following the Menger approach (Menger et al, 1989), the ketoacids were then coupled with 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphatidylcholine (lysoPC 3), mediated by DCC and DMAP, to give the corresponding 1-palmitoyl-2-(n 00 -oxostearoyl)-sn-glycero-3-phosphatidylcholines 4 in yields of ca. 40%.…”

“…1), according to the procedure Menger et al (1989). To assist in assignment and detection several derivatives were prepared 13 C-enriched in both carbonyls.…”

Anisotropic aggregation and phase transition in Langmuir monolayers of methyl/ethyl esters of 2,3-dihydroxy fatty acids

“…Menger et al [13] studied a series of octadecanoic acids each possessing a hydroxyl group at varying locations of the alkyl chain (8-, 10-, 12-, or 16-). Most of these acids exhibit "looping" conformations where both the polar substituent and polar head group contacted the aqueous subphase.…”