Lipids hydrogen bonding systems, other

Av in SC cannot be explained by polarity and hydrogen-bonding of the surrounding medium alone. Rather the results are explained better in terms of hindered fluorophore reorientation in the excited state, similar to results obtained with other lipid systems [7,11-13]. Thus, the unusual Stokes shifts seen with AF probes in SC suggests a rather rigid environment in the lipid lamellae, which hinder the fluorophore reorientation. 

One of the most well-developed system that exemplifies the stacked-disk motif is the work of Ghadiri and coworkers on cyclic D,L-peptides [89,91-93]. The disks are held together through hydrogen bonds and intermolecular contacts between the peptide side chains. The potential for derivatization and functionalization is great because the disks are made from amino acids. These materials have shown the ability to assemble into lipid bilayers and transport ions across them. In addition these materials have recently been shown to act as self-assembled antibacterial agents with utility as therapeutics [93]. There are other systems that have been synthesized from shape persistent macrocycles to assemble into tubes [91,94]. 

The same group further revised the nanotubes by attaching peptides to the pillararene backbones (Fig. 8.5e) [29]. For molecules that bear the D-Phe-L-Phe-D-Phe-COOH sequence, H NMR, IR, and molecular modeling studies revealed that the pillar[n] arene derivatives adopted a tubular conformation in both solution and lipid bilayer membranes due to the induction of the intramolecular hydrogen bonding formed from the amide groups of the peptide chains (Fig. 8.5f). Compared with other mbular systems, this kind of unimolecular nanotubes have several unique... 

The r-alkyl desaturase system, a microsomal mixed-function oxidase responsible for the biosynthesis of ethanolamine plasmalogens from alkyl lipids (Fig. 6), was initially characterized in the early 1970s (F. Snyder, 1971 A. Paltauf, 1973). The reverse of this reaction (i.e., conversion of an alk-l -enyl moiety to an alkyl chain via a reductase) has not been observed. The alkyl desaturase is a unique activity since it can specifically and stereospecifically abstract hydrogen atoms from C-1 and C-2 of the 0-alkyl chain of an intact phospholipid molecule to form the cis double bond of the O-alk-l -enyl moiety. Only intact l-alkyl-2-acyl-in-glycero-3-phosphoethanolamine is known to serve as a substrate for the alkyl desaturase. As with other reactions in complex ether phospholipid synthesis, the molecular identity of the responsible enzyme is unknown. 

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