Lipid Nanotubes and Microtubes:  Experimental Evidence for Unsymmetrical Monolayer Membrane Formation from Unsymmetrical Bolaamphiphiles

Abstract

Unsymmetrical bolaamphiphiles, ω-[N-β-d-glucopyranosylcarbamoyl]alkanoic acids, with even-numbered oligomethylene chains (12, 14, 16, 18, and 20 carbons) self-assembled in water to form lipid nano- and microtubes. The tubular assemblies were separated by centrifugation and examined by transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy to study the molecular packing within the tubular membranes. The nanotubes encapsulated the staining reagent phosphotungstate, which revealed them to be hollow cylinders up to several hundred micrometers long with 30−43-nm outer diameters and 14−29-nm inner diameters. By comparing the membrane stacking periodicity obtained from powder X-ray diffraction analysis of the dehydrated tubes with the molecular packing within single crystals, we found that the nanotubes consist of an unsymmetrical monolayer lipid membrane (MLM) in which the molecules are packed in a parallel fashion. This suggests that the inner surface of the nanotubes is covered with carboxy headgroups and the outer surface with 1-glucosamide headgroups. The inner diameters of the lipid nanotubes could be controlled in the range 17.7−22.2 nm in steps of ∼1.5 nm/two carbons by varying the oligomethylene spacer length. The microtubes had three types of molecular arrangements. The first type was a symmetrical MLM in which the molecules were packed in an antiparallel fashion. The other two types had unsymmetrical MLM stacking with head-to-head and head-to-tail motifs. Increasing the number of oligomethylene spacers stabilized the unsymmetrical MLM structure in both nano- and microtubes.

pH-triggered formation of nanoribbons from yeast-derived glycolipid biosurfactants

“…The bending angle, estimated to be α~ 33°, a value which is comparable with the one that has been reported by Masuda et al, 58 suggests an interlayer packing in the ribbon plane , as shown in scheme in Figure 7. The close analysis of the full width at half These techniques probe through-space 1 H-1 H (< 5 Å) and 13 C-1 H proximities using the nuclear spin interactions (dipolar coupling).…”

pH-Driven Self-Assembly of Acidic Microbial Glycolipids

“…If the considerations above can partially explain the consistency among our data, they cannot explain the difference in morphology between the G-C18:0 sample, forming infinite bilayer membranes, and a very similar compound extensively studied by Masuda et al 30 forming nanotubes. The major difference between the two molecules resides in the chemical nature of the linker between the glucopyranoside ring and the fatty acid: acetal group in G-C18:0 and a carbamoyl group in the case of Masuda's sample.…”

Self‐assembled organic nanotubes: Toward attoliter chemistry

“…We have achieved for the first time the precise control of the inner diameters of selfassembled LNTs by newly designing wedge-shaped amphiphiles 1(n) (n ¼ 12, 13, 14, 16, 18, and 20) (Scheme 1). 48 Two terminal hydrophilic groups of different size glucopyranose and carboxylic acid headgroups were covalently linked to an oligomethylene spacer (carbon numbers ¼ 12À20). Self-assembled organic nanotubes from 1(14), 1(16), 1 (18), and 1 (20) possess inner diameters in the 17.7À22.2 nm range at intervals of $1.5 nm, with an increment of two carbons in the spacer chains (Fig.…”

“…Detailed Xray analysis confirmed that the molecules pack in a parallel fashion to form an unsymmetrical monolayer membrane, leading to different inner and outer surfaces covered with carboxylic and sugar hydroxyl groups, respectively. 48,49 These asymmetric supramolecular nanotubes are promisingly applicable to fill nanomaterials or biomacromolecules selectively into their hollow cylinders. It is known that the molecular packing of wedge-shaped amphiphiles in a solid state would include totally four types of polymorphism, depending on two types of polymorph and polytype for each.…”