Web Release Date: January 8,
Growth Process and Molecular Packing of a Self-assembled Lipid Nanotube: Phase-Contrast Transmission Electron Microscopy and XRD Analyses
and
Department of Chemistry, Faculty of Science, Tokyo University of Science (TUS), Funagawara-machi 12, Ichigaya, Shinjuku-ku, Tokyo 162-0826, Japan, SORST, Japan Science and Technology Agency (JST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan, Nanoarchitectonics Research Center (NARC), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan, and Okazaki Institute for Integrative Bioscience, National Institute of Natural Sciences, 5-1 Higashiyama, Myodaiji-cho, Okazaki, Aichi 444-8787, Japan
Received August 12, 2007
In Final Form: October 16, 2007
Abstract:
Phase-contrast transmission electron microscopy (PC-TEM) and quick freezing method have been combined to
study the initial growing process of a self-assembled lipid nanotube in water. The PC-TEM enabled us to detect thin
lamellar edge structure and the very fast growth of the newborn edge to a thin tube with high contrast. The thin tube
acts as a core structure for further growth into thick complete lipid nanotube. The initially formed nanotube structure
is denoted as a "core tube". The core tube has uniform wall structure that consists of five lamellar layers and the inner
and outer diameters of the core tube are 130 and 180 nm, respectively. The evaluated lamellar spacing of 4.6 nm is
well compatible with that measured by X-ray diffraction. We also discussed the molecular packing of the nanotube
from the pitch angle determined by the PC-TEM images, X-ray diffraction pattern in wide-angle region, and IR
spectroscopy. The subcell structure of the nanotube is assigned to an orthorhombic type. The twisting angle between
the neighboring lipid molecules is determined as ca. 0.26
for the first time; it is a crucial parameter for the formation
of a lipid nanotube in chiral packing but has not been elucidated before.
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