Local Environment and Property of Water inside the Hollow Cylinder of a Lipid Nanotube

Abstract

We investigated the local environment of water confined inside the hollow cylinder of lipid nanotubes (LNTs) by time-resolved fluorescent measurements and attenuated-total-reflectance infrared (ATR-IR) spectroscopy. The LNT was obtained by self-assembly of cardanyl glucosides in water at room temperature and had an open-ended cylindrical nanospace with a diameter of 10-15 nm, a length of 10-100 microm, and hydrophilic inner and outer surfaces. We introduced a fluorescent probe of 8-anilinonaphthalene-1-sulfonate into the confined water and observed an extremely slow dynamic Stokes shift with a correlation time of 1.26 ns, which was 2-3 orders of magnitude longer than that of bulk-phase water. From the peak shift of the fluorescent spectrum, the local solvent polarity (ET(30)) of the confined water was estimated as 50 kcal/mol, which is 20% lower than that in bulk water. ATR-IR measurements showed that the hydrogen-bond network of water inside the LNT was more developed than that in bulk water at room temperature, which is in contrast to the water in other self-assembled confined geometries, such as Aerosol-OT (AOT) reversed micelles.

Self‐assembled organic nanotubes: Toward attoliter chemistry

“…60 Furthermore, confined water in the LNT hollow cylinder of 4 with 10 nm inner diameters proved to exhibit the physical properties of structured water similar to intracellular water. 61,62 In our early work, we found that capillary action enables the LNTs to encapsulate aqueous solutions or dispersions containing such guest substances into their internal hollow cylinders. [63][64][65] Thus, the self-assembled LNTs from 5 or 6 (Scheme 1) have been observed to encapsulate a variety of biomacromolecules, such as cadmium sulfide (2À3 nm) [ Fig.…”

“…76,77 This theoretical D-value is well compatible with our experimental results for the solid-state organic nanochannels with two open ends. We can envisage several possible causes for the relatively smaller D values: electrostatic attraction between charged surfaces of the nanotube and guest, 51,53 relatively larger viscosity of the confined water, 61 and diffusion in a restricted geometry. 5 …”

Hydration of Ions in Confined Spaces and Ion Recognition Selectivity

“…It is known that materials confined in nanospaces show structures and/or dynamics different from those exhibited in bulk. [1][2][3][4][5][6][7][8][9][10][11] Such unusual properties, which become more apparent as the size of the space decreases, partly come from the effects of the walls surrounding the spaces. 2,6 The interaction of compounds with the wall becomes more dominant with decreasing size of the space.…”

Molecular Self-Assembly into One-Dimensional Nanotube Architectures and Exploitation of Their Functions

“…90 The viscosity of the confined water shows 3-4 cP, corresponding to that of bulk water at À20 C. That value is 3-4 times as large as that of water at room temperature. Thus, the water in geometrically confined nanospace displays many unique properties different from general bulk water.…”

“…Thus, the water in geometrically confined nanospace displays many unique properties different from general bulk water. 90,91 Furthermore, the self-assembled nanotubes from 13 displayed a novel function, encapsulating guest substances with 10-50 nm dimensions into the nanochannel shaped by the hollow cylinders. In particular, capillary action allows us to effectively fill the nanotubes with, for example, gold nanoparticles (1-50 nm), 92,93 cadmium sulfide (2-3 nm), 87 magnetite (ca.…”