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Spectroscopic imaging studies of nanoscale polarity and mass transport phenomena in self-assembled organic nanotubes

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Abstract

Synthetic organic nanotubes self-assembled from bolaamphiphile surfactants are now being explored for use as drug delivery vehicles. In this work, several factors important to their implementation in drug delivery are explored. All experiments are performed with the nanotubes immersed in ethanol. First, Nile Red (NR) and a hydroxylated Nile Red derivative (NR-OH) are loaded into the nanotubes and spectroscopic fluorescence imaging methods are used to determine the apparent dielectric constant of their local environment. Both are found in relatively nonpolar environments, with the NR-OH molecules preferring regions of relatively higher dielectric constant compared to NR. Unique two-color imaging fluorescence correlation spectroscopy (imaging FCS) measurements are then used along with the spectroscopic imaging results to deduce the dielectric properties of the environments sensed by mobile and immobile populations of probe molecules. The results reveal that mobile NR molecules pass through less polar regions, likely within the nanotube walls, while immobile NR molecules are found in more polar regions, possibly near the nanotube surfaces. In contrast, mobile and immobile NR-OH molecules are found to locate in environments of similar polarity. The imaging FCS results also provide quantitative data on the apparent diffusion coefficient for each dye. The mean diffusion coefficient for the NR dye was approximately two-fold larger than that of NR-OH. Slower diffusion by the latter could result from its additional hydrogen bonding interactions with polar triglycine, amine, and glucose moieties near the nanotube surfaces. The knowledge gained in these studies will allow for the development of nanotubes that are better engineered for applications in the controlled transport and release of uncharged, dipolar drug molecules.

Graphical abstract: Spectroscopic imaging studies of nanoscale polarity and mass transport phenomena in self-assembled organic nanotubes

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Publication details

The article was received on 31 May 2017, accepted on 11 Jul 2017 and first published on 13 Jul 2017


Article type: Paper
DOI: 10.1039/C7CP03672H
Citation: Phys. Chem. Chem. Phys., 2017, Advance Article
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    Spectroscopic imaging studies of nanoscale polarity and mass transport phenomena in self-assembled organic nanotubes

    H. Xu, S. Nagasaka, N. Kameta, M. Masuda, T. Ito and D. A. Higgins, Phys. Chem. Chem. Phys., 2017, Advance Article , DOI: 10.1039/C7CP03672H

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