Self-Assembly of a Water-Soluble Tricyclic Heterocycle into J-Type Rosette Nanotubes
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Self-Assembly of a Water-Soluble Tricyclic Heterocycle into J-Type Rosette Nanotubes Gabor Borzsonyi, Rachel L. Beingessner, Takeshi Yamazaki, Jae-Young Cho, Andrew J. Myles, Andriy Kovalenko and Hicham Fenniri* National Institute for Nanotechnology, National Research Council (NINT-NRC) and Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2, Canada. ABSTRACT The synthesis and self-assembly of a water-soluble, tricyclic, self-complementary heterocycle that features the hydrogen bond donor-acceptor arrays of both guanine (G) and cytosine (C) juxtaposed between a pyridine ring is presented. In solution, this tricycle, which has been termed xK1, self-assembles into Rosette Nanotubes (RNTs) that have an inner diameter of 1.4 nm. Unlike the RNTs formed from the bicyclic congener K1, we demonstrate that xK1 with its extended π system, forms a J-type RNT assembly determined through UV-Vis, CD and fluorescence spectroscopy experiments. This observation brings the possibility of developing electrically conducting RNTs for applications in the areas of photovoltaics and molecular wires. INTRODUCTION The G∧C motif (K1, Figure 1) is a self-complementary bicyclic hybrid molecule of the DNA bases guanine and cytosine [1]. In solution, it self-assembles into tubular architectures called Rosette Nanotubes (RNTs) [2] which have an internal diameter of ~1 nm. By covalently functionalizing the G∧C motif using standard synthetic strategies, the physical and chemical properties of the RNTs can be easily modified for specific applications, since these groups are expressed on the outer periphery. For applications including drug delivery, we wanted to include in our repertoire, RNTs that have larger internal diameters. To this end, we have recently described the synthesis of a tricyclic version of the G∧C motif, called xG∧C, which has a pyridine ring juxtaposed between the guanine and cytosine faces and readily self-assembles in organic solvents (DMF and DMSO) into RNTs that have an extended internal diameter of 1.4 nm [3]. In this proceeding, we now describe the synthesis and self-assembly of the water-soluble congener called xK1 (Figure 1), which is functionalized with the amino acid lysine [4]. Unlike xG∧C or any of the functionalized bicyclic G∧C motifs we have previously studied, here we demonstrate that xK1 self-assembles into J-type RNTs that have an exceptionally high molar ellipticity value. As J-aggregate materials have been used as organic photoconductors [5], LED’s [6], sensitizers [7] and photovoltaics [8], this work provides exciting application possibilities for this family of RNTs. EXPERIMENT The synthesis of xK1 was accomplished in 9 steps from trichloro compound 1 [9] with an average stepwise yield of 76% (Figure 2). All new compounds were characterized by 1H and 13C NMR and HRMS as well as by elemental analysis for xK1 [4].
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Figure 1. K1 and xK1 modules (A) and the RNTs self-assembled from xK1, top (B) and side (C) views. SEM Imaging. SEM samples were prepared by floating a carbon-coated 400-m
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