Templated Amplification of an Unexpected Receptor for C₇₀

Abstract

We recently reported that a self-assembled helical nanotube [1] formed of naphthalene diimide (NDI) molecules functionalized with amino acids [2] (Figure 1 a) can complex a string of C 60 fullerene molecules. [3] We now show that C 70 templates the formation of a new discrete receptor at the expense of preformed nanotubes.[4] This behavior, which resembles that of a dynamic combinatorial system, [5] was unexpected. As C 60 and C 70 share the same small diameter (Figure 1 b), we had anticipated that the same complexation mode would be possible (Figure 1 c).When a solution of 1 nanotubes (denoted 1 N ) in dry chloroform was allowed to stand over excess solid C 70 , it significantly darkened over time (Figure 2 a, inset). Figure 2 shows the UV absorption spectra of different solutions of 1 and C 70 . Precise calculation of solubility enhancement and NDI/C 70 ratios was difficult and unreliable, as the extinction coefficient for the complex is not the sum of the individual contributions of NDI and C 70 , as can be seen for the 384-nm band of NDI (Figure 2 a). The NDI/C 70 ratio was calculated to be around five using measurements at 258 nm. Other wavelengths, both in the UV and visible regions of the spectra, did not yield reliable values for the NDI/C 70 stoichiometry.Unlike the C 60 -solubilizing NDI nanotube, [3] the NDI/C 70 complex gives no indication of interactions between C 70 molecules in the visible absorption spectrum (Figure 2 b). Close contacts between C 70 molecules have been reported to shift the 470-nm maximum to 490 nm in solid films [6] and aggregates.[7] The absence of a peak corresponding to interactions between C 70 molecules is a strong indication that the C 70 receptor is radically different in nature from the C 60 one.This supposition is confirmed by the difference of circular dichroism (CD) spectra between 3 N alone and 3/C 70 solutions, both shown in Figure 3 for the same enantiomer of 3. Although the signal at 384 nm changes to the opposite sign with increasing concentration, this is not the case for all parts of the spectrum. This evolution to a radically different CD spectrum and the fact that derivatives 1 and 2 give similar CD

Wraparound Hosts for Fullerenes: Tailored Macrocycles and Cages

“…[63] In this context, spectacular results have been reported by Sanders and co-workers with the morphological tuning of amino acid based self-assemblies. [64] The helical structures developed by this team, [65a,b] as well as by the groups of Toniolo [65c] and Kawauchi and Yashima, [66] are extremely promising materials both for the purification of higher fullerenes and for their chiral resolution. These results pave the way for developing efficient and structurally simple materials which will allow the purification of higher fullerenes on larger scales.…”

Interactions Between Amino Acid‐Tagged Naphthalenediimide and Single Walled Carbon Nanotubes for the Design and Construction of New Bioimaging Probes

“…It has already been shown that certain NDI networks may adjust their adaptable tubular cavities in order to encapsulate via aromatic stacking guests with diameters in the range of 1 nm (for C 60 [57] or C 70 [58] ). DFT computational modeling was used to aid our understanding of the geometry adopted by an isolated NDI molecule in the presence of a SWNT and the nature of its interactions with this aromatic guest.…”

“…[86] The circular dichroism (CD) spectrum at the free NDI absorbance (330-400 nm) was assigned to interactions between the NDI couplets of sequential interacting NDI chromophores. [87] Changes in the relative position of these moieties lead to changes in the CD fingerprint of the supramolecular assembly. CD spectroscopy showed new features for the NDI@ SWNT composite which are due to NDI upon absorption onto the carbon nanomaterial, i.e., the sequential interacting NDIs change their relative position, leading to changes in the 380 nm region of circular dichroism spectrum and the appearance of a new signal in the 260-280 nm region (Figure 3b).…”

“…[54,55] These dynamic structures are capable of recognizing and solubilizing fullerenes and ion pairs: [56] the Sanders group has shown that carbon materials such as C 60 sense the helicity of the NDI host environment [57] whereas C 70 provoked an entirely unexpected reorganization to give a hexameric receptor. [58] The NDI supramolecular nanotubes which have cavities with diameters in the range of 1-2 nm created by hydrogen bonding have been shown to act as receptors for aromatic molecules including naphthalene-based guests or fullerenes. [59,60] Fluorescence imaging studies on fluorescent carbon nanotubes have thus far focused primarily on the measurement of the steady state spatial changes in emission intensity or wavelength.…”

Wirte für Fullerene: maßgeschneiderte Makrocyclen und Käfige

“…[63] In diesem Zusammenhang erzielten Sanders und Mitarbeiter spektakuläre Ergebnisse mit der morphologischen Feinabstimmung selbstorganisierter Aminosäuraggre-gate. [64] Die helicalen Strukturen, die von dieser Gruppe [65a,b] sowie von den Gruppen um Toniolo [65c] und Kawauchi und Yashima [66] …”