Hydrogen Bonded Organic Nanotubes

Inspired by the remarkable functions of tubular stractures in biology, chemists have shown enormous interest in the development of nano-sized tubular stractures [3]. Among these structures, nanombes composed of hydrogen bonded organic molecules are particularly interesting due to their potential applications in ion sensing, molecular inclusion and separation, catalysis, molecular devices, chemotherapy, transmembrane transport, as well as drag delivery [4]. 

Department of Chemistry, Fudan University, 220 Handan Road, Shanghai 200433, China e-mail houjl fudan.edu.cn 

2 Strategies for the Construction of Hydrogen Bonding-Driven Organic Nanotubes 

---

The cyclic octapeptide cycfo-[-(D-Ala-L-Glu-D-Ala-L-Gln)2-] has been designed by Ghadiri and co-workers to generate a hydrogen-bonded organic nanotube having an internal diameter of approximately 0.7-0.8 nm (Fig. 20.1.5). 

Fig. 8.1 Schematic presentation of strategies for the construction of hydrogen bonded organic nanotubes. Nanotubes from unimolecular, a helical, b tubular molecules, supramolecular, c bundles of rod-like molecules, d the stacking of macrocyclic molecules, and e aggregation of wedge-like molecules. The dotted red lines represent hydrogen bonding...

Sanders and coworkers have recently found supramolecular helical arrays of C o molecules in the tubular cavity of helical organic nanotubes composed of a-amino acid functionalized naphthalenediimides (10), which self-assembled to form hydrogen-bonded helical nanotubes in a nonpolar solution and in the solid state (Figure 6.11) [59]. The CD spectrum of the L-10-C,so complex exhibited weak but apparent Cotton effects at 595 and 663 nm due to electronic transitions of C o as... 

The rational synthesis of peptide-based nanotubes by self-assembling of polypeptides into a supramolecular structure was demonstrated. This self-organization leads to peptide nanotubes, having channels of 0.8 nm in diameter and a few hundred nanometer long (68). The connectivity of the proteins in these nanotubes is provided by weak bonds, like hydrogen bonds. These structures benefit from the relative flexibility of the protein backbone, which does not exist in nanotubes of covalently bonded inorganic compounds. 

The self-assembling cyclic D,L-cc-peptide nanotubes described demonstrate high stability on surfaces even after two months exposure to ambient temperature. NDI peptide nanotubes 18 may provide a facile method for the preparation of a new class of synthetic biomaterials [16b, 34a]. Recently Sanders and co-workers demonstrated the formation of amino acid-derived NDI hydrogen-bonded supramo-lecular organic M-helical nanotubes in nonpolar solvents and also in the solid state [34b]. The hydrogen-bonded supramolecular nature of the helical nanotubes was confirmed by the circular dichroism (CD) spectrum in chloroform with the addition of methanol, destruction of the supramolecular nanotubes was observed, due to the capabilities of such an aprotic solvent to compete for hydrogen-bond interactions [34b]. 

Pantog GD, Pengo P, Sanders JKM (2007) Hydrogen-bonded helical organic nanotubes. Angew Chem Int Ed 46 194-197... 

Abstract We review various types of hydrogen bond characteristics based on our theoretical work of diverse chemical systems. The systems include water clusters, hydrated clusters, enzymes, ionophores/receptors, and assembled molecules such as organic nanotubes. Special features of weak, normal, short, short strong H-bonding are discussed in terms of structures, interaction energies, and spectra. Various -ir-type H-bonds are also discussed. 

This calls for the 1,4-addition to take place at least at some positions, which prevents the fluorinated tube from being an electric conductor. Fluorinated nanotubes differ from the unmodified species not only in electric conductivity. There are rather more characteristics being changed. Fluorinated tubes dissolve, for instance, in some organic solvents Uke DMF, THF, and different alcohols. Most of aU, the solubility in 2-propanol and 2-butanol is increased. Hydrogen bonds between the protons of the hydroxy groups and the fluorine atoms of the nanotubes are assumed to cause an effective solvation. 

---