Giant nanotubes loaded with artificial peroxidase centers: self-assembly of supramolecular amphiphiles as a tool to functionalize nanotubes.

Molecular self-assembly, a general phenomenon in nature, plays a pivotal role in biological functions. Inspired by the abundance of self-assembly processes in biological systems, considerable effort has been devoted to the design and synthesis of self-assembly-based nanostructures for their various applications in chemistry, biology, and materials science. 3] Among a number of other designed nanostructures, nanotubes formed by self-assembled amphiphilic molecules have attracted much attention. So far various supramolecular nanotubes consisting of many identical amphiphilic molecules as building blocks have been developed. The traditional types of amphiphiles (surfactants), and also various superamphiphiles (e.g., amphiphilic block copolymers) 5,6b,c] and recently giant biohybrid amphiphiles, have been found to exhibit interesting self-assembly behaviors. In general, the practical methods for generating nanotubes share a common feature: the amphiphilic molecules are designed through covalent linking. Unlike these traditional covalent synthesis pathways, the “supramolecular amphiphile” concept has attracted intense scientific and technological attention. In recent years, supramolecular amphiphiles formed through noncovalent driving forces have been developed as a new type of building block for future fabrication of supramolecular architectures through multilevel self-assembly. Among them, host–guest interactions, such as those of cyclodextrin (CD) systems, have proven to be important for constructing supramolecular amphiphiles. 8, 9] The selfassembly of host–guest superamphiphiles can provide opportunities not only for structural versatility but also for functional modulation of nanomaterials, because the easy introduction of chemical moieties on host or guest molecules would provide an important tool to functionalize the selfassembled nanostructures. As examples, Zhang and co-workers reported that reversible supramolecular assemblies of an azobenzene-containing surfactant with a-CD can be reversibly controlled by photostimuli. Recently, Kim s group reported a strategy for designing nanotubes, in which the supramolecular recognition of CD and dendrons transforms the self-assembled structures from the vesicle to the CDcovered nanotube. Up to now a few examples have been reported of the use of conventional CDs as host molecules to form supramolecular amphiphiles for fabricating nanostructures; however, giant nanotubes formed by directly selfassembled supramolecular amphiphiles have not yet been described. Herein, we report a novel way to construct giant nanotubes triggered by direct self-assembly of CD-based host– guest superamphiphiles. The spontaneously formed nanotubes were functionalized with the catalytic moieties of glutathione peroxidase (GPx) by modifying the host molecule CD. Furthermore, by manipulating the surface of the nanotubes with a molecular imprinting strategy, the main catalytic components were fabricated on the scaffold of giant nanotubes. Thus, the artificial GPx center with high peroxidase activity was loaded on these well-defined nanotubes. We demonstrate that the strategy of CD-based self-assembly of supramolecular amphiphiles has great potential for the construction of functional nanomaterials and could become a powerful tool to functionalize nanotubes. The construction of biologically functional nanotubes may open a pathway for the design of advanced materials and devices, and the fabrication of nanotubes with enzymatic function would have potential applications in biosensors and biomedicine. Thus, we wondered whether we could directly obtain nanotubes with enzymatic function by combining artificial selenoenzyme design with CD-based self-assembly of supramolecular amphiphiles in aqueous solution. This idea is very challenging, since taking a nanotube as a scaffold to construct the active sites of GPx has not yet been explored. GPx is a well-known selenoenzyme that catalyzes the reduction of harmful hydroperoxides by glutathione (GSH), and plays an important role in the organism antioxidant defense mechanism in protecting biomembranes and other cellular components from oxidative damage. In recent years, there has been increasing interest in mimicking the [*] Y. Tang, L. P. Zhou, J. X. Li, Dr. Q. Luo, Dr. X. Huang, P. Wu, Y. G. Wang, J. Y. Xu, Prof. J. C. Shen, Prof. Dr. J. Q. Liu State Key Laboratory of Supramolecular Structure and Materials College of Chemistry, Jilin University 2699 Qianjin Road, Changchun 130012 (P.R. China) Fax: (+ 86)431-8519-3421 E-mail: junqiuliu@jlu.edu. cn