title: Organogelation-controlled topochemical [2+2] cycloaddition and morphological changes: from nanofiber to peculiar coaxial hollow toruloid-like nanostructures.
abstract: Novel amphiphilic molecules composed of naphthylacryl and L-glutamide moieties (1-NA and 2-NA) have been designed and their organogel formation in various organic solvents as well as their self-assembled nanostructures have been investigated. Both compounds formed organogels in many organic solvents, ranging from nonpolar to polar, and self-assembled into essentially nanofiber structures, although some twist or belt structures could be observed in certain solvents. A gel of compound 2-NA in ethanol initially self-assembled into nanofibers and then these were transformed into a family of coaxial hollow toruloid-like (CHTL) nanostructures under irradiation, in which various toroids and disks of different sizes were stacked coaxially. We have established that a topochemical [2+2] cycloaddition in the organogel triggers this transformation. When the gel was fabricated into xerogels in which no ethanol remained, such morphological changes could not happen. This might be the first report of an organogel, in which both organized nanofibers and solvent coexist, controlling a topochemical reaction as well as the self-assembled nanostructures formed. Due to the formation of the toruloid-like nanostructures, the gel collapsed to a precipitate. However, upon heating this precipitate with ethanol, it redissolved and then formed a gel and self-assembled into nanofibers once more. Thus, a reversible morphological transformation between nanofibers and an unprecedented series of toruloid-like nanostructures can be induced by alternately heating and irradiating the gel.
authors.affiliation: Beijing National Laboratory for Molecular Science, CAS Key Laboratory of Colloid Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190 (P. R. China), Fax: (+86) 10-6256-9564.
authors.forename: Xiufeng
authors.initials: X
authors.lastname: Wang
authors.forename: Pengfei
authors.initials: P
authors.lastname: Duan
authors.forename: Minghua
authors.initials: M
authors.lastname: Liu
keywords: L-glutamide; nanostructures; organogels; self-assembly; topochemical reaction