Formation of extended probe–cyclodextrin nanotubular supra structures: Endogenous surfactants triggered on-demand release Arabinda Mallick a,⇑ , Basudeb Haldar b,⇑ , Ujjal Kanti Roy c,⇑ a Department of Chemistry, Kashipur Michael Madhusudan Mahavidyalaya, Purulia, West Bengal 723132, India b Department of Chemistry, Vivekananda Mahavidyalaya, Burdwan, Sripally, Burdwan, West Bengal 713103, India c Department of Chemistry, Deshabandhu Mahavidyalaya, Chittaranjan, West Bengal 713331, India article info Article history: Received 16 April 2013 In final form 27 June 2013 Available online 4 July 2013 abstract Steady state absorption, emission, and picosecond time resolved fluorescence and transmission electron microscopic (TEM) techniques have been exploited to substantiate and characterize the formation of a substrate—anchored b-cyclodextrin nanotubular suprastructure in aqueous medium. Experimental results reveal that suprastructure is originated from a purely ground state interaction between a newly developed bisindole based drug molecule namely 3,3 0 -bis(indolyl)-4-chlorophenylmethane (BICPM) with b-cyclodextrin. The bound drug molecule is susceptible to be released out from the supramolecular com- plex in a controlled manner by the use of endogenous surfactants and is poised to serve a significant pur- pose in targeted drug delivery preferably at the intestinal region. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The design and preparation of supramolecular nanostructures is one of the challenging fields with increasing attention because of their intrinsic scientific interest and technological applications in diverse fields like carrier for targeted drug or gene delivery, bio- chemical sensor, electronic or photonic material, nanoreactor etc. Self-assembly is a more friendly strategy for the preparation of the suprastructures compared to synthesizing them bond by bond. Spontaneous or induced self-assembly and chemical transforma- tion of biological or organic subunits (molecules, macromolecules, and supramolecules) in a wide range of scientific fields are crucial subjects for the accomplishment of well defined nanostructures and the precise control of the function of supramolecules at the molecular level [1–15]. Under appropriate conditions, different types of cyclodextrin aggregates can be formed, such as catenanes [7], rotaxanes [7], polyrotaxanes [8], and threaded cyclodextrins [9] that do not involve any covalent bonding between the cyclo- dextrins and the other molecules. Li and his co-workers [10] found that b-CD or c-CD can form rodlike nanotubes by including a mol- ecule, i.e., all-trans-1,6-diphenyl-1,3,5-hexatriene (DPH). Agbaria and Gill [11,12] found that some oxazole molecules, such as PBD, 2,5-diphenyl 1,3-oxazole (PPO), 2,5-diphenyl 1,3,4-oxadiazole (PPD), and 2,5-(4,40-diphenyl) 1,3,4-oxazole (BBOD) can form 2:1 binary inclusion complexes with c-CD at relatively lower concentrations. At higher concentrations, however, these inclusion complexes can form extended nanotubes [11,12]. In particular, vesicular and tubular assemblies are of much interest because of their unique characteristics as biomimetic systems. With potential applications across the food chain (in pes- ticides, vaccines, veterinary medicine and nutritionally-enhanced food), these nano- and micro-formulations are being developed day by day. Self-assembly of synthetic building blocks by non- covalent interactions is thus expected to provide a unique method- ology for the development of supramolecular functional materials of the new generation [1,2,4,9–13]. The topic demands attention from the medical research considering the prospective application of these nanostructures for selected and targeted drug delivery. Cyclodextrin (CD) are interesting microvessels capable of embedding appropriately sized molecules and the resulting supra- molecules can serve as an excellent miniature models for nano-bio conjugates [1–4]. These conjugates are drawing much attention to the chemists as well as biologists because of its widespread application in the pharmaceutical industry; especially due to their importance as micro vessel for the selective drug delivery. Because of this particular property, CDs are able to complex various organic compounds in aqueous solution and are of special interest in pharmacology and supramolecular chemistry. Some interesting examples include trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT), [16,17] and 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ) [18,19] which self-assemble to form extended aggregates that are supported together when in- cluded inside CD channels. These studies have successfully demon- strated the formation of chromophore-anchored supramolecular aggregates. Numerous CD-based inclusion complexes have been 0009-2614/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cplett.2013.06.057 ⇑ Corresponding authors. E-mail addresses: ampcju@yahoo.co.in (A. Mallick), pcbhaldar@yahoo.co.in (B. Haldar), uroccu@gmail.com (U.K. Roy). Chemical Physics Letters 580 (2013) 82–87 Contents lists available at SciVerse ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett