Cite this: RSC Advances, 2013, 3, 12384 Interaction of semicarbazide and thiosemicarbazide pyrene derivatives with anionic and cationic micelles: changed character of pyrene due to alteration in charge density induced by the side chains Received 1st March 2013, Accepted 7th May 2013 DOI: 10.1039/c3ra41029c www.rsc.org/advances Arnab Maity, Shrabanti Das, Soumik Mandal, Parna Gupta and Pradipta Purkayastha* A semicarbazide and a thiosemicarbazide derivative of pyrene have been synthesized keeping in mind the pharmaceutical potentiality of the molecules. The molecules differ in structure only at the CLO and the CLS groups. The presence of the amine group in the vicinity of the O and the S atoms distributes the p-electrons in the pyrene differently making the pyrene moiety in the semicarbazide more hydrophobic than that in the thiosemicarbazide. Because of this different electron distribution in the ground state of the molecules, they interact variably with either cationic or anionic micelles. The compounds are found to attach to the cationic micelles at the surface through electrostatic interactions between the pyrene electrons and the surfactant head groups, varying in the strength of the binding. The exaggerated electron density towards the S counterpart in the thiosemicarbazide drives the molecule to move to the Stern layer, whereas, due to a greater electron cloud over the pyrene moiety of the semicarbazide it stays inside the palisade layer of the anionic micelle. We have used fluorescence spectroscopy to investigate the interactions. The different extents of the distribution of these medically potent compounds in biomimicking cationic and anionic micelles could further open up their biological applications. 1 Introduction Pyrene is regularly used as a very efficient fluorescent dye to be used as an indicator for the presence of ions, 1 small molecules, 2,3 nucleic acids, 4,5 or proteins. 6,7 Pyrene is extre- mely sensitive to the polarity of the medium and also has been potentially used as a polarity sensor. 8–10 Two pyrene molecules in vicinity to each other form an excimer, one of them being in the ground state. However, the strength of the excimer depends on the microenvironment. The pyrene excimer also shows a long lifetime (up to 100 ns) than normal chromo- phores in biological fluids (less than 10 ns). 4–6 Based on the potentiality of pyrene, it has been used as fluorescent tags for biomolecules to be used in biological applications. In order to know the biosystems, mimics to such environments are created and from the behavior of small molecules in such environments significant outcomes are obtained. The struc- ture and dynamics of organized multimolecular assemblies that act as potential biomimics, such as micelles or mem- branes, are well known through numerous experimental and theoretical methods. Pyrene is one of the most studied compounds in micelle environments. Generally, in micelles created by cationic surfactants, such as, cetyl trimethylammonium bromide (CTAB), pyrene is found to exist at the micelle–water inter- face. 11 Thus, the bromide ions of the surfactant molecules act as a quencher for the pyrene secluded in micelles. In a recent report, the authors have shown that the fluorescence of micellized pyrene in CTAB is influenced in different ways by diverse nucleotide monophosphates, which showed the existence of the pyrene molecules at the surface of the CTAB micelles. 11 The electron rich pyrene rings electrostatically interact with the quarternary ammonium groups to obtain stability. 12 Thus, evidently there are large differences between the maximum solubility of pyrene (and other arenes) in anionic and cationic micelles. Hence, one would rightly expect pyrene (and other similar probes) to be solubilized closer to the micelle surface and the pyrene microenvironment to be more polar in CTAB than in anionic micelles (e.g., formed by sodium dodecyl sulfate (SDS)). 12 Pyrene has been proved to exist in the palisade layer of anionic micelles of SDS by experimental and theoretical investigations. 13,14 Hence, the solubilized pyrene molecules reside in the palisade layer of micelles, near the polar head groups, where they sense a relatively high polar environment but lower than that in the Department of Chemical Sciences, Indian Institute of Science Education and Research, Kolkata, Mohanpur, WB, 741252, India. E-mail: pradiptp@gmail.com; Fax: +91 33 2587 3020; Tel: +91 33 2587 3121 RSC Advances PAPER 12384 | RSC Adv., 2013, 3, 12384–12389 This journal is ß The Royal Society of Chemistry 2013 Published on 07 May 2013. Downloaded by Indian Institute of Science Education & Research Kolkata on 11/07/2013 09:01:20. View Article Online View Journal | View Issue