1298 New J. Chem., 2013, 37, 1298--1301 This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013 Cite this: New J. Chem., 2013, 37, 1298 Synthesis of an upper- and lower-rim functionalized calix[4]arene for detecting calcium ions using a microcantilever sensor† Paris E. Georghiou,* a Shofiur Rahman, a Gopikishore Valluru, a Louise N. Dawe, a S. M. Saydur Rahman, b Abdullah N. Alodhayb b and L. Y. Beaulieu* b A new thioacetate-bearing cone-conformer calix[4]arene has been synthesized and shown to be a sensitive microcantilever self- assembled monolayer coating for calcium ion detection in aqueous solutions. There is much on-going research involving the use of calixarenes in a variety of nanotechnological applications. 1a–c A major structural feature that calixarenes offer is the robustness of the basic mole- cular architecture provided by the four phenyl rings, in the case of calix[4]arenes (1), which are linked to form a bowl-like array (Fig. 1). The upper- and lower-rims of calixarenes can both be selectively chemically modified to produce, in principle, a vast number of derivatives 2 whose molecular receptor or ‘‘host–guest’’ properties can be fine-tuned. In particular, such modified calixarenes have been used to selectively bind to a variety of cationic and anionic ‘‘guests’’. As a result, there have been numerous studies involving the solution-phase complexation of modified calixarenes with many different ionic and non-ionic guests. 3 Recently a great deal of attention has been directed towards host–guest sensing by calixarenes on solid surfaces. 4,5 Dabestani and coworkers 6 reported one of the earliest examples of the use of a calix[4]arene coated as a self-assembled monolayer (SAM) onto the gold surface of a microcantilever sensor. They showed this to be a sensitive and selective detector for cesium ions. Their calixarene, which was in a 1,3-alternate conformation, was functionalized only at the lower rim, with a benzocrown-6 ether linking a pair of distal phenyl groups, and each of the remaining pairs has 11-mercapto-1-undecanoxy ethers. The thiol groups were used to ‘‘anchor’’ the modified calix[4]arene to the gold surface of the microcantilever as a SAM. Apart from the patent literature, 7 to the best of our knowledge, there are no other reports on calixarene-modified microcantilever sensor applications. Thundat and coworkers reported an ultrasensitive chromate ion microcantilever sensor coated with a SAM triethyl-12-mercaptododecylammonium bromide layer. 8 Ji and coworkers recently described a novel selective beryllium ion detector using a microcantilever coated with a benzo-9-crown-doped chitosan-gelatin hydrogel. 9 Apart from the hydrogel approach of Ji, most of the SAMs on gold surfaces which have been reported, especially those involving calixarenes, have employed thiol groups 3 or the disulfide group of thiotic acid, 10 to bind to the gold. The exact mechanism involved in such binding is still not fully understood. 11 In this paper we describe the synthesis and use of a thioacetate-bearing calix[4]arene 2, which in the solid state is seen to be in a pinched cone conformation. 12 We have found that this new calixarene can also form a SAM on gold (Fig. 2), which has been characterized by both Scanning Electron Microscopy (SEM) and Scanning Tunneling Microscopy (STM). The calixarene layer Fig. 1 Two different forms of representations of the structure of a calix[4]arene (1) showing the ‘‘upper’’ and ‘‘lower’’ rims, which can have different functional groups represented as ‘‘X’’ and ‘‘R’’ respectively. a Department of Chemistry, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador, Canada A1B3X7. E-mail: parisg@mun.ca; Fax: +1 709 864 3702; Tel: +1 709 864 8517 b Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador, Canada A1B3X7. E-mail: lbeaulieu@mun.ca; Fax: +1 709 864 8739; Tel: +1 709 864 6203 † Electronic supplementary information available: 1 H-, 13 C-NMR and ESI-MS data for compounds 2 and 6. CCDC 924365 (2). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3nj00223c Received (in NJBRA) 27th February 2013, Accepted 13th March 2013 DOI: 10.1039/c3nj00223c www.rsc.org/njc NJC LETTER Published on 13 March 2013. Downloaded by Memorial University of Newfoundland on 18/11/2013 02:42:33. View Article Online View Journal | View Issue