J. Sep. Sci. 2013, 00, 1–9 1 Zden ˇ ek Kej´ ık 1,2 Robert Kapl ´ anek 1 Jakub Rak 1,3* Marie Pl ´ atov ´ a 1 Magda Vosmansk ´ a 1 Pavel Mart ´ asek 2 Vladim´ ır Kr ´ al 1,3 1 Department of Analytical Chemistry, Faculty of Chemical Engineering, Institute of Chemical Technology, Prague, Czech Republic 2 Department of Pediatrics, First Faculty of Medicine, Charles University in Prague, Prague, Czech Republic 3 Zentiva R&D, Part of Sanofi- Aventis, Prague, Czech Republic Received February 4, 2013 Revised April 21, 2013 Accepted April 21, 2013 Research Article A novel sorbent for chromatographic separations: A silica matrix modified with non-covalently bonded tetrakis(-cyclodextrin)–porphyrin conjugates We prepared new phases for LC that consisted of silica modified with non-covalently bonded tetrakis(-cyclodextrin)–porphyrin (where cyclodextrin is CD) conjugates. The effects of the porphyrin core, type of spacer and -CD moieties on the behaviours of the modified phases for the separation of aromatic compounds (benzene, toluene, ethylbenzene, propylben- zene, butylbenzene, pentylbenzene, o-terphenyl, triphenylene, phenol and caffeine) and fluorinated aromatic compounds (pentafluorobenzonitrile, pentafluoronitrobenzene and hexafluorobenzene) were studied using the Tanaka test. The results indicate that the non- covalent substitution of silica with CD-based macromolecules that have a porphyrin core can be a very effective method for preparing novel sorbents with specific chromatographic properties for applications in LC. Keywords: Chromatography / Cyclodextrin–porphyrin conjugates / Hydrophobic interaction / Non-covalently modified silica / Tanaka test DOI 10.1002/jssc.201300116 1 Introduction One of the most exploited areas of analytical chemistry during the past decades has been the molecular recognition and sep- aration of structurally similar compounds. This goal can be achieved using chromatographic methods, including LC. A key factor that determines the efficiency, including the selec- tivity and retentivity, of an LC method is the stationary phase. Modifying the stationary phase, which is usually silica-based, with various specific ligands such as cyclodextrins (CDs) and their derivatives can greatly improve the intrinsic limits of the stationary phase [1–9]. CDs have been extremely appealing to investigators for a long time in the field of analytical chemistry because of their ability to form inclusion complexes with vari- ous hydrophobic species in aqueous solutions [2, 4, 10]. Natu- ral CDs are cyclic oligosaccharides that consist of -1,4-linked -D-(+)-glucopyranose units with a relatively hydrophobic in- ner cavity and a hydrophilic outer surface. Natural CDs can be selectively modified based on the different reactivities and degrees of steric hindrance of the primary and secondary hy- droxyl groups that are presented both on the wider and nar- rower rims of the CD cones [2]. An advantage of a selective Correspondence: Dr. Robert Kapl´ anek, Department of Analytical Chemistry, Faculty of Chemical Engineering, Institute of Chemical Technology, Technick ´ a 5, 166 28 Prague 6, Czech Republic E-mail: robert.kaplanek@vscht.cz Abbreviations: CD, cyclodextrin; MD, molecular dynamic; QD, quantum dynamic modification approach is the cooperation of the connected moieties for improving interactions with and recognition of target analytes. The appropriate combination of the relatively hydrophobic nature and size of the CD cavity with the specific features of the ad hoc attached molecules results in fascinat- ing compounds, including enzyme mimics, abiotic receptors and molecular actuators [2, 11–13]. The conjugation of CDs with various building blocks is used to prepare supramolecular systems with interesting properties and potential applications. It has been reported that CD–porphyrin conjugates are promising structural motifs for designing functional supramolecular assem- blies [14–16], supramolecular enzyme mimics and models of carotene dioxygenases [17, 18] or cytochrome P-450 enzymes [19, 20], energy/electron transfer systems [21] and multi-modal drug delivery systems [22, 23]. Precise knowl- edge about the mechanism of their interaction with and recognition of target molecules is necessary for the systematic design and development of these motifs. This objective can benefit from applied LC methods that use silica phases that have been modified with covalently [5, 24] or non-covalently bonded functional supramolecular systems. In this work, we present the preparation of two novel silica phases modified with non-covalently bonded tetrakis(-CD)-porphyrin conju- gates and the study of their chromatographic characteristics. ∗ Additional corresponding author: Jakub Rak, E-mail: jakub.rak@gmail.com C  2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com