Complex Formation of Crown Ethers with the Cucurbit[6]uril–Spermidine and Cucurbit[6]uril–Spermine Complex in Aqueous Solution HANS-JU ¨ RGEN BUSCHMANN 1, *, LUCIA MUTIHAC 2 and ECKHARD SCHOLLMEYER 1 1 Deutsches Textilforschungszentrum Nord-West e.V., Adlerstrasse 1, D-47798 Krefeld, Germany 2 Department of Analytical Chemistry, University of Bucharest, 4-12 Blvd. Regina Elisabeta, 703461 Bucharest, Romania (Received: 26 July 2004; in final form: 26 January 2005) Key words: amine complexes, crown ethers, cucurbituril, mixed complexes Abstract Alkyl amines are able to form complexes with either crown ethers or cyclodextrins or cucurbit[6]uril. The same is known for polyamines such as spermidine and spermine. However, the simultaneous formation of such polyamines with crown ethers and cucurbit[6]uril has not been studied. The ability of polyamines such as spermidine and spermine to form mixed complexes with different ligands, e.g. crown ethers and cucurbit[6]uril has been studied in aqueous solution using pH-metric and calorimetric titrations. The thermodynamic data of reaction between crown ethers with spermidine, spermine and their cucurbit[6]uril complexes have been determined. The presence of cucurbit[6]uril on the polyamines has no important influence upon the reaction of these amines with crown ethers. The reactions between polyamines, cucurbit[6]uril and crown ethers are simple examples for the self organization of molecules due to specific interactions. Introduction Cucurbit[6]uril is a very promising macrocyclic ligand. Though it was first synthesized in 1905 [1] it took a long time before this structure was established in 1981 [2]. Cucurbit[6]uril is formed during the reaction of urea and glyoxal followed by a reaction with formaldehyde in strong acidic solution. It was already noticed by Behrend et al. [1] that this compound is able to react with inorganic ions and organic molecules to form crystalline or insoluble products. Mock [3] studied the complex formation between cucurbit[6]uril and nitrogen containing organic molecules. He observed that parts of these molecules are included within the cavity of the ligand. The protonated amino groups interact with the six carbonyl groups located at each portal of the cavity. In the case of diamines, the most stable complexes are formed if both nitrogen atoms interact with the carbonyl groups at each portal. The stability of the complexes formed decreases if the number of methylene groups is too small or too high. In these cases only one amino group is able to interact with the six carbonyl groups located at one portal. Since the first results reported by Mock the number of published papers about cucur- bit[6]uril increases rapidly from year to year. In the meantime, several derivatives of cucurbit[6]uril have been synthesized. The number of glycoluril units varies between 5 and 10 [4–7]. The complex formation of cucurbit[6]uril with organic molecules [3, 8–10] and inorganic salts has been studied in detail [11–15]. The high complex stabilities of cucurbit[6]uril with some diamines and spermine favour the formation of rotaxanes and polyrotaxanes [16–19]. Even higher ordered structure can be obtained using these complexes with cucurbituril [20, 21]. With benzoyl or naphthoyl stopper groups the [2] rotaxanes with cucurbit[6]uril are able to form complexes with a-, b- and c-cyclodextrin [22]. Due to the complex formation with cyclodextrins the solubility of the complexed rotaxanes increases. The nitrogen atoms of spermine and spermidine not involved in the complex formation with cucurbituril should be able to form complexes with macrocyclic ligands, e.g. crown ethers. As a result, mixed complexes of spermine and spermidine with two different ligands should be present in solution. In this paper, we want to present the first experimental results for the formation of these complexes. Experimental Spermidine, spermine, pentylamine (all Fluka), Ba(ClO 4 ) 2 , the crown ethers 12-crown-4 (12C4), 15- crown-5 (15C5) and 18-crown-6 (18C6) (all Merck) are used without further purification. The synthesis and purification of cucurbit[6]uril, see Figure 1, has already been described in detail [7]. As solvent bidistilled water * Author for correspondence. E-mail: buschmann@dtnw.de Journal of Inclusion Phenomena and Macrocyclic Chemistry (2005) 53:85–88 Ó Springer 2005 DOI 10.1007/s10847-005-1253-2