Supramolecular Assembly of Protonated Xanthine Alkaloids in Their Perchlorate Salts

Abstract

Single crystal X-ray structures of new perchlorate salts of a series of four xanthine alkaloids, for example, xanthine (xt), caffeine (cf), theophylline (tp), and theobromine (tb) are reported. The treatment of xanthine derivatives with 70% of HClO 4 afforded their salts Hxt 3 ClO 4 3 2(H 2 O), 1; Htp 3 ClO 4 , 2; Htb 3 ClO 4 , 3; and Hcf 3 ClO 4 3 H 2 O, 4. Xanthine form dimers via N(9)-H 3 3 3 O-C( 6) hydrogen bond in the crystal structure. Of the two possible resonance structures of the protonated imidazoles, one of the structures was found to be major in xanthine, theobromine, and caffeine salts, while both structures are of equal contribution in theophylline salts. These observations also have been verified by using the structural information available in the Cambridge Structural Database. Interestingly, xanthine 1 is present as a dihydrate and 4 as a monohydrate, whereas 2 and 3 are crystallized without any water. Thus, proton transfer from the strong acid HClO 4 to the weakly basic imidazole ring of xanthines occurs which leads to the build up of H-bonded supramolecular networks.

Wenn sich Kompetenzen ergänzen

“…The intramolecular interactions can be self‐pairing of thb molecules by hydrogen bonding (Figure 1). The amide‐to‐amide thb dimers are quite frequently encountered in materials containing these organic molecules 6,7. The donor‐acceptor distances between the amide‐N atom and carbonyl‐O atom are 2.797(8) and 2.852(7) Å, respectively, which is consistent with hydrogen bonds of medium strength 8…”

Supramolecular networks supported by the anion...π linkage of Keggin-type heteropolyoxotungstates

“…The former establish bonds to the carbonyl or solvent O atoms [NÁ Á ÁO = 2.62 (2)-2.776 (18) Å ], whereas the amide donors are bonded to anions [NÁ Á ÁO = 2.822 (19)-2.95 (2) Å ]. The same segregation of structural roles adopted by two N-H donors is relevant for theobrominium perchlorate (Biradha et al, 2010). These primary interactions unite the cations into finite linear chains The hydrogen bonding in the structure of (2) involving three unique cations (A, B and C) and ethanol solvent molecules.…”

“…However, the reliability of anionÁ Á Á interactions as a synthon for supramolecular synthesis with purine bases is rather low. The structures of most solids of this type, for instance, different xanthinium perchlorates (Biradha et al, 2010), are governed more by the competitive conventional hydrogen bonding of small anions. A very different situation may arise for larger polyhedral oxometalates.…”

Polyoxotungstates in Molecular Boxes of Purine Bases

“…The investigation of interactions between POMs and biomolecules in general [11] as well as between POMs and purine bases in particular are interesting for three major reasons: (1) They are interesting from the structural point of view, due to a multitude of possibilities of non-covalent interactions of the purine bases [12]; (2) The resulting hybrid organic-inorganic solids are in focus of current scientific research in order to elucidate the possibilities of a targeted design of functional materials; (3) They might shed some light onto the mechanism of the pharmacological action of polyoxoanions [9].…”