Pattern and Protonation Effect of Benzene Dicarboxylate Anion Species in Self-assembly System

A novel macrocycle host with flexible structure and big cavity, cyclo[2](2,6-bis(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene) (i.e. 1(4) (+) ), was effectively synthesized through cyclization reaction between 1,4-bisbromo- methylbenzene and 2,6-di(1H-imidazol-1-yl)pyridine. The binding and self-assembly properties of macrocycle host 1(4+) with a series of benzene dicarboxylate anion guests (i.e. mono-terephthalate anion 2, di-terephthalate anion 3, mono-isophthalate anion 4, di-isophthalate anion 5, mono-phthalate anion 6 or di-phthalate anion 7) were studied in detail via H-1 NMR spectroscopy, diffusion ordered NMR spectroscopy (DOSY), nuclear Overhauser effect spectroscopy (NOESY) in solution, electrospray ionization mass spectrometry (ESI-MS) in gas phase, and X-ray single crystallography in solid state. The result implied that macrocycle host 1(4+) and mono-terephthalate anion (2) or di-isophthalate anion (5) form pseudorotaxane structure, even more complex supramolecular self-assembly structure (e.g. pseudo-oligarotaxne [1(4+)center dot 2](n)(3n+)). Meanwhile the other guest anions adopt the "outside" binding modes in the complexation with 1(4+). It is also found that the thermodynamic equilibrium(s) and association constants of the complexes between macrocycle host 1(4+) and a series of benzene dicarboxylate anion guest species are different via H-1 NMR Job-plots and H-1 NMR spectroscopic titrations in solution: (1) the stoichiometry values suggested that host 1(4+) can bind equivalent or more mono-anion guests than di-anion species from the same benzene dicarboxylic acid; (2) comparing the association constants of 1 : 1 (host : guest) complex between 1(4+) and mono-anion species resulted in K-a[1(4+)center dot 2]>K-a[1(4+)center dot 4]>K-a[1(4+)center dot 6]; the similar comparison was carried out for di-anion species interactions and obtained Ka[1(4+)center dot 3]>K-a[1(4+)center dot 5]>K-a[1(4+)center dot 7]; the result suggest that the pattern of the anion highly influences the thermostability of the 1 : 1 complex. It is speculated that the pattern and protonation factors of the benzene dicarboxylate anion guests determine their interactions with macrocycle 1(4+), including binding modes, stoichiometries, association constants, and so on. The finding will help to direct the following novel supramolecular self-assembly construction involving macrocycle host and multi-carboxylate anion species.