水溶液中における多核亜鉛錯体の超分子化学
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概要
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We report novel supramolecular polyhedrons formed by three-dimensional self-assembly of multinuclear zinc (II) 12-membered tetraamine (=cyclen= 1,4,7,10-tetraazacyclododecane) complexes with potentially multidentate ligands such as cyanuric acid (CA) and trithiocyanuric acid (TCA) in aqueous solution. Two new supermolecular frameworks were isolated by self-assembly of a tris (Zn^2+-cyclen) (Zn_3L^1) with di-(CA^2-) or tri-deprotonated cyanuric acid (CA^3-) in aqueous solution. One was a very stable 2 : 3 complex of Zn_3L^1 and CA^2- formed above pH6, which was stable in aqueous solution at neutral pH. The second was an unexpected supramolecular complex formed by 4 : 4 self-assembly of Zn_3L^1 and CA^3-, which was isolated by allowing a 1 : 1 mixture of Zn_3L^1 and CA to stand in aqueous solution at pH 11.5. X-ray crystal analysis showed a highly symmetric 4 : 4 assembly complex with a cuboctahedral exterior and an inner hollow, which was schematically represented as a truncated tetrahedron formed by binding four equilateral triangles and four scalene hexagons with each other through CA^3--Zn^2+ bonds. The 4 : 4 complex was found to be stable only in solid form or in DMSO solution and tends to revert to the 2 : 3 complex in the presence of H_2O. This problem has been overcome by replacing CA with TCA, of which the thioimide functions possess lower pK_a values than those of CA. TCA acted as a tridentate donor for three Zn_3L^1 at neutral pH to yield a similar type of 4 : 4 self-assembling super-complex, in which the deprotonated TCA^3- in an aromatic 1,3,5-triazine binds to Zn_3L^1 through Zn^2+-S^- (exocyclic) coordination bonds, and thus the 4 : 4 assembly is a chiral twisted cuboctahedron. More interestingly, this supramolecular capsule was found to be stabilized by encapsulation of various size-matched and hydrophobic guest molecules such as adamantane in the twisted truncated cavity. Finally, we succeeded in synthesizing new supramolecular trigonal prisms from linear multinuclear zinc complexes such as p-Zn_2L^2 and p,p-Zn_3L^3 with TCA^3- in aqueous solution at neutral pH, which are stabilized by Zn^2+-S^- or Zn^2+-N^- coordination bonds and hydrogen bonds in aqueous solution at neutral pH. Thus we discovered a new approach to the design of various supramolecular structures in aqueous solution.
- 社団法人日本薬学会の論文
- 2002-12-01