The current development in the intramolecular aromatic-ring stacking interactions in the complexes with compositions of DNA and heteroaromatic N-bases has been reviewed to a great extent, especially the significant contributions in several important systems about ternary mixed-ligand complexes, including nucleotide-metal ion-po-lyaromatic amine, amino acid-metal ion-polyaromatic amine, nucleotide-metal ion-pyridine-like aromatic amine, nucleo-tide-metal ion-amino acid, nucleotide-metal ion-nucleic acid base, nucleic acid base-metal ion, and the important factors affecting the intramolecular aromatic-ring stacking interac-tions in the complexes. Based on the study of stacking inter-action in the complexes, the mechanism of interaction be-tween DNA molecules and complexes of heteroaromatic N-bases has been established, which is crucial for the design and synthesis of the complexes acting as molecular devices of DNA.
Jl Liangnian & LE XueyiDepartment of Chemistry, Key Laboratory for the Gene Engineering of the Ministry of Education of China, and State Key Laboratory of Ultrafast Laser Spectroscopy, Zhongshan University, Guangzhou 510275, China
The stability constants of the ternary M(Bic)(Bzim)+ complexes, where M2+ = Cu2+, Ni2+ or Zn2+, Bic- = the anion of N, N-bis(2-hydroxyethyl) glycine and Bzim = benzimidazole, were determined by potentiometric pH titration in aqueous solution. One of them (M2+ = Cu2+) was also separately determined by spectrophotometry. The results show that these ternary complexes are stabler than expected on statistical grounds. The enhanced stability of the ternary M(Bic) (Bzim)+ complexes is attributed to the πA-πB cooperative effect between Bic- and benzimidazole. Besides, compared with Cu(Bic) (Bzim)+ and Ni(Bic) (Bzim)+, the ternary Zn(Bic) (Bzim)+ complex has relatively high stability. The crystal structure of [Cu(Bic)(Bzim)]ClO4 was determined by single crystal X-ray diffraction techniques. The copper atom has a trigonal-bipyramidal geometry, the basal plane is formed by an oxygen atom of the carboxylato group and two hydroxyl oxygen atoms, the apical position is occupied by a nitrogen atom of Bic- and a nitrogen atom of benzimidazole. The molecular structure of Cu(Bic) (Bzim)+ in aqueous solution is different from that in the crystalline state. The results of ESR and electronic spectra show that the structure of this complex is octahedron in aqueous solution.
