Ruthenium(II) Complex of Hbopip:  Synthesis, Characterization, pH-Induced Luminescence “Off−On−Off” Switch, and Avid Binding to DNA

• Published in: The journal of physical chemistry. B 2006-02, Vol.110 (5), p.2364-2371
• Main Authors: Han, Mei-Jiao, Gao, Li-Hua, Lü, Yuan-Yuan, Wang, Ke-Zhi
• Format: Article
• Language: English
• Subjects: Binding, Competitive; Buffers; DNA - chemistry; Ethidium - chemistry; Ferricyanides - chemistry; Hydrogen-Ion Concentration; Intercalating Agents - chemical synthesis; Luminescence; Luminescent Measurements; Organometallic Compounds - chemical synthesis; Ruthenium Compounds - chemical synthesis; Sodium Chloride - chemistry; Spectrophotometry, Ultraviolet; Viscosity
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp0548570

A novel ruthenium(II) complex of [Ru(bpy)2(Hbopip)](ClO4)2 (in which bpy = 2,2‘-bipyridine, Hbopip = 2-(4-benzoxazolyl)phenylimidazo[4,5-f][1,10]phenanthroline) was synthesized and characterized. The spectrophotometric pH titrations of the complex showed that it acted as a pH-induced luminescence “off−on−off” switch:  a luminescence off−on switch with a luminescence enhancement factor of I pH=3.0/I pH=1.0 = 20 occurring over a narrow pH range of 1.00−3.00 plus a luminescence on−off switch with a luminescence enhancement factor of 3 over a pH range of 3.20−9.40. The excited-state ionization constant of the complex derived, pK a1* = 3.06, is 1.36 pK a units greater than the ground-state pK a1 = 1.70, and pK a2* = 5.01 and pK a3* = 8.22 are comparable to the ground-state pK a2 = 5.23 and pK a3 = 8.22, respectively. The complex avidly bound to calf thymus DNA with a large binding constant of (1.2 ± 0.3) × 107 M-1 in buffered 50 mM NaCl, as evidenced by UV−vis and luminescence titrations, steady-state emission quenching by [Fe(CN)6]4-, DNA competitive binding with ethidium bromide, viscosity measurements, and DNA melting experiments.