title: Synthesis, characterization, DNA-binding and spectral properties of complexes [Ru(L)4(dppz)]2+ (L=Im and MeIm).
abstract: Two new Ru(II) complexes [Ru(L)(4)(dppz)](2+) (L=imidazole (Im), 1-methylimidazole (MeIm); dppz=dipyrido[3,2-a:2',3'-c]phenazine), have been synthesized and characterized in detail by elemental analysis, (1)H NMR, Electrospray ionization mass spectrometry (ESI-MS) and UV-visible (UV-Vis) spectroscopic techniques. The interaction of these complexes with calf thymus DNA (CT-DNA) has been explored by using electronic absorption titration, competitive binding experiment, circular dichroism (CD), thermal denaturation and viscosity measurements. The experimental results show that: both the two complexes can bind to DNA in an intercalation mode; the DNA-binding affinity of complex [Ru(Im)(4)(dppz)](2+)1 (K(b)=2.5 x 10(6)M(-1)) is greater than that of complex [Ru(MeIm)(4)(dppz)](2+)2 (K(b)=1.1 x 10(6)M(-1)). Moreover, it is very interesting to find that the circular dichroic spectrum of DNA-complex 1 adduct, in which both bands centered at 277 nm and 236 nm are all negative, is very different from those of DNA-complex 2 adduct and other Ru(II) complexes binding to DNA in general intercalation mode. It may be due to the hydrogen-bonding effect or the contribution of induced CD signals of complex 1. Another interesting finding is that the hypochromism of the complexes is not linear relation to their DNA-binding affinities. In order to deeply study these experimental phenomena and trends, the density functional theory (DFT) and time-dependent DFT (TDDFT) computations were carried out, and on the basis of the DFT/TDDFT results and the frontier molecular orbital theory, the trend in DNA-binding affinities, the spectral properties as well as the interesting phenomena of larger extent of hypochromism but relatively smaller K(b) values for the title complexes have been reasonably explained.
authors.affiliation: Key Laboratory of Bioinorganic and Synthetic Chemistry of the Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, PR China.
authors.forename: Lan-Mei
authors.initials: LM
authors.lastname: Chen
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.forename: Jin-Can
authors.initials: JC
authors.lastname: Chen
authors.forename: Cai-Ping
authors.initials: CP
authors.lastname: Tan
authors.forename: Shuo
authors.initials: S
authors.lastname: Shi
authors.forename: Kang-Cheng
authors.initials: KC
authors.lastname: Zheng
authors.forename: Liang-Nian
authors.initials: LN
authors.lastname: Ji
mesh_terms: D002942:Circular Dichroism; D004247:DNA / Q000378:metabolism*; D007093:Imidazoles / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D012428:Ruthenium / Q000737:chemistry / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D007093:Imidazoles; D009942:Organometallic Compounds; D012428:Ruthenium; D004247:DNA; C427203:calf thymus DNA