Photoinduced ligand exchange and DNA binding of cis-[Ru(phpy)(phen)(CH3CN)2]+ with long wavelength visible light

The complex cis-[Ru(phpy)(phen)(CH3CN)2](+) (phpy=2-phenylpyridine, phen=1,10-phenanthroline) was investigated as a potential photodynamic therapy (PDT) agent. This complex presents desirable photochemical characteristics including a low energy absorption tail extending into the PDT window (600-850nm) and photoinduced exchange of the CH3CN ligands, generating a species analogous to the chemotherapy drug cisplatin. Furthermore, photochemical reactivity can be controlled through selective irradiation into the Ru-phen singlet metal-to-ligand charge transfer ((1)MLCT) band (λirr=500 nm) of [Ru(phpy)(phen)(CH3CN)2](+) in the presence of excess t-butylammonium chloride (TBACl) resulting in efficient photoinduced production of [Ru(phpy)(phen)(CH3CN)Cl] (Φ=0.25). This lower energy irradiation resulted in greater quantum yield of photosubstitution when compared to direct irradiation into the Ru-phpy (1)MLCT peak (λirr=450 nm; Φ=0.08) in CH2Cl2. It was found that the lower quantum yield observed for irradiation into the Ru→phpy(-)(1)MLCT band results from significant orbital mixing of the phpy(-) ligand with the t2g-type filled set in the metal, giving this state significant ligand-centered character. Lastly, this complex produced a decrease in the mobility of linearized ds-DNA when irradiated with λirr≥420nm, indicative of covalent binding by the transition metal complex similar to that observed for cisplatin. No change in mobility was found for the same samples kept in the dark indicating, unlike cisplatin, DNA binding of cis-[Ru(phpy)(phen)(CH3CN)2](+) only occurs with the activation of light. These observations support the use of cis-[Ru(phpy)(phen)(CH3CN)2](+) as a potential PDT agent by the photoinduced generation of a cisplatin analog.

Electronic tuning of ruthenium complexes by 8-quinolate ligands

A series of Ru(II) complexes were synthesized with the deprotonated forms of the ligands 8-hydroxyquinoline (quo(-)) and 5-NO(2)-8-hydroxyquinoline (5-NO(2)-quo(-)) as analogs to the prototypical complex [Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine). Electrochemistry, spectroscopy and density functional theory calculations were utilized to investigate the electronic tuning of the occupied t(2g)-type orbitals of the metal center with variation in the ligation sphere. The maximum of the lowest energy absorption of complexes containing one, two and three 8-quinolate ligands progressively redshifts from 452 nm in [Ru(bpy)(3)](2+) to 510 nm in [Ru(bpy)(2)(quo)](+), 515 nm in [Ru(bpy)(quo)(2)] and 540 nm in [Ru(quo)(3)](-) in water. This bathochromic shift results from the increase in energy of the occupied t(2g)-type orbital across the series afforded by coordination of each subsequent quo(-) ligand to the Ru(II) center. Time-dependent density functional theory calculations along with electrochemical analysis reveals that the lowest energy transition has contributions in the highest occupied molecular orbital from both the quo(-) ligand and the metal, such that the lowest energy transition is not from an orbital that is purely metal-centered in character as in [Ru(bpy)(3)](2+).

Efficient DNA photocleavage by [Ru(bpy)2(dppn)]2+ with visible light

The population and reactivity of two low-lying excited states in [Ru(bpy)(2)(dppn)](2+) (bpy = 2,2'-bipyridine, dppn = benzo[i]dipyrido[3,2-a:2',3'-c]phenazine), a weakly emissive (3)MLCT state and a long-lived ligand-centered (3)pipi* state, lead to efficient photoinduced DNA damage. Irradiation with visible light results in nearly complete DNA cleavage within 30 s (lambda(irr) > or = 455 nm), likely from the combined action of guanine oxidation and the production of reactive oxygen species derived from (1)O(2).

The tobacco mosaic virus assembly origin RNA. Functional characteristics defined by directed mutagenesis

The in vitro reassembly of tobacco mosaic virus (TMV) begins with the specific recognition by the viral coat protein disk aggregate of an internal TMV RNA sequence, known as the assembly origin (Oa). This RNA sequence contains a putative stem-loop structure (loop 1), believed to be the target for disk binding in assembly initiation, which has the characteristic sequence AAGAAGUCG exposed as a single strand at its apex. We show that a 75-base RNA sequence encompassing loop 1 is sufficient to direct the encapsidation by TMV coat protein disks of a heterologous RNA fragment. This RNA sequence and structure, which is sufficient to elicit TMV assembly in vitro, was explored by site-directed mutagenesis. Structure analysis of the RNA identified mutations that appear to effect assembly via a perturbation in RNA structure, rather than by a direct effect on coat protein binding. The binding of the loop 1 apex RNA sequence to coat protein disks was shown to be due primarily to its regularly repeated G residues. Sequences such as (UUG)3 and (GUG)3 are equally effective at initiating assembly, indicating that the other bases are less functionally constrained. However, substitution of the sequences (CCG)3, (CUG)3 or (UCG)3 reduced the assembly initiation rate, indicating that C residues are unfavourable for assembly. Two additional RNA sequences within the 75-base Oa sequence, both of the form (NNG)3, may play subsidiary roles in disk binding. RNA structure plays an important part in permitting selective protein-RNA recognition, since altering the RNA folding close to the apex of the loop 1 stem reduces the rate of disk binding, as does shortening the stem itself. Whereas the RNA sequence making up the hairpin does not in general affect the specificity of the protein-RNA interaction, it is required to present the apex signal sequence in a special conformation. Mechanisms for this are discussed.