Photoinduced Electron Transfer in Ruthenium Bipyridyl Complexes: Evidence for the Existence of a Cage with Molecular Oxygen

Stepwise synthesis, characterization, DNA binding properties and cytotoxicity of diruthenium oligopyridine compounds conjugated with peptides

Although the interactions of oligopyridine ruthenium complexes with DNA have been widely studied, the biological activity of similar diruthenium oligopyridine complexes conjugated with peptides has not been investigated. Herein, we report the stepwise synthesis and characterization of diruthenium complexes with the general formula [(L^a)Ru(tppz)Ru(L^b)]ⁿ⁺ (tppz = 2,3,5,6-tetra(2-pyridyl)pyrazine, L^a = 2,2':6',2''-terpyridine or 4-phenyl-2,2':6',2''-terpyridine and L^b = 2,2':6',2''-terpyridine-4'-CO(Gly¹-Gly²-Gly³-LysCONH₂) (5), (6), n = 5; 2,2':6',2''-terpyridine-4'-CO(Gly¹-Gly²-Lys¹-Lys²CONH₂) (7), (8), n = 6; 2,2':6',2''-terpyridine-4'-CO(Ahx-Lys¹Lys²CONH₂) (9), (10), n = 5, Ahx = 6-aminohexanoic acid). The compounds [(trpy)Ru(tppz)Ru(trpy-CO₂H)](PF₆)₄, (2)(PF₆)₄, [(ptrpy)Ru(tppz)Ru(trpy-CO₂H)](PF₆)₄, (3)(PF₆)₄ and [(ptrpy)Ru(tppz)Ru(trpy)](PF₆)₄, (4)(PF₆)₄ were also characterized by single crystal X-ray methods. Moreover, the interactions of the chloride salts (5), (6) and (4) with the self-complementary dodecanucleotide duplex d(5'-CGCGAATTCGCG-3')₂ were studied by NMR spectroscopic techniques. The results show that complex (4) binds in the central part of the oligonucleotide, from the minor groove through the ligand ptrpy, while the ligand trpy, which was located on the other side of the diruthenium core, does not contribute to the binding. Complex (5) binds similarly, through the ligand ptrpy. However, the induced upfield shifts of the ptrpy proton signals are significantly lower than the corresponding ones in the case of (4), indicating much lower binding affinity. This is clear evidence that the tethered peptide Gly¹-Gly²-Gly³-Lys¹CONH₂ hinders the complex binding, even though it contains groups that are able to assist it (e.g., the positively charged amino group of lysine, the peptidic backbone, the terminal amide). Complex (6) shows a non-specific binding, interacting through electrostatic forces. The chloride salts of (4), (5) and (6) had insignificant effects on the cell cycle distribution and marginal cytotoxicity (IC₅₀ > 750 μM) against human lung cancer cell lines H1299 and H1437, indicating that their binding to the oligonucleotide is not a sufficient condition for their cytotoxicity.

Synthesis and characterization of ruthenium(II)-oligopyridine-peptide conjugates. Interactions of the diasteromeres Δ- and Λ-[Ru(bpy)2(4-COY-4'-Mebpy)]Cl2 (Y=Gly-Lys(1)-Lys(2)CONH2, Lys(1)-Gly-Lys(2)CONH2, Lys(1)-Lys(2)-GlyCONH2) with the oligonucleotide d(5'-CGCGAATTCGCG-3')2

Diastereomeric complexes of the general formulae Λ- and Δ-[Ru(bpy)2(4-COY-4'-Mebpy)]Cl2 where bpy=2,2'-bipyridine and Y=Gly-Lys(1)-Lys(2)CONH2, Lys(1)-Gly-Lys(2)CONH2, Lys(1)-Lys(2)-GlyCONH2, were synthesized and characterized. The ability of these compounds to bind to the oligonucleotide duplex d(5'-CGCGAATTCGCG-3') was studied with NMR techniques. Complex Λ-2, Λ-[Ru(bpy)2(4-COLys(1)-Gly-Lys(2)CONH2),4'-Mebpy)]Cl2 (Mebpy=methyl-2,2'-bipyridine), interacts non-specifically causing changes for both complex and oligonucleotide (1)H NMR signals. Both Λ-1, Λ-[Ru(bpy)2(4-COGly-Lys(1)-Lys(2)CONH2),4'-Mebpy)]Cl2 and Λ-3, Λ-[Ru(bpy)2(4-COLys(1)-Lys(2)-GlyCONH2),4'-Mebpy)]Cl2, were bound to the oligonucleotide through both lysine aliphatic chains, indicating that the side chains of the sequential lysines create a kind of "clamp" to connect the complex with the oligonucleotide. Complex Δ-1, Δ-[Ru(bpy)2(4-COGly-Lys(1)-Lys(2)CONH2),4'-Mebpy)]Cl2, interacts with the oligonucleotide duplex with both lysine side chains in a manner similar to Λ-1. Δ-2, Δ-[Ru(bpy)2(4-COLys(1)-Gly-Lys(2)CONH2),4'-Mebpy)]Cl2, interacts with the oligonucleotide with the bipyridine ligands. In addition, the formation of a hydrogen bond between the Gly-NH and the carbonyl groups of the oligonucleotide bases was detected. A completely different binding mode was observed for Δ-3 Δ-[Ru(bpy)2(4-COLys(1)-Lys(2)-GlyCONH2),4'-Mebpy)]Cl2, which at a ratio of 1:1 ([Ru]/[nucleotide]) opens the oligonucleotide strands. In addition, participation of all three peptidic NH of Δ-3 in hydrogen bonds was observed.

Oligopyridine-ruthenium(II)-amino acid conjugates: synthesis, characterization, DNA binding properties and interactions with the oligonucleotide duplex d(5'-CGCGCG-3')2

Diastereomeric oligopyridine-ruthenium(II)-amino acid conjugated complexes of the general formulas Lambda- and Delta-[Ru(bpy)(2)(4,4'(CO(2)Y)(2)-bpy)](2+), where Y = L-AlaCONH(2), L-LysCONH(2), L-HisCONH(2), L-TyrCONH(2)), were synthesized and characterized. Their binding properties with ct-DNA and the oligonucleotide duplex d(5'CGCGCG-3')(2), by means of circular dichroism (CD), NMR spectroscopy and DNA thermal denaturation (T(m)) curves were studied. CD and T(m) data indicate that all diastereomeric complexes bind to the DNA major groove, Delta-diastereomers in a similar manner, while Lambda-diastereomers in dependence of the nature of the amino acid. NMR studies of d(5'CGCGCG-3')(2), and the complexes Delta-1, Delta-2, Lambda-1 and Lambda-2 indicate that Delta-1 and Delta-2 were bound having the ancillary bpy ligands towards the DNA groove, while the corresponding Lambda-1 and Lambda-2 were orientated in a similar way, facing the ligand 4,4'(CO(2)Y)(2)bpy towards the DNA major groove. Photoinduced DNA cleavage was observed in all cases studied, which take place through singlet oxygen production. Delta-4 and Lambda-4 show the lower photoinduced cleavage yield, probably because the singlet oxygen ((1)O(2)) oxidizes not only the DNA phosporodiesteric bonds but the tyrosine's phenolic OH bond as well.

Synthesis and Assembly with Mesoporous Silica MCM-48 of Platinum(II) Porphyrin Complexes Bearing Carbazyl Groups: Spectroscopic and Oxygen Sensing Properties

The synthesis and spectroscopic characterization of a series of luminescent platinum meso-tetrakis{3,5-di[(N-carbazyl)n-alkyloxyphenyl]}porphyrin (Pt-8Cn-TPP, n-alkyl = (CH2)n, n = 4, 6, and 8) are presented. The protonated platinum porphyrins ([Pt-8Cn-TPPH8]8+) were assembled with mesoporous silica MCM-48 resulting in the assembly materials [Pt-8Cn-TPPH8]8+/MCM-48. The luminescence of [Pt-8Cn-TPPH8]8+/MCM-48 can be extremely quenched by molecular oxygen with very high sensitivity (I0/I100 > 5000) and rapid response time (0.04 s) suggesting that the [Pt-8Cn-TPPH8]8+/MCM-48 system can be employed to develop high performance oxygen sensors. Among this assembly system, [Pt-8C8-TPPH8]8+/MCM-48 exhibits the highest sensitivity. Even if the concentration of oxygen is 0.1%, the luminescence intensity of [Pt-8C8-TPPH8]8+/MCM-48 can be quenched by 86%.