Probing the Interaction of [Ru(phen)₂(dppz)]²⁺ with Single-Stranded DNAWhat Degree of Protection Is Required for Operation of the “Light-Switch Effect”?

Abstract

Time-resolved and steady-state luminescence and transient resonance Raman measurements have been carried out on the complex [Ru(phen) 2 dppz] 2+ (1) in the presence of single-stranded (ss) DNA that is either covalently attached to or mixed in 1:1 ratio with the complex. The well-known enhancement of luminescence (the "lightswitch" effect) exhibited by (1) when intercalated to double-stranded DNA is also observed in the presence of the single-stranded material, under conditions of covalent attachment or simple mixing. The evidence from both the luminescence and the transient Raman studies suggests that the enhancement need not necessarily reflect deep intercalation of the dppz ligand between the bases of the ss material.

Interaction of Ruthenium(II)[(1,10-phenanthroline)2benzodipyrido[3,2-a:2',3'-c]-phenazine]2+with Single Stranded Poly(dA) and Poly(dT): Turning off the Light Switch

“…This conclusion is in contrast with the case of [Ru(phen) 2 complex was affected by the length and nature of the base. 15,16 Therefore, it was concluded that for the [Ru(phen) 2 -DPPZ] 2+ complex both the base and phosphate group are involved in the luminescent complex.…”

“…11 However, the mechanism for the light switch effect of the [Ru(phen) 2 DPPZ] 2+ complex upon its association with single stranded DNAs is not clear yet, because the single stranded DNA cannot provide any intercalation pocket, i.e., non-polar environment for the incoming Ru(II) complex. 15,16 In the case of the [Ru(phen) 2 BDPPZ] 2+ complex, the luminescence quantum yield decreases proportionally with respect to the solution's polarity except in the cases of DMF and MeCN. Although the reason for these two exceptions is unclear, the "light switch off" effect of the [Ru(phen) 2 -BDPPZ] 2+ complex may be attributed to the increase in the environmental polarity upon its association with the negatively charged phosphate groups of the single stranded 2+ complex in the presence of single stranded DNAs are also pronounced.…”

“…Therefore, it is conclusive that the gradual increase in the ligand size affects the interaction of the Ru(II) complexes with the single stranded DNA. The size of the [Ru(phen) 2 DPPZ] 2+ complex may allow it to fit into the cavity 15 formed by the single stranded DNA or to interact with both the DNA base and the phosphate groups, 16 while the [Ru(phen) 2 BDPPZ] 2+ complex is too large for these interactions.…”

“…[11][12][13][14] Although the intercalation of the large DPPZ ligand between the DNA base pair has been deemed to be the origin of the light switch effect, it has recently been reported that the luminescence intensity can also be largely enhanced by the association of the [Ru(phen) 2 DPPZ] 2+ complex with a single stranded DNA which cannot provide any intercalation pocket. 15,16 In the complex formed between [Ru(phen) 2 DPPZ] 2+ and single stranded oligonucleotides, the hydrophobic environment for the [Ru(phen) 2 DPPZ] 2+ complex may be provided by a cavity formed from the single stranded DNA. 15 The formation of a luminescent complex involving the [Ru(phen) 2 …”

“…15,16 In the complex formed between [Ru(phen) 2 DPPZ] 2+ and single stranded oligonucleotides, the hydrophobic environment for the [Ru(phen) 2 DPPZ] 2+ complex may be provided by a cavity formed from the single stranded DNA. 15 The formation of a luminescent complex involving the [Ru(phen) 2 …”