Cleavage of DNA by Proton-Coupled Electron Transfer to a Photoexcited, Hydrated Ru(II) 1,10-Phenanthroline-5,6-dione Complex
Bibliographic record
Abstract
Visible light irradiation of a ruthenium(II) quinone-containing complex, [(phen)(2)Ru(phendione)](2+) (1(2+)), where phendione = 1,10-phenanthroline-5,6-dione, leads to DNA cleavage in an oxygen independent manner. A combination of NMR analyses, transient absorption spectroscopy, and fluorescence measurements in water and acetonitrile reveal that complex 1(2+) must be hydrated at the quinone functionality, giving [(phen)(2)Ru(phenH(2)O)](2+) (1H(2)O(2+), where phenH(2)O = 1,10-phenanthroline-6-one-5-diol), in order to access a long-lived (3)MLCT(hydrate) state (τ ∼ 360 ns in H(2)O) which is responsible for DNA cleavage. In effect, hydration at one of the carbonyl functions effectively eliminates the low-energy (3)MLCT(SQ) state (Ru(III) phen-semiquinone radical anion) as the predominant nonradiative decay pathway. This (3)MLCT(SQ) state is very short-lived (<1 ns) as expected from the energy gap law for nonradiative decay, (1) and too short-lived to be the photoactive species. The resulting excited state in 1H(2)O(2+)* has photophysical properties similar to the (3)MLCT state in [Ru(phen)(3)](2+)* with the added functionality of basic sites at the ligand periphery. Whereas [Ru(phen)(3)](2+)* does not show direct DNA cleavage, the deprotonated form of 1H(2)O(2+)* does via a proton-coupled electron transfer (PCET) mechanism where the peripheral basic oxygen sites act as the proton acceptor. Analysis of the small molecule byproducts of DNA scission supports the conclusion that cleavage occurs via H-atom abstraction from the sugar moieties, consistent with a PCET mechanism. Complex 1(2+) is a rare example of a ruthenium complex which 'turns on' both reactivity and luminescence upon switching to a hydrated state.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".