Gas-Phase Formation of Radical Cations of Monomers and Dimers of Guanosine by Collision-Induced Dissociation of Cu(II)−Guanosine Complexes
Bibliographic record
Abstract
An electrosprayed water/methanol solution of guanosine and Cu(NO 3 ) 2 was observed to give rise to gas-phase copper complexed ions of [CuL n ] •2+, [CuL(MeOH) n ] •2+, and [CuG n (NO 3 )] •+, as well as the ions [L] •+, [L + H] +, [G] •+, and [G + H] + (L = guanosine, G = guanine). The Collision-Induced Dissociation (CID) of [CuL 3 ] •2+ and [CuL(MeOH) n ] •2+ ( n = 2, 3) generates guanosine radical cations [L] •+, while dimeric guanosine radical cations [L 2 ] •+ are generated in the dissociation of [CuL 4 ] •2+ . Protonated guanosine [L + H] + is one of the main products in the primary dissociation of [CuL 2 ] •2+, while the dissociation of the higher-order [CuG 2 ] •2+ produces the [G] •+ radical cation. The guanosine dimer radical cation, [L 2 ] •+ presumably arises from the interaction of two guanosine molecules via proton and hydrogen bonding and is observed to dissociate into [L + H] + and [L − H] • at low energies. We propose that the first two ligands bind strongly with Cu(II) through N7 and O6 to form a [CuL 2 ] •2+ complex with a four-coordinated planar structure and that a third ligand binds loosely with copper to form [CuL 3 ] •2+ . Additional ligation observed in the formation of [CuL n ] •2+ ( n ≤ 6) ions is presumed to occur by hydrogen bonding. The ribose group of guanosine appears to play an important role in the stabilization of the doubly charged Cu−guanosine complex and in intraligand proton transfer upon CID. The molecular radical cations [L] •+ observed in the ESI-MS spectrum at low declustering potentials originate primarily from [CuL(MeOH) 2,3 ] •2+ complexes which can dissociate more easily than [CuL 3 ] •2+ .
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| 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 source (direct Gemma or distilled Codex), 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".