Reaction of arylnitrenium ions with guanine derivatives: <i>N</i><sup>1</sup>-methylguanosine and <i>N</i><sup>2</sup>,<i>N</i><sup>2</sup>-dimethylguanosine
Bibliographic record
Abstract
A prior flash photolysis study of the direct reaction of arylnitrenium ions with 2'-deoxyguanosine identified a second intermediate that grew in as the transient nitrenium ion reacted with the nucleoside. This intermediate was identified as the the product of the addition of the nitrenium ion to the C-8 position of guanine prior to loss of the C-8 proton the C-8 intermediate. A feature of the C-8 intermediate is that it exists in acidbase forms. This behavior was evident in both a spectroscopic analysis as well as in the ratepH profile, which showed a break around pH 4 from a pH-independent reaction to a reaction that was first-order in H+. The present study was designed to identify the structure of the conjugate base form. This involved a kinetic study of the decay of the C-8 intermediate derived from the reaction of the 2-fluorenylnitrenium ion with N1-methylguanosine and N2,N2-dimethylguanosine. The rationale was that the former is unable to lose the N-1 proton, while the latter cannot deprotonate at the NH2 group. The ratepH profiles clearly show that it is the N-1 proton that is acidic. The rate constants for the C-8 intermediate of N2,N2-dimethylguanosine show the same downward break observed with 2'-deoxyguanosine and guanosine associated with conversion to the conjugate base form. In contrast, the rate constants for the N1-methylguanosine intermediate are independent of pH. Rate constants for the reaction forming the C-8 intermediate are also reported. These show that the reaction of nitrenium ions with the N2,N2-dimethylguanine derivative is significantly faster (except where the reactions are diffusion controlled). This is consistent with the initial step of the reaction of an arylnitrenium ion and guanine occurring by direct addition at C-8. The developing positive charge in such a reaction can be delocalized to the C-2 position where π donors such as NH2 and NMe2 can exert a stabilizing effect.Key words: nitrenium, arylnitrenium, guanosine, DNA adduct.
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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".