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
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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 N 1 -methylguanosine and N 2 ,N 2 -dimethylguanosine. The rationale was that the former is unable to lose the N-1 proton, while the latter cannot deprotonate at the NH 2 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 N 2 ,N 2 -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 N 1 -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 N 2 ,N 2 -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 NH 2 and NMe 2 can exert a stabilizing effect.Key words: nitrenium, arylnitrenium, guanosine, DNA adduct.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.003 | 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 it