Abnormal Solvent Effects on Hydrogen Atom Abstraction. 2.\nResolution of the Curcumin Antioxidant Controversy. The Role of\nSequential Proton Loss Electron Transfer
Bibliographic record
Abstract
The rates of reaction of 1,1-diphenyl-2-picrylhydrazyl (<b>dpph</b><b><sup>•</sup></b><sup></sup>) radicals with curcumin\n(<b>CU</b>, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione), dehydrozingerone (<b>DHZ</b>, “half-curcumin”), and isoeugenol (<b>IE</b>) have been measured in methanol and ethanol and in two non-hydroxylic solvents, dioxane and ethyl acetate, which have about the same hydrogen-bond-accepting\nabilities as the alcohols. The reactions of all three substrates are orders of magnitude faster in the\nalcohols, but these high rates can be suppressed to values essentially equal to those in the two\nnon-hydroxylic solvents by the addition of acetic acid. The fast reactions in alcohols are attributed\nto the reaction of <b>dpph</b><b><sup>•</sup></b><sup></sup> with the <b>CU</b>, <b>DHZ</b>, and <b>IE</b> <i>anions</i> (see <i>J. Org. Chem</i>. <b>2003</b>, <i>68</i>, 3433), a\nprocess which we herein name sequential proton loss electron transfer (SPLET). The most acidic\ngroup in <b>CU</b> is the central keto−enol moiety. Following <b>CU</b>'s ionization to a monoanion, ET from\nthe [−(O)CCHC(O)−]<sup>-</sup> moiety to <b>dpph</b><b><sup>•</sup></b><sup></sup> yields the neutral [−(O)CCHC(O)−]<sup>•</sup> radical moiety which\nwill be strongly electron withdrawing. Consequently, a phenolic proton is quickly lost into the alcohol\nsolvent. The phenoxide anion so formed undergoes charge migration to produce a neutral phenoxyl\nradical and the keto−enol anion, i.e., the same product as would be formed by a hydrogen atom\ntransfer (HAT) from the phenolic group of the <b>CU</b> monoanion. The SPLET process cannot occur in\na nonionizing solvent. The controversy as to whether the central keto−enol moiety or the peripheral\nphenolic hydroxyl groups of <b>CU</b> are involved in its radical trapping (antioxidant) activity is therefore\nresolved. In ionizing solvents, electron-deficient radicals will react with <b>CU</b> by a rapid SPLET\nprocess but in nonionizing solvents, or in the presence of acid, they will react by a slower HAT\nprocess involving one of the phenolic hydroxyl groups.
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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) | 0.000 | 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) | 0.000 | 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".