The unexpected formation of [M − H]<sup>+</sup> species during MALDI and dopant‐free APPI MS analysis of novel antineoplastic curcumin analogues
Bibliographic record
Abstract
Unusual ionization behavior was observed with novel antineoplastic curcumin analogues during the positive ion mode of matrix-assisted laser desorption ionization (MALDI) and dopant-free atmospheric pressure photoionization (APPI). The tested compounds produced an unusual significant peak designated as [M - H](+) ion along with the expected [M + H](+) species. In contrast, electrospray ionization, atmospheric pressure chemical ionization and the dopant-mediated APPI (dopant-APPI) showed only the expected [M + H](+) peak. The [M - H](+) ion was detected with all evaluated curcumin analogues including phosphoramidates, secondary amines, amides and mixed amines/amides. Our experiments revealed that photon energy triggers the ionization of the curcumin analogues even in the absence of any ionization enhancer such as matrix, solvent or dopant. The possible mechanisms for the formation of both [M - H](+) and [M + H](+) ions are discussed in this paper. In particular, three proposed mechanisms for the formation of [M - H](+) were evaluated. The first mechanism involves the loss of H2 from the protonated [M + H](+) species. The other two mechanisms include hydrogen transfer from the analyte radical cation or hydride abstraction from the neutral analyte molecule.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".