Fast Decarboxylation of Aliphatic Amino Acids Induced by 4-Carboxybenzophenone Triplets in Aqueous Solutions. A Nanosecond Laser Flash Photolysis Study
Notice bibliographique
Résumé
Quenching of the 4-carboxybenzophenone triplet ( 3 CB*) by H 2 N−CH 2 −CO 2 −Et and by amino acid anions of the general formula NR 2 −CR 2 −CO 2 -, where R is H or Me, has been investigated in basic aqueous solution. Spectral analysis of the primary products on the microsecond time scale showed that the major quenching process was electron transfer to 3 CB*, producing the CB •- radical anion and the R 2 N •+ −CR 2 −CO 2 - zwitterion aminium radical. However, on a nanosecond time scale, a small amount of (CBH) • was also formed, and this was attributed to a rapid proton transfer from about 10% of the aminium radicals to the CB •- anion radicals within the primary solvent cage. The values of the overall primary quenching rate constants were (8.5 ± 0.9) × 10 8 M -1 s -1 for N, N -dimethylglycine, (1.3 ± 0.1) × 10 8 M -1 s -1 for glycine, (1.5 ± 0.2) × 10 8 M -1 s -1 for alanine, (1.3 ± 0.1) × 10 8 M -1 s -1 for glycine ethyl ester, and (0.3 ± 0.03) × 10 8 M -1 s -1 for α-methylalanine. The introduction of methyl groups into the glycine structure resulted in a pattern of reactivity similar to that observed for amines. Except in the case of glycine ethyl ester, there were strong secondary growths of CB •- . This was attributed to the reduction of CB by the R 2 N− • CR 2 species produced from the decarboxylation of the R 2 N •+ −CR 2 −CO 2 - aminium species. The second-order rate constants for CB reduction by the aminoalkyl radicals are (3.2 ± 0.4) × 10 8 M -1 s -1 for H 2 N− • CH 2, (1.7 ± 0.3) × 10 9 M -1 s -1 for H 2 N− • C(Me)H, and (1.8 ± 0.3) × 10 9 M -1 s -1 for H 2 N− • CMe 2 . The transfer of protons from aminium radicals within the solvent cage gives rise to • NR−CR 2 −CO 2 - aminyl radicals, and these are known to undergo β-elimination of CO 2 •- . There was evidence for the presence of aminyl radicals in the case of α-methylalanine, where a small tertiary growth of CB •-, due to the reduction of CB by CO 2 •-, was observed. The magnitude of this growth matched the yield of (CBH) • from the spectral analysis of the primary products. In further experiments, the R 2 N •+ −CR 2 −CO 2 - zwitterion aminium radicals were deprotonated by bulk OH - when NaOH was added at concentrations in the range of 1−4 M. As expected, this produced a lowering of the CB •- yield from the R 2 N− • CR 2 radicals and an increase from the CO 2 •- species. An analysis of this effect was made assuming a diffusion-controlled rate of 1 × 10 10 M -1 s -1 for the transfer of the proton from R 2 N •+ −CR 2 −CO 2 - to OH - . It indicated that the rate constant for transfer of the proton from R 2 N •+ −CR 2 −CO 2 - to CB •- within the solvent cage was (6.9 ± 1.5) × 10 9 s -1 . The rate constant for the decarboxylation of the aminium species was estimated to be (8.7 ± 0.5) × 10 10 s -1 . The latter rate is at least 1 order of magnitude above those observed for decarboxylations of aliphatic acyloxyl radicals in aqueous media.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».