The Stability of Aryl Carbanions Derived from Pyridine<i>N</i>-Oxide: The Role of Resonance in Stabilizing Aryl Anions

Koehn, Scott K.; Tran, Ngoc L.; Gronert, Scott; Wu, Weiming

doi:10.1021/ja906473v

Cited by 11 publications

(7 citation statements)

References 23 publications

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“…1 outlines the formation of deprotonated uracil-5-carboxylic acid from the solution containing uracil-5-carboxylic acid by ESI. Our previous work 35 and that of others 49,50 often involve molecules whose most acidic site is on the carboxylic acid group itself. Here, the N 1 site is the most acidic, yielding parent anions that are predominantly deprotonated there.…”

Section: Experimental Methodsmentioning

confidence: 94%

Anionic derivatives of uracil: fragmentation and reactivity

Cole

Wang

Snow

et al. 2014

Phys. Chem. Chem. Phys.

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Uracil is an essential biomolecule for terrestrial life, yet its prebiotic formation mechanisms have proven elusive for decades. Meteorites have been shown to contain uracil and the interstellar abundance of aromatic species and nitrogen-containing molecules is well established, providing support for uracil's presence in the interstellar medium (ISM). The ion chemistry of uracil may provide clues to its prebiotic synthesis and role in the origin of life. The fragmentation of biomolecules provides valuable insights into their formation. Previous research focused primarily on the fragmentation and reactivity of cations derived from uracil. In this study, we explore deprotonated uracil-5-carboxylic acid and its anionic fragments to elucidate novel reagents of uracil formation and to characterize the reactivity of uracil's anionic derivatives. The structures of these fragments are identified through theoretical calculations, further fragmentation, experimental acidity bracketing, and reactivity with several detected and potential interstellar species (SO2, OCS, CS2, NO, N2O, CO, NH3, O2, and C2H4). Fragmentation is achieved through collision induced dissociation (CID) in a commercial ion trap mass spectrometer, and all reaction rate constants are measured using a modification of this instrument. Experimental data are supported by theoretical calculations at the B3LYP/6-311++G(d,p) level of theory. Lastly, the astrochemical implications of the observed fragmentation and reaction processes are discussed.

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Section: Experimental Methodsmentioning

confidence: 94%

Anionic derivatives of uracil: fragmentation and reactivity

Cole

Wang

Snow

et al. 2014

Phys. Chem. Chem. Phys.

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“…The identical stabilities of carbanion 9 , which is derived from the much more polar 4-pyridone, and carbanion 8 suggests that the contribution from the carbene resonance structure 9a is quite limited. 17 Overall, the carbanions are unusually stable for sp 2 hybridized carbanions. For comparison, the α-carbanion derived from pyridine has a proton affinity of 391 kcal/mol.…”

Section: Resultsmentioning

confidence: 98%

Stabilities of uracil and pyridone-based carbanions: a systematic study in the gas phase and solution and implications for the mechanism of orotidine-5′-monophosphate decarboxylase

et al. 2013

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The stabilities of the C6-centered carbanions derived from 1,3-dimethyluracil, N-methyl-2-pyridone, and N-methyl-4-pyridone were systematically investigated in the gas phase and in DMSO and water solutions. The stabilities of the carbanions in the gas phase and DMSO were directly measured through their reactions with carbon acids with known proton affinity or pKa values. The stabilities of the carbanions in DMSO were also probed through their kinetic isotope effects of protonation over deuteriation using acids with different acidity. The stabilities of the carbanions in water were determined through the rates of hydrogen-deuterium exchange reactions of the corresponding conjugate acids. The carbanions derived from the two pyridones were found to have the same stability, whereas the carbanion derived from 1,3-dimethyluracil was more stable. The order of the stability of the carbanions showed no correlation with the decarboxylation rates of their corresponding carboxylic acids. The implications of the results for the mechanism of orotidine-5′-monophosphate decarboxylase (ODCase) are discussed.

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“…Zhang et al acid condition, 36,37 which led to expansion of the hydrophobic core and accelerated release of Nile Red. 38 Moreover, when being treated with 10 mM GSH, fluorescence intensity of CCM-NR significantly decreased and ∼80% of Nile Red was released after cultured for 24 hours (Figure 5E and F).…”

mentioning

confidence: 99%

Folic acid-targeted disulfide-based cross-linking micelle for enhanced drug encapsulation stability and site-specific drug delivery against tumors

Zhou¹,

Yang²,

Wang³

et al. 2016

IJN

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Although the shortcomings of small molecular antitumor drugs were efficiently improved by being entrapped into nanosized vehicles, premature drug release and insufficient tumor targeting demand innovative approaches that boost the stability and tumor responsiveness of drug-loaded nanocarriers. Here, we show the use of the core cross-linking method to generate a micelle with enhanced drug encapsulation ability and sensitivity of drug release in tumor. This kind of micelle could increase curcumin (Cur) delivery to HeLa cells in vitro and improve tumor accumulation in vivo. We designed and synthesized the core cross-linked micelle (CCM) with polyethylene glycol and folic acid-polyethylene glycol as the hydrophilic units, pyridyldisulfide as the cross-linkable and hydrophobic unit, and disulfide bond as the cross-linker. CCM showed spherical shape with a diameter of 91.2 nm by the characterization of dynamic light scattering and transmission electron microscope. Attributed to the core cross-linking, drug-loaded CCM displayed higher Nile Red or Cur-encapsulated stability and better sensitivity to glutathione than noncross-linked micelle (NCM). Cellular uptake and in vitro antitumor studies proved the enhanced endocytosis and better cytotoxicity of CCM-Cur against HeLa cells, which had a high level of glutathione. Meanwhile, the folate receptor-mediated drug delivery (FA-CCM-Cur) further enhanced the endocytosis and cytotoxicity. Ex vivo imaging studies showed that CCM-Cur and FA-CCM-Cur possessed higher tumor accumulation until 24 hours after injection. Concretely, FA-CCM-Cur exhibited the highest tumor accumulation with 1.7-fold of noncross-linked micelle Cur and 2.8-fold of free Cur. By combining cross-linking of the core with active tumor targeting of FA, we demonstrated a new and effective way to design nanocarriers for enhanced drug encapsulation, smart tumor responsiveness, and elevated tumor accumulation.

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The Stability of Aryl Carbanions Derived from PyridineN-Oxide: The Role of Resonance in Stabilizing Aryl Anions

Cited by 11 publications

References 23 publications

Anionic derivatives of uracil: fragmentation and reactivity

Anionic derivatives of uracil: fragmentation and reactivity

Stabilities of uracil and pyridone-based carbanions: a systematic study in the gas phase and solution and implications for the mechanism of orotidine-5′-monophosphate decarboxylase

Folic acid-targeted disulfide-based cross-linking micelle for enhanced drug encapsulation stability and site-specific drug delivery against tumors

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