The pK a 's of Aromatic Sulfinic Acids 1

Tron

et al. 2015

Chemistry A European J

Singlet oxygen ((1)O2) is an important reactive oxygen species in biology that has deleterious effects. Proteins constitute the main target of (1)O2 in cells. Several organisms are able to mount a transcriptional defense against (1)O2. ChrR and MBS are two proteins with Zn(Cys)2(His)2 zinc finger sites that are involved in the regulation of the defense against (1)O2. In this article, we investigate the reactivity of Zn⋅CPF, a Zn(Cys)2(His)2 classical ββα zinc finger, with (1)O2. We show that Zn⋅CPF interacts with (1)O2 mainly by physical quenching using a combination of (1)O2 luminescence quenching and kinetic competition experiments. The chemical reaction, which accounts for 5% of the interaction, leads to oxidation of cysteines but not histidines. Primary photooxidation products, identified by HPLC and mass spectrometry, are sulfinate (75±5%) and disulfides (25±5%). The peptides that have a single cysteine thiolate oxidized into a sulfinate are still able to bind one equivalent Zn(2+) but with a dramatic reduction of the binding constant compared to Zn⋅CPF despite the preservation of the ββα fold, as shown by NMR and CD titrations. Finally, Zn⋅CPF is compared to Zn⋅LTC, a treble clef Zn(Cys)4 zinc finger, to gain further insight into the behavior of zinc fingers toward (1)O2.

Section: Biological Consequences Of Sulfinate Formation In Zinc Fingersmentioning

confidence: 94%

Reactivity of a Zn(Cys)₂(His)₂ Zinc Finger with Singlet Oxygen: Oxidation Directed toward Cysteines but not Histidines

Tron

et al. 2015

Chemistry A European J

“…The pK a values of BSA, PTSA, HCl, H 2 SO 4 , and acetic acid are 3.5, 1.99, À1.75, À1.75, and 4.76, respectively. [22] Although the pK a of LSA has not yet been reported, it is reasonable to conjecture that its pK a may be close to that of BSA, PTSA, and methyl sulfonic acid (pK a = À1.75) because of the acidic sulfonic group. Weak acids are not able to perform electrophilic substitution reactions of creosol with formaldehyde, whereas strong acids may possibly promote side reactions, which thus results in poor yields of the bisphenols.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Lignin‐Derived Bisphenols Catalyzed by Lignosulfonic Acid in Water for Polycarbonate Synthesis

et al. 2015

Lignosulfonic acid, a byproduct of the paper industry, was demonstrated to be an efficient and green catalyst in water for the stoichiometric condensation of creosol with formaldehyde to synthesize lignin-derived renewable bisphenols. The distribution and structures of the products were confirmed by 1 H NMR, 13 C NMR, and FTIR spectroscopy and X-ray analysis; furthermore, a possible reaction mechanism was proposed. A polycarbonate was prepared from the bisphenol product and characterized as a model application, and thermogravimetric analysis (TGA) showed that decomposition occurred in a single stage with the maximum rate of degradation at approximately 420 8C. Differential scanning calorimetry (DSC) analysis showed that the glass transition temperature and melting peak of the polycarbonate were approximately 122 and 314 8C, respectively. The environmentally friendly characteristics of this study are featured by the integrated utilization of a biorenewable feedstock, a green biomacromolecule catalyst, and a green solvent for the preparation of valuable biochemicals and materials.

“…Indeed, 2,6-dibromopyridine offered a small improvement to the reaction (comparing entries 8 and 4) albeit lutidine was deleterious (entry 9), perhaps due to its strong basicity (pKa of its conjugated acid: 6.77). Sodium toluenesulfinate, with a moderate basicity (pKa of its conjugate acid: 1.99 13 ), led to an acceptable reaction rate and 79% yield (entry 10). Subsequent catalyst screening (entries 11-14) revealed that bulky BrettPhos was uniquely effective as the Au(I) ligand, rendering both a high yield and excellent chemoselectivity (i.e., 2a / 3a ).…”

mentioning

confidence: 99%

Experimental and Computational Evidence for Gold Vinylidenes: Generation from Terminal Alkynes via a Bifurcation Pathway and Facile C–H Insertions

et al. 2011

Facile cycloisomerization of (2-ethynylphenyl)alkynes is proposed to be promoted synergistically by two molecules of BrettPhosAuNTf2, affording tricyclic indenes in mostly good yields. A gold vinylidene is most likely generated as one of the reaction intermediates based on both mechanistic studies and theoretical calculations. Different from the well-known Rh, Ru and W counterparts, this novel gold species is highly reactive and undergoes facile intramolecular C(sp3)-H insertions as well as O-H and N-H insertions. The formation step for the gold vinylidene is predicted theoretically to be complex with a bifurcated reaction pathway. The pyridine N-oxide acts as a weak base to facilitate the formation of an alkynylgold intermediate, and the bulky BrettPhos ligand in the gold catalyst likely plays a role in sterically steering the reaction toward the gold vinylidene formation.