Novel keto-enol tautomerism in 1,3,5-trihydroxybenzene systems

Dynamic Modulation of Keto-Enol Tautomerism in Electrolytes for Aqueous Zinc Batteries

The reversibility of zinc (Zn) anode is subject to adverse reactions. Herein we design a dynamic modulation strategy via enol-keto tautomerism to inhibit the side reactions, thus improving the reversibility of the Zn anode. Density functional theory calculations and experimental results demonstrate the keto form of additives can be adsorbed on the Zn anode, inhibiting dendrite growth, while the enol form can serve as a bidentate ligand to participate in the construction of solvation sheath for Zn2+, enhancing the kinetics of Zn2+ transport, simultaneously suppressing water activity and reducing HER and corrosion. Consequently, the Zn anode with optimal electrolyte additive achieves high reversibility, where Zn||Zn symmetric cells operate over 4000 h at 10 mA cm-2/10 mAh cm-2, and Zn||Cu asymmetric cells have a life for 930 h at 10 mA cm-2/10 mAh cm-2. Further, this dynamic modulation enables Zn||V2O5 full cells to work over 5000 cycles with a capacity retention of 83% at 5 A g-1, and the Zn||Br2 pouch cells deliver a high capacity of ∼180 mAh. This study offers an original perspective on the dynamic regulation of electrolytes for Zn anode.

Keto-enol tautomerism of β-diketo molecules in the presence of graphitic materials through π-π stacking

The pseudo aromatic structures of the enol forms of β-diketo molecules are stabilized on the surface of graphitic materials through π-π interaction. This phenomenon has been studied through a relative binding energy calculation using density functional theory. The intermolecular interaction as well as the relative stability of the keto or enol tautomer is also influenced by the functional groups attached to the graphitic materials. The theoretical results are supported by spectroscopic evidence. Our study with three different graphitic materials, with a comparable extent of π-electrons and acid functionalities, reveals that π-π interaction is the main governing factor for the stability of the enol forms. Then comes the role of intermolecular H-bonding between the adsorbate and adsorbent. This can stabilize both the keto and enol tautomers, according to the arrangements of the functional groups and the geometry of the β-diketo molecules. Acid groups on the adsorbent can enhance enolization through H-bonding, but an excess of functional groups may decrease the possibility of π-π interaction by disrupting the π-clouds of the graphitic surface and pushing the adsorbate and adsorbent away from each other beyond a π-π stacking distance. In that situation, H-bonding becomes crucial for determining the relative stability. Our results indicate that graphitic materials with acid functionalities across their edges, and ample π-cloud, are the most suitable catalysts for enolization.

A chemoenzymatic process for preparation of highly purified dehydroepiandrosterone in high space-time yield

Dehydroepiandrosterone (DHEA) is an important neurosteroid hormone to keep human hormonal balance and reproductive health. However, DHEA was always produced with impurities either by chemical or biological method and required high-cost purification before the medical use. To address this issue, a novel chemoenzymatic process was proposed and implemented to produce DHEA. An acetoxylated derivate of 4-androstene-3,17-dione (4-AD) was generated by chemical reaction and converted into DHEA by an enzyme cascade reaction combining a hydrolysis reaction with a reduction reaction. The hydrolysis reaction was catalyzed by a commercial esterase Z03 while the reduction reaction was catalyzed by E. coli cells co-expressing a 3β-hydroxysteroid dehydrogenase SfSDR and a glucose dehydrogenase BtGDH. After the condition optimization, DHEA was synthesized at a 100 mL scale under 100 mM of substrate loading and purified as white powder with the highest space-time yield (4.80 g/L/h) and purity (99 %) in the biosynthesis of DHEA. The successful attempt in this study provides a new approach for green synthesis of highly purified DHEA in the pharmaceutical industry.

Facile synthesis of O-acylhydroxamates via reaction of oxime chlorides with carboxylic acids

A simple and efficient method for the synthesis of O-acylhydroxamate derivatives from oxime chlorides and carboxylic acids was developed. The reaction affords clean and facile access to diverse O-acylhydroxamates in high yields (up to 85%). The chemical structure of a typical product was confirmed using single-crystal X-ray structure analysis.

Photoinduced Irreversible Intramolecular Proton Transfer of Arnebinones B, D, and E: The Case of Photoenolization at the p-Benzoquinone-CH2/CH-π System

Arnebinones B, E, and D (1-3) have been found to be sensitive to light, generating complex and diverse proton transfer products when triggered by light. A unique two-step irreversible intramolecular proton transfer of 1 produced five scalemic mixtures, of which four possessed intriguing dual planar chirality. The unprecedented orientation epimerization equilibrium of the intra-annular double bond was first observed and researched in the homologous meroterpenoids by HPLC monitoring and DFT calculations. A "p-benzoquinone-CH₂/CH-π" moiety in the structure was the common key feature for the occurrence of this type of photoenolization reaction. The product transformation processes and universality of this photoinduced irreversible proton transfer reaction were analyzed together with the cytotoxic activities of arnebinones B, D, and E, and their photoreaction products.