Exact solutions of an asymmetric double well potential

Journal of Mathematical Chemistry - The analytical solutions of an asymmetric double well potential $$V(x)=a\, x^2-b\, x^3+c\, x^4$$ are found to be a triconfluent Heun function $$H_{T}(\alpha ,...     

The invalidity of intermolecular proton transfer triggered twisted intramolecular charge transfer in excited state for 2-(4′-diethylamino-2′-hydroxyphenyl)-1H-imidazo-[4,5-b]pyridine

The excited-state dynamics of the excited-state proton transfer and intramolecular twisted charge transfer (TICT) reactions of a molecular photoswitch 2-(4′-diethylamino-2′-hydroxyphenyl)-1H-imidazo-[4,5-b]pyridine (DHP) in aprotic and alcoholic solvents have been theoretically investigated by using time-dependent density functional theory. The excited-state intramolecular proton transfer (ESIPT) reaction of DHP proceeding upon excitation in all the solvents has been confirmed, and the dual emission has been assigned to the enol and keto forms of DHP. However, for methanol and ethanol solvents within strong hydrogen-bonded capacity, the intermolecular hydrogen bonds between DHP and methanol/ethanol would promote an excited-state double proton transfer (ESDPT) along the hydrogen-bonded bridge. Importantly, the previous proposed ESDPT-triggered TICT mechanism of DHP in methanol and ethanol was not supported by our calculations. The twist motion would increase the total energy of the system for both the products of ESIPT and ESDPT. According to the calculations of the transition states, the ESDPT reaction occurs much easier in keto form generated by ESIPT. Therefore, a sequential ESIPT and ESDPT mechanism of DHP in methanol and ethanol has been reasonably proposed.     

Organocatalytic Enantioselective Pictet–Spengler Reaction of α-Ketoesters: Development and Application to the Total Synthesis of (+)-Alstratine A

We report herein an asymmetric Pictet–Spengler reaction of α-ketoesters. In the presence of a catalytic amount of simple alanine-derived squaramide and p-nitrobenzoic acid, reaction of tryptamines with methyl 2-oxoalkanoates afforded the corresponding 1-alkyl-1-methoxycarbonyl tetrahydro-β-carbolines (THBCs) in high yields and ee values. A primary kinetic isotope effect (KIE=4.5) using C2-deteurium-labelled tryptamine indicates that rearomatization through deprotonation of the pentahydro-β-carbolinium ion could be the rate- and enantioselectivity-determining step. A concise enantioselective total synthesis of (+)-alstratine A, a hexacyclic cagelike monoterpene indole alkaloid, featuring this reaction as a key step, was subsequently accomplished. Remeasurement of the [a]_D value of the natural product indicates that natural alstratine A is dextrorotatory rather than levorotatory as it was initially reported in the isolation paper.     

捕捉环加成反应中的有机亚铜中间体构筑氮杂环化合物研究进展

铜(I)盐催化的环加成反应,如叠氮-炔[3+2]环加成(Cu AAC)、不饱和化合物与异氰基化合物的[3+2]环加成、硝酮-炔的环加成(Kinugasa反应)是构建多类氮杂环的高效合成方法,被广泛应用于有机合成的各个领域.近年来,针对几类环加成反应中产生的有机亚铜中间体的多样性转化吸引了国内外很多课题组的注意,基于对这些环加成反应中有机亚铜中间体的捕捉,多类串联及多组分反应得以发展,从而成功实现了一系列多取代杂环或稠环结构的高效构建.本综述总结了这一领域的研究进展,按照所经历的有机亚铜中间体的类型进行分类,包括:(1)Cu AAC反应中产生的三氮唑亚铜中间体;(2)炔烃与异氰化合物[3+2]环加成反应中产生的2H-吡咯基亚铜中间体;(3) Kinugasa反应中产生的烯醇亚铜中间体.期望此综述能够有助于研究者了解有机亚铜中间体捕捉策略的发展、应用现状及不足之处,进一步推动铜催化转化的发展.     

Reversible Switching CuII/CuI Single Sites Catalyze High-rate and Selective CO2 Photoreduction

Herein, we first design a model of reversible redox-switching metal–organic framework single-unit-cell sheets, where the abundant metal single sites benefit for highly selective CO₂ reduction, while the reversible redox-switching metal sites can effectively activate CO₂ molecules. Taking the synthetic Cu-MOF single-unit-cell sheets as an example, synchrotron-radiation quasi in situ X-ray photoelectron spectra unravel the reversible switching Cu^II/Cu^I single sites initially accept photoexcited electrons and then donate them to CO₂ molecules, which favors the rate-liming activation into CO₂^δ−, verified by in situ FTIR spectra and Gibbs free energy calculations. As an outcome, Cu-MOF single-unit-cell sheets achieve near 100 % selectivity for CO₂ photoreduction to CO with a high rate of 860 μmol g⁻¹ h⁻¹ without any sacrifice reagent or photosensitizer, where both the activity and selectivity outperform previously reported photocatalysts evaluated under similar conditions.     

Pd0-Catalyzed Asymmetric Carbonitratation Reaction Featuring an H-Bonding-Driven Alkyl−PdII−ONO2 Reductive Elimination

Reductive elimination of alkyl−Pd^II−O is a synthetically useful yet underdeveloped elementary reaction. Here we report that the combination of an H-bonding donor [PyH][BF₄] and AgNO₃ additive under toluene/H₂O biphasic system can enable such elementary step to form alkyl nitrate. This results in the Pd⁰-catalyzed asymmetric carbonitratations of (Z)-1-iodo-1,6-dienes with (R)-BINAP as the chiral ligand, affording alkyl nitrates up to 96 % ee. Mechanistic studies disclose that the reaction consists of oxidative addition of Pd⁰ catalyst to vinyl iodide, anion ligand exchange between I⁻ and NO₃⁻, alkene insertion and S_N2-type alkyl−Pd^II−ONO₂ reductive elimination. Evidences suggest that H-bonding interaction of PyH⋅⋅⋅ONO₂ can facilitate dissociation of O₂NO⁻ ligand from the alkyl−Pd^II−ONO₂ species, thus enabling the challenging alkyl−Pd^II−ONO₂ reductive elimination to be feasible.     

Durable Electrocatalytic Reduction of Nitrate to Ammonia over Defective Pseudobrookite Fe2TiO5 Nanofibers with Abundant Oxygen Vacancies

We propose the pseudobrookite Fe₂TiO₅ nanofiber with abundant oxygen vacancies as a new electrocatalyst to ambiently reduce nitrate to ammonia. Such catalyst achieves a large NH₃ yield of 0.73 mmol h⁻¹ mg⁻¹_cat. and a high Faradaic Efficiency (FE) of 87.6 % in phosphate buffer saline solution with 0.1 M NaNO₃, which is lifted to 1.36 mmol h⁻¹ mg⁻¹_cat. and 96.06 % at −0.9 V vs. RHE for nitrite conversion to ammonia in 0.1 M NaNO₂. It also shows excellent electrochemical durability and structural stability. Theoretical calculation reveals the enhanced conductivity of this catalyst and an extremely low free energy of −0.28 eV for nitrate adsorption at the presence of vacant oxygen.     

Modulating Triplet Excited States of Organic Semiconductors via Tuning Molecular Conformation for Dual-ratiometric Thermometers

The dual-ratiometric thermometry is one of highly accurate methods for microscopic thermal measurement in biological systems. Herein, a series of chromone derivatives with noncovalently intramolecular interactions (NIIs) were designed and synthesized for ratiometric thermometers. The triplet states of these organic compounds were systematically tuned upon regulating the conformation with NIIs to yield efficient room temperature phosphorescence and large wavelength difference between fluorescence and phosphorescence simultaneously. As a result, an unprecedent organic 3D dual-ratiometric thermometer was established based on the intensity ratio and lifetime ratio of fluorescence/phosphorescence vs temperature, which was used for in vitro and in vivo bio-thermometry with high accuracy. This work provides a novel method to achieve organic dual ratiometric thermometers via tuning the triplet excited states.     

Chemo-, Stereo- and Regioselective Fluoroallylation/Annulation of Hydrazones with gem-Difluorocyclopropanes via Tunable Palladium/NHC Catalysis

Defluorinative manipulation of polyfluorinated molecules has shown great promise due to its granting of synthetic versatility to inert C−F bonds. The development of chemo-, stereo- and regioselective strategies to realize highly efficient formation of either the linear/branched or E/Z products from gem-difluorocyclopropanes (gem-F₂CPs) is a challenging task. Herein, we have realized palladium/NHC-catalyzed fluoroallylation/annulation of hydrazones with gem-F₂CPs that incorporate the hydrazone N₂ moiety into the products. The thermodynamically unstable fluorinated E-allylation products with aryl ketone hydrazones were obtained for the first time, while the di-alkyl ketone hydrazones yielded the monofluorinated products with branched selectivity under similar reaction conditions. With aldehyde hydrazones, two kinds of pyrazoles were obtained via a defluorinative allylation/annulation cascade, in which different carbon atoms of gem-F₂CPs could be incorporated into the pyrazole rings regiospecifically. DFT calculations revealed that the divergent selectivity was kinetically controlled and the final C−C bond formation proceeded through a 7-membered TS.     

Scalable Green Synthesis of Robust Ultra-Microporous Hofmann Clathrate Material with Record C3H6 Storage Density for Efficient C3H6/C3H8 Separation

Developing porous materials for C₃H₆/C₃H₈ separation faces the challenge of merging excellent separation performance with high stability and easy scalability of synthesis. Herein, we report a robust Hofmann clathrate material (ZJU-75a), featuring high-density strong binding sites to achieve all the above requirements. ZJU-75a adsorbs large amount of C₃H₆ with a record high storage density of 0.818 g mL⁻¹, and concurrently shows high C₃H₆/C₃H₈ selectivity (54.2) at 296 K and 1 bar. Single-crystal structure analysis unveil that the high-density binding sites in ZJU-75a not only provide much stronger interactions with C₃H₆ but also enable the dense packing of C₃H₆. Breakthrough experiments on gas mixtures afford both high separation factor of 14.7 and large C₃H₆ uptake (2.79 mmol g⁻¹). This material is highly stable and can be easily produced at kilogram-scale using a green synthesis method, making it as a benchmark material to address major challenges for industrial C₃H₆/C₃H₈ separation.