SOME TOPOLOGICAL PROPERTIES OF BENZENOID Sn,Tn-ISOMERS WITH n-RADICAL CONNECTION

We consider a series of benzenoid isomers obtained by attaching fragments to ann-radical. Some of their topological properties, such as the number of Kekulé patterns and the maximum number of aromatic π-sextets are established. Research of this author is supported in part by the RDG grant of the Pennsylvania State University.     

Ring-opening Polymerization of Enantiopure Bicyclic Ether-ester Monomers toward Closed-loop Recyclable and Crystalline Stereoregular Polyesters via Chemical Upcycling of Bioplastic

Although great successes have been achieved, the preparation of closed-loop recyclable polyesters with high working temperatures still remains as a big challenge. Herein, we present the syntheses of a series of enantiopure bicyclic ether-ester monomers by upcycling of poly(3-hydroxybutyrate) bioplastic. The “living”/controlled ring-opening polymerizations of these enantiopure monomers to produce stereoregular polyesters with controlled molecular weights and well-defined chain ends were achieved. The effects of stereoconfiguration and substituent on polymerization kinetics and thermodynamics as well as the thermal properties of resultant polyesters were investigated. Of note, the stereoregular polyesters are semi-crystalline materials with melting temperatures up to 176 °C, even higher than the commodity polyolefin plastics. These polyesters can be depolymerized back to recover pristine monomers, thus successfully establishing a closed-loop life cycle.     

A pre-column derivatization high-performance liquid chromatography method for simultaneous determination of short-chain and medium-chain fatty acids in a fecal sample

Short-chain and medium-chain fatty acids have plentiful biological functions, which play a crucial role in the diagnosis and therapy of many diseases. Herein, a new method for simultaneous quantifying 17 short-chain and medium-chain fatty acids with high-performance liquid chromatography coupled with an ultraviolet detector was developed and the pre-column derivatization by indole-3-acetic acid hydrazide was performed to improve the separation and detection. The conditions of the derivatization reaction were systematically investigated. Subsequently, the method was validated and the results showed a satisfactory linearity (linear regression coefficients > 0.9969), the limit of detection (4.0×10⁻³–1.9×10⁻² μmol/L), precision (0.9%–7.3% for intra-day and 2.0%–9.8% for inter-day), recovery (90.0%–109.1% with relative standard deviation <7.7%) and stability (0.1%–3.3% for standard solution and 0.2%–3.9% for fecal sample). Finally, the established method was successfully applied to quantify short-chain and medium-chain fatty acids in the feces of healthy control and diabetic rats. Eleven kinds of short-chain and medium-chain fatty acids were detected and six of them showed a significant difference between the control group and the model group.     

Large-scale preparation of five polar polyphenols including three isomers from Phyllanthus emblica Linn. by preparative high-speed counter-current chromatography

The separation of polar compounds is challenging work due to poor retention and insufficient selectivity. In the present study, an efficient strategy for large-scale preparation of five polar polyphenols including three isomers from Phyllanthus emblica Linn has been established by preparative high-speed counter-current chromatography. Macroporous resin column chromatography was used for the enrichment of the polar polyphenols. However, sugar and other ultra-polar impurities were co-washed out with the targets. Liquid-liquid extraction with ethyl acetate/water (1/1, v/v) solvent system was developed to remove the ultra-polar impurities with a clearance rate of 95%. Finally, the targets were introduced to preparative high-speed counter-current chromatography for separation using ethyl acetate/n-butanol/acetic acid/water (2/7/1/10, v/v/v/v) solvent system. As a result, 191 mg of Mucic acid 1,4-lactone 5-O-gallate, 370 mg of β-Glucogallin, 301 mg of Gallic acid, 195 mg of Mucic acid 1,4-lactone 3-O-gallate and 176 mg of Mucic acid 1,4-lactone 2-O-gallate with purity higher than 98% were obtained from 1.5 g of sample. Mucic acid 1,4-lactone 3-O-gallate, Mucic acid 1,4-lactone 3-O-gallate, and Mucic acid 1,4-lactone 2-O-gallate are isomers. The results showed that high-speed counter-current chromatography could be well developed for the separation of polar compounds from natural products.     

单原子配位结构及与载体相互作用的调控用于二氧化碳电催化还原

The combustion of fossil fuels increases atmospheric carbon dioxide (CO₂) concentrations, leading to adverse impacts on the planetary radiation balance and, consequently, on the climate. Fossil fuel utilization has contributed to a marked rise in global temperatures, now at least 1.2 ℃ above 'pre-industrial' levels. To meet the 2015 Paris Agreement target of 1.5 ℃ above pre-industrial levels, considerable efforts are required to efficiently capture and utilize CO₂. Among the different strategies developed for converting CO₂, electrochemical CO₂ reduction (ECR) to valuable chemicals using renewable energy is expected to revolutionize the manufacture of sustainable "green" chemicals, thereby achieving a closed anthropogenic carbon cycle. However, CO₂ is a thermodynamically stable and kinetically inert molecule that requires high electrical energy to bend the linear O＝C＝O bond by attacking the C atom. To facilitate the ECR with good energy efficiency, it is essential to lower the reaction overpotential as well as maintain a high current density and desirable product selectivity; therefore, the design and development of advanced electrocatalysts are crucial. A plethora of heterogeneous and homogeneous materials has been explored in the ECR. Among these materials, single-atom catalysts (SACs) have been the focus of most extensive research in the context of ECR. A SAC with isolated metal atoms dispersed on a supporting host exhibits a unique electronic structure, well-defined coordination environment, and an extremely high atom utilization maximum; thus, SACs have emerged as promising materials over the last two decades. Single-atom catalysis has covered the periodic table from d-block and ds-block metals to p-block metals. The types of support materials for SACs, ranging from metal oxides to tailored carbon materials, have also expanded. The adsorption strength and catalytic activity of SACs can be effectively tuned by modulating the central metal and local coordination structure of the SACs. In this article, we discuss the progress made to date in the field of single-atom catalysis for promoting ECR. We provide a comprehensive review of state-of-the-art SACs for the ECR in terms of product distribution, selectivity, partial current density, and performance stability. Special attention is paid to the modification of SACs to improve the ECR efficiency. This includes tailoring the coordination of the heteroatom, constructing bimetallic sites, engineering the morphologies and surface defects of supports, and regulating surface functional groups. The correlation of the coordination structure of SACs and metal-support interactions with ECR performance is analyzed. Finally, development opportunities and challenges for the application of SACs in the ECR, especially to form multi-carbon products, are presented.     

Mechanistic studies in the synthesis of a series of thieno-expanded xanthosine and guanosine nucleosides

During the synthetic pursuit of guanosine (tri-G) and xanthosine (tri-X) tricyclic nucleosides analogues, an interesting side product was discovered. In an effort to uncover the mechanistic factors leading to this result, a series of reaction conditions were investigated. It was found that by varying the conditions, the appearance of the side product could be controlled. In addition, the yield of the desired products could be manipulated to afford either a 50:50 mix of both tri-G and tri-X, or a majority of one or the other. To demonstrate the broad utility of the method, it was also adapted to the synthesis of guanosine and xanthosine from 5-amino-1-β-d-ribofuranosyl-4-imidazolecarboxyamide (AICAR). The mechanistic details surrounding the synthetic efforts are reported herein.     

Amorphous Porous Organic Polymers Based on Schiff‐Base Chemistry for Highly Efficient Iodine Capture

Porous organic polymers (POPs) have been considered as prominent adsorbents for volatile iodine. So far, both crystalline and amorphous POPs have accomplished excellent iodine capture capability. Considering the difficulty and challenges in preparing perfect crystalline POPs, more explorations into developing versatile amorphous POPs are needed. Herein, amorphous POPs based on the Schiff‐base reaction were designed and synthesized for volatile iodine removal. Four amorphous POPs products named as NDB‐H , NDB‐S , ADB‐HS , and ADB‐S obtained under different solvothermal conditions were investigated in terms of their morphologies, porosity, and their iodine enrichment performance in detail. It is noteworthy that excellent efficiency for removing iodine vapor was acquired for NDB‐S (≈425 wt %), ADB‐HS (≈345 wt %), and ADB‐S (≈342 wt %). Remarkably, NDB‐H exhibited an iodine capture capacity up to ≈443 wt %. Excellent reusability was obtained as well. Amorphous NDB‐H has accomplished an extremely high iodine capture performance, illustrating the great chance to exploit versatile amorphous POPs for iodine enrichment and removal based on Schiff‐base chemistry.     

Regioselective biomimetic oxidation of halogenated resveratrol for the synthesis of (±)-ε-viniferin and its analogues

FeCl₃·6H₂O-promoted biomimetic oxidations of 3,5-dihalogeno-resveratrol in different acetone systems produced several coupling intermediates bearing distinct dimeric skeletons with moderate yields. The subsequent deprotection reactions of brominated coupling products achieved the efficient synthesis of natural products (±)-ε-viniferin, (±)-ampelosin B, and (±)-gnetins F, as well as an unnatural oligostilbene. The coupling mechanisms for the formation of different dimeric structures were also proposed.     

Toroid Formation through a Supramolecular “Cyclization Reaction” of Rodlike Micelles

Constructing polymeric toroids with a uniform, tunable size is challenging. Reported herein is the formation of uniform toroids from poly(γ-benzyl-l -glutamate)-graft-poly(ethylene glycol) (PBLG-g-PEG) graft copolymers by a two-step self-assembly process. In the first step, uniform rodlike micelles are prepared by dialyzing the polymer dissolved in tetrahydrofuran (THF)/N,N′-dimethylformamide (DMF) against water. With the addition of THF in the second step, the rodlike micelles curve and then close end-to-end to form uniform toroids, which resemble a cyclization reaction.     

Stepwise Photocatalytic Dissociation of Methanol and Water on TiO(2)(110)

We have investigated the photocatalysis of partially deuterated methanol (CD(3)OH) and H(2)O on TiO(2)(110) at 400 nm using a newly developed photocatalysis apparatus in combination with theoretical calculations. Photocatalyzed products, CD(2)O on Ti(5c) sites, and H and D atoms on bridge-bonded oxygen (BBO) sites from CD(3)OH have been clearly detected, while no evidence of H(2)O photocatalysis was found. The experimental results show that dissociation of CD(3)OH on TiO(2)(110) occurs in a stepwise manner in which the O-H dissociation proceeds first and is then followed by C-D dissociation. Theoretical calculations indicate that the high reverse barrier to C-D recombination and the facile desorption of CD(2)O make photocatalytic methanol dissociation on TiO(2)(110) proceed efficiently. Theoretical results also reveal that the reverse reactions, i.e, O-H recombination after H(2)O photocatalytic dissociation on TiO(2)(110), may occur easily, thus inhibiting efficient photocatalytic water splitting.