Indirectly Detected DNP-Enhanced 17O NMR Spectroscopy: Observation of Non-Protonated Near-Surface Oxygen at Naturally Abundant Silica and Silica-Alumina

Recent studies have shown that dynamic nuclear polarization (DNP) can be used to detect ¹⁷O solid-state NMR spectra of naturally abundant samples within a reasonable experimental time. Observations using indirect DNP, which relies on ¹H mediation in transferring electron hyperpolarization to ¹⁷O, are currently limited mostly to hydroxyls. Direct DNP schemes can hyperpolarize non-protonated oxygen near the radicals; however, they generally offer much lower signal enhancements. In this study, we demonstrate the detection of signals from non-protonated ¹⁷O in materials containing silicon. The sensitivity boost that made the experiment possible originates from three sources: indirect DNP excitation of ²⁹Si via protons, indirect detection of ¹⁷O through ²⁹Si nuclei using two-dimensional ²⁹Si{¹⁷O} D-HMQC, and Carr-Purcell-Meiboom-Gill refocusing of ²⁹Si magnetization during acquisition. This ²⁹Si-detected scheme enabled, for the first time, 2D ¹⁷O−²⁹Si heteronuclear correlation spectroscopy in mesoporous silica and silica-alumina surfaces at natural abundance. In contrast to the silanols showing motion-averaged ¹⁷O signals, the framework oxygens exhibit unperturbed powder patterns as unambiguous fingerprints of surface sites. Along with hydroxyl oxygens, detection of these moieties will help in gaining more atomistic-scale insights into surface chemistry.     

Antimicrobial Activity of Pyrazinamide Coordination Frameworks Synthesized by Mechanochemistry

The urge for the development of a more efficient antibiotic crystalline forms led us to the disclosure of new antibiotic coordination frameworks of pyrazinamide, a well-known drug used for the treatment of tuberculosis, with some of the novel compounds unravelling improved antimycobacterial activity. Mechanochemistry was the preferred synthetic technique to yield novel compounds, allowing the reproduction of a 1D zinc framework, the synthesis of a novel hydrogen bonding manganese framework, and three new compounds with silver. The structural characterization of the novel forms is presented along with stability studies. The increased antimicrobial activity of the new silver-based frameworks against Escherichia coli, Staphylococcus aureus, and Mycobacterium smegmatis is particularly relevant.     

Prebiotic Route to Thymine from Formamide—A Combined Experimental–Theoretical Study

Synthesis of RNA nucleobases from formamide is one of the recurring topics of prebiotic chemistry research. Earlier reports suggest that thymine, the substitute for uracil in DNA, may also be synthesized from formamide in the presence of catalysts enabling conversion of formamide to formaldehyde. In the current paper, we show that to a lesser extent conversion of uracil to thymine may occur even in the absence of catalysts. This is enabled by the presence of formic acid in the reaction mixture that forms as the hydrolysis product of formamide. Under the reaction conditions of our study, the disproportionation of formic acid may produce formaldehyde that hydroxymethylates uracil in the first step of the conversion process. The experiments are supplemented by quantum chemical modeling of the reaction pathway, supporting the plausibility of the mechanism suggested by Saladino and coworkers.     

In situ preparation of hetero-polymers/clay nanocomposites by CUAAC click chemistry

A series of polymer/clay nanocomposites containing mechanistically two different polymers, poly(ethylene glycol) (PEG) and poly(epsilon caprolactone) (PCL), were prepared by simultaneous copper(I)-catalyzed alkyne-azide cycloaddition click reactions. Both clickable polymers, PEG-Alkyne and PCL-Alkyne, were simultaneously clicked on to azide-functional montmorillonite (MMT-N₃) nanoclay to get corresponding PEG-PCL/MMT nanocomposites. The chemical structures of the resulting nanocomposites were verified by following azide and silicone-oxygen bands using FT-IR and characteristic bands of PEG and PCL segments using ¹H-NMR spectroscopy. The combined XRD and TEM analysis confirmed that all PEG-PCL/MMT nanocomposites had partially exfoliated/intercalated morphologies. In addition, the increase of MMT-N₃ loading not only improved the onset and maximum degradation temperatures of the nanocomposites but also their char yields. Furthermore, the incorporation of MMT-N₃ in the polymer matrix did not significantly influence the crystallization behavior of both PEG and PCL segments.     

Novel nonperipheral octa-3-hydroxypropylthio substituted metallo-phthalocyanines: synthesis,characterization, and investigation of their electrochemical,photochemical and computational properties

The current study describes the synthesis, electrochemical, computational, and photochemical properties of octa (3-hydroxypropylthio) substituted cobalt (II) ( 4 ), copper (II) ( 5 ), nickel (II) ( 6 ) and zinc(II) ( 7 ) phthalocyanine derivatives. These novel compounds were characterized by elemental analysis,¹H,¹³C NMR, FT-IR, UV-Vis, and MS. The redox behaviors of these metallo-phthalocyanines were investigated by the cyclic voltammetric method. The optimized molecular structure and gauge-including atomic orbital (GIAO)¹H and¹³C NMR chemical shift values of these phthalocyanines in the ground state had been calculated by using B3LYP/6–31G(d,p) basis set. The outcomes of the optimized molecular structure were given and compared with the experimental NMR values. The photochemical properties including photodegradation and singlet oxygen generation of zinc(II) phthalocyanine were studied in DMSO solution for the determination of its photosensitizer behaviors.     

Solvent-free 1,6-conjugate arylation of para-quinone methides: A greener approach to unsymmetrical triarylmethanes

A highly efficient arylation of para-quinone methides (p-QMs) with N,N-dimethylaniline under solvent free condition has been developed, which proceeded via a para-toluenesulfonic acid (TsOH)-promoted 1,6-conjugated addition pathway. This methodology provided a green and sustainable methodology to construct various novel unsymmetrical triarylmethanes (TAMs) with the advantages of good functional group tolerance, scalability, and regioselectivity.     

Recent progress in the synthesis of sulfonyl fluorides for SuFEx click chemistry

Since the sulfur(VI) fluoride exchange reaction (SuFEx) was introduced by Sharpless and co-workers in 2014, this new-generation click chemistry has emerged as an efficient and reliable tool for creating modular intermolecular connections. Sulfonyl fluorides, one of the most important sulfur(VI) fluoride species, have attracted enormous attention in diverse fields, ranging from organic synthesis and material science, to chemical biology and drug discovery. This review aims to introduce seminal and recent progresses on the synthetic methods of sulfonyl fluorides, which include aromatic, aliphatic, alkenyl, and alkynyl sulfonyl fluorides. While not meant to be exhaustive, the purpose is to give a timely overview and insight in this field, and stimulate the development of more efficient synthetic methods of sulfonyl fluorides.     

绿色氧化法制备联苯类化合物的研究性实验设计与实践*

以苯甲醛和丙酮为原料,利用Robinson增环反应先制备3-甲基-5-苯基环己-2-烯-1-酮,再引导学生设计并研究了水相绿色氧化3-甲基-5-苯基环己-2-烯-1-酮合成联苯类化合物3-乙氧基-5-甲基-1,1′-联苯的影响因素,利用核磁共振确定了产物结构。该研究性实验教学以绿色化学为中心,结合了2步连续反应,产物易提纯且产率高,并开展了开放式大型分析仪器教学和测试,对学生有机合成实验能力和科学研究能力的培养具有很好的教学效果。     

化学系统性思维的背景、应用与特征*

当今地球与社会系统所面临的可持续发展、气候变化、环境退化等全球性挑战问题,用还原主义方法不足以应对,需要化学教育等领域的工作者采用系统性思维方法。梳理了国外学者在应用化学系统性思维理解化学学科系统复杂性、化学学习系统层级性、化学教育系统整合性的研究进展。概述了化学系统性思维具有重视跨学科关联、整体综合思考目标系统问题、强调可持续发展的全球观念等特征。建议加强化学教育内外部系统的协作,注重各学段化学课程与教学的跨学科、系统性,重视学生解决化学问题的认识方式差异。     

雨课堂与腾讯课堂联用的“有机化学”线上教学设计与实践*

基于智慧教学工具“雨课堂”为主和“腾讯课堂”为辅的双平台联用组合,将“雨课堂”优秀的教学互动和全周期记录学习活动表现的功能与“腾讯课堂”网络直播高峰期画面卡顿少、师生可以语音互动的优点结合起来,充分发挥“以学生为中心”的教学理念,探讨了有机化学课程的线上教学设计,并在教学班级中进行了广泛实践。实践证明,“雨课堂”直播为主和“腾讯课堂”为辅的双平台联用教学模式能保证教学质量、激发学生的学习兴趣和提高学生的学习效果。