Addition of some α-halo ethers to unsaturated compounds

Summary The addition was carried out of 2-acetoxyethyl chloromethyl ether and of 2-chloroethyl chloromethyl ether to isobutene, to allyl chloride, to styrene, and to allyl acetate and also of 2-acetoxyethyl chloromethyl ether to butadiene and to ethyl cinnamate.     

How mobile NMR can help with the conservation of paintings

The conservation of paintings is fundamental to ensure that future generations will have access to the ideas of the grand masters who created these art pieces. Many factors, such as humidity, temperature, light, and pollutants, pose a risk to the conservation of paintings. To help with painting conservation, it is essential to be able to noninvasively study how these factors affect paintings and to develop methods to investigate their effects on painting degradation. Hence, the use of mobile nuclear magnetic resonance (NMR) as a method of investigation of paintings is gaining increased attention in the world of Heritage Science. In this mini-review, we discuss how this method was used to better understand the stratigraphy of paintings and the effect different factors have on the painting integrity, to analyze the different cleaning techniques suitable for painting conservation, and to show how mobile NMR can be used to identify forgeries. It is also important to keep in mind its limitations and build upon this information to optimize it to extend its applicability to the study of paintings and other precious objects of cultural heritage.     

Size-Exclusion Chromatography: A Twenty-First Century Perspective

Now in its sixth decade, size-exclusion chromatography (SEC) remains the premier method by which to determine the molar mass averages and distributions of natural and synthetic macromolecules. Aided by its coupling to a variety and multiplicity of detectors, it has also shown its ability to characterize a host of other physicochemical properties, such as branching, chemical, and sequence length heterogeneity size distribution; chain rigidity; fractal dimension and its change as a function of molar mass; etc. SEC is also an integral part of most macromolecular two-dimensional separations, providing a second-dimension size-based technique for determining the molar mass of the components separated in the first dimension according to chemical composition, thus yielding the combined chemical composition and molar mass distributions of a sample. While the potential of SEC remains strong, our awareness of the pitfalls and challenges inherent to it and to its practice must also be ever-present. This Perspective aims to highlight some of the advantages and applications of SEC, to bring to the fore these caveats with regard to its practice, and to provide an outlook as to potential areas for expansion and growth.

     

杨石先对农药化学学科的重要贡献及其学术思想

杨石先先生一生献身于我国的教育事业与化学学科的发展,在62年中为我国培养了无数高质量的科教人才。他除了长期担任南开大学校长之外, 还创建了我国大学第一个专职研究所,即元素有机化学研究所。他率先开展了我国元素有机化学与农药化学的科学研究,领导了元素有机化学国家重点实验室的建立,是我国元素有机化学和农药化学的奠基人和开拓者。他倡导用有机化学的专业知识,科学和系统地开展农药化学研究,组建队伍获得20项科研成果,发表上百篇科学与论述性论文,为我国开展自主创新农药研究事业作出重要贡献。在农药化学学科的学术思想中,他强调要弄清该学科的交叉性、系统性和内在规律性,倡导要学习国际先进经验,要结合国情自主创新,要为国家经济服务,要对世界农药科技做出贡献。他毕生对人才培养给予了特别的重视,为我国科技事业持续发展作出了重大贡献。     

Designing for sustainability with biocatalytic and chemoenzymatic cascade processes

Cascade reactions have been widely recognized to cut costs, decrease solvent usage, and reduce cycle times in chemical processes. Recently, biocatalytic cascades have altered how we design synthetic routes to complex molecules to achieve sustainable commercial processes for pharmaceutical, agricultural, and fine chemical industries. With advancements in protein engineering and an increase in the number of enzyme classes available to chemists, industrial and academic groups alike have endeavored to expand the scope of biocatalysis from single reactions to multi-enzyme cascades to rapidly build complex molecular structures. Recent reports have drawn inspiration from biosynthetic pathways and have applied engineered enzymes to in vitro enzymatic cascades. Furthermore, combining transition-metal catalysis and enzymes in one-pot chemoenzymatic cascades likewise serves to broaden the scope of biocatalysis, enabling traditional chemical reactions to be performed under mild aqueous conditions. In this article, we review recent biocatalytic and chemoenzymatic cascades from 2019 to 2021.     

“The Fitness of Their Union”: Travel and Health in the Letters of Humphry and Jane Davy

The letters of Humphry Davy and his circle, to be published shortly, shed new light on his marriage to Jane Apreece. This paper examines the journeys undertaken by the couple, together and separately, with particular attention to the therapeutic benefits they sought from travel. I argue that their increasingly divergent itineraries reflected a growing understanding that Humphry and Jane had different humoral temperaments or constitutions, leading them to seek different climatic conditions to cure their ailments. While Jane’s temperament was classified as melancholic, requiring her to travel to warmer and sunnier climes during the English winter, Humphry’s was believed to be sanguine, meaning he had to avoid excessive heat along with stimulating food and drink. He relied on classical ideas about individuals’ different humoral constitutions, and the therapies appropriate to them, while measuring atmospheric variables to determine the best places to restore his health. The Davys’ letters reveal the beliefs about bodily differences and atmospheric conditions that shaped their therapeutic travels.     

Electrochemical approaches for the detection of amyloid-β, tau,and α-synuclein

According to the World Health Organization, there are 47 million people worldwide who are afflicted with dementia today, and this is expected to rise to 132 million by 2050. Therefore, it is pertinent to develop efficient analytical methods such as electrochemical biosensors to study these disorders and diagnose them early. This review highlights some of the recent key developments in the use of electrochemical biosensors to study the biomarkers related to neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. Especially, we focus on the applications of electrochemistry to analyze amyloid-β and tau related to Alzheimer's disease and α-synuclein related to Parkinson's disease.     

Hygienic aspects related to burial

Burial grounds are generally provided by local authorities in cemeteries (subject to planning consent and to compliance with any considerations for environmental health). Their design has been submitted to studies of hydrogeological characteristics of soil with regard to its ability to purify wastewater coming from corpse decomposition, its ability to avoid the infiltration of pollutants in groundwater, and its ability to skeletonize buried corpses within the given times foreseen by the law in force. Greater environmental awareness has necessitated that new and existing burial grounds are assessed to determine the environmental load which they could release to soil or any downstream component. This problem arises in countries where there is a high density of built-up areas, a custom of disposing of the dead by burial, a lack of available spaces and suitable soils to designate as burial grounds. This paper reports some results from a study carried out on ground lands of Italy in order to revise articles 82 and 83 of the Decree No 285 of 1990 in force in relation to burial grounds. Soil permeability to water and air is a parameter of critical importance in relation to purification and/or diffusion of leachates from inhumed corpses in the soil, and in relation to its influence on the time necessary to completely skeletonize a human corpse.     

Advancing the Drug Discovery and Development Process

The current state of affairs in the drug discovery and development process is briefly summarized and then ways to take advantage of the ever‐increasing fundamental knowledge and technical knowhow in chemistry and biology and related disciplines are discussed. The primary motivation of this Essay is to celebrate the great achievements of chemistry, biology, and medicine and to inform and inspire students and academics to enter the field of drug discovery and development while, at the same time, continue to advance the fundamentals of their disciplines. It is also meant to encourage and catalyze multidisciplinary partnerships between academia and industry as scientists attempt to merge their often complementary interests and expertise to achieve new improvements and breakthroughs in their respective fields, and the common goal of applying them to the discovery and invention of new and better medicines, especially in areas of unmet needs.     

Static fatigue fracture of polyethylene: A morphological analysis

The fracture properties of a number of high-density polyethylenes were evaluated and related to their morphology. The resistance to initiation of fracture is related to the resistance to voiding of the materials and the rate of coalescence of voids. The propensity of the materials to void has been shown to be related to the size of the amorphous region. The resistance to propagation of the fracture is also related to the above factors as well as the ease of stretching and rupture of fibrils. The ease of fibril formation has been shown to be related to the degree of perfection of the crystallites.     

Functional molecules in electronic circuits

Molecular electronics is a fascinating field of research contributing to both fundamental science and future technological achievements. A promising starting point for molecular devices is to mimic existing electronic functions to investigate the potential of molecules to enrich and complement existing electronic strategies. Molecules designed and synthesized to be integrated into electronic circuits and to perform an electronic function are presented in this article. The focus is set in particular on rectification and switching based on molecular devices, since the control over these two parameters enables the assembly of memory units, likely the most interesting and economic application of molecular based electronics. Both historical and contemporary solutions to molecular rectification are discussed, although not exhaustively. Several examples of integrated molecular switches that respond to light are presented. Molecular switches responding to an electrochemical signal are also discussed. Finally, supramolecular and molecular systems with intuitive application potential as memory units due to their hysteretic switching are highlighted. Although a particularly attractive feature of molecular electronics is its close cooperation with neighbouring disciplines, this article is written from the point of view of a chemist. Although the focus here is largely on molecular considerations, innovative contributions from physics, electro engineering, nanotechnology and other scientific disciplines are equally important. However, the ability of the chemist to correlate function with structure, to design and to provide tailor-made functional molecules is central to molecular electronics.     

On a formula of Braun and Rebane for variational bounds to overlap

A recent formula of Braun and Rebane for variational bounds to overlap is shown to be closely related to the methods of Rayner and of Weinhold for the same problem, and is extended to give upper and lower bounds to overlap in both ground and excited states.     

Polylactic acid/polypropylene polyblend fibers for better resistance to degradation

Polyblend fibers were produced from five ratios of polylactic acid/polypropylene (PLA/PP) in an effort to improve the resistance to hydrolysis and biodegradation, and to improve the dyeability of PLA. The inherent limitations of PLA such as its relatively poor resistance to hydrolysis have restricted the use of PLA. When made into polyblend fibers, the two polymers, PLA and PP, show partial compatibility and the mechanical properties of the blends are inferior compared to the pure PLA or PP fibers. However, PLA in the blends had substantially better resistance to biodegradation and hydrolysis, and dyeability with disperse dyes, resulting in a polyblend fiber with much better resistance to hydrolysis and similar dyeability to PLA. Blending PP with PLA could be a simple and effective method to create a new fiber with better resistance to hydrolysis and lower price than PLA, and better dyeability, sustainability and faster degradability than PP.     

成都经济生态区大气降尘中镉赋存形态的研究

采用Tessier连续提取法对成都经济生态区不同区域的24个大气降尘样中镉的赋存形态进行了研究。研究结果表明,大气降尘中的镉主要以残留态形态存在;各形态镉在总镉中所占百分比含量由大到小排列顺序依次是:残留态,碳酸盐结合态,交换态,铁锰结合态,有机结合态;交换态镉、碳酸盐结合态镉这两种具有较高生物有效性的形态镉在总镉中所占的平均百分比含量分别是6.420%和8.917%;铁锰氧化物结合态、有机结合态、残留态镉这三种形态镉生物有效性很低,分别在总镉中所占的平均百分比含量分别是3.419%、2.365%和78.907%。通过分析可得出,汽油和煤的燃烧以及工厂排放镉能加大城市大气降尘的镉污染。     

中职本科贯通应用型人才培养的无机化学教学探索

中职本科贯通生的中职阶段学习与普通高中学习存在着较大的区别,由于对基础知识未进行过系统强化训练,中职学生的理论知识较为薄弱;但由于较早进相关工厂见习或顶岗操作,其形象思维能力较强。在无机化学教学中,根据中职本科贯通生的特点,多采取探究式教学,让学生根据工厂生产中遇到的情况用自己的语言来描述一些概念和定义,"发现"一些原理,有利于培养应用型人才。     

A membrane electrode for nitrate and other univalent anions

A membrane electrode has been developed which is responsive to nitrate and other univalent anions but non-responsive to sulphate and other multivalent anions and to cations other than hydrogen. The membrane is prepared by polymerizing a mixture of phenol, formaldehyde, ammonia and nickel nitrate directly to a film for mounting in the usual cell-with-membrane assembly. Response to hydrogen ion is 0.30 mV per pH unit, to nitrate 0.60 mV per pNO(3) (activity) unit. Based on chemical composition and behaviour, physical properties, and electrical response, a structure and mechanism for exchange with hydrogen ion and nitrate ion and for internal electrical conduction has been postulated. Applications have been made to the determination of nitrate and to the detection of end-points.     

Determination of gaseous and particulate carbonyls in air by gradient-elution micellar electrokinetic capillary chromatography

A new continuous-flow gradient-elution micellar electrokinetic capillary chromatography method is developed for the determination of airborne carbonyls after derivatization with 2,4-dinitrophenylhydrazine. A total of 16 carbonyls can be determined with detection limits ranging from 0.94 to 8.50 mg/L, working range from 4.72 to 346 mg/L, and repeatabilities (relative standard deviation, n=5) from 1.23 to 4.6% or 3.93 to 7.6% for migration time and peak area, respectively. Coupling with denuder-filter sampling, a preliminary survey has been conducted to determine gaseous and particulate carbonyls from air sampled at a roadside station. The method is shown to have sufficient sensitivity for 1-h sampling of ambient carbonyls with detection limits ranging from 0.045 to 1.2 microg/m3 and working range from 0.11 to 43.3 microg/m3 at a flow rate of 10 Lpm. The method requires minimal modification of commercially available capillary electrophoresis equipment and can differentiate gaseous and particulate carbonyls to provide essential information and objective data for adopting effective measures to combat the discharge of carbonyl compounds to the atmosphere.     

Free-energy component analysis of 40 protein-DNA complexes: a consensus view on the thermodynamics of binding at the molecular level

Noncovalent association of proteins to specific target sites on DNA--a process central to gene expression and regulation--has thus far proven to be idiosyncratic and elusive to generalizations on the nature of the driving forces. The spate of structural information on protein--DNA complexes sets the stage for theoretical investigations on the molecular thermodynamics of binding aimed at identifying forces responsible for specific macromolecular recognition. Computation of absolute binding free energies for systems of this complexity transiting from structural information is a stupendous task. Adopting some recent progresses in treating atomic level interactions in proteins and nucleic acids including solvent and salt effects, we have put together an energy component methodology cast in a phenomenological mode and amenable to systematic improvements and developed a computational first atlas of the free energy contributors to binding in approximately 40 protein-DNA complexes representing a variety of structural motifs and functions. Illustrating vividly the compensatory nature of the free energy components contributing to the energetics of recognition for attaining optimal binding, our results highlight unambiguously the roles played by packing, electrostatics including hydrogen bonds, ion and water release (cavitation) in protein-DNA binding. Cavitation and van der Waals contributions without exception favor complexation. The electrostatics is marginally unfavorable in a consensus view. Basic residues on the protein contribute favorably to binding despite the desolvation expense. The electrostatics arising from the acidic and neutral residues proves unfavorable to binding. An enveloping mode of binding to short stretches of DNA makes for a strong unfavorable net electrostatics but a highly favorable van der Waals and cavitation contribution. Thus, noncovalent protein-DNA association is a system-specific fine balancing act of these diverse competing forces. With the advances in computational methods as applied to macromolecular recognition, the challenge now seems to be to correlate the differential (initial vs. final) energetics to substituent effects in drug design and to move from affinity to specificity.     

Atmospheric oxidation mechanism of p-xylene: a density functional theory study

We report an investigation of the mechanistic features of OH-initiated oxidation reactions of p-xylene using density function theory (DFT). Reaction energies for the formation of the aromatic intermediate radicals have been obtained to determine their relative stability and reversibility, and their activation barriers have been analyzed to assess the energetically favorable pathways to propagate the p-xylene oxidation. OH addition is predicted to occur dominantly at the ortho position, with branching ratios of 0.8 and 0.2 for ortho and ipso additions, respectively, and the calculated overall rate constant is in agreement with available experimental studies. Under atmospheric conditions, the p-xylene peroxy radicals arising from initial OH and subsequent O(2) additions to the ring are shown to cyclize to form bicyclic radicals, rather than to react with NO to lead to ozone formation. With relatively low barriers, isomerization of the p-xylene bicyclic radicals to more stable epoxide radicals likely occurs, competing with O(2) addition to form bicyclic peroxy radicals. The study provides thermochemical and kinetic data for assessment of the photochemical production potential of ozone and formation of toxic products and secondary organic aerosol from p-xylene oxidation.