非金属元素的同素异形体(一)——氢和硼的同素异形体概述

进行了同素异形体概念的探讨。简要叙述了氢和硼2种典型非金属元素形成的各种同素异形体的存在、组成以及结构、制备和性质,首次将多种硼富勒烯、硼纳米管、硼单层平面等晶态硼的内容补充在硼的同素异形体中,并强调了计算化学对同素异形体的预测和现代科学技术发展对制备的作用及其在材料中的应用。     

非金属元素的同素异形体(二)——再谈碳的同素异形体

以“同一元素的不同形态的纯单质互称同素异形体”来定义,对数目众多的碳的同素异形体进行了归纳,它们可分为石墨、金刚石、富勒烯碳原子簇和新型纳米材料等4类。简要叙述了各种同素异形体的存在、组成、结构、制备、性质,并强调了计算化学对同素异形体的预测和现代科学技术发展对制备的作用及其在材料中的应用。     

金属锡的同素异形体

从传统白锡、灰锡到新型低维锡烯、锡量子点,归纳总结了第四主族元素锡的各种同素异形体,介绍了其结构、制备、性质及应用等方面,进一步丰富了无机金属元素同素异形体的学习。     

非金属元素砷的同素异形体研究进展*

依据砷化学的快速发展,分别对砷元素3种典型单质(灰砷、黑砷、黄砷)以及多种新型结构的砷同素异形体的制备、结构、化学特性及应用等方面进行综合介绍,为砷元素的教学及科研提供全新且丰富的素材。     

非金属元素同素异形体化学(三)——硅的同素异形体

对数目众多的硅的同素异形体进行了全面归纳,它们可分为硅纳米晶的不同物相类、纳米结构硅物质、硅原子簇和硅烯等4大类。简要叙述了各种同素异形体的存在、组成和结构、制备和性质,并强调了计算化学对同素异形体的预测和现代科学技术发展对制备的作用及其在材料中的应用。     

同素异形体与多晶型体

在化学教学中,特别是在讨论元素单质性质时,常常使用术语"同素异形体".然而不同的教科书对"同素异形体"下了不同的定义,即使同一作者对"同素异形体"也作了不同的解释.这样就使得"同素异形体"的概念变得模糊起来,更为重要的     

硫的同素异形体*

硫是固态同素异形体数量最多的元素。但就单质硫的同素异形体而言,教材中并没有详细概述。根据硫化学的研究进展,全面考察了硫的同素异形体的种类,讨论了它们的制备、晶体结构及其相互转化,着重体现了科学技术对其同素异形体扩展的重要作用,完善了硫同素异形体在教学中的深入介绍。同时,也体现了科学研究对本科教学内容改革的推进作用。     

具有螺共轭结构的碳的同素异形体:glitter碳

介绍碳的新的同素异形体glitter碳的结构及螺共轭特征,对碳的同素异形体的结构进行了比较。     

非金属元素硒的同素异形体*

结合史实文献和最新研究成果,汇总了硒的同素异形体,可分为气态硒、液态硒、固体硒、纳米硒和硒团簇等5类,重点介绍了固体硒、纳米硒和硒团簇的种类、结构、性质、制备和应用等。完善了硒同素异形体在教学中的深入介绍,有助于体现科学研究对本科教学内容改革的推进作用。     

金属锑的同素异形体概述

结合最新研究进展,归纳总结了金属锑的同素异形体,包括块体锑(灰锑、爆炸性锑、黑锑、黄锑)和纳米锑(锑烯、锑纳米管)。介绍了锑的各种同素异形体的组成、结构、性质、制备和应用等,为丰富金属元素的教学和扩展研究提供重要素材。     

Micro-Raman and Tip-Enhanced Raman Spectroscopy of Carbon Allotropes

Summary: Raman spectroscopic data are obtained on various carbon allotropes like diamond, amorphous carbon, graphite, graphene and single wall carbon nanotubes by micro-Raman spectroscopy, tip-enhanced Raman spectroscopy and tip-enhanced Raman spectroscopy imaging, and the potentials of these techniques for advanced analysis of carbon structures are discussed. Depending on the local organisation of carbon the characteristic Raman bands can be found at different wavenumber positions, and e.g. quality or dimensions of structures of the samples quantitatively can be calculated. In particular tip-enhanced Raman spectroscopy allows the investigation of individual single wall carbon nanotubes and graphene sheets and imaging of e.g. local defects with nanometer lateral resolution. Raman spectra of all carbon allotropes are presented and discussed.     

On the possibility of the existence of molecular nitrogen allotropes

The possibility of the existence of nitrogen molecules with an even number of atoms of composition N₄, N₆, N₈, and N₁₀ has been discussed with the use of the QCISD and G3 quantum-chemical methods. From these data, a conclusion has been made that three new nitrogen allotropes with an even number of atoms in a molecule can exist, namely, N₄ shaped as a rectangle and regular tetrahedron and N₆ with a shape remotely resembling an “open book.” The bond lengths and bond and torsion angles in each of these molecules have been reported.     

Investigation of the relative stabilities of various allotropic phases of elemental tellurium under pressure and their interconversion paths by electronic structure calculations and crystal structure analyses

Elemental tellurium adopts a number of different structures under pressure. The relative stabilities of these allotropes and the interconversion between them were examined on the basis of first principles electronic band structure calculations with and without external pressure. The relative stabilities of the allotropes were also analyzed by estimating the overall strength of covalent bonding on the basis of the Te-Te overlap populations determined from tight-binding electronic structure calculations. The crystal structures of the allotropes were analyzed to determine how one form can transform into another form under pressure. Our study leads to the energy profile of tellurium as a function of pressure consistent with experiment, shows that the relative stabilities of the allotropic phases of Te are mainly governed by the overall strength of covalent bonding, and that all the allotropes are intimately related in structure, and one form can be readily converted to another form under pressure via a simple interconversion path.     

氧化领域的“姐妹花”:氧气和臭氧

概述了氧气与臭氧这对同素异形体的发现过程、结构及应用情况,其中重点介绍了氧气在催化氧化醇方面的应用和臭氧在催化氧化废水中有机污染物方面的应用,发现2者具有共同的氧化特点,均是依赖产生含氧活性物种来加快氧化反应的进行;同时发现由于2者结构的不同,导致催化剂在其各自所参与的催化氧化过程中发挥的作用不同。     

基于从头计算法的三维碳同素异形体结构设计

由于独特的成键特性,在不同温度和压强下,碳具有丰富的结构特性。除了实验上已发现各种同素异形体,理论计算也预言了丰富的新结构。在本文中,我们对第一性原理计算预言的三维碳同素异形体做了综述,特别地,我们着重关注了泡沫状的碳结构。碳泡沫主要由石墨片断以各种碳键连接而成,具体多孔结构及较大的表面积。另外,针对由低维碳结构,如碳富勒烯、纳米芽、纳米管及石墨烯等组成的三维碳超结构以及其他三维碳晶体我们也做了概述。这些新型碳结构有的由混杂的sp-sp²碳或者纯sp²碳组成(H-6, bct-4, C-20, K₄等),有的质量密度比金刚石还大(C₈, hP3, tl12, tp12等),有的可以由石墨在室温高压下转化而成(M碳, bct-4碳, W碳, Z碳等)。在这些预言的碳同素异形体中,有些在将来可能在实验室合成。     

抗高血压药物的构效关系研究进展

我国对抗高血压药的研究始于20世纪50年代。随着研究的不断深入,抗高血压药物朝着高效、长效、高度心血管选择性、多器官保护作用以及低副作用方向发展,不断在原有化合物模型的基础上对化合物进行结构修饰,发展了单环及多环含氮杂环类抗高血压药物。文章从结构与活性的角度分析了近年来国内外杂环类抗高血压药及其衍生物的构效关系。     

Identification des allotropes S6 et S7 du soufre dans le trophosome du vestimentifère Riftia pachyptila

The two sulphur allotropes S₆ and S₇ were characterised by gas chromatography/mass spectrometry coupling experiments in trophosomes of Riftia pachyptila (Vestimentifera), which inhabit hydrothermal vents. Both allotropes (approximately 3% for both) are associated with the usual form S₈ that represents about 97% of the total sulphur fraction. These new natural varieties of sulphur could be due to bacterial oxidation of hydrogen sulphide in extreme conditions (about 300 kg cm^–2). However, the occurrence of the same allotropes in mineral sulphur from different origin, terrestrial and extraterrestrial as well, could indicate that natural sulphur is a mixture of these three allotropes, with proportions depending on its geographical origin.     

Acetylenic Coupling: A Powerful Tool in Molecular Construction

Acetylenic coupling is currently experiencing some of the most intensive study of its long history. Rigid and sterically undemanding di- and oligoacetylene moieties, which are frequently encountered in natural products, are finding increasing application as key structural elements in synthetic receptors for molecular recognition. Interesting electronic and optical properties of extensively pi-conjugated systems have spurred research into new linear oligoalkynes and acetylenic carbon allotropes. The synthetic challenges associated with these efforts have in turn spawned new methods. While classical Glaser conditions are still frequently used for homocoupling, the demand for increasingly selective heterocoupling conditions has provided the focus of research over the past decades. These efforts have undoubtedly been hampered by a relatively poor mechanistic understanding of these processes. More recently, palladium-catalyzed coupling methods have led to improvements in both the selectivity and reliability of acetylenic homo- and heterocouplings and paved the way for their application to ever more complicated systems. The variety of acetylenic coupling protocols, the current mechanistic understanding, and their application in natural product and targeted synthesis are discussed comprehensively for the first time in this review, with an emphasis on the most recently developed methods, and their application to the synthesis of complex macromolecular structures.