L-半胱氨酸与L-胱氨酸间相互转化的拉曼光谱研究

以石墨烯/纳米银为基底,采用拉曼光谱方法,研究了L-半胱氨酸与L-胱氨酸间的相互转化。随着体系pH值的变化,2 550 cm-1处S─H键的伸缩振动峰以及500 cm-1处S─S键的伸缩振动峰发生了明显变化,可以清楚地观察到L-半胱氨酸与L-胱氨酸间的相互转化,而延长激光曝光时间并没有观察到此变化。这表明溶液pH值是影响S─H键与S─S键间相互转化的主导因素。     

煤及油母中常见C-X(X=N,S)的解离能

煤及油页岩中除了碳、氢和氧原子是主要的组成元素外,氮和硫等杂原子大都以C-X（X=N,S）的键合形式存在,在其结构及转化利用中同样发挥重要的作用。认识C-X的解离能,有助于建立氮、硫热解过程中的迁移模型,丰富对煤及油母中常见化学键性质的认识,对发展高效清洁的能源利用技术至关重要。利用双杂化密度泛函方法,系统研究了煤及油母中典型C-X键的解离能（BDE）范围。研究结果表明,煤及油母中常见C-N和C-S键的BDE值范围分别是154.1~55.7 kcal·mol^-1和83.0~56.6 kcal·mol^-1。在热解过程中,苯硫类自由基以及苯胺类自由基会在初期产生,其次才是巯基、胺类自由基等侧链取代自由基脱落。C-S键的整体BDE值范围比其他类型化学键更低,各类化学键最低BDE值的高低顺序符合O-H > C-H > C-C > C-N > C-S > C-O的规律,其中,只有当有PhOx生成时,C-S > C-O,否则C-O > C-S。     

霍州煤氧化性气氛下热解预脱硫及硫的变迁

利用流化床反应系统对霍州原煤在氧气浓度(体积分数)分别为2.5%,5.5%和8.5%O2-N2混合气,热解温度分别为400℃,500℃,600℃,700℃和800℃,热解停留时间为20min的条件下进行了热解预脱硫的研究.结果表明,在氧气浓度为5.5%,热解温度为700℃时的脱硫效果最佳,脱硫率可达70%以上.而且,与惰性气氛下热解相比,半焦产率没有明显降低.当继续加大氧气浓度或升高热解温度时,虽然脱硫率有所增加,但是半焦产率却大大降低,且半焦产率的降幅要大于脱硫率的升幅.通过热解质谱(PY-MS)实验表明,在1%O2-He气氛下,SO2和CO2在500℃以前的逸出趋势基本相同,这说明氧气在低温时对不稳定有机硫中的C-S键能够选择性断裂,此时煤中的C-C键不受影响;随后CO也开始逸出,使得它们的逸出趋势稍微发生了变化,最后这三个峰基本在同时达到了最大,这是由于随着温度的升高,C-S键被氧气选择性断裂的同时,C-C键也大量参与到了反应中来,使氧气由原来的过量变得相对不足,从而使得部分碳转化为CO.     

硅酸锆分子振动模及其高温原位Raman光谱

用密度泛函理论对硅酸锆常温下的振动模进行模拟计算,并与实测的Raman和红外光谱进行了对比,解释了各振动模的归属.对硅酸锆晶体在升温过程中的Raman光谱的变化进行了研究.结果表明:随着温度上升,内振动模的红移明显,υ3(SiO4)伸缩振动模(B1g)红移最大,波数从常温时的1 006 cm-1红移至1 823 K时的937 cm-1.各振动模不断展宽且相对强度减弱,表明硅酸锆在升温过程中逐渐无序化,但[SiO4]四面体并没有聚合.升温过程中硅酸锆分解成ZrO2和SiO2.     

热处理聚苯硫醚的红外光谱分析

利用红外光谱技术对不同温度下在密炼机中热处理的聚苯硫醚(PPS)树脂进行分析;研究了热处理前后PPS的结构变化,探讨了PPS的热交联机理。结果表明:与未处理PPS相比,热处理后PPS的苯环的C—CH而内变形振动峰、笨环C—H面外弯曲振动峰、亚砜基伸缩振动峰及C—S面内伸缩振动峰向高位偏移;PPS经热处理后发生了氧化交联,且交联发生在苯环上,氧化发生在硫醚键上。     

中子辐照半绝缘SiC单晶的光学性质

利用荧光光谱、紫外-可见-近红外透射光谱和Raman光谱对经1.67×1020n/cm2中子辐照的半绝缘SiC的光学性质进行了研究。结果表明:中子未辐照的和辐照后退火温度低于1000℃的样品未出现任何发射峰;1200℃退火的样品在510、540和575nm处出现了3个绿色发射峰,其中,510和540 nm处的发射峰在经过1 600℃退火后依然存在。中子辐照导致SiC的截止波长由393 nm增大到1 726 nm;随退火温度提高,截止波长逐渐减小,并在1600℃退火后完全回复。Raman光谱显示:辐照诱发了许多新的振动模,如187、278、435和538cm-1处的Si—Si键振动模,600、655和709 cm-1处的Si—C键振动模和1419cm-1处C—C键振动模。辐照缺陷引起声子限制效应,表现为FTO2/6和FLO0/6Raman特征峰的不对称性展宽和红移。在低于1000℃退火阶段,主要表现为不对称性展宽和红移逐渐减弱;在高于1000℃退火阶段,主要表现为辐照产生的新Raman峰逐渐消失。     

二氯化锡催化合成杂环化合物的研究进展

二氯化锡是一种重要的还原剂,同时也是一种良好的催化剂,具有较高的反应活性和选择性,可以有效的促进多官能团化合物发生分子内及分子间的还原环化反应。文章主要介绍了二氯化锡催化C-N键、N-N键及C-S键的形成从而合成一系列杂环化合物的研究进展。     

介孔ZrO_2-SiO_2的制备及催化稠油水热裂解性能

采用溶胶-凝胶法,吐温40为介孔碳源,制备出介孔ZrO_2-SiO_2催化剂。采用稠油的水热裂解反应评价了催化剂的降粘性能。结果表明,较合适的Zr/Si摩尔比为0.29,其对稠油的降粘率为78.3%。催化改质后,S含量明显降低,氢碳比(n_H/n_C)增加,说明稠油在催化剂的作用下应该发生了加氢裂解反应,导致部分C-S键断裂。     

Progress of metallic nanoparticles catalysts in Ullmann reaction

因纳米金属粒子具有大的表面积和高的反应活性,因此作为新型的催化剂在有机合成领域得到了越来越多的应用.主要从C-C键、C-N键、C-O键和C-S键的形成角度,概括了各种金属纳米粒子催化乌尔曼反应的研究进展     

Bu_4NI/TBHP催化构建化学键的研究进展

相比传统的过渡金属催化反应,绿色、高效、无金属参与的反应对环境保护和成本的节省均具有重要意义,受到了科学工作者的广泛关注。本文综述了近年来Bu_4NI/TBHP催化体系在C-N键、C-O键、C-C键、C-S键和C-P键生成反应中的研究进展。     

Organometallic-like C-H bond activation and C-S bond formation on the disulfide bridge in the RuSSRu core complexes

C-S bond formations on the disulfide bridge in the dinuclear Ru(III) complexes have been found in the reaction with unsaturated organic molecules, such as alkenes and ketones. The reactions are initiated by the organometallic-like C-H bond activation. Through the mechanistic study of these novel reactions, the specific nature of the disulfide bridging ligand has been unveiled: (i) the double bond character of the sulfur-sulfur bond, which allows the Diels-Alder-type [4 + 2] cycloaddition reaction with butadiene to form a C(4)S(2) ring, (ii) the C-H bond activation on the S-S bond forming a C-S bond. All of the C-H activation reactions and the ensuing C-S bond formation reactions suggest that the disulfide ligand can act in a manner similar to the transition metal centers of the organometallic complexes.     

Py-MS Study of Sulfur Behavior during Pyrolysis of High-sulfur Coals under Different Atmospheres

In this study sulfur pyrolysis behavior of two Chinese high sulfur coals and their treated coal samples was investigated by Py-MS at a heating rate of 5 °C/min from room temperature to 1025 °C under hydrogen, helium and 2% O₂-He. It is found that the internal and external hydrogen do not show hydrogenation ability at temperature below 400 °C, due to no H₂S formation at this temperature region for all the coal samples. At temperature higher than 400 °C, not only the indigenous hydrogen but also indigenous oxygen can react with sulfur-containing radicals to form H₂S or SO₂. The evolution of H₂S and SO₂ displays the same profiles in pyrolysis of ZY pyrite-free coal under He, further revealing that after the breakage of C-S bond in the organic sulfur structure in coal to form sulfur-containing radicals, which can equally react with indigenous hydrogen and oxygen. The similar tendency between evolution of CO₂ and SO₂ and the same ending temperature also shows that not only C-S but also C-C bond can be broken in pyrolysis of ZY coals under 2% O₂-He atmosphere. However, unlike SO₂ evolution, CO₂ emission increases in the temperature ranging from 500 °C to 800 °C in LZ raw and deashed coals, implying the breakage of C-C bond at high temperature, which might be related to their low coal rank and high pyrite content.     

团簇As_4S与As_4Se稳定性与芳香性的理论研究

结合密度泛函和二级微扰理论,对As4S和As4Se团簇进行结构优化和频率分析.结果表明两者基态都采取单重态平面五角形构型(C2v,1A1)。分子轨道分析表明每个基态都有三个双电子占据的、高度离域的π型价分子轨道,符合4N+2芳香性电子规则。所有相邻As–As、As–M(M=S,Se)键的Wiberg键级(自然键轨道分析)和键长都处于相应单、双键数值之间;预测的各向异性磁化率和核独立化学位移都为较大负值,以上证据充分表明As4S和As4Se基态都表现出强芳香性。     

Rotational Distributions in the Photodetachment of IHI− and in the I + HI Reaction: The Influence of IHI Transition State Resonances

Franck-Condon factors which determine IHI⁻ photodetachment spectra have been calculated using a three-dimensional coupled-channel reactive scattering program. These Franck-Condon factors show peaks as a function of energy that are in reasonable agreement with measured spectra due to Neumark and co-workers. Some of these peaks are due to IHI transition state resonances and others are due to direct scattering reactive threshold effects. An analysis of the rotational distributions associated with the Franck-Condon factors indicates that when direct scattering is dominant, the distributions peak at the rotational state which is nearest to its effective reaction threshold. At energies where IHI transition state resonances are important, the rotational distribution changes, thus providing a characteristic signature of resonance formation. The I + HI bimolecular rotational distributions are also considered, and they also show important differences between direct and resonant energies.     

In silico identification of structure requirement for novel thiazole and oxazole derivatives as potent fructose 1,6-bisphosphatase inhibitors

Fructose 1,6-bisphosphatase (FBPase) has been identified as a drug discovery target for lowering glucose in type 2 diabetes mellitus. In this study, a large series of 105 FBPase inhibitors were studied using a combinational method by 3D-QSAR, molecular docking and molecular dynamics simulations for a further improvement in potency. The optimal 3D models exhibit high statistical significance of the results, especially for the CoMFA results with r(ncv) (2), q(2) values of 0.986, 0.514 for internal validation, and r(pred) (2), r(m) (2) statistics of 0.902, 0.828 statistics for external validation. Graphic representation of the results, as contoured 3D coefficient plots, also provides a clue to the reasonable modification of molecules. (1) Substituents with a proper length and size at the C5 position of the thiazole core are required to enhance the potency; (2) A small and electron-withdrawing group at the C2 position linked to the thiazole core is likely to help increase the FBPase inhibition; (3) Substituent groups as hydrogen bond acceptors at the C2 position of the furan ring are favored. In addition, the agreement between 3D-QSAR, molecular docking and molecular dynamics simulation proves the rationality of the developed models. These results, we hope, may be helpful in designing novel and potential FBPase inhibitors.     

Compounded effect of vacancy on interfacial thermal transport in diamond-graphene nanostructures

By employing molecular dynamics simulations, it is observed that the distance of the vacancy(s) from the diamond-graphene interface is a determinant of interfacial resistance. In this study, we explain this relationship in two inter-related approaches. (1) A vacancy situated close to the interface reduces the interfacial resistance, suggesting that phonon dynamics around the vacancy contribute to reduce the interfacial barrier. Vibrational density of state calculations show that phonon scattering processes at an interfacial vacancy(s) influence the interfacial transmission significantly. This is attributed to inelastic mode conversion processes at the vacancy(s) that create modes with frequencies and velocities which match well with those in the interfacial diamond, resulting in the drop of interfacial thermal resistance as the location of vacancy approaches the interface. (2) Radial distribution function analyses indicate the conformity nature of interfacial diamond bonds and the contraction/lengthening of interfacial graphene bonds as the vacancy position is varied. These structural changes improve/weaken the matching of the interfacial bond length and result in mode conversion processes that modify the amount of mismatch in the vibrational density of states and phonon velocities in the two media.     

A mechanistic approach to the thermal degradation of α-olefin sulfonates

Determination of the thermal stability of α-olefin sulfonates (AOS) via the conventional activation energy approach was found to be impractical because of the difficulties arising from the fact that α-olefin sulfonates are mixtures of hydroxyalkane sulfonates and alkene sulfonates. Each of these components of AOS was studied independently and found to follow a complicated thermal degradation path. We found that the thermal degradation of hydroxyalkane sulfonate is a base-catalyzed process. At elevated temperatures, hydroxyalkane sulfonates are first converted into an intermediate which is still surface active before degrading further to a non-surface active product by a second mechanism. The rate-determining step of the degradation process was found not to involve a cleavage of the C-S bond as observed for other types of sulfonates. Our work indicates that the first step of the thermal degradation of alkene sulfonates involves isomerization of double bonds followed by cleavage of the C-S bond. The thermal degradation of alkene sulfonates is catalyzed by acids.     

噻唑类杀虫剂的研究进展

目前杂环化合物的发展呈现出多元化的趋势,其中噻唑类化合物是近年来发展的一个新亮点。尤其噻唑基团引入到各种不同的化合物结构中,通过结构修饰能产生一系列具有广谱生物活性化合物,使得它在新型超高效农药创制中发挥出越来越重要的作用。本文从杀虫方面对噻唑化合物的生物活性研究进行了综述,重点介绍了该类化合物的一些生物活性研究方面的工作,简述了不同取代基团对噻唑类衍生物生物活性的影响,并对它的发展趋势和应用前景作了展望。     

Photomodulation of the proton affinity and acid gated photochromism of a novel dimethylaminophenyl thiazole diarylethene

The acid-gated photochromism and the photomodulation of fluorescence and proton affinity of a novel dimethylaminophenyl thiazole diarylethene in MeCN were investigated from a kinetic point of view. Photomodulation of the proton affinities has been estimated from acid titrations and numerical modelling of the acid induced T-photochromism. The basicities of the thiazole and dimethylamino protonation sites are different by only one pK unit. Upon ring- closure, their relative proton affinities are reversed. Our investigations underline the role of the thiazole protonation in the carbon-carbon bond weakening of the closed form and validate the role of the proton as catalyst in the gated T-photochromism.