Detection of molecular interactions at membrane surfaces through colloid phase transitions

The molecular architecture of-and biochemical processes within--cell membranes play important roles in all living organisms, with many drugs and infectious disease agents targeting membranes. Experimental studies of biochemical reactions on membrane surfaces are challenging, as they require a membrane environment that is fluid (like cell membranes) but nevertheless allows for the efficient detection and characterization of molecular interactions. One approach uses lipid membranes supported on solid substrates such as silica or polymers: although the membrane is trapped near the solid interface, it retains natural fluidity and biological functionality and can be implanted with membrane proteins for functional studies. But the detection of molecular interactions involving membrane-bound species generally requires elaborate techniques, such as surface plasmon resonance or total internal reflection fluorescence microscopy. Here we demonstrate that colloidal phase transitions of membrane-coated silica beads provide a simple and label-free method for monitoring molecular interactions on lipid membrane surfaces. By adjusting the lipid membrane composition and hence the pair interaction potential between the membrane-supporting silica beads, we poise our system near a phase transition so that small perturbations on the membrane surface induce dramatic changes in the macroscopic organization of the colloid. We expect that this approach, used here to probe with high sensitivity protein binding events at membrane surfaces, can be applied to study a broad range of cell membrane processes.     

中介尺度活塞式内燃机氢氧燃烧过程的数值模拟

中介尺度条件下的氢氧预混燃烧,其燃烧速率主要由化学反应速度决定。于是采用层流有限速率模型,运用详细氢氧19步基元反应化学动力学机理和动态网格数值方法,对中介尺度准气体动力循环活塞式热力发动机超高燃烧负荷率氢氧预混燃烧过程进行了模拟。研究表明:中介尺度移动边界微小封闭空间的氢氧预混燃烧具有稳定性;采用表面炽热点火形式的中介尺度准气体动力循环的活塞式内燃机,能够实现工质高温吸热、内能增加和对外做功的完整热力学过程;而循环周期、初始压力、相对燃空比等运行参数对移动边界微小封闭空间的氢氧燃烧过程具有复杂的影响。     

TATB高温高压下初始分解反应的分子动力学模拟

在凝聚相含能材料的反应过程中,反应体系往往需要高温高压的反应条件,且其中原子、分子的反应往往具有不同于气态分子的反应路径.因此,除需对体系分子的结构及电子性质进行计算分析外,还需对体系分子做反应动力学分析.本文采用ReaxFF分子动力学方法模拟了凝聚相下1,3,5-三氨基-2,4,6-三硝基苯(TATB)分子的初始反应过程,通过对分子产物随时间的分布、分子产物在不同时间段内的分布等分析,总结了其在反应初期的一些反应过程.结果显示,C-NO2键的断裂及质子转移为引起更复杂化学反应的初始反应.     

6种城市下垫面热环境效应对比研究

选择6种具有代表性的城市下垫面(沥青路面、水泥路面、荷兰砖地面、草地、嵌草砖地面、大理石地面)作为观测对象,基于热红外成像技术对其地表温度特征进行观测,系统分析不同城市下垫面地表温度的日变化以及季节变化特征,并利用不同下垫面温度的时间标准差、空间标准差及时空数据标准差定量揭示城市不同下垫面地表温度的时空变化特征,对比研究不同下垫面的热环境效应,结果如下。1)不同下垫面地表温度的日变化一般呈先上升后下降的单峰形态,草地地表温度在不同季节的日变化波动差异较大。沥青的地表温度在全年均为最高,对热环境的影响较大;嵌草砖和大理石在全年的温度均较低,对热环境具有较好的缓解作用,且缓解作用在夏季最显著。2)不同下垫面地表日均温度全年均高于大气温度,表明城市下垫面对大气在一年中都有加热作用。3)气温、太阳辐射以及空气相对湿度对下垫面地表温度的影响均较为显著;气温和太阳辐射与下垫面地表温度之间呈正相关关系,对下垫面以增温作用为主;空气相对湿度与下垫面地表温度之间呈负相关关系,对下垫面增温起抑制作用。4)嵌草砖的热环境稳定性较草地和大理石要好;沥青路面的温度变化特征最能代表本研究观测区域下垫面地表温度的时空变化特征。研究结果对了解城市不同下垫面热环境具有一定参考意义,可为缓解城市热环境提供科学依据。     

Ti-MWW催化烯丙醇环氧化制环氧丙醇的动力学研究

以水为溶剂,H2O2为氧化剂,Ti-MWW催化烯丙醇环氧化制备环氧丙醇的反应条件温和,产率高,对环境友好,并考察了反应温度、烯丙醇和H2O2的配比对环氧化反应的影响以及温度和pH值对副反应的影响.在此基础上提出了可能的反应机理,建立了主、副反应的动力学模型,确定了模型参数并对模型进行了检验.     

Interaction of hydrogen with metal nitrides and imides

The pursuit of a clean and healthy environment has stimulated much effort in the development of technologies for the utilization of hydrogen-based energy. A critical issue is the need for practical systems for hydrogen storage, a problem that remains unresolved after several decades of exploration. In this context, the possibility of storing hydrogen in advanced carbon materials has generated considerable interest. But confirmation and a mechanistic understanding of the hydrogen-storage capabilities of these materials still require much work. Our previously published work on hydrogen uptake by alkali-doped carbon nanotubes cannot be reproduced by others. It was realized by us and also demonstrated by Pinkerton et al. that most of the weight gain was due to moisture, which the alkali oxide picked up from the atmosphere. Here we describe a different material system, lithium nitride, which shows potential as a hydrogen storage medium. Lithium nitride is usually employed as an electrode, or as a starting material for the synthesis of binary or ternary nitrides. Using a variety of techniques, we demonstrate that this compound can also reversibly take up large amounts of hydrogen. Although the temperature required to release the hydrogen at usable pressures is too high for practical application of the present material, we suggest that more investigations are needed, as the metal-N-H system could prove to be a promising route to reversible hydrogen storage.     

微结构疏水表面的液滴浸润特性

以聚二甲基硅氧烷(PDMS)为基底采用光刻蚀法制备了具有不同粗糙度的微方柱结构疏水表面,研究了微结构疏水表面的液滴浸润特性.结果表明,微方柱高度对表观接触角影响很小,但会显著影响疏水表面液滴浸润状态的稳定性,当微方柱边长和间距一定时,存在一个临界高度,当微方柱高度大于该临界值时,液滴具有良好的稳定性.通过对不同温度下疏水表面液滴浸润状态的研究表明,在露点温度至环境温度区间内,随着温度的增加,表观接触角呈增大趋势;在环境温度至沸点温度区间内,随着温度的升高,表观接触角呈减小的趋势.研究认为,合理的微结构尺寸和应用环境温度对液滴浸润状态的稳定具有重要意义.     

Synthesis of well-defined functional crystals by high temperature gas-phase reactions

Over the past decades, there have been many synthesis methods on producing well-defined crystals, due to their enormous application potentials in industrial field. Among them, high temperature gas-phase reactions （HTGR） approach may be one of the most promising processes for fabrication of well-defined crystals with controllable structure, size, shape, and composition. This review is focused on the recent progresses in synthesizing well-defined crystalline TiO2 dominated with, respectively, {001 } facets and { 105 } facets, one-dimensional ZnO and SnO2 nanorods/nanowires, MoS2 nanosheets as well as GaP, InP, and GaAs nanowires via HTGR approach. Although these research works were currently carried out on experimental scale, it is worth to note that the industrial importance of this HTGR approach for design and fabri- cation of well-defined crystals in the future owing to its advantages of continuous and scalable production with controlled dimensions and low cost.     

北京大学校园夏季气象场的数值模拟

北京大学校园北部有未名湖等水域和树木冠层绿地, 与南部教学、生活区建筑物路面为主的布局在下垫面热力性质上存在显著差异。为定量研究夏季校园内不同区域气象场、舒适度的空间分布和时间变化, 为校园活动和游览提供参考, 利用北京大学城市冠层模式, 结合校园实际下垫面分布情况, 进行数值模拟研究。研究结果表明, 9 月份校园北部温度低于南部, 15: 00 温差可达 6. 7℃。路面上 由于潜热通量小, 温度高于其他下垫面, 和水面温差最大可达 10. 6℃。空气湿度北部高于南部。温度分布影响局地风场变化, 在 15:00 产生低温辐散流场。引入表征人体舒适度的温湿指数(THI) , 路面上有 50% 时间处于 “热”等级, 高于其他下垫面的20% 。研究结果可以为评估校园环境规划的气象效应提供科学依据。     

Enzyme dynamics and hydrogen tunnelling in a thermophilic alcohol dehydrogenase.

Biological catalysts (enzymes) speed up reactions by many orders of magnitude using fundamental physical processes to increase chemical reactivity. Hydrogen tunnelling has increasingly been found to contribute to enzyme reactions at room temperature. Tunnelling is the phenomenon by which a particle transfers through a reaction barrier as a result of its wave-like property. In reactions involving small molecules, the relative importance of tunnelling increases as the temperature is reduced. We have now investigated whether hydrogen tunnelling occurs at elevated temperatures in a biological system that functions physiologically under such conditions. Using a thermophilic alcohol dehydrogenase (ADH), we find that hydrogen tunnelling makes a significant contribution at 65 degrees C; this is analogous to previous findings with mesophilic ADH at 25 degrees C. Contrary to predictions for tunnelling through a rigid barrier, the tunnelling with the thermophilic ADH decreases at and below room temperature. These findings provide experimental evidence for a role of thermally excited enzyme fluctuations in modulating enzyme-catalysed bond cleavage.     

A quantum fluid of metallic hydrogen suggested by first-principles calculations

It is generally assumed that solid hydrogen will transform into a metallic alkali-like crystal at sufficiently high pressure. However, some theoretical models have also suggested that compressed hydrogen may form an unusual two-component (protons and electrons) metallic fluid at low temperature, or possibly even a zero-temperature liquid ground state. The existence of these new states of matter is conditional on the presence of a maximum in the melting temperature versus pressure curve (the 'melt line'). Previous measurements of the hydrogen melt line up to pressures of 44 GPa have led to controversial conclusions regarding the existence of this maximum. Here we report ab initio calculations that establish the melt line up to 200 GPa. We predict that subtle changes in the intermolecular interactions lead to a decline of the melt line above 90 GPa. The implication is that as solid molecular hydrogen is compressed, it transforms into a low-temperature quantum fluid before becoming a monatomic crystal. The emerging low-temperature phase diagram of hydrogen and its isotopes bears analogies with the familiar phases of 3He and 4He (the only known zero-temperature liquids), but the long-range Coulomb interactions and the large component mass ratio present in hydrogen would result in dramatically different properties.     

High resolution structure of the RNA duplex [U(U-A)6A]2

RNA is involved in many biological functions, ranging from information storage and transfer to the catalysis of reactions involving both nucleic acids and proteins. Previous crystallographic studies on RNA oligomeric chains provide only averaged structures or information limited in resolution. The oligomer [U(U-A)6A]2 was chosen for the study of protein-RNA interactions in viruses. Its size and base composition mimic portions of the genomic RNA in alfalfa mosaic virus that bind to the amino terminus of the viral subunit. The actual sequence was designed to guarantee the formation of a single species of duplex and to facilitate the production of the pure oligomer in large quantities. The molecular structure, derived from the 2.25 A resolution X-ray diffraction data, allows the most detailed analysis of an A-RNA helix reported to date. Two kinks are observed that divide the duplex into three blocks, each close to a canonical A-helical conformation. A few intermolecular hydrogen bonds involving 2'-hydroxyl groups stabilize this peculiar conformation of the RNA, which may be related to the temperature used for the crystallization (35 degrees C). The structure demonstrates both the plasticity of the RNA molecule and the role of the 2'-hydroxyl groups in intermolecular interactions.     

航空发动机矢量喷管作动器电磁阀通油不冷却工况热分析

分析了航空发动机矢量喷管作动器电磁阀在通油不冷却工况所处热环境。建立了电磁阀热分析计算模型及其热平衡方程组。编制源程序进行了求解。结果表明:因为电磁阀尾部附近的作动器总体主油路仍然工作,带走热量;所以电磁阀在额定工况、通油不冷却工况下可正常工作。另外,还对影响电磁阀温度的四个主要因素:环境温度、焦耳热、入口油温、作动器总体主油路流量进行了一系列研究,得到了各因素对电磁阀温度的影响规律。其中,环境温度对电磁阀温度影响最大。当无量纲环境温度小于1.53时,电磁阀温度在可承受极限温度范围内,可以正常工作;当无量纲环境温度高于1.53时,电磁阀将处于超温状态,不能正常工作。     

从AGCU硫回收工艺谈抗HIC钢的要求

AGCU硫回收工艺的主要反应造成了设备的湿硫化氢环境,湿硫化氢环境导致应力腐蚀,抗HIC钢是用于此类工作环境的主要材料,总结出抗HIC钢的材料要求和制造要求。     

未知环境表面的超声波探测实验研究

针对机器人未知工作环境,提出了一种基于超声波传感器的探测方法.建立了探测系统的结构模型,阐述了系统的工作原理,并分别对平面、圆弧曲面、斜面以及竖直面等未知环境基本组成面的探测进行了实验研究.实验结果表明,超声波测距仪不适合曲率半径小的圆弧曲面探测.对于其他三类环境表面的探测,给出了各自的探测策略和数据处理方法,主要包括:斜面探测需要用三个超声波传感器,竖直面探测需要补偿由于开角引起的误差,平面探测需要补偿由传感器运动引起的动态测量误差等.     

阻氚涂层辐照-渗氢耦合装置的设计

本文设计了一套用于阻氚涂层质子辐照与氢渗透耦合的实验装置,利用四川大学原子核科学技术研究所的2×3 MV 串列加速器来研究阻氚涂层(TPB)高温、辐照、渗氢性能. 详细介绍了该装置的总体设计目标和主要组成部分,如试样架、含氢渗透气体回路及设计原理. 利用该装置获取TPB涂料的相关数据,为今后利用质子原位辐照技术研究辐照对高温环境下氢气渗透性能的影响奠定了基础. 本文还对装置参数和试验参数的优化进行了探讨.     

Anatase TiO2 single crystals with a large percentage of reactive facets

Owing to their scientific and technological importance, inorganic single crystals with highly reactive surfaces have long been studied. Unfortunately, surfaces with high reactivity usually diminish rapidly during the crystal growth process as a result of the minimization of surface energy. A typical example is titanium dioxide (TiO2), which has promising energy and environmental applications. Most available anatase TiO(2) crystals are dominated by the thermodynamically stable {101} facets (more than 94 per cent, according to the Wulff construction), rather than the much more reactive {001} facets. Here we demonstrate that for fluorine-terminated surfaces this relative stability is reversed: {001} is energetically preferable to {101}. We explored this effect systematically for a range of non-metallic adsorbate atoms by first-principle quantum chemical calculations. On the basis of theoretical predictions, we have synthesized uniform anatase TiO(2) single crystals with a high percentage (47 per cent) of {001} facets using hydrofluoric acid as a morphology controlling agent. Moreover, the fluorated surface of anatase single crystals can easily be cleaned using heat treatment to render a fluorine-free surface without altering the crystal structure and morphology.     

Catalytic C-H functionalization by metal carbenoid and nitrenoid insertion

Novel reactions that can selectively functionalize carbon-hydrogen bonds are of intense interest to the chemical community because they offer new strategic approaches for synthesis. A very promising 'carbon-hydrogen functionalization' method involves the insertion of metal carbenes and nitrenes into C-H bonds. This area has experienced considerable growth in the past decade, particularly in the area of enantioselective intermolecular reactions. Here we discuss several facets of these kinds of C-H functionalization reactions and provide a perspective on how this methodology has affected the synthesis of complex natural products and potential pharmaceutical agents.     

Observation of Pt-{100}-p(2×2)-O reconstruction by an environmental TEM

The surface structure of noble metal nanoparticles usually plays a crucial role during the catalytic process in the fields of energy and environment. It has been studied extensively by surface analytic methods, such as scanning tunneling microscopy. However, it is still challenging to secure a direct observation of the structural evolution of surfaces of nanocatalysts in reaction(gas and heating) conditions at the atomic scale. Here we report an in-situ observation of atomic reconstruction on Pt {100} surfaces exposed to oxygen in an environmental transmission electron microscope(TEM). Our high-resolution TEM images revealed that Pt-{100}-p(2×2)-O reconstruction occurs during the reaction between oxygen atoms and{100} facets. A reconstruction model was proposed, and TEM images simulated according to this model with different defocus values match the experimental results well.