Detection of trace molecular species using degenerate four-wave mixing

Spectroscopies that make use of laser light have provided an important tool to modern researchers for the nonintrusive analysis of chemical systems. The strengths and limitations of these spectroscopic techniques often determine the viability of scientific investigations. The unique properties of degenerate four-wave mixing, a nonlinear optical technique, have recently been found to provide powerful capabilities for a wide range of applications.     

Boundary layer profiles in plasma chemical vapor deposition

A nonlinear optical spectroscopy based on degenerate four-wave mixing has made possible direct measurements of species temperature and concentration profiles through the boundary layer of a reactive plasma at atmospheric pressure. Spectra were obtained for CH and C(2) radicals over a range of conditions including those for the plasma chemical vapor deposition of diamond films. Numerical simulations based on a one-dimensional stagnation-point flow model are in good agreement with the measurements. The CH mole fraction is shown to rise and fall as a function of distance from the substrate, which is compelling experimental evidence for the complex chemistry that is occurring in the plasma boundary layer.     

A 160-femtosecond optical image processor based on a conjugated polymer

Degenerate ground-state conjugated polymers exhibit large third-order nonlinear optical susceptibilities, including substantial two-photon absorption. With the use of a machine architecture suited to these material properties, ultrafast optical processors are possible. A four-wave mixing optical correlator was built with an air-stable, processable, degenerate ground-state conjugated polymer, poly(1,6-heptadiester). The continuously updatable processor correlates two 5000-pixel images in less than 160 femtoseconds, achieving peak processing rates of 3 x 10(16) operations per second.     

Entangled images from four-wave mixing

Two beams of light can be quantum mechanically entangled through correlations of their phase and intensity fluctuations. For a pair of spatially extended image-carrying light fields, the concept of entanglement can be applied not only to the entire images but also to their smaller details. We used a spatially multimode amplifier based on four-wave mixing in a hot vapor to produce twin images that exhibit localized entanglement. The images can be bright fields that display position-dependent quantum noise reduction in their intensity difference or vacuum twin beams that are strongly entangled when projected onto a large range of different spatial modes. The high degree of spatial entanglement demonstrates that the system is an ideal source for parallel continuous-variable quantum information protocols.     

利用单线虫多重PCR技术快速制备DNA分子量标准

基于单只线虫6对染色体及多重PCR技术建立一种特异性扩增特定长度核酸片段的方法,进而探索其在常规核酸分子量标准制备中的应用。利用多重PCR引物设计及特异性评估软件以秀丽线虫6对染色体为模板,分别设计扩增不同长度核酸片段的特异性引物对,并直接对单只秀丽线虫进行多重PCR扩增,采用20g/L琼脂糖凝胶电泳进行分离鉴定并采集图像,通过系统研究优化获得特异性高的1～6重PCR扩增产物,产物大小经鉴定与预期目的条带一致,6重PCR扩增产物条带与常规分子量标准DL 2 000相应条带完全吻合,说明采用该方法能够有效制备特定片段大小的分子量标准。     

Vibrational transition moment angles in isolated biomolecules: a structural tool

Infrared spectroscopy is used extensively in the study of isolated biomolecules, but it becomes less useful as it is applied to systems of increasing complexity. Even if the individual vibrational bands can be resolved spectroscopically, their assignment becomes problematic when they are more closely spaced than can be determined using ab initio methods. We describe a method that helps to alleviate this difficulty by measuring the direction of the vibrational transition moment for each vibrational band. The molecules of interest (adenine and cytosine) are cooled to 0.37 kelvin in liquid helium nanodroplets and oriented in a large dc electric field. A polarized infrared laser is then used to determine the directions of the infrared transition moments relative to the permanent dipole moment. Comparisons with ab initio calculations provide detailed structural information, including experimental evidence for nonplanarity of adenine and three tautomers of cytosine.     

分子植物育种助推南繁种业转型升级

异地加代可以经济有效地加快育种进程。长期以来,海南省作为中国最南端省份,只在冬季用来进行育种材料的扩繁和加代,其周年可以种植农作物的自然气候和环境并未得到充分有效地利用。分子标记辅助育种与其他现代育种技术相融合,将助推南繁种业从单一的繁殖加代向资源引进和评价、育种选择、纯度检测、种质交流和产权保护等在内的全产业链模式转变,实现从海南冬繁到周年育种的转变,将海南的南繁地理和生态优势转化为南繁与育种相整合的全产业链优势,加快育种进展、提高育种效率,促进种业发展。本文讨论了海南地理生态优势与南繁种业现状,南繁种业转型升级的必要性和可能性,以及所面临的挑战和机遇。实现南繁种业的转型升级有赖于异地选择观念的转变、国家相关政策的支持、分子育种平台的支撑、生物安全防控、品种保护制度的建立和完善、资源共享和交流机制的形成。数量和群体遗传、基因型和环境互作、分子设计和大数据构成了南繁种业转型升级所需的育种理论。分子设计包括宏观水平的个体设计、群体设计和物种设计,微观水平的基因设计、代谢设计和网络设计。高通量精准表现型鉴定、环境型鉴定、信息处理和网络技术、决策支撑系统等是南繁种业转型升级所需的育种平台。作...     

环状共轭多烯烃简并分子轨道的群论处理

以苯分子为例用群论方法对简并能级进行了处理,得出了用群论方法处理环状共轭多烯烃(CnHn)简并能级分子轨道的一般方法,证明了简并分子轨道的不同表示形式实质上是等价的,介绍了3-8元环状共轭多烯烃的分子轨道。     

基于高SBS阈值的HNLF产生高重复频率超短光脉冲

基于光纤中的四波混频(FWM)产生高重复频率超短光脉冲的原理,并为抑制光纤中的受激Brillouin散射(SBS),采用非均匀掺杂高SBS阈值非线性光纤,通过FWM对双拍频信号进行整形压缩,实验上获得了100GHz的高重复率超短光脉冲序列,进而分析了入纤功率对输出光脉冲的影响。     

Single-molecule fluorescence experiments determine protein folding transition path times

The transition path is the tiny fraction of an equilibrium molecular trajectory when a transition occurs as the free-energy barrier between two states is crossed. It is a single-molecule property that contains all the mechanistic information on how a process occurs. As a step toward observing transition paths in protein folding, we determined the average transition-path time for a fast- and a slow-folding protein from a photon-by-photon analysis of fluorescence trajectories in single-molecule F?rster resonance energy transfer experiments. Whereas the folding rate coefficients differ by a factor of 10,000, the transition-path times differ by a factor of less than 5, which shows that a fast- and a slow-folding protein take almost the same time to fold when folding actually happens. A very simple model based on energy landscape theory can explain this result.     

The rotational spectrum of the water-hydroperoxy radical (H2O-HO2) complex

Peroxy radicals and their derivatives are elusive but important intermediates in a wide range of oxidation processes. We observed pure rotational transitions of the water-hydroperoxy radical complex, H2O-HO2, in a supersonic jet by means of a Fourier transform microwave spectrometer combined with a double-resonance technique. The observed rotational transitions were found to split into two components because of the internal rotation of the water moiety. The molecular constants for the two components were determined precisely, supporting a molecular structure in which HO2 acts as a proton donor to form a nearly planar five-membered ring, and one hydrogen atom of water sticks out from the ring plane. The structure and the spectral splittings due to internal rotation provide information on the nature of the bonding interaction between open- and closed-shell species, and they also provide accurate transition frequencies that are applicable to remote sensing of this complex, which may elucidate its potential roles in atmospheric and combustion chemistry.     

A molecular photodiode system that can switch photocurrent direction

We prepared a molecular photodiode system in which the photocurrent direction can be switched by choosing the wavelength of an irradiating light. The molecular system is composed of two types of helical peptides that carry different chromophores and have different directions of dipole moments when they are immobilized on gold. The mixed, self-assembled monolayer generated an anodic photocurrent when one of the two chromophores was photoexcited, whereas the photocurrent switched to being cathodic when the other chromophore was photoexcited. The opposite current response arises from the dipole moment of each helical peptide, which accelerates electron transfer in the same direction.     

3种甜樱桃病毒PNRSV、PDV及LChV-2的多重RT-PCR检测方法的建立与应用

【目的】建立可同时检测李属坏死环斑病毒（Prunus necrotic ringspot virus,PNRSV）、李矮缩病毒（Prune dwarf virus,PDV）、樱桃小果病毒2（Little cherry virus-2,LChV-2）的多重RT-PCR检测方法。【方法】以复合感染3种病毒的甜樱桃病株叶片为材料,采用CTAB法提取样本总RNA,选用随机六聚体引物对植物样本总RNA进行反转录,所得cDNA作为多重RT-PCR的扩增模板。根据GenBank中PNRSV、PDV、LChV-2基因组序列共设计6对特异引物,分别通过单一RT-PCR和多重RT-PCR筛选出可用于同时检测3种甜樱桃病毒的引物组合。对多重RT-PCR的退火温度及循环数进行优化,以筛选出各引物组合的最适扩增条件。分别以单一感染PNRSV、PDV、LChV-2、复合感染3种病毒、单一感染樱桃病毒A（Cherry virus A,CVA）及甜樱桃无毒苗为样本,对多重RT-PCR引物的特异性进行分析。选取复合感染3种病毒的甜樱桃总RNA的反转录产物为初始模板,按照梯度稀释法依次将模板稀释为2、22、23、24、25倍,在相同PCR反应体系及反应条件下分别对各引物组合的灵敏度进行分析。多重RT-PCR的扩增条带经凝胶回收试剂盒回收纯化后连接至pMD18-T vector,克隆测序,以验证多重RT-PCR检测的准确性。并应用该方法对山东泰安地区甜樱桃生产园中间隔栽培的中国樱桃进行检测。【结果】筛选到2个可以应用的引物组合,组合1“PNRSV-S1/A1、PDV-S2/A2、LChV2-S1/A1”可分别特异性地扩增733、467、337 bp的片段。组合2“PNRSV-S1/A1、PDV-S3/A3、LChV2-S1/A1”可分别扩增得到733、265、337 bp的片段。扩增产物大小与预期相符。多重RT-PCR反应条件优化结果显示,在退火温度52℃、35个循环条件下,2个引物组合的检测效果均较为理想。特异性分析结果显示,2个引物组合均能特异性检测其各自的靶病毒。灵敏度分析结果显示,2个引物组合在cDNA的23×稀释液中仍能特异性扩增,但扩增条带的强度稍有差异,其对植物总RNA的反转录产物的最低检测浓度为107.9 ng•μL-1。克隆测序及序列分析表明,2个引物组合对各自靶病毒的检测结果可靠。应用该方法对9个中国樱桃样本进行检测,结果显示,测试样品均至少感染了2种病毒,其中5个样品复合感染了3种病毒,2个样品同时感染PDV和LChV-2,2个样品同时感染PNRSV和LChV-2。【结论】应用建立的多重RT-PCR检测方法可稳定、准确、灵敏的同时检测单一或复合侵染的3种甜樱桃病毒。     

多重PCR快速检测槟榔黄化植原体和槟榔隐症病毒1体系的建立

由槟榔黄化植原体(arecapalmyellowleafphytoplasma,AYLP)引起的黄化病和槟榔隐症病毒1(Areca palm velarivirus 1, APV1)引起的黄叶病毒病是危害槟榔树最严重的两种病害,对海南槟榔产业造成了巨大的经济损失,建立快速的检测技术对于两种病害的预警防控具有重要意义。利用多重PCR(Multiplex PCR)技术同时检测AYLP和APV1,即AYLP巢式PCR第一轮结束后,再使用一次多重PCR对两种病原同时进行扩增,最后进行电泳观察结果。结果显示,通过对多重PCR浓度体系和退火温度进行优化,在一个体系中成功扩增出AYLP和APV1,得到525和311 bp两条特异性大小条带。多重PCR检测与单一PCR检测结果完全一致,并且与单一PCR检测方法比较,多重PCR方法精简了操作步骤,提高了检测效率,显著降低了检测成本,为槟榔黄化病和黄叶病毒病的常规诊断提供了新方法。因此,该技术在AYLP和APV1常规检测中具有重要的应用价值。     

分子标记技术在花生品种鉴定中的研究进展

分子标记技术不受季节与发育期的限制,对纯合体或杂合体均可进行鉴定,该技术所得的遗传标记具有诸多优越性。运用分子标记技术构建指纹图谱,进而鉴定品种的纯度,可为育种工作提供可靠保障。目前,分子标记技术在花生品种鉴定中得到广泛的应用。文中介绍了几种常用的分子标记技术及其在花生品种鉴定中的应用,同时展望了分子标记技术在花生中的应用前景。     

Identification and Detection of Actinobacillus pleuropneumoniae in Infected and Subclinically Infected Pigs by Multiplex PCR Based on the Genes ApxIVA and OmlA

PCRs based on different genes of Actinobacillus pleuropneumoniae have been developed for detecting and identifying A. pleuropneumoniae. Some of them could amplify positive fragments from the phylogenetically closely related species bacteria. To improve veracity and specificity of PCR, a species-specific multiplex PCR assay was developed to identify and detect A. pleuropneumoniae, based on the 3＇-terminus of the species-specific apxlVA gene and the already existing species-specific primers in the omlA gene. Both 346-bp and 950-bp fragments could be simultaneously amplified from all A. pleuropneumoniae reference strains and isolates, and the species specificity of the assay was evaluated with a collection of ten strains representing eight different species bacteria including species normally found in the respiratory tracts of swine. All of these strains turned out negative in the multiplex PCR. All sequences of products of multiplex PCR randomly sampled were also correct. The sensitivity of the multiplex PCR was determined to be 10 pg of A. pleuropneumoniae DNA. The multiplex PCR and bacterial isolation were compared to determine their sensitivities by using experimentally infected pigs and clinical disease pigs. The multiplex PCR was more sensitive than bacterial isolation. The multiplex PCR was also evaluated on mixed bacterial cultures from clinical healthy pigs. 26/100 （26%） of the subclinically infected pigs were detected from clinical healthy pigs. The results indicate that the multiplex PCR assay is a sensitive, highly specific, and effective diagnostic tool for identification and detection of A. pleuropneumoniae.     

7对猪源性成分检测相关引物的特异性评测

为了评测物种鉴定PCR体系的特异性及其影响因素,实验对猪源性成分鉴定相关的7对引物就退火温度、镁离子浓度和不同Taq酶的影响进行了研究。结果表明,退火温度和镁离子浓度对PCR特异性有着重要影响,而其中2对引物优化后仍与鼠、兔、牛、羊、鸡和鸭有非特异性扩增。不同的Taq酶对引物特异性也有重要影响,本实验中r Taq酶在7对引物PCR体系中特异性最佳。通过对引物体系的优化和选择不同的Taq酶,可以有效提高特异性,减少非特异性扩增,为建立物种鉴定的PCR体系及多重PCR提供了基础。     

Molecular thermodynamics for chemical process design

Chemical process design requires quantitative information on the equilibrium properties of a variety of fluid mixtures. Since the experimental effort needed to provide this information is often prohibitive in cost and time, chemical engineers must utilize rational estimation techniques based on limited experimental data. The basis for such techniques is molecular thermodynamics, a synthesis of classical and statistical thermodynamics, molecular physics, and physical chemistry.