表面增强拉曼光谱和电化学方法研究中性条件下咪唑对镍电极的缓蚀作用

利用表面增强拉曼光谱技术(SERS)研究了咪唑在镍电极表面的吸附机理和吸附方式,并分别比较了镍电极在加入咪唑前后溶液中的循环伏安曲线和极化曲线,计算了其缓蚀效率。结果表明,在镍电极表面,咪唑起到了较好的缓蚀效果;在研究电位区间内所得的SERS谱图中,面内振动峰占据了主导地位,咪唑是以垂直略带倾斜的方式吸附在镍电极表面的;而N—H面内弯曲振动峰(1 173 cm-1)的出现和pH值接近中性的研究体系证明了咪唑是以中性咪唑分子的形式存在;低波数区N—Ni伸缩振动峰(214 cm-1)的出现进一步验证了咪唑通过N原子与镍电极表面略带倾斜的吸附方式。     

Twisting DNA: single molecule studies

Over the past 10 years a number of new techniques have emerged that allow the manipulation of single DNA molecules and other biopolymers (RNA, proteins, etc.). These experiments have permitted the measurement of the DNA stretching and twisting elasticity and have consequently revealed the essential role played by the DNA mechanical properties in its interactions with proteins. We shall first describe the different methods used to stretch and twist single DNA molecules. We will then focus on its behaviour under torsion, especially by discussing the different methods used to estimate its torsional modulus.     

一种改进型单分子操纵装置及其应用

改进了单分子横向磁镊装置,可以直接用于观察单个DNA分子的伸长和扭转并随时更换样品池内的溶液,还可以同时操纵多个DNA分子,大大提高实验效率.此方法可以提供01到40pN范围的拉力,足以满足大部分单分子DNA实验的要求.用该装置实时观测到了DNA分子在拉力作用下的伸长以及在旋转磁场作用下的扭转,并成功地观察到了分子马达拉动DNA的动力学过程,从而验证了该装置的实用性. 关键词： 横向磁镊 单分子操纵 DNA拉伸 DNA扭转     

Adsorption dynamics of double-stranded DNA on a graphene oxide surface with both large unoxidized and oxidized regions

The adsorption dynamics of double-stranded DNA (dsDNA) molecules on a graphene oxide (GO) surface are important for applications of DNA/GO functional structures in biosensors, biomedicine and materials science. In this work, molecular dynamics simulations were used to examine the adsorption of different length dsDNA molecules (from 4 bp to 24 bp) on the GO surface. The dsDNA molecules could be adsorbed on the GO surface through the terminal bases and stand on the GO surface. For short dsDNA (4 bp) molecules, the double-helix structure was partially or totally broken and the adsorption dynamics was affected by the structural fluctuation of short dsDNA and the distribution of the oxidized groups on the GO surface. For long dsDNA molecules (from 8 bp to 24 bp) adsorption is stable. By nonlinear fitting of the contact angle between the axis of the dsDNA molecule and the GO surface, we found that a dsDNA molecule adsorbed on a GO surface has the chance of orienting parallel to the GO surface if the length of the dsDNA molecule is longer than 54 bp. We attributed this behavior to the flexibility of dsDNA molecules. With increasing length, the flexibility of dsDNA molecules also increases, and this increasing flexibility gives an adsorbed dsDNA molecule more chance of reaching the GO surface with the free terminal. This work provides a whole picture of adsorption of dsDNA molecules on the GO surface and should be of benefit for the design of DNA/GO based biosensors.     

Electrophoretic collision of a DNA molecule with an insulating post

We study the dynamics of single DNA molecules driven by an electric field into a stationary obstacle. These collisions are broadly classified as "hook" and "roll-off" events. We show that obstacle-induced electric field gradients stretch impacting DNA and thus greatly influence the hooking probability. Consequently, in addition to collision geometry, determination of the hooking probability depends on the Deborah number (De) for 0.5相似文献   

Surface-enhanced Raman scattering of λ -DNA

By using the molecular combing method, we stretched DNA molecules with colloidal silver nanoparticles adsorbed on them. Surface-enhanced Raman scattering (SERS) spectra were recorded in this particular DNA/Ag system. We also studied SERS spectra of DNA molecules in solution. The spectra of DNA in different concentration solution show distinct differences, and we speculate that the coiling states of DNA molecules are different in different concentrations, leading to the spectral differences. PACS 33.20.Fb; 42.62.Fi; 78.67.-n; 73.20.Mf; 87.64.-t     

Controlled assembly of DNA nanostructures on silanized silicon and mica surfaces for future molecular devices

In order to establish key technology for future molecular devices, we have explored the assembly behaviour of λ-deoxyribonucleic acid (DNA) molecules adsorbed on silanized mica and silanized oxide silicon surfaces by using atomic force microscopy (AFM). AFM experiments show that λ-DNA molecules can be hardly adsorbed on untreated mica and oxidized silicon surfaces, but can be strongly adsorbed onto aminosilanized mica and oxidized silicon surfaces. Importantly, DNA molecules can be assembled into linear DNA alignment, and can also self-assemble into various network structures on the silanized surfaces. Our experimental observations have demonstrated the feasibility of assembling DNA-based nanostructures by varying surface chemistry of substrates, and offer useful clues in constructing DNA-based nanodevices for nanoelectronics and biomolecular computation as well as quantum computation.     

DNA Intercalation in Neutral Multilamellar Membranes: Experiments and Theory

We report both an experimental and a theoretical work on the effect of confinement on a biological polymer (DNA) incorporated to multilamellar phase. We can see that even when no electrostatic interaction are involved this semi-flexible polymer can be incorporated in between the membranes. X-ray provides experimental evidence for the existence of a mixed DNA/Phospholipid structure. The nature of the DNA ordering is briefly described. A theoretical model is developed to describe the phase diagram. We emphasize the role of the isotropic/nematic transition of the DNA molecules to explain the ability to confine DNA in membranes.     

Frequency shifts in the spectra of molecules adsorbed on metals,with emphasis on the infrared spectrum of adsorbed CO

Two processes are considered which cause the frequency of the band maximum in the infrared absorption spectrum of molecules adsorbed on metals to shift with increasing coverage. The first arises from the coverage-dependent modification of the local field acting on an adsorbed molecule while the second originates from vibrational coupling arising from a through-metal interaction between molecules adsorbed on different metal atoms. Infrared absorption strengths are discussed and the method used heretofore to obtain the extinction coefficients of adsorbed molecules is questioned. In particular, a factor of 2 which results from the constructive superposition of the incident and reflected electric fields is shown to be often ignored. We show that dipolar (through-space) coupling is too weak to account for the magnitudes of the shifts recently observed for CO on single-crystal Pt and Pd as coverage progressed from low to high values. Vibrational coupling is also shown to account for the disparity in the intensities of the two bands observed when ¹²CO and ¹³CO are coadsorbed on supported metals. Similar experiments on single-crystal surfaces are suggested to help determine to what extent the observed spectral frequency shifts are derived from adsorbate—adsorbate coupling as opposed to other mechanisms.     

Adhesion-induced lateral phase separation in membranes

Adhesion between membranes is studied using a phenomenological model, where the inter-membrane distance is coupled to the concentration of sticker molecules on the membranes. The model applies to both adhesion of two flexible membranes and to adhesion of one flexible membrane onto a second membrane supported on a solid substrate. We mainly consider the case where the sticker molecules form bridges and adhere directly to both membranes. The calculated mean-field phase diagrams show an upward shift of the transition temperature indicating that the lateral phase separation in the membrane is enhanced due to the coupling effect. Hence the possibility of adhesion-induced lateral phase separation is predicted. For a particular choice of the parameters, the model exhibits a tricritical behavior. We also discuss the non-monotonous shape of the inter-membrane distance occurring when the lateral phase separation takes place. The inter-membrane distance relaxes to the bulk values with two symmetric overshoots. Adhesion mediated by other types of stickers is also considered. Received 12 January 2000 and Received in final form 15 May 2000     

Absence of dc-conductivity in lambda-DNA

The electrical conductivity of biomaterials on a molecular scale is of fundamental interest in the life sciences. We perform first principles electronic structure calculations, which clearly indicate that lambda-DNA chains should present large resistance values. We also present two direct procedures to measure electrical currents through DNA molecules adsorbed on mica. The lower limit for the resistivity is 10(6) Omega . cm, in agreement with our calculations. We also show that low energy electron bombardment induces a rapid contamination and dramatically affects the measured conductivity, thus providing an explanation to recent reports of high DNA conductivity.     

Chemical reactions of water molecules on Ru(0 0 0 1) induced by selective excitation of vibrational modes

Tunneling electrons in a scanning tunneling microscope were used to excite specific vibrational quantum states of adsorbed water and hydroxyl molecules on a Ru(0 0 0 1) surface. The excited molecules relaxed by transfer of energy to lower energy modes, resulting in diffusion, dissociation, desorption, and surface-tip transfer processes. Diffusion of H₂O molecules could be induced by excitation of the O-H stretch vibration mode at 445 meV. Isolated molecules required excitation of one single quantum while molecules bonded to a C atom required at least two quanta. Dissociation of single H₂O molecules into H and OH required electron energies of 1 eV or higher while dissociation of OH required at least 2 eV electrons. In contrast, water molecules forming part of a cluster could be dissociated with electron energies of 0.5 eV.     

The adsorption of CO on transition metal clusters: A case study of cluster surface chemistry

We present a discussion of recent experimental studies on the interaction of single CO molecules with transition metal clusters in the gas-phase, typically in the size range of 3 to more than 20 atoms, emphasizing specifically the insights gained from vibrational spectroscopy. Trends across the transition metals (TM) for molecular vs. dissociative chemisorption as well as for adsorption geometries are discussed and compared with the behaviour of CO adsorbed on extended surfaces. The dependence of the frequency of the internal CO stretch vibration on the size and charge of the cluster enables one to gauge quantitatively the effects of charge transfer between deposited nanoparticles and the substrate as well as of electron transfer due to the binding of co-adsorbed species.     

Adhesion of giant unilamellar vesicles on double-end grafted DNA carpets

We have recently shown that the bio-mimetic adhesion of Giant Unilamellar Vesicles on carpets of lambda-phage DNAs, grafted by one end to the substrate, leads to DNA scraping and stapling. As the lipid adhesion patch is built, outward forces stretch the DNA, while adhesion patch formation staples the chains into frozen conformations, trapped between the GUV membrane and the substrate. Analysis of the scraped and stapled DNA conformations provides a wealth of information about the membrane/polymer interactions at play during the formation of a bio-adhesive contact zone. In this paper we report new phenomena revealed by scraping and stapling phenomena associated with the bio-mimetic adhesion of Giant Unilamellar Vesicles on carpets of lambda-phage DNAs that were grafted to the substrate by both ends. In particular, the peculiar shapes of stapled DNA observed in this case, suggest that the membrane exerces not only outward radial forces during patch formation, but is is also able to confine the DNA molecules in the orthoradial direction.     

Adsorbate interactions and surface excess entropy

Using the Gibbs definition of surface excess properties and classical statistics of the adsorbed molecules, it is shown that interactions between these molecules can in some cases increase the surface excess entropy. This is in contradistinction to the classical result for a field-free bulk phase gas, but similar to effects which are possible for quantum gases.Research supported by National Science Foundation Grant No. GP33535X.     

Ag(110)表面吸附酞菁铜分子的紫外光电子谱研究

用紫外光电子能谱(UPS)研究了酞菁铜分子在Ag(110)单晶表面上的吸附,随着酞菁铜分子覆盖度增加,衬底Ag的3d电子信号逐渐减弱,在此能带区域出现两个新的谱峰,这两个与吸附有机分子轨道有关的谱峰的束缚能分别为4.45 和6.36 eV.随着覆盖度的增加,在结合能为1.51和9.20 eV处又出现了两个谱峰,它们同样来自吸附有机分子的轨道.随着覆盖度的继续增加,上述四个谱峰的强度逐渐增加,其能量位置均发生了明显的偏移.根据角分辨光电子能谱的实验结果,酞菁铜分子的分子平面基本与衬底表面平行.密度泛函理论计 关键词： 酞菁铜 紫外光电子谱 吸附电子态 密度泛函理论     

金属和半导体表面吸附分子的荧光猝灭

本文提出了分子吸附于金属或半导体表面呈现荧光猝灭现象的新的理论解释,认为荧光猝灭现象是由于处于激发态的吸附分子和等离子体振荡之间能量迁移的结果。文中并提出了“受迫等离激元”概念。     

带电多孔二氧化硅纳米颗粒在硫醇/磷脂混合双层膜上的非特异性吸附

制备了表面带阴/阳离子的多孔二氧化硅纳米颗粒, 通过QCM-D研究了颗粒在不同pH值环境下与磷脂膜的非特异性吸附情况. 结果表明, NH₂-MSN 在4–8的pH值范围内与磷脂膜相互吸引, 而COOH-MSN由于与磷脂膜的电性始终保持一致而无法发生吸附现象. 本研究能够帮助理解和预测纳米颗粒与细胞膜间的相互作用, 为药物输运提供载体, 有助于多孔二氧化硅纳米颗粒在药物输运体系中的应用. 关键词： 多孔二氧化硅纳米颗粒 磷脂膜 非特异性吸附 QCM-D     

拉直的单个DNA分子的全内反射荧光实时成像研究

全内反射荧光(TIRF)成像技术利用穿透深度仅200 nm左右的隐失波来激发诱导荧光,探测灵敏度和图像信噪比大大提高,成为单分子研究的有力工具。分子梳技术利用DNA末端与固体表面的结合力和周围流体流动产生的侧向力将DNA分子拉伸并平铺在表面上。结合这两种技术,对分子梳拉直的单个DNA分子进行了清晰的实时荧光成像,发现TIRF成像条件下DNA分子与荧光探针YOYO-1组成的复合体可自然避免发生光敏断裂现象;实时监测了单个DNA-YOYO-1复合体的光漂白过程,通过对激发光照射时间与探测器曝光时间进行同步控制,可大幅降低光漂白程度,为拉直的单个DNA分子的长时间实时观察和成像研究优化了实验条件,为实时、可视化地研究其与蛋白质相互作用的动力学过程奠定了基础。