Synchrotron X-ray techniques for the investigation of structures and dynamics in interfacial systems

This review focuses on recent results obtained by synchrotron X-ray techniques applied to the characterization of interfacial systems, with main emphasis on flat interfaces and on colloidal systems. The techniques covered are, for structural determinations: X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and grazing incidence X-ray excited fluorescence (GIXF), while dynamics are investigated by X-ray photon correlation spectroscopy (XPCS) mainly in the grazing-incidence geometry (GIXPCS).The systems reviewed are, in order of growing complexity, floating Langmuir monolayers, supported films of lipids and proteins, polymeric films, buried interfaces, colloidal systems and gels formed by colloids either in 3D or in the form of 2D interfacial layers. Recent results are critically discussed, and some interesting directions of development are outlined, having also in mind new technical developments such as X-ray free electron laser sources and micro-focused synchrotron beamlines.     

Gel formation and aging in weakly attractive nanocolloid suspensions at intermediate concentrations

We report x-ray photon correlation spectroscopy (XPCS) and rheometry experiments to study the temporal evolution of gel formation and aging in suspensions of silica nanocolloids possessing a tunable short-range attraction. The colloid volume fractions, φ = 0.20 and 0.43, are below the glass regime at high concentration and above the fractal regime at low concentration. Following a sudden initiation of the interparticle attraction, the suspensions display a protracted latency period in which they remain fluid before acquiring a measurable elastic shear modulus. The duration of the latency period and the subsequent rate of increase of the modulus vary strongly with the strength of the attraction. The XPCS results indicate dynamic heterogeneity among the colloids during this gel formation in which a growing fraction of the particles become localized. The temporal evolution of this localization correlates with that of the rheology. In particular, the time scale over which the fraction of localized particles increases tracks the duration of the latency period. Also, at φ = 0.20 the localization length characterizing the motion of the localized fraction scales onto the shear modulus with no free parameters as predicted by a self-consistent theory based on mode coupling [K. S. Schweizer and G. Yatsenko, J. Chem. Phys. 127, 164505 (2007)], while deviations from the predicted scaling at φ = 0.43 are observed near the gel point. The XPCS results also reveal slow, hyperdiffusive motion of the colloids in the newly formed gels that is attributed to strain from the relaxation of internal stress. While some features of this motion correlate with the evolving rheology, others appear decoupled from the macroscopic mechanical behavior.     

Transmission Electron Microscopy as a Powerful Tool for Investigating Lithium-ion Battery Materials

Transmission electron microscopy(TEM) stands out as one of the most powerful tools for characterizing materials at multiple scales and dimensions. This unique technique has nowadays been widely employed in investigating the lithium-ion battery(LIB) materials. The present perspective paper focuses on several LIB related aspects that are recently revealed by using TEM. Finally, we present outlook on the future directions of TEM for LIB research and development.     

Dynamics of colloidal particles in ice

We use x-ray photon correlation spectroscopy (XPCS) to probe the dynamics of colloidal particles in polycrystalline ice. During freezing, the dendritic ice morphology and rejection of particles from the ice created regions of high particle density, where some of the colloids were forced into contact and formed disordered aggregates. The particles in these high density regions underwent ballistic motion, with a characteristic velocity that increased with temperature. This ballistic motion is coupled with both stretched and compressed exponential decays of the intensity autocorrelation function. We suggest that this behavior could result from ice grain boundary migration.     

表面增强拉曼光谱:应用和发展

表面增强拉曼光谱技术(Surface-enhanced Raman spectroscopy,SERS)是一种具有超高灵敏度的指纹光谱技术,目前已广泛应用于表面科学、材料科学、生物医学、药物分析、食品安全、环境检测等领域,是一种极具潜力的痕量分析技术。 本文对SERS技术及相关的针尖增强拉曼光谱(Tip-enhanced Raman spectroscopy,TERS),壳层隔绝纳米粒子增强拉曼光谱(Shell-isolated nanoparticle-enhanced Raman spectroscopy,SHINERS)技术的发展及应用进行了综合评述,并探讨了其未来的研究热点及发展方向。     

In situ monitoring of metal nanoparticle self-assembly on protein-functionalized glass by broadband optical waveguide spectroscopy

Broadband, time-resolved optical waveguide (OWG) spectroscopy has been used for in situ, real-time investigation into the self-assembly of metal nanoparticle monolayers. The OWG spectroscopy makes it possible to use the transverse electric (TE) and transverse magnetic (TM) modes to measure surface plasmon absorption of immobilized metal nanoparticles in two directions, parallel and normal to the waveguide surface. Therefore, this technique can provide direction-dependent information on the metal nanoparticles at the interface. In this paper, a 50-microm-thick glass plate was used as a slab waveguide and the kinetics of Au nanoparticle adsorption on a hemoglobin-functionalized glass substrate was examined in the early stage of self-assembly. The findings show that with the TE mode the surface plasmon resonance (SPR) behavior for immobilized Au nanoparticles is different from that with the TM mode.     

Electromembrane extraction—Three‐phase electrophoresis for future preparative applications

The purpose of this article is to discuss the principle and the future potential for electromembrane extraction (EME). EME was presented in 2006 as a totally new sample preparation technique for ionized target analytes, based on electrokinetic migration across a supported liquid membrane under the influence of an external electrical field. The principle of EME is presented, and typical performance data for EME are discussed. Most work with EME up to date has been performed with low‐molecular weight pharmaceutical substances as model analytes, but the principles of EME should be developed in other directions in the future to fully explore the potential. Recent research in new directions is critically reviewed, with focus on extraction of different types of chemical and biochemical substances, new separation possibilities, new approaches, and challenges related to mass transfer and background current. The intention of this critical review is to give a flavor of EME and to stimulate into more research in the area of EME. Unlike other review articles, the current one is less comprehensive, but put more emphasis on new directions for EME.     

Mechanical anisotropy in biaxially oriented polyvinyl chloride

The mechanical anisotropy of polyvinyl chloride oriented in two perpendicular directions with different draw ratios has been studied. The results are compared with the anisotropy of uniaxial samples oriented at a common draw ratio. The propagation velocities of ultrasonic pulses have been measured by an immersion technique. Longitudinal wave velocities have been measured in three principal planes over a wide range of propagation directions. The limitations of measuring velocities in the planes containing the draw axes were mitigated by use of a special slicing technique. Measurements were performed at 2 MH_z and 25°C. Velocities of the transverse waves were measured for incident wave angles greater than the critical angle. From these measurements, five elastic moduli were calculated for the uniaxially oriented samples, and nine elastic moduli were obtained for the biaxially oriented samples. In biaxially oriented samples, the moduli along the draw axes are directly proportional to the draw ratio in the same direction.     

太赫兹时域光谱技术在化学领域中应用的新进展

随着超快激光技术的发展及其人们对太赫兹(THz)电磁波波段及与脉冲光源认识的进一步深入,太赫兹时域光谱(THz-TDS)技术作为一种新的、快速发展的光谱分析方法在许多领域备受关注。尤其在化学领域,THz-TDS技术已得到了广泛的应用,并显示出了广阔的应用前景。本文介绍了THz技术的特点、THz辐射的产生、探测及其信号处理;讨论了该技术在化学及其相关领域中的应用;初步探讨了该技术在化学领域应用中一些亟待解决的问题及今后发展的方向。     

The use of radionuclides for the study of crystal structure of solids

It is well known that by the coordinated action of atoms arranged in rows and planes in the crystal lattice, the motion of charged particles such as protons, alpha particles and heavier ions can be influenced so that their range in the single crystals is considerably enhanced in low-index directions. A technique has been developed based on such enhanced penetration (channeling) of radioactive atoms (²²⁰Rn) emitted by recoil with a 100 keV energy from a²²⁴Ra point source to record channeling patterns which show the crystal structure. The radioactive recoil atoms impinging from this source on the surface of a single crystal penetrate deeper in places where their direction of impact is identical with low index crystal directions and planes. These places can be visualized by autoradiography when having first stripped a thin layer from the surface corresponding to the random range of the atoms. This technique is generally applicable in close packed crystals and gives information about the crystal structure of very thin surface layers.     

Measurement of anisotropic refractive indices of free-standing polymer film

A new technique has been developed to measure the optical refractive indices in the parallel and perpendicular directions to the film surfaces and applied to measure the refractive indices of free-standing polymer films. The refractive indices were obtained by measuring the reflectivity as a function of the incident angle. The angle dependence of the reflectivity which results from the interference of the light beam reflected from the front and rear interfaces of the film was analysed by means of the Fresnel equation. This technique can be used to measure the refractive indices in three major axes, i.e. one out-of plane axis and two in-plane axes of the sample. This technique gives values for the refractive indices and the thickness simultaneously with an accuracy comparable to that measured by optical wave-guide technique. The validity of the technique has been tested with polymer films of known refractive indices such as poly(methyl methacrylate) and polyimide (PMDA-ODA).     

联用技术在生物体系化合物分析中的应用进展

介绍了目前分离分析生物体系化合物的一般步骤和注意事项.综述了联用技术在生物体系化合物分析中的应用进展情况.展望了联用技术在生物体系化合物分析中的发展方向和应用前景.     

New trends in the electrochemical sensing of dopamine

Since the early 70s electrochemistry has been used as a powerful analytical technique for monitoring electroactive species in living organisms. In particular, after extremely rapid evolution of new micro and nanotechnology it has been established as an invaluable technique ranging from experiments in vivo to measurement of exocytosis during communication between cells under in vitro conditions. This review highlights recent advances in the development of electrochemical sensors for selective sensing of one of the most important neurotransmitters—dopamine. Dopamine is an electroactive catecholamine neurotransmitter, abundant in the mammalian central nervous system, affecting both cognitive and behavioral functions of living organisms. We have not attempted to cover a large time-span nor to be comprehensive in presenting the vast literature devoted to electrochemical dopamine sensing. Instead, we have focused on the last five years, describing recent progress as well as showing some problems and directions for future development.     

Trennung von Kationen auf einem Filterpapierstreifen

Zusammenfassung Für die Trennung mehrerer, in einem Tropfen gelöster Kationen auf einem Filterpapierstreifen wurde ein Gerät entwickelt. Das der Ringofentechnik grundsätzlich ähnliche Verfahren bietet den Vorteil, daß die Gemischkomponenten nach zwei Richtungen ausgewaschen und auf einer sehr kleinen Fläche konzentriert und nachgewiesen werden können.

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Separation of cations on a strip of filter paper

Summary A device has been developed for the separation on a strip of filter paper of several cations that are present in a single drop. The procedure, that fundamentally resembles the ring furnace technique, offers the advantage that the components of the mixture can be washed out in two directions and concentrated on a very small area and detected.

     

A robust partial least squares regression method with applications

Partial least squares (PLS) regression is a linear regression technique developed to relate many regressors to one or several response variables. Robust methods are introduced to reduce or remove the effect of outlying data points. In this paper, we show that if the sample covariance matrix is properly robustified further robustification of the linear regression steps of the PLS algorithm becomes unnecessary. The robust estimate of the covariance matrix is computed by searching for outliers in univariate projections of the data on a combination of random directions (Stahel—Donoho) and specific directions obtained by maximizing and minimizing the kurtosis coefficient of the projected data, as proposed by Peña and Prieto [1]. It is shown that this procedure is fast to apply and provides better results than other methods proposed in the literature. Its performance is illustrated by Monte Carlo and by an example, where the algorithm is able to show features of the data which were undetected by previous methods. Copyright © 2008 John Wiley & Sons, Ltd.     

钻石对顶砧(Diamond Anvil Cell,DAC)高压产生技术及在高压条件下的光物理和光化学研究

高压作为一个重要的物理参量引入到科学研究的各个领域将会大大扩展研究的范围.本文介绍了一种简单安全的产生高压的技术和在高压条件下进行的一些光物理和光化学研究工作,并指出了今后在高压光物理和光化学研究领域的若干重要研究方向.     

分子印迹技术在蛋白质识别中的应用进展

分子印迹技术是一种制备具有分子识别能力的聚合物的有效技术,已经广泛应用于制备对小分子具有选择性的分子印迹聚合物,但制备能够特异性识别生物大分子--蛋白质的分子印迹聚合物的研究仍然具有挑战性。本文讨论了制备蛋白质分子印迹聚合物的难点,评述了目前印迹蛋白质的方法及各自的优缺点,展望了蛋白质印迹技术的发展趋势。     

The potential of mid infrared spectroscopy (MIRS) for real time bioprocess monitoring

The need for effective bioprocess (fermentation) monitoring is growing in importance due to the rapid pace of change in the fermentation industry, and attendant financial pressures. Vibrational spectroscopy has shown great promise in bioprocess monitoring. In particular, recently attention has been focused on the capability of mid infrared spectroscopy (MIRS) to monitor multiple analytes in highly complex fermentation fluids. The potential of this powerful analytical technique is critically evaluated by discussion of relevant studies. The advantages and limitations of MIR are discussed in the context of “rival” technologies, such as near infrared, focusing especially on employing such techniques in bioprocesses for real time (either in situ or ex situ) measurements. The potential barriers to the development of MIRS for real time monitoring are identified and further research directions highlighted.     

Extracting maximum information from polarized surface vibrational spectra: application to etched, H-terminated Si(110) surfaces

A general method to maximize the information extracted from polarized surface absorption spectra is developed and applied to the study of etched Si(110) surfaces. In essence, this technique transforms spectra from the experimental reference frame, which is defined by the direction of the surface electric field during irradiation by s- and p-polarized light, into a more appropriate Cartesian reference frame defined by the surface normal and the plane of incidence. If the Cartesian reference frame is aligned with high symmetry directions of the system, significant spectral simplification can result. This analysis relies on the well-known boundary conditions on interfacial electric fields and is independent of any adsorbate screening or the effective dielectric constant of the adsorbate layer. The validity of this analysis is demonstrated on the spectra of NH4F-etched, H-terminated Si(110). The transition dipole moments of the symmetric and antisymmetric Si[Single Bond]H stretch modes associated with flat terraces are polarized along the [110] and [001] directions, respectively. Two additional modes with transition dipoles polarized along the [001] and [110] directions are assigned to defect species associated with microfaceting and other surface roughness. Data taken in two different experimental geometries are shown to be in excellent quantitative agreement, confirming the validity of the technique. Additionally, the measured adsorbate layer dielectric constant is in good agreement with previously reported values for hydrogen-terminated silicon surfaces.     

X-Ray Crystallography as a Tool to Determine Three-Dimensional Structures of Commercial Enzymes Subjected to Treatment in Pressurized Fluids

The study of enzyme function often involves a multi-disciplinary approach. Several techniques are documented in the literature towards determining secondary and tertiary structures of enzymes, and X-ray crystallography is the most explored technique for obtaining three-dimensional structures of proteins. Knowledge of three-dimensional structures is essential to understand reaction mechanisms at the atomic level. Additionally, structures can be used to modulate or improve functional activity of enzymes by the production of small molecules that act as substrates/cofactors or by engineering selected mutants with enhanced biological activity. This paper presentes a short overview on how to streamline sample preparation for crystallographic studies of treated enzymes. We additionally revise recent developments on the effects of pressurized fluid treatment on activity and stability of commercial enzymes. Future directions and perspectives on the the role of crystallography as a tool to access the molecular mechanisms underlying enzymatic activity modulation upon treatment in pressurized fluids are also addressed.