Brownian and advective dynamics in microflow studied by coherent X‐ray scattering experiments

Combining microfluidics with coherent X‐ray illumination offers the possibility to not only measure the structure but also the dynamics of flowing samples in a single‐scattering experiment. Here, the power of this combination is demonstrated by studying the advective and Brownian dynamics of colloidal suspensions in microflow of different geometries. Using an experimental setup with a fast two‐dimensional detector and performing X‐ray correlation spectroscopy by calculating two‐dimensional maps of the intensity auto‐correlation functions, it was possible to evaluate the sample structure and furthermore to characterize the detailed flow behavior, including flow geometry, main flow directions, advective flow velocities and diffusive dynamics. By scanning a microfocused X‐ray beam over a microfluidic device, the anisotropic auto‐correlation functions of driven colloidal suspensions in straight, curved and constricted microchannels were mapped with the spatial resolution of the X‐ray beam. This method has not only a huge potential for studying flow patterns in complex fluids but also to generally characterize anisotropic dynamics in materials.     

Reaction between alkyl isocyanides and isopropylidene Meldrum’s acid in the presence of bidentate nucleophiles

Summary The reaction between alkyl isocyanides and isopropylidene Meldrum’s acid in the presence of 1,2-ethanediol leads to N ¹-(alkyl)-2-(5,7-dioxo-1,4-dioxepane-6-yl)-2-methylpropanamides. 1,3-Propanediol or 1,4-butanediol produce hydroxyalkyl 1-(tert-butyl)-4,4-dimethyl-2,5-dioxo-3-pyrrolidinecarboxylates. When the reaction was performed in the presence of catechol, bis(2-hydroxyphenyl) 2-[2-(tert-butylamino)-1,1-dimethyl-2-oxoethyl]malonate was obtained. 2-Aminophenols react with alkyl isocyanides in the presence of isopropylidene Meldrum’s acid to produce 1-alkyl-N ³-(2-hydroxyaryl)-4,4-dimethyl-2,5-dioxo-3-pyrrolidinecarboxamides in good yields.     

Local structure of amorphous tellurium studied by EXAFS

The local structure of an amorphous tellurium (a‐Te) film was investigated by extended X‐ray absorption fine‐structure analysis. The covalent bond length shortens and the Debye–Waller factor of the intra‐chain decreases in a‐Te compared with trigonal Te (t‐Te). The value of the intra‐chain coordination number is close to two, which is the value for t‐Te, and the inter‐chain interaction weakens. These results suggest that the primary chain structure remains intact, but the secondary structure is disrupted. The decrease in the inter‐chain interaction strengthens the intra‐chain interaction.     

Tracking extended mucociliary transport activity of individual deposited particles: longitudinal synchrotron X‐ray imaging in live mice

To assess potential therapies for respiratory diseases in which mucociliary transit (MCT) is impaired, such as cystic fibrosis and primary ciliary dyskinesia, a novel and non‐invasive MCT quantification method has been developed in which the transit rate and behaviour of individual micrometre‐sized deposited particles are measured in live mice using synchrotron phase‐contrast X‐ray imaging. Particle clearance by MCT is known to be a two‐phase process that occurs over a period of minutes to days. Previous studies have assessed MCT in the fast‐clearance phase, ～20 min after marker particle dosing. The aim of this study was to non‐invasively image changes in particle presence and MCT during the slow‐clearance phase, and simultaneously determine whether repeat synchrotron X‐ray imaging of mice was feasible over periods of 3, 9 and 25 h. All mice tolerated the repeat imaging procedure with no adverse effects. Quantitative image analysis revealed that the particle MCT rate and the number of particles present in the airway both decreased with time. This study successfully demonstrated for the first time that longitudinal synchrotron X‐ray imaging studies are possible in live small animals, provided appropriate animal handling techniques are used and care is taken to reduce the delivered radiation dose.     

Temperature dependence of the Ho L2‐edge XMCD spectra of Ho6Fe23

An X‐ray magnetic circular dichroism (XMCD) study performed at the Ho L_2,3‐edges in Ho₆Fe₂₃ as a function of temperature is presented. It is demonstrated that the anomalous temperature dependence of the Ho L₂‐edge XMCD signal is due to the magnetic contribution of Fe atoms. By contrast, the Ho L₃‐edge XMCD directly reflects the temperature dependence of the Ho magnetic moment. By combining the XMCD at both Ho L₂‐ and L₃‐edges, the possibility of determining the temperature dependence of the Fe magnetic moment is demonstrated. Then, both μ_Ho(T) and μ_Fe(T) have been determined by tuning only the absorption L‐edges of Ho. This result opens new possibilities of applying XMCD at these absorption edges to obtain quantitative element‐specific magnetic information that is not directly obtained by other experimental tools.     

2-(3’,4’-二羧基苯氧基)苯甲酸配体桥联的锌(Ⅱ)配合物的合成、结构及荧光性质

以2-(3’,4’-二羧基苯氧基)苯甲酸(H3DPBA)和1,3-二(4-吡啶基)-丙烷(bpp)为配体,与Zn(Ac)2通过水热反应,获得了一维链状配合物Zn(DPBA)(bpp)。该配合物的一个不对称单元包括一个Zn(Ⅱ)离子,一个DPBA配体和一个bpp配体。Zn(Ⅱ)离子与四个氧原子及一个氮原子配位,其配位数为5。固态配合物在375nm处出现强的发射峰,来自于配体的π~*—π跃迁。与配体的荧光发射光谱比较,配合物的荧光发射峰发生了蓝移,而且配合物的荧光发射强度有大幅度增强。讨论了配合物在常见溶剂中和金属阳离子中的荧光性质。实验结果表明不同有机小分子或不同金属阳离子对配合物的荧光强度有不同程度的影响,有机小分子硝基苯和Fe~(3+)使配合物荧光猝灭,该Zn(Ⅱ)-配合物可用于硝基苯的检测以及水和乙醇体系中Fe~(3+)的检测。     

Simulations of Co‐GISAXS during kinetic roughening of growth surfaces

The recent development of surface growth studies using X‐ray photon correlation spectroscopy in a grazing‐incidence small‐angle X‐ray scattering (Co‐GISAXS) geometry enables the investigation of dynamical processes during kinetic roughening in greater detail than was previously possible. In order to investigate the Co‐GISAXS behavior expected from existing growth models, calculations and (2+1)‐dimension simulations of linear Kuramoto–Sivashinsky and non‐linear Kardar–Parisi–Zhang surface growth equations are presented which analyze the temporal correlation functions of the height–height structure factor. Calculations of the GISAXS intensity auto‐correlation functions are also performed within the Born/distorted‐wave Born approximation for comparison with the scaling behavior of the height–height structure factor and its correlation functions.     

Stereochemical analysis of ferrocene and the uncertainty of fluorescence XAFS data

Methods for the quantification of statistically valid measures of the uncertainties associated with X‐ray absorption fine structure (XAFS) data obtained from dilute solutions using fluorescence measurements are developed. Experimental data obtained from 10 mM solutions of the organometallic compound ferrocene, Fe(C₅H₅)₂, are analysed within this framework and, following correction for various electronic and geometrical factors, give robust estimates of the standard errors of the individual measurements. The reliability of the refinement statistics of standard current XAFS structure approaches that do not include propagation of experimental uncertainties to assess subtle structural distortions is assessed in terms of refinements obtained for the staggered and eclipsed conformations of the C₅H₅ rings of ferrocene. Standard approaches (XFIT, IFEFFIT) give refinement statistics that appear to show strong, but opposite, preferences for the different conformations. Incorporation of experimental uncertainties into an IFEFFIT‐like analysis yield refinement statistics for the staggered and eclipsed forms of ferrocene which show a far more realistic preference for the eclipsed form which accurately reflects the reliability of the analysis. Moreover, the more strongly founded estimates of the refined parameter uncertainties allow more direct comparison with those obtained by other techniques. These XAFS‐based estimates of the bond distances have accuracies comparable with those obtained using single‐crystal diffraction techniques and are superior in terms of their use in comparisons of experimental and computed structures.     

Simple dose rate measurements for a very high synchrotron X‐ray flux

Dose measurements based on methylene blue (MB) bleaching, widely used for ultraviolet light, can also be applied to X‐rays including very high flux levels. This method has been tested by using both MB bleaching and Fricke dosimetry for a conventional monochromatic X‐ray source and then for `white‐beam' synchrotron radiation. The results show that MB bleaching dosimetry can easily measure X‐ray doses up to at least 10⁵ Gy s^?1, as long as the MB concentration is sufficiently high. This condition can be verified from the deviations from linearity of the bleaching versus exposure time.