Molecular structure and fracture properties of ZrO<Subscript>X</Subscript>/Epoxysilane hybrid films

The mechanical reliability of hybrid films depends critically on their fracture properties which are controlled largely by the film composition and molecular structure. We have investigated the adhesive and cohesive fracture properties of hybrid films processed from 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetra n-propoxyzirconium (TPOZ), for which the roles of molecular structure and composition have not been well established. The influences of film Zr/GPTMS ratio, silane crosslinking, and substrate composition on fracture resistance were quantified in terms of the critical strain energy release rate, G_C Film fracture energy was found to increase, then decrease with increasing Zr/GPTMS ratio. Removal of the epoxy rings of GPTMS from the film was found to drastically decrease the cohesive fracture energy of the film as well as the adhesive fracture energy of the film/epoxy interface. Finally, films deposited on silicon had much higher fracture energies compared to those deposited onto aluminum and titanium from identical sols. FTIR, XPS, and AFM were used to characterize the film structure and fracture surfaces. The molecular-scale mechanisms responsible for the observed trends are discussed. These results provide new insights into the interaction between the substrate chemistry, molecular structure, and mechanical reliability of hybrid sol-gel films.     

Cross‐Reactive Sensor Arrays for the Detection of Peptides in Aqueous Solution by Fluorescence Spectroscopy

A simple but powerful method for the sensing of peptides in aqueous solution has been developed. The transition‐metal complexes [PdCl₂(en)], [{RhCl₂Cp*}₂], and [{RuCl₂(p‐cymene)}₂] were combined with six different fluorescent dyes to build a cross‐reactive sensor array. The fluorescence response of the individual sensor units was based on competitive complexation reactions between the peptide analytes and the fluorescent dyes. The collective response of the sensor array in a time‐resolved fashion was used as an input for multivariate analyses. A sensor array comprised of only six metal–dye combinations was able to differentiate ten different dipeptides in buffered aqueous solution at a concentration of 50 μM . Furthermore, the cross‐reactive sensor could be used to obtain information about the identity and the quantity of the pharmacologically interesting dipeptides carnosine and homocarnosine in a complex biological matrix, such as deproteinized human blood serum. The sensor array was also able to sense longer peptides, which was demonstrated by differentiating mixtures of the nonapeptide bradykinin and the decapeptide kallidin.     

Detecting the "afterglow" of 13C NMR in proteins using multiple receivers

We show that the weak signal that remains after (13)C-detected experiments (the (13)C "afterglow") can still be measured with high sensitivity by proton detection. This is illustrated by the incorporation of two experiments, 2D (HA)CACO and 3D (HA)CA(CO)NNH, into a single pulse sequence that makes use of two receivers in parallel. In cases where the sensitivity is not limiting, such as applications to small proteins, the inclusion of the projection-reconstruction method permits the recording of both spectra in only 15 min. High-quality data sets for the 143 residue nuclease A inhibitor (2 °C, correlation time 17.5 ns) were obtained in 3 h, illustrating the utility of the method even in studies of moderately sized proteins.     

Stabilization of the Charge‐Separated States of Covalently Linked Zinc Porphyrin–Triphenylamine–[60]Fullerene

Spectroscopic, redox, computational, and electron transfer reactions of the covalently linked zinc porphyrin–triphenylamine–fulleropyrrolidine system are investigated in solvents of varying polarity. An appreciable interaction between triphenylamine and the porphyrin π system is revealed by steady‐state absorption and emission, redox, and computational studies. Free‐energy calculations suggest that the light‐induced processes via the singlet‐excited porphyrin are exothermic in benzonitrile, dichlorobenzene, toluene, and benzene. The occurrence of fast and efficient charge‐separation processes (≈10¹² s^?1) via the singlet‐excited porphyrin is confirmed by femtosecond transient absorption measurements in solvents with dielectric constants ranging from 25.2 (benzonitrile) to 2.2 (benzene). The rates of the charge separation processes are much less solvent‐dependent, which suggests that the charge‐separation processes occur at the top region of the Marcus parabola. The lifetimes of the singlet radical‐ion pair (70–3000 ps at room temperature) decrease substantially in more polar solvents, which suggests that the charge‐recombination process is occurring in the Marcus inverted region. Interestingly, by utilizing the nanosecond transient absorption spectral technique we can obtain clear evidence about the existence of triplet radical‐ion pairs with relatively long lifetimes of 0.71 μs (in benzonitrile) and 2.2 μs (in o‐dichlorobenzene), but not in toluene and benzene due to energetic considerations. From the point of view of mechanistic information, the synthesized zinc porphyrin–triphenylamine–fulleropyrrolidine system has the advantage that both the lifetimes of the singlet and triplet radical‐ion pair can be determined.     

The Conformations of Amino Acids on a Gold(111) Surface

The interactions of amino acids with inorganic surfaces are of interest for biologists and biotechnologists alike. However, the structural determinants of peptide–surface interactions have remained elusive, but are important for a structural understanding of the interactions of biomolecules with gold surfaces. Molecular dynamics simulations are a tool to analyze structures of amino acids on surfaces. However, such an approach is challenging due to lacking parameterization for many surfaces and the polarizability of metal surfaces. Herein, we report DFT calculations of amino acid fragments in vacuo and molecular dynamics simulations of the interaction of all amino acids with a gold(111) surface in explicit solvent, using the recently introduced polarizable gold force field GolP. We describe preferred orientations of the amino acids on the metal surface. We find that all amino acids preferably interact with the gold surface at least partially with their backbone, underlining an unfolding propensity of gold surfaces.     

Uranium speciation in biofilms studied by laser fluorescence techniques

Biofilms may immobilize toxic heavy metals in the environment and thereby influence their migration behaviour. The mechanisms of these processes are currently not understood, because the complexity of such biofilms creates many discrete geochemical microenvironments which may differ from the surrounding bulk solution in their bacterial diversity, their prevailing geochemical properties, e.g. pH and dissolved oxygen concentration, the presence of organic molecules, e.g. metabolites, and many more, all of which may affect metal speciation. To obtain such information, which is necessary for performance assessment studies or the development of new cost-effective strategies for cleaning waste waters, it is very important to develop new non-invasive methods applicable to study the interactions of metals within biofilm systems. Laser fluorescence techniques have some superior features, above all very high sensitivity for fluorescent heavy metals. An approach combining confocal laser scanning microscopy and laser-induced fluorescence spectroscopy for study of the interactions of biofilms with uranium is presented. It was found that coupling these techniques furnishes a promising tool for in-situ non-invasive study of fluorescent heavy metals within biofilm systems. Information on uranium speciation and uranium redox states can be obtained.     

偏微分方程求解的一种新颖方法-格子Boltzmann模型

介绍了一种偏微分方程求解的一种新颖方法格子Boltzmann模型,详细分析了它的基本理论和基本原理.并通过不可压Navier-Stokes方程组和二维含源项扩散方程的数值模拟计算实例,说明格子Boltzmann方法的有效性,展示了广阔的应用前景,为今后更深入的研究和广泛应用提供参考.     

Local realism of macroscopic correlations

We identify conditions under which correlations resulting from quantum measurements performed on macroscopic systems (systems composed of a number of particles of the order of the Avogadro number) can be described by local realism. We argue that the emergence of local realism at the macroscopic level is caused by an interplay between the monogamous nature of quantum correlations and the fact that macroscopic measurements do not reveal properties of individual particles.     

Bending insensitivity of fiber Bragg gratings in suspended-core optical fibers

This Letter presents simulation and experimental results that explore bending insensitivity of fiber Bragg gratings in suspended-core optical fibers. The implementation of thin silica bridge in the fibers enhances index contrast of the fiber core and reduces bending-induced strain transfer to the fiber core. This fiber design lead to a reduction of over 7 times in strain-induced fiber Bragg grating resonant peak shifts in the suspended-core fiber compared with that in standard telecommunication fiber, and an 0.14 dB bending loss at a bending radius of 6.35 mm.