Making circles with N and O : Cyclic tripeptides containing an unnatural Cα‐tetrasubstituted THF amino acid are prepared by copper(I) and palladium(0)‐catalyzed N‐ and O‐arylation reactions. The reactions give access to side chain‐modified derivatives of the unnatural amino acid and macrocyclic peptidomimetics.
Summary: Temperature-induced and solvent composition-induced phase separation in solutions of poly(N-isopropylmethacrylamide) (PIPMAm) and other thermoresponsive polymers as studied by NMR and infrared (IR) spectroscopy is discussed. The fraction p of phase-separated units (units with significantly reduced mobility) and subsequently, e.g., thermodynamic parameters characterizing the coil-globule phase transition induced by temperature, were determined from reduced integrated intensities in high-resolution 1H NMR spectra. This approach can be especially useful in investigations of phase separation in solutions of binary polymer systems. Information on behaviour of water during temperature-induced phase transition was obtained from measurements of 1H NMR relaxation times of HDO molecules. NMR and IR spectroscopy were used to investigate PIPMAm solutions in water/ethanol (D2O/EtOH) mixtures where the phase separation can be induced by solvent composition (cononsolvency). Some differences in globular-like structures induced by temperature and solvent composition were revealed by these methods. 相似文献
An immunochromatographic lateral flow dipstick assay for the fast detection of microcystin-LR was developed. Colloid gold
particles with diameters of 40 nm were used as red-colored antibody labels for the visual detection of the antigen. The new
dipstick sensor is capable of detecting down to 5 μg·l−1 (ppb; total inversion of the color signal) or 1 ppb (observation of color grading) of microcystin-LR. The course of the labeling
reaction was observed via spectrometric wave shifts caused by the change of particle size during the binding of antibodies.
Different stabilizing reagents showed that especially bovine serum albumin (BSA) and casein increase the assays sensitivity
and the conjugate stability. Performance of the dipsticks was quantified by pattern processing of capture zone CCD images.
Storage stability of dipsticks and conjugate suspensions over 115 days under different conditions were monitored. The ready-to-use
dipsticks were successfully tested with microcystin-LR-spiked samples of outdoor drinking- and salt water and applied to the
tissue of microcystin-fed mussels.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
Surface interactions provide a class of mechanisms which can be employed for propulsion of micrometer and nanometer sized particles. We investigate the related efficiency of externally and self-propelled swimmers. A general scaling relation is derived showing that only swimmers whose size is comparable to, or smaller than, the interaction range can have appreciable efficiency. An upper bound for efficiency at maximum power is 1/2. Numerical calculations for the case of diffusiophoresis are found to be in good agreement with analytical expressions for the efficiency. 相似文献
We present highly efficient 480 and 800 nm upconversion emissions in Tm3+/Yb3+ co-doped water-free low silica calcium aluminosilicate glass under excitation at 976 nm. As a result of this efficient upconversion process, a luminescent switching with the excitation intensity has been observed. The switching is explained and discussed using rate equations analysis and saturation effects. By means of fitting of the experimental data point, it was possible to obtain the value of the energy transfer parameter related to the transition 2F5/2, 3H4→2F7/2, 1G4. The value of this parameter is higher than that of materials like YLF. This switching mechanism could be used in the development of sensors and networks for optical processing and optical communications. 相似文献
High-resolution photoelectron spectroscopy of in situ prepared films of GeSb2Te4 reveals significant differences in electronic and chemical structure between the amorphous and the crystalline phase. Evidence for two different chemical environments of Ge and Sb in the amorphous structure is found. This observation can explain the pronounced property contrast between both phases and provides new insight into the formation of the amorphous state. 相似文献
A time domain optical coherence tomography (OCT) system without moving parts is described, which is based on multiheterodyning utilizing two mode-locked femtosecond lasers. By synchronizing the two lasers to slightly different repetition rates and coupling to an interferometric OCT setup, we obtain amplitude-modulated beat signals representing the structure of the specimen under investigation. Our system is suitable for biological imaging as well as technical applications. We demonstrate high axial imaging depths of 150 mm with up to 5000 axial scans per second, achieving equivalent path scanning velocities of 750 m/s. 相似文献