Short transverse relaxation times of Calpha and Cbeta single-quantum coherences reduce the sensitivity of triple-resonance experiments involving transfers of Calpha/Cbeta or Halpha/Hbeta coherences. Multiple-quantum line-narrowing techniques improve the relaxation properties of 13C coherences, thereby increasing the sensitivity of the experiment. In the present work, we describe PFG-CBCA(CO)NH and PFG-HBHA(CO)NH experiments that utilize heteronuclear multiple-quantum coherences in a simultaneous constant-time period to obtain completely decoupled spectra with improved sensitivity. Results indicate that approximately 30% of cross peaks show an average enhancement of approximately 15% in the CBCA(CO)NH experiment. In the related HBHA(CO)NH experiment, approximately 97% of the cross peaks show an average enhancement of approximately 40%. 相似文献
In this paper, we summarise the development of off-axis electron holography on biological samples starting in 1986 with the first results on ferritin from the group of Tonomura. In the middle of the 1990s strong interest was evoked, but then stagnation took place because the results obtained at that stage did not reach the contrast and the resolution achieved by conventional electron microscopy.
To date, there exist only a few (12) publications on electron holography of biological objects, thus this topic is quite small and concise. The reason for this could be that holography is mostly established in materials science by physicists. Therefore, applications for off-axis holography were powerfully pushed forward in the area of imaging, e.g. electric or magnetic micro- and nanofields. Unstained biological systems investigated by means of off-axis electron holography up to now are ferritin, tobacco mosaic virus, a bacterial flagellum, T5 bacteriophage virus, hexagonal packed intermediate layer of bacteria and the Semliki Forest virus. New results of the authors on collagen fibres and surface layer of bacteria, the so-called S-layer 2D crystal lattice are presented in this review. For the sake of completeness, we will shortly discuss in-line holography of biological samples and off-axis holography of materials related to biological systems, such as biomaterial composites or magnetotactic bacteria. 相似文献
The need for a molecular depth profiling technique to study organic layers has become a strong incentive in the SIMS community in the last few years, especially with the recent successes obtained with cluster ion beam depth profiling. In this work, we have investigated a thoroughly different approach by using very low energy (down to 200 eV) monoatomic or diatomic ions to sputter organic matter. Quite surprisingly, we were able to retain specific molecular information on various polymers even at very high fluence.Polymethylmethacrylate (PMMA) and polyethylene terephthalate (PET) films were depth-profiled with 200 eV Cs+ and 500 eV O2+ ions. With 200 eV Cs ions, the best profiles were obtained in the negative mode, due to a strong negative ionisation yield enhancement related to Cs retention in the polymer. A relatively high and stable signal from the most characteristic ions was measured all over the layer.With 500 eV O2+, real molecular depth-profiles were also obtained in both the positive and the negative modes. Once again, the main characteristic fragments of PET or PMMA remain detectable with stable yields all over the profile. 相似文献
Nanoscale metal sulfides are of tremendous potential in biomedicine. Generally, the properties and performances of metal sulfide nanoparticles (NPs) are highly related to their structures, sizes and morphologies. Recently, a strategy of using sulfur-containing protein–metal-ion networks for preparing metal sulfide embedded nanocomposites was proposed. Within the networks, proteins can play multiple roles to drive the transformation of these networks into protein-encapsulated metal sulfide NPs with ultrasmall size and defined structure (as both a template and a sulfur provider) or metal sulfide NP–protein hydrogels with injecting and self-healing properties (as a template, a sulfur provider, and a gelator) in a controlled manner. In this Concept, the synthesis strategy, the formation mechanism, and the biomedical applications of the gained nanocomposites are presented. Moreover, the challenges and opportunities of using protein–metal ion networks to construct functional materials for biomedical applications are analyzed. 相似文献
This study developed an open‐tubular capillary electrochromatography protocol for the analysis of antipyretic analgesic drugs, which used a multifunctional homopolymer as coating. A controlled/living radical polymerization strategy was adopted to obtain poly(N‐acryloxysuccinimide) with a tunable chain‐length. The homopolymer coating enhanced the separation performance by contributing to the hydrophobic and hydrogen‐bonding interactions between the analytes and the homopolymer. The effect of polymer chain‐length and buffer pH and concentration on the separation efficiency was evaluated. In this approach, baseline separation of the three test drugs was achieved within 15 min. The repeatability of the prepared homopolymer coating was investigated, with the relative standard deviations < 2.88% observed in intra‐ and interday runs. Good linearity in the 5–800 µM range (R2 ≥ 0.998) demonstrates that accurate quantitative analysis of real samples was achieved. Moreover, the proposed assay was used to quantify the three drugs (aminopyrine, 4‐aminoantipyrine, and phenacetin) in urine samples, achieving recovery rates between 92.1 and 108.7%. This promising methodology may be used for the analysis of drugs in real bio‐samples and for the development of unique homopolymer coatings for open‐tubular capillary electrochromatography systems. 相似文献
Four new zinc (II) complexes [Zn (HL1H)Br2] (1), [Zn (HL1H)Cl2] (2), [Zn2(HL2)Br3] (3), and [Zn (HL2)Cl] (4) have been synthesized by adopting template synthetic strategy and utilizing two homologous Schiff base ligands (H2L1 = 4-bromo-2-{[2-(2-hydroxyethylamino)-ethylimino]-methyl}-6-methoxyphenol, H2L2 = 4-bromo-2-{[3-(2-hydroxyethylamino)propylimino]methyl}-6-methoxyphenol), differing in one -CH2- unit in the ligating backbone, by adopting template synthetic strategy. All the complexes have been characterized by single crystal X-ray diffraction analysis as well as by other routine physicochemical techniques. Ligand mediated structural variations have been observed and rationalized by density functional theoretical (DFT) calculations. Interaction of the complexes 1–4 with Bovine Serum Albumin protein (BSA) has been studied by different spectroscopic techniques. A complete thermodynamic profile (ΔHo, ΔSo and ΔGo) was evaluated initially from the change in absorption and fluorescence spectra upon addition of BSA to the complexes. Appreciable binding constant values in the range ~ 0.94–4.51 × 104 M−1 indicate efficient binding tendency of the complexes to BSA with the sequence 1 ≅ 2 > 3 ≅ 4. Circular dichroism (CD), isothermal calorimetric titration experiments, molecular docking and molecular dynamics have been performed to gain deep insight into the binding regions of complex 1 to BSA. Experimental evidences suggest an interaction of zinc complexes at the surface of BSA protein and this particular binding has been exploited to determine unknown concentration of BSA protein. For this purpose complex 1 was explored as a BSA protein quantification tool. 相似文献
Phase-resolved information is necessary for many coastal wave problems, for example, for the wave conditions in the vicinity of harbor structures. Two-dimensional (2D) depth-averaging shallow water models are commonly used to obtain a phase-resolved solution near the coast. These models are in general more computationally effective compared with computational fluid dynamics software and will be even more capable if equipped with a parallelized code. In the current article, a 2D wave model solving the depth-averaged continuity equation and the Euler equations is implemented in the open-source hydrodynamic code REEF3D. The model is based on a nonhydrostatic extension and a quadratic vertical pressure profile assumption, which provides a better approximation of the frequency dispersion. It is the first model of its kind to employ high-order discretization schemes and to be fully parallelized following the domain decomposition strategy. Wave generation and absorption are achieved with a relaxation method. The simulations of nonlinear long wave propagations and transformations over nonconstant bathymetries are presented. The results are compared with benchmark wave propagation cases. A large-scale wave propagation simulation over realistic irregular topography is shown to demonstrate the model's capability of solving operational large-scale problems. 相似文献
Endocytic pathways are practical routes for the intracellular delivery of biomacromolecules. Along with this, effective strategies for endosomal cargo release into the cytosol are desired to achieve successful delivery. Focusing on compositional differences between the cell and endosomal membranes and the pH decrease within endosomes, we designed the lipid-sensitive and pH-responsive endosome-lytic peptide HAad. This peptide contains aminoadipic acid (Aad) residues, which serve as a safety catch for preferential permeabilization of endosomal membranes over cell membranes, and His-to-Ala substitutions enhance the endosomolytic activity. The ability of HAad to destabilize endosomal membranes was supported by model studies using large unilamellar vesicles (LUVs) and by increased intracellular delivery of biomacromolecules (including antibodies) into live cells. Cerebral ventricle injection of Cre recombinase with HAad led to Cre/loxP recombination in a mouse model, thus demonstrating potential applicability of HAad in vivo. 相似文献