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71.
Cooperative,Reversible Self‐Assembly of Covalently Pre‐Linked Proteins into Giant Fibrous Structures 下载免费PDF全文
Saadyah Averick Orsolya Karácsony Jacob Mohin Dr. Xin Yong Nicholas M. Moellers Bradley F. Woodman Prof. Weipu Zhu Prof. Ryan A. Mehl Prof. Anna C. Balazs Prof. Tomasz Kowalewski Prof. Krzysztof Matyjaszewski 《Angewandte Chemie (International ed. in English)》2014,53(31):8050-8055
We demonstrate a simple bioconjugate polymer system that undergoes reversible self‐assembling into extended fibrous structures, reminiscent of those observed in living systems. It is comprised of green fluorescent protein (GFP) molecules linked into linear oligomeric strands through click step growth polymerization with dialkyne poly(ethylene oxide) (PEO). Confocal microscopy, atomic force microscopy, and dynamic light scattering revealed that such strands form high persistence length fibers, with lengths reaching tens of micrometers, and uniform, sub‐100 nm widths. We ascribe this remarkable and robust form of self‐assembly to the cooperativity arising from the known tendency of GFP molecules to dimerize through localized hydrophobic patches and from their covalent pre‐linking with flexible PEO. Dissipative particle dynamics simulations of a coarse‐grained model of the system revealed its tendency to form elongated fibrous aggregates, suggesting the general nature of this mode of self‐assembly. 相似文献
72.
The “water layer test” is a crucial validation step of solid‐contact ion‐selective electrodes. It can confirm or contest the claim that the tested electrode is indeed a genuine solid contact electrode without an aqueous film between the ion‐selective membrane and its solid contact. Information about the presence of a water layer is essential for the interpretation of drifts in the electrode potentials commonly experienced with solid contact electrodes. Since its publication, the water layer test has been ubiquitously used, but without a standardized protocol the interpretation (or misinterpretation) of the test results led to uncertainties in the conclusions. Through both experiments and simulations based on theoretical models we have investigated the experimental parameters that can influence the results of the water layer test. We propose guidelines to minimize the possibility of misinterpretation of the results of the water layer test by considering the key factors that affect the shape of transients recorded during the water layer test. Most importantly, we emphasize the importance of allowing sufficient time for conditioning the tested electrode before the water layer test and providing adequate time for equilibration during the experiment. Using a thin ion‐selective membrane and thin solid‐contact layer for the tests is also recommended. 相似文献
73.
Dong‐Hao Li Cynthia L. Schreiber Bradley D. Smith 《Angewandte Chemie (International ed. in English)》2020,59(29):12154-12161
The near‐infrared window of fluorescent heptamethine cyanine dyes greatly facilitates biological imaging because there is deep penetration of the light and negligible background fluorescence. However, dye instability, aggregation, and poor pharmacokinetics are current drawbacks that limit performance and the scope of possible applications. All these limitations are simultaneously overcome with a new molecular design strategy that produces a charge balanced and sterically shielded fluorochrome. The key design feature is a meso‐aryl group that simultaneously projects two shielding arms directly over each face of a linear heptamethine polyene. Cell and mouse imaging experiments compared a shielded heptamethine cyanine dye (and several peptide and antibody bioconjugates) to benchmark heptamethine dyes and found that the shielded systems possess an unsurpassed combination of photophysical, physiochemical, and biodistribution properties that greatly enhance bioimaging performance. 相似文献
74.
Ian A. Maxwell Bradley R Morrison Robert G Gilbert David F Sangster Donald H Napper 《Macromolecular Symposia》1992,53(1):233-242
Measurements of the rate coefficients characterising the entry of free radicals into seed particles in styrene emulsion polymerizations has allowed the rate determining step for entry to be identified. This was found to be the rate of production of oligomeric species in the aqueous phase by monomer addition to the primary free radicals. Once formed the subsequent diffusion of these species to the latex particles (and their incorporation within these particles) is relatively fast, contrary to the assumptions of the previous diffusion controlled theories. The experimental results imply that the entering free radicals contain only two or three monomer units. Thermodynamic considerations show that such species should be both water soluble and surface active. Similar conclusions have been reached for other sparingly water soluble monomers, such as butyl acrylate and butyl methacrylate. 相似文献
75.
A simple means is deduced for determining conditions for secondary particle formation in emulsion polymerization systems in systems where the amount of added surfactant is below the cmc. A new radical formed from initiator in the aqueous phase will undergo some polymerization with aqueous-phase monomer, but must have three possible eventual fates: aqueous-phase termination, entry into a preexisting particle, or creation of a new particle. The means for determining the onset and extent of secondary nucleation is to modify HUFT theory to take into account a successful model for entry [ Macromolecules, 24, 1629 (1991)] which states that entry occurs if and only if the aqueous-phase radical has achieved a critical degree of polymerization z. Particle formation below the cmc is by homogeneous/coagulative nucleation which (if coagulation is ignored) gives an upper bound to the rate of formation of precursor particles; these are of a degree of polymerization Jcrit > z. The resulting equations are readily solved, and require only a knowledge of the aqueous-phase propagation and termination rate coefficients (the latter is very high: ca. 109 dm3 mol−1 s−1 for termination between the very small radicals), z and jcrit. Easily applied means are given for estimating all these quantities. The treatment gives good accord with experimentally observed conditions for the onset of secondary nucleation in low-surfactant systems (including taking in situ micellization into account). 相似文献
76.
Levi Evans Yiqui Shen Abigail Bender Leah E. Burnett Musheng Li Justine S. Habibian Tong Zhou Bradley S. Ferguson 《Molecules (Basel, Switzerland)》2021,26(5)
Plant-based foods, like fruits, vegetables, whole grains, legumes, nuts, seeds and other foodstuffs, have been deemed as heart healthy. The chemicals within these plant-based foods, i.e., phytochemicals, are credited with protecting the heart. However, the mechanistic actions of phytochemicals, which prevent clinical endpoints, such as pathological cardiac hypertrophy, are still being elucidated. We sought to characterize the overlapping and divergent mechanisms by which 18 selected phytochemicals prevent phenylephrine- and phorbol 12-myristate 13-acetate-mediated cardiomyocyte enlargement. Of the tested 18 compounds, six attenuated PE- and PMA-mediated enlargement of neonatal rat ventricular myocytes. Cell viability assays showed that apigenin, baicalein, berberine hydrochloride, emodin, luteolin and quercetin dihydrate did not reduce cell size through cytotoxicity. Four of the six phytochemicals, apigenin, baicalein, berberine hydrochloride and emodin, robustly inhibited stress-induced hypertrophy and were analyzed further against intracellular signaling and genome-wide changes in mRNA expression. The four phytochemicals differentially regulated mitogen-activated protein kinases and protein kinase D. RNA-sequencing further showed divergence in gene regulation, while pathway analysis demonstrated overlap in the regulation of inflammatory pathways. Combined, this study provided a comprehensive analysis of cardioprotective phytochemicals. These data highlight two defining observations: (1) that these compounds predominantly target divergent gene pathways within cardiac myocytes and (2) that regulation of overlapping signaling and gene pathways may be of particular importance for the anti-hypertrophic actions of these phytochemicals. Despite these new findings, future works investigating rodent models of heart failure are still needed to understand the roles for these compounds in the heart. 相似文献
77.
78.
Hendargo HC Bower BA Reinstein AS Shepherd N Tao YK Izatt JA 《Optics Communications》2011,284(19):4847-4851
Spectral domain phase microscopy (SDPM) is an extension of spectral domain optical coherence tomography (SDOCT) that exploits the extraordinary phase stability of spectrometer-based systems with common-path geometry to resolve sub-wavelength displacements within a sample volume. This technique has been implemented for high resolution axial displacement and velocity measurements in biological samples, but since axial displacement information is acquired serially along the lateral dimension, it has been unable to measure fast temporal dynamics in extended samples. Depth-Encoded SDPM (DESDPM) uses multiple sample arms with unevenly spaced common path reference reflectors to multiplex independent SDPM signals from separate lateral positions on a sample simultaneously using a single interferometer, thereby reducing the time required to detect unique optical events to the integration period of the detector. Here, we introduce DESDPM and demonstrate the ability to acquire useful phase data concurrently at two laterally separated locations in a phantom sample as well as a biological preparation of spontaneously beating chick cardiomyocytes. DESDPM may be a useful tool for imaging fast cellular phenomena such as nervous conduction velocity or contractile motion. 相似文献
79.
80.
Meyer BS 《Physical review letters》2002,89(23):231101
Matter expanding sufficiently rapidly and at high enough entropy per nucleon can enter a heavy-element synthesis regime heretofore unexplored. In this extreme regime, more similar to nucleosynthesis in the early universe than to that typical in stellar explosive environments, there is a persistent disequilibrium between free nucleons and abundant alpha particles, which allows heavy r-process nucleus production even in matter with more protons than neutrons. This observation bears on the issue of the site of the r process, on the variability of abundance yields from r-process events, and on constraints on neutrino physics derived from nucleosynthesis. 相似文献