The development of highly sensitive fluorescent probes in combination with innovative optical techniques is a promising strategy for intravital noninvasive quantitative imaging. Cyanine fluorochromes ...belong to a superfamily of dyes that have attracted substantial attention in probe design for molecular imaging. We have developed a novel paradigm to introduce a Turn-ON mechanism in cyanine molecules, based on a distinctive change in their π-electrons system. Our new cyanine fluorochrome is synthesized through a simple two-step procedure and has an unprecedented high fluorescence quantum yield of 16% and large extinction coefficient of 52 000 M–1cm–1. The synthetic strategy allows one to prepare probes for various analytes by introducing a specific triggering group on the probe molecule. The probe was equipped with a corresponding trigger and demonstrated efficient imaging of endogenous hydrogen peroxide, produced in an acute lipopolysaccharide-induced inflammation model in mice. This approach provides, for the first time, an available methodology to prepare modular molecular Turn-ON probes that can release an active cyanine fluorophore upon reaction with specific analyte.
Polymer conjugation is an efficient approach to improve the delivery of drugs and biological agents, both by protecting the body from the drug (by improving biodistribution and reducing toxicity) and ...by protecting the drug from the body (by preventing degradation and enhancing cellular uptake). This review discusses the journey that polymer therapeutics make through the body, following the ADME (absorption, distribution, metabolism, excretion) concept. The biological factors and delivery system parameters that influence each stage of the process will be described, with examples illustrating the different solutions to the challenges of drug delivery systems in vivo.
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We studied the structural evolution during the formation of large-pore cubic I a3̅d silica-based mesoporous materials, synthesized with Pluroinc P123 and butanol as structure directing agents. We ...used cryogenic high resolution scanning electron microscopy (cryo-HRSEM) and freeze-fracture-replication (FFR) transmission electron microscopy (TEM). Typically a silica precursor is added to an acid-catalyzed solution of Pluronic P123 and butanol. The latter serves as a cosolute, which can be added either at the beginning of the reaction, or after precipitation and the formation of a hexagonal phase. In this study we focused on the structural evolution from the hexagonal phase to the final cubic phase in the two different reactions. The same structural evolution with different kinetics was detected for both reactions. Cryo-HRSEM and FFR-TEM images revealed that from the hexagonal phase a perforated layer (PL) phase is formed, which later evolves into a bicontinuous structure. The final cubic phase forms within the layers, maintaining their orientation. We suggest a formation mechanism involving cylinder merging for the hexagonal to PL transition. Upon additional polymerization of the silica, the PL phase relaxes into the stable I a3̅d cubic phase. Another minor mechanism detected involves the direct transition between the hexagonal to the final cubic phase through cylinder branching.
The effect of sonication and freezing–thawing on the aggregate size and dynamic surface tension of aqueous dipalmitoylphosphatidylcholine (DPPC) dispersions was studied by cryogenic-transmission ...electron microscopy (cryo-TEM), dynamic light scattering (DLS), UV–vis spectroturbidimetry, and surface tensiometry. When 1000 ppm (0.1 wt%) DPPC dispersions were prepared with a certain protocol, including extensive sonication, they contained mostly frozen vesicles and were quite clear, transparent, and stable for at least 30 days. The average dispersed vesicles diameter was 80 nm in water and 90 nm in standard phosphate saline buffer. After a freeze–thaw cycle, this dispersion became turbid, and precipitates of coagulated vesicles were observed with large particles of average size of
1.5
×
10
3
nm
. The vesicle coagulation is due to the local salt concentration increase during the freezing of water. This dispersion has much higher equilibrium and dynamic surface tension than those before freezing. When this freeze–thawed dispersion was subjected to a resonication at 55 °C, smaller vesicles with sizes of ca. 70 nm were produced, and a lower surface tension behavior was restored as before freezing. Similar behavior was observed at 30 ppm DPPC. These results indicate that the freeze–thaw cycle causes substantial aggregation and precipitation of the vesicles. These results have implications for designing efficient protocols of lipid dispersion preparation and lung surfactant replacement formulations in treating respiratory disease and for effective administration.
Cryo-TEM of DPPC dispersions of frozen vesicles.
This study focuses on the formation mechanism of the bicontinuous cubic Ia3̅d mesoporous material KIT-6, both on the molecular and on the mesoscopic levels. KIT-6 is synthesized with Pluronic P123 ...(PEO20PPO70PEO20), low acid concentration, and n-butanol at 40 °C. Through in situ EPR measurements on a series of spin-labeled Pluronic molecules introduced at minute quantities into the reaction mixture, changes in the hydrophobicity and the mobility of the polymer chains during the reaction were observed. In addition, to learn more on the functionality of the butanol in this synthesis, freeze-quench electron spin–echo envelope modulation (ESEEM) measurements on reaction mixtures in D2O and in butanol-d 10 were preformed. The above experiments gave information on variations in the butanol location and content in the micellar structures during the formation of KIT-6. The evolution of the solution nanostructures was determined by cryo-TEM. Five main stages were resolved: the first two occurred during the first 140 min of the reaction, where condensation of the silica oligomers takes place at the micellar/water interface; this induces depletion of water and butanol molecules from the core−corona interface and reduces the mobility of the ends of the Pluronic chains located at the corona−water interface. This in turn leads to a transition from spheroidal micelles to threadlike micelles and to their aggregation toward the end of the second stage. During the third stage, precipitation (140–160 min), reorganization in the micellar structure, and a change in the relative sizes of core and corona take place. The fourth stage, that ends around 6 h, involves the formation of a hexagonal phase, through accelerated condensation of silica oligomers in the corona, accompanied by extensive depletion of water and butanol molecules. The presence of butanol in the micelle corona is essential in the last stage, 6–24 h, where the cubic phase is formed. We show that the addition of butanol to the reaction mixture of SBA-15 after the formation of the hexagonal phase leads to the formation of the cubic phase.
The stability and state of aggregation of aqueous fibrinogen (FB) and dipalmitoylphosphatidylcholine (DPPC) vesicles in water or buffer at 25 °C were studied with dynamic light scattering (DLS), ...UV−vis spectroturbidimetry (ST), and cryo-transmission electron microscopy (cryo-TEM). In water, when 1000 ppm (0.10 wt %) DPPC dispersions were prepared with a protocol including extensive sonication, they contained mostly vesicles and were quite clear, transparent, and stable for at least 30 days. FB mixtures with water (0.075 wt %) were quite unstable and biphasic. They formed large aggregates which eventually precipitated. The addition of DPPC vesicles into these unstable FB dispersions reversed FB aggregation and precipitation and produced stable translucent microdispersions. The inferred lipid/protein aggregates were limited in size, with average diameters ranging from 200 to 300 nm. In buffer, DPPC dispersions were also clear and quite stable, with average dispersed particles diameter of ca. 90 nm. FB dissolved in aqueous buffer and formed transparent and stable solutions. Adding salt to an aggregated FB dispersion in water reversed the aggregation. FB aggregated and redissolved in the presence of the citrate and after the citrate was removed. There was no effect of citrate (present in FB initially) in the FB aggregation or redissolution. FB molecules in buffer form dimers or higher aggregates. Their average aggregation number is 2, determined with Rayleigh scattering analysis of turbidity data. The average hydrodynamic diameter of FB solutions from DLS was 30 nm. Mixing a stable FB solution in buffer and a stable DPPC dispersion in buffer produced highly unstable mixtures, in which large aggregates precipitated. These results have implications in understanding the interactions of lipids and proteins in many biological applications and food processing applications.
Social place-cells in the bat hippocampus Omer, David B; Maimon, Shir R; Las, Liora ...
Science (American Association for the Advancement of Science),
01/2018, Letnik:
359, Številka:
6372
Journal Article
Recenzirano
Social animals have to know the spatial positions of conspecifics. However, it is unknown how the position of others is represented in the brain. We designed a spatial observational-learning task, in ...which an observer bat mimicked a demonstrator bat while we recorded hippocampal dorsal-CA1 neurons from the observer bat. A neuronal subpopulation represented the position of the other bat, in allocentric coordinates. About half of these "social place-cells" represented also the observer's own position-that is, were place cells. The representation of the demonstrator bat did not reflect self-movement or trajectory planning by the observer. Some neurons represented also the position of inanimate moving objects; however, their representation differed from the representation of the demonstrator bat. This suggests a role for hippocampal CA1 neurons in social-spatial cognition.
Navigation and episodic memory depend critically on representing temporal sequences. Hippocampal 'time cells' form temporal sequences, but it is unknown whether they represent context-dependent ...experience or time per se. Here we report on time cells in bat hippocampal area CA1, which, surprisingly, formed two distinct populations. One population of time cells generated different temporal sequences when the bat hung at different locations, thus conjunctively encoding spatial context and time-'contextual time cells'. A second population exhibited similar preferred times across different spatial contexts, thus purely encoding elapsed time. When examining neural responses after the landing moment of another bat, in a social imitation task, we found time cells that encoded temporal sequences aligned to the other's landing. We propose that these diverse time codes may support the perception of interval timing, episodic memory and temporal coordination between self and others.
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•An O2-independent l-lactate biosensor was developed.•Both DET and MET processes can be achieved using the FMN-LDH enzyme.•Grafting improves the bioanode stability up to 20 h of ...continuous operation.•The developed bioanodes were utilized in BFC configurations.•The BFC generates a power output of 200 µW/cm2 under oxygen saturation conditions.
Lactate sensing has high importance for metabolic disease diagnostics, food spoilage, sports medicine, or the construction of biofuel cell devices. Therefore, continuous lactate sensing devices which enable accurate detection should be developed. Here we present the overexpression and utilization of FMN-lactate dehydrogenase from Saccharomyces cerevisiae for oxygen-insensitive, continuous amperometric lactate biosensing. The developed sensors exhibit a high signal-to-noise ratio, low interference effect, and a wide range of linear responses using both direct and mediated electron transfer configurations. The thionine-based mediated electron transfer configuration was stable for 8 h of continuous activity and two weeks of periodic activity with storage at 4 °C. We further grafted the redox mediators on multiwall carbon nanotubes to lower the redox mediator leaching effect. The developed grafting technique improved the biosensor stability and allowed continuous operation for at least 20 h. Both the mediator-entrapped and the grafted bioanodes were further coupled with a bilirubin oxidase-based biocathode to construct a biofuel cell device. The various biofuel cells have generated a maximal power output of 110 µW/cm2 under atmospheric conditions and 200 µW/cm2 under oxygen saturation.
