Molecular biology has benefited by tags encoded into expressed proteins for their identification and purification. The protein of interest is constructed with DNA that includes an added "tail" sequence coding for a string of amino acids that bind to an antibody, a metal column, or a some other binding couple. Common genetic tags include 6x-histidines that bind Ni-NTA, Flag that binds to anti-flag antibodies, strep-tag that binds to strep-tactin, c-myc that binds to antibody, calmodulin binding domain that binds to calmodulin, cellulose binding domain that binds cellulose, glutathione-S-transferase that binds glutathione, streptavidin binding peptide that binds streptavidin, and a number of others. These genetic constructs can also be used for protein localization and tracking within a cell. Although green fluorescent protein has been similarly programmed in as a "tail" fusion protein for following proteins in a cell by light microscopy, EM requires a dense label, such as gold. One may use anti-GFP gold labels, but another approach is to derivatize gold nanoparticles with the binding couple for the tags commonly used in protein expression. The tags can be much smaller that GFP, and the binding couples can be much smaller than antibodies. For example, a 1.4 nm gold particle synthesized with the nitrilotriacetic acid (NTA) group charged with nickel was previously shown to bind specifically to 6x-His tagged proteins with visualization by EM [1]. Here we extend this technology to a larger 5 nm gold particle. The purpose for a larger particle is for better visibility directly in the TEM. The 1.4 nm particle is directly visible in ice or on a thin film, but becomes difficult to see in stains or in thicker samples, such as tissue sections. Although silver or gold enhancement that grows the particle is possible, a 5 nm particle may be seen directly without enhancement, and reduce the steps required for preparation. Enhancement also leads to more particle size variation, and this is also avoided. Fig. 1 shows the derivatized 5 nm gold particles in TEM. When incubated with the protein ISWI from the ACF chromatin remodeling complex, synthesized with a His tag, a conjugate peak appeared in the chromatogram (Fig. 2), and its spectrum indicated both gold and protein presence. A control experiment was to incubate the Ni-NTA-5 nm with ISWI without the 6x-His tag. In this case, virtually no binding to the protein was seen as evidenced by the absence of the conjugate peak (Fig. 2).
The extraction of caffeine from green tea leaves and cocoa beans is a common industrial process for the production of decaffeinated beverages and pharmaceuticals. The choice of the solvent critically determines the yield of this extraction process. Being an environmentally benign and recyclable solvent, supercritical carbon dioxide (scCO 2 ) has emerged as the most desirable green solvent for caffeine extraction. The present study investigates the solvation properties of caffeine in scCO 2 at two different temperatures (318 and 350 K) using molecular dynamics simulations. Unlike in water, the caffeine molecules in scCO 2 do not aggregate to form clusters due to relatively stronger caffeine−CO 2 interactions. A well-structured scCO 2 solvent shell envelops each caffeine molecule as a result of strong electron−donor−acceptor (EDA) and hydrogenbonding interactions between these two species. Upon heating, although marginal site-specific changes in the distribution of nearest CO 2 around caffeine are observed, the overall distribution is retained. At a higher temperature, the caffeine−CO 2 hydrogen-bonding interactions are weakened, while their EDA interactions become relatively stronger. The results underscore the importance of the interplay of these interactions in determining stable solvent structures and solubility of caffeine in scCO 2 .
Gas-solid fluidization has a wide range of industrial applications like catalytic reactions, combustion, gasification, etc. In a number of these applications, there is particle size reduction during the operation leading to severe entrainment and limitation of operating velocity. The various problems associated with particles of different sizes or changing particles sizes could be overcome by adopting tapered beds in fluidization operation.In the present investigation, the fluidization phenomenon in tapered beds has been critically assessed through experimental investigations using particles of different sizes and materials and wide range of apex angles of the vessels. The effect of particle size and apex angle on the fluidization behaviour is clearly brought out which has not been reported so far in literature. The importance of compressive force existing in tapered beds is highlighted.In addition, correlations for all hydrodynamic characteristics, viz. critical fluidization velocity, minimum velocity for full fluidization, maximum velocity for defluidization, peak pressure drop, fluctuation ratio, compressive force, and hysteresis have been developed some of which are proposed for the first time.La fluidisation gaz-solide revêt un vasteéventail d'applications industrielles comme les réactions catalytiques, la combustion, la gazéification, etc. Pour un certain nombre deces applications, il y a une réduction granulométrique durant l'activité menantà un entraînement età une limitation intenses de la vitesse de fonctionnement. Les divers problèmes liés aux particules de dimensions différentes ou aux dimensions de particules changeantes pourraientêtre surmontésen adoptant les lits coniques dans les activités de fluidisation. Dans le cadre de la présenté etude, lephénomène de fluidisation dans les lits coniques aétéévalué de façon critique au moyen devérifications expérimentales employant des particules de dimensions et de matières différentes et d'un vasteéventail d'angles de sommet de fluidiseurs. L'effet de la dimension des particules et del'angle des sommets sur le comportement de la fluidisation est nettement mis enévidence, ce quin'a pasété soulevéà venir jusqu'ici dans la documentation. L'importance de la force decompression qui existe dans les lits coniques est mise enévidence. De plus, les corrélations relativement a l'ensemble des caractéristiques hydrodynamiques, c.-à-d. la vitesse de fluidisation critique, la vitesse minimale de fluidisation complète, la vitesse maximale de défluidisation, la chute des pics de pression, le taux de fluctuation, la force de compression et l'hystérésis, ontétéélaborées, certaines d'entre ellesétant avancées pour la première fois.
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