Diffusion and binding

Species that diffuse into concrete can bind to a certain degree with components of the cement matrix, e. g. chlorides bind with aluminate phases or are adsorbed on C-S-H carbon dioxide reacts with alkaline components, in particular Ca(OH)2. The gradual consumption of these compounds modifies the conditions of diffusion, which can no longer simply be described by Pick s second law but require a corrective term. 

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Samitz, M.H. and S.A. Katz. 1976. Nickel-epidermal interactions diffusion and binding. Environ. Res. 11 34-39. 

Phase-separation immunoassays have been reported, in which the solid phase particles are formed after the immunoreaction is completed.(42) Phase-separation immunoassays are advantageous since the unstirred layer of solution near a solid surface alters diffusion and binding kinetics at the surface in comparison with the properties of the bulk solution. In phase-separation assays for IgG and IgM, capture antibodies are bound with monomers suitable for styrene or acrylamide polymerization.(42) Monomer-labeled capture antibodies are reacted with analyte and with fluorescein- and/or phycoerythrin-labeled antibodies in a sandwich assay, followed by polymerization of the monomers. Fluorescence of the resulting particles is quantitated in a FACS IV flow microfluorometer, and is directly proportional to analyte concentration. 

Free steroids that do not bind with plasma proteins enter target cells by passive diffusion and bind with cytoplasmic soluble-binding proteins (acceptor region), forming a steroid-protein complex. This enters the nucleus, where it interacts with steroid receptors on chromatin. 

Given the complexity in molecular transport in tissues, understanding mechanisms of convection, diffusion, and binding in the interstitial space regardless of administration techniques may provide the means to overcome transport barriers for more uniform and adequate delivery of large therapeutic agents in solid tumors. 

Estrogen is produced in the ovaries and secreted into the blood, whereupon it enters target cells throughout the body. It enters the cells via passive diffusion and binds to specific proteins called estrogen receptors,... 

Steroid hormones (e.g., cortisol and estrogen) are hydro-phobic and insoluble in water. These hormones circulate in plasma, reversibly bound to transport proteins (e.g., cortisol-binding globulin and sex-hormone binding globulin) with only a small fraction free or unbound available to exert physiological action.The half-life of steroid hormones is 30 to 90 minutes. Free steroid hormones, being hydrophobic, enter the cell by passive diffusion and bind with intracellular receptors either in the cytoplasm or the nucleus. ... 

Lipid-soluble hormones are transported in plasma bound to carrier proteins with only a small fi-action of the hormone being in the free or unbound state. The free hormone enters the cell via passive diffusion and binds to intracellular receptors in the cytoplasm or, more often, the nucleus (Figure 28-1). These receptors are characterized by a hormone-binding domain, a deoxyribonucleic acid (DNA)-binding domain, and an amino-terminal variable domain. Just as the interaction of protein or polypeptide hormones with cell-surface receptors changes the conformation of the receptor protein, the binding of a lipid-soluble hormone... 

Fig. 9.4 The colony lift screen. Step 1 Bacteria are spread on a Supor (low protein binding) filter on YTG -agar plate and grown for lOh at 30°C to form microcolonies. Step 2 The Supor filter is placed on top of cellulose-acetate filter on IPTG containing plate at 30°C for 16 h (induction of scFv-CBD expression). During the induction period the scFv-CBD fusion are secreted, diffuse and bind tightly to the cellulose acetate filter. Step 3 The colonies on Supor filter are saved for recovery later. The cellulose acetate filter is processed with labeled antigen as illustrated in the cartoon. Step 4 Probable binders are identified on the cellulose-acetate filter and colonies picked from the master Supor filter. These candidates are later verified by ELISA for specificity...

The mechanism of glucocorticoids is complex and not fully known. The glucocorticoid enters the cell through passive diffusion and binds to its specific receptor. There are between 5000 and 100,000 receptors per cell. Steroids exhibit various binding affinities to the vast number of receptors in almost every tissue and therefore elicit a wide variety of biologic effects. 

The purpose of this article is to formulate a model which considers simultaneous diffusion and binding reaction within the immobilized adsorbent particles. The model has been developed for batch adsorption processes. It can however be easily modified to predict product adsorption in other reactor configurations. 

Single component diffusion and binding. Figure 4 shows four cases which were simulated to observe the effects of immobilization in hydrogel and reduction of adsorbent particle size. Case (a) represents a freely suspended adsorbent particle of radius 1.1 mm. Case (b) represents the same size particle immobilized in a hydrogel bead of 2.8 mm. In case (c), the same adsorbent particle as in cases (a) and (b) was assumed to be crushed to 80 smaller particles which were immobilized within a hydrogel bead of radius 2.8 mm. Case (d) represents the extreme situation in which the adsorbent particle was crushed to fine powder such that the total number of particles within the immobilized bead may be regarded as infinite. This is also... 

Two component diffusion and binding. There is a frequent possibility of having one or more oompounds present in the fermentation broth which may compete for the available ligands in the adsorbent particles. The objective here is to optimize the bead design so as to maximize the purity of the desired product adsorbed onto the adsorbent particles. In order to numerically simulate such a situation it was assumed that two compounds are being adsorbed onto the immobilized adsorbents a desired product 1 and an undesired by-product 2. The adsorption rate constant for the desired product, K., is assumed to be 10 times that of the undesired product, K,. The diffusivities for both of these products are assumed to be similar. Two additional parameters are defined to study the dynamic behavior of such systems. 

Have a network conducive to ligand diffusion and binding to occur... 

Ab Initio Study of the F Centers in CaF2 Calculations of the Optical Absorption, Diffusion and Binding Energies. 

The competition between diffusion and binding for the following recognition reaction, between the target molecule B and the receptor A, obeying a Langmuirian kinetic law may be described as follows ... 

Figure 18.9 Kinetics of F-COX-2 inhibitor. The imaging probe enters tissue via hydrophobic diffusion and binds to COX-2, which is overexpressed in cancer. The inserted image, obtained 25 50 min after tracer injection, demonstrates low Uver and lung background activity but moderate tracer accumulation in the skeleton, which is explained by late defluorination of the compound. Focally increased tracer activity in the left axilla is due to tracer contamination (arrow).

Figure 18.10 Kinetics of F-EGFR-kinase inhibitors. The inhibitor enters the cell by diffusion and binds covalently to the intracellular kinase domain of the EGFR. The inserted images demonstrate the biodistribution of the labeled compound in a vervet monkey. At 20 min after injection, the tracer shows rapid biliary clearance into the bowel. At 80-100 min, tracer uptake in the skeleton consistent with defluorination is noted (arrow).

Note It is very important to aggressively dunk the arrays up and down for a few seconds when they are first exposed to the succinic anhydride solution. This seems to eliminate diffusion and binding of the DNA away from the original spot (manifested as comet tails that emanate from the spots after the subsequent hybridization step see Protocol 27.5). 

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