Concentration effect, compartmentalized

Keeping in mind all three DNA structure levels, primary, secondary, and tertiary, it is essential to understand that the lower level will mediate but not fully determine the higher structural level. In other words, the secondary as well as tertiary DNA structures of ODN in solution will be affected by many physical and chemical parameters, such as temperature, pH, salt content, compound concentration, etc. When evaluating complex biochemical systems, additional factors have to be taken into consideration possible interactions of ODN with a variety of other molecules and macromolecules in solution, local concentration effects and compartmentalization, biological half-life, etc. Hence when designing a DIMS ODN compound, its 3-D structure will not be fully predictable. 

Considerations of radical compartmentalization and higher polymer concentration effects are not sufficient to describe the processes that build branched polymer molecules in emulsion polymerization, and the effects of limited space must be properly taken into account [266-269]. 

The (effective) concentration of reactants is small, which is especially important in second-order reactions. It may be due to small total concentrations, to compartmentalization or immobilization, or to a complicated cascade of reactions with several side-tracks that consume reactants for other reactions. 

Of probably greater importance is the effect of local concentration gradients. For example, analysis for a given constituent in the entire meat mass does not reflect the real concentration at a given point. For example, DNA is localized in the nuclei and lipid is localized predominantly in the adipose cells. Another factor of potential influence in reaction schemes for nitrite is the fact that polar-nonpolar interfaces are present as a result of structural compartmentalization. In an adipose cell, the lipid is contained as the body of the cell, but it is surrounded by a thin layer of sarcoplasmic protein. Therefore, large surface areas are involved. 

Substrate availability to the cell is affected by the supply of raw materials from the environment. The plasma membranes of cells incorporate special and often specific transport proteins (translocases) or pores that permit the entry of substrates into the cell interior. Furthermore pathways in eukaryotic cells are often compartmentalized within cytoplasmic organelles by intracellular membranes. Thus we find particular pathways associated with the mitochondria, the lysosomes, the peroxisomes, the endoplasmic reticulum for example. Substrate utilization is limited therefore by its localization at the site of need within the cell and a particular substrate will be effectively concentrated within a particular organelle. The existence of membrane transport mechanisms is crucial in substrate delivery to, and availability at, the site of use. 

The rate of dispersion (co)polymerization of PEO macromonomers passes through a maximum at a certain conversion. No constant rate interval was observed and it was attributed to the decreasing monomer concentration. At the beginning of polymerization, the abrupt increase in the rate was attributed to a certain compartmentalization of reaction loci, the diffusion controlled termination, gel effect, and pseudo-bulk kinetics. A dispersion copolymerization of PEO macromonomers in polar media is used to prepare monodisperse polymer particles in micron and submicron range as a result of the very short nucleation period, the high nucleation activity of macromonomer or its graft copolymer formed, and the location of surface active group of stabilizer at the particle surface (chemically bound at the particle surface). Under such conditions a small amount of stabilizer promotes the formation of stable and monodisperse polymer particles. 

As previously discussed, compartmental models can be effectively used to project plasma concentrations that would be achieved following different dosage regimens and/or multiple dosing. However, for these projections to be accurate, the drug PK profile should follow first-order kinetics where various PK parameters such as CL, V,h T /2, and F% do not change with dose. 

From the above it can be concluded that in many instances the introduction of an artificial radionuclide into the environment provides us with a natural tracer experiment. Indeed, this is the basis for the application of deterministic compartmental models, based on tracer kinetics, to radioecology (Whicker and Schultz, 1982). This approach is largely based on the assumption that radionuclide movements will exhibit first order kinetics although the existence of naturally-occurring tracees (stable isotopes) at relatively high abundance may result in more complex concentration-dependent kinetics. Furthermore, nutrient analogues may exert even more complex effects on processes such as radioion absorption across root plasma membranes this will become evident later in the chapter. 

During the first decades of the development of pharmacokinetic science, a lag time in pharmacological response after intravenous administration was often treated by applying a compartmental approach. If the plasma concentration declined in a biexponential manner, the observed pharmacodynamic effect was fitted to plasma or tissue compartment concentrations. Due to the lag time of effects, a successful fit was sometimes obtained between effect and tissue drug level [414]. However, there is no a priori reason to assume that the time course of a drug concentration at the effect site must be related to the kinetics in tissues that mainly cause the multiexponential behavior of the plasma time-concentration course. A lag time between drug levels and dynamic effects can also occur for drugs described by a one-compartment model. 

Micro emulsion droplets and micellar aggregates can catalyse or inhibit chemical reactions by compartmentalization and by concentration of reactants and products. The catalytic effect in micelles has been widely studied, a typical reaction being base catalysed hydrolysis of lipophilic esters. This rate enhancement is normally referred to as micellar catalysis. The analogous effect occurring in microemulsions may be called microemulsion catalysis. 

The ability of micellar solutions and mlcroemulslons to dissolve and compartmentalize both polar and non-polar reactants has a significant effect on chemical reactivity. An Idealized representation of a typical micelle catalyzed reaction is depicted In Figure 2. Here the non-polar reactant is solubilized within the micelle while the ionic reactant is at the surface. The polar head groups of the surfactants generate a charge at the micelle surface which serves to attract an oppositely charged water soluble reactant increasing the concentration of that reactant near the micelle. The result Is an enhanced reaction rate. 

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