Partition model

Kamens R, M Jang, K Leach (1999) Aerosol formation from the reaction of a-pinene and ozone using a gas-phase-kinetics-aerosol partitioning model. Environ Sci Technol 33 1430-1438. 

The octanol-water partition model has several limitations notably, it is not very biological. The alternative use of liposomes (which are vesicles with walls made of a phospholipid bilayer) has become more widespread [149,162,275, 380—4441. Also, liposomes contain the main ingredients found in all biological membranes. 

Partition Models for Equilibrium Distribution of Chemicals in Environmental Compartments... 

Two classes of mathematical models have been developed those which are specific and attempt to describe the transport and degradation of a chemical in a particular situation and those which are general or "evaluative" and attempt to generally classify the behavior of chemicals in a hypothetical environment. The type of modeling discussed here, equilibrium partitioning models, fall into the latter category. Such models attempt, with a minimum of information, to predict expected environmental distribution patterns of a compound and thereby identify which environmental compartments will be of primary concern. 

In its simplest form a partitioning model evaluates the distribution of a chemical between environmental compartments based on the thermodynamics of the system. The chemical will interact with its environment and tend to reach an equilibrium state among compartments. Hamaker(l) first used such an approach in attempting to calculate the percent of a chemical in the soil air in an air, water, solids soil system. The relationships between compartments were chemical equilibrium constants between the water and soil (soil partition coefficient) and between the water and air (Henry s Law constant). This model, as is true with all models of this type, assumes that all compartments are well mixed, at equilibrium, and are homogeneous. At this level the rates of movement between compartments and degradation rates within compartments are not considered. 

These hydrolytic profiles have been obtained mostly in homogeneous buffered aqueous solutions, but the natural water body contains many kinds of dissolved and suspended matters such as humic substances, metal oxides, and clay particles. The distribution of nonionic pyrethroid molecules in these matters can be explained in terms of a partition model. The association with these matters reduces the fraction of... 

Hudson, R. J. M. (1998). Modeling the fate of metals in aquatic systems the mechanistic basis of particle-water partitioning models, Crit. Rev. Anal. Chem., 28, 19-26. 

The studies on phospholipid bilayers with defined amounts of charged component are helpful to explain the partition characteristics in biological membranes. Liposome water partition data of propranolol in lipids from kidney epithelial cells (a common model system in pharmaceutical sciences for the uptake into the gastrointestinal tract) have been successfully described with partition models developed for pure bilayers or defined mixtures [159]. Since lipophilic cations and anions can be used as probes for the membrane potential, their interaction with microbial and mitochondrial membranes has been studied... 

Using values of ac determined from solubility measurements, Fu and Luthy (50) found an average value of a equal to 0.51, which shows that the decrease in K c was half of that expected from the increase in solubility. This was interpreted as evidence that the cosolvent was swelling the organic fraction of the soil and consequently increasing the accessibility to the organic matter (50) in accordance with the gel-partition model (31). 

The evidence presented in the literature on the dominance of a partition mechanism in the process of adsorption of a nonionic organic pollutant onto SOM does not mean, for instance, that the physical adsorption model based on weak chemical forces of interaction can be ignored or excluded [82,99,107,109, 114,115,183,192,204-218]. The following summary is a critical evaluation for reconsidering the universal applicability of the partitioning model to various nonionic compounds onto SP0M [82,84,92,103,113,130,182,184,185,187,193, 219,220,222-226] ... 

Since SOM is not uniform in all solid phases, it cannot be universally treated as a well-defined organophilic phase. The appreciable variation of reported Kom values for many nonionic compounds between soils/sediments with change in SOM composition is a strong argument limiting the universality of the partitioning model. 

Estimations of partitioning models based on K0M correlations with Kow or solubility are acceptable as long as the limitations of these correlations are taken into consideration. 

One of the main assumptions of the Donnan partition model is that two well-defined phases (polymer and solution) exist and the electrostatic potential presents a sharp transition between them. This approximation is fulfilled when the typical decay length of the electrostatic potential (Debye length) is much shorter than the film thickness. The other limiting situation is that where all the redox sites are located in a plane and thus the Debye length is larger than the film thickness. This situation can be described by the surface potential model ... 

From a survey of the literature in chemically modified electrodes [13], one can identify simple phenomenological models that have been very successful for the analysis of a particular aspect of the experimental data. Such models are, for instance, the Dorman partition model [24, 122], the Laviron [158], Albery [159] and Anson models [127] to account for the nonideal peak width, the Smith and White model for the interfacial potential distribution [129], and so on. Most of these models contain one or more adjustable parameters that give some partial information about the system. For example, the lateral interaction model proposed by Anson [127] provides a value for the lateral interactions between oxidized and reduced sites, but does not explain the origin of the interactions, neither does it predict how they depend on the experimental conditions or the polymer structure. In addition, none of these models provide information on the interfacial structure. 

It has already been shown in Chapter 4 (section 4.2.1) that from the thermodynamic point of view the process described by Eq. (16.2) can be modeled by the sum of its partial processes (extraction steps), irrespective of whether they really proceed or not. That is because Gibbs free energy is the function of state and its total change does not depend on the reaction path. According to the complex formation-partition model [76], one can distinguish two main steps in extraction of metal ions ... 

The reported QM and MM calculations on extraction of metal ions do not comprise as a rule the whole process described by the complex formation-partition model. The calculations rarely aim at the determination of the... 

Separation factors predicted by the partition model are compared with the experimental data from reference (13) in Figure 7. The partition model predicts the magnitude of the separation factor better than the parallel capillary model (see Figure 1), however the parallel capillary model predicts the shape of the curves better. This suggests that neither model alone is sufficient to account for the separation. 

Figure 3. Separation factor-particle diameter behavior computed from the pore-partitioning model showing the effect of the Hamaker constant at a low eluant ionic strength (O.OOl M). Other parameters are = 0.60, interstitial capillary radius = l6 fim, pore radius = fim,...

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