Partition coefficient compositional control

Figure 15. Variation in Dxh for garnet versns reciprocal temperature for experimental data sources listed in Table lb at a variety of pressures n = 33). A distinction is made between mantle solidus partition coefficients (Salters and Longhi 1999 Salters et al. 2002 McDade et al. 2003a,b) and the rest. Note the strong temperatnre dependence, which is qnalitatively similar to that incorporated in Equation (25b). The scatter is due to additional compositional controls.

The physico-chemical parameters of the chemical stimuli which have been shown to have relevance and to be interrelated to the sensory response it elicits as specific odor or taste, are the factors controlling concentration at the receptor areas (solubility, hydrophilicity, lipophilicity, volatility, and partition coefficients), molecular features (size, shape, stereochemical and chirality factors and functional groups), and electronic features (polarity and dipoles) controlling positioning and contact at receptor surfaces (53). Many of these physico-chemical data are not available for many of the chemical stimulants, and till they are gathered, structure-response studies will be much restricted. The effects of interactions of the above parameters appear to a larger degree in the perception of odor, the dimensions of which are many and complex viz. nuances, composite... 

The behavior of some siderophile elements is controlled by the composition of the metal, and, in particular, the Fe/Ni ratio. Because the activity coefficient of a siderophile element, M, may be different in a nickel-rich metal than an iron-rich metal, an understanding of this effect is necessary before partition coefficients can be successfully applied to a natural system. A good example is tin, which has a low activity coefficient in iron-rich metal, and a high activity coefficient in nickel-rich metal (Figure 8 Capobianco et al., 1999). Metal composition can change as a function of/o, and this can then change the solubility in the silicate melt. In addition, the Fe/Ni ratio in metal is sometimes used to impose a specific/o on a system. These effects are linked and must be unraveled first in order to understand tin in planetary mantles (Righter and Drake, 2000). 

Sometimes unravelling the separate effects of temperature and composition can be difficult, especially where the liquidus temperature of a melt is a function of composition. Such is the problem with Ni partitioning between olivine and a basaltic melt. Two experimental studies, published at the same time, seem to show conflicting results. Leeman and Lindstrom (1978) showed that the prime control on the olivine partition coefficient for Ni in a natural basaltic melt was temperature whilst Hart and Davis (1978) showed that there is clear inverse correlation between the melt composition and partition coefficient. To resolve the apparent conflict... 

Sr, Eu) with the less mobile HFS elerhehts (Y, Hf, Zr, Ti, Nb, Ta). On the one hand the LIL element concentrations may be a function of the behaviour of a fluid phase, whilst the HFS element concentrations are controlled by the chemistry of the source and the crystal/melr processes which have taken place during the evolution of the rock. Partition coefficients for the HFS elements in the major rock-forming minerals in a range of melt compositions are summarized in Tables 4.1 to 4.3. 

The chemical structure of an encapsulated molecule is an important parameter that can influence the partition coefficient and then the controlled release into a food. Alcohols and short-chained esters had higher partition coefficients in the oil/polymer system, than in the water/polymer system. Several studies have attempted to model the relationship between the encapsulated molecule, the composition of the food, and the partition coefficient (Arab Tehrany and Desobry 2004). It is also known that matrix crystallinity and glass transition of the matrix are key factors for an efficient controlled release of an active compound. A controlled transition from glassy to rubbery state (temperature, water activity) leads to the best system for good food preservation. A lot of work stiU has to be done to allow perfect control of an active compound release. 

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