Partition coefficient ionic

Apparent partition coefficient (logZ)) at an ionic strength of / = 0.02M, log P value of the neutral microspecies and the acidic dissociation constant of 5 was calculated (97ANC4143). The distribution coefficient of 5 was determined between 1-octanol and universal buffer in the pH range 3-10 at a... 

Palladium, D. of as dimethylglyoximate. (g) 463 as nioximate, (g) 474 by EDTA, (ti) 329 Paper chromatography 229 see Thin layer chromatography Parallax errors due to, 85 Parallel determinations 132 Partial ionic equations 850, (T) 851 Partition chromatography 13. 217 Partition coefficient 162 Patton and Reeder s indicator 317, 328 Peptisation 419. 421... 

Aqueous solutions are not suitable solvents for esterifications and transesterifications, and these reactions are carried out in organic solvents of low polarity [9-12]. However, enzymes are surrounded by a hydration shell or bound water that is required for the retention of structure and catalytic activity [13]. Polar hydrophilic solvents such as DMF, DMSO, acetone, and alcohols (log P<0, where P is the partition coefficient between octanol and water) are incompatible and lead to rapid denaturation. Common solvents for esterifications and transesterifications include alkanes (hexane/log P=3.5), aromatics (toluene/2.5, benzene/2), haloalkanes (CHCI3/2, CH2CI2/I.4), and ethers (diisopropyl ether/1.9, terf-butylmethyl ether/ 0.94, diethyl ether/0.85). Exceptionally stable enzymes such as Candida antarctica lipase B (CAL-B) have been used in more polar solvents (tetrahydrofuran/0.49, acetonitrile/—0.33). Room-temperature ionic liquids [14—17] and supercritical fluids [18] are also good media for a wide range of biotransformations. 

In an attempt to increase the ionic liquid/hexane partition coefficient, a new salen ligand appended with an imidazolium salt was developed (Fig. 5) [18]. Unfortunately, modification of the ligand caused a dramatic reduction in the enantioselectivity - down to 57% ee at most - although the reasons for this behavior remain unclear. 

Solute Flux Solute partitioning between the upstream polarization layer and the solvent-filled membrane pores can be modeled by considering a spherical solute and a cylindrical pore. The equilibrium partition coefficient 0 (pore/bulk concentration ratio) for steric exclusion (no long-range ionic or other interactions) can be written as... 

For symmetrical electrolytes, of, e.g., type 1 1, such a liquid-liquid interface, in equilibrium, is described by the standard Galvani potential, usually called the distribution potential. This very important quantity can be expressed in the three equivalent forms, i.e., using the ionic standard potentials, or standard Gibbs energies of transfer, and employing the limiting ionic partition coefficients [3] ... 

There are three possibilities of letting the neutral species appear in the ionic partition diagram. Indeed, as the partition coefficient of the neutral species is neither potential- nor pH-dependent, the variable can be either the neutral species in the aqueous phase or that in the organic phase. However, to account for the experimental reality, it is more convenient to introduce the total mole number of neutral species [297], defined as ... 

V. Gobry, F. Re5miond and H. H. Girault, Refinment of Ionic Partition Diagrams and Determination of Partition Coefficients of Multiprotic Compounds by Electrochemistry at the Interface between Two Immiscible Electrolyte Solutions, submitted. 

Figure 4. Fits of lattice strain model to experimental mineral-melt partition coefficients for (a) plagioclase (run 90-6 of Blundy and Wood 1994) and (b) elinopyroxene (ran DC23 of Blundy and Dalton 2000). Different valence cations, entering the large cation site of each mineral, are denoted by different symbols. The curves are non-linear least squares fits of Equation (1) to the data for each valence. Errors bars, when larger than symbol, are 1 s.d. Ionic radii in Vlll-fold coordination are taken from Shannon (1976).

The approach taken here is to use the lattice strain model to derive the partition coefficient of a U-series element (such as Ra) from the partition coefficient of its proxy (such as Ba) under the appropriate conditions. Clearly the proxy needs to be an element that forms ions of the same charge and similar ionic radius to the U-series element of interest, so that the pair are not significantly fractionated from each other by changes in phase composition, pressure or temperature. Also the partitioning behavior of the proxy must be reasonably well constrained under the conditions of interest. Having established a suitable partition coefficient for the proxy, the partition coefficient for the U-series element can then be obtained via rearrangement of Equation (2) (Blundy and Wood 1994) ... 

Figure 11. The clinopyroxene-liquid partition coefficient for 4+ ions entering the M2-site shown as a function of the ionic radins of the trace cation. Changes in clinopyroxene composition along a solid solntion lead to small changes in the dimensions of M2 (ro Jw 2>), which can lead in turn to changes in the relative fractionation between 4+ ions of similar ioiuc radii, such as and Th" (shown as vertical lines). We contrast the partitioning behavior of a diopside-rich clinopyroxene = 1 044 A) and a...

Partition coefficients for Po can be derived from those for Th using Equation (8) and the ionic radii in Table 2. We have not modified the ionic radius for Po" from the value... 

Perhaps the biggest challenge in estimating U-series partition coefficients is the case of protactinium partitioning into garnet. The difficulty arises because the ionic radius of... 

Figure 24. Lattice strain model applied to zircon-melt partition coefficients from Hinton et al. (written comm.) for a zircon phenocryst in peralkaline rhyolite SMN59 from Kenya. Ionic radii are for Vlll-fold coordination (Shannon 1976). The curves are fits to Equation (1) at an estimated eraption temperature of 700°C (Scaillet and Macdonald 2001). Note the excellent fit of the trivalent lanAanides, with the exception of Ce, whose elevated partition coefficient is due to the presence of both Ce and Ce" in the melt, with the latter having a much higher partition coefficient into zircon. The 4+ parabola cradely fits the data from Dj, and Dy, through Dzi to Dih, but does not reproduce the observed DuIDjh ratio. We speculate that this is due to melt compositional effects on Dzt and (Linnen and Keppler 2002), and possibly other 4+ cations, in very silicic melts. Because of its Vlll-fold ionic radius of 0.91 A (vertical line), Dpa is likely to be at least as high as Dwh, and probably considerably higher.

Benzoic acid derivatives also altered the electrical potential across the cell membrane in neurons of the marine mollusk Navanax lnermls (46). Salicylic acid (1-30 mM) caused a depolarization very rapidly (1-2 min) and decreased the ionic resistance across the membrane. As pH was decreased, more salicylic acid was required to reverse the effect of pH on the membrane potential (47). This result is contradictory to the influence of pH on the amount of salicylic acid required to affect mineral absorption in roots (32). The ability of a series of salicylic and benzoic acid derivatives to increase PD correlated with their octanol/water partition coefficients and pKa values (48). The authors proposed that the organic acid anions bound directly to membranes to produce the observed results. 

---