Partitioning experiments

The evaluation of the apparent ionization constants (i) can indicate in partition experiments the extent to which a charged form of the drug partitions into the octanol or liposome bilayer domains, (ii) can indicate in solubility measurements, the presence of aggregates in saturated solutions and whether the aggregates are ionized or neutral and the extent to which salts of dmgs form, and (iii) can indicate in permeability measurements, whether the aqueous boundary layer adjacent to the membrane barrier, Umits the transport of drugs across artificial phospholipid membranes [parallel artificial membrane permeation assay (PAMPA)] or across monolayers of cultured cells [Caco-2, Madin-Darby canine kidney (MDCK), etc.]. 

Figure 5. Variation in apparent lattice-site Young s Modulus ) with molar anorthite content of the host crystal for the plagioclase partitioning experiments of Blundy and Wood (1994)., Ej and...

By analogy with clinopyroxene it is likely that Pa enters the orthopyroxene M2 site. In light of the fact that Du and Dxh in orthopyroxene are approximately ten times lower than in clinopyroxene, it is likely that Z)pa is also lower in orthopyroxene. However, this effect is offset to some extent by the smaller M2 site in orthopyroxene, which will tend to be more favourable to Pa than the M2 site in clinopyroxene. We have used the electrostatic model, applied to the two orthopyroxene-melt partitioning experiments of McDade et al. (2003a,b) to derive (Fig. 13). Both datasets, at 1.5 and 3 GPa, are... 

Experimental verification of the observational inferences is complicated by the difficulty of performing mineral/fluid partitioning experiments at high temperatures and pressures and their dependence on /O2 and complexing agents in the fluid (especially COs and Cl ). Nevertheless some attempts have been made (e g., Tatsumi et al. 1986 Brenan et al. 1994, 1995 Keppler 1996 Ayers et al. 1998 Johnson and Plank 1999). 

The complexing ability of crown ethers in solvents of low polarity has been studied using two-phase partition experiments (Frensdorf, 1971b). The equilibrium between an aqueous solution of the salt (MX) and an organic solution containing the crown ether (Cr) is given by (2). Further dissociation of... 

Wright I, Grady MM, PUlinger CT (1990) The evolution of atmospheric C02 on Mars the perspective from carbon isotope measurements. 1 Geophys Res 95 14789-14794 Wunder B Meixner A, Romer R, Wirth R, Heinrich W (2005) The geochemical cycle of boron constraints from boron isotope partitioning experiments between mica and fluid. Lithos 84 ... 

Blum J.D., Wasserburg G.J., Hutcheon i.D., Beckett J.R., and Stolper E.M. (1989) Diffusion, phase equilibria and partitioning experiments in the Ni-Fe-Ru system. Geochim. Cos-mochim. Acta 53, 483-489. 

Equilibrium Partitioning Experiments. The equilibrium partitioning of americium-III between gray hornblende schist and rock equilibrated water was determined in batch partitioning experiments with rectangular blocks of gray hornblende schist ( 5). The surface area sorption coefficient, K, was determined to be 4.5 . 5 mL/cm where... 

Note that if Kf has been determined from solubility measurements, ywsaU is strictly valid only for saturated conditions. For dilute solutions y,wsalt can be determined from measurements of air-water or organic solvent-water partition constants at different salt concentrations. From the few compounds for which ywsa,t has been determined by both solubility and air-water or solvent-water partitioning experiments, because of the large scatter in the data, it is not clear whether Kf varies with organic solute concentration. It can, however, be concluded that, if there is an effect, it is not very large. 

Certain organic liquids also dissolve sulphur dioxide, and a direct comparison of the solubility in water and in chloroform has been effected by partition experiments,4 in which measurement is made of the distribution of the gas between the two solvents in contact with one... 

To determine the alkylation efficiencies of these selected glycidyl ethers, syntheses of HMHEC polymers were conducted using wood pulp and ethylene oxide, using the same glycidyl ethers used in the partitioning experiments (Table 1). The details on the synthesis of HMHEC polymers directly from wood pulp and ethylene oxide have been reported elsewhere. 

Partition experiments provide a very powerful approach for the detection of intermediates. 

Table 7.3 Kinetic constants for the hydrolysis of S-acyl-L-amino acid esters by a-chymotrypsin at 25°C. pll 7.8, and ionic strength 0.1 M, determined by partitioning experiments" ...

The validity of partitioning experiments and some possible experimental errors... 

Neither the occurrence of a constant value of Vmax or a constant product ratio is sufficient proof of the presence of an intermediate. It was seen for alkaline phosphatase that a constant value for Vmax is an artifact, and also that there is no a priori reason why the attack of acceptors on a Michaelis complex should not also give constant product ratios. In order for partitioning experiments to provide a satisfactory proof of the presence of an intermediate, they must be linked with rate measurements. When the rate measurements are restricted to steady state kinetics, the most favorable situation is when the intermediate accumulates. If the kinetics of equations 7.5 to 7.7 hold, it may be concluded beyond a reasonable doubt that an intermediate occurs. The ideal situation is a combination of partitioning experiments with pre-steady state studies, as described for chymotrypsin and amides. 

Chapter 8 (section C3) presents stereochemical evidence that the hydrolysis of /3-o-galactosides catalyzed by /3-galactosidase (equation 7.11) involves two successive displacements on the C-l carbon—i.e., involves an intermediate. Further evidence for an intermediate from partitioning experiments is presented in Table 7.10. There is constant partitioning between water and methanol.39-41... 

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