Partition rate

Lipophilicity is intuitively felt to be a key parameter in predicting and interpreting permeability and thus the number of types of lipophilicity systems under study has grown enormously over the years to increase the chances of finding good mimics of biomembrane models. However, the relationship between lipophilicity descriptors and the membrane permeation process is not clear. Membrane permeation is due to two main components the partition rate constant between the lipid leaflet and the aqueous environment and the flip-flop rate constant between the two lipid leaflets in the bilayer [13]. Since the flip-flop is supposed to be rate limiting in the permeation process, permeation is determined by the partition coefficient between the lipid and the aqueous phase (which can easily be determined by log D) and the flip-flop rate constant, which may or may not depend on lipophilicity and if it does so depend, on which lipophilicity scale should it be based ... 

The partition rates of orbencarb and I in aqueous solutions (pH 2-12) into ethyl acetate-n-hexane (1 1, v/v) were as high as 87-90%, and the partition rate did not differ depending on the pH of the liquid. On the other hand, the recovery of II from aqueous solutions into ethyl acetate-n-hexane (1 1, v/v) was 85% at pH 2, 34% at... 

Partition rate constant ratios from product analyses 72... 

One can correct the observed distribution of 1,2-C and 1,2-H products so as to reflect only the carbenic pathway.28 The corrected 1,2-C/1,2-H ratio (4.8), coupled with a pyridine ylide absolute rate constant for overall carbene rearrangement (kc + % = 6.8 x 107 s 1), gives the partitioned rate constants kc = 5.6 x 107 s 1 and ifeH = 1.2 x 107 s-1.28 The dominance of 1,2-C over 1,2-H in this system will be discussed below. 

We have focused on determining partition rate constant ratios for a variety of reactions of ion pairs, and of absolute rate constants from these ratios. This has been accomplished by use of one of the rate constants from this product ratio as a clock for the second reaction. 

When the rate constants are large numbers (fast reactions), both the numerators and the denominators of Eq. (5.94) can be divided by k-. Since kjk. = A da and ( i) can be neglected relative to the other terms in the sum (A da A + A -I- A ), an equation identical with Eq. (5.73) is obtained for which only diffusion controls the partition rate. At the other extreme, when interfacial film diffusion is very fast, and the reactions are very slow, we can set 1 > QcA + k-i A ) and the rate equation becomes equal to... 

Laboratory Unit Fire Hazard Class Fire Separation-Fire-Resistive Partition Rating ... 

Isotope fractionation methods for characterizing biochemical pathway mechanisms, SITE-SPECIFIC ISOTOPE FRACTIONATION FOR CHARACTERIZING BIOCHEMICAL MECHANISMS Isotope partitioning rate laws,... 

The rate of H2Oz consumption and the OH production were directly related to total iron concentration. The concentrations of hydroxyl radical produced were controlled by the rate of reaction with dissolved constituents. Rate constants for adsorption (ka) and desorption (kd) of PCBs from particles were calculated by regression of data from 1.5 to 5 hr. Adsorption rate constants were estimated from Equation (6.130) assuming that the partitioning rate constants between 2 and 5 hr without OH could be used for calculation of equilibrium partition coefficients Ky)... 

On a reverse-phase column, separation occurs because each compound has different partition rates between the solvent and the packing material. Left alone, each compound would reach its own equilibrium concentration in the solvent and on the solid support. However, we upset conditions by pumping fresh solvent down the column. The result is that components with the highest affinity for the column packing stick the longest and wash out last. This differential washout or elution of compounds is the basis for the HPLC separation. The separated, or partially separated, discs of each component dissolved in solvent move down the column, slowly moving farther apart, and elute in turn from the column into the detector flow cell. These separated compounds appear in the detector as peaks that rise and fall when the detector signal is sent to a recorder or computer. This peak data can be used either to quantitate, with standard calibration, the amounts of each material present or to control the collection of purified material in a fraction collector. 

Moody, R.P., Carroll, J.M., Kresta, A.M.E. (1987) Automated high performance liquid chromatography and liquid scintillation counting determination of pesticide mixture octanol/water partition rates. Toxicol. Ind. Health 3, 479 -90. 

The argument that kinetics are important has lead to the present study of in vitro partitioning rates. How are such data to be used There are several stages, which are developing in parallel in the literature. 

Compare partitioning rate data to molecular features, e.g., is rate proportional to partition coefficient Are there common structural features associated with rapid or slow transport ... 

There is a possible negative feedback to control the increase in CO2 in the atmosphere by increasing the partition rate after you reach some concentration of the CO2 in the atmosphere. 

Figure 2 shows a displacement procedure as well as the concentration procedure in the HSCCC column after most ions in the sample are extracted on the top of the stationary phase. If sample contains two kinds of divalent metal ions (Cu and Cd) in a large amount of solution, each metal might be arranged by difference of its affinity or partition rate to the stationary phase. As Cd ion is usually more extractable than Cu ion, Cd can displace Cu at the end (left) of the Cu band in the stationary phase. However, the bandwidth of Cd is increasing until the entire sample was introduced into the column. 

Our group has based the modelling on the classical redox mechanisms involving cations, anions and solvent, which lead to a generalized partition rate for species i Ji < 0 for inserting species) ... 

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