Equilibrium dialysis studies

In a typical equilibrium dialysis study of charged polysaccharides an indicator ion, L (chromate), is included in the supporting electrolyte medium (phosphate buffer, pH 6.8, I 0.08) to allow assessment of the effective net charge of the polyanions via a modified form of Eq. 31, namely. 

Equilibrium dialysis studies indicate around 10 repeat VP units (base moles) are required to form favorable complexes. This figure can rise to several hundred for methyl orange and other anions depending on structure. 

Smoluk GD, Fahey RC, Ward JF (1986) Equilibrium dialysis studies of the binding of radioprotector compounds to DNA. Radiat Res 107 194-204... 

Equilibrium dialysis studies on the relative affinities of weakly bound cations with varying base composition DNA have demonstrated that tetraalkylammonium ions bind more tightly to dA dT rich DNA compared to dG dC rich DNA (43). 

Fig. 4. Scatchard plots for the binding of tilorone hydrochloride to calf thymus DNA (a) Me. lysodeikticus DNA (b) poly (dA-dT) poly (dA-dT) (c) and poly (dG-dC) poly (dG-dC) (d). Each different symbol corresponds to a separate experiment. Thus, each figure represents a set of 4 or 5 separate experiments, r is moles of bound tilorone/base pair concentration and (u) is the concentration of unbound tilorone. Equilibrium dialysis was carried out by a procedure and an apparatus (Dianorm, supplied by Dr. Virus KG, Bonn, Germany) described by Weder et al.61 Dialysing membrane (0.02S mm thick) was sandwiched between two halves of a Teflon (round) macro-cell (dialysable volume = 1 ml). The DNA, or labelled tilorone solutions were introduced by separate micro syringes on either side of the membrane through the side valves. The valves were closed air tight and the macro-cells were fixed into a rotating machine. All equilibrium dialysis studies were carried out at 20°, and at 10 rotations/min. Under these conditions equilibrium was attained in 4-5 hr. After the equilibrium was reached 0.8 ml of the solution from either side of the membrane was withdrawn by microsyringes and the radioactivity was determined using dioxan scintillation fluid...

Equilibrium-dialysis studies showed two equivalent, sugar-binding sites on each isolectin intrinsic association-constants (Ka ) were 1450 230 M l for binding to D-mannose and 773 126 M I to methyl a-D-glucopyranoside. 453... 

Results Summary for the Equilibrium Dialysis Study of the Tris(l,10-phenanthroline)chromium(III) Ion, Cr(phen)3]3+,... 

Physicochemical parameters. Partition coefficients are the most common type of physicochemical parameter in a PBPK model. Values for these quantities can be measured through experimental means (e.g., equilibrating tissue homogenates in a vial with an atmosphere containing the test chemical [9,10], or from ultrafiltration/equilibrium dialysis studies for nonvolatile chemicals), or through the use of quantitative structure activity/property relationships (QSA(P)Rs) [11],... 

Once the structure of the PBPK model is formulated, the next step is specifying the model parameters. These can be classified into a chemical-independent set of parameters (such as physiological characteristics, tissue volumes, and blood flow rates) and a chemical-specific set (such as blood/tissue partition coefficients, and metabolic biotransformation parameters). Values for the chemical-independent parameters are usually obtained from the scientific literature and databases of physiological parameters. Specification of chemical-specific parameter values is generally more challenging. Values for one or more chemical-specific parameters may also be available in the literature and databases of biochemical and metabolic data. Values for parameters that are not expected to have substantial interspecies differences (e.g., tissue/blood partition coefficients) can be imputed based on parameter values in animals. Parameter values can also be estimated by conducting in vitro experiments with human tissue. Partitioning of a chemical between tissues can be obtained by vial equilibration or equilibrium dialysis studies, and metabolic parameters can be estimated from in vitro metabolic systems such as microsomal and isolated hepatocyte syterns. Parameters not available from the aforementioned sources can be estimated directly from in vivo data, as discussed in Section 43.4.5. 

The other main application of FST to open systems has involved the study of preferential interactions. This is particularly important for understanding the effects of a cosolvent on the properties of biomolecules—the urea-induced denaturation of proteins, for example. The major source for thermodynamic data on small molecule binding to proteins has been equilibrium dialysis studies (Timasheff 1998a). More recently, this has been complemented by isopiestic distillation studies (Anderson, Courtenay, and Record 2002). Both approaches provide thermodynamic descriptions of cosolvent interactions with proteins that can be used to rationalize the effects of cosolvents on protein stability obtained from isothermal-isobaric studies (Smith 2004). 

Schomacker etal. (1988) labelled human blood serum with Yb in vitro and showed, by alcohol fractionation at low temperature, that 95% of the radioactivity was associated with the albumin. Equilibrium dialysis studies in vitro using HSA-ianthan-ide solutions or whole human serum yielded values for the association constant for the lanthanide-albumin complex ranging, with increasing atomic number and decreasing ionic radius, from log Kp, = 4.7 for Ce to log = 9.5 for Yb, table 9. 

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