Experimental designs for optimizing the purification of immunoglobulin G by mixed-mode chromatography.

The main aim of this study was to define the optimal adsorption and elution conditions for the purification of human immunoglobulin G (IgG) by mixed-mode chromatography using the multimodal resin Capto MMC. To this end, Central Composite Experimental Design (ED) was performed for both the adsorption and desorption stages. In the first case, the conditions were systematically studied in batch mode while in the latter case, these were performed in column. For both studies, the experimental design was conducted using high-purity human IgG samples. Buffer pH and concentration as well as the salt concentration were the parameters under study in the ED. Adsorption kinetics and equilibrium experiments were performed under the best conditions defined in the ED (phosphate buffer 60 mmol/L, pH 6.75, no salt). The equilibrium experimental data were fit to the Langmuir equation, with maximum uptake qmax equal to 549.2 mg/g. The qmax value found for IgG in Capto MMC was quite high as compared to other chromatographic techniques that employ single modes of interaction. Regarding elution, the best conditions were obtained with acetate buffer (56.40 mmol/L), pH 5.2 and 0.2 mol/L NaCl. An ultimate recovery of 46.96% for high-purity IgG was achieved. Thus, the effectiveness of Capto MMC for IgG adsorption and recovery could be confirmed. Moreover, electrophoretic runs in the human serum indicated that although co-elution of HSA and IgG proteins occurs, substantial HSA removal and a high IgG recovery were achieved in the elution step.

Monte Carlo simulations of non-Fickian water transport in a saturated porous gel.

A Monte Carlo algorithm, which incorporates tensile effects as well as diffusion, is proposed. It provides a description of water transport in a drying porous gel close to saturation permitting an interpretation of magnetic resonance imaging profiles. Boltzmann's transformation of the one-dimensional diffusion equation is employed to examine the onset of a non-Fickian transport regime caused by the collective motion of diffusers associated with tensile forces.

Mobility and free radical concentration effects in proton-electron double-resonance imaging.

The dependence of the enhancement of proton-electron double-resonance images upon the mobility of the proton bearing molecules, of the concentration of free radicals, and of the pulsed saturating RF power is studied in a magnetic field of 16 mT. The data exhibit a behavior which, in the potentially interesting region of small free radical concentration, may differ substantially from the high-concentration regime depending upon experimental conditions. The results permit a clearer understanding of the factors determining enhancement and contrast in images obtained by dynamic nuclear polarization.