PubMed · 9479211
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B Faller. 1997. [Peritoneal dialysis. Principles].. https://pubmed.ncbi.nlm.nih.gov/9479211/
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We investigated the conductivity of binary mixtures of different volume to volume ratios of liquid polyethylene glycol 200 (PEG 200) and solid PEG 6000. The conductivity was measured using a specially designed cell, which could be filled with the sample to be analysed. The results were analysed by the help of the percolation theory and its basic equation: X=S(p-p(c))(q) with X=gamma the conductivity and X=k the dissolution rate constant of binary mixtures with p the concentration of PEG 200 including Mepyraminmaleat as a marker substance. The intrinsic dissolution rate was determined spectrophotometrically. The simultaneous determination of the critical exponent q and the percolation threshold p(c) of the conductivity experiment yielded the following values q=1.83+/-0.05 and p(c)=11.6+/-1.1% with a squared correlation coefficient R(2)=0. 9986. For q=mu=2.00 fixed the percolation threshold is equal to p(c)=8.4+/-1.3% with R(2)=0.9984. Thus if the same percolation threshold p(c)=8.4+/-1.3% is adopted for the dependence of the dissolution process q becomes equal to q approximately mu=1. 94+/-0.045. R(2)=0.9991. This result is in excellent agreement with the theoretical prediction that the permeability of a porous network scales in the same way as the conductivity.
The headspace of vials containing oxygen-sensitive formulations is filled with a nitrogen blanket. This paper presents the development of a mathematical model to predict the oxygen and nitrogen permeation rates through the walls of plastic CZ-resin vials. The model estimates the time required for a nitrogen-filled vial to reach ambient nitrogen and oxygen levels. The permeation of oxygen and nitrogen through the vial is governed by Fick's law and may be described by an exponential equation. Using the values for oxygen and nitrogen permeation through CZ-resin vial, the half-lives for the decrease in nitrogen level and increase in oxygen level was found to be 150 days and 15 days, respectively. This result can be attributed to the greater permeability of CZ-resin vial to oxygen (79.06 cm(3)-mm/m(2)-24 h-atm) when compared with nitrogen (12 cm(3)-mm/m(2)-24 h-atm). The ingress of oxygen into CZ-resin vials was determined experimentally and it was found to verify the model. These results indicate that CZ-resin vials may be inappropriate for packaging oxygen-sensitive formulations even in the presence of a nitrogen-filled headspace.
A protein chain must move relative to the solvent molecules and explore many conformations when it folds from the extended unfolded state to the compact native state. Experimental and theoretical approaches suggest that diffusional processes in fact contribute to the kinetics of protein folding. We describe here how variations of the solvent viscosity can be employed to uncover the diffusional contributions to a folding reaction and assess the use of transition state theory and Kramers' rate theory for the analysis of protein folding reactions.