ISSN:
1432-1424
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Biologie
,
Chemie und Pharmazie
Notizen:
Summary The permeability and reflection behavior of cross-linked collagen films in dilute salt solutions have been investigated by measurements of net volume flow, isotopic exchange of THO and of Ca45, and osmotic pressure. Complementary measurements of swelling, membrane resistance, membrane potential, and streaming potential are presented. Measurements were performed in the pH range of 5 to 1.5, at temperatures between 25 and 52 °C, and in the presence of KCl, 10−2 m or CaCl2, 10−3 m. Under the conditions adopted, the membrane carries a net positive charge and undergoes large changes in degree of swelling (Donnan effect) and structure (crystal → amorphous transition). The results indicate that when pH is lowered the filtration coefficientL p decreases in the crystalline state (pH 5 to 3), increases during the conformational transition (pH 3 to 2), and decreases in the amorphous state (pH〈2). It appears thatL p is affected more by such properties as structure and porosity (i.e., mechanical resistance to flow) than properties related to the charged character of the membrane. The reflection coefficient σ increases when pH is lowered until pH ∼3, and decreases upon further lowering of pH. Such behavior is described in terms of the competition between swelling (due to both the Donnan effect and the melting transition) and fixed-charge density. Values of fixed-charge density derived on the basis of a theoretical expression for σ were found to be in good agreement with independent titration data.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF01868099
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