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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Pharmaceutical research 12 (1995), S. 1614-1617 
    ISSN: 1573-904X
    Keywords: pKa ; stratum corneum ; fatty acid ; ionization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The apparent pKa of the fatty acids within hydrated (30 % w/w) model human stratum corneum (SC) lipid mixtures should be measured. Methods. The degree of ionisation of the fatty acids was calculated as a function of pH using Fourier transform infra-red spectroscopy. The relative intensity of the stretching bands of the unionized and ionized carboxylic groups was determined and fitted to the relevant expression for ionic equilibrium of a monoprotic acid. The pKa was then calculated for increasing proportion of unsaturated fatty acid in the lipid mixture. Results. Values for pKa in the range 6.2-7.3 were found, increasing with greater proportion of oleic acid. These are some 1.5-3 pH units higher than the pKas of fatty acids in molecular solution. Conclusions. As there exists a pH-gradient across the SC, the degree of ionisation will also vary. In the innermost SC layers, a pH of 7 will produce 90% ionization of the fatty acids and head-group repulsion will be great. At the SC surface, the pH of 5 will cause almost minimal head-group repulsion, tending to increase crystallinity and promote a bilayer structure.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 120 (1993), S. 119-126 
    ISSN: 1573-4919
    Keywords: liposome stability ; liposome-blood interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Lipid composition and specially their electrostatic properties, were found to greatly influence the stability of liposomes in human blood serum. The amount and type of serum proteins bound to the liposomes were also clearly influenced by lipid composition and charge of liposomes. a good correlation was found between the amount of serum proteins adsorbed to a given type of liposome and its instability as measured by the release of an encapsulated fluorescent probe. Liposomes that bind the highest amount of protein were the least stable, except for the case of liposomes containing gangliosides, which were fairly stable even at a high amount of bound protein. Liposomes with neutral charge containing phosphatidylcholine were the most stable and bound the lowest amount of protein. Liposomes with positive charge behaved similarly to those with neutral charge. However, the stability of negatively charged liposomes was very dependent on their composition. Those liposomes containing only one class of negatively charged phospholipids bound a great amount of protein and were very unstable. However, those liposomes containing also phosphatidylcholine bound less protein and were more stable. The examination of the electrophoresis patterns of serum proteins bound to the different types of liposomes indicated the presence of specific proteins which correlated with liposome instability. (Mol Cell Biochem120: 119–126, 1993)
    Type of Medium: Electronic Resource
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