Journal
JOURNAL OF CONTROLLED RELEASE
Volume 69, Issue 2, Pages 309-322Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S0168-3659(00)00317-5
Keywords
polycations; polyethylenimine; synthesis; buffer capacity; intrinsic viscosity; Mark-Houwink parameters
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Five new polyethylenimines (PEI) were synthesized by polymerization of aziridine in aqueous solution and compared to several commercially available PEI used for gene transfer. Polymers were characterized by C-13 NMR spectroscopy, capillary viscosimetry, potentiometric titration and Cu(II) complex formation to gain insight into structural and functional properties. C-13 NMR analysis revealed differences in the extent of branching based on the ratio of primary, secondary and tertiary amino groups. An amino group ratio 1 degrees :2 degrees :3 degrees =1:2:1 was obtained for the synthesized PEI, whereas commercially available PEI generally showed a higher degree of branching (1:1:1). Capillary viscosimetry of aqueous PEI solutions with a sufficient amount of salt gave Mark-Houwink parameters of alpha =0.26 and K-V=1.00 cm(3)/g for the commercially available polymers. In case of the synthesized polymers, variation of reaction conditions yielded viscosity average molar masses (M-v) in the range of 8000-24000 g/mol. PEI solutions were investigated by potentiometric titration analysis showing that their buffer capacity was not significantly influenced by molar mass or polymer structure. The pK(a) values (8.18-9.94) and the buffer capacity beta (0.08-0.014 mol/l) were of comparable magnitude. This study highlights the necessity of more detailed characterization methods for PEI used in gene transfer protocols since physico-chemical properties do not reflect the vast differences found in transfection efficiencies. (C) 2000 Elsevier Science B.V. All rights reserved.
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