Low molecular weight polyethylenimine (1800 Da, also referred to as oligoethylenimines,\nOEI) was modified with amino acids, including two aromatic amino acids (tryptophan, phenylalanine)\nand an aliphatic amino acid (leucine). The substitution degree of amino acids could be controlled by\nadjusting the feeding mole ratio of the reactants. Fluorescence spectroscopy and circular dichroism\nexperiments demonstrated that the indole ring of tryptophan may intercalate into the DNA base\npairs and contribute to efficient DNA condensation. In vitro gene expression results revealed that\nthe modified OEIs (OEI-AAs) may provide higher transfection efficiency even than high molecular\nweight polyethylenimine (25 kDa, PEI), especially the aromatic tryptophan substituted OEI. Moreover,\nOEI-AAs exhibited excellent serum tolerance, and up to 137 times higher transfection efficiency than\nPEI 25 kDa that was obtained in the presence of serum. The cytotoxicity of OEI-AAs is much lower\nthan PEI 25 kDa. This study may afford a new method for the development of low molecular weight\noligomeric non-viral gene vectors with both high efficiency and biocompatibility.
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