Abstract: A polymer containing an N-linked sialo-glycan wherein a sialo-glycan is condensed to a ?-polyglutamic acid using a chemical compound having an amino group on one end and a carboxyl group on another end and represented by the structural formula (I). Formula (I) (In the formula, Z means a hydroxy group or a residue represented by the formula (II), and n represents an integer of 10 or more, with the proviso that any one or more of the Z's is represented by the formula in (II).) Formula (II) (In the formula, X means a hydroxy group or an acetylamino group, Y1 and Y2 mean a hydroxyl group or an N-acetylneuraminic acid residue, L means a hydrocarbon, an m represents 0 or an integer of 1 or 2, with the proviso that Y1 and Y2 are not the same.

Abstract: The present invention provides novel phospholipid derivatives. Furthermore, the present invention provides lipid membrane structures excellent in gene/nucleic acid introduction efficiency into a cell.