her represent hydrogen, an optionally substituted straight-chained or branched, saturated or unsaturated alkyl, aryl, alkylaryl or alkylene group composed of three to 24 C atoms, in which a carboxyl alkyl or dicarboxyl-alkyl residue composed of two to 24 C atoms is particularly preferred and X represents an atom or a group of atoms with a positive charge and n denotes the number 1 or 2, have prove