A compound of general formula (I): in which: R is selected from the group consisting of (C1-C25)alkyl, (C2-C25)alkenyl, aryl, (C7-C10)aralkyl； n and m are each independently an integer of two to eight； p is one or two； A is selected from the group consisting of -B-, -B-(CH2)r-B-, -B-(CH2)r-B-(CH2)z-B-, wherein r and z are an integer from 2 to 8, B is a -NR1- or -N(R2)2+1/pQ-p group, in which R1 is selected from hydrogen, (C1-C4)alkyl, (C1-C4)acyl, tert-butoxycarbonyl, and R2 is selected from hydrogen and (C1-C4)alkyl； Q-p is an anion selected from chloride, bromide, iodide, nitrate, sulphate, hydrogen sulphate, perchlorate, R3COO- wherein R3 has the same meanings as R, independently from one another and R4-O-SO3- wherein R4 is (C2-C14)alkyl with the proviso that, when Q-p is selected from chloride, bromide, iodide, nitrate, sulphate, hydrogen sulphate, perchlorate, R is not (C1-C4)alkyl.
