th a compound of formula III Z--(CH2)p --Q III in which Q represents --OH, --SH, --NH2 or --NHR in which R is an alkyl group having 1 to 4 carbon atoms, Z represents an aliphatic group having 2 to 10 C atoms and carrying at least one tertiary amino group or represents a heterocyclic group having at least one basic ring nitrogen atom not bonded to a hydrogen atom,