A compound of the formula I or II ##STR10## in which R.sup.1 and R.sup.2 independently of one another represent H--(CH.sub.2).sub.a --(O---CH.sub.2).sub.b).sub.c --O, where a=0 to 4, b=1 to 4 and c=1 to 7, an alkoxy or arylalkoxy group with 1 to 20 carbon atoms, an alkane- or aralkanesulfonyloxy group with 1 to 7 carbon atoms or a tetrahydropyranyloxy radical, or R.sup.1 and R.sup.2 together represent an oxygen atom bonded in an ether-like manner or an acetal or ketal radical ##STR11## where R.sup.3 and R.sup.4 independently or one another represent a hydrogen atom, an alkyl group with 1 to 20 carbon atoms or a phenyl group, A.sup.1 and A.sup.2 are identical and represent a hydroxyl group, chloride, bromide, iodide, nitrate, acetate, trifluoroacetate, trifluorosulfonate or perchlorate, or A.sup.1 represents sulfate or carbonate and A.sup.2 represents H.sub.2 O, or A.sup.1 or A.sup.2 together represent the diamion or an organic acid selected from the group consisting of oxalic, malonic, hydroxymalonic, ethylmalonic, succinic, maleic, aconitic, 3,6,9-trioxaundecanedioic, 1- or 1,2-cyclobutanedicarboxylic, phthalic, 3- or 4- carboxyphthalic and 3,4-dicarboxyphthalic acid, or A.sup.1 and A.sup.2 together represent a recurring anionic unit of a polymeric compound selected from the group consisting of dextran sulfate, chondroitin sulfate, galactan sulfate, polyglutamic acid or polyitaconic acid.