| abstract |
Comounds having the formula <IMAGE> wherein: a is 2 or 3; b is an integer from 0 to 4; Me(a+) is an ion of an element of atomic number from 57 to 70 or an ion of a transition metal of atomic number 21-29, 42 or 44; E(b+) is one or more physiologically biocompatible cation of an inorganic or an organic base or amino acid, said cation representing a total positive charge of b units; S is the group -A-O-R wherein: A is -(CH2)m-; -CH2-C(CH3)2-; m is an integer from 1 to 5; R is H; linear or branched alkyl of 1 to 8 carbon atoms, said carbon atoms being unsubstituted or substituted by one or more hyroxy group; aralkyl of 1 to 4 aliphatic carbon atoms; phenyl or phenyl substituted by halogen, amino, hydroxy or trifluoromethyl; (poly)-oxa-alkyl of 1 to 10 oxygen atoms and from 3 to 30 carbon atoms; R1 is R2 or -CH2COOZ; -CH(CH3)COOZ; -(CH2)n-N(CH2COOZ)2; hydroxy-arylalkyl radical in which the aryl radical is unsubstituted or substituted by hydroxy; R2 is -CH2COOZ; -CH(CH3)COOZ; with the proviso that when R1 is -CH2COOZ or -CH(CH3)COOZ, R2 is other than -CH2COOZ and -CH(CH3)-COOZ <IMAGE> wherein: R3 is -CH2COOZ; -CH(CH3)COOZ; a monovalent radical having the structure S-CH-COOZ; X is a direct chemical bond; -O-; -S-; -NH-; -N-CH2COOZ; -N-CH(CH3)COOZ; n is the integer 2 or 3, with the proviso that when X is a direct chemical bond, n is 1, 2 or 3; Z is H or a negative charge; with the proviso that, unless R represents a trifluoromethyl substituted phenyl or R1 is R2, Me(a+) is different from Fe(2+), Fe(3+), Gd(3+)and Mn(2+) and with the proviso that when R1 is R2 every molecule can contain not more than 500 nitrogen atoms. |