suitable alkyl groups for use with the invention include methyl ethyl propyl isopropyl butyl cyclohexyl heptyl and octyl suitable alkoxy groups include methoxy ethoxy propoxy butoxy pentoxy hexoxy heptoxy and octoxy hydroxyalkyl groups suitable for use with the invention include both mono and poly hydroxyalkyls such as hydroxyethyl 2 hydroxypropyl 2 3 dihydroxypropyl 2 3 4 trihydroxybutyl tris hydroxymethyl methyl and 2 hydroxy 1 hydroxymethyl ethyl suitable alkoxyalkyl groups include methoxymethyl 2 3 dimethoxypropyl tris methoxymethyl methyl and 2 methoxy 1 methoxymethyl ethyl the compositions of formula iii are suitable for use with a variety of modalities including x rays magnetic resonance imaging and radiopharmaceuticals the functionality of the r 2 r 10 groups of the compositions of formula iii of the present inventions afford the additional capability of derivatization to biomolecules and synthetic polymers biomolecule refers to all natural and synthetic molecules that play a role in biological systems biomolecules include hormones amino acids peptides peptidomimetics proteins deoxyribonucleic acid dna ribonucleic acid rna lipids albumins polyclonal antibodies receptor molecules receptor binding molecules monoclonal antibodies a fragment of monoclonal antibody and aptamers specific examples of biomolecules include insulins prostaglandins growth factors liposomes and nucleic acid probes examples of synthetic polymers include polylysine arborols dendrimers cyclodextrins the advantages of using biomolecules include enhanced tissue targeting.