Artificial metalloglycoclusters: compact saccharide shell to induce high lectin affinity as well as strong luminescence.

Tris-bipyridine ferrous and ruthenium complexes carrying various saccharide appendages have been investigated to develop sensory systems for monitoring saccharide-binding phenomena. Ferrous O-glycoclusters having spacer moieties inserted between saccharide appendages and the complex core showed enhanced affinities to lectins, but ferrous N-glycoclusters, in which the saccharide-appendages are directly linked to the complex core via amide linkage, had low lectin-affinities. Molecular dynamics calculation indicated that the O-glycoclusters have flexible and densely packed saccharide clusters, in contrast to the octahedrally fixed saccharide arrays of N-glycoclusters. Flexibility of saccharide clusters is essential for their enhanced affinity, probably to induce conformational change to fit the recognition sites of lectins. According to these insights, ruthenium O-glycoclusters have been designed as luminescence biosensors. The ruthenium complexes carrying alpha-manno clusters exhibited excellent affinities (IC(min) = 9.0 x 10(-)(8) M) to concanavalin A (ConA). It is suggested from conformational analysis that densely packed mannoclusters can be fit properly to the recognition site of ConA. The binding was enthalpicaly driven (deltaH degrees = -21.8 kcal/mol). This binding behavior is quite similar to that of 1-3/1-6 trimannoside to ConA. They have strongly amplified luminescence (Phi(em) = 0.15), and their luminescence intensities were changed (approximately 40%) upon binding to the specific lectins. The ruthenium glycoclusters can be a suitable sensory system for saccharide-binding phenomena.