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 α-manno clusters exhibited excellent
affinities (ICmin = 9.0 × 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 (ΔH° = −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 (Φem = 0.15), and their
luminescence intensities were changed (∼40%) upon binding to the specific lectins. The ruthenium
glycoclusters can be a suitable sensory system for saccharide-binding phenomena.