Part I Nanoparticle-based designation of multivalent carbohydrate-lectin interactions Part II Development of new promoters for stereoselective green glycosylation
Gorityala Bala Kishan
Date of Issue2011
School of Physical and Mathematical Sciences
In part I of the thesis we have designed and explained a novel bio-sensor system to explore multivalent interactions between carbohydrates and lectins. Goldnanoparticles decorated with carbohydrates resemble to natural cell systems and exert multivalent interactions on specific lectins. Design of this bio-sensor relies on two characteristic features of carbohydrates and goldnanoparticles; (a) carbohydrate diols can interact with boronic acids with high affinity through reversible ester formation (b) when a fluorescent dye tagged boronic acid couples with encapsulated goldnanoparicles, its fluorescence quenches. We have synthesized some carbohydrate-monomodified goldnanoparticles and fluorescein boronic acid ligand. When these carbohydrate- monomodified goldnanoparticles bind with fluorescein bornonic acid ligand, fluorescence intensity of resulting complex drastically decreases. Upon the addition of a lectin to this system, fluorescence intensity again increases. Each carbohydrate is specific to particular lectin and based on this phenomenon the incoming lectin molecule replaces fluorescein boronic acid ligand from fluorescein-bronic acid-carbohydrate encapsulated goldnanoparticle complex to release fluorescein boronic acid ligand which in turn increases the fluorescence intensity. This system acts as “Turn-on/Turn-off” system. Based on this system we have extensively studied various carbohydrate-lectin interactions. This bio-sensor system is simple, efficient, cost effective and above all with high sensitivity. The limit of detection (sensitivity) of this system was found to be 4.9 nM. This system was successfully applied on cell cultures and the results showed fluorescein bronic acid-carbohydrate grafted goldnanoparticle system could be used as fluorescent probe. In part II, we have developed two renewable catalytic systems to carryout stereoselective glycosylation.