Abstract: A compound of formula I is disclosed: wherein each R1 is independently wherein W is an aryl, alkyl or heteroaryl group, each of which may be independently and optionally substituted by one or more of: OH, halogen, an isothiocyanate group, a haloacetamide, maleimide, COOH, NO2, NH2, alkyl, haloalkyl, alkoxy, (CO)n(O)mZ, a polyethylene glycol group, an alkyl sulfonate group, an alkyl-COOH group, a substituted or unsubstituted benzyl group, or a sugar derivative; R2 is H, a halogen, an isothiocyanate group, a haloacetamide, maleimide, Y-aryl or Y-heteroaryl, where Y is O, S, NH, C(O) or CO2, and where said aryl or heteroaryl group may be optionally substituted by one or more of: OH, halogen, an isothiocyanate group, a haloacetamide, maleimide, COOH, NO2, NH2, alkyl, haloalkyl, alkoxy, (CO)n?(O)m?Z?, a polyethylene glycol group, an alkyl sulfonate group, an alkyl-COOH group, a substituted or unsubstituted benzyl group, or a sugar derivative; Z and Z? are each independently silicon-containing protecti