In preferred embodiments of {HEAD ~ the first two aspects} of {TAIL ~ the invention}, the bridge comprises the unit A, ##STR3## where: R3 R6 are independently selected from H, a halogen, alkoxy and alkyl groups of C5 or less, and tertiary amines; and B is a linker to the maleimido function 
of
In preferred embodiments of { HEAD ~ the first two aspects } of { TAIL ~ the invention } , the bridge comprises the unit A , # # STR3 # # where : R3 R6 are independently selected from H , a halogen , alkoxy and alkyl groups of C5 or less , and tertiary amines ; and B is a linker to the maleimido function
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH