In preferred embodiments of {HEAD ~ the first two aspects} of 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 {TAIL ~ the maleimido function} 
In preferred embodiments of { HEAD ~ the first two aspects } of 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 { TAIL ~ the maleimido function }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD 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 TAIL TAIL TAIL TAIL TAIL TAIL TAIL