Patent ID: 8030341

Claim:
A compound of the formula I: wherein R 1 and R 2 are the same or different and each of R 1 and R 2 is H or CH 3 ; R 3 and R 5 are the same or different and each of R 3 and R 5 is H, CH 3 , or C 2 H 5 ; R 4 is H or CH 3 ; X is a spacer selected from a group comprising NH—(CH 2 ) n —NH, wherein n is from 1 to about 20, and 3—NH—(CH 2 ) n -6—NH—(CH 2 )m-2(1H)-pyrazinone, wherein n and m are the same or different and each of n and m is from 1 to about 20.