, said atom being independently selected from the group consisting of O, S and N wherein N is part of the functionality N (E)p R, where E is selected from the group consisting of CO and SO2, p is an integer from 0-1, and R is selected from the group consisting of H, lower alkyls and halogenated lower alkyls; Z is a group linking X and Y comprising a chain of 1-2 carbon atoms in length, and wh