Patent ID: 8536162

Claim:
A compound having the formula in which: one or more of R 1 through R 6 is -L′ in which L′ is a member selected from the group consisting of —(C 1 -C 4 alkyl)-NH 2 , —(C 1 -C 4 alkyl)-C(═O)—NH 2 , —(C 1 -C 4 alkyl)-NH—CO 2 H, —(C 1 -C 4 alkyl)-C(═O)—NH—(C 1 -C 4 alkyl)-NH 2 , and —(C 1 -C 4 alkyl)-NH—C(═O)—(C 1 -C 4 )—NH 2 ; and the remainder of R 1 through R 6 are independently selected from the group consisting of H and C 1 -C 6 alkyl.