Changes in the hydrogen bonding pattern in ferrocene peptides

Disubstituted peptide ferrocenes conjugates were prepared from ferrocenedicarboxylic acid (Fc(OH)(2)) and glycineethylester. After conversion of the resulting ester Fc(Gly-OEt)(2) 1 into the corresponding acid Fc(Gly-OH)(2) 2 by ester hydrolysis, significant structural changes take place in the way the molecules interact with each other. Complex I adopts a 1,3'-conformation showing extensive intermolecular H-bonding forming 1-D chains, whereas complex 2 displays a compact 1,2'-conformation in which the NH on one strand engage in strong intramolecular cross-strand H-bonding involving the amide C=O on the opposite strand. Additional intermolecular H-bonding in 2 allows the formation of a 2-D net. In essence, ester-deprotection allows us to switch the ferrocene conformation and the H-bonding pattern. (C) 2004 Elsevier B.V. All rights reserved.